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Devis BELLUCCI

Ricercatore t.d. art. 24 c. 3 lett. B
Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

2022 - Bioactive Glasses in Periodontal Regeneration: Existing Strategies and Future Prospects—A Literature Review [Articolo su rivista]
Cannillo, Valeria; Salvatori, Roberta; Bergamini, Stefania; Bellucci, Devis; Bertoldi, Carlo
abstract


2022 - Deposition of bioactive glass coatings based on a novel composition containing strontium and magnesium [Articolo su rivista]
Canas, E.; Orts, M. J.; Sanchez, E.; Bellucci, D.; Cannillo, V.
abstract

In this work a novel bioactive glass composition was used to deposit coatings by means of plasma spraying. Different coatings were manufactured and optimized by varying the processing parameters and were studied by X-ray diffraction and scanning electron microscopy. Moreover, the bioactivity was assessed by in vitro tests in Simulated Body Fluid solution. The coatings displayed the typical microstructure of atmospheric plasma sprayed coatings, that is a coating made up by the stacking of melted splats, with different thicknesses, porosities and crystalline phases depending on the spraying parameters used. The work showed that all the coatings are denser and with less porosity than those observed for plasma sprayed coatings of the well-known 45S5 bioactive glass, with similar particle size deposited under the same spraying conditions. The in vitro tests demonstrated the bioactive aptitude of all the coatings, on whose surface an hydroxycarbonate apatite layer formed after 7 days of soaking.


2022 - Low-Temperature Sintering of a New Bioactive Glass Enriched with Magnesium Oxide and Strontium Oxide [Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria
abstract


2022 - Spark plasma sintering, mechanical and in-vitro behavior of a novel Sr- and Mg-containing bioactive glass for biomedical applications [Articolo su rivista]
Angioni, D.; Orru, R.; Cao, G.; Garroni, S.; Iacomini, A.; Bellucci, D.; Cannillo, V.
abstract

The so-called BGMS10, a bioactive glass containing 10 mol.% SrO and 10 mol.% MgO, displays a low inclination to crystallize, as confirmed by its high activation energy (538.9 kJ/mol). Such peculiar aspect and the beneficial use of SPS allow for the obtainment of 99.7 % dense and fully amorphous products at 750 °C. The incipient crystallization in the glass is observed when temperature is increased to 850 °C, while 95 wt. % crystallized ceramics are produced at 950 °C. Main crystalline phases are α- and β-CaSiO3, with grain size of 89 and 97 nm, respectively. Glass crystallization is accompanied by Young's modulus increase from 90.92 to 98.38 GPa. On the other hand, partially crystallized samples (850 °C) exhibit higher Vickers hardness (718.8) compared to fully crystallized ones (619.8), which show lower density (98.6 %). In-vitro tests in SBF indicate that the silica-gel film preceding apatite nucleation is mostly formed on the amorphous substrate region.


2021 - Bioactive glass applications: A literature review of human clinical trials [Articolo su rivista]
Cannio, M.; Bellucci, D.; Roether, J. A.; Boccaccini, D. N.; Cannillo, V.
abstract

The use of bioactive glasses in dentistry, reconstructive surgery, and in the treatment of infections can be considered broadly beneficial based on the emerging literature about the potential bioactivity and biocompatibility of these materials, particularly with reference to Bioglass® 45S5, BonAlive® and 19-93B3 bioactive glasses. Several investigations have been performed (i) to obtain bioactive glasses in different forms, such as bulk materials, powders, composites, and porous scaffolds and (ii) to investigate their possible applications in the biomedical field. Although in vivo studies in animals provide us with an initial insight into the biological performance of these systems and represent an unavoidable phase to be performed before clinical trials, only clinical studies can demonstrate the behavior of these materials in the complex physiological human environment. This paper aims to carefully review the main published investigations dealing with clinical trials in order to better understand the performance of bioactive glasses, evaluate challenges, and provide an es-sential source of information for the tailoring of their design in future applications. Finally, the paper highlights the need for further research and for specific studies intended to assess the effect of some specific dissolution products from bioactive glasses, focusing on their osteogenic and angio-genic potential.


2021 - Composite scaffolds for bone tissue regeneration based on pcl and mg-containing bioactive glasses [Articolo su rivista]
Petretta, M.; Gambardella, A.; Boi, M.; Berni, M.; Cavallo, C.; Marchiori, G.; Maltarello, M. C.; Bellucci, D.; Fini, M.; Baldini, N.; Grigolo, B.; Cannillo, V.
abstract

Polycaprolactone (PCL) is widely used in additive manufacturing for the construction of scaffolds for tissue engineering because of its good bioresorbability, biocompatibility, and processa-bility. Nevertheless, its use is limited by its inadequate mechanical support, slow degradation rate and the lack of bioactivity and ability to induce cell adhesion and, thus, bone tissue regeneration. In this study, we fabricated 3D PCL scaffolds reinforced with a novel Mg-doped bioactive glass (Mg-BG) characterized by good mechanical properties and biological reactivity. An optimization of the printing parameters and scaffold fabrication was performed; furthermore, an extensive microtopog-raphy characterization by scanning electron microscopy and atomic force microscopy was carried out. Nano-indentation tests accounted for the mechanical properties of the scaffolds, whereas SBF tests and cytotoxicity tests using human bone-marrow-derived mesenchymal stem cells (BM-MSCs) were performed to evaluate the bioactivity and in vitro viability. Our results showed that a 50/50 wt% of the polymer-to-glass ratio provides scaffolds with a dense and homogeneous distribution of Mg-BG particles at the surface and roughness twice that of pure PCL scaffolds. Compared to pure PCL (hardness H = 35 ± 2 MPa and Young’s elastic modulus E = 0.80 ± 0.05 GPa), the 50/50 wt% formulation showed H = 52 ± 11 MPa and E = 2.0 ± 0.2 GPa, hence, it was close to those of trabecular bone. The high level of biocompatibility, bioactivity, and cell adhesion encourages the use of the composite PCL/Mg-BG scaffolds in promoting cell viability and supporting mechanical loading in the host trabecular bone.


2020 - A Comprehensive Review of Bioactive Glass Coatings: State of the Art, Challenges and Future Perspectives [Articolo su rivista]
Sergi, Rachele; Bellucci, Devis; Cannillo, Valeria
abstract


2020 - A Novel Bioactive Glass Containing Therapeutic Ions with Enhanced Biocompatibility [Articolo su rivista]
Sergi, Rachele; Bellucci, Devis; Salvatori, Roberta; Anesi, Alexandre; Cannillo, Valeria
abstract


2020 - A Review of Bioactive Glass/Natural Polymer Composites: State of the Art [Articolo su rivista]
Sergi, Rachele; Bellucci, Devis; Cannillo, Valeria
abstract

Collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose are biocompatible and non-cytotoxic, being attractive natural polymers for medical devices for both soft and hard tissues. However, such natural polymers have low bioactivity and poor mechanical properties, which limit their applications. To tackle these drawbacks, collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose can be combined with bioactive glass (BG) nanoparticles and microparticles to produce composites. The incorporation of BGs improves the mechanical properties of the final system as well as its bioactivity and regenerative potential. Indeed, several studies have demonstrated that polymer/BG composites may improve angiogenesis, neo-vascularization, cells adhesion, and proliferation. This review presents the state of the art and future perspectives of collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose matrices combined with BG particles to develop composites such as scaffolds, injectable fillers, membranes, hydrogels, and coatings. Emphasis is devoted to the biological potentialities of these hybrid systems, which look rather promising toward a wide spectrum of applications.


2020 - A new bioactive glass with extremely high crystallization temperature and outstanding biological performance [Articolo su rivista]
Bellucci, D.; Veronesi, E.; Dominici, M.; Cannillo, V.
abstract

In this work, a new bioactive glass was designed, prepared by means of a melt-quenching route and characterized in terms of both thermal properties and biological performance. The main objective was to obtain a novel product with high temperature of crystallization in view of possible thermal treatments, as well as remarkable biological responsiveness. Thermal behavior was investigated by heating microscopy, differential thermal analysis (DTA) and sintering tests. The glass displayed a very high crystallization temperature and the samples remained completely amorphous after sintering. Bioactivity was evaluated by means of Simulated Body Fluid (SBF) assay, which is a widely used method to preliminary investigate samples' reactivity in vitro; the glass showed a strong apatite forming ability. Additionally, in order to exclude cytotoxic effects, biocompatibility was verified according to ISO standard 10993. Finally, the biological potential of the new glass was tested by using an innovative 3D cellular model, that mimicked the potential clinical application of a given biomaterial. Human bone marrow mesenchymal stem cells (BM-MSCs) were employed to study the performance of bioactive glass granules in such 3D cellular model. The results showed that the bioactive glass supported human BM-MSCs adhesion, colonization and bone differentiation. Thus, this new bioactive glass looks particularly promising for orthopedic applications, bone tissue engineering and regenerative medicine, especially when a thermal treatment is necessary for the production of specific devices.


2020 - Chitosan-Based Bioactive Glass Gauze: Microstructural Properties, In Vitro Bioactivity, and Biological Tests [Articolo su rivista]
Sergi, Rachele; Bellucci, Devis; Salvatori, Roberta; Cannillo, Valeria
abstract

Passive commercial gauzes were turned into interactive wound dressings by impregnating them with a chitosan suspension. To further improve healing, and cell adhesion and proliferation, chitosan/bioactive glass wound dressings were produced with the addition of (i) 45S5, (ii) a Sr- and Mg-containing bioactive glass, and (iii) a Zn-containing bioactive glass to the chitosan suspension. SEM and FTIR analyses evidenced positive results in terms of incorporation of bioactive glass particles. Bioactivity was investigated by soaking chitosan-based bioactive glass wound dressings in simulated body fluid (SBF). Cell viability, proliferation, and morphology were investigated using NIH 3T3 (mouse embryonic fibroblast) cells by neutral red (NR) uptake and MTT assays. Furthermore, the wound-healing rate was evaluated by means of the scratch test, using NIH 3T3. The results showed that bioactive glass particles enhance cell adhesion and proliferation, and wound healing compared to pure chitosan. Therefore, chitosan-based bioactive glass wound dressings combine the properties of the organic matrix with the specific biological characteristics of bioactive glasses to achieve chitosan composites suitable for healing devices.


2020 - Effects of a Novel Bioactive Glass Composition on Biological Properties of Human Dental Pulp Stem Cells [Articolo su rivista]
Di Tinco, Rosanna; Sergi, Rachele; Bertani, Giulia; Pisciotta, Alessandra; Bellucci, Devis; Carnevale, Gianluca; Cannillo, Valeria; Bertoni, Laura
abstract


2020 - Hydroxyapatite/bioactive glass functionally graded materials (FGM) for bone tissue engineering [Articolo su rivista]
Luginina, M.; Angioni, D.; Montinaro, S.; Orru, R.; Cao, G.; Sergi, R.; Bellucci, D.; Cannillo, V.
abstract

In this work, HA/bioactive glass Functionally Graded Materials (FGMs) are obtained for the first time by means of Spark Plasma Sintering (SPS). Two series of highly dense 5 layered products, namely FGMS1 and FGMS2, are prepared under optimized SPS conditions, i.e. 1000 °C/2 min/16 MPa and 800 °C/2 min/50 MPa, respectively, using a die with varying cross section. Results arising from XRD, SEM, mechanical and biological characterization in SBF, evidence that lower temperature and higher-pressure levels used for FGMS2 samples provide better materials in terms of microstructure, compactness, hardness, elastic modulus and in vitro bioactivity. Indeed, a fully sintered and crack-free microstructure with no crystallisation at the top layer (100% bioactive glass) is correspondingly produced. The obtainment of such FGMs is quite promising, since it permits to vary the relative volume fractions of the two constituents and, consequently, tailor the biological response for specific clinical applications.


2020 - Impact of Surface Functionalization by Nanostructured Silver Thin Films on Thermoplastic Central Venous Catheters: Mechanical, Microscopical and Thermal Analyses [Articolo su rivista]
Marchiori, Gregorio; Gambardella, Alessandro; Berni, Matteo; Bellucci, Devis; Cassiolas, Giorgio; Cannillo, Valeria
abstract


2020 - In vitro studies of solution precursor plasma-sprayed copper-doped hydroxyapatite coatings with increasing copper content [Articolo su rivista]
Unabia, Romnick B; Candidato, Rolando T; Pawłowski, Lech; Salvatori, Roberta; Bellucci, Devis; Cannillo, Valeria
abstract

In this present study, in vitro characterization on bioactivity and biocompatibility of the copper-doped hydroxyapatite (Cu-HA) coatings deposited onto Ti6Al4V alloy with increasing copper content obtained using solution precursor plasma spray process were evaluated under simulated body fluid (SBF) and cytotoxicity tests. The growth of flake-like structures was observed at the coatings' surface after 7 days of immersion in SBF. Elemental composition analysis showed a calcium-deficient carbonate-containing apatite for the grown layer. Broadening of the HA peaks were also observed in the X-ray diffraction patterns and infrared absorption spectra of the immersed coatings associated with the possible formation of an amorphous layer at the surface of the coatings. Copper incorporation does not alter the bioactivity of HA but only slowed down for 10 mol% copper content. Cytotoxicity evaluation using MTT assays showed that 3 mol% Cu-HA coating was not toxic under in vitro characterizations.


2020 - On the in Vitro Biocompatibility Testing of Bioactive Glasses [Articolo su rivista]
Bellucci, Devis; Veronesi, Elena; Dominici, Massimo; Cannillo, Valeria
abstract


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 - 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 - 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 - Plasma-assisted deposition of bone apatite-like thin films from natural apatite [Articolo su rivista]
Bianchi, Michele; Gambardella, Alessandro; Graziani, Gabriela; Liscio, Fabiola; Cristina Maltarello, Maria; Boi, Marco; Berni, Matteo; Bellucci, Devis; Marchiori, Gregorio; Valle, Francesco; Russo, Alessandro; Marcacci, Maurilio
abstract

In orthopedics and dentistry, novel approaches for fabricating biomimetic and mechanically robust bioactive coatings are highly desirable in order to truly improve the clinical results of coated implants compared to uncoated ones. In this paper, a biological-like apatite coating is deposited for the first time by plasma-assisted deposition of a natural apatite source. Specifically, we deposited bone apatite-like (BAL) thin films from bone apatite targets by pulsed electron deposition (PED). Morphology, composition, structure and mechanical properties of as-deposited and annealed BAL and stoichiometric hydroxyapatite (HA) films were investigated. While as-deposited BAL and HA films were poorly crystalline at room temperature, they crystallized to an extent very close to that of natural apatite when annealed at 400 °C. In addition, FTIR analysis pointed out that BAL films closely resembled the composition of the starting natural apatite target. Finally, nanoindentation tests indicated that BAL films with high mechanical properties could be deposited by PED.


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&nbsp;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&nbsp;°C for the glass with MgO; at 750&nbsp;°C with SrO; at 759&nbsp;°C with MgO and SrO). The sintered samples achieved good mechanical properties, with a Young's modulus ranging between 57.9&nbsp;±&nbsp;6.7 for the MgO-SrO modified composition and 112.6&nbsp;±&nbsp;8.0&nbsp;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.


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 - 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 - 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.


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


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 - 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.


2006 - Controlling spin phases of few electrons in artificial molecules by magnetic fields [Articolo su rivista]
Rontani, M; Goldoni, Guido; Bellucci, D; Molinari, Elisa
abstract

We investigate the phase diagram of realistic vertically coupled quantum dots under a magnetic field of arbitrary strength and direction. The ground state wave function of four electrons is determined by means of the full configuration interaction method, able to accurately treat electron-electron correlation, which can dominate at experimentally attainable fields. (C) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


2006 - Full configuration interaction approach to the few-electron problem in artificial atoms [Articolo su rivista]
Rontani, M; Cavazzoni, C; Bellucci, D; Goldoni, Guido
abstract

We present a new high performance configuration interaction code optimally designed for the calculation of the lowest-energy eigenstates of a few electrons in semiconductor quantum dots (also called artificial atoms) in the strong interaction regime. The implementation relies on a single-particle representation, but it is independent of the choice of the single-particle basis and, therefore, of the details of the device and configuration of external fields. Assuming no truncation of the Fock space of Slater determinants generated from the chosen single-particle basis, the code may tackle regimes where Coulomb interaction very effectively mixes many determinants. Typical strongly correlated systems lead to very large diagonalization problems; in our implementation, the secular equation is reduced to its minimal rank by exploiting the symmetry of the effective-mass interacting Hamiltonian, including square total spin. The resulting Hamiltonian is diagonalized via parallel implementation of the Lanczos algorithm. The code gives access to both wave functions and energies of first excited states. Excellent code scalability in a parallel environment is demonstrated; accuracy is tested for the case of up to eight electrons confined in a two-dimensional harmonic trap as the density is progressively diluted up to the Wigner regime, where correlations become dominant. Comparison with previous quantum Monte Carlo simulations in the Wigner regime demonstrates power and flexibility of the method.


2006 - Quantum phases of correlated electrons in artificial molecules under magnetic fields [Articolo su rivista]
Bellucci, Devis; Rontani, Massimo; Goldoni, Guido; Molinari, Elisa
abstract

We investigate the stability of few-electron quantum phases in vertically coupled quantum dots under a magnetic field of arbitrary strength and direction. The orbital and spin stability diagrams of realistic devices containing up to five electrons, from strong to weak interdot coupling, is determined. Correlation effects and realistic sample geometries are fully taken into account within the full configuration interaction method. In general, the magnetic field drives the system into a strongly correlated regime by modulating the single-particle gaps. In coupled quantum dots different components of the field, either parallel or perpendicular to the tunneling direction, affect single-dot orbitals and tunneling energy, respectively. Therefore the stability of the quantum phases is related to different correlation mechanisms, depending on the field direction. Comparison of exact diagonalization results with simple models allows one to identify the specific role of correlations.


2005 - Biexcitons in artificial molecules with in-plane magnetic field [Articolo su rivista]
Bellucci, D.; Troiani, Filippo; Goldoni, Guido; Molinari, Elisa
abstract

We theoretically investigate the effect of a magnetic field perpendicular to the tunneling direction on the ground-state properties of biexcitons in coupled quantum dots. The single-particle states are computed by numerically solving the 3D Scrodinger equation. The biexciton states are obtained by means of a configuration-interaction approach, which fully accounts for the intra- and inter-dot Coulomb correlations. We show that the biexciton ground state undergoes nontrivial transitions as a function of the applied magnetic field, which can be traced back to unexpected carrier localizations. (C) 2004 Elsevier B.V. All rights reserved.


2005 - Collective properties of electrons and holes in coupled quantum dots [Relazione in Atti di Convegno]
Goldoni, Guido; Troiani, F.; Rontani, M.; Bellucci, D.; Molinari, Elisa
abstract

We discuss the properties of few electrons and electron-hole pairs confined in coupled semiconductor quantum dots, with emphasis on correlation effects and the role of tunneling. We shall discuss, in particular, exact diagonalization results for biexciton binding energy, electron-hole localization, magnetic-field induced Wigner molecules, and spin ordering.


2005 - Interacting electrons in artificial molecules with magnetic field of arbitrary direction [Articolo su rivista]
Bellucci, D.; Troiani, Filippo; Goldoni, Guido; Molinari, Elisa
abstract

We theoretically investigate the mechanisms for the magnetic field-induced singlet-triplet transition of two electrons in vertically coupled quantum dots, as a function of the field strength and direction. Our numerical approach is based on a real-space description of single-particle states in realistic samples and exact diagonalization of carrier-carrier Coulomb interaction. The three-electron system is also discussed, and we show that the magnetic field drives non-trivial transitions in the ground and excited states. (C) 2004 Elsevier B.V. All rights reserved.


2005 - Magnetic-field-dependent optical properties and interdot correlations in coupled quantum dots [Articolo su rivista]
Bellucci, D; Troiani, F; Goldoni, Guido; Molinari, Elisa
abstract

We theoretically investigate the properties of neutral and charged excitons in vertically coupled quantum dots, as a function of the in-plane magnetic field. The single-particle states are computed by numerically solving the 3D effective-mass equation, while the neutral- and charged-exciton states are obtained by means of a configuration interaction approach. We show that the field determines an enhancement of the interdot correlations, resulting in unexpected carrier localization. The field effect on the excitonic binding energies is also discussed, and is shown to strongly depend on the charging. (c) 2004 Elsevier B.V. All rights reserved.


2004 - Competing mechanisms for singlet-triplet transition in artificial molecules [Articolo su rivista]
Bellucci, D.; Rontani, Massimo; Troiani, Filippo; Goldoni, Guido; Molinari, Elisa
abstract

We study the magnetic field induced singlet/triplet transition for two electrons in vertically-coupled quantum dots by exact diagonalization of the Coulomb interaction. We identify the different mechanisms occurring in the transition, involving either in-plane correlations or localization in opposite dots, depending on the field direction. Therefore, both spin and orbital degrees of freedom can be manipulated by field strength and direction. The phase diagram of realistic devices is determined.


2004 - Neutral and charged electron-hole complexes in artificial molecules: quantum transitions induced by the in-plane magnetic field [Articolo su rivista]
Bellucci, D.; Troiani, Filippo; Goldoni, Guido; Molinari, Elisa
abstract

We theoretically investigate the properties of neutral and charged excitons and of the biexciton in vertically coupled quantum dots, as a function of the in-plane magnetic field B-parallel to. The main effect of the field consists in the suppression of the bonding-antibonding splitting, and in the resulting enhancement of the interdot correlations. As a consequence, the excitons form with the additional carrier a bound or an unbound complex depending on the sign of the charging, whereas the biexciton undergoes a transition between different quantum states with increasing B-parallel to. The discussed behaviors and transitions show up in the field dependence of experimentally accessible quantities, such as the charged-exciton and biexciton binding energies.


2004 - Spin-spin interaction in artificial molecules with in-plane magnetic field [Articolo su rivista]
Bellucci, D; Rontania, M; Goldoni, Guido; Troiani, F; Molinari, Elisa
abstract

We investigate theoretically the spin-spin interaction of two-electrons in vertically coupled QDs as a function of the angle between magnetic field and growth axis. Our numerical approach is based on a real-space description of single-particle states in realistic samples and exact diagonalization of carrier-carrier Coulomb interaction. In particular, the effect of the in-plane field component on tunneling and, therefore, spin-spin interaction will be discussed; the singlet-triplet phase diagram as a function of the field strength and direction is drawn.