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Valeria CANNILLO

Professore Associato presso: Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

2019 - A new bioactive glass/collagen hybrid composite for applications in dentistry [Articolo su rivista]
Bellucci, D.; Salvatori, R.; Giannatiempo, J.; Anesi, A.; Bortolini, S.; Cannillo, V.
abstract

Bioactive glasses (BGs) are currently employed in a wide range of medical and dentistry applications by virtue of their bone-bonding ability. The incorporation of BGs into a collagen matrix may be used to combine the regenerative potential of these materials with the specific biological advantages of collagen. However, most of the collagen/BG composites reported in the literature are scaffolds and there is a lack of moldable putties or injectable systems. Here, granules of an innovative BG containing strontium and magnesium were mixed with collagen and PEG to obtain a putty (BGMS/C) suitable for dental applications. For the sake of comparison, granules of 45S5 Bioglass®, the gold standard among BGs, were used to prepare a 45S5/collagen putty. Both the composites were evaluated in vitro with respect to murine fibroblasts. The materials showed an excellent biocompatibility, making them interesting for possible applications in dentistry and reconstructive surgery. Moreover, BGMS/C seems to stimulate cell proliferation.


2019 - A new collagen/bioactive glass hybrid composite for dental applications. [Abstract in Rivista]
Giannatiempo, J.; Bortolini, S.; Giavatto, M. A.; BIANCHI, A.; Natali, A.; Berzaghi, A.; Bellucci, D.; Cannillo, V.; Consolo, U.
abstract


2019 - Advanced open-celled structures from low-temperature sintering of a crystallization-resistant bioactive glass [Articolo su rivista]
Elsayed, H.; Romero, A. R.; Bellucci, D.; Cannillo, V.; Bernardo, E.
abstract

Most materials for bone tissue engineering are in form of highly porous open-celled components (porosity > 70%) developed by means of an adequate coupling of formulations and manufacturing technologies. This paper is dedicated to porous components from BGMS10 bioactive glass, originally designed to undergo viscous flow sintering without crystallization, which is generally known to degrade the bioactivity of 45S5 bioglass. The adopted manufacturing technologies were specifically conceived to avoid any contamination and give excellent control on the microstructures by simple operations. More precisely, 'green' components were obtained by digital light processing and direct foaming of glass powders suspended in a photosensitive organic binder or in an aqueous solution, activated with an organic base, respectively. Owing to characteristic quite large sintering window of BGMS10 glass, sintering at 750 °C caused the consolidation of the structures generated at room temperature, without any evidence of viscous collapse.


2019 - Bioactive glasses and glass-ceramics versus hydroxyapatite: Comparison of angiogenic potential and biological responsiveness [Articolo su rivista]
Bellucci, Devis; Braccini, Simona; Chiellini, Federica; Balasubramanian, Preethi; Boccaccini, Aldo R; Cannillo, Valeria
abstract

Different bioactive glasses (BGs), bioceramics, and their composites were extensively analyzed in terms of biological responsiveness and angiogenic potential. In particular several inorganic materials were considered, namely the widely used 45S5 BG, an experimental BG with low tendency to crystallize, other three experimental BGs doped with strontium and/or magnesium, a commercial hydroxyapatite (HA), and two BG-HA composites (with varying percentages of BG and HA). All these materials were ad hoc prepared and in vitro tested by means of an extensive biological analysis, such as MC3T3-E1 cell viability and proliferation by direct contact assay, alkaline phosphatase activity, mineralized matrix deposition analysis by alizarin red staining, as well as evaluation of angiogenic potential and vascular endothelial growth factor release using ST2 cells. Thus, this investigation allows gaining a deeper insight into the biological performance of different inorganic material categories, and to critically compare the different possible solutions, as bone/tissue substitutes for enhanced healing and repair, in terms of bioactivity and regenerative potential.


2019 - Biomeccanica ed evoluzione tecnica delle barre in Cr-Co per implanto-protesi fisse full arch – Prima Parte. [Articolo su rivista]
Rossi, G.; Bortolini, S.; Cannillo, V.; BIANCHI, A.; Nanni, M.; Lelièvre, F
abstract


2019 - Design of a novel procedure for the optimization of the mechanical performances of 3D printed scaffolds for bone tissue engineering combining CAD, Taguchi method and FEA [Articolo su rivista]
Marchiori, G.; Berni, M.; Boi, M.; Petretta, M.; Grigolo, B.; Bellucci, D.; Cannillo, V.; Garavelli, C.; Bianchi, M.
abstract

In order to increase manufacturing and experimental efficiency, a certain degree of control over design performances before realization phase is recommended. In this context, this paper presents an integrated procedure to design 3D scaffolds for bone tissue engineering. The procedure required a combination of Computer Aided Design (CAD), Finite Element Analysis (FEA), and Design methodologies Of Experiments (DOE), firstly to understand the influence of the design parameters, and then to control them. Based on inputs from the literature and limitations imposed by the chosen manufacturing process (Precision Extrusion Deposition), 36 scaffold architectures have been drawn. The porosity of each scaffold has been calculated with CAD. Thereafter, a generic scaffold material was considered and its variable parameters were combined with the geometrical ones according to the Taguchi method, i.e. a DOE method. The compressive response of those principal combinations was simulated by FEA, and the influence of each design parameter on the scaffold compressive behaviour was clarified. Finally, a regression model was obtained correlating the scaffold's mechanical performances to its geometrical and material parameters. This model has been applied to a novel composite material made of polycaprolactone and innovative bioactive glass. By setting specific porosity (50%) and stiffness (0.05 GPa) suitable for trabecular bone substitutes, the model selected 4 of the 36 initial scaffold architectures. Only these 4 more promising geometries will be realized and physically tested for advanced indications on compressive strength and biocompatibility.


2019 - Framework metallici a barra per impianti multipli: soluzioni a confronto. [Articolo su rivista]
Bortolini, S.; Testori, T.; Nanni, M.; Cannillo, V.; BIANCHI, A.; Rossi, G.; Consolo, U.
abstract


2019 - Human mesenchymal stem cell combined with a new strontium-enriched bioactive glass: An ex-vivo model for Bone Regeneration [Articolo su rivista]
Bellucci, D.; Veronesi, E.; Strusi, V.; Petrachi, T.; Murgia, A.; Mastrolia, I.; Dominici, M.; Cannillo, V.
abstract

A 3D cellular model that mimics the potential clinical application of a biomaterial is here applied for the first time to a bioactive glass, in order to assess its biological potential. A recently developed bioactive glass (BGMS10), whose composition contained strontium and magnesium, was produced in the form of granules and fully investigated in terms of biocompatibility in vitro. Apart from standard biological characterization (Simulated Body Fluid (SBF) testing and biocompatibility as per ISO10993), human bone marrow mesenchymal stromal/stem cells (BM-MSCs) were used to investigate the performance of the bioactive glass granules in an innovative 3D cellular model. The results showed that BGMS10 supported human BM-MSCs adhesion, colonization, and bone differentiation. Thus, bioactive glass granules seem to drive osteogenic differentiation and thus look particularly promising for orthopedic applications, bone tissue engineering and regenerative medicine.


2019 - SBF assays, direct and indirect cell culture tests to evaluate the biological performance of bioglasses and bioglass-based composites: Three paradigmatic cases [Articolo su rivista]
Bellucci, Devis; Salvatori, Roberta; Anesi, Alexandre; Chiarini, Luigi; Cannillo, Valeria
abstract

A novel bioglass composition (BGMS10), containing strontium and magnesium and characterized by an ultra-high crystallization temperature, is here employed for the first time to produce different composites with the addition of specific amounts of hydroxyapatite. After an investigation of the samples’ bioactivity in vitro in a simulated body fluid solution (SBF) – according to a widely used protocol – the biocompatibility of the new materials was tested with respect to murine fibroblasts both by direct and indirect tests, in order to evaluate possible cytotoxic effects of the materials’ eluates. Although none of the samples were cytotoxic and their bioactivity in SBF increased with the increasing amount of the glass in the composite, thus showing the best performance in the case of pure BGMS10 glass, the findings of the biological investigation did not confirm those arising from the SBF assay. Surprisingly, while the composites with the lowest glass amount showed an enhanced biocompatibility in direct tests, on the contrary their biological responsiveness is typically lower in the indirect ones, based on filtered materials’ extracts. This fact could be ascribed to the high release of particulate from the composites, which are more porous than the glassy samples: in fact, such pronounced dissolution may affect both the cell viability and the absorbance readings used in the colorimetric assays. The pure BGMS10 glass showed the best biological response only in the cell proliferation test (which is an indirect contact test), being able to stimulate cell proliferation in particular after 24 h. For these reasons, when considering bioactive glasses and bioglass-based composites, the results of direct cell culture assays should be integrated with those obtained by indirect ones, while the findings regarding the in vitro bioactivity in SBF should be interpreted with great care.


2019 - Spark plasma sintered CaO-rich bioglass-derived glass-ceramics with different crystallinity ratios: A detailed investigation of their behaviour during biological tests in SBF [Articolo su rivista]
Montinaro, S.; Luginina, M.; Garroni, S.; Orrù, R.; Delogu, F.; Bellucci, D.; Cannillo, V.; Cao, G.
abstract

The in-vitro behaviour of three series of dense materials with different crystallization degree and phases produced by Spark Plasma Sintering (SPS) from CaO-rich bioglass powders is investigated by soaking them up to 14 days in Simulated Body Fluid (SBF). The completely amorphous materials produced after 2 min at 730 °C display the more pronounced substrate-solution interaction. This is highly beneficial for the rapid generation (<3 days) of an apatite layer on the substrate surface. Larger amounts of such phase are also produced during the entire immersion period. These characteristics are moderately mitigated when 80 wt.% of the glass is crystallized at 850 °C with the main formation of α-CaSiO3. Nonetheless, more severe SPS conditions (1000 °C, 20 min) lead to specimens rich of β-CaSiO3 that still retain 12 wt.% of the amorphous nature while scarcely interact with SBF. The apatite formation is correspondingly delayed (7 days) and its amount significantly decreased.


2019 - Zinc containing bioactive glasses with ultra-high crystallization temperature, good biological performance and antibacterial effects [Articolo su rivista]
Sergi, R.; Bellucci, D.; Salvatori, R.; Maisetta, G.; Batoni, G.; Cannillo, V.
abstract

Novel bioactive glasses with different amount of zinc oxide (ZnO), namely 2, 3.8 and 5 mol%, were designed, produced by a melt-quenching route and investigated in terms of biological performance. Proper amounts of ZnO were added to a previously developed bioactive glass containing strontium and magnesium, characterized by an ultra-high crystallization temperature. Thus, the aim of the work was to obtain a bioactive glass with high crystallization temperature in view of an eventual thermal treatment, as well as antibacterial properties (due to the antimicrobial effect of zinc, as reported in the literature). Bioactivity was investigated by immersion in Simulated Body Fluid (SBF), which is a commonly used protocol to evaluate samples' bioactivity in vitro. Additionally, in order to exclude the possible cytotoxicity of Zn containing bioactive glasses, a biological investigation using MLO-Y4 cells was carried out, both by direct (NR uptake) and indirect (MTT) contact tests. Finally, the antibacterial effects of the produced bioactive glasses against Staphylococcus epidermidis (Gram-positive), Pseudomonas aeruginosa and Escherichia coli (both Gram-negative) were investigated.


2018 - A novel bioactive glass containing strontium and magnesium with ultra-high crystallization temperature [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria
abstract

Bioactive glasses, and in particular the "gold standard" 45S5 Bioglass® (45S5), are employed in medical practice by virtue of their ability to bond to bone. However, the tendency to crystallize of such systems during thermal treatments, which are necessary in several processing routes, is among the reasons that prevent a broader use of these materials. Here a novel bioglass composition (BGMS10), containing strontium and magnesium and a low content of alkali oxides, is presented. Compared to 45S5, the BGMS10 is characterized by a remarkably higher crystallization temperature (932 °C), larger processing window and it can be sintered at lower temperature (737 °C), thus maintaining its amorphous nature and pronounced bioactivity, as confirmed by in vitro tests. For these reasons, BGMS10 is a great candidate for the realization of specific products which require a thermal treatment, such as scaffolds for bone repair, composites and bioactive coatings.


2018 - Bioactive Zn-doped hydroxyapatite coatings and their antibacterial efficacy against Escherichia coli and Staphylococcus aureus [Articolo su rivista]
Sergi, Rachele; Bellucci, Devis; Candidato, Rolando T.; Lusvarghi, Luca; Bolelli, Giovanni; Pawlowski, Lech; Candiani, Gabriele; Altomare, Lina; De Nardo, Luigi; Cannillo, Valeria
abstract

Zinc-doped hydroxyapatite (HA + Zn) has aroused increasing interest in bone contact applications, for its capacity to modulate osteoblast activity and for the antibacterial properties of zinc ions. In this study, HA + Zn coatings deposited by the Solution Precursor Plasma Spraying (SPPS) process were characterized. This method employs solution feedstocks providing simple and effective ion doping and resulting in the deposition of lamellae of smaller size than the conventional Atmospheric Plasma Spraying method. After a comprehensive microstructural characterization of the coatings, their bioactivity, cytotoxicity, and antibacterial efficacy were investigated. The coatings' bioactivity was confirmed by soaking them in Simulated Body Fluid (SBF), a commonly-used protocol to evaluate samples' bioactivity in vitro. Further, the coatings were non-cytotoxic against human osteoblast Saos-2-cells and, additionally, they showed antibacterial effects against Escherichia coli and Staphylococcus aureus. The HA + Zn coatings obtained showed higher efficacy against the gram-positive S. aureus than against the gram-negative Escherichia coli. These findings demonstrate the potential of the SPPS method for fabricating Zn-doped hydroxyapatite coatings, and show that Zn ions impart antibacterial properties against E. coli and S. aureus bacteria.


2018 - Bioglass and bioceramic composites processed by Spark Plasma Sintering (SPS): biological evaluation Versus SBF test [Articolo su rivista]
Bellucci, D.; Salvatori, R.; Cannio, M.; Luginina, M.; Orrù, R.; Montinaro, S.; Anesi, A.; Chiarini, L.; Cao, G.; Cannillo, V.
abstract

The biocompatibility of hydroxyapatite (HA), a lab-made bioglass (BGCaMIX) with high crystallization temperature and different HA/BGCaMIX composites, pro- duced by Spark Plasma Sintering (SPS), was tested with respect to murine osteocytes both by direct and indirect tests, in order to also investigate possible cytotoxic effects of the samples’ extracts. Previous investigations demon- strated that the samples’ bioactivity, evaluated in a simu- lated body fluid solution (SBF), increased with the increas- ing amount of BGCaMIX in the sample itself. Although none of the samples were cytotoxic, the findings of the bi- ological evaluation did not confirm those arising from the SBF assay. In particular, the results of direct tests did not show an enhanced “biological performance” of materials with higher glass content. This finding may be due to the high release of ions and particulate from the glass phase. On the contrary, the performance of the BGCaMIX alone is better for the indirect tests, based on filtered samples’ extracts. This work further demonstrates that, when con- sidering bioglasses and HA/bioglass composites, the re- sults of the SBF assays should be interpreted with great care, making sure that the results arising from direct con- tact tests are integrated with those arising from the indirect ones.


2018 - Bone regeneration by novel bioactive glasses containing strontium and/or magnesium: A preliminary in-vivo study [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Anesi, Alexandre; Salvatori, Roberta; Chiarini, Luigi; Manfredini, Tiziano; Zaffe, Davide
abstract

In this work, a set of novel bioactive glasses have been tested in vivo in an animal model. The new compositions, characterized by an exceptional thermal stability and high in vitro bioactivity, contain strontium and/or magnesium, whose biological benefits are well documented in the literature. To simulate a long-term implant and to study the effect of the complete dissolution of glasses, samples were implanted in the mid-shaft of rabbits' femur and analyzed 60 days after the surgery; such samples were in undersized powder form. The statistical significance with respect to the type of bioactive glass was analyzed by Kruskal-Wallis test. The results show high levels of bone remodeling, several new bone formations containing granules of calcium phosphate (sometimes with amounts of strontium and/or magnesium), and the absence of adverse effects on bone processes due to the almost complete glass dissolution. In vivo results confirming the cell culture outcomes of a previous study highlighted that these novel bioglasses had osteostimulative effect without adverse skeletal reaction, thus indicating possible beneficial effects on bone formation processes. The presence of strontium in the glasses seems to be particularly interesting.


2018 - Direct ink writing of silica-carbon-calcite composite scaffolds from a silicone resin and fillers [Articolo su rivista]
Elsayed, Hamada; Carraro, Francesco; Agnoli, Stefano; Bellucci, Devis; Cannillo, Valeria; Ferroni, Letizia; Gardin, Chiara; Zavan, Barbara; Bernardo, Enrico
abstract

Calcite-based composite scaffolds have been successfully 3D-printed by direct ink writing, starting from a paste comprising a silicone polymer and calcite (CaCO3) powders. The firing in nitrogen, at 600 °C, after preliminary cross-linking step at 350 °C, determined the transformation of the polymer matrix into a silica-carbon nano-composite, embedding unreacted calcite particles. Compared to previously developed silica-calcite scaffolds, obtained after firing in air, the new composites exhibited a significant strength improvement (up to ∼10 MPa, for a total open porosity of 56%). The new formulation did not compromise the in vitro bioactivity and the biocompatibility of the scaffolds, as shown by dissolution studies in SBF and preliminary cell culture tests, with human fibroblasts. Due to the simplicity of the processing and the outstanding mechanical performances, the developed scaffolds are promising candidates for bone tissue engineering applications.


2018 - In-Vitro Cytotoxicity Evaluation of Three Low-Friction Abutment Coatings [Abstract in Rivista]
Giavatto, M. A.; Consolo, U.; Bortolini, S.; Bianchi, A.; Natali, A; Giannatiempo, J; Cucchi, A; Bellucci, D; Salvatori, R; Cannillo, V.
abstract

Objectives: Plaque accumulation and mechanical wear are two main risk factors of implant-prosthetic failure. To reduce the occurrence of these complications, prototypical abutments ("Star Abutment”, PhD Course in Industrial and Environmental Engineering, Modena, Italy) were realised and the literature reviewed to identify eligible coatings for enhancing mechanical and chemical surface properties. Zirconium Nitride (ZrN), Diamond-Like Carbon (DLC), and Superlattice CrN/NbN (CrN/NbN) coated some abutments, and then Neutral Red Uptake Cytotoxicity Direct Contact Test was performed to primarily evaluate the biocompatibility of these surfaces. Methods: Four specimens for each test group were sterilized, then each group placed in a plate directly contacting with Dulbecco’s modified Eagle's medium (DMEM) (Invitrogen, Karlshue, Germany) containing BALB/3T3 murine fibroblasts (Istituto Zooprofilattico, Brescia, Italy) at standard temperature (37°C±1°C), humidity (90%± 5%) and CO2 concentration (5%±1%). Two additional plates were used as positive (DMEM with 0.45% phenol solution) and negative (DMEM) control groups. Samples were analyzed at 24, 48 and 72 hours with optical microscope (Nikon, Japan) for cytomorphological evaluation and, after treatment with 0.2% Neutral Red, spectrophotometry analysis (HP 8452A Diode-Array, Hewlett-Packard, USA) was performed with λ set at 540nm to obtain fibroblasts survival rates for each test and control group: non-coated (NC), ZrN-coated, DLC-coated, CrN/NbN-coated, negative control (CTRL-) and positive control (CTRL+). Results: Optical analysis showed no inhibition halo for each test specimens at 24, 48 and 72 hours. Spectrophotometry analysis showed no cytotoxicity for each test specimens at 24, 48 and 72 hours. Detailed results are reported in the attached graphics. Conclusions: ZrN, DLC, and CrN/NbN coatings showed no cytotoxicity with BALB/3T3 murine fibroblasts after 24, 48 and 72 hours. These results encourage the research on Star Abutments. Up to January 2018, this seems to be the first application of a Superlattice CrN/NbN coating in dentistry.


2017 - A comparative in vivo evaluation of bioactive glasses and bioactive glass-based composites for bone tissue repair [Articolo su rivista]
Bellucci, Devis; Anesi, Alexandre; Salvatori, Roberta; Chiarini, Luigi; Cannillo, Valeria
abstract

In this work a set of novel materials for bone tissue regeneration have been tested in vivo in an animal model. In fact, despite many studies have been devoted to amorphous 45S5 Bioglass®, there is lack in the literature of works aimed to study the in vivo performance of heat-treated – and thus partially crystallized – 45S5. As widely reported, crystallization limits the bioactivity of 45S5 and is the main reason that prevents a broader use of this material. Thus, in the present work, a recently developed bioactive glass (BG_Ca/Mix) is tested, since previous investigations demonstrated that BG_Ca/Mix is particularly promising by virtue of both its high bioactivity and lower tendency to crystallize with respect to 45S5. BG_Ca/Mix sintered powders and two composites, which contain BG_Ca/Mix and an increasing percentage (20&nbsp;wt% or 70&nbsp;wt%) of hydroxyapatite (HA), were considered. As a term of comparison, 45S5 sintered powders were also studied. The samples were implanted in rabbits' femurs and harvested after 8&nbsp;weeks. The histological analysis demonstrated that BG_Ca/Mix has an osteoconductive ability slightly higher than that of 45S5 glass-ceramics, followed by that of the composites, which may represent the starting point for obtaining systems with degradation rate tailored for a given clinical application. Moreover, the 45S5 samples were locally cracked, probably because of a non-uniform dissolution in the physiological environment. On the contrary such cracks, which could lead to implant instability and unsuitable mechanical performance, were not observed in BG_Ca/Mix.


2017 - Direct ink writing of silica-bonded calcite scaffolds from preceramic polymers and fillers [Articolo su rivista]
Fiocco, L.; Elsayed, H.; Badocco, D.; Pastore, P.; Bellucci, D.; Cannillo, V.; Detsch, R.; Boccaccini, ALDO ROBERTO; Bernardo, E.
abstract

Silica-bonded calcite scaffolds have been successfully 3D-printed by direct ink writing, starting from a paste comprising a silicone polymer and calcite powders, calibrated in order to match a SiO2/CaCO3 weight balance of 35/65. The scaffolds, fabricated with two slightly different geometries, were first cross-linked at 350 °C, then fired at 600 °C, in air. The low temperature adopted for the conversion of the polymer into amorphous silica, by thermo-oxidative decomposition, prevented the decomposition of calcite. The obtained silica-bonded calcite scaffolds featured open porosity of about 56%-64% and compressive strength of about 2.9-5.5 MPa, depending on the geometry. Dissolution studies in SBF and preliminary cell culture tests, with bone marrow stromal cells, confirmed the in vitro bioactivity of the scaffolds and their biocompatibility. The seeded cells were found to be alive, well anchored and spread on the samples surface. The new silica-calcite composites are expected to be suitable candidates as tissue-engineering 3D scaffolds for regeneration of cancellous bone defects.


2017 - Innovative hydroxyapatite/bioactive glass composites processed by spark plasma sintering for bone tissue repair [Articolo su rivista]
Bellucci, Devis; Desogus, Luca; Montinaro, Selena; Orrù, Roberto; Cao, Giacomo; Cannillo, Valeria
abstract

Hydroxyapatite-based composites (HA-C) with bioglass as second phase are usually produced by hot-pressing or pressureless sintering. However, such methods require thermal levels which exceed the crystallization temperature of the glass, with possible negative effects on the bioactivity of the final system. Spark plasma sintering (SPS) is a powerful consolidation technique in terms of both processing time and temperature. In this work SPS has been employed, for the first time, to obtain HA-C with an innovative bioglass as second phase. Such glass was designed to be used whenever a thermal treatment is required, thanks to its low tendency to crystallize. A systematic study is conducted to identify the optimal sintering conditions for preparing highly dense composites and, at the same time, to minimize the crystallization of the glassy phase. The obtained samples are highly bioactive and display higher compactness and hardness with respect to the counterparts produced by conventional sintering methods.


2017 - Pulsed Electron Deposition of nanostructured bioactive glass coatings for biomedical applications [Articolo su rivista]
Bellucci, Devis; Bianchi, Michele; Graziani, Gabriela; Gambardella, Alessandro; Berni, Matteo; Russo, Alessandro; Cannillo, Valeria
abstract

Due to poor mechanical properties and brittleness of bioactive glasses, the deposition of bioactive glass coatings on bioinert metallic implants for bone regeneration is a promising route to combine the high bioactivity of the glassy phase with the mechanical strength of metallic substrate. The Pulsed Electron Deposition (PED) technique has been recently demonstrated to be an effective method to fabricate highly-adherent and nanostructured bioactive thin films and coatings, with fine control over film composition. In this paper, we investigated the deposition by PED of 45S5 Bioglass® and of a novel CaO-rich bioactive glass, also containing potassium oxide. Composition, microstructure, surface morphology, wettability and adhesion to the titanium substrate were assessed for both as-deposited and annealed coatings. All samples exhibited a nanostructured surface morphology and high hydrophilicity, both positive features for biological applications. In particular, annealed samples exhibited increased roughness and adhesion degree to the titanium substrate compared to the as-deposited ones. The results showed in this paper suggest that bioactive glass coatings deposited by PED are promising for being further investigated as bioactive coatings for bone implants.


2017 - Role of magnesium oxide and strontium oxide as modifiers in silicate-based bioactive glasses: Effects on thermal behaviour, mechanical properties and in-vitro bioactivity [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Salvatori, Roberta; Anesi, Alexandre; Chiarini, Luigi; Cannillo, Valeria
abstract

The composition of a CaO-rich silicate bioglass (BG_Ca-Mix, in mol%: 2.3 Na2O; 2.3 K2O; 45.6 CaO; 2.6 P2O5; 47.2 SiO2) was modified by replacing a fixed 10 mol% of CaO with MgO or SrO or fifty-fifty MgO-SrO. The thermal behaviour of the modified glasses was accurately evaluated via differential thermal analysis (DTA), heating microscopy and direct sintering tests. The presence of MgO and/or SrO didn't interfere with the thermal stability of the parent glass, since all the new glasses remained completely amorphous after sintering (treatment performed at 753 °C for the glass with MgO; at 750 °C with SrO; at 759 °C with MgO and SrO). The sintered samples achieved good mechanical properties, with a Young's modulus ranging between 57.9 ± 6.7 for the MgO-SrO modified composition and 112.6 ± 8.0 GPa for the MgO-modified one. If immersed in a simulated body fluid (SBF), the modified glasses after sintering retained the strong apatite forming ability of the parent glass, in spite of the presence of MgO and/or SrO. Moreover, the sintered glasses, tested with MLO-Y4 osteocytes by means of a multi-parametrical approach, showed a good bioactivity in vitro, since neither the glasses nor their extracts caused any negative effect on cell viability or any inhibition on cell growth. The best results were achieved by the MgO-modified glasses, both BGMIX_Mg and BGMIX_MgSr, which were able to exert a strong stimulating effect on the cell growth, thus confirming the beneficial effect of MgO on the glass bioactivity.


2016 - Functionally graded materials for orthopedic applications – an update on design and manufacturing [Articolo su rivista]
Sola, Antonella; Bellucci, Devis; Cannillo, Valeria
abstract

Functionally graded materials (FGMs) are innovative materials whose composition and/or microstructure gradually vary in space according to a designed law. As a result, also the properties gradually vary in space, so as to meet specific non-homogeneous service requirements without any abrupt interface at the macroscale. FGMs are emerging materials for orthopedic prostheses, since the functional gradient can be adapted to reproduce the local properties of the original bone, which helps to minimize the stress shielding effect and, at the same time, to reduce the shear stress between the implant and the surrounding bone tissue, two critical prerequisites for a longer lifespan of the graft. After a brief introduction to the origin of the FGM concept, the review surveys some representative examples of graded systems which are present in nature and, in particular, in the human body, with a focus on bone tissue. Then the rationale for using FGMs in orthopedic devices is discussed more in detail, taking into account both biological and biomechanical requirements. The core of the paper is dedicated to two fundamental topics, which are essential to benefit from the use of FGMs for orthopedic applications, namely (1) the computational tools for materials design and geometry optimization, and (2) the manufacturing techniques currently available to produce FGM-based grafts. This second part, in its turn, is structured to consider the production of functionally graded coatings (FGCs), of functionally graded 3D parts, and of special devices with a gradient in porosity (functionally graded scaffolds). The inspection of the literature on the argument clearly shows that the integration of design and manufacturing remains a critical step to overpass in order to achieve effective FGM-based implants.


2016 - Hydroxyapatite and tricalcium phosphate composites with bioactive glass as second phase: State of the art and current applications [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

Calcium phosphates are among the most common biomaterials employed in orthopaedic and dental surgery. The efficacy of such systems as bone substitutes and bioactive coatings on metallic prostheses has been proved by several clinical studies. Among these materials, hydroxyapatite (HA) and tricalcium phosphate (TCP) play a prominent role in medical practice since the '80s. In the last years, numerous attempts to combine HA or TCP with bioactive glasses have been made. There are two main motivations for sintering calcium phosphates with a glassy phase: on the one hand, it is possible to tune the dissolution of the final system and to enhance its biological response through the synergistic combination of two bioactive phases; on the other hand, the glass acts as a sintering aid with the aim to increase the densification of the composite and thus its mechanical strength. In this sense, TCP and HA are penalized by their relatively poor fracture toughness and tensile strength compared to natural bone, which makes it impossible to use them in load-bearing applications. Moreover, the bioactivity index of pure calcium phosphates is typically lower with respect to that of many bioactive glasses. In this review, the state of the art and current applications of composites, based on HA or TCP with bioactive glass as second phase, are presented and discussed. A special emphasis is given to the processing and mechanical behaviour of these systems, together with their biological implications, as a function of the composition of the glass employed as second phase.


2015 - Bioactive glass/hydroxyapatite composites: Mechanical properties and biological evaluation [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Anesi, Alexandre; Salvatori, Roberta; Chiarini, Luigi; Cannillo, Valeria
abstract

Bioactive glass/hydroxyapatite composites for bone tissue repair and regeneration have been produced and discussed. The use of a recently developed glass, namely BG_Ca/Mix, with its low tendency to crystallize, allowed one to sinter the samples at a relatively low temperature thus avoiding several adverse effects usually reported in the literature, such as extensive crystallization of the glassy phase, hydroxyapatite (HA) decomposition and reaction between HA and glass. The mechanical properties of the composites with 80wt.% BG_Ca/Mix and 20wt.% HA are sensibly higher than those of Bioglass® 45S5 reference samples due to the presence of HA (mechanically stronger than the 45S5 glass) and to the thermal behaviour of the BG_Ca/Mix, which is able to favour the sintering process of the composites. Biocompatibility tests, performed with murine fibroblasts BALB/3T3 and osteocites MLO-Y4 throughout a multi-parametrical approach, allow one to look with optimism to the produced composites, since both the samples themselves and their extracts do not induce negative effects in cell viability and do not cause inhibition in cell growth.


2015 - Classical Bioglass® and innovative CaO-rich bioglass powders processed by Spark Plasma Sintering: A comparative study [Articolo su rivista]
Desogus, L.; Cuccu, A.; Montinaro, S.; Orrù, R.; Cao, G.; Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

Densification and crystallization phenomena taking place when a recently developed CaO-rich bioactive glass and conventional 45S5 Bioglass® are processed by Spark Plasma Sintering (SPS) are examined. Fully dense and wholly amorphous products can be obtained from the new glass composition at 730 ◦ C after 2min dwell time. Moreover, temperatures equal or higher than 830◦C are needed to induce crystal- lization (- and -CaSiO3) in the parent glass. Conversely, Na6Ca3Si6O18 crystals are formed in sintered 45S5 samples produced under optimal conditions (550◦C, 2min), although the glassy character is still preserved. Products resulting from the innovative glass powders generally display higher hardness and local elastic modulus. Devitrification also provides improvements in this system. In contrast, mechanical properties become slightly worsen when classical bioglass is processed at 600 ◦ C. This can be probably associated to the corresponding decrease in compactness which, apparently, overcomes the benefits arising from the crystallization progress.


2015 - Comparison between Suspension Plasma Sprayed and High Velocity Suspension Flame Sprayed bioactive coatings [Articolo su rivista]
Bolelli, Giovanni; Bellucci, Devis; Cannillo, Valeria; Gadow, Rainer; Killinger, Andreas; Lusvarghi, Luca; Müller, Philipp; Sola, Antonella
abstract

This paper assesses the diverse potentialities of two different suspension spraying processes, namely High Velocity Suspension Flame Spraying (HVSFS) and Suspension Plasma Spraying (SPS), for the deposition of bioactive coatings based on hydroxyapatite and on a new, custom-made K2O–Na2O–CaO–P2O5–SiO2 bioactive glass. With both feedstock types, the HVSFS process imparts high in-flight velocities to the particles and aggregates released after solvent vaporisation, resulting in well flattened, tightly bound lamellae. The coatings, b50 μm thick and very dense, have hardness and elastic modulus values close to those of the corresponding bulk materials. They can be employed as high-quality bioactive layers on metallic implantable devices. Few days of soaking in simulated body fluid (SBF) results in the re-precipitation of a surface hydroxyapatite layer, albeit through different mechanisms. In HVSFS bioactive glass coatings, ion leaching turns the surface into a silica gel, onto which hydroxyapatite subsequently deposits. In HVSFS hydroxyapatite, the amorphous fraction is progressively dissolved and microcrystalline hydroxyapatite precipitates onto the remaining coating layer. The SPS technique, due to the lower in-flight velocity of particles and agglomerates, always produces more po- rous, rougher layers with columnar-like growth. They are not mechanically strong, but their peculiar structure can be useful for specific, functional applications. The high surface area of porous SPS bioactive glass coatings favours ion leaching and fast dissolution in simulated body fluid (SBF); hence, it is suggested that SPS bioglass could be useful as a rapidly resorbable layer. SPS hydroxyapatite, by contrast, is more stable than the corresponding HVSFS layer, despite its porosity, because of the higher crystallinity. After the amorphous fraction is dissolved in SBF, newly formed hydroxyapatite does not constitute a surface layer but precipitates inside the pores, suggesting that a sealing pre-treatment in SBF could be a means to tune porosity and phase composition.


2015 - Composite scaffolds for controlled drug release: role of the polyurethane nanoparticles on the physical properties and cell behaviour [Articolo su rivista]
Gentile, Piergiorgio; Bellucci, Devis; Sola, Antonella; Mattu, Clara; Cannillo, Valeria; Ciardelli, Gianluca
abstract

Localised delivery of appropriate biomolecule/drug(s) can be suitable to prevent postoperative infections and inflammation after scaffold implantation in vivo. In this study composite shell scaffolds, based on an internally produced bioactive glass and a commercial hydroxyapatite, were surface coated with a uniform polymeric layer, embedded with thermo-stable polyesterurethane (PU)-based nanoparticles (NPs), containing an anti-inflammatory drug (indomethacin; IDCM). The obtained functionalised scaffolds were subjected to physico-mechanical and biological characterisations. The results indicated that NPs incorporation into the gelatin coating of the composite scaffolds: 1) not changed significantly the micro-architecture of the scaffolds in terms of mean pore diameter and pore size distribution; 2) increased the compressive modulus; and 3) allowed to a sustained IDMC release (65-70% of the loaded-drug) within the first week of incubation in physiological solution. On the other hand, the NPs incorporation did not affect the biocompatibility of composite scaffolds, as evidenced by viability and alkaline phosphatase (ALP) activity of MG63 human osteoblast-like cells.


2015 - Consolidation of different hydroxyapatite powders by SPS: Optimization of the sintering conditions and characterization of the obtained bulk products [Articolo su rivista]
Cuccu, A.; Montinaro, S.; Orrù, R.; Cao, G.; Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

The difference in purity, particle size, microstructure, and thermo-chemical stability of three commercially available hydroxyapatite powders are found to play an important role during their consolidation using spark plasma sintering (SPS) as well as strongly affect the characteristics of the resulting sintered bodies. A fully dense material without secondary phases was obtained by SPS at 900 1C, when using the relatively small sized, with refined grains and high purity powders. The sintered product, consisting of sub-micrometer sized hydroxyapatite grains, displayed optical transparency and good mechanical properties. In contrast, the higher temperature levels (up to 1200 1C) needed to sinter powders with larger particles, or finer ones which contain additional phases, lead to products with coarser microstructures and/or significant amount of β-TCP as a result of HAp decomposition. Optical characteristics, hardness and elastic modulus of the resulting sintered samples are correspondingly worsened.


2015 - Properties of Al2O3 coatings by High Velocity Suspension Flame Spraying (HVSFS): Effects of injection systems and torch design [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Gadow, R.; Killinger, A.; Lusvarghi, Luca; Manfredini, Tiziano; Müller, P.
abstract

Through the High Velocity Suspension Flame Spraying (HVSFS) process, fine (sub-micrometric) oxide ceramic particles can be sprayed at high velocity to achieve denser and more finely structured layers, compared to those obtained by conventional thermal spraying. This paper explores the effect of some key HVSFS hardware components on the properties of Al2O3 coatings. Two feedstock powders with different particle size distributions, dispersed in isopropanol medium, were processed by setting up the HVSFS torch with combustion chambers of different lengths and with two distinct injection systems: a water-cooled mechanical injector, delivering a con- tinuous stream of suspension, or a gas-atomiser injector. The use of the atomising injection system and of longer combustion chambers, promoting better fragmentation of the liquid stream and better homogenisation with the gas flow, can suppress the formation of defects between coating layers, resulting in remarkably high tensile adhesive/cohesive strength values, up to ≈70 MPa. All coat- ings are under compressive residual stress, the magnitude of which varies between −150 MPa and −300 MPa depending on the maximum surface temperature attained during spraying, and have a microhardness of 1000–1200 HV0.1. Quite mild wear rates of ≈1 ∗ 10−6 mm3/(Nm) are obtained by ball-on-disk tests performed under sliding conditions severe enough to cause complete failure of reference HVOF-sprayed Al2O3. Wear mech- anisms involve the formation and fatigue delamination of a smooth surface tribofilm. Detailed analyses of both coatings and single splats also reveal that extremely fast quenching of very small mol- ten droplets caused the formation of ≈20 wt.% glassy Al2O3. Glass transition at 527 °C and three crystallisation reactions at about 800, 1000 and 1180 °C were revealed by differential thermal analysis (DTA).


2014 - Bioactive glass/ZrO2 composites for orthopaedic applications [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

Binary biocomposites were realized by combining yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) with a bioactive glass matrix. Few works are available regarding composites containing zirconia and a relatively high content of glass because the resulting samples are usually biocompatible but not bioactive after thermal treatment. In the present research, the promising properties of the new BG_Ca–K glass, with its low tendency to crystallize and high apatite-forming ability, allowed us to sinter the composites at a relatively low temperature with excellent effects in terms of bioactivity. In addition, it was possible to benefit from the good mechanical behaviour of Y-TZP, thus obtaining samples with microhardness values that were among the highest reported in the literature. After a detailed analysis regarding the thermal behaviour of the composite powders, the sintered bodies were fully characterized by means of x-ray diffraction, SEM equipped with EDS, density measurements, volumetric shrinkage determination, mechanical testing and in vitro evaluation in a simulated body fluid (SBF) solution. According to the experimental results, the presence of Y-TZP improved the mechanical performance. Meanwhile, the BG_Ca–K glass, which mainly preserved its amorphous structure after sintering, provided the composites with a good apatite-forming ability in SBF.


2014 - Enamelled coatings produced with low-alkaline bioactive glasses [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

Enamelling is a relatively easy and inexpensive technique to produce glass coatings. In this contribution, three different low-alkaline bioactive glasses, modified with Na2O and/or K2O for a total alkaline content of 4.6 mol%, were enamelled on Ti6Al4V substrates for potential orthopaedic applications. The glasses in powder form were applied by means of a precipitation-based method and thermally treated in the 800–850 °C range; in particular, the enamelling temperature required to obtain uniform coatings increased with increasing K2O amounts. The SEM observation revealed that the coatings were about 100 μm thick, with a crack-free interface with the metal substrate mediated by the development of titanium oxides. Even if the low-alkaline glasses are characterised by a high crystallization temperature, the coatings underwent a partial devitrification, especially in the presence of K2O. However, the development of bioactive crystalline species, such as wollastonite, was ben- eficial, in that the new phases not only improved the local mechanical properties (in terms of Vickers microhard- ness, from 232.1 ± 76.8 HV for the Na2O-modified glass coating to 317.9 ± 48.8 for the K2O-modified one), but still preserved the apatite-forming ability in a simulated body fluid.


2014 - Functional bioactive glass topcoats on hydroxyapatite coatings: analysis of microstructure and in-vitro bioactivity [Articolo su rivista]
Cattini, Andrea; Bellucci, Devis; Sola, Antonella; L., Pawłowski; Cannillo, Valeria
abstract

A bioactive glass topcoat was introduced to modify the surface morphology and in-vitro reactivity of hydroxyap- atite (HA) coatings for biomedical applications. With this aim, a CaO-rich bioactive glass, termed BG_Ca (wt.%: 4.7 Na2O, 42.3 CaO, 6.1 P2O5, and 46.9 SiO2), was selected due to its good bioactivity and low tendency to crystallize at high temperature. The standard HA coatings were sprayed through atmospheric plasma spray (APS) on steel sub- strates starting from commercial powders (“APS-HA” samples). The HA coatings, in turn, were subsequently coated with a thin layer of bioactive glass by suspension plasma spray (SPS), thus obtaining the duplex systems (“APS-HA/SPS-BG_Ca” samples). The samples with and without the BG_Ca layer were analysed by microstructur- al characterization and by in vitro tests in simulated body fluid (SBF). The analysis revealed an increased reactiv- ity of the APS-HA/SPS-BG_Ca samples compared to the glass-free APS-HA coatings.


2014 - Hydroxyapatite-tricalcium phosphate-bioactive glass ternary composites [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Lusvarghi, Luca; Cannillo, Valeria
abstract

In this work hydroxyapatite, β-tricalcium phosphate and a new bioactive glass have been used to produce ternary composites for orthopedic applications. Thanks to the particular properties of the glass, whose formulation delays the devitrification processes at high temperature, sintering the composites at a relatively low temperature (800 1C) has been possible. In this way, two basic aims have been reached, since the glass preserved its amorphous nature and the reactions between the constituent phases were substantially reduced. Moreover, the ternary composites had a dense and uniform microstructure, which resulted in good mechanical properties (Vickers micro-hardness: 280722HV; elastic modulus: 28.773.6 GPa). In vitro tests confirmed the apatite-forming ability of the composites soaked in a Simulated Body Fluid (SBF). Basing on the obtained results, the new ternary composites represent an intriguing alternative to conventional biomedical materials whenever a controlled bone- bonding rate is required.


2014 - Mg- and/or Sr- doped Tricalcium phosphate/bioactive glass composites: synthesis, microstructure and biological responsiveness [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; I., Caciotti; C., Bartoli; M., Gazzari; A., Bianco; F., Chiellini; Cannillo, Valeria
abstract

Presently, there is an increasing interest towards the composites of calcium phosphates, especially β-tricalcium phosphate (TCP), and bioactive glasses. In the present contribution, the recently developed BG_Ca/Mix glass has been used because its low tendency to crystallize allows to sinter the composites at relatively low temperature (i.e. 850 °C), thus minimizing the glass devitrification and the interaction with TCP. A further improvement is the introduction of lab-produced TCP powders doped with specific ions instead of non-doped commercial pow- ders, since the biological properties of materials for bone replacement can be modulated by doping them with certain metallic ions, such as Mg and Sr. Therefore, novel binary composites have been produced by sintering the BG_Ca/Mix glass with the addition of pure, Mg-substituted, Sr-substituted or Mg/Sr bisubstituted TCP pow- ders. After an accurate characterization of the starting TCP powders and of the obtained samples, the composites have been used as three-dimensional supports for the culture of mouse calvaria-derived pre-osteoblastic cells. The samples supported cell adhesion and proliferation and induced promising mechanisms of differentiation towards an osteoblastic phenotype. In particular, the Mg/Sr bi-doped samples seemed to better promote the differentiation process thus suggesting a combined stimulatory effect of Mg2+ and Sr2+ ions


2014 - Microstructural design of functionally graded coatings composed of suspension plasma sprayed hydroxyapatite and bioactive glass [Articolo su rivista]
Cattini, Andrea; Bellucci, Devis; Sola, Antonella; Pawłowski, Lech; Cannillo, Valeria
abstract

Various bioactive glass/hydroxyapatite (HA) functional coatings were designed by the suspension plasma spraying (SPS) technique. Their microstructure, scratch resistance, and apatite-forming ability in a simulated body fluid (SBF) were compared. The functional coatings design included: (i) composite coating, that is, randomly distributed constituent phases; (ii) duplex coating with glass top layer onto HA layer; and (iii) graded coating with a gradual changing composition starting from pure HA at the interface with the metal substrate up to pure glass on the surface. The SPS was a suitable coating technique to produce all the coating designs. The SBF tests revealed that the presence of a pure glass layer on the working surface significantly improved the reactivity of the duplex and graded coatings, but the duplex coating suffered a relatively low scratch resistance because of residual stresses. The graded coating therefore provided the best compromise between mechanical reliability and apatite-forming ability in SBF. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 551-560, 2014.


2014 - Novel processing of bioglass ceramics from silicone resins containing micro- and nano-sized oxide particle fillers [Articolo su rivista]
Fiocco, L; Bernardo, E; Colombo, P; Cacciotti, I; Bianco, A; Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

Highly porous scaffolds with composition similar to those of 45S5 and 58S bioglasses were successfully produced by an innovative processing method based on preceramic polymers containing micro- and nano-sized fillers. Silica from the decomposition of the silicone resins reacted with the oxides deriving from the fillers, yielding glass ceramic components after heating at 1000°C. Despite the limited mechanical strength, the obtained samples possessed suitable porous architecture and promising biocompatibility and bioactivity characteristics, as testified by preliminary in vitro tests.


2014 - Preliminary studies on the valorization of animal flour ash for the obtainment of active glasses [Articolo su rivista]
Barbieri, Luisa; Andreola, Nora Maria; Bellucci, Devis; Cannillo, Valeria; Lancellotti, Isabella; A., Lugari; Rincon, J. M. a.; M., Romero; Sola, Antonella
abstract

Animal flour ash, rich in phosphorous, calcium and alkaline oxides, has been used to formulate (i) controlled-release fertilizers, since they manage to release the nutrient elements (P, K) at a low rate, and (ii) bioactive glasses. (i) Four formulations were tailored using different amounts of animal flour ash (35–48 wt%), potassium carbonate (10–25 wt%) and a fixed amount of glassy sand (40wt%) in order to get glasses and glass-ceramics. The materials were characterised from a chemical (XRF), crystallographic (XRD) and microstructural (SEM/EDS) point of view. Moreover, in order to check the ability to release the macro-and micro-nutrients, tests were conducted to determine the kinetics of glass dissolution in different media (2% citric acid solution, 1% hydrochloric acid solution and ammonium citrate solution). The results obtained allowed to confirm all samples show a very low solubility in water (less than 1%) and high values (>40%) of P, Ca, K and Na in the other media. (ii) The rich content of phosphorous and calcium oxides makes the animal waste-derived ash a potential low-cost raw material to produce bioactive glasses. The analysis was focused on a bioactive glass, named BG_Ca, whose composition comes from the standard Bioglass® 45S5, got by increasing as much as possible the CaO content to combine a controlled behaviour during processing and a good apatite-forming ability in a simulated body fluid (SBF). This preliminary investigation shows that animal flour ash is a versatile material,which may be successfully used for several applications as various as the production of fertilisers and the preparation of bioactive glasses.


2014 - Sol-gel derived bioactive glasses with low tendency to crystallize: synthesis, post-sintering bioactivity and possible application for the production of porous scaffolds. [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Salvatori, Roberta; Anesi, Alexandre; Chiarini, Luigi; Cannillo, Valeria
abstract

A new sol-gel (SG) method is proposed to produce special bioactive glasses (BG_Ca family) characterized by a low tendency to devitrify. These formulations, derived from 45S5 Bioglass®, are characterized by a high content of CaO (45.6 mol%) and by a partial or complete substitution of sodium oxide with potassium oxide (total amount of alkaline oxides: 4.6 mol%), which increases the crystallization temperature up to 900°C. In this way, it is possible to produce them by SG preserving their amorphous nature, in spite of the calcination at 850°C. The sintering behavior of the obtained SG powders is thoroughly investigated and the properties of the sintered bodies are compared to those of the melt-derived (M) counterparts. Furthermore, the SG glass powders are successfully used to produce scaffolds by means of a modified replication technique based on the combined use of polyurethane sponges and polyethylene particles. Finally, in the view of a potential application for bone tissue engineering, the cytotoxicity of the produced materials is evaluated in vitro.


2014 - Suspension thermal spraying of hydroxyapatite: microstructure and in vitro behaviour [Articolo su rivista]
Bolelli, Giovanni; Bellucci, Devis; Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella; N., Stiegler; P., Müller; A., Killinger; R., Gadow; L., Altomare; L., De Nardo
abstract

In cementless fixation of metallic prostheses, bony ingrowth onto the implant surface is often promoted by osteoconductive plasma-sprayed hydroxyapatite coatings. The present work explores the use of the innovative High Velocity Suspension Flame Spraying (HVSFS) process to coat Ti substrates with thin homogeneous hydroxy- apatite coatings. The HVSFS hydroxyapatite coatings studied were dense, 27–37 μm thick, with some transverse microcracks. La- mellae were sintered together and nearly unidentifiable, unlike conventional plasma-sprayed hydroxyapatite. Crystallinities of 10%–70% were obtained, depending on the deposition parameters and the use of a TiO2 bond coat. The average hardness of layers with low (b24%) and high (70%) crystallinity was ≈3.5 GPa and ≈4.5 GPa respectively. The distributions of hardness values, all characterised by Weibull modulus in the 5–7 range, were narrower than that of conventional plasma-sprayed hydroxyapatite, with a Weibull modulus of ≈3.3. During soaking in simulated body fluid, glassy coatings were progressively resorbed and replaced by a new, pre- cipitated hydroxyapatite layer, whereas coatings with 70% crystallinity were stable up to 14 days of immersion. The interpretation of the precipitation behaviour was also assisted by surface charge assessments, performed through Z-potential measurements. During in vitro tests, HA coatings showed no cytotoxicity towards the SAOS-2 osteoblast cell line, and surface cell proliferation was comparable with proliferation on reference polystyrene culture plates.


2013 - A new hydroxyapatite-based biocomposite for bone replacement [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; M., Gazzarri; F., Chiellini; Cannillo, Valeria
abstract

Since the 1970s, various types of ceramic, glass and glass–ceramic materials have been proposed and used to replace damaged bone in many clinical applications. Among them, hydroxyapatite (HA) has been successfully employed thanks to its excellent biocompatibility. On the other hand, the bioactivity of HA and its reactivity with bone can be improved through the addition of proper amounts of bioactive glasses, thus obtaining HA-based composites. Unfortunately, high temperature treatments (1200 °C ÷ 1300 °C) are usually required in order to sinter these systems, causing the bioactive glass to crystallize into a glass–ceramic and hence inhibiting the bioactivity of the resulting composite. In the present study novel HA-based composites are re- alized and discussed. The samples can be sintered at a relatively low temperature (800 °C), thanks to the em- ployment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5 Bioglass®. The rich glassy phase, which can be preserved during the thermal treatment, has excellent effects in terms of in vitro bioactivity; moreover, compared to composites based on 45S5 Bioglass® having the same HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferation.


2013 - Bioactive glass-based composites for the production of dense sintered body and porous scaffolds [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

Recently several attempts have been made to combine calcium phosphates, such as β-tricalcium phosphate (β-TCP) and, most of all, hydroxyapatite (HA), with bioactive glasses of different composition, in order to develop composites with improved biological and mechanical performance. Unfortunately, the production of such systems usually implies a high-temperature treatment (up to 1300 °C), which may result in several drawbacks, including crystallization of the original glass, decomposition of the calcium phosphate phase and/or reactions between the constituent phases, with non-trivial consequences in terms of microstructure, bioactivity and mechanical properties of the final samples. In the present contribution, novel binary compos- ites have been obtained by sintering a bioactive glass, characterized by a low tendency to crystallize, with the addition of HA or β-TCP as the second phase. In particular, the composites have been treated at a relatively low temperature (818 °C and 830 °C, depending on the sample), thus preserving the amorphous structure of the glass and minimizing the interaction between the constituent phases. The effects of the glass compo- sition, calcium phosphate nature and processing conditions on the composite microstructure, mechanical properties and in vitro bioactivity have been systematically discussed. To conclude, a feasibility study to obtain scaffolds for bone tissue regeneration has been proposed.


2013 - Suspension plasma sprayed bioactive glass coatings: effects of processing on microstructure, mechanical properties and in-vitro behaviour [Articolo su rivista]
Cattini, Andrea; L., Łatka; Bellucci, Devis; Bolelli, Giovanni; Sola, Antonella; Lusvarghi, Luca; L., Pawłowski; Cannillo, Valeria
abstract

Bioactive glass coatings deposited via suspension plasma spraying were studied to improve the adhesion between orthopaedic implants and bone. Fine powders of a bioactive glass, named BG_Ca, having composition (in wt.%): 4.7 Na2O, 42.3 CaO, 6.1 P2O5, 46.9 SiO2, were produced and dispersed in ethanol to form a suspension used as a feedstock. Various sets of spray parameters were applied in order to define the influence of the deposition process on the final coating properties. Consequently, the coatings were characterized in as-sprayed state and after soaking in a simulated body fluid (SBF) for different periods ranging from 1 to 14 days. The microstructural investigations were carried out using environmental scanning electron microscope (ESEM) and X-ray diffraction (XRD). The coatings’ adhesion to the substrate was evaluated by means of scratch tests. Finally, hardness and elastic modulus were determined by means of depth-sensing indentation methods.


2013 - Suspension plasma spraying of optimized functionally graded coatings of bioactive glass/hydroxyapatite [Articolo su rivista]
Cattini, Andrea; Bellucci, Devis; Sola, Antonella; L., Pawłowski; Cannillo, Valeria
abstract

The innovative suspension plasma spraying (SPS) technique was applied to produce a bioactive glass/hydroxy- apatite (HA) multi-layered functionally graded coating (FGC). The constituent phases were selected to combine the high bone-bonding ability of bioactive glasses (on the surface of the FGC) with the long-term stability of HA (close to the interface with the metal substrate). The fabrication method was optimised using the suspension feed rates which took into account the different deposition efficiencies of bioactive glasses and of HA. During the deposition process, which was carried out with a SG-100 torch an industrial robot was used to realise the torch movement and the spraying parameters were optimised in view of industrial applications of the coatings. A microstructural investigation was performed on the FGC using Raman spectroscopy and environmental scan- ning electron microscopy (ESEM) coupled with X-EDS microanalysis. The analysis confirmed that the obtained compositional gradient met the designed one. The coatings were characterised both in as-sprayed state and after soaking in a simulated body fluid (SBF) for periods ranging from 1 to 14 days. The FGC exhibited a strong reactivity in SBF and a high scratch resistance even after immersion, confirming its potential for biomedical applications.


2012 - A new highly bioactive composite for bone tissue repair [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

In the last few years several attempts have been made to combine hydroxyapatite (HA) with bioactive glasses of different composition, with the aim to obtain composite materials with improved bioactivity or mechanical properties for hard tissue surgery applications. However, high-temperature treatments are usually required in order to sinter HA-based composites, causing the bioactive glass to crystallize into a glass–ceramic, with possible negative effects on its bioactivity. Recently, a new glass composition, named BioK and inspired by the 45S5 Bioglass s , has been formulated by substituting the sodium oxide with the potassium oxide. The potassium oxide is expected to reduce the tendency to crystallize of the parent glass. In this work, for the first time the BioK is applied to realize HA-based composites. The novel samples can be sintered at a relative low temperature (7501C) compared with the widely studied HA/45S5 Bioglass s composites. The new glass formulation and the relatively low sintering temperature of the BioK-based composites greatly help to preserve the amorphous nature of the glass. According to in vitro tests, this has excellent effects in terms of bioactivity. Moreover Vickers microindentation measurements show that the BioK-containing composites preserve their local mechanical properties during immersion in body fluids.


2012 - Biomimetic coating on bioactive glass-derived scaffolds mimicking bone tissue [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; P., Gentile; G., Ciardelli; Cannillo, Valeria
abstract

Bioceramic ‘‘shell’’ scaffolds, with a morphology resembling the cancellous bone microstructure, have been recently obtained by means of a new protocol, developed with the aim to overcome the limits of the conventional foam replication technique. Because of their original microstruc- ture, the new samples combine high porosity, permeability, and manageability. In this study, for the first time, the novel bioactive glass shell scaffolds are provided with a gelatin- based biomimetic coating to realize hybrid implants whichmimic the complex morphology and structure of bone tissue. Moreover, the presence of the coating completely preserves the in vitro bioactivity of the bioactive glass samples, whose surfaces are converted into hydroxyapatite after a few days of immersion in a simulated body fluid solution (SBF).


2012 - Cermet coatings with Fe-based matrix as alternative to WC-CoCr: mechanical and tribological behaviour [Articolo su rivista]
Bolelli, Giovanni; T., Börner; Bozza, Francesco; Cannillo, Valeria; G., Cirillo; Lusvarghi, Luca
abstract

Recently, cermet coatings with Fe-based metal matrix have emerged as a less hazardous and more environ- mentally friendly alternative to WC–Co-based ones, which have known inhalation toxicity problems. This study therefore aimed to validate WC-based cermet coatings with Fe-based matrix, obtained using a com- mercially available feedstock powder, as an alternative to WC–CoCr. HVOF-sprayed WC–15 wt.%FeCrAl layers were therefore obtained using different oxygen and fuel (kerosene) flow rates and powder feed rates; their mechanical and tribological properties were compared to HVOF- sprayed WC–10 wt.% Co–4 wt.%Cr. The WC–FeCrAl coatings always exhibited equi-biaxial compressive residual stress state and possessed dense microstructures, with homogeneous metal matrix, but they contained more oxide inclusions than WC–CoCr. Their characteristics were significantly affected by the normalised oxygen-fuel ratio (λ). Small but meaningful differences existed between the ball-on-disc sliding wear rates of the various WC– FeCrAl coatings, the best sample being that with the most favourable combination of compressive residual stress, low oxidation and high hardness/modulus (H/E) ratio. Its sliding wear resistance was comparable to that of WC–CoCr. The cyclic ball impact resistance of WC–FeCrAl layers was also comparable to that of WC–CoCr, but the dry particle abrasion resistance was inferior, because of the brittleness induced by the oxide inclusions.


2012 - Deposition mechanisms in high velocity suspension spraying: Case study for two bioactive materials [Articolo su rivista]
Bolelli, Giovanni; Stiegler, Nico; Bellucci, D.; Cannillo, Valeria; Gadow, Rainer; Killinger, A.; Lusvarghi, Luca; Luca, Sola; Antonella,
abstract

Two different oxide-based bioactive materials, namely tricalcium phosphate (TCP) and K2O–CaO–P2O5–SiO2 bioactive glass (“Bio-K”), were processed by the High Velocity Suspension Flame Spraying (HVSFS) technique. Single splats were deposited onto polished cold glass plates using a custom-built experimental set up. In addition, complete coatings were deposited onto pre-heated Ti plates. Deposited splats and coatings were examined by scanning and transmission electron microscope (SEM, TEM) techniques and their phase composition was investigated by micro-Raman spectroscopy. The 3-D profiles of single splats were also reconstructed through atomic force microscopy (AFM). Based on the experimental results, explanations of the deposition mechanisms were put forward, discussing the different heating and melting behaviour of particles and agglomerates. The critical particle sizes needed to obtain deposition of molten splats at impact, and their solidification behaviour onto cold vs. hot surfaces were studied as well. Most importantly, the splats can only be formed by molten droplets comprised within a given size range (“sprayability window”). Smaller droplets possess insufficient thermal and mechanical inertia to overcome the stagnation flow in front of the substrate; larger ones are mostly unmelted. This “sprayability window” depends on the deposition process itself and on the physical properties of sprayed materials.


2012 - Elaboration and mechanical characterization of multi-phase alumina-based ultra-fine composites [Articolo su rivista]
P., Palmero; Sola, Antonella; V., Naglieri; Bellucci, Devis; M., Lombardi; Cannillo, Valeria
abstract

Al2O3-10 vol.% YAG and Al2O3-10 vol.% ZrO2 bi-phase composites as well as Al2O3-5 vol.% YAG-5 vol.% ZrO2 tri-phase composite were developed by controlled sur- face modification of an alumina powder with inorganic pre- cursors of the second phases. Green bodies were produced by dry pressing and slip casting and then sintered at 1500 °C. In particular, slip casting led to fully dense, defect-free, and highly homogenous samples, made of a fine dispersion of the second phases into the micronic alumina matrix, as observed by SEM. The mechanical characterization proved the pre- dominant role of the final density on the Vickers hardness, while the elastic modulus was affected by the volume fraction of the constituent phases, in fairly good agreement with the rule of mixture prediction. The fracture toughness values of the bi- and tri-phase materials were similar, and their crack paths revealed the importance of the thermal residual stresses at the matrix-reinforcement interfaces, promoting inter- granular propagations


2012 - Functionally graded WC-Co/Ni-Al HVOF coatings for damage tolerance, wear and corrosion protection [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; Rosa, Roberto; A., Valarezo; W. B., Choi; R., Dey; C., Weyant; S., Sampath
abstract

The manufacturing of a HVOF-sprayed functionally graded coating (FGC), consisting of two NiAl/WC–Co composite layers with increasing cermet content and a pure WC–Co topmost layer, is discussed in this paper. As the stress build-up during spraying, measured via curvature method, is reduced in the NiAl-rich layers, thick coatings can be deposited with lower risk of delamination, in comparison to a pure WC–Co thick layer. Thermal stresses within the layers and the stainless steel substrate, measured from low temper- ature thermal cycling tests, are also reduced. The mechanical behaviour of the top layer in the graded struc- ture at relatively low loads (i.e. pin-on-disk) is equivalent to the same layer without gradation, whereas at high loads (i.e. ball-drop impact test) the enhanced compliance with depth increases the load bearing capa- bility of the graded structure. Electrochemical corrosion tests demonstrate no significant interconnected porosity and therefore, no interaction of the graded layers with the topmost WC–Co layer. The deterioration of the deeper layers under wear and corrosive conditions are also tested to investigate their performance in the scenario that the top layer coating wears out exposing the deeper layers to the surface.


2012 - Heat treatment of Na2O-CaO-P2O5-SiO2 bioactive glasses: densification processes and postsintering bioactivity [Articolo su rivista]
Sola, Antonella; Bellucci, Devis; M. G., Raucci; S., Zeppetelli; L., Ambrosio; Cannillo, Valeria
abstract

Because of their excellent bioactivity, bioactive glasses are increasingly diffused to produce biomedical devi- ces for bone prostheses, to face the dysfunctions that may be caused by traumatic events, diseases, or even natural aging. However, several processing routes, such as the production of scaffolds or the deposition of coatings, include a thermal treat- ment to apply or sinter the glass. The exposure to high tem- perature may induce a devetrification phenomenon, altering the properties and, in particular, the bioactivity of the glass. The present contribution offers an overview of the thermal behavior and properties of two glasses belonging to the Na2O- CaO-P2O5-SiO2 system, to be compared to the standard 45S5 Bioglass VR . The basic goal is to understand the effect of both the original composition and the thermal treatment on the per- formance of the sintered glasses. The new glasses, the one (BG_Na) with a high content of Na2O, the other (BG_Ca) with a high content of CaO, were fully characterized and sinteringtests were performed to define the most interesting firing cycles. The sintered samples, treated at 880°C and 800°C respectively, were investigated from a microstructural point of view and their mechanical properties were compared to those of the bulk (not sintered) glass counterparts. The effect of sin- tering was especially striking on the BG_Ca material, whose Vickers hardness increased from 598.9 6 46.7 HV to 1053.4 6 35.0 HV. The in vitro tests confirmed the ability of the glasses, both in bulk and sintered form, of generating a hydroxyapatite surface layer when immersed in a simulated body fluid. More accurate biological tests performed on the sintered glasses proved the high bioactivity of the CaO-rich composition even after a heat treatment.


2012 - High Velocity Suspension Flame Sprayed (HVSFS) Hydroxyapatite Coatings for Biomedical Applications [Articolo su rivista]
N., Stiegler; Bellucci, Devis; Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; Sola, Antonella
abstract

In this study, hydroxyapatite (HAp) coatings were deposited on Ti plates by the high-velocity suspension flame spraying (HVSFS) technique. The process characteristic, the microstructure and phase composi- tion of the coatings are significantly influenced by the solvent and by the design of the combustion chamber (CC) of the HVSFS torch. Water-based suspensions always lead to fairly low surface tem- peratures ( 350 °C), deposition efficiencies <40%, and produce coatings with low amount of crystalline HAp, which tend to dissolve very rapidly in simulated body fluid (SBF) solutions. DEG-based suspen- sions, when sprayed with properly-designed CCs, produce deposition efficiencies of 45-55% and high surface temperatures (550-600 °C). In these coatings, the degree of crystallinity increases from the bottom layer to the top layer, probably because the increasingly large surface temperature can eventually favour re-crystallisation of individual lamellae during cooling. These coatings are much more stable in SBF solutions.


2012 - High Velocity Suspension Flame Sprayed (HVSFS) potassium-based bioactive glass coatings with and without TiO2 bond coat [Articolo su rivista]
Bellucci, Devis; Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; Sola, Antonella; N., Stiegler
abstract

Titanium plates were coated by high-velocity suspension flame spraying (HVSFS) technique using a novel bioactive glass composition based on the K2O–CaO–P2O5–SiO2 composition (“Bio-K”). On half of the samples, an atmospheric plasma sprayed (APS) TiO2 bond coat was preliminarily deposited; suspensions of attrition- milled micron-sized glass powders, dispersed in a water + isopropanol mixture, were then sprayed onto both bare and bond-coated plates using five different process parameter sets. The microstructure of the coatings is independent of the presence of the bond coat but is strongly influenced by the deposition parameters. If the latter result in surface temperatures larger than the glass transition tem- perature of the Bio-K composition, large-scale viscous flow allows the expansion of the air entrained in the porosities, developing large rounded pores. When this phenomenon is avoided, denser layers are obtained. In tensile adhesion tests, porous layers fail cohesively at low loads, whereas adhesive/cohesive failure occurs in denser layers. In this latter case, the adhesion strength is significantly improved by the bond coat, reaching maximum values of 17 MPa. When immersed in simulated body fluid (SBF), the coating surface is rapidly converted into a silica gel because of ion leaching. A hydroxyapatite layer starts precipitating on top of it after 3 days and grows into a uniform film (of ≈ 10 μm thickness) after 2 weeks.


2012 - Low temperature sintering of innovative bioactive glasses [Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract

Two innovative glass compositions based on the commonly used 45S5 Bioglass® were developed by increasing the calcium quan- tity and replacing the sodium oxide with a specific content of potassium oxide. The new glasses, named BG_Ca/K and BG_Ca/Mix, can be prepared using a conventional melting process and show a very low tendency to crystallize. Thanks to this peculiarity, BG_Ca/K and BG_Ca/Mix powders can be sintered at a relatively low temperature (800°C) to obtain sam- ples of high compactness and bioactivity, since their amorphous nature is preserved. Consequently, the proposed glasses are perfect for making specific products such as scaffolds or hydroxyapatite-based composites. Furthermore, the relatively low alkali amount in the new compositions gives rise to a slow ion leaching in simulated body fluid, thus avoiding abrupt changes in pH that can damage osteoblasts or negatively affect their behavior.


2012 - Processing and characterization of innovative scaffolds for bone tissue engineering [Articolo su rivista]
Bellucci, Devis; F., Chiellini; G., Ciardelli; M., Gazzarri; P., Gentile; Sola, Antonella; Cannillo, Valeria
abstract

A new protocol, based on a modified replication method, is proposed to obtain bioactive glass scaffolds. The main feature of these samples, named ‘‘shell scaffolds’’, is their external surface that, like a compact and porous shell, provides both high permeability to fluids and mechanical support. In this work, two different scaffolds were prepared using the following slurry components: 59 % water, 29 % 45S5 BioglassÒ and 12 % polyvinylic binder and 51 % water, 34 % 45S5 BioglassÒ, 10 % polyvinylic binder and 5 % polyethylene. All the proposed samples were charac- terized by a widespread microporosity and an intercon- nected macroporosity, with a total porosity of 80 % vol. After immersion in a simulated body fluid (SBF), the scaffolds showed strong ability to develop hydroxyapatite, enhanced by the high specific surface of the porous systems. Moreover preliminary biological evaluations suggested a promising role of the shell scaffolds for applications in bone tissue regeneration. As regards the mechanical behaviour, the shell scaffolds could be easily handled without damages, due to their resistant external surface. More specifically, they possessed suitable mechanical properties for bone regeneration, as proved by compression tests performed before and after immersion in SBF.


2012 - Synthesis and Thermal Stability of Hydroxyapatite- Coated Zirconia Nanocomposite Powders [Articolo su rivista]
F., Bondioli; Cannillo, Valeria; Ferrari, Anna Maria; A., Tewari
abstract

Hydroxyapatite (HA) is a well-known and valuable implant material with biocompatibility and bioactive properties. Full uti- lization of the unique properties of hydroxyapatite bulk ceramics is, however, enhanced by a proper reinforcement, i.e., by prepa- ration of composites. The goal of this study was to synthesize a HA-coated zirconia composite nanopowders by the precipitation of HA in presence of zirconia. The idea was to avoid, in this way, uncontrolled agglomeration of the zirconia nanostructured rein- forcement during the sintering step.


2011 - A new generation of scaffolds for bone tissue engineering [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Cattini, Andrea; Sola, Antonella
abstract

The design of bioceramic scaffolds, i.e. artificial structures employed as temporary templates for cell proliferation, is a crucial issue in bone tissue reconstruction and regeneration. An ideal scaffold should be highly porous and bioactive. Additionally, a resistant and permeable surface is required in order to have manageable samples. The production of scaffolds by means of the widely used replication method can lead to samples with weak and brittle surfaces and poor mechanical properties, therefore alternative preparation procedures are necessary. In this work a new protocol to realize bioceramic scaffolds is presented. The obtained samples have an original structure, characterized by an external resistant surface together with a highly porous internal network. The external surface, which behaves as a load-bearing structure for the entire scaffold, guarantees high permeability and manageability. Here the proposed protocol is briefly discussed, together with an overview on the structure of the realized samples. Finally, some preliminary data regarding the scaffolds in-vitro bioactivity are reported


2011 - A new highly bioactive composite for scaffold applications: a feasibility study [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Hydroxyapatite (HA) has been widely investigated as scaffolding material for bone tissue engineering, mainly for its excellent biocompatibility. Presently, there is an increasing interest in the composites of hydroxyapatite with bioactive glasses, with the aim to obtain systems with improved bioactivity or mechanical properties. Moreover, modifying the ratio between bioactive glass and hydroxyapatite results in the possibility of controlling the reaction rate of the composite scaffold in the human body. However, high temperature treatments are usually required in order to sinter HA-based composites, causing the bioactive glass to crystallize into a glass-ceramic, with possible negative effects on its bioactivity. In the present research work, a glass composition belonging to the Na2O-CaO-P2O5-SiO2 system, with a reduced tendency to crystallize, is applied to realize HA-based composites. The novel samples can be sintered at a relative low temperature (750 °C) compared to the widely studied HA/45S5 Bioglass® composites. This fact greatly helps to preserve the amorphous nature of the glass, with excellent effects in terms of bioactivity, according to in vitro tests. As a first application, the obtained composites are also tested to realize highly porous scaffolds by means of the standard burning out method.


2011 - A new potassium-based bioactive glass: sintering behavior and possible applications for bioceramic scaffolds [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Providing structural support while maintaining bioactivity is one of the most important goals for bioceramic scaffolds, i.e. artificial templates which guide cells to grow in a 3D pattern, facilitating the formation of functional tissues. In the last few years, 45S5 Bioglass1 has been widely investigated as scaffolding material, mainly for its ability to bond to both hard and soft tissues. However, thermal treatments to improve the relatively poor mechanical properties of 45S5 Bioglass1 turn it into a glass-ceramic, decreasing its bioactivity. Therefore, the investigation of new materials as candidates for scaffold applications is necessary. Here a novel glass composition, recently obtained by substituting the sodium oxide with potassium oxide in the 45S5 Bioglass1 formulation, is employed in a feasibility study as scaffolding material. The new glass, named BioK, has the peculiarity to sinter at a relatively low temperature and shows a reduced tendency to crystallize. In this work, BioK has been employed to realize two types of scaffolds. The obtained samples have been fully characterized from a microstructural point of view and compared to each other. Additionally, their excellent bioactivity has been established by means of in vitro tests


2011 - A revised replication method for bioceramic scaffolds [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract


2011 - Bioactive glass coatings: a review [Articolo su rivista]
Sola, Antonella; Bellucci, Devis; Cannillo, Valeria; Cattini, Andrea
abstract

Bioactive glasses, discovered by Hench and co-workers at the end of the 1960s, are among the most promising biomaterials for bone repair and reconstruction, mainly thanks to their high bioactivity index. Unfortunately, due to their brittleness and relatively poor mechanical properties, their clinical applications are limited to non-load bearing implants. However, bioactive glasses can be successfully employed as coatings on bioinert metallic substrates, in order to combine high bioactivity with mechanical strength. After a brief introduction to the main properties of biomaterials and bioactive glasses, the present paper provides an overview of the different approaches and available techniques to realise bioactive glass coatings, with a particular emphasis on thermal spray, which is nowadays one of the most popular coating procedures.


2011 - Calcium and potassium addition to facilitate the sintering of bioactive glasses [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Nowadays bioactive glasses are diffused in medical practice due to their excellent bioactivity. However high temperature treatments, which are commonly required in several processing routes, may induce the glass to crystallize into a glass-ceramic, with possible negative effects on its bioactivity. In this work a new bioactive glass composition, inspired by the widely used Bioglass® 45 S5, was formulated by increasing the calcium content and substituting the sodium oxide with potassium oxide. The novel glass can be treated at a relatively low temperature (800 °C) and it is characterized by a reduced tendency to crystallize with excellent effects in terms of bioactivity, according to in vitro tests. Therefore, the new composition opens intriguing scenarios whenever a thermal treatment is required to apply or to sinter the glass, such as in the production of scaffolds or the deposition of coatings.


2011 - Coefficient of thermal expansion of bioactive glasses: available literature data and analytical equation estimates [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Bioactive glasses are able to develop a tenacious bond with human bone tissues and therefore they are largely used in orthopaedic and dental implants. However, due to their brittleness, they are mainly applied as coatings on tough substrates, such as titanium, alumina and zirconia. The reliability of bioactive glass coatings is deeply influenced by their thermodilatometric compatibility with the substrate, which may govern the development of dangerous thermal stresses at the interface. In spite of the technological relevance of the coefficient of thermal expansion (CTE) of bioactive glasses, few papers are specifically dedicated to such topic. In the present contribution, more than 70 bioactive glasses were reviewed in the literature, in order to investigate the relation existing between their composition and their CTE. Then four analytical models were applied to estimate the CTE of the same glasses and the calculated values were compared to the experimental results, in order to assess the reliability of the models and define an effective tool to predict the CTE. In particular, on the basis of the literature data and calculated values, the effect of modifier oxides and intermediate oxides, such as KO and MgO, on the CTE was discussed.


2011 - Deposizione di rivestimenti in Al2O3 mediante High Velocity Suspension Flame Spraying (HVSFS): caratteristiche dei riporti ed effetto dei parametri operativi [Articolo su rivista]
Bolelli, Giovanni; B., Bonferroni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch; N., Stiegler
abstract

The HVSFS (High Velocity Suspension Flame Spraying) technique is a novel thermal spray process which consists of a modification to a standard gas-fuelled HVOF system in order to enable feeding of the torch with a liquid suspension instead of a dry powder. The suspension consists of fine (micrometre- or nanometer-sized) particles dispersed in a liquid medium. This process enables the deposition of relatively thin (&lt;100 μm) and dense ceramic coatings, which could not be obtained by standard thermal spraying, since the flowability of very fine powders in dry form is too poor to allow proper feeding. These flowability problems are overcome by employing a liquid medium as carrier. Using such fine particles, the average lamella size is reduced compared to conventional thermal spray coatings, which is beneficial for improved smoothness (lower surface toughness in as-deposited condition) and density (better packing, smaller pores) and allows the deposition of homogeneous layers of reduced thickness. The properties of a HVSFS-deposited coating are critically affected by the properties of the suspension and particularly by the nature of the solid phase (primary particle size distribution, agglomeration behaviour); however, systematic studies on this relationship have not been performed yet. In this research, HVSFS Al2O3 coatings were therefore produced using three different suspensions, each containing a different fine alumina powder, dispersed in a water + isopropanol mixture: a micrometric powder (d50 ≈ 2 μm) and two nanometric ones with identical average size (d50 ≈ 70 nm) but different agglomeration behaviour. All suspensions contained 20 wt.% of solid phase. Each suspension was sprayed using two distinct parameter sets, so that a total of 6 different coatings were obtained. The results showed that, irrespective of the process parameters, the suspension containing micrometric particles yielded harder (HV0.05 = 1200 - 1300 kg/mm2) and smoother (Ra ≈ 1.3 μm) coatings. It was noted that micron-sized particles have low tendency to agglomeration; therefore, when the solvent (water + isopropanol mixture) evaporates in the thermal spray gas jet, the suspension releases many individual micrometric particles of 1 - 2 μm diameter. These particles are fully melted at impact and, on account of their high impact velocity, they result in a dense and homogeneous stacking of well-flattened lamellae. Although these coatings also exhibit the largest tensile residual stresses (between 50 MPa and 100 MPa), their excellent cohesive strength endows them with superior sliding wear resistance (tested under "ball-on-disk" configuration against sintered alumina spheres) in comparison to the other HVSFS-deposited coatings and to conventional HVOF-sprayed Al2O3 coatings. As nanometre-sized particles are always agglomerated within the suspension, the resulting lamella size does not depend on the size of the (nanometric) primary particles, but on that of the agglomerates, which are released in the gas jet when the liquid phase evaporates. When agglomerates are sufficiently small (0.5 - 2.5 μm), quite dense coatings can be achieved; excessively large agglomerates, by contrast, tend to remain unmelted, giving rise to defective coatings and impairing the deposition efficiency. In conclusion, the HVSFS process was shown to be able to produce high-quality coatings, superior to those obtained by conventional thermal spraying techniques; however, proper control over the behaviour of the solid phase must be acquired; in particular, individual particles or agglomerates should ideally be comprised between 0.5 and 2.5 μm in order to optimize density, hardness, smoothness and deposition efficiency.


2011 - In situ Raman spectroscopic investigation of bioactive glass reactivity: Simulated Body Fluid solution VS TRIS-buffered solution [Articolo su rivista]
Bellucci, Devis; Bolelli, Giovanni; Cannillo, Valeria; Cattini, Andrea; Sola, Antonella
abstract

In the present contribution, the innovative in-situ Raman micro-spectroscopy was applied to investigate the in vitro reactivity of various bioactive glasses. All the investigated glasses belonged to the Na2O\K2O-CaO-P2O5-SiO2 system, but contained sensibly different percentages of network modifiers. The glasses were immersed for increasing times, up to 96 hours, in simulated body fluid (SBF) and in tris-buffered (TRIS) solution. In this way, two fundamental items were addressed, i.e. the effect of the glass composition and the nature of the soaking fluid on the overall reactivity. As regards the SBF, all the glasses were able to promote the formation of a hydroxyl-carbonate apatite (HCA) surface layer in very short times. The reaction rate was particularly quick for the 45S5 Bioglass® and for its potassium-based variant (BioK), however all the glasses could form a continuous HCA layer already after 96 hours. The observed difference in reaction kinetics may be due to the glass composition, since the glasses relatively poor in Na ions (BG_Ca) experience slower ion release in the first stages of the HCA formation, while the glasses relatively poor in Ca ions (BG_Na) undergo slower nucleation and growth of HCA. The development of HCA was also observed in TRIS, but the reaction rate was generally slower than in SBF. In fact, while the SBF is a complicated solution supersaturated in apatite, which favours the precipitation of HCA, the TRIS is a simple tris(hydroxymethyl)aminomethane solution in water, which does not provide the ions for the HCA formation. As a consequence, the aforementioned effects due to the glass composition were even more evident in TRIS than in SBF. Nevertheless the TRIS could represent a valuable alternative to the standard SBF whenever a slow reaction rate might be beneficial, such as, for example, in order to better observe the samples evolution.


2011 - Macroporous Bioglass® -derived glass scaffolds for bone tissue regeneration [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella; F., Chiellini; M., Gazzarri; C., Migone
abstract

Since it was introduced at the end of the ‘60s, the 45S5 Bioglass1 has played a fundamental role among the materials for orthopedic applications because of its ability to build a stable bond with the surrounding bone. The recent development of bone tissue engineering has led the interest of many scientists in the design of Bioglass1-based scaffolds, i.e. porous systems able to drive and foster the bone tissue regrowth. Among the available techniques to realize scaffolds, the polymer burning out method, which employs organic particles as pore generating agents in a ceramic matrix, combines versatility and low cost. In spite of the advantages of the polymer burning out method, this technique has been rarely applied to 45S5 Bioglass1 and a systematic feasibility study has not been carried out on this issue yet. In order to fill this gap, in the present contribution the polymer burning out method was employed to design macroporous scaffolds based on 45S5 Bioglass1. Different amounts of organic phase were used to obtain samples with different porosity. The samples were characterized from a microstructural point of view, in order to evaluate the pore morphology, dimension and degree of interconnectivity. Such findings proved that a proper setting of the processing parameters made it possible to achieve very high porosity values, among the best ones obtained in the literature with the same technique, together with an appreciable mechanical behaviour, according to compression tests. Finally, the scaffolds bioactivity was assessed by means of in vitro tests in a simulated body fluid (SBF) solution. Moreover, in the view of a potential application for bone tissue engineering, a preliminary biological evaluation of the obtained scaffolds to sustain cell proliferation was carried out.


2011 - Microstructure and in vitro behaviour of 45S5 bioglass coatings deposited by high velocity suspension flame spraying (HVSFS) [Articolo su rivista]
L., Altomare; Bellucci, Devis; Bolelli, Giovanni; Bonferroni, Benedetta; Cannillo, Valeria; L., De Nardo; R., Gadow; A., Killinger; Lusvarghi, Luca; Sola, Antonella; N., Stiegler
abstract

The high-velocity suspension flame spraying technique (HVSFS) was employed in order to deposit 45S5 bioactive glass coatings onto titanium substrates, using a suspension of micron-sized glass powders dispersed in a water ? isopropanol mixture as feedstock. By modifying the process parameters, five coatings with different thick- ness and porosity were obtained. The coatings were entirely glassy but exhibited a through-thickness micro- structural gradient, as the deposition mechanisms of the glass droplets changed at every torch cycle because of the increase in the system temperature during spraying. After soaking in simulated body fluid, all of the coatings were soon covered by a layer of hydroxyapatite; furthermore, the coatings exhibited no cytotoxicity and human osteosar- coma cells could adhere and proliferate well onto their surfaces. HVSFS-deposited 45S5 bioglass coatings are therefore highly bioactive and have potentials as replace- ment of conventional hydroxyapatite in order to favour osseointegration of dental and prosthetic implants.


2011 - Un vetro al potassio per l’ingegneria tissutale [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; G., Ciardelli; P., Gentile; Sola, Antonella
abstract


2011 - Una nuova tipologia di scaffold per ingegneria tissutale ossea [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Cattini, Andrea; Sola, Antonella
abstract


2010 - A new bioactive glass composition for bioceramic scaffolds [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Bioactive-glass-derived scaffolds are crucial in bone tissue engineering since they act as temporary templates for tissue regrowth, providing structural support to the cells in a resulting 3D architecture. However, many issues remain open with regard to their design. On the one hand, bioceramic scaffolds should be bioactive, highly porous and should possess adequate mechanical properties; on the other hand, attempts to improve the mechanical properties of the widely used 45S5 Bioglass ® turn the bioactive glass itself into a glass-ceramic, with non-trivial effects on the resulting scaffold bioactivity. In this work, for the first time a new bioactive glass composition was employed to produce scaffolds for bone tissue engineering. The new glass composition can be treated at a relatively low temperature and it is characterized by a reduced tendency to crystallize compared to the 45S5 Bioglass ®. Moreover, the presented scaffolds are realized with a recently developed technique described here in detail. The resulting samples are highly porous and bioactive. Additionally, they possess a resistant and at the same time permeable surface similar to a shell, which ensures good manageability.


2010 - A new generation of scaffolds for bone tissue engineering [Capitolo/Saggio]
Bellucci, Devis; Cannillo, Valeria; Cattini, Andrea; Sola, Antonella
abstract


2010 - An overview of the effects of thermal processing on bioactive glasses [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Bioglass® 45S5 is widely used in biomedical applications due to its ability to bond to bone and even to soft tissues. The sintering ability of Bioglass® powders is a key factor from a technological point of view, since its govern the production of advanced devices, ranging from highly porous scaffolds to functionalized coatings. Unfortunately this particular glass composition is prone to crystallize at the temperature required for sintering and this may impair the bioactivity of the original glass. For these reasons, a prerequisite to tailor the fabrication of Bioglass®-derived implants is to understand the interaction between sintering, crystallization and bioactivity. In this work the structural transformations which occur during the heat treatment of Bioglass® are reviewed and a special attention is paid to the sintering and crystallization processes. Moreover the bioactivity of the final glass-ceramics is discussed and some alternative glass formulations are reported.


2010 - Bioactivity of thermal plasma synthesized bovine hydroxyapatite/glass ceramic composites [Relazione in Atti di Convegno]
C. P., Yoganand; V., Selvarajan; Mahmoud, Rouabhia; Cannillo, Valeria; Sola, Antonella
abstract

Bone injuries and failures often require the inception of implant biomaterials. Research in this area is receiving increasing attention worldwide. A variety of artificial bone materials, such as metals, polymeric materials, composites and ceramics, are being explored to replace diseased bones. Calcium phosphate ceramics are currently used as biomaterials for many applications in both dentistry and orthopedics. Bioactive silicate-based glasses show a higher bioactive behaviour than calcium phosphate materials. It is very interesting to study the mixtures of HA and silicate-based glasses. In the present study; natural bovine hydroxyapatite / SiO2–CaO–MgO glass composites were produced using the Transferred arc plasma (TAP) melting method. TAP melting route is a brisk process of preparation of glass-ceramics in which the raw materials are melted in the plasma and crystallization of the melt occurs while cooling down at a much faster rate in relatively short processing times compared to the conventional methods of manufacture of glass ceramics/composites. It is well known that; one essential step to the understanding of the biological events occurring at the bone tissue/material interface is the biological investigation by in vitro tests. Cell lines are commonly used for biocompatibility tests, and are very efficient because of their reproducibility and culture facility. In this study, we report the results of a study on the response of primary cultures of human fibroblast cells to TAP melted bioactive glass ceramics.


2010 - Bioceramic scaffolds: where materials science meets life – Part I [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Tissue engineering is a new and highly multidisciplinary field. The main objective is to realize “living alternatives” for harvested tissues to be employed in reconstructive surgery. A key issue for tissue engineering is the design of scaffolds, i.e. artificial temporary structures acting as extracellular matrices to support the tissue regrowth. After a brief introduction on biomaterials, the main properties of scaffolds are reviewed, with a particular emphasis on scaffolds for bone tissue engineering, which can be used whenever a skeletal defect occurs because of trauma, diseases or degenerative pathologies. Bioceramic scaffolds have the great advantage to interact with bone tissue by forming a direct bond. Moreover, they can resorb in a predictable way, at the same rate as the bone tissue is repaired. The recent development of a new generation of scaffolds, based on the highly bioactive Bioglass®, is addressed. The realization of these structures is then explored discussing the widely used sponge replication and burning out techniques.


2010 - Bioceramic scaffolds: where materials science meets life – Part II [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract


2010 - Characterization and in vitro bioactivity of natural hydroxyapatite based bio-glass-ceramics synthesized by thermal plasma processing [Articolo su rivista]
C. P., Yoganand; V., Selvarajan; Cannillo, Valeria; Sola, Antonella; E., Roumeli; O. M., Goudouri; K. M., Paraskevopoulos; Mahmoud, Rouabhia
abstract

Natural bovine hydroxyapatite/SiO2–CaO–MgO glass–ceramics were produced using the transferred arc plasma (TAP) processing method. Homogeneous mixtures of HA/25 wt% SiO2–CaO–MgO and HA/50 wt% SiO2–CaO–MgO batches obtained by dry mixing the respective compositions in a ball mill were processed in argon plasma using the TAP torch at 5 kW for 1, 2 and 3 min, respectively. The synthesized glass–ceramic samples were studied for phase composition, microstructure and bioactivity. The phase study of the synthesized glass–ceramics revealed the formation of calcium phosphate silicate with traces of calcium silicate. The structural study by SEM revealed that the prepared samples possessed smooth glassy surface morphology. The in vitro-bioactivity of the TAP synthesized glass–ceramics was examined in simulated body fluid (SBF). The SBF test results confirmed the development of crystalline carbonated apatite phase after 12 days of immersion. The cytocompatibility was evaluated through human fibroblast cell proliferation. The fibroblasts culture results showed that the sample was non- toxic and promoted cell growth.


2010 - Cristallizazione e bioattività: gli effetti del trattamento termico sui vetri bioattivi [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Manfredini, Tiziano; Sola, Antonella
abstract


2010 - Damage tolerant functionally graded WC-Co/Stainless Steel HVOF coatings [Articolo su rivista]
A., Valarezo; Bolelli, Giovanni; W. B., Choi; S., Sampath; Cannillo, Valeria; Lusvarghi, Luca; Rosa, Roberto
abstract

In this paper, effective damage tolerance of a functionally graded coating (FGC) deposited by high velocity oxygen fuel (HVOF) spraying is observed. The thick FGC (≈1.2 mm) consists of 6 layers with a stepwise change in composition from 100 vol.% ductile AISI316 stainless steel (bottom layer) to 100 vol.% hard WC-12Co (top layer) deposited onto an AISI316 stainless steel substrate. Damage tolerance is observed via 1) an increase in compliance with depth, and 2) an increase in fracture resistance by containment, arrest and deflection of cracks. A smooth gradation in the composition and hardness through the coating thickness is found by scanning electron microscopy and depth-sensing microindentation, respectively. The in-situ curvature measurement technique reveals that during the deposition of the FGC, compressive stresses exist in the lower, metallic layers owing to peening effect of successive impact, and these gradually evolve to high tensile, in the top layers. Tensile stresses appear to be due to quenching alone; thermal stresses are low because of the gradation. All of this is beneficial for the deposition of a thick coating.The FGC structure shows the ability to reduce cracking with increased compliance in the top layer during static and dynamic normal contact loading, while retaining excellent sliding wear resistance (ball-on-disk tests). Results are discussed in comparison to the behavior and properties of coatings of similar individual compositions and thicknesses, as well as a thick monolithic WC-12Co sprayed coating. Further improvements in the processing are proposed to enhance the adhesion strength and avoid coating delamination under high load contact-fatigue conditions.


2010 - Different approaches to produce coatings with bioactive glasses: enameling vs plasma spraying [Articolo su rivista]
Cannillo, Valeria; Sola, Antonella
abstract

Two alternative approaches, enamelling and plasma spraying, were tested to deposit coatings made with two different bioactive glasses: the established Bioglass ® 45S5, which is considered as a term of comparison, and the experimental BioK. The strong points and weaknesses of the two methods were highlighted. From the analysed samples, it resulted that the enamelling approach works well on thermally stable substrates and creates a strong bond, characterized by a compositional gradient, with alumina substrates. However the coating thickness must be carefully controlled to limit the thermal residual stresses and the glass formulation should be designed to reduce the glass tendency to crystallize. Instead plasma spraying is suitable for any kind of substrate and is highly automatizable, but the equipment is expensive and the coatings are likely to retain some defectiveness, which makes a post-deposition thermal treatment necessary. Both enamelling and plasma spraying may induce crystallization phenomena, depending on the glass formulation. The introduction of potassium oxide in the glass composition, such as in the BioK, may be useful to hinder the crystallization.


2010 - Effect of the suspension composition on the microstructural properties of high velocity suspension flame sprayed (HVSFS) Al2O3 coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch; Romagnoli, Marcello
abstract

Seven different Al2O3-based suspensions were prepared by dispersing two nano-sized Al2O3 powders (having analogous size distribution and chemical composition but different surface chemistry), one micron-sized powder and their mixtures in a water+isopropanol solution. High velocity suspension flame sprayed (HVSFS) coatings were deposited using these suspensions as feedstock and adopting two different sets of spray parameters. The characteristics of the suspension, particularly its agglomeration behaviour, have a significant influence on the coating deposition mechanism and, hence, on its properties (microstructure, hardness, elastic modulus). Dense and very smooth (Ra ~ 1.3 μm) coatings, consisting of well- flattened lamellae having a homogeneous size distribution, are obtained when micron-sized (~1 -2 μm) powders with low tendency to agglomeration are employed. Spray parameters favouring the break-up of the few agglomerates present in the suspension enhance the deposition efficiency (up to >50%), as no particle or agglomerate larger than ~2.5 μm can be fully melted. Nano-sized powders, by contrast, generally form stronger agglomerates, which cannot be significantly disrupted by adjusting the spray parameters. If the chosen nanopowder forms small agglomerates (up to few microns), the deposition efficiency is satisfactory and the coating porosity is limited, although the lamellae generally have a wider size distribution, so that roughness is somewhat higher. If the nanopowder forms large agglomerates (on account of its surfacechemistry), poor deposition efficiencies and porous layers are obtained. Although suspensions containing the pure micron-sized powder produce the densest coatings, the highest deposition efficiency (~70%) is obtained by suitable mixtures of micron-and nano-sized powders, on account of synergistic effects


2010 - Highly porous polycaprolactone-45S5 bioglass® scaffolds for bone tissue engineering [Articolo su rivista]
Fabbri, Paola; Cannillo, Valeria; Sola, Antonella; A., Dorigato; F., Chiellini
abstract

Highly porous biocompatible composites made of polycaprolactone (PCL) and 45S5 Bioglass® (BG) were prepared by a solid-liquid phase separation method (SLPS). The composites were obtained with BG weight contents varying in the range 0-50%, using either dimethylcarbonate (DMC) or dioxane (DIOX) as solvent, and ethanol as extracting medium. The porosity of the scaffolds was estimated to be about 88-92%. Mechanical properties showed a dependence on the amount of BG in the composites, but also on the kind of solvent used for preparation, composites prepared with DIOX showing enhanced stress at deformation with respect to composites prepared with DMC (stress at 60% of deformation being as high as 214 ± 17 kPa for DIOX-prepared composites and 98 ± 24 kPa for DMC-prepared ones, with 50% wt/wtPCL of glass), as well as higher elastic modulus (whose value was 251 ± 32 kPa for DIOX-prepared scaffolds and 156 ± 36 kPa for DMC-prepared ones, always with 50% wt/wtPCL of glass). The ability of the composites to induce precipitation of hydroxyapatite was positively evaluated by means of immersion in simulated body fluid and the best results were achieved with high glass amounts (50% wt/wtPCL). In-vitro tests of cytotoxicity and osteoblast proliferation showed that, even if the scaffolds are to be considered non-cytotoxic, cells suffer from the scarce wettability of the composites.


2010 - La modellazione quale strumento per la previsione del comportamento e delle funzionalità [Articolo su rivista]
Cannillo, Valeria; Montorsi, Monia
abstract


2010 - Microstructure and in-vitro behaviour of a novel High Velocity Suspension Flame Sprayed (HVSFS) bioactive glass coating [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; Sola, Antonella; N., Stiegler
abstract

Bioactive glass coatings based on a novel SiO2-P2O5-CaO-K2O system (“Bio-K”) were deposited by the High-Velocity Suspension Flame Spraying (HVSFS) technique. Attrition-milled micrometric powder particles, dispersed in water+isopropanol, were sprayed onto Ti plates. The coatings remained entirely glassy, but the glass underwent some structural alterations during processing. After soaking in simulated body fluid (SBF), a quite uniform hydroxyapatite layer was developed on the coatings, which indicates they may have the potential to favour osseointegration of prosthetic implants.


2010 - Monte Carlo simulation of microstructure evolution in biphasic systems [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

Over the past few decades, a variety of models have been proposed in order to investigate the grain growth kinetics and the development of crystallographic textures in polycrystalline materials. In particular, a full understanding of the microstructure evolution is a key issue for ceramic systems, since their mechanical or thermal behaviour is intimately related to their microstructure. Moreover, the development of appropriate simulative tools is crucial to reproduce, control and finally optimize the solid-state sintering process of ceramics. Monte Carlo simulations are particularly attractive because of their ability to reproduce the statistical behaviour of atoms and grain boundaries with time. However, Monte Carlo simulations applied to two-phase materials, such as many ceramic systems, result complex because both grain growth and diffusion processes should be taken into account. Here the Monte Carlo Potts model, which is widely used to investigate the crystallization kinetics for monophasic systems, is modified and extended to biphasic ones. The proposed model maps the microstructure onto a discrete lattice. Each lattice element contains a number representing its phase and its crystallographic orientation. The grain formation and growth are simulated by appropriate switching and reorientation attempts involving the lattice elements. The effect of temperature is also discussed.


2010 - Potassium based bioactive glass for bone tissue engineering [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; G., Ciardelli; P., Gentile; Sola, Antonella
abstract

A fundamental issue for the restoration of bone defects according to a tissue engineering approach is the development of highly porous bioactive scaffolds. The polymer burning out method is widely employed to fabricate bioceramic scaffolds because of its versatility, simplicity and low cost. However, the resulting scaffolds may suffer low porosity and non-interconnected pores. In the present contribution a new fabrication method is presented. Thanks to a recently developed potassium-based bioactive glass, which has the peculiarity to be sintered at a relatively low temperature (i.e. 750 C), it was possible to use sodium chloride particles as pore generating agents, which helped to maintain the shape of the struts during the entire sintering process. The salt particles can be easily removed by immersing the scaffold in water, giving place to a structure that combines high porosity (in the 70–80 vol.% range) with interconnected pores and an appreciable mechanical behaviour (Young’s modulus in the 3.4–3.7 MPa range according to compression tests).


2010 - Processing and characterisation of High-Velocity Suspension Flame Sprayed (HVSFS) bioactive glass coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch
abstract

The High-Velocity Suspension Flame Spraying (HVSFS) technique was employed in order to deposit bioactive glass coatings onto titanium substrates. Two different glass compositions were examined: the classical 45S5 Bioglass and a newly-developed SiO2–CaO–K2O–P2O5 glass, labelled as “Bio-K”. Suitable raw materials were melted in a furnace and fritted by casting into water. The frit was dry-milled in a porcelain jar and subsequently attrition-milled in isopropanol. The resulting micron- sized powders were dispersed in a water+isopropanol mixture, in order to prepare suitable suspensions for the HVSFS process. The deposition parameters were varied; however, all coatings were obtained by performing three consecutive torch cycles in front of the substrate. The thickness and porosity of the coatings were significantly affected by the chosen set of deposition parameters; however, in all cases, the layer produced during the third torch cycle was thicker and denser than the one produced during the first cycle. As the system temperature increases during the spraying process, the particles sprayed during the last torch cycle remain at T &gt; Tg while they spread, so that interlamellar viscous flow sintering takes place, favouring the formation of such denser microstructure. Both coatings are entirely glassy; however, micro-Raman spectroscopy reveals that, whereas the 45S5 coating is structurally identical to the corresponding bulk glass, the “Bio-K” coating is somewhat different from the bulk one.


2010 - Production of Bioglass® 45S5-Polycaprolactone composite scaffolds via salt leaching [Articolo su rivista]
Cannillo, Valeria; F., Chiellini; Fabbri, Paola; Sola, Antonella
abstract

Polycaprolactone (PCL)-Bioglass 45S5 (45S5) composite scaffolds were produced by means of the salt- leaching technique. Various salts (NaCl, NaHCO3, and a mixture of them) were used with the aim of opti- mising the pores network; moreover several glass weight fractions and glass particle sizes were tested. The so-obtained composite scaffolds were characterized from a microstructural, mechanical and biolog- ical point of view; in particular, in view of the biomedical application of the materials, both in vitro and cytotoxicity tests were performed. The microstructure of the composite scaffolds possessed a well-devel- oped interconnected porosity, ideal for bone regeneration and vascularization. The mechanical properties of the PCL matrix were not altered by the introduction of the glass and the scaffolds ensured an easy han- dling. As regards the bioactivity, the prolonged contact of the 45S5 particles with the water used to remove the salt probably induced a reaction which promoted the development of calcite and altered the glass composition, suppressing the development of hydroxyapatite in vitro; however the response to the cytotoxicity test was promising, confirming the relevance of the PCL-45S5 composite scaffolds and justifying future efforts to improve the production technique, in order to limit the glass alteration


2010 - Shell scaffolds: a new approach towards high strength bioceramic scaffolds for bone regeneration [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract

A key issue for bone tissue engineering is the design of bioceramic scaffolds combining high porosity with adequate mechanical properties. Furthermore, a resistant surface is required in order to have manageable samples for both in vivo and in vitro applications. Here a new protocol that aims to give an appropriate response to these issues is developed. The realized shell scaffolds, obtained combining a modified replication technique with the usual polymer burning-out method, look rather promising mainly thanks to their manageability, porosity and permeability. In this preliminary work the developed technique is discussed, together with an overview on the structure of the realized samples.


2010 - Steel particles-porcelain stoneware composite tiles: an advanced experimental-computational approach [Articolo su rivista]
Cannillo, Valeria; L., Esposito; G., Pellicelli; Sola, Antonella; A., Tucci
abstract

Innovative porcelain stoneware tiles with a surface layer containing 2.4wt% of stainless-steel particles were produced by the Double Charge Technology. Considering this layer as a composite material, the effects of the metal particles on the mechanical behaviour of the ceramic matrix were extensively investigated in terms of Young’s modulus, fracture toughness and flexural strength. With this aim, composite materials were prepared by using the same silicate-based ceramic matrix with increasing weight percentages of the same stainless-steel powder. The composites were accurately characterised. In particular, due to the high sintering temperature, possible changes at the interface between metal particles and ceramic matrix were thoroughly analysed by means of SEM and EDS microanalysis. To clarify the role of the observed chromium-rich interphase on the mechanical behaviour of the steel particles-stoneware composites, analytical equations were used and simulations were performed by using the Object Oriented Finite element method (OOF).


2010 - Structural characterisation of High Velocity Suspension Flame Sprayed (HVSFS) TiO2 coatings [Articolo su rivista]
E., Bemporad; Bolelli, Giovanni; Cannillo, Valeria; D., De Felicis; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch; M., Sebastiani
abstract

The microstructural features of TiO2 coatings, deposited by High Velocity Suspension Flame Spraying(HVSFS) from a suspension of titania nanoparticles, were investigated by Focused Ion Beam (FIB)+ScanningElectron Microscopy (SEM) techniques, by Transmission Electron Microscopy (TEM) and by micro-Ramanspectroscopy, and were compared to those of conventional HVOF-sprayed TiO2. Proper selection of theHVSFS deposition parameters results in coatings consisting of a dense matrix, made up by the efficientsuperposition of well-flattened micrometric lamellae, with homogeneously distributed porosity containingsub-micrometric re-solidified spherical particles. Unlike conventional HVOF coatings, lamella boundaries arehardly discernible, no intralamellar cracking occurs and equiaxed crystals appear instead of columnar ones. Ahomogeneous distribution of anatase and rutile is also found. Modifications to the spray parameters can giverise to large, unmelted agglomerates, scattered throughout the coating and having poor cohesion to thesurrounding material. These agglomerates retain the original phase composition of the nanopowder.


2010 - Surface modification of Al-Al2O3 composites by laser treatment [Articolo su rivista]
Cannillo, Valeria; Sola, Antonella; M., Barletta; A., Gisario
abstract

Heat treatment of ceramic-reinforced aluminium matrix composites (AMCs) using a high-power diode laser (HPDL) was investigated.


2010 - Wear behaviour of high velocity suspension flame sprayed (HVSFS) Al2O3 coatings produced using micron- and nano-sized powder suspensions [Articolo su rivista]
Bolelli, Giovanni; Bonferroni, Benedetta; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch; N., Stiegler
abstract

Three Al2O3-based suspensions were prepared using two nano-sized Al2O3 powders (having analogous size distribution and chemical composition but different agglomeration behaviour) and a micron-sized one. High velocity suspension flame sprayed (HVSFS) coatings were produced using these suspensions as feedstock and adopting two different sets of deposition parameters.The coatings produced by the micrometric powder suspension are denser and more wear resistant (as revealed by ball-on-disk testing) than those deposited using the two nanopowder suspensions, irrespective of the deposition parameters. The tribological behaviour of all coatings is dictated by the formation and subsequent removal of surface tribofilms: these tribofilms are more stable in the coatings obtained by the micrometric powder suspension, although they exhibit the largest tensile residual stress (as determined by X-ray diffraction and hole drilling techniques).Even though the as-deposited coatings are quite smooth (Ra around 1.3–2 μm), polishing to Ra around 0.1 μm further improves the wear resistance in all cases, as it delays the onset of tribofilm delamination phenomena.


2009 - Advances in High Velocity Suspension Flame Spraying (HVSFS) [Articolo su rivista]
J., Rauch; Bolelli, Giovanni; A., Killinger; R., Gadow; Cannillo, Valeria; Lusvarghi, Luca
abstract

Three suspensions, containing oxide nanoparticle single phases, (Al2O3, 3YSZ and Cr2O3) were prepared and sprayed using High Velocity Suspension Flame Spraying (HVSFS) technique. The coatings were characterized concerning their mechanical properties by means of nano indenter hardness measurements (all coatings) and ball on disk tribometry (Al2O3, 3YSZ). APS and HVOF sprayed Al2O3 coatings were characterized under same conditions for comparison. X-ray diffraction analysis was performed on HVSF sprayed Al2O3 and Cr2O3 coatings and a plasma-sprayed Cr2O3 coating for comparison. A Williamson–Hall line profile analysis was performed to estimate and compare crystallite size in the coatings


2009 - Alumina-YAG composites: preparation, experimental characterization and numerical modelling [Articolo su rivista]
Cannillo, Valeria; P., Palmero; Manfredini, Tiziano; L., Montanaro
abstract

Al2O3/YAG composite powders have been synthesised by reverse strike precipitation. The powders were characterised by DTA/TG simultaneous analysis, the phase evolution was studied by XRD analysis, while the crystallite formation and growth were followed by TEM observations. A fully dense, homogenous material was obtained by sintering 900°C pre-treated powders at 1600°C for 3 h. For limiting grain growth, both a doping with 500 ppm MgO followed by a free sintering and a fast sintering procedure involving a high heating rate (50°C/min) were performed. The sintered bodies were then characterised by SEM observation and Vickers indentation. Moreover, a numerical model was employed in order to estimate the mechanical properties of the composite materials starting fromthe single constituent phase properties.


2009 - Chemical durability and microstructural analysis of glasses soaked in water and in biological fluids [Articolo su rivista]
Cannillo, Valeria; F., Pierli; Ronchetti, Ivonne; Siligardi, Cristina; Zaffe, Davide
abstract

A new glass, obtained from Bioglass BG45S5 original composition by substituting CaO with MgO, was produced and its chemical durability and microstructural characteristics were compared with that of Bioglass1. The two glasses (labelled as BG45 and MG45) were soaked up to 4 weeks at physiological temperature in different solutions, i.e. bi-distilled water, Hank’s Buffered Salt Solution 61200 (labelled as HBSS+), Hank’s Buffered Salt Solution 14170 (labelled as HBSS ), and Kokubo’s SBF. Moreover, the influence of either flat or flake surfaces was analysed for both glasses. Results showed that the chemical durability of a glass in saline at 37 8C, evaluated through pH and ICP-AES chemical analysis of the leached components, depended mainly on the chemical composition of the soaking solution. Moreover, the MG45 glass never exhibited hydroxyapatite crystal formation on its surface also after soaking in calcium- containing solutions. The apatite crystallisation and deposition mechanism, typical of a bioactive glass, was induced only if the glass itself contained calcium. The contemporaneous presence of calcium in the glass and in the soaking solution improved the reactivity of the glass, as apatite crystals nucleated in a shorter time and grew more quickly. As regards the morphology of the glass surface, rougher surfaces favoured the formation of hydroxyapatite crystals on glasses containing calcium


2009 - Deposition of TiO2 coatings: Comparison between High Velocity Suspension Flame Spraying (HVSFS), atmospheric plasma spraying and HVOF-spraying [Relazione in Atti di Convegno]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; R., Gadow; A., Killinger; J., Rauch; E., Bemporad; M., Sebastiani
abstract

A TiO2 (anatase) nanopowder suspension was processed by High Velocity Suspension Flame Spraying (HVSFS). The resulting coatings were characterized and compared to conventional atmospheric plasma sprayed (APS) and HVOFsprayed ones. The HVSFS operating parameters can be adjusted in order to achieve dense coatings, with a fine (nearnanosized) structure and a homogeneous distribution of anatase and rutile: these coatings have lower pore interconnectivity and higher wear resistance than APS and HVOF ones. Alternatively, quite large unmelted agglomerates of anatase nanoparticles can be embedded in the coating, increasing the porosity and the anatase content for enhanced photocatalytic efficiency.


2009 - Design of Experiments (DOE) for the Optimization of Titania–hydroxyapatite Functionally Graded Coatings [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella
abstract

Titania–hydroxyapatite functionally graded coatings were deposited on titanium alloy substrates by plasma spraying. Because it was necessary to spray together the titania and the hydroxyapatite powders to obtain the graded system, the first target of the present study was to optimize the process parameters in order to obtain a high-quality coating. A 23 Design of Experiments was applied to define the optimal values of plasma torch power, hydrogen flux, and spraying distance. This defined set of parameters (38 kW, 5 SLPM, and 90 mm, respectively) was used to spray the most promising graded coating, which was characterized and postheat treated


2009 - Editorial. Special Issue: Advanced Ceramics: Innovative Strategies for their Preparation, Characterisation and Modelling [Articolo su rivista]
Cannillo, Valeria
abstract

non presente


2009 - Effect of a Heat Treatment on the Bioactivity of Titania-Hydroxyapatite Functionally Graded Coatings [Relazione in Atti di Convegno]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella
abstract


2009 - Effect of porosity on the elastic properties of porcelainized stoneware tiles by a multi-layered model [Articolo su rivista]
Cannillo, Valeria; L., Esposito; E., Rambaldi; Sola, Antonella; A., Tucci
abstract

Porcelainized stoneware represents a leading product in the world market of ceramic tiles, thanks to its relevant bending strength (with respectto other classes of tiles) and extremely low water absorption: these properties derive from its really low content of residual porosity. Nevertheless,an accurate investigation of the cross section of a porcelainized stoneware tile reveals a non-uniform distribution of the residual pores through thethickness, which results in a spatial gradient of properties. Porcelainized stoneware, therefore, may be looked at as a functionally graded material.In the present research, commercial porcelainized stonewares were analysed in order to define the effect of the residual porosity and its spatialdistribution on the mechanical properties of tiles. Polished cross sections of porcelainized stoneware tiles were investigated by optical and scanningelectron microscopy in order to define the content and distribution of residual pores as a function of distance from the working surface. For eachporcelainized stoneware, the local elastic properties of the ceramic matrix were measured by a depth-sensing Vickers micro-indentation technique,then the so-obtained microstructural images and elastic properties were used to model the stoneware tile mechanical properties. In particular, thecross section of each tile was described as a multi-layered system, each layer of which was considered as a composite material formed by a ceramicmatrix and residual pores. The elastic properties of each layer were predicted by applying analytical equations derived from the theory of compositematerials and, as a new approach, by performing microstructure-based finite element simulations. In order to validate the proposed multi-layeredmodel and identify the most reliable predictive technique, the numerical results were compared with experimental data obtained by a resonancebasedmethod.


2009 - In vitro characterisation of plasma-sprayed apatite/wollastonite glass-ceramic biocoatings on titanium alloys [Articolo su rivista]
Cannillo, Valeria; J., Colmenares Angulo; Lusvarghi, Luca; F., Pierli; S., Sampath
abstract

Some ceramics have the ability to form direct bonds with surrounding tissues when implanted in the body. Among bioactive ceramics, the A/W (Apatite/Wollastonite) glass-ceramic, containing apatite and wollastonite crystals in the glassy matrix, has been largely studied because of good bioactivity and used in some fields of medicine, especially in orthopaedics and dentistry. However, medical applications of bioceramics are limited to non-load bearing applications because of their poor mechanical properties. In this study, A/W powders, obtained from industrial and high grade quality raw materials, were thermally sprayed by APS (atmospheric plasma spraying) on Ti-6Al-4V substrates, in order to combine the good bioactivity of the bioceramic and the good mechanical strength of the titanium alloy base material. The microstructure and the resulting properties were evaluated depending on processing parameters and post-processing thermal treatments. The morphology and the microstructure of the coatings were observed by SEM and the phase composition was examined by X-ray diffraction. The bioactivity of the coatings was evaluated by soaking the samples in a Simulated Body Fluid (SBF) for 1, 2 and 5 weeks. The bioactive behaviour was then correlated with the thermal treatments and the presence of impurities (in particular Al2O3) in the coatings.


2009 - Microstructural and Tribological Investigation of High-Velocity Suspension Flame Sprayed (HVSFS) Al2O3 Coatings [Articolo su rivista]
Bolelli, Giovanni; Johannes, Rauch; Cannillo, Valeria; Andreas, Killinger; Lusvarghi, Luca; Rainer, Gadow
abstract

Al2O3 coatings were manufactured by the high-velocity suspension flame spraying (HVSFS) technique using a nanopowder suspension. Their structural and microstructural characteristics, micromechanical behavior, and tribological properties were studied and compared to conventional atmospheric plasma sprayed and high-velocity oxygen-fuel-sprayed Al2O3 coatings manufactured using commercially avail- able feedstock. The HVSFS process enables near full melting of the nanopowder particles, resulting in very small and well flattened lamellae (thickness range 100 nm to 1 lm), almost free of transverse microcracking, with very few unmelted inclusions. Thus, porosity is much lower and pores are smaller than in conventional coatings. Moreover, few interlamellar or intralamellar cracks exist, resulting in reduced pore interconnectivity (evaluated by electrochemical impedance spectroscopy). Such strong interlamellar cohesion favors much better dry sliding wear resistance at room temperature and at 400 °C.


2009 - Microstructural and in vitro characterisation of High-Velocity Suspension Flame Sprayed (HVSFS) bioactive glass coating [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch
abstract

The paper reports the first attempt at employing the innovative High-Velocity Suspension Flame Spraying (HVSFS) technique in order to deposit bioactive glass coatings. Fine (micrometric) glass particles having a composition similar to that of the A-W (apatite-wollastonite) bioactive glass-ceramic as proposed by Kokubo were dispersed into a 50% water + 50% isopropanol solvent mixture and the resulting suspension (containing 20 wt.% glass powder) was thermally sprayed onto Ti plates using a modified high velocity oxy-fuel torch.Each torch pass produces a dense coating layer, featuring strong cohesion between lamellae thanks to viscous flow sintering along the interlamellar boundary. However, some porosity exists between different layers deposited during successive torch passes.In-vitro bioactivity tests indicate that the coatings interact remarkably with the simulated body fluid (SBF), developing a thick silica-rich layer containing hydroxyapatite crystals.


2009 - Microstructural and mechanical changes by chemical ageing of glazed ceramic surfaces [Articolo su rivista]
Cannillo, Valeria; L., Esposito; E., Rambaldi; Sola, Antonella; A., Tucci
abstract

In the present work, several ceramic tiles, characterised by different glazes, were considered in order to define the role played by the glassy and crystalline phases on the leaching mechanisms and the deterioration of the mechanical properties. The glazedworking surfaces were subjected to chemical attack by using a strong basic solution and the chemical analysis of the leached solutions was performed. Before and after the chemical attack, the glazed surfaces of the samples were analysed from both the microstructural and mechanical point of view. In this context, the microstructure was observed by SEM and analysed by X-ray diffraction. In order to define other possible changes, roughness measurements, Vickers hardness and micro-scratch tests were also performed. The results made it possible to deepen the understanding of the mechanisms of elements release caused by the chemical attack and their implications on microstructural and mechanical degradation of the working surface of glazed ceramic tiles.


2009 - Nanoceramic based High-Velocity Suspension Flame Sprayed (HVSFS) of hydroxylapatite coatings for biomedical applications [Capitolo/Saggio]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; N., Stiegler
abstract


2009 - Post-deposition laser treatment of plasma sprayed titania-hydroxyapatite functionally graded coatings [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella; M., Barletta
abstract

The viability of a high power diode laser source as effective post-deposition treatment technique of functionally graded titania-HA coatings was checked. In particular, several laser treatments were performed on various coatings plasma-sprayed under different conditions to verify the presence of an operative window large enough for practical purposes and, subsequently, to identify the most promising settings of the laser parameters. Laser power as low as 80-100 W and focus distance as high as -4mm were found to be the most feasible choice to improve the overall coating properties as well as to inhibit undesired secondary reactions between calcium phosphates and titania. Finally, the best set of the laser parameters were applied to a pure HA coating and to a titania-HA graded one, plasma-sprayed under the same conditions, to perform a comparative evaluation.


2009 - Potassium-based composition for a bioactive glass [Articolo su rivista]
Cannillo, Valeria; Sola, Antonella
abstract

The increasing need for biomedical devices, required to face dysfunctions of natural tissues and organs caused by traumatic events, diseases and simple ageing, has drawn attention onto new materials, that could be able to positively interact with the human body. Among them, Bioglass1 is firmly diffused in medical practice, thanks to its high bioactivity. In particular, due to its brittleness, it is mainly applied as a coating onto tougher bionert substrates; nevertheless, its bioactivity may be altered by the crystallization phenomena that could be involved by its processing. With the aim of reducing the tendency to crystallize, a new glass composition, inspired by the 45S5 Bioglass1, was formulated by substituting the sodium oxide with potassium oxide. A parallel characterization of the new glass and the 45S5 Bioglass1 was carried out in order to define the effect of the potassium oxide on the thermal behaviour, mechanical properties and bioactivity. The results proved that the thermo-mechanical properties, as well as the in vitro response of the two glasses were comparable; however, preliminary tests to produce glass coatings by enamelling evidenced a higher stability of the new glass that, unlike the 45S5 Bioglass1, did not crystallize during processing.


2009 - Processing and characterisation of High-Velocity Suspension Flame Sprayed (HVSFS) bioactive glass coatings [Capitolo/Saggio]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch; Sola, Antonella
abstract

The High-Velocity Suspension Flame Spraying (HVSFS) technique was employed in order to deposit bioactive glass coatings onto titanium substrates. Two different glass compositions were examined: the classical 45S5 Bioglass and a newly-developed SiO 2 –CaO–K 2 O–P 2 O 5 glass, labelled as "Bio-K". Suitable raw materials were melted in a furnace and fritted by casting into water. The frit was dry-milled in a porcelain jar and subsequently attrition-milled in isopropanol. The resulting micron-sized powders were dispersed in a water+isopropanol mixture, in order to prepare suitable suspensions for the HVSFS process. The deposition parameters were varied; however, all coatings were obtained by performing three consecutive torch cycles in front of the substrate. The thickness and porosity of the coatings were significantly affected by the chosen set of deposition parameters; however, in all cases, the layer produced during the third torch cycle was thicker and denser than the one produced during the first cycle. As the system temperature increases during the spraying process, the particles sprayed during the last torch cycle remain at T > Tg while they spread, so that interlamellar viscous flow sintering takes place, favouring the formation of such denser microstructure. Both coatings are entirely glassy; however, micro-Raman spectroscopy reveals that, whereas the 45S5 coating is structurally identical to the corresponding bulk glass, the "Bio-K" coating is somewhat different from the bulk one.


2009 - Properties of High Velocity Suspension Flame Sprayed (HVSFS) TiO2 coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch
abstract

TiO2 coatings were manufactured by the High Velocity Suspension Flame Spraying (HVSFS) technique using a nanopowder suspension. Their microstructure, nanohardness, tribological properties and photocatalytic activity were studied and compared to conventional atmospheric plasma sprayed (APS) and HVOF-sprayed TiO2 coatings manufactured using commercially available feedstock. The HVSFS process leaves a fairly large freedom to adjust coating properties (thickness, porosity, anatase content, hardness, etc…) according to the desired objective. Layers with higher anatase content and higher porosity can be produced to achieve higher photocatalytic efficiency, better than conventional APS and HVOF TiO2. Alternatively, dense protective layers can be deposited, possessing lower porosity and pore interconnectivity and better wear resistance than as- deposited APS and HVOF layers. In all cases, HVSFS-deposited layers are thinner (20 µm–60 µm) than those which can be obtained by conventional spraying processes


2009 - Role of process type and process conditions on phase content and physical properties of thermal sprayed TiO2 coatings [Articolo su rivista]
J. R., Colmenares Angulo; Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella; S., Sampath
abstract

Thermal spray represents an advantageous technique for depositing large-area titanium dioxide coat- ings that are of interest for both traditional wear-resistant coatings as well as functional applications such as photo- induced decontamination surfaces. Numerous past studies have examined the phase evolution and properties of TiO2 coatings using different thermal spray processes or parameters. In this paper, an integrated study of thermal sprayed TiO2 was conducted with different thermal spray devices and process parameters for a single feedstock powder comprising the metastable anatase phase. The aforementioned variables are correlated with in-flight par- ticle state (particle temperature and velocity), phase evolution, and coating physical properties. The results are represented through the framework of process maps which connect process parameters with material properties. Based on the phase characterization, an initial exploration of the metastable phase evolution during thermal spray deposition of TiO2 is proposed. Furthermore, the sprayed TiO2 coat- ings show varying degrees of electrical conductivity associated with process-induced stoichiometric changes (vacancy generation) in the TiO2. The effects of these stoichiometric changes as well as extrinsic microstructural attributes (pores, cracks, interfaces), contribute to the complex electrical response of the coatings. This integrated study provides insights into the process–microstructure– property relationship with the ultimate goal of tailoring the functionality of spray deposited oxide thick films.


2009 - Short range investigation of sub-micron zirconia particles [Relazione in Atti di Convegno]
M. C., Caracoche; J. A., Martìnez; P. C., Rivas; F., Bondioli; Cannillo, Valeria; Ferrari, Anna Maria
abstract

The Perturbed Angular Correlations technique was used to determine the nanoconfigurations and their thermal behavior in two non-aggregated zirconia nanospheres of unlike sizes obtained by adding different water amounts during preparation. Three residues containing- Zr surroundings were determined for the non-crystalline starting zirconias, the two organics containing- ones being particle size dependent. Upon crystallization, the nanospheres showed the stabilization of both tetragonal (t´- and t- forms) and cubic (Xc- form) phases. Nevertheless, their amounts, temperature of appearance and thermal evolution depended on the residues containing- precursors. It was observed, in addition, that the structure of the smaller nanospheres became gradually monoclinic. The bigger spheres remained stabilized up to the highest temperatures certainly due to their lower specific surface area that favors the permanence of the oxygen defective t´- form.


2009 - Thermal and physical characterisation of apatite/wollastonite bioactive glass-ceramics [Articolo su rivista]
Cannillo, Valeria; F., Pierli; S., Sampath; Siligardi, Cristina
abstract

Glass–ceramics, containing apatite and wollastonite (A/W) crystals in the MgO–CaO–SiO2–P2O5 glassy matrix, show the ability to form tight chemical bonds with living tissues when implanted in the body, as demonstrated by Kokubo and co-workers. However, the medical applications are mainly limited to non-load bearing conditions because of their poor mechanical properties. To overcome this drawback, a coating of the A/W glass–ceramic could be deposited onto a titanium substrate, in order to combine the good bioactivity of the bioceramic and the good mechanical strength of the titanium alloy base material. In this study, A/W powders obtained from commercial raw materials were thermally sprayed by APS (atmospheric plasma spraying) on Ti–6Al–4V substrates. Since in the as-sprayed conditions the coating microstructure was defective because of pores and cracks, thermal treatments on A/W plasma-sprayed coatings were conducted to enhance the coating microstructure. In order to gain a de...


2008 - A FIB study of sharp indentation testing on plasma-sprayed TiO2 [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; F., PIGHETTI MANTINI; Gualtieri, Enrico; C., Menozzi
abstract

Instrumented sharp indentation is often employed formicromechanical investigation of thermal-spray coatings.However, rather complex dependenciesof measured values on indentation load have been reported. To verify the possible influence of sub-surface cracking,Vickers and Berkovich indentations onplasma-spray TiO2 were sectioned by FIB. Remarkable sub-surface cracking was found for indentations performed on the coating cross-section, even forrather low loads (1 N).Much less sub-surface cracking occurs when indenting the top surface, indicatingmaterial anisotropy. This preliminary investigationhighlights the need for thorough studies of sub-surface cracking during instrumented sharp indentation.


2008 - Cobalt doped glass for the fabrication of percolated glass-alumina functionally graded materials [Articolo su rivista]
Cannillo, Valeria; D., Mazza; Siligardi, Cristina; Sola, Antonella
abstract

The present research was focused on the development of a new glass to produce glass–alumina FGMs. The glass formulation, belonging to theCaO–ZrO2–SiO2 system, was doped with cobalt, by adding a small molar percentage (about 0.1 mol%) of CoO, in order to obtain a blue glass,which could be useful to appreciate the final compositional gradient. The glass was accurately characterized, evaluating its thermal behaviour, itsmechanical properties, and its attitude to crystallize during a thermal treatment. Subsequently, the glass was used to produce glass–alumina FGMsvia percolation and the so obtained specimens were analysed in order to evaluate the effect of the glass infiltration. The possible development ofnew crystal phases, in particular, was tested via micro X-ray diffraction and the elastic properties gradient associated with the compositionalgradient was measured via depth-sensing Vickers microindentation.


2008 - Effects of different production techniques on glass-alumina functionally graded materials [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Siligardi, Cristina; Sola, Antonella
abstract

Glass–alumina functionally graded materials were obtained using two different methods: percolation, which was representative of naturaltransport based processes, and plasma spraying, which was representative of constructive processes. The specimens produced in this way wereinvestigated to evaluate the effect of production techniques on the final microstructure and gradient, which, in turn, govern the properties andperformances of the graded systems. Moreover, post-production heat treatments were performed in order to improve the reliability of the materialsexamined.


2008 - Electrochemical comparison between corrosion resistance of some thermally sprayed coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Giovanardi, Roberto; Lusvarghi, Luca
abstract

Electrochemical polarisation and impedance spectroscopy tests in0.1 M HCl and 0.1 M H2SO4 solutions were performed on HVOF-sprayedcermet coatings (WC–17% Co, WC–10% Co–4% Cr) and AtmosphericPlasma-Sprayed (APS) ceramics (Al2O3, Al2O3–13 wt%TiO2, Cr2O3) with APSbond coat (Ni–Co–Cr–Al–Y). Reference tests were also performed on hardchrome electroplating. Plasma-sprayed coatings offer limited substrateprotection owing to interconnected porosity, although the bond coat promotessome forms of passivation in H2SO4. HVOF-sprayed cermets possess goodcorrosion resistance in both environments. Chrome electroplating showscomparatively better corrosion resistance in H2SO4, but worse in HCl.


2008 - In-vitro behaviour of titania-hydroxyapatite functionally graded coatings [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Pierli, Fiorenza; Sola, Antonella
abstract

The in vitro behaviour of titania–hydroxyapatite graded coatings obtained by plasma sprayingwas investigated by a microstructural and mechanical point of view. To verify the bioactivity of thegraded coatings, as sprayed and after thermal treatment, in vitro tests were performed insimulated body fluid. Furthermore, since the mechanical properties of the coatings may bealtered by the immersion in simulated body fluid, the local elastic properties were measured onthe cross-section by means of a depth sensing Vickers microindentation technique beforeimmersion (reference materials) and after soaking for 1 week (short term response) and 4 weeks(long term response), separately investigating the titania and the hydroxyapatite rich zones toaccount for the compositional gradient. The results proved that the presence of titania in thecoating did not suppress the bioactivity, which, on the contrary, was inhibited by the heattreatment. However, the heat treated samples showed higher mechanical properties and reduceddissolution rates.


2008 - Investigation of High-Velocity Suspension Flame Sprayed (HVSFS) glass coatings [Articolo su rivista]
Bolelli, Giovanni; J., Rauch; Cannillo, Valeria; A., Killinger; Lusvarghi, Luca; R., Gadow
abstract

High-Velocity Suspension Flame Spraying (HVSFS) has recently emerged as a potential alternative to conventional HVOF-spraying:employing liquid suspensions instead of dry powder feedstock enables the use of very fine grain-sized particles, resulting in small-sized lamellae.Thin, low-porosity coatings can thus be manufactured. This paper details the first attempt at manufacturing glass coatings using the HVSFStechnique: these coatings can have multiple applications (anti-corrosion coatings on metal and ceramic substrates, bio-compatible coatings, etc). ACaO–ZrO2–SiO2 glass frit was selected for this attempt. Excellent potentialities emerged (very low porosity), but some problems still existed (big“droplet-like” features on the coating surface), which have recently been largely overcome thanks to process modifications.© 2008 Elsevier B.V. All rights reserved.


2008 - Local and medium range structure of erbium containing glasses: a molecular dynamics study [Articolo su rivista]
Corradi, Anna; Cannillo, Valeria; Montorsi, Monia; Siligardi, Cristina
abstract

Erbium containing glasses cover an important role in optical communications and laser technology. The local environment of the ionsconstituting the three dimensional network exerts a strong influence on the chemical and physical properties of the glasses. In particularthe network modifier cations strongly influence the short and intermediate range order of the glass structure. The structural modificationsinduced by the alumina addition in the glass matrix, as a function of the erbium oxide concentration, have been studied using moleculardynamics (MD) simulations. While at low Er2O3 concentration the network former action of the Al3+ leads to a more polymerized glassnetwork, at higher Er2O3 content the influence of the alumina on the erbium local structure is limited. Further investigation points outmicro-heterogeneity in the Na+ and Ca2+ distribution as a function of the alumina concentration.


2008 - Production and characterization of plasma sprayed TiO2-hydroxyapatite functionally graded coatings [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella
abstract

Among bioactive ceramics, hydroxyapatite (HAp) has been widely studied, especially as a coating onto metallic substrates. In clinical applications,coating delamination has been observed, close to the interface between coating and substrate. This is due to a mismatch in the thermal expansioncoefficients of HAp and titanium/titanium alloy. In order to improve the adhesion, a proper bond coat may be introduced. In this work, a functionallygraded coating TiO2–HAp, in which the composition gradually changed from TiO2 to HAp, was deposited onto Ti6Al4V substrates by atmosphericplasma spraying (APS). With the aim of defining the best spraying parameters to obtain the graded system, preliminary coatings of pure TiO2 andpure HAp were deposited by varying systematically the typical spraying conditions, such as the torch power and H2 flux. The preliminary coatingswere characterized by means of SEM, that confirmed the strong dependence of the microstructure on the torch power, and X-ray diffraction, thatshowed the significant influence exerted by the hydrogen flux on the crystallinity and thermal decomposition of HAp. The results of the preliminaryinvestigations were used to optimise the spraying conditions for the FGM deposition and, accordingly, the final graded coating was obtained andcharacterized. Post-deposition heat treatments were performed in order to improve further the graded coating and their effect on the mechanicalproperties was evaluated via Vickers micro-indentation tests. The investigation showed that, after raising the temperature, the crystallinity of HApand the Vickers hardness increased, however, at high temperature (more than 750 ◦C), the stress induced by the re-crystallization promoted thepropagation of cracks and weakened the interface.


2007 - Characterization of glass-alumina functionally graded coatings obtained by plasma spraying [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Siligardi, Cristina; Sola, Antonella
abstract

Glass-alumina functionally graded coatings (FGCs) were produced Via plasma spraying, a deposition technique for thick (> 10-20 mu m) coatings production, which ensures high flexibility and good reliability. The samples were obtained by building a graded glass-alumina coating onto an alumina substrate; the coatings were designed as multi-layered systems, each layer having a mean composition slightly different from the neighbouring ones. Two different compositional gradients were considered (front 100 vol.% alumina to 100 vol.% glass and from 80-20 vol.% glass to 100 vol.% glass) and several heat treatments were performed in order to improve the substrate-coating interface and induce a controlled transformation (sintering and/or crystallization) of the glassy phase. After a preliminary screening of the as-sprayed and the heat treated samples, the most interesting ones were carefully characterized, especially from a mechanical point of view. In fact, tests Such as Vickers micro-indentation allowed to appreciate the effects of the graded compositional profile and the consequences induced by thermal treatments. (c) 2006 Elsevier Ltd. All rights reserved.


2007 - Glass-alumina Functionally Graded Materials produced by plasma-spraying [Relazione in Atti di Convegno]
Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract

The present work was focused on glass-alumina functionally graded materials. Thesamples, produced by plasma spraying, were built as multi-layered systems by depositing severallayers of slightly different composition, since their alumina and glass content was progressivelychanged. After fabricating the graded materials, several, proper characterization techniques were setup to investigate the gradient in composition, microstructure and related performances. A particularattention was paid to the observation of the graded cross sections by scanning electron microscopy,which allowed to visualize directly the graded microstructural changes. The scanning electronmicroscopy (SEM) inspection was integrated with accurate mechanical measurements, such assystematic depth-sensing Vickers microindentation tests performed on the graded cross sections.


2007 - Glass-ceramic Functionally Graded Materials produced with different methods [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract

Functionally graded materials (FGMs) are innovative composite materials characterized by a gradual spatial change in composition, microstructure and related properties. This work was focused on glass-alumina functionally graded materials, produced via percolation of molten glass into a sintered polycrystalline alumina substrate and via plasma spraying. The glass composition, belonging to the CaO-ZrO2-SiO2 system, was purposely designed in order to minimize the difference between the coefficients of thermal expansion of the constituent phases, which may induce thermal residual stresses in service or during fabrication. The ingredient materials as well as the resultant FGMs were carefully characterized. In particular, a great attention was devoted to the microstructural investigation of the penetration profile. (c) 2006 Elsevier Ltd. All rights reserved.


2007 - Microstructural and tribological comparison of HVOF-sprayed and post-treated M-Mo-Cr-Si (M = Co, Ni) alloy coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; Montorsi, Monia; F., PIGHETTI MANTINI; M., Barletta
abstract

High velocity oxygen-fuel (HVOF)-spayed wear resistant Co-28%Mo-17%Cr3%Si and Ni-32%Mo-15%Cr-3%Si coating, both as sprayed and after heat treatments at 600°C for 1h, have benn studied.


2007 - Prediction of the elastic properties profile in glass-alumina functionally graded materials [Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Siligardi, Cristina; Sola, Antonella
abstract

Glass-alumina functionally graded materials were obtained by percolation and alternatively by plasma spraying. The paper develops a reliable model to predict the functional gradient of the analysed systems. A finite element code, which was able to handle microstructural images, was employed to estimate the effective elastic properties along the gradient direction. The calculated values were compared with experimental data acquired by means of systematic microindentation tests. The computational approach was compared with analytical tools such as the rule of mixture. The results revealed that the elastic properties were significantly influenced by microstructural features such as the shape of the ingredient materials domains and the presence of pores at the grain boundaries. This was particularly evident in the sprayed FGMs, due to their peculiar lamellar microstructure. Even if the coating-substrate interface properties were difficult to include in the model, the numerical simulations fitted fairly well the experimental data. (c) 2006 Elsevier Ltd. All rights reserved.


2007 - Surface acoustic wave depth profiling of functionally graded material [Articolo su rivista]
J., Goossens; P., Leclaire; X., Xu; C., Glorieux; L., Martinez; Sola, Antonella; Siligardi, Cristina; Cannillo, Valeria; T., VAN DER DONK; J. P., Celis
abstract

The potential and limitations of Rayleigh wave spectroscopy to characterize the elastic depth profileof heterogeneous functional gradient materials are investigated by comparing simulations of thesurface acoustic wave dispersion curves of different profile-spectrum pairs. This inverse problem isshown to be quite ill posed. The method is then applied to extract information on the depth structureof a glass-ceramic alumina functionally graded material from experimental data. The surfaceacoustic wave analysis suggests the presence of a uniform coating region consisting of a mixture ofAl2O3 and glass, with a sharp transition between the coating and the substrate. This is confirmed byscanning electron microscope with energy dispersive x-ray analysis.


2007 - Synthesis and sinterability of hydroxyapatite-coated zirconia nanopowders [Relazione in Atti di Convegno]
F., Bondioli; Cannillo, Valeria; Ferrari, Anna Maria; Manfredini, Tiziano
abstract

Hydroxyapatite (HAp), is a well-known and a valuable implant material with biocompatibility and bioactive properties. Full utilisation of the unique properties of hydroxyapatite bulk ceramics is, however, possible only after its proper reinforcement, i.e. by preparation of composites. In zirconia reinforced hydroxyapatite composites (HAp-ZrO2) it is possible to combine extremely advantageous properties of both biomaterials, previously applied separately. The goal of this study was to synthesized a HAp-coated zirconia composite powder by the precipitation of HAp in presence of zirconia. HAp was precipitated in order to obtain 3, 5, 10, 15, 30 and 50 wt % zirconia reinforced composite powders. The obtained powders were fully characterized in order to determine their properties and sinterability.


2007 - Technological properties of celsian reinforced glass matrix composites [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; A., Motori; F., Patuelli; A., Saccani; Sola, Antonella
abstract

Monoclinic celsian derived from an innovative route, i.e. cation exchanged zeolites heat-treated at low temperature, was added at differentcontents (10, 20, 30 wt%) to a glass matrix, in order to improve its mechanical and electrical performances. The effect of the celsian reinforcementwas evaluated by testing several properties of the composite materials, such as the elastic modulus, abrasion resistance, flexural strength andelectrical insulation. The results so far obtained suggest that the addition of the monoclinic celsian to the glass matrix may produce low-costparticulate composites with interesting technological properties.


2006 - Analysis of crack propagation in alumina-glass functionally graded materials [Relazione in Atti di Convegno]
Cannillo, V.; Lusvarghi, L.; Manfredini, T.; Montorsi, M.; Siligardi, C.; Sola, A.
abstract

abstract


2006 - Design and optimisation of glass-celsian composites [Articolo su rivista]
Cannillo, Valeria; E., Carlier; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina
abstract

The aim of this paper is to fabricate novel glass matrix composites reinforced by means of celsian particulate. In fact. the attractive features of celsian, such as chemical stability and high mechanical resistance, can be favourably exploited in order to obtain enhanced-performance composites with respect to bulk glass. A design of experiments (DOE) procedure has been utilized to optimise the fabrication route of glass-celsian composites. This method allowed the determination of the optimal processing conditions for the obtainment of a fully dense material with a good particulate dispersion.


2006 - Glass alumina composite coatings by plasma spraying. Part II: microstructure-based modelling of mechanical properties [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano; Montorsi, Monia
abstract

The mechanical properties of composite glass-alumina coatings produced by plasma spraying, as described in Part 1, were numerically characterized with relation to the peculiar microstructure. Finite element meshes were created for the most significant coating typologies, starting from SEM acquired microstructures. The coatings elastic properties and fracture behaviour were characterized as a function of relevant microstructural features. The results confirm that the coatings are anisotropic, with a lower elastic modulus in the direction perpendicular to the substrate plane (spray direction), because of the lamellar microstructure; increasing the alumina volume fraction increases the elastic modulus value both in the spray and transverse direction. Moreover, it is found that cracks start from large, irregular pores, and propagate easily through the glass areas, but are stopped by alumina. Smaller individual glass areas hinder crack propagation. The post-deposition thermal treatment described in Part I produces tensile residual stresses in the glass and compressive ones in the alumina; thus, the arresting effect of the latter on cracks propagation is greatly enhanced. (c) 2005 Elsevier B.V. All rights reserved.


2006 - Glass-alumina composite coatings by plasma spraying. Part I: Microstructural and mechanical characterization [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano
abstract

Composite coatings on ceramic tiles have been produced by plasma-spraying waste glass powders together with alumina as reinforcing phase. Obtaining a tough coating, in which a high amount of waste glass can be recycled, is the aim of the study. Glass powders with different particle size distributions were tested; coatings with increasing glass volume fractions (0%, 20%, 40%, 60%, 80%, 100%) were sprayed. Furthermore, two different kinds of alumina feedstocks were employed, namely, a commercial plasma-spray powder and a more economical laboratory manufactured spray-dried powder. Vickers microhardness, fracture toughness and abrasion resistance have been measured. The coatings were tested both in as-sprayed condition and after a thermal treatment. An abrasion resistance comparable to common industrial glazes has been obtained with as much as 60% of glass volume fraction, employing fine glass powders (< 45 mu m). No significant decrease in mechanical proper-ties has been noticed replacing the commercial alumina powder with the spray-dried one. (c) 2005 Elsevier B.V. All rights reserved.


2006 - Glass-alumina functionally graded materials: their preparation and compositional profile evaluation [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Siligardi, Cristina; Sola, Antonella
abstract

This work was focused on glass-alumina functionally graded materials (FGMs). For the glass phase, a proper composition was chosen belonging to the ternary system CaO-ZrO2-SiO2 and the substrate was made up of a sintered, high-purity polycrystalline alumina. Both of the ingredient materials were carefully characterized. The fabricated functionally graded materials were analysed in detail, by observing them under a scanning electron microscope (SEM) coupled with an X-ray energy dispersive spectrometer (X-EDS). The depth of penetration of the glass and the compositional profile were evaluated by means of a SEM-image elaboration. Moreover, this work applied an analytical model to predict the depth of penetration as a function of time and fabricating parameters such as temperature.


2006 - Influence of Al2O3 addition on thermal and structural properties of erbium doped glasses [Articolo su rivista]
Corradi, Anna; Cannillo, Valeria; Montorsi, Monia; Siligardi, Cristina
abstract

Changes in the structural properties of Er3+ doped soda-lime silicate glasses were investigated as a function of Al2O3 content. A combined approach of experimental techniques and molecular dynamic simulations (MD) was used to evaluate the structural features directly correlated to the glass properties. The experimental results in term of density, thermal properties as well as microstructural and mineralogical data showed a significant variation when increasing the alumina content from 10 mol% to 15 mol%. These results were compared to the MD information and discussed: changes in erbium and aluminium local configuration, due to the glass structural evolution as a function of the alumina concentration, have been investigated.


2006 - Mechanical and tribological properties of electrolytic hard chrome and HVOF-sprayed coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; Ricco, S.
abstract

The microstructure, mechanical properties (Vickers microhardness, fracture toughness, elastic modulus) and tribological behaviour (abrasion and unlubricated sliding wear resistance) of various kinds of electrolitic hard chrome (EHC) coatings and of metallic and cermet HVOF-sprayed coatings (WC-17Co, WC-10Co-4Cr, Co-28Mo-17Cr-3Si) have been studied. EHC coatings are very tough, in fact no cracks could be produced with 10 N Vickers microindentations. However, their superficial morphology and Vickers microhardness are significantly affected by the substrate preparation technique, the deposition process characteristics, and by post-deposition treatments. This causes the coatings to show different behaviors in different wear conditions; in particular, harder coatings are more abrasion-resistant, but undergo a more severe mass loss under unlubricated sliding conditions. HVOF-sprayed cermet coatings are harder but less tough than EHC ones. Therefore, they undergo a comparable or even higher mass loss when subjected to three-body abrasion conditions. However, their two-body sliding resistance definitely overcomes that of EHC coatings, because they form a tough and uniform surface film protecting them from further damage.


2006 - Microscale computational simulation and experimental measurement of thermal residual stresses in glass-alumina functionally graded materials [Articolo su rivista]
Cannillo, Valeria; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella; G., DE PORTU; L., Micele; G., Pezzotti
abstract

Glass-alumina functionally graded materials are new attractive composite materials, that can achieve peculiar mechanical properties due to their gradual compositional variation. Nevertheless, the difference between the coefficients of thermal expansion of the constituent phases may result in significant thermal residual stresses in service or during fabrication. A proper (glass formulation can minimize the mismatch in thermo-mechanical properties, thus relevantly reducing the mean value of the resultant thermal stresses. However, it is a crucial requirement to evaluate the effect of microstructural discreteness and randomness oil the actual stress distribution in functionally graded materials. With this aim,a computational model which applies the finite element method at the microscale is used. The careful modelling of the real microstructural details enables to accurately predict the local stress values and distribution. In order to verify the reliability of the computational simulations, the residual thermal stresses were also experimentally measured by means of a piezo-spectroscopic technique. The comparison between the numerical and the experimental results validate the microstructure-based model.


2006 - Microstructure-based modelling and experimental investigation of crack propagation in glass-alumina functionally graded materials [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract

The aim of the present work was the determination of the fracture mechanisms in glass-alumina functionally graded materials (FGMs). The investigation was performed by means of a combined approach based on microscale computational simulations, which provided for an accurate modelling of the actual FGM microstructure, and experimental analysis. The numerical results proved that microstructural defects, such as pores, deeply influenced the damage evolution. On the contrary, the minimization of the mismatch in the coefficients of thermal expansion of the ingredient materials allowed to obtain low thermal residual stresses, which did not relevantly affect the crack propagation. In order to support the numerical model, microindentation tests were performed on the cross-section of FGM specimens and the experimentally observed crack paths were compared to the computationally predicted ones. (c) 2005 Elsevier Ltd. All rights reserved.


2006 - Modeling of ceramic particles filled polymer-matrix nanocomposites [Articolo su rivista]
Cannillo, Valeria; Bondioli, Federica; Lusvarghi, Luca; Montorsi, Monia; M., Avella; M. E., Errico; M., Malinconico
abstract

In this work, the mechanical properties of polymer matrix-ceramic fillers nanocomposites were investigated. A PCL (poly-caprolactone) matrix was reinforced with increasing amount of nano-sized silica particles in the range 1-2.5% by weight, and the resulting properties were determined as a function of reinforcement characteristics and volume fraction. In order to gain a deeper insight into the mechanical behaviour of such nanocomposites, a numerical model able to reproduce the peculiar composite features was set up. The study focussed on the effect of particles size and amount on the achieved increment in the overall stiffness. The computational approach revealed that a third phase, namely the interphase, has to be taken into account in the model in order to accurately reproduce the experimental results.


2006 - Plasma-sprayed graded ceramic coatings on refractory materials for improved chemical resistance [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; C., Lugli; Lusvarghi, Luca; Manfredini, Tiziano
abstract

Plasma-sprayed ceramic coatings were manufactured on sintered alumina-mullite refractory bricks to improve their chemical resistance to molten glass. Mullite and alumina powders were employed. Graded layered coatings were designed and produced, to reduce the thermal expansion mismatch with the substrate: in all cases, the upper layer consisted in pure alumina (very resistant to chemical attack); alumina-mullite intermediate layers were added to match the low thermal expansion of the porous substrates. Plasma-sprayed coatings definitely improved both the abrasion resistance and the chemical resistance to long-time (8 h at 1400 degrees C) contact with molten glass, since the coating preserved its original microstructure. However, in thermal shock tests, some transverse cracks appeared; thus, thermal cycling tests in presence of molten glass indicated that, after a few cycles, the glass can penetrate down to these cracks. The tested samples were studied by means of scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD).


2006 - Poly(epsilon-caprolactone)-based nanocomposites: Influence of compatibilization on properties of poly(epsilon-caprolactone)-silica nanocomposites [Articolo su rivista]
M., Avella; F., Bondioli; Cannillo, Valeria; E., Di Pace; Me, Errico; Ferrari, Anna Maria; B., Focher; M., Malinconico
abstract

In the present paper, results about preparation and characterization of poly(F-caprolactone) (PCL) based nanocomposites filled with silica nanoparticles are reported. In order to promote polymer/inorganic nanofiller compatibility and to increase the interfacial adhesion between the two components, silica nanoparticles surface has been functionalised by grafting a M-w = 10,000 Da PCL onto it. Successively, PCL based nanocomposites have been prepared by extrusion process. The relationships among size, amount of the nanofiller, organic coating and the final properties have been investigated. The morphological analysis has revealed that the silica functionalization can provide a useful method of preparation of the nanocomposites with the achievement of a fine, a good dispersion and a strong adhesion level. Thermal characterization has shown an improved thermal stability due to the presence of the silica nanoparticles, especially in the case of modified nanofillers. Finally mechanical tests revealed an increase of the Young´s modulus in the PCL based nanocomposites.


2006 - Preparation and characterization of epoxy resins filled with submicron spherical zirconia particles [Articolo su rivista]
Bondioli, Federica; Cannillo, Valeria; Fabbri, Elena; Messori, Massimo
abstract

Submicron spherical zirconia particles were synthesized and used as a reinforcement for epoxy resins. In fact, recent developments indicate that a significant improvement in the thermoset polymer performance may be obtained by using submicron inorganic filler. In this paper, different composites with weight fraction of the filler in the range 1-5% were prepared and characterized in terms of mechanical properties. A numerical model suitable for the description of such materials was set up and employed to estimate the properties as functions of the reinforcement content.


2006 - Preparation and experimental characterization of glass-alumina functionally graded materials [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Siligardi, Cristina; Sola, Antonella
abstract

This work aims at investigating the effects of the processing conditions on the final microstructure of glass-alumina functionally graded materials (FGMs). The ingredient materials, i.e. a polycrystalline sintered alumina and a CaO-ZrO2-SiO2 glass, were accurately characterized, since their mechanical and thermal properties may deeply influence the fabricating process and the overall FGM behaviour. The functionally graded materials were obtained by means of percolation of the molten glass into the alumina substrate. Two types of samples were considered-the Bulk FGMs, produced starting from a glass bulk, and the Powder FGMs, produced starting from a glass powder; in both cases four different heating cycles were attempted. The functionally graded materials were analysed using a SEM-EDS and a X-ray diffractometer. Great attention was devoted to the resulting microstructure; moreover the depth of penetration was measured and related to the fabricating parameters, such as time and temperature.


2006 - Synthesis and nanocomposite sintering of hydroxyapatite-coated zirconia nanopowders [Relazione in Atti di Convegno]
Bondioli, Federica; Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano; Ferrari, Anna Maria
abstract

Hydroxyapatite (HAP), Ca10(PO4)6(OH)2, is a well-known and a valuable implant material with biocompatibility and bioactive properties. Full utilisation of the unique properties of hydroxyapatite bulk ceramics is, however, enhanced by a proper reinforcement, i.e. by preparation of composites. The goal of this study was to synthesize a HAP-coated zirconia composite powder by the precipitation of HAP in presence of zirconia. The idea was to avoid uncontrolled agglomeration of the zirconia nanostructured reinforcement during the sintering step. ZrO2 nanopowders, previously synthesized by hydrothermal crystallisation, were added in an appropriate amount to an intensively stirred aqueous suspension of Ca(OH)2. HAP was precipitated by addition of H2PO4 at controlled pH in order to obtain a 50:50 composite powders. The obtained powders, fully characterized by TEM, XRD, TG-DTA and BET, were used for the preparation of the nanostructured composite speciments. The sintered materials were characterized in order to evaluate their structural and morphological properties.


2006 - Wear behaviour of thermally sprayed ceramic oxide coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano
abstract

The wear resistance of plasma-sprayed ceramic coatings (Al2O3, Al2O3-13%TiO2, Cr2O3) has been investigated through pin-on-disk and dry sand-steel wheel tests, has been correlated to microstructural and micromechanical characteristics (microhardness, fracture toughness) and has been compared to well-known platings (such as Cr electroplating and electroless Ni) and HVOF-sprayed cermets (WC-17%Co, WC-10%Co-4%Cr). Plasma-sprayed ceramics are hard but brittle: dry particles abrasion occurs through splats detachment. The toughest coating (Al2O3) displays the highest wear resistance, which in fact overcomes HVOF-sprayed cermets and Cr electroplating, when a low number of wheel revolutions are considered. In pin-on-disk tests, no coating undergoes wear loss against the 100Cr6 ball, that possess lower hardness. Against the alumina ball, Al2O3 and Al2O3-TiO2. coatings show high wear rates and friction coefficients (due to chemical affinity), while Cr2O3 possesses better wear resistance, lower friction coefficient and inflicts less wear on the counterpart. Cr2O3 wear scar consists in plastically deformed splats and debris forming a quite adherent protective tribofilm. (c) 2006 Elsevier B.V. All rights reserved.


2005 - A stochastic model of damage accumulation in complex microstructures [Articolo su rivista]
Cannillo, Valeria; W. C., Carter
abstract

A statistical approach for modeling fracture in brittle materials is presented. In particular, a microstructural-based finite element code called OOF is used in conjunction with a stochastic representation of failure that relies on the Weibull law. The OOF code, which maps materials microstructures onto finite element meshes, enables to calculate the local stress states; these stresses are used along with the statistical criterion for brittle fracture in order to determine microcrack formation and propagation. Computer simulations are performed on several microstructures of different materials types, e.g., laminates, particulate composites and polycrystals. The damage accumulation due to microcracking is characterized by the stereological measure of failed material and is investigated in order to assess the effect of microstructural features on the failure mechanism. Moreover, the approach allows to analyze the influence of the characteristic parameters for brittle materials on damage evolution.


2005 - Characterisation of glass matrix composites reinforced with lead zirconate titanate particles [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; F., Tavoni; Ej, Minay; Ar, Boccaccini
abstract

A new type of glass matrix composite reinforced with ferroelectric particulate secondary phase was investigated. Samples containing lead zirconate titanate (PZT) particles in a silicate lead glass were fabricated. Various sintering strategies were tested in order to optimise the processing route. The densest samples were obtained by hot-pressing. The composites were characterized by means of SEM observations, X-ray diffraction, differential thermal analysis and Vickers indentations. In order to get a deeper insight into the thermo-mechanical behaviour of the material, a FEM based numerical model was prepared and applied. In particular, the crack-particle interaction was assessed and thus possible toughening mechanisms were investigated. By means of the numerical modelling supported by SEM observations, traditional toughening mechanisms (e.g. crack deflection, particle debonding) were ruled out. Since the experimentally measured indentation fracture toughness of the composite is significantly higher than that of the unreinforeed glass, the findings suggest that a new toughening mechanism may be active, based on the piezoelectric effect.


2005 - Epoxy-silica nanocomposites: Preparation, experimental characterization and modeling [Articolo su rivista]
Bondioli, Federica; Cannillo, Valeria; Fabbri, Elena; Messori, Massimo
abstract

Silica nanoparticles having different sizes were obtained by the sol-gel process and characterized. The prepared nanoparticles were subsequently used as reinforcing fillers to prepare epoxy-based composites with a silica content ranging from I to 5 wt %. SEM analysis and tensile tests carried out on the silica-epoxy nanocomposites indicated the absence of particle aggregation and a reinforcing effect in terms of increased elastic modulus. Mechanical properties were also modeled by using a finite element code able to construct a numerical model from a microstructural image of the material. A more reliable model was prepared by considering the presence of an interphase layer surrounding the particles with intermediate elastic properties between the epoxy and the inclusions and a characteristic size proportional to the particle radius.


2005 - Experimental and computational analyses of lead zirconate titanate reinforced glass matrix composites for structural applications [Relazione in Atti di Convegno]
Cannillo, V.; Tavoni, Francesca; Garcia, R. E.; Boccaccini, A. R.
abstract

The mechanical reliability of glass matrix composites depends on the properties of the composite constituents, e.g. matrix and reinforcement. In many cases, microstructural variables, such as the volume fraction of the reinforcing secondary phase, the crystallographic anisotropy of the involved materials, and the physical coupling between the underlying thermodynamic fields, influences the macroscopic mechanical behaviour, in particular fracture toughness. In this paper, the mechanical properties of lead silicate glass matrix composites reinforced with 30wt% lead zirconate titanate (PZT) ferroelectric particles were studied. The samples were fabricated by hot pressing, and characterized by means of SEM, X-ray diffraction, DTA, and Vickers' indentation techniques. For this material, the stress fields at the tip of an advancing crack should be able to re-orient the ferroelectric domains in the PZT inclusions, inducing local crack-arrest, thus contributing to an increase of the macroscopic fracture toughness. Microstructural effects, such as crack-particle interactions were analysed using a FEM-based numerical approach. A good agreement between predicted crack propagation patterns and those obtained experimentally by the indentation technique was found. Numerical and experimental results suggest that traditional toughening mechanisms such as crack deflection, thermal cooling residual stresses, and load-transfer toughening are not active in the studied glass/PZT composites.


2005 - Experimental characterization and computational simulation of glass-alumina functionally graded surfaces [Relazione in Atti di Convegno]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, A.
abstract

Functionally graded materials are a new and attractive class of materials incorporating an engineered spatial variation in composition and/or microstructure: this idea has immediately revealed successful since it allows to reach peculiar mechanical properties such as resistance to wear and contact damage. As a matter of fact, the final behaviour of a Functionally Graded Material is mainly influenced by its graded composition and/or microstructure. Therefore a good fabrication technique should provide a high control and reproducibility of the spatial variation in composition and/or microstructure; on the other hand, a reliable model should take into account the gradient in order to accurately predict the final behaviour of a Functionally Graded Material. The present study is focused on glass-alumina FGMs: the compositional variation, which occurs along only one direction, has been realized through percolation of a molten glass into a bulk polycrystalline alumina. The resulting Functionally Graded Coatings have been carefully characterized through Scanning Electron Microscopy, X-ray diffraction, classical mechanical tests and analysis. Moreover, their behaviour has been modeled by means of a microstructure-based FEM method. A great attention has been paid to the validation of the computational model on the basis of the experimental data. Furthermore, the experimental and the computational approaches have been combined in order to define the correlation between fabrication parameters, such as time and temperature, and resulting gradients in composition and microstructure as well as related performances. Since changes in material properties can be easily evaluated, the resulting model may be useful to simulate the material response to a given thermo-mechanical loading and to tailor the gradient as a function of the specific application.


2005 - Finite element modelling of brittle matrix composites [Capitolo/Saggio]
Cannillo, Valeria; A. R., Boccaccini
abstract

Description of microstructure-based finite element modelling of the mechanical properties of particulate brittle matrix composites and of porous solids


2005 - La modellazione a calcolatore nella scienza dei materiali [Articolo su rivista]
Cannillo, Valeria; Montorsi, Monia
abstract

Tecniche di modellazione a calcolatore nella scienza dei materiali


2005 - Mechanical performance and fracture behaviour of glass-matrix composites reinforced with molybdenum particles [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina; Manfredini, Tiziano; Montorsi, Monia; Veronesi, Paolo; E. J., Minay; A. R., Boccaccini
abstract

A borosilicate glass-matrix composite has been fabricated by addition of molybdenum particles in various volume fractions. In order to systematically investigate the effect of metallic particulate reinforcement on the overall composite mechanical behaviour, a FEM based numerical model was prepared. The study focused on the global elastic and fracture response of the composites. By studying crack propagation patterns, toughening mechanisms such as crack deflection and load transfer were detected, thus enabling to assess the influence of second phase volume fraction on composite fracture toughness. Microscopy observations of fracture surfaces were performed to support the numerical results. © 2005 Elsevier Ltd. All rights reserved.


2005 - New frontiers in engineered materials: fabrication processes and relevant applications of Functionally Graded Materials [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract

Functionally GradedMaterials (FGMs) are a newand attractive class ofcomposite materials,characterized by anengineered spatial variationin composition andmicrostructure. Anappropriate design of thecompositional andmicrostructural gradientensures a gradual change ofproperties andperformances, which can betailored to the assignedapplication requirements.The optimization of the finalFGM, however, isconditioned not only by theunderstanding of thecorrelation existing betweencomposition/microstructureand material behaviour, butalso by the adoption of asuitable fabricationtechnique. In the presentpaper, therefore, specialattention will be paid to theproduction of FunctionallyGraded Materials. Finally abrief overview of theirapplications will beprovided


2005 - Plasma-sprayed glass-ceramic coatings on ceramic tiles: microstructure, chemical resistance and mechanical properties [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano; Siligardi, Cristina; C., Bartuli; A., Loreto; T., Valente
abstract

This article reports the characterisation and optimisation of glass-ceramic coatings plasina-sprayed on traditional ceramic substrates, dealing with microstructures, chemical resistance, and superficial mechanical properties. A CaO-ZrO2-SiO2 (CZS) frit, capable of complete crystallization after proper thermal treatment, has been employed: due to its refractory nature, its firing temperature in a traditional process would be unbearable for common substrates. The frit was plasma-sprayed onto ceramic tiles and a post-process thermal treatment has been developed in order to sinter and crystallize the coating, employing much lower temperatures than a traditional ceramic firing cycle. The microstructure of both as-sprayed and treated coatings has been evaluated with SEM and EDS, acid resistance tests have been performed. Vickers microhardness, superficial fracture toughness, deep abrasion resistance, elastic modulus and coating adhesion have been evaluated. Unglazed stoneware and an industrial glaze were also tested for comparison and an experiment was made to produce a CZS-based glaze to ascertain the inadequacy of traditional firing. As-sprayed coatings have a typical plasma-spraying defective microstructure, but a thermal treatment with 30´ isotherm at 850 degrees C plus 15´ isotherm at 1050 degrees C allows good densification, excellent adhesion and complete crystallization, with formation of wollastonite-2M and many small Ca2ZrSi4O12 grains. Thus, the coating outperforms stoneware by 50% in abrasion resistance, possessing higher fracture toughness, thanks to the continuous crack deflections due to the numerous crystals. Fracture toughness appears to be the property most correlated to abrasion resistance, because brittle fracture is the dominant abrasion mechanism. Hardness and elastic modulus reflect quite well the coating inner cohesion. Treated coatings porosity is lower than industrial glazes and stoneware.


2005 - Processing glass-pyrochlore composites for nuclear waste encapsulation [Articolo su rivista]
S., Pace; Cannillo, Valeria; J., Wu; D. N., Boccaccini; S., Seglem; A. R., Boccaccini
abstract

Glass matrix composites have been developed as alternative materials to immobilize nuclear solid waste, in particular actinides. These composites are made of soda borosilicate glass matrix, into which particles of lanthanum zirconate pyrochlore are encapsulated in concentrations of 30 vol.%. The fabrication process involves powder mixing followed by hot-pressing. At the relatively low processing temperature used (620 degrees C), the pyrochlore crystalline structure of the zirconate, which is relevant for containment of radioactive nuclei, remains unaltered. The microstructure of the composites exhibits a homogeneous distribution of isolated pyrochlore particles in the glass matrix and strong bonding at the matrix-particle interfaces. Hot-pressing was found to lead to high densification (95% th.d.) of the composite. The materials are characterized by relatively high elastic modulus, flexural strength, hardness and fracture toughness. A numerical approach using a microstructure-based finite element solver was used in order to investigate the mechanical properties of the composites.


2005 - Sintering of metal fibre reinforced glass matrix composites using microwave radiation [Articolo su rivista]
Ej, Minay; Ar, Boccaccini; Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina
abstract

The application of microwave radiation to sinter a chopped metal fibre reinforced glass matrix composite without the use of a susceptor material to preheat the powder compact has been demonstrated. The system considered was a soda borosilicate glass powder requiring a relatively low sintering temperature, mixed with 2 or 10 vol.-% Hastelloy X fibres. Single mode microwave heating was performed using radiation of 2.45 GHz in an applicator operating in the TE103 mode. Samples could be sintered in less than 5 min. Samples heated in the maximum of the electric field showed increased pore shrinkage in comparison with samples sintered in the maximum of the magnetic field. The present work demonstrates that metallic additions may be used to eliminate the requirement of a susceptor material (usually SiC) to heat powder glass samples in a short time to a temperature at which it would be able to couple with the microwaves in order for sintering to occur.


2005 - Structural characterization of neodymium containing glasses by molecular dynamics simulation [Articolo su rivista]
Corradi, Anna; Cannillo, Valeria; Montorsi, Monia; Siligardi, Cristina; Cormack, An
abstract

Structural characterization of neodymium containing glasses was performed by using molecular dynamic simulations. Chemical and physical properties of glasses are strongly related to the local environment of the different ions constituting the three dimensional network. In rare earth containing glasses the modifications of the basic structural units and the physical properties of the host material strongly depend on the rare earth ion content. In this work molecular dynamic simulations (MD) have been used to characterize the structural modification induced by the Nd3+ addition into a silicate glasses. The increase of the NBO species in the glass structure has been observed as a results of the increasing Nd2O3 content. This results compare well with the experimental evidences that indicates the glass depolymerization promoted by the neodymium addition. The structural length scale associated with the rare earth clustering process, experimentally observed, have been also investigated. MD results reveals the presence of Nd-O-Nd linkages which indicate the possibility of the rare earth cations to clusterize in the glass network. The presence of Nd3+ rich regions promotes the concentration quenching phenomena that are associated to the drastic changes in the glass amplification efficiency experimentally observed for neodymium containing glasses.


2005 - The anorthite-diopside system: structural and devitrification study. Part I: structural characterization by molecular dynamic simulations [Articolo su rivista]
Bonamartini Corradi, A.; F., Bondioli; Cannillo, Valeria; Ferrari, Anna Maria; Lancellotti, Isabella; Montorsi, Monia
abstract

Molecular dynamic simulations of glasses belonging to the anorthite-diopside system have been performed in order to obtain an atomistic description of the material's structure. The structural parameters obtained by the simulations allow to confirm that the glass materials are characterized by a very similar short-range environment. The main differences have been observed in the intermediate-range order of the structure that describe the distribution and the packing of the tetrahedra constituting the three-dimensional networks. It is shown that the glass materials with composition close to the two extremes, corresponding to the pure glass anorthite or pure glass diopside, display the typical structural features of the tectosilicates and inosilicates subclass of minerals, respectively, to which anorthite and diopside crystals belong.


2004 - Characterisation of CaO-ZrO2-SiO2 glasses by MAS-NMR and molecular dynamics [Articolo su rivista]
Barbieri, Luisa; Cannillo, Valeria; Leonelli, Cristina; Montorsi, Monia; Siligardi, Cristina; P., Mustarelli
abstract

In this work a wide series of compositions, belonging to the CZS ternary system, are analysed. The linear expansion coefficient of the glass materials is experimentally determined and the results are interpreted by comparison with the structural information derived by molecular dynamics simulations and by Si-29-MAS-NMR. The analysis of the alpha values indicate that, while the ZrO2 acts as network former in these glasses, CaO shows network modifier behaviour producing a decrease of the network complexity. The characterisation of the short and intermediate range structure, obtained by the MD and Si-29-MAS-NMR analysis, allows one to define the relationships between the structure modifications induced by the different oxides, and the physical properties of the glasses experimentally observed.


2004 - Computational simulations for the optimisation of the mechanical properties of alumina-glass Functionally Graded Materials [Capitolo/Saggio]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract

Functionally graded materials are finding increasing applications especially as protective coatings, due to their mechanical properties such as resistance to wear and contact damage. It is well known that the microstructure of FGMs governs the resulting global properties. Finite element simulations can be successfully used to characterize the performance of these materials, provided that the computational model is able to take into account microstructural variations along the thickness. In this work, Functionally Graded Materials obtained by percolation of a glass into a bulk polycrystalline alumina are considered and the effect of the microstructure on the overall behavior is investigated by means of a microstructure-based FEM approach. The model is validated by comparison with experimental data, and can be employed in order to optimize the design of these graded surfaces.


2004 - Computational simulations for the optimization of the mechanical properties of alumina-glass functionally graded materials [Capitolo/Saggio]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract

Computational simulations for the optimization of the mechanical properties of alumina-glass functionally graded materials


2004 - Control of pore size by metallic fibres in glass matrix composite foams produced by microwave heating [Articolo su rivista]
Ej, Minay; Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina; Ar, Boccaccini
abstract

The application of microwave radiation as the heating source for the fabrication of glass foams reinforced with metallic fibres has been investigated. A soda-borosilicate glass powder was chosen for the matrix. The metal fibres were Hastelloy X fibres in volume concentration of 0, 2 and 10%. The fibre diameter was 8 pm and length was 100 mum. The microwave heating process was carried out in a self constructed over-moded microwave applicator operating at the 2.45 GHz ISM frequency. The glass foamed during processing leading to greater than 50 vol.% of spherical pores. The samples were characterised in terms of pore size and distribution, density, metal fibre distribution and interface characteristics. Adding stainless steel fibres to the glass composite prevented the glass from fracturing during processing and resulted in a more even distribution of finer pores. It is proposed that porosity formed during microwave heating as a consequence of localised glass matrix overheating in correspondence with the presence of metal fibres, caused by the preferential microwave absorption exhibited by the Hastelloy X fibres themselves and by the micro-regions of the matrix heated well above the glass softening temperature.


2004 - Glass matrix composites with lead zirconate titanate particles processed by microwave heating [Relazione in Atti di Convegno]
Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina; E. J., Minay; A. R., Boccaccini
abstract

The possibility of toughening glass and ceramics by addition of a piezoelectric particulate secondary phase is the focus of current research. It is hypothesised that stress concentrations at the tip of an advancing crack can re-orient piezoelectric domains within the reinforcement in the direction of the stress field around the crack, thus dissipating energy which contribute to fracture toughness increment of the composite. Previous work has focussed on producing glass/piezoelectric inclusion composites by conventional sintering. This process is accompanied by extended porosity formation, as well as Pb depletion in the PZT phase. In several cases, the long processing times required to fully sinter the glass matrix lead to glass-PZT reactions and to loosing the stoichiometry of the PZT inclusions. In this study, the novel production of new glass matrix composites reinforced with piezoelectric inclusions by using microwave heating was investigated. Specifically, lead-zirconate-titanate (PZT) particles in lead silicate and borosilicate glass matrices were considered. Mixtures of glass and PZT powders were prepared and used to fabricate powder compacts by uniaxial cold-pressing. In order to achieve densification, the compacts were subsequently heated in a single mode applicator, connected to a generator operating at the 2.45 GHz ISM frequency. T


2004 - I materiali nanostrutturati: preparazione, proprietà e prospettive di applicazione dei nanoceramici [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano
abstract

preparazione, proprietà e prospettive di applicazione dei nanoceramici


2004 - Investigation of the mechanical properties of Mo-reinforced glass-matrix composites [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; A. R., Boccaccini
abstract

One approach for reducing the inherent brittleness and flaw sensitivity of glass is to fabricate a composite material by incorporating particles or fibers in the glass matrix. In order to fully understand the toughening mechanisms in composites, it is useful to develop predictive models able to describe the mechanical behavior and its dependence on microstructure. To this aim, numerical models can be used in order to assess the effect of the glass-matrix composite microstructure on the effective macroscopic mechanical and fracture properties. An innovative microstructure-based finite element code is used to describe the mechanical performance of glass matrix composites. This code is able to convert digitized images of the material microstructure into a finite element grid, so that all microstructural details such as inclusion size, morphology and volume fraction can be incorporated in the model. In this study, a borosilicate glass matrix composite reinforced with molybdenum particles is characterized using the aforementioned microstructure-based FEM approach in terms of residual stresses and elastic properties.


2004 - Porous glasses with controlled porosity: Processing and modelling of mechanical properties [Relazione in Atti di Convegno]
A. R., Boccaccini; Cannillo, Valeria; Leonelli, Cristina; Veronesi, Paolo
abstract

Porous glass specimens containing designed spheroidal porosity are used as model materials to test the prediction capability of theoretical and numerical approaches for the Young's modulus of porous materials. In particular, a finite element model called OOF, which converts a real microstructural image into a 2-D finite element mesh, has been adopted in order to assess the effect of porosity and pore structure on the Young's modulus.


2004 - Preparation, characterisation and computational study of poly(epsilon-caprolactone) based nanocomposites [Articolo su rivista]
M., Avella; Bondioli, Federica; Cannillo, Valeria; Me, Errico; Ferrari, Anna Maria; B., Focher; M., Malinconico; Manfredini, Tiziano; Montorsi, Monia
abstract

In recent years, scientific and industrial interest has been focused on the preparation of organic/inorganic nanocomposites because of their unique hybrid properties correlated with the enormous interfacial adhesion region that is a characteristic of nanoparticles. The objective of the whole research was to improve poly-caprolactone (PCL) mechanical and barrier performances by using silica spherical nanoparticles for filling. In particular, in order to improve the polymeric matrix/inorganic nanofiller's interfacial adhesion and consequently to achieve a fine nanometric dispersion, silica nanoparticles have been chemically modified by grafting onto them a hydroxyl end-capped PCL, after wheich they have been melt blended with high molecular weight PCL. In the present paper, details on the synthesis, morphology and mechanical properties of the prepared nanocomposites are reported. Moreover, a numerical tool has been used to predict the mechanical properties of the nanocomposite, starting from the morphology of the material observed by scanning electron micrography, and the individual properties of the constituents.


2004 - Processing of novel glass matrix composites by microwave heating [Articolo su rivista]
Ej, Minay; Ar, Boccaccini; Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina
abstract

The application of microwave radiation as the heating source for the processing of glass matrix composites containing metallic particles has been investigated. A borosilicate glass powder was chosen for the matrix. The metal inclusions investigated were molybdenum, tungsten, aluminium. titanium. nickel and iron particles in volume concentration of 10%. The average particle size of primary metallic particles varied between 2 and 50 mum. The microwave heating process was carried out in a self-constructed multimode microwave applicator operating at the 2.45 GHz ISM frequency. For comparison, samples were also made by conventional powder technology and sintering. The microwave- and conventionally-processed samples were characterised in terms of: particle distribution, density and glass/metal particle interfacial characteristics. The microwave-processed samples had densities up to 96% of that of the conventionally-processed samples and were obtained in significantly shorter times (7 min versus similar to7 h). In case of glass/Mo composites, a recently developed computational model based on the OOF finite element code was used in order to calculate the residual thermal stresses in the samples.


2004 - Properties/Structure Relationships in Innovative PCL-SiO2 Nanocomposites [Articolo su rivista]
M., Avella; Bondioli, Federica; Cannillo, Valeria; S., Cosco; M. E., Errico; Ferrari, Anna Maria; B., Focher; M., Malinconico
abstract

Poly(caprolactone) (PCL) based nanocomposites filled with Silica (SiO2) nanoparticles were prepared and the relationships between their structure and properties were investigated. Silica nanoparticles were synthesized by Stober method. Surface of silica nanoparticles were successively functionalized in order to promote matrix/filler compatibilization and to improve interfacial adhesion. Morphological analysis performed on the fractured surface of samples revealed that the compatibilization process permitted to obtain an homogeneous and discrete distribution of the nanoparticles into polymeric matrix. Mechanical test showed that in the presence of a strong interphase, the elastic modulus increases of about 25% than the neat polymeric matrix value. Preliminary modelling analysis was also performed in order to assess the correlation existing between a computational model and experimental data.


2004 - Strctural characterization of rare earth containing glasses by molecular dynamic simulation [Relazione in Atti di Convegno]
A., Bonamartini Corradi; Cannillo, Valeria; Montorsi, Monia; Siligardi, Cristina; A. N., Cormack
abstract

rare-earth (RE) containing glasses are largely used in technological applications such as optical fiber amplifiers, upconversion and glass laser. Glasses containing respectively Nd2O3 and Er2O3 are considered and the data obtained by MD simulations are used to analyse the different environment of Nd3+ and Er3+ in the glass matrix.


2004 - Use of numerical approaches to predict mechanical properties of brittle bodies containing controlled porosity [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Ar, Boccaccini
abstract

when designing a porousmaterial, it is important to control not only the porosityand pore morphology, but also the pore spatial positioning,if the mechanical properties, in particular fracturestrength, are to be optimized. To this aim, suitableproduction techniques should be developed in order toguarantee an homogeneous dispersion of pores.


2003 - Computational simulations for the assessment of the mechanical properties of glass with controlled porosity [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina; Manfredini, Tiziano; Montorsi, Monia; Ar, Boccaccini
abstract

Porous glass with closed controlled porosity is used as a model system in order to numerically assess the effect of pores on the macroscopic mechanical and fracture behavior of brittle solids. A computational code called OOF, which converts digitalized two-dimensional (2-D) images of materials microstructures into finite element meshes, is adopted, so that the effect of 2-D microstructural features (e. g. pore size and shape) on the global mechanical response of the material can be determined. Firstly, microstructures of porous glass bodies containing isolated pores were considered. These specimens were numerically investigated in terms of fracture initiation and propagation: the numerical model predicted that larger pores initiate fracture, in agreement with experimental results. Then, the effect of porosity on the elastic and fracture properties was thoroughly investigated by means of model two-dimensional microstructures consisting of selected area fractions of pores (equivalent to pore volume fractions in three dimensions) and with prescribed pore shape, orientation and dimensions. In particular, the effect of pore dimension and shape was studied, finding that the critical stress for crack initiation scales with pore dimension and aspect ratio, i.e. oblate and larger pores oriented perpendicularly to the stress direction cause a higher reduction of strength of the specimen. Finally, several 2-D microstructures characterized by different values of area fraction of pores of the same shape were investigated, in order to determine the variation of elastic properties and the fracture response of porous glasses with pore content. The study confirms the suitability of the 2-D OOF code to investigate the mechanical and fracture behavior of porous materials. Issues regarding the limitation of the model due to its 2-D character are also discussed where appropriate.


2003 - Experimental and MD simulations study of CaO-ZrO2-SiO2 glasses [Articolo su rivista]
Barbieri, Luisa; Cannillo, Valeria; Leonelli, Cristina; Montorsi, Monia; P., Mustarelli; Siligardi, Cristina
abstract

Glasses belonging to the CaO-ZrO2-SiO2 ternary system were prepared by melting raw materials at 1600°C. Several properties of the glassy materials, such as density and thermal behavior, were experimentallydetermined, and the results were interpreted by comparison with the structural information derived frommolecular dynamics simulations and from 29Si-MAS NMR. A detailed analysis of the short- and intermediaterangestructure was performed to define the role played by the different atoms present in the glass formulationand to correlate the structural modifications to the macroscopic properties of this class of glasses.


2003 - Numerical modelling of the fracture behaviour of a glass matrix composite reinforced with alumina platelets [Articolo su rivista]
Cannillo, Valeria; Pellacani, Gian Carlo; Leonelli, Cristina; Ar, Boccaccini
abstract

In this work the fracture behaviour of a composite material constituted by a borosilicate glass matrix reinforced with Al2O3 platelets is studied by means of a numerical model. This material, which was experimentally investigated in a previous paper, is characterised by the presence of thermal residual stresses that arise upon cooling from the processing temperature due to the thermal expansion coefficients mismatch between the matrix and the reinforcements. A numerical model based on finite element simulations of realistic composite microstructures was adopted for the present material. The crack propagation was studied using finite elements coupled with selected failure criteria (Griffith and Weibull approaches) implemented inside the elements. Computational determination of crack propagation during failure is compared with previously obtained experimental data and microscopy images of platelet-crack interactions, showing that the model provides results in good agreement with the experimental observations. (C) 2002 Elsevier Science Ltd. All rights reserved.


2003 - Short range order characterization of materials belonging to the CaO-MgO-Al2O3-SiO2 system: a molecular dynamic study [Articolo su rivista]
Corradi, Anna; Cannillo, Valeria; Montorsi, Monia
abstract

characterization of glasses belonging to the CaO-MgO-Al2O3-SiO2 system by MD simulations


2003 - Simulazioni computazionali per lo studio di materiali di interesse applicativo [Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia
abstract

descrizione di tecniche di modeling per materiali di interesse applicativo


2003 - Stochastic modeling of the mechanical behavior and reliability of brittle or moderately damage-tolerant materials [Capitolo/Saggio]
Cannillo, Valeria; W. C., Carter
abstract

Structural materials often have variations in their microstructures and, in some cases, the material properties that derive from microstructure. Thus, it would be reasonable to utilize a statistical approach that considers the effect of these variations. In materials that accumulate some damage before failure, material properties may depend on slight variations in microstructure as these can have significant effect on stress singularities. Therefore, it would be useful to adopt a tool able to account for the microstructural effects on the global response. To this aim, a statistical approach for brittle fracture is used in conjunction with a microstructural-based finite element model, OOF. This computational tool, that operates directly on microstructural images, is employed to investigate the effect of microstructural features on the mechanical behavior of several typologies of complex materials. Computer simulations are performed to analyze the reliability and damage accumulation of laminated microstructures, random polycrystals and particulate composites. Moreover, FGMs (Functionally graded materials) are considered in order to investigate the effect of microstructure variations through thickness on the fracture behavior.


2002 - Hermetic Glass Bodies with Controlled Porosity: Processing and Properties [Relazione in Atti di Convegno]
A. R., Boccaccini; J. L., Spino; Cannillo, Valeria
abstract

inevstigation of porous glass


2002 - Numerical models for thermal residual stresses in Al2O3 platelets/borosilicate glass matrix composites [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina; A. R., Boccaccini
abstract

In this paper, we model and numerically study thermal residual stresses in a borosilicate glass reinforced with Al2O3 platelets. This composite material was experimentally characterized in a previous work, The aim of this paper is to investigate further the thermal residual stresses in these composites that are responsible for toughening and to assess the variation or the thermal residual stresses with platelets content. A numerical model based on finite element simulations of the given microstructures is used. Computational tests are compared both with previously obtained experimental data and with simplified theoretical equations. The model provides consistent results which are in agreement with experimental measurements, Moreover. the numerical approach presented here is able to take into account the effect of particle shape on residual thermal stresses. which could not be computed easily by theoretical equations.


2002 - Numerical models of the effect of heterogeneity on the behavior of graded materials [Relazione in Atti di Convegno]
Cannillo, Valeria; Manfredini, Tiziano; Corradi, Anna; Wc, Carter
abstract

Gradients in the elastic modulus of a surface can affect the hardness of that surface, as demonstrated in recent papers [1, 2]. It has been experimentally verified that enhanced hardness can be obtained by dispersing a variable concentration of second phase particles in a matrix and cosintering. However, the nature of the processing conditions results in a microstructure that has variations in its lateral (in-surface-plane) properties and variations about the optimal gradient due to the discrete nature of the second phase particulate microstructure: these materials have stochastically graded microstructures, In this paper, we generate a series of microstructures that have the same average surface gradient, but with variable placement of the second phase, in order to analyze numerically the effect of stochasticity on the predicted optimal material properties. We characterize the effect of stochastic placement of second phase particles on the hardness and toughness of these materials which have a specified gradient in their surface elastic coefficients.


2002 - On the behavior of dissipative time integration methods near the resonance condition [Articolo su rivista]
Cannillo, Valeria; Mancuso, Massimo
abstract

THE BEHAVIOR OF DISSIPATIVE TIME INTEGRATIONMETHODS NEAR THE RESONANCE CONDITION IS ANALYZED


2001 - A simple approach for determining the in situ fracture toughness of ceramic platelets used in composite materials by numerical simulations [Articolo su rivista]
Cannillo, Valeria; Corradi, Anna; Leonelli, Cristina; Ar, Boccaccini
abstract

The present study is an example of thedetermination of an intrinsic value of fracture toughnessof embedded particles in a rigid matrix, by meansof a parametric study using the microstructural FEM code OOFand the validation by comparison with experimentalobservations.


2001 - Enhancing the mechanical properties of porcelain stoneware tiles: a microstructural approach [Articolo su rivista]
C., Leonelli; F., Bondioli; Veronesi, Paolo; Romagnoli, Marcello; Manfredini, Tiziano; Pellacani, Gian Carlo; Cannillo, Valeria
abstract

This paper focuses on the complexities of the microstructure and phase development in porcelain stoneware tiles produced following industrial fast single firing cycles. A microstructural investigation was conducted to determine if the addition of selected low cost minerals would improve mechanical properties. The minerals tested were quartz, mullite and kyanite. Uniaxially pressed samples were submitted to the same industrial firing schedule and tested according to the European tile standards before further microstructural analysis. All the requirements specified in UNI EN normative concerning BIa class tiles were fulfilled; moreover, mullite and kyanite added formulations showed sensible increases in mechanical properties, especially as far as flexural strength and abrasion resistance are concerned.


2001 - Micromechanics principles applied to fracture propagation in porcelain stoneware tiles [Relazione in Atti di Convegno]
Leonelli, Cristina; F., Bondioli; Veronesi, Paolo; Cannillo, Valeria; Romagnoli, Marcello; Manfredini, Tiziano
abstract

The possibility of discussing the mech. properties of porcelain stoneware tiles with a scientific approach typically used in the investigation of the composite materials is studied. A thorough microstructural investigation was conducted to det. if the addn. of selected low-cost minerals would improve mech. properties. The minerals tested were quartz, mullite, and kyanite. Uniaxially pressed samples were submitted to the same industrial firing schedule and tested according to European tile stds. before further microstructural anal.


2001 - Modeling and simulations at microscopical scale in materials science and engineering: a review [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina
abstract

Review of the modeling and simulations techniques at microscopical scale in materials science and engineering


2001 - Numerical simulations for the crashworthiness design of metal frames [Articolo su rivista]
Cannarozzi, Mario; Cannillo, Valeria
abstract

The paper describes the use of numerical simulations for the crashworthiness design of metal frames


2001 - Porcelain stoneware as a composite material: identification of strengthening and toughnening mechanisms [Articolo su rivista]
Leonelli, Cristina; Veronesi, Paolo; Cannillo, Valeria; Pellacani, Gian Carlo; A. R., Boccaccini
abstract

Porcelain stoneware is studied using the principles usually applied for composite materials


2000 - Computation and simulation of reliability parameters and their variations in heterogeneous materials [Articolo su rivista]
Cannillo, Valeria; Wc, Carter
abstract

Two numerical methods for reliability assessment for composite microstructures under arbitrary loading are presented: a Monte Carlo (MC) technique that assigns discrete failure probabilities from local stresses and empirical failure probabilities, and a parametric probability product (PP) method where the joint probability of survival is from a product over a set of heterogeneous finite elements. The two methods are verified for known cases and then applied to random composite microstructures that are not amenable to direct analysis. While the MC method is computationally more expensive and less accurate than the PP method, it produces a distribution of failure predictions. The distribution places confidence intervals on survival probabilities or estimates for the number of physical experiments required to predict Weibull parameters. A composite microstructure does not have a failure distribution of the same form as its homogeneous composite parts, but its form is readily understood. (C) 2000 Acra Metallurgica inc. Published by Elsevier Science Ltd. All rights reserved.


2000 - Spurious resonances in numerical time integration methods for linear dynamics [Articolo su rivista]
Cannillo, Valeria; Mancuso, Massimo
abstract

This paper deals with the accuracy of time integration methods for linear dynamics when applied near the resonance condition. An approach for the analysis is considered which allows spurious resonance conditions to be detected. The analysis of Newmark methods shows the existence of such conditions which can adversely affect the quality of numerical computations, As an alternative, a higher order algorithm, which can be viewed as a generalization of the trapezoidal rule, is investigated. The analysis reveals that the spurious disturbance near the resonance condition is greatly reduced. The reported numerical tests confirm the theoretical predictions and demonstrate that high-quality simulations can be obtained by means of higher order algorithms.