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Antonella SOLA
Ricercatore Legge 240/10 - t.det.
Dipartimento di Scienze e Metodi dell'Ingegneria
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Pubblicazioni
2024
- Advancing the additive manufacturing of PLA-ZnO nanocomposites by fused filament fabrication
[Articolo su rivista]
Chong, W. J.; Pejak Simunec, D.; Trinchi, A.; Kyratzis, I.; Li, Y.; Wright, P.; Shen, S.; Sola, A.; Wen, C.
abstract
Poly(lactic acid)-zinc oxide (PLA-ZnO) nanocomposites for fused filament fabrication have potential applications in the biomedical field as they combine the bio-compatibility of PLA with the antibacterial properties of ZnO. This work investigates the effects of masterbatch mixing strategy, ZnO concentration and ZnO surface treatment (silanisation) on the printability and the mechanical performance of the nanocomposites as a pre-requirement to the wider uptake of these materials. The results showed that the printability decreased as the filler loading increased. However, the surface treatment of the ZnO powder enhanced the matrix-filler interfacial interactions and reduced the thermal degradation of PLA. This ameliorated the printability and the tensile properties of the nanocomposites filled with up to 5 wt.% of ZnO. Moreover, despite the additional thermal treatment, melt-mixing prevented the degradative effect induced by the solvent used for solvent mixing. Future work will focus on assessing the antibacterial properties of the nanocomposite FFF parts.
2024
- Defect detection by multi-axis infrared process monitoring of laser beam directed energy deposition
[Articolo su rivista]
Herzog, T.; Brandt, M.; Trinchi, A.; Sola, A.; Hagenlocher, C.; Molotnikov, A.
abstract
Laser beam directed energy deposition (DED-LB) is an attractive additive manufacturing technique to produce versatile and complex 3D structures on demand, apply a cladding, or repair local defects. However, the quality of manufactured parts is difficult to assess by inspection prior to completion, and parts must be extensively inspected post-production to ensure conformance. Consequently, critical defects occurring during the build go undetected. In this work, a new monitoring system combining three infrared cameras along different optical axes capable of monitoring melt pool geometry and vertical displacement throughout deposition is reported. By combining multiple sensor data, an automated algorithm is developed which is capable of identifying the formation of structural features and defects. An intersecting, thin-walled geometry is used to demonstrate the capability of the system to detect process-induced porosity in samples with narrow intersection angles, which is validated using micro-CT observations. The recorded results indicate the root cause of this process-induced porosity at the intersection, and it is shown that advanced toolpath planning can eliminate such defects. The presented methodology demonstrates the value of multi-axis monitoring for identifying both defects and structural features, providing an advancement towards automated detection and alert systems in DED-LB.
2024
- Process monitoring and machine learning for defect detection in laser-based metal additive manufacturing
[Articolo su rivista]
Herzog, T.; Brandt, M.; Trinchi, A.; Sola, A.; Molotnikov, A.
abstract
Over the past several decades, metal Additive Manufacturing (AM) has transitioned from a rapid prototyping method to a viable manufacturing tool. AM technologies can produce parts on-demand, repair damaged components, and provide an increased freedom of design not previously attainable by traditional manufacturing techniques. The increasing maturation of metal AM is attracting high-value industries to directly produce components for use in aerospace, automotive, biomedical, and energy fields. Two leading processes for metal part production are Powder Bed Fusion with laser beam (PBF-LB/M) and Directed Energy Deposition with laser beam (DED-LB/M). Despite the many advances made with these technologies, the highly dynamic nature of the process frequently results in the formation of defects. These technologies are also notoriously difficult to control, and the existing machines do not offer closed loop control. In the present work, the application of various Machine Learning (ML) approaches and in-situ monitoring technologies for the purpose of defect detection are reviewed. The potential of these methods for enabling process control implementation is discussed. We provide a critical review of trends in the usage of data structures and ML algorithms and compare the capabilities of different sensing technologies and their application to monitoring tasks in laser metal AM. The future direction of this field is then discussed, and recommendations for further research are provided.
2023
- Biodegradable PLA-ZnO nanocomposite biomaterials with antibacterial properties, tissue engineering viability, and enhanced biocompatibility
[Articolo su rivista]
Chong, Wei Juene; Shen, Shirley; Li, Yuncang; Trinchi, Adrian; Pejak Simunec, Dejana; Kyratzis, Ilias (Louis); Sola, Antonella; Wen, Cuie
abstract
Polylactic acid (PLA) is a well-known biomaterial on account of its biocompatibility and biodegradability. Zinc oxide (ZnO) nanofillers may endow PLA with advantageous antibacterial and tissue regenerative properties, but may also compromise the biocompatibility of PLA. Several strategies have been developed to improve the biomedical practicality of such composites. The importance of surface properties on amplifying the therapeutic properties and safety of a material enables two potential strategies: (i) surface modification of ZnO nanoparticles, and (ii) surface engineering of the PLA/ZnO composites. Moreover, the controllable biodegradation of PLA allows a third possible strategy: (iii) biodegradation-controlled release of ZnO. The first part of this review introduces the controllable degradation of PLA and the mechanisms of therapeutic properties and cytotoxicity of ZnO. Following this, the paper highlights current research trends regarding the biomedical application of PLA-based ZnO nanocomposites. The final section of this review discusses the potential use of ZnO in tuning the degradation rate of PLA, and the possibility of manipulating the surface properties of ZnO nanoparticles and PLA/ZnO composites in order to optimize the therapeutic properties and safe usage of PLA/ZnO composites in the biomedical field.
2023
- Boron-induced microstructural manipulation of titanium and titanium alloys in additive manufacturing
[Articolo su rivista]
Sola, A.; Trinchi, A.
abstract
While the role of boron (B) has been thoroughly clarified in titanium (Ti) castings, the microstructural changes triggered in additive manufacturing (AM) are still the subject of debate in the literature. Many contributions have confirmed the B-induced microstructural refinement in Ti-based AM parts. The formation of TiB in titanium matrix composites (TMCs) may increase strength. In some cases, B may also promote the columnar-to-equiaxed transition, thus mitigating the anisotropic effects associated with the strong epitaxial growth of unidirectional columnar grains typical of AM. However, as critically discussed in this review, some pitfalls remain. Due to fast cooling, the microstructural evolution in AM may deviate from equilibrium, leading to a shift of the Ti-B eutectic point and to the formation of out-of-equilibrium phases. Additionally, the growth of TiB may undermine the ductility and the crack propagation resistance of AM parts, which calls for appropriate remediation strategies.
2023
- Conducting polymer-based nanostructured materials for brain–machine interfaces
[Articolo su rivista]
Ziai, Y.; Zargarian, S. S.; Rinoldi, C.; Nakielski, P.; Sola, A.; Lanzi, M.; Truong, Y. B.; Pierini, F.
abstract
As scientists discovered that raw neurological signals could translate into bioelectric information, brain–machine interfaces (BMI) for experimental and clinical studies have experienced massive growth. Developing suitable materials for bioelectronic devices to be used for real-time recording and data digitalizing has three important necessitates which should be covered. Biocompatibility, electrical conductivity, and having mechanical properties similar to soft brain tissue to decrease mechanical mismatch should be adopted for all materials. In this review, inorganic nanoparticles and intrinsically conducting polymers are discussed to impart electrical conductivity to systems, where soft materials such as hydrogels can offer reliable mechanical properties and a biocompatible substrate. Interpenetrating hydrogel networks offer more mechanical stability and provide a path for incorporating polymers with desired properties into one strong network. Promising fabrication methods, like electrospinning and additive manufacturing, allow scientists to customize designs for each application and reach the maximum potential for the system. In the near future, it is desired to fabricate biohybrid conducting polymer-based interfaces loaded with cells, giving the opportunity for simultaneous stimulation and regeneration. Developing multi-modal BMIs, Using artificial intelligence and machine learning to design advanced materials are among the future goals for this field. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.
2023
- Electrical capability of 3D printed unpoled polyvinylidene fluoride (PVDF)/thermoplastic polyurethane (TPU) sensors combined with carbon black and barium titanate
[Articolo su rivista]
Simunec, D. P.; Breedon, M.; Muhammad, F. U. R.; Kyratzis, L.; Sola, A.
abstract
The development of three-dimensional (3D) printed sensors attracts high interest from the smart electronic industry owing to the significant geometric freedom allowed by the printing process and the potential for bespoke composite feedstocks being imbued with specific material properties. In particular, feedstock for material extrusion (MEX) additive manufacturing by fused filament fabrication can be provided with piezoelectricity and electrical conductivity. However, piezoelectricity often requires electrical poling for activation. In this study, a candidate material containing thermoplastic polyurethane (TPU) and carbon black (CB) with conductive and flexible properties is incorporated with piezoelectric elements like polyvinylidene fluoride (PVDF) and barium titanate (BaTiO3) to assess its suitability for sensor applications without electrical poling. Texturing the surface of BaTiO3 particles and adding tetraphenylphosphonium chloride (TPPC) to the composite are evaluated as non-poling treatments to improve the sensor response. It was found that TPU and PVDF produced segregated domain structures within the printed sensors that aligned along the printing direction. Due to the effect of this preferential orientation combined with the presence of raster-raster interfaces, printed sensors exhibited significant electrical anisotropy registering greater electrical waveforms when the electrodes aligned parallel to the raster direction. An improvement of current baseline from 0.4 µA to 12 µA in the parallel direction was observed in sensors functionalised with both treatments. Similarly, when the waveform responses were measured under a standardised impact force, current amplitudes in both orientations registered a twofold increase for any impact force when both treatments were applied to the feedstock material. The results achieved within this study elucidate how composite formulations can enhance the sensor response prior to conducting electrical poling.
2023
- Embedding Function within Additively Manufactured Parts: Materials Challenges and Opportunities
[Articolo su rivista]
Trinchi, A.; Sola, A.
abstract
As additive manufacturing (AM), particularly metal and polymer-based 3D printing, progresses from a scientific curiosity to an industry mainstay, there is an increasing desire for parts to take on secondary roles beyond their primary, typically structural or mechanical, function. This may enable unique and broad-ranging functional customization, including monitoring part performance or its local environment, provisions for unique identifiers in tracking, anticounterfeiting, quality control, and even product certification. Many materials and processing compatibility requirements must be addressed to achieve embedded function, as embedded fillers or additives must not compromise either the part's production or its primary function. Herein, the material, technological, and processing challenges are highlighted for embedding function into parts produced by some of the most popular AM techniques, with examples provided from the literature. While it is possible to produce cavities within 3D printed parts and place functional components within them postbuild, approaches, herein, specifically explore direct incorporation of functional agents, fillers, and additives during the build process that imparts ancillary function. It is hoped to inspire exploration of the possibilities and enhancements achievable through functional AM. On account of its versatility, binder jetting is analyzed as a case study, with novel approaches for embedding new functions outlined.
2023
- Facilitating the additive manufacture of high-performance polymers through polymer blending: A review
[Articolo su rivista]
Simunec, D. P.; Jacob, J.; Kandjani, A. E. Z.; Trinchi, A.; Sola, A.
abstract
Fused Filament Fabrication (FFF, a.k.a. fused deposition modeling, FDM) is presently the most widespread material extrusion (MEX) additive manufacturing technique owing to its flexibility and robustness. Nonetheless, it remains underutilized in load-bearing applications, as often seen in aerospace, automotive and biomedical industries. This is largely due to the processing challenges associated with high performance polymers (HPPs) like poly-ether-ether-ketone (PEEK) or polyetherimide (PEI). Compared with commercial-grade plastics such as polylactic acid (PLA), parts produced with HPPs have outstanding mechanical properties and thermal stability. However, HPPs have bulkier chemical structures and stronger intermolecular forces than common FFF feedstock materials, and this results in much higher printing temperatures and greater melt viscosities. The demanding processing requirements of HPPs have thus impaired their adoption within FFF. Polymer blending, which consists in properly mixing HPPs with other thermoplastics, makes it possible to alleviate these printing issues, while also providing additional advantages such as improved tensile strength and reduced friction. Further to this, manipulating the crystallisation processes of HPPs mitigates distortion or warping upon printing. This review explores some emerging trends in the field of HPP blends and how they address the challenges of excessive melt viscosity, polymer crystallization, moisture uptake, and part shrinkage in 3D printing. Also, the various structural/mechanical/chemical enhancements that are afforded to FFF parts through HPP blending are critically analysed based on recent examples from the literature. Such insights will not only aid researchers in this field, but also facilitate the development of novel, 3D printable HPP blends.
2023
- Hierarchical composite coating for enhancing the tensile behaviour of textile-reinforced mortar (TRM)
[Articolo su rivista]
Signorini, Cesare; Sola, Antonella; Nobili, Andrea
abstract
We describe a novel class of interface-functionalised textile-reinforced mortar (TRM) composite materials reinforced with basalt and alkali-resistant glass multifilament textiles embedded in a commercially available hybrid lime-cement mortar, usually applied for masonry retrofitting. Spotlight is set on improving the mechanical (tensile) performance of the system through a scalable and easy-to-apply surface treatment for the dry textiles. The treatment consists in soaking the textiles in highly-diluted epoxy resin, to which rice husk ash (RHA) is later added, acting as pozzolanic filler. The resulting functionalised textiles exhibit remarkable adhesion with the matrix owing to the presence of RHA having high specific surface area and rich amorphous content. Three different RHA powders are assessed and their performance is compared to that of plain silica fume. The role of RHA milling is also discussed. The RHA/epoxy coating significantly improves the ultimate tensile strength and energy dissipation capability of the TRMs. In particular, for basalt-textile reinforced composites, the mean tensile strength is three times as large as that of uncoated specimens, whereas the dissipated energy at failure is nearly four times as much. Furthermore, the surface treatment qualitatively changes the cracking pattern of the TRMs, for many diffused small cracks appear during tensile testing, and this provides evidence of effective stress distribution in the matrix as a result of superior interface adhesion.
2023
- Inaugural editorial
[Articolo su rivista]
Wen, Cuie; Sola, Antonella
abstract
It is our privilege to start the first issue of our new Journal “Smart Materials in Manufacturing” (SMMF). Owing to their ability to transform and react over time due to a controlled response to an external stimulus, smart materials are becoming mainstream in several fields of research for advanced applications in biomedicine, robotics, transportation, and defense. SMMF aims to explore how smart materials can be successfully manufactured into actuating structures capable of real-word functionality. New submissions are welcome that investigate and discuss existing and emerging methods for processing novel smart materials and systems, for characterising such constructs, and for assessing their morphing ability.
2023
- Open challenges in tensile testing of additively manufactured polymers: A literature survey and a case study in fused filament fabrication
[Articolo su rivista]
Sola, A.; Chong, W. J.; Pejak Simunec, D.; Li, Y.; Trinchi, A.; Kyratzis, I. L.; Wen, C.
abstract
Additive manufacturing (AM, also commonly termed 3D printing) is progressing from being a rapid prototyping tool to serving as pillar of the Industry 4.0 revolution. Thanks to their low density and ease of printing, polymers are receiving increasing interest for the fabrication of structural and lightweight parts. Nonetheless, the lack of appropriate standards, specifically conceived to consistently verify the tensile properties of polymer parts and benchmark them against conventional products, is a major obstacle to the wider uptake of polymer AM in industry. After reviewing the standardisation needs in AM with a focus on mechanical testing, the paper closely examines the hurdles that are encountered when existing standards are applied to measure the tensile properties of polymer parts fabricated by fused filament fabrication (FFF, aka fused deposition modeling, FDM), which is presently the most popular material extrusion AM technique. Existing standards are unable to account for the numerous printing parameters that govern the mechanical response of FFF parts. Moreover, the literature suggests that the raster- and layer-induced anisotropic behaviour and the complicated interplay between structural features at different length scales (micro/meso/macro-structure) undermine pre-existing concepts regarding the specimen geometry and classical theories regarding the size effect, and ultimately jeopardise the transferability of conventional tensile test standards to FFF parts. Finally, the statistical analysis of the tensile properties of poly(lactic acid) (PLA) FFF specimens printed according to different standards (ASTM D638 type I and ASTM D3039) and in different sizes provides experimental evidence to confirm the literature-based argumentation. Ultimately, the literature survey, supported by the experimental results, demonstrates that, until dedicated standards become available, existing standards for tensile testing should be applied to FFF with prudence. Whilst not specified in conventional standards, set-up and printing parameters should be fully reported to ensure the repeatability of the results, rectangular geometries should be preferred to dumbbell-like ones in order to avoid premature failure at the fillets, and the size of the specimens should not be changed arbitrarily.
2023
- Recycling as a Key Enabler for Sustainable Additive Manufacturing of Polymer Composites: A Critical Perspective on Fused Filament Fabrication
[Articolo su rivista]
Sola, A.; Trinchi, A.
abstract
Additive manufacturing (AM, aka 3D printing) is generally acknowledged as a “green” technology. However, its wider uptake in industry largely relies on the development of composite feedstock for imparting superior mechanical properties and bespoke functionality. Composite materials are especially needed in polymer AM, given the otherwise poor performance of most polymer parts in load-bearing applications. As a drawback, the shift from mono-material to composite feedstock may worsen the environmental footprint of polymer AM. This perspective aims to discuss this chasm between the advantage of embedding advanced functionality, and the disadvantage of causing harm to the environment. Fused filament fabrication (FFF, aka fused deposition modelling, FDM) is analysed here as a case study on account of its unparalleled popularity. FFF, which belongs to the material extrusion (MEX) family, is presently the most widespread polymer AM technique for industrial, educational, and recreational applications. On the one hand, the FFF of composite materials has already transitioned “from lab to fab” and finally to community, with far-reaching implications for its sustainability. On the other hand, feedstock materials for FFF are thermoplastic-based, and hence highly amenable to recycling. The literature shows that recycled thermoplastic materials such as poly(lactic acid) (PLA), acrylonitrile-butadiene-styrene (ABS), and polyethylene terephthalate (PET, or its glycol-modified form PETG) can be used for printing by FFF, and FFF printed objects can be recycled when they are at the end of life. Reinforcements/fillers can also be obtained from recycled materials, which may help valorise waste materials and by-products from a wide range of industries (for example, paper, food, furniture) and from agriculture. Increasing attention is being paid to the recovery of carbon fibres (for example, from aviation), and to the reuse of glass fibre-reinforced polymers (for example, from end-of-life wind turbines). Although technical challenges and economical constraints remain, the adoption of recycling strategies appears to be essential for limiting the environmental impact of composite feedstock in FFF by reducing the depletion of natural resources, cutting down the volume of waste materials, and mitigating the dependency on petrochemicals.
2023
- Self-assembly meets additive manufacturing: Bridging the gap between nanoscale arrangement of matter and macroscale fabrication
[Articolo su rivista]
Sola, Antonella; Trinchi, Adrian; Hill, Anita J.
abstract
New methods are emerging to combine the self-assembly of matter and additive manufacturing, so that new devices and constructs can simultaneously harness the unique molecular and nanostructural features afforded by self-assembly and the macroscale design freedom of additive manufacturing. The aim of this review is to analyse the body of literature and explore the crossover area where boundaries dissolve and self-assembly meets additive manufacturing (SAMAM). As a preliminary framework for this new area of research, the different experimental approaches to SAMAM can be grouped in three main categories, whereby SAMAM can be based on local interactions between molecules or nanoparticles, on 3D-printing induced forces, or on externally applied force fields. SAMAM offers numerous opportunities, such as the design of new printable materials, the ability to surpass conventional trade-offs in materials properties, the control of structural features across different length scales, process intensification and improved eco-sustainability. However, most research so far has been focused on polymer-based materials, and additional effort is needed to understand how SAMAM can be leveraged in metal- and ceramic-based additive manufacturing. On account of the weak inter-layer bonding often reported along the growth direction, it would also be interesting to explore whether SAMAM could effectively remediate undesidered anisotropic effects in additively manufactured parts.
2022
- Additive manufacturing of antibacterial PLA-ZnO nanocomposites: Benefits, limitations and open challenges
[Articolo su rivista]
Chong, W. J.; Shen, S.; Li, Y.; Trinchi, A.; Pejak, D. (Louis) Kyratzis I.; Sola, A.; Wen, C.
abstract
Polymeric biomaterials such as polylactic acid (PLA) play a prominent role in the advancement of biomedical additive manufacturing (AM). PLA offers indeed a very advantageous combination of thermo-mechanical properties and functional attributes, as it is biobased, biodegradable, biocompatible and easy to print. However, PLA can be damaged by common sterilization methods and is sensitive to most chemical disinfectants, and this may impair its widespread usage. One of the most promising ways to overcome this shortcoming is to provide PLA with embedded antibacterial activity by the addition of appropriate fillers such as zinc oxide (ZnO) nanoparticles. After a detailed introduction to the basic properties of PLA and ZnO nanoparticles, the present review analyzes the main variables that govern the antibacterial activity of PLA-ZnO nanocomposites. Current applications and related manufacturing processes are also presented to showcase the importance of having embedded antibacterial functions in demanding applications such as food packaging and wound dressing. Emphasis is then placed on the emerging literature of the AM of PLA-ZnO nanocomposites, with a focus on fused filament fabrication (also known as fused deposition modeling). Existing gaps and hurdles related to the development and 3D printing of such composites is critically discussed. It is envisioned that a deeper understanding of the processability, thermo-mechanical behavior, biocompatibility and antibacterial efficacy of additively manufactured PLA-ZnO nanocomposites will foster their adoption in the biomedical field and, ultimately, in all circumstances where it is crucial to limit infection transmission.
2022
- Emerging Research in Conductive Materials for Fused Filament Fabrication: A Critical Review
[Articolo su rivista]
Pejak Simunec, D.; Sola, A.
abstract
The progress of Industry 4.0 and the advancement of robotic design are revealing a significant gap in the capabilities of current manufacturing techniques and the selection of materials that are available in electronics. Present-day electrical systems largely rely on metals, but there is a driving need to develop new electrically conductive objects with a wide range of material properties, including expanded flexibility and softness, and with increasingly complex geometries. Electrically conductive composites can replace traditional metal-based systems. In particular, thermoplastic composites become electrically conductive with the incorporation of conductive fillers or polymers while retaining to a large extent the processability of the thermoplastic matrix. This is where fused filament fabrication (FFF), an additive manufacturing (AM) technique capable of processing a variety of thermoplastic-matrix feedstock materials, can be leveraged to create electrically conductive objects with new functionalities. While there is an increasing number of publications describing the FFF of electrical objects such as sensors and circuits, there is no comprehensive review outlining the functioning mechanisms, drawbacks, and advantages of FFF as applied to conductive materials. The present review fills this lacuna by offering a critical analysis of the specific challenges and solutions to promote FFF of electrically conductive polymers and composites.
2022
- Highly Dissipative Fiber-Reinforced Concrete for Structural Screeds
[Articolo su rivista]
Signorini, Cesare; Sola, Antonella; Malchiodi, Beatrice; Nobili, Andrea
abstract
Synthetic fibers, especially polypropylene (PP) fibers, are emerging as a viable reinforcement for concrete, on account of their excellent durability, affordability, anti-spalling capability, low density, and magnetic transparency. Yet, the chemical nature of PP hinders the development of strong bonds at the fiber-to-matrix interface, with negative effects on the mechanical performance. To overcome this difficulty, in this research fibers are either chemically attacked (etched) or coated through sol-gel nanosilica deposition in order to promote their affinity to the hydration products in the binder. Three-point bending tests at different scales are carried out on unnotched specimens, including large-scale beams consisting of PP-reinforced concrete for structural screeds. Functionalization, especially in the form of silica coating, improves the binder-fiber interaction, which is responsible for a remarkable increment in the specific energy dissipated at failure, with respect to untreated fibers. Most importantly, both surface treatments induce a substantial hardening response as opposed to the softening behavior that is characteristic of low-dosage fiber-reinforced concrete. We conclude that surface functionalization, and especially nanosilica coating, offers significant advantages for better exploiting the reinforcing effect of PP fibers, and these carry over at different scales. In particular, results appear promising for screeds, which advocate optimal mechanical performance and durability while keeping the fiber content to a minimum.
2022
- How Can We Provide Additively Manufactured Parts with a Fingerprint? A Review of Tagging Strategies in Additive Manufacturing
[Articolo su rivista]
Sola, A.; Sai, Y.; Trinchi, A.; Chu, C.; Shen, S.; Chen, S.
abstract
Additive manufacturing (AM) is rapidly evolving from “rapid prototyping” to “industrial production”. AM enables the fabrication of bespoke components with complicated geometries in the high-performance areas of aerospace, defence and biomedicine. Providing AM parts with a tagging feature that allows them to be identified like a fingerprint can be crucial for logistics, certification and anti-counterfeiting purposes. Whereas the implementation of an overarching strategy for the complete traceability of AM components downstream from designer to end user is, by nature, a cross-disciplinary task that involves legal, digital and technological issues, materials engineers are on the front line of research to understand what kind of tag is preferred for each kind of object and how existing materials and 3D printing hardware should be synergistically modified to create such tag. This review provides a critical analysis of the main requirements and properties of tagging features for authentication and identification of AM parts, of the strategies that have been put in place so far, and of the future challenges that are emerging to make these systems efficient and suitable for digitalisation. It is envisaged that this literature survey will help scientists and developers answer the challenging question: “How can we embed a tagging feature in an AM part?”.
2022
- Materials Requirements in Fused Filament Fabrication: A Framework for the Design of Next-Generation 3D Printable Thermoplastics and Composites
[Articolo su rivista]
Sola, A.
abstract
Fused filament fabrication (FFF), also known as fused deposition modeling, is the leading technology for polymer-based additive manufacturing. The simplicity, along with the cleanness, the affordability, and the multi-material capability, are some of the main advantages that have prompted this success. Nonetheless, the uptake of FFF in industry is hampered by the limited functionality of commercial filaments, that are often based on plain thermoplastics. The future growth of FFF into new markets needs a significant improvement of available materials. However, materials requirements in FFF are complicated and often mutually conflicting. Whereas heuristic approaches to materials design imply significant costs in terms of time, energy, and materials, a critical survey of the main requirements that a new material should fulfill in order to be printable and suitable for commercial adoption is still missing. In order to bridge this gap, the present paper analyzes the workflow from filament production to end-of-life disposal of printed objects, and, for each step, brings to light the governing materials properties. Wherever possible, practical guidelines are given on acceptable values. Existing lacks of knowledge are identified to direct future studies. The ultimate goal is to provide a road map to making materials development in FFF more efficient.
2022
- New Frontiers in Cementitious and Lime-Based Materials and Composites
[Articolo su rivista]
Signorini, C.; Sola, A.; Chakraborty, S.; Volpini, V.
abstract
Cement and lime currently are the most common binders in building materials. However, alternative materials and methods are needed to overcome the functional limitations and environmental footprint of conventional products. This Special Issue is entirely dedicated to “New frontiers in cementitious and lime-based materials and composites” and gathers selected reviews and experimental articles that showcase the most recent trends in this multidisciplinary field. Authoritative contributions from all around the world provide important insights into all areas of research related to cementitious and lime-based materials and composites, spanning from structural engineering to geotechnics, including materials science and processing technology. This topical cross-disciplinary collection is intended to foster innovation and help researchers and developers to identify new solutions for a more sustainable and functional built environment.
2022
- Preliminary Assessment of Rice Husk Ash (RHA) as Functional Interphase Agent in Sustainable Composite Systems for Structural Strengthening
[Relazione in Atti di Convegno]
Sola, Antonella; Signorini, Cesare; Hanuskova, Miriam; Zapparoli, Mauro
abstract
Over the last few years, the effectiveness of textile-reinforced mortar (TRM) composite systems for structural retrofitting has led to the widespread adoption of these materials in the practice and to the issue of up-to-date design guidelines. Nonetheless, the weak interfacial bonding that is frequently observed between matrix and fibres is likely to cause inconsistent failure modes and, generally speaking, to severely limit the reinforcing potential of the textile. A promising solution to tackle this issue consists in treating the surface of the reinforcing fibres with a functional coating to improve the adhesion at the interphase. In this paper, a pilot study is presented to assess the effectiveness of a fully sustainable polymer coating, consisting in polyvinyl alcohol (PVA) loaded with with rice husk ash (RHA) or with a 50/50 mixture of RHA and silica fume (SF). The coating was applied on basalt fabrics to reinforce TRM coupons that were mechanically tested under uni-axial tensile loads. The mechanical properties of the TRM samples were significantly increased by up to 20%, and the peak load was attained at a higher deformability level, which is a clue of the enhanced ductility of the reinforced elements.
2022
- UIT - A Universal Identifier of Things to Bridge Cyber and Physical Worlds
[Relazione in Atti di Convegno]
Sai, Y.; Chu, C.; Trinchi, A.; Sola, A.; Shen, S.; Chen, S.
abstract
Ensuring the integrity of product manufacture information and securely verifying the authenticity of a component is critical for both manufacturers and customers. However, traditional product identifying solutions offer little protection over counterfeit and cyber-attack. We propose a Blockchain-based product identification and certification system called Universal Identifier of Things (UIT) that enables fast product authenticity verification using low-cost devices. We leverage additive manufacturing technologies to embed a unique identifier into a product. The identifier is then digitalized by generating a digital certificate which is stored on Blockchain during the whole product life cycle for various applications/services (provenance, traceability, product warranty and call-back, etc.). We prove this concept by integrating 3D printing and Hyperledger Blockchain technologies to demonstrate that we can ensure the integrity of products with UIT by bridging the cyber and physical worlds.
2021
- Synergy between topology optimization and additive manufacturing in the automotive field
[Articolo su rivista]
Mantovani, Sara; Barbieri, SAVERIO GIULIO; Giacopini, Matteo; Croce, Alessandro; Sola, Antonella; Bassoli, Elena
abstract
This article purposes on developing and on re-interpreting the numerical results of a topology optimization for a structural component built via additive manufacturing. A critical appraisal of the optimization results is presented by modeling the feasible component with a holistic approach that merges structural and manufacturing requirements. The procedure is expected to provide a design guideline for similar applications of practical relevance, toward an increase of the right-first-time parts that is required to bring additive manufacturing to its full competitiveness. Topology optimization of a steering upright for a Formula SAE racing car was performed by targeting weight minimization while complying with severe structural constraints, like global and local stiffness performance. Cornering, bumping and braking vehicle conditions were considered. The optimization constraints were evaluated via finite element analysis on a reference component, where the loading conditions were retrieved from telemetry data. The reference part was manufactured by computer numerical control machining from a solid aluminum block. Spurred by the interpretation of the topology optimization predictions, a new upright geometry was designed and validated by calculating its stress field and the possible occurrence of Euler buckling. The new upright was 9% lighter than the reference component. The new geometry was analyzed according to Design for Additive Manufacturing principles to choose the orientation on the build platform and the supports’ location and geometry. The part was successfully manufactured and proved consistent with the application.
2020
- Designing epoxy viscosity for optimal mechanical performance of coated Glass Textile Reinforced Mortar (GTRM) composites
[Articolo su rivista]
Signorini, C.; Nobili, A.; Sola, A.; Messori, M.
abstract
Preliminary epoxy coating of the reinforcing fabric provides an effective approach for improving matrix-to-fabric strength in inorganic matrix composites. We investigate the effect of epoxy resin dilution in acetone on uni-axial tensile performance of coated alkali-resistant (AR) glass fabric embedded in a lime-based matrix. Remarkably, it is found that dilution has a mixed effect on performance and this trend is consistently retrieved for strength, ductility and energy dissipation. Indeed, performance initially decays and then it suddenly raises to a level close to or even exceeding that of the undiluted specimens. It is postulated that this behaviour is caused by resin viscosity, that falls off exponentially with the dilution degree. Once a viscosity threshold is breached, epoxy is capable of penetrating inside the yarn and thereby prevents telescopic failure, that is the sliding of the outer over the inner glass filaments. Furthermore, the interphase surface area increases dramatically and this enhances performance and narrows scattering. Besides, optimal viscosity is reached at an unexpectedly high dilution degree, whence material cost is significantly reduced. A cost-to-performance comparison of common strengthening technologies is presented, which shows that diluted epoxy composites score comparably to FRPs. It is concluded that epoxy coating optimization plays an important role in designing inorganic matrix composites.
2020
- Distribution depth of stone consolidants applied on-site: Analytical modelling with field and lab cross-validation
[Articolo su rivista]
Ban, M.; Aliotta, L.; Gigante, V.; Mascha, E.; Sola, A.; Lazzeri, A.
abstract
An analytical model was applied in order to understand the distribution depth of cured stone consolidants. The model is grounded on a case study of Vienna's St. Stephen's Cathedral and was verified against drilled cores examined by SEM and image analysis, on-site drilling resistance measurements and laboratory-based mechanical tests. The results reveal that the variation of the concentration gradient with penetration depth resembles an exponential decline. The deposition of the cured consolidant is governed by capillary forces upon drying within water-based nano-zirconia dispersions and water/alcohol-based colloidal silica. This effect is less pronounced within reactive consolidants, which undergo polycondensation reactions, as with alkoxysilanes.
2020
- Effect of shot peening conditions on the fatigue life of additively manufactured A357.0 parts
[Articolo su rivista]
Gatto, A.; Sola, A.; Tognoli, E.
abstract
Fatigue performance can be a critical attribute for the production of structural parts or components via additive manufacturing (AM). In comparison to the static tensile behavior of AM components, there is a lack of knowledge regarding the fatigue performance. The growing market demand for AM implies the need for more accurate fatigue investigations to account for dynamically loaded applications. A357.0 parts are processed by laser-based powder bed fusion (L-PBF) in order to evaluate the effect of surface finishing on fatigue behavior. The specimens are surface finished by shot peening using φ = 0.2 and φ = 0.4 mm steel particles and φ = 0.21-0.3 mm zirconia-based ceramic particles. The investigation proves that all the considered post-processing surface treatments increase the fatigue resistance of as-built parts, but the effect of peening with φ = 0.4 mm steel particles or with ceramic particles is more pronounced than that of peening with φ = 0.2 mm steel particles, although this treatment has the same Almen A value as the ceramic one. The surface morphology and the crack surface of the samples are also investigated.
2020
- Electron beam melting in biomedical manufacturing
[Capitolo/Saggio]
Nouri, A.; Sola, A.
abstract
Electron beam melting (EBM) is an additive manufacturing technique that uses an electron beam to selectively fuse and consolidate the metal powder. The final object is built up layer-by-layer according to a computer-aided design or, in case of customized biomedical implants, according to a computed tomography of the patient. This chapter introduces the basic concepts of EBM and the advantages and limitations of applying this technique in biomedical manufacturing. Subsequently, the chapter is describing the processing steps of EBM, the consolidation mechanisms, and the potential microstructural defects of the finished parts. A thorough discussion is provided about the EBM capability of producing cellular structures, dental implants, and orthopedic prostheses, with an emphasis on customized parts. The chapter closes with a survey of the challenges and the future developments of EBM to fabricate biomedical devices.
2020
- Failure mechanism of silica coated polypropylene fibres for Fibre Reinforced Concrete (FRC)
[Articolo su rivista]
Signorini, C.; Sola, A.; Malchiodi, Beatrice; Nobili, A.; Gatto, A.
abstract
This work investigates the effect of a fast, acid-catalysed sol-gel silica nano-coating on the mechanical performance of draw-wire Polypropylene (PP) fibres used as dispersed reinforcement in Fibre Reinforced Concrete (FRC). The failure mechanism is investigated. To this aim, the role of curing time is also considered. Mechanical performance is assessed in pull-out and three-point bending tests of un-notched beams. Coating deeply affects the post-cracking behaviour of FRC, which shifts from brittle (plain concrete), to softening (uncoated) and finally to plastic-softening (coated fibres). Remarkably, 28-day curing improves over 8-day curing in terms of energy dissipation capability for coated fibres only. This suggests that fibre-to-matrix bond enhancement moves the failure mechanism from delamination at the interface to failure in the interphase zone. In the former case, failure is inconsistent and occurs independently from the curing time while in the latter failure depends on the matrix quality.
2020
- Is there a future for additive manufactured titanium bioglass composites in biomedical application? A perspective
[Articolo su rivista]
Mani, N.; Sola, A.; Trinchi, A.; Fox, K.
abstract
Additive manufacturing (AM) of orthopedic implants is growing in popularity as it offers almost complete design flexibility and freedom, meaning complex geometries mimicking specific body parts can be easily produced. Novel composite materials with optimized functionalities present opportunities for 3D printing osteoconductive implants with desirable mechanical properties. Standard metals for bone implants, such as titanium and its alloys, are durable and nontoxic but lack bioactivity. Bioactive glasses promote strong bone formation but are susceptible to brittle failure. Metal-bioactive glass composites, however, may combine the mechanical reliability of metals with the bone-bonding ability of bioactive glasses, potentially reducing the incidence of implant failure. Processing such composites by AM paves the way for producing unprecedented bespoke parts with highly porous lattices, whose stiffness can be tailored to meet the mechanical properties of natural bone tissue. This Perspective focuses on titanium-bioactive glass composites, critically discussing their processability by AM and highlighting their potential as a next-generation implantable biomaterial.
2020
- Optimal epoxy dilution for epoxy-coated textile reinforced mortar (Trm): An experimental perspective
[Relazione in Atti di Convegno]
Signorini, C.; Nobili, A.; Sola, A.; Messori, M.
abstract
The effect of epoxy dilution with acetone on the mechanical performance of epoxy-coated alkali-resistant glass (ARG) fabric embedded in a lime-based mortar is studied experimentally. The mechanical behaviour of the composite system is assessed in uni-axial tensile tests, according to the ICC guidelines. Epoxy is diluted in acetone and several concentrations, namely 10%, 25%, 50%, 75% and 90%, are considered in an attempt to define a decay law for strength, ductility and dissipated energy at failure. Although epoxy-coating promotes a striking improvement of the mechanical performance with respect to the uncoated specimens, epoxy dilution appears to little affect the global response, even at very low epoxy-to-solvent ratios. Actually, a notable increase in the ultimate strength and strain as well as dissipation capacity are evidenced for 75% dilution. Indeed, epoxy resin is able to uniformly impregnate the bundles of the yarns in a very thin layer, still preserving its contribution to the mechanical performance. In fact, wettability of the yarns plays a fundamental role in the mechanical performance of the laminate for it limitates telescopic failure. A threshold of viscosity is identified. Above this limit, the high quality of impregnation overcomes the issue of the reduction of the amount of epoxy resin in the coating. Besides, dilution strongly promotes the ease of application, as a result of the resin viscosity being sharply reduced. Most remarkably and contrarily to common expectation, the specific energy dissipated at failure exhibits a maximum point, whence an optimal dilution ratio exists which best balances interphase strength and ductility.
2020
- Technological Feasibility of Lattice Materials by Laser-Based Powder Bed Fusion of A357.0
[Articolo su rivista]
Sola, A.; Defanti, S.; Mantovani, S.; Merulla, A.; Denti, L.
abstract
Lattice materials represent one of the utmost applications of additive manufacturing. The promising synergy between additive processes and topology optimization finds full development in achieving components that comprise bulky and hollow areas, as well as intermediate zones. Yet, the potential to design innovative shapes can be hindered by technological limits. The article tackles the manufacturability by laser-based powder bed fusion (L-PBF) of aluminum-based lattice materials by varying the beam diameter and thus the relative density. The printing accuracy is evaluated against the distinctive building phenomena in L-PBF of metals. The main finding consists in identification of a feasibility window that can be used for development of lightweight industrial components. A relative density of 20% compared with fully solid material (aluminum alloy A357.0) is found as the lowest boundary for a 3-mm cell dimension for a body-centered cubic structure with struts along the cube edges (BCCXYZ) and built with the vertical edges parallel to the growth direction to account for the worst-case scenario. Lighter structures of this kind, even if theoretically compliant with technical specifications of the machine, result in unstable frameworks.
2019
- Development of solvent-casting particulate leaching (SCPL) polymer scaffolds as improved three-dimensional supports to mimic the bone marrow niche
[Articolo su rivista]
Sola, Antonella; Bertacchini, Jessika; D'Avella, Daniele; Anselmi, Laura; Maraldi, Tullia; Marmiroli, Sandra; Messori, Massimo
abstract
The need for new approaches to investigate ex vivo the causes and effects of tumor and to achieve improved cancer treatments and medical therapies is particularly urgent for malignant pathologies such as lymphomas and leukemias, whose tissue initiator cells interact with the stroma creating a three-dimensional (3D) protective environment that conventional mono- and bi-dimensional (2D) models are not able to simulate realistically. The solvent-casting particulate leaching (SCPL) technique, that is already a standard method to produce polymer-based scaffolds for bone tissue repair, is proposed here to fabricate innovative 3D porous structures to mimic the bone marrow niche in vitro. Two different polymers, namely a rigid polymethyl methacrylate (PMMA) and a flexible polyurethane (PU), were evaluated to the purpose, whereas NaCl, in the form of common salt table, resulted to be an efficient porogen. The adoption of an appropriate polymer-to-salt ratio, experimentally defined as 1:4 for both PMMA and PU, gave place to a rich and interconnected porosity, ranging between 82.1 vol% and 91.3 vol%, and the choice of admixing fine-grained or coarse-grained salt powders allowed to control the final pore size. The mechanical properties under compression load were affected both by the polymer matrix and by the scaffold's architecture, with values of the elastic modulus indicatively varying between 29 kPa and 1283 kPa. Preliminary tests performed with human stromal HS-5 cells co-cultured with leukemic cells allowed us to conclude that stromal cells grown associated to the supports keep their well-known protective and pro-survival effect on cancer cells, indicating that these devices can be very useful to mimic the bone marrow microenvironment and therefore to assess the efficacy of novel therapies in pre-clinical studies.
2019
- Effect of Three Different Finishing Processes on the Surface Morphology and Fatigue Life of A357.0 Parts Produced by Laser‐Based Powder Bed Fusion
[Articolo su rivista]
Gatto, Andrea; Bassoli, Elena; Denti, Lucia; Sola, Antonella; Tognoli, Emanuele; Comin, Andrea; Porro, Juan Antonio; Cordovilla, Francisco; Angulo, Ignacio; Ocaña, Jose Luis
abstract
A357.0 parts are processed by laser-based powder bed fusion and surface
finished via plastic media blasting, ceramic sand blasting, and laser shock
processing. The morphological analysis proves that plastic media blasting
causes the most effective peak removal, the most efficient decrease in valley
depth, and the greatest reduction in surface roughness. All the surface
finishing processes enhance the fatigue life, however ceramic sand blasting
bring about the greatest increase in the value of σmax for an infinite fatigue
life limit of 2106 cycles. The experimental results suggest therefore that
the infinite fatigue life value is more sensitive to the residual stress state
engendered by ceramic sand blasting than to the reduction in surface
roughness. Breakthrough cracks start at the interface between crushed or
modified surface particles and the underlying macro-surface. However, at a
distance of a few hundred microns from the crack initiation point, the
fracture surface morphology become cellular for all the specimens.
2019
- Effect of expandable and expanded graphites on the thermo-mechanical properties of polyamide 11
[Articolo su rivista]
Oulmou, F.; Benhamida, A.; Dorigato, A.; Sola, A.; Messori, M.; Pegoretti, A.
abstract
The preparation and thermo-mechanical characterization of composites based on polyamide 11 (PA11) filled with various amounts of both expandable and expanded graphites are presented. Investigation conducted using X-ray diffraction (XRD), scanning electron microscopy and surface area analyses indicated how graphite expanded under the selected processing conditions. The XRD analysis on PA11/graphite composites revealed no change in the crystal form of the PA11, while the presence of diffraction peaks associated to the graphite-stacked lamellae can be still detected. All the investigated composites showed an improvement of the thermal stability and mechanical properties (elastic and storage moduli).
2019
- Effect of high temperature exposure on epoxy-coated glass textile reinforced mortar (GTRM) composites
[Articolo su rivista]
Messori, M.; Nobili, A.; Signorini, C.; Sola, A.
abstract
An experimental investigation on the mechanical performance of epoxy-coated Alkali-Resistant (AR) glass textile reinforced mortar subjected to elevated temperature is presented. Two epoxy coatings are considered, which differ by the hardening agent alone. After 56 days dry curing, specimens are heated up to four different temperatures. After cooling down to ambient temperature, specimens are assessed in uni-axial tensile test according to Annex A of AC434. First cracking strength and elongation, ultimate tensile strength and elongation, cracked and uncracked moduli, transition point location and energy dissipation capability are evaluated. It is found that, in the explored temperature range, degradation is surprisingly mild and strongly dependent on the resin which is taken as coating agent. Indeed, temperature exposure may lead to strength enhancement. This positive outcome takes place at the expense of ductility and it is traced back, through Differential Scanning Calorimetry (DSC), to a post-curing process. Nonetheless, energy dissipation still decreases with temperature and, remarkably, with the same power-law behaviour for both resins. Such behaviour is compatible with a cumulative Weibull distribution, that is adopted in thermal damage models for resins, and it indicates that the underlying damage mechanism indeed operates on the resin at the fabric-to-matrix interface. (C) 2019 Elsevier Ltd. All rights reserved.
2019
- Effect of powder recycling in laser-based powder bed fusion of Ti-6Al-4V
[Articolo su rivista]
Denti, L.; Sola, A.; Defanti, S.; Sciancalepore, C.; Bondioli, F.
abstract
Additive manufacturing (AM) has shown promise to process parts for end-use applications, however stringent requirements must be fulfilled in terms of reliability and predictability. The expensiveness of raw materials for AM, especially for metal-based Powder Bed Fusion (PBF), brings about the need for a careful recycling of powder, but the effect of powder reuse on both processing conditions and final part performance is still the focus of intensive research in the open literature. Although ASTM F2924-14 specifies the virgin-to-used powder ratio to be introduced to manufacture titanium-6aluminum-4vanadium (Ti-6Al-4V) components by PBF, a deeper understanding of the effect of powder recycling on the mechanical properties of finished parts is expected to foster a more efficient and safe reuse. The present contribution is therefore addressed to investigate the consequence of Ti- 6Al-4V powder recycling on the flowability, particle size distribution and morphology of the feedstock material as well as on the density and tensile performance of built parts. In order to quantify the recyclability of powders, a new "average usage time" (AUT) parameter is defined to account for both the real usage time of the powder and the virgin-to-used powder mixing ratio. The new parameter, whose applicability can be readily extended to any kind of feedstock powder, offers a significant contribution to achieve a more consistent and economical recycling of raw materials for PBF processing.
2019
- Experimental approach to measure the restraining force in deep drawing by means of a versatile draw bead simulator
[Articolo su rivista]
Bassoli, E.; Sola, A.; Denti, L.; Gatto, A.
abstract
The extreme personalization of the sports car industry requires the development of reliable and affordable techniques for the in-house set-up and control of processing conditions in deep drawing of body-in-white parts. In order to cope with this urgent need, a handy draw bead simulator (DBS) is proposed to measure the restraining force exerted on a sheet metal by the draw bead during deep drawing. The apparatus can be integrated into a common tensile testing machine and the male-female parts of the DBS are variable to account for different geometries of the draw bead and for different thicknesses of the sheet metal. For validation, the DBS is operated to reproduce the effect of a draw bead working on an Al6014-T4 strip according to assigned industrial conditions. Tensile tests repeated on the metal strip after drawing open the way to quantify work hardening effects. The new DBS can be applied to measure the restraining force and investigate the specific role of the draw bead in deep drawing, but it may also be used to verify the predictivity of computational models, thus supporting the development of simulations for feasibility studies and tool design optimization.
2019
- Lime-cement textile reinforced mortar (TRM) with modified interphase
[Articolo su rivista]
Signorini, Cesare; Sola, Antonella; Nobili, Andrea; Siligardi, Cristina
abstract
Background: Lack of interphase compatibility between the fabric and the matrix significantly impairs the load-bearing capacity of textile reinforced mortar (TRM). In this study, we consider the application of two inorganic surface coatings for enhancing the interphase bond properties. Methods: Either of two silica-based coatings, namely nano- and micro-silica, were applied to alkali-resistant glass (ARG) and to hybrid carbon–ARG woven fabric. Mechanical performance of TRM reinforced with the uncoated and the coated fabric was compared in uniaxial tensile tests. Results: Mechanical testing provides evidence of a remarkable enhancement in terms of ultimate strength and deformability for the coated specimens. This effect can be ascribed to the improved hydrophilicity of the fibers’ surface and to the activation of pozzolanic reaction at the interphase. In addition, penetration of nano- and microparticles in the bundle of the textile yarns reduces the occurrence of telescopic failure.
2019
- Microstructural porosity in additive manufacturing: The formation and detection of pores in metal parts fabricated by powder bed fusion
[Articolo su rivista]
Sola, Antonella; Nouri, Alireza
abstract
2019
- On the effectiveness of different surface finishing techniques on A357.0 parts produced by laser-based powder bed fusion: Surface roughness and fatigue strength
[Articolo su rivista]
Denti, L.; Sola, A.
abstract
Laser-based powder bed fusion (L-PBF) is an additive manufacturing (AM) technique that uses a computer-controlled laser beam as the energy source to consolidate a metal powder according to a layer-upon-layer strategy in order to manufacture a three dimensional part. This opens the way for an unprecedented freedom in geometry, but the layer-wise build-up strategy typically results in a very poor surface finish, which is affected by the staircase effect and by the presence of partially molten particles. Surface finishing treatments are therefore necessary to obtain an adequate surface finish, to improve the fatigue behavior and to meet mechanical and aesthetic needs. The present contribution systematically compares numerous surface finishing techniques, including laser shock processing, plastic media blasting, sand blasting, ceramic shot peening and metal shot peening with steel particles of different sizes (ϕ = 0.2 mm and ϕ = 0.4 mm). The results show that all the proposed methods improve the surface quality and the fatigue life of A357.0 L-PBF parts. However, the achievement of the lowest surface roughness does not necessarily correspond to the best fatigue performance, thus suggesting that multiple mechanisms may be active and that besides surface roughness also residual stresses contribute to increase the fatigue strength.
2019
- Powder morphology in thermal spraying
[Articolo su rivista]
Nouri, Alireza; Sola, Antonella
abstract
2019
- Solid-state phase transformations in thermally treated Ti-6Al-4V alloy fabricated via laser powder bed fusion
[Articolo su rivista]
Mengucci, P.; Santecchia, E.; Gatto, A.; Bassoli, E.; Sola, A.; Sciancalepore, C.; Rutkowski, B.; Barucca, G.
abstract
Laser Powder Bed Fusion (LPBF) technology was used to produce samples based on the Ti-6Al-4V alloy for biomedical applications. Solid-state phase transformations induced by thermal treatments were studied by neutron diffraction (ND), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Although, ND analysis is rather uncommon in such studies, this technique allowed evidencing the presence of retained β in α' martensite of the as-produced (#AP) sample. The retained β was not detectable byXRDanalysis, nor by STEM observations. Martensite contains a high number of defects, mainly dislocations, that anneal during the thermal treatment. Element diffusion and partitioning are the main mechanisms in the α ↔ β transformation that causes lattice expansion during heating and determines the final shape and size of phases. The retained β phase plays a key role in the α' → β transformation kinetics.
2019
- Structure and properties of polyamide 11 nanocomposites filled with fibrous palygorskite clay
[Articolo su rivista]
Benobeidallah, B.; Benhamida, A.; Dorigato, A.; Sola, A.; Messori, M.; Pegoretti, A.
abstract
Various amounts (up to 10 wt%) of palygorskite nanofibers functionalized by 3-aminopropyltriethoxysilane (APTES) coupling agent were used to reinforce polyamide 11 nanocomposites prepared by melt compounding. The covalent bonding of the silane on the palygorskite surface was confirmed by infrared spectroscopy and thermogravimetric analysis. X-ray diffraction revealed the retention of the α-form of polyamide crystals upon the addition of both natural and silane treated palygorskite nanorods. All the investigated nanocomposites showed an improvement of the thermal stability, especially when surface treated palygorskite nanofibers were considered. Tensile tests and dynamic mechanical thermal analyses on the prepared materials evidenced how the incorporation of palygorskite nanofibers significantly increased the elastic and the storage moduli of polyamide, and this enhancement was more evident when natural palygorskite nanorods were used.
2018
- Angiogenic and inflammatory potential of Scleral Ossicles, novel natural biomaterials for bone regeneration
[Abstract in Rivista]
Checchi, Marta; Bertacchini, Jessika; Magaro', MARIA SARA; Ferretti, Marzia; Sola, Antonella; Bisi, Francesca; Messori, Massimo; Ribatti, Domenico; Maurel, Delphine; Palumbo, Carla
abstract
The aim of this work is the analysis of the angiogenic and inflammatory potential of the Scleral Ossicles (SOs), already analysed by the structural viewpoint, and the development of a functionalized-SOs-construct. The final goal is to improve the healing of critical-size bone fractures.
2018
- Development of laser-based powder bed fusion process parameters and scanning strategy for new metal alloy grades: A holistic method formulation
[Articolo su rivista]
Bassoli, Elena; Sola, Antonella; Celesti, Mattia; Calcagnile, Sandro; Cavallini, Carlo
abstract
In spite of the fast growth of laser-based powder bed fusion (L-PBF) processes as a part of everyday industrial practice, achieving consistent production is hampered by the scarce repeatability of performance that is often encountered across different additive manufacturing (AM) machines. In addition, the development of novel feedstock materials, which is fundamental to the future growth of AM, is limited by the absence of established methodologies for their successful exploitation. This paper proposes a structured procedure with a complete test plan, which defines step-by-step the standardized actions that should be taken to optimize the processing parameters and scanning strategy in L-PBF of new alloy grades. The method is holistic, since it considers all the laser/material interactions in different local geometries of the build, and suggests, for each possible interaction, a specific geometry for test specimens, standard energy parameters to be analyzed through a design of experiment, and measurable key performance indicators. The proposed procedure therefore represents a sound and robust aid to the development of novel alloy grades for L-PBF and to the definition of the most appropriate processing conditions for them, independent of the specific AM machine applied.
2018
- Fatigue behavior of as-built L-PBF A357.0 parts
[Articolo su rivista]
Bassoli, Elena; Denti, Lucia; Comin, Andrea; Sola, Antonella; Tognoli, Emanuele
abstract
Laser-based powder bed fusion (L-PBF) is nowadays the preeminent additive manufacturing (AM) technique to produce metal parts. Nonetheless, relatively few metal powders are currently available for industrial L-PBF, especially if aluminum-based feedstocks are involved. In order to fill the existing gap, A357.0 (also known as A357 or A13570) powders are here processed by L-PBF and, for the first time, the fatigue behavior is investigated in the as-built state to verify the net-shaping potentiality of AM. Both the low-cycle and high-cycle fatigue areas are analyzed to draw the complete Wohler diagram. The infinite lifetime limit is set to 2 × 106stress cycles and the staircase method is applied to calculate a mean fatigue strength of 60 MPa. This value is slightly lower but still comparable to the published data for AlSi10Mg parts manufactured by L-PBF, even if the A357.0 samples considered here have not received any post-processing treatment.
2018
- Mechanical performance of epoxy coated AR-glass fabric Textile Reinforced Mortar: Influence of coating thickness and formulation
[Articolo su rivista]
Messori, Massimo; Nobili, Andrea; Signorini, Cesare; Sola, Antonella
abstract
The mechanical performance of epoxy coated AR-glass fabric reinforced composite is investigated. A three-stage manufacturing process is considered, which involves fabric surface functionalization, liquid coating deposition and long-term setting and finally fabric embedment in the mortar matrix. Two epoxy coatings are considered, which only differ by the hardening agent. However, coating thickness is significantly diverse as a result of modified viscosity during liquid deposition. Performance is assessed in uni-axial tension as well as in three-point bending and it is expressed in terms of strength curves, data dispersion, crack pattern and failure mechanism. Remarkably, despite being very similar, the analyzed coatings produce a significantly different performance, especially when data dispersion is incorporated and design limits are considered. Indeed, although both coatings are able to consistently deliver fabric rupture at failure, only the thinnest is associated with small data scattering and an almost plastic post-peak behavior in bending. The associated design elongation limit reaches the maximum allowed value according to the ICC guidelines. In fact, it appears that coating thickness plays a crucial role in determining mechanical performance and fabric flexibility. The proposed manufacturing process proves extremely effective at enhancing matrix-to-fabric adhesion and thereby prevent telescopic failure.
2018
- Metal particle shape: A practical perspective
[Articolo su rivista]
Nouri, A.; Sola, A.
abstract
The choice of appropriate processing conditions in powder metallurgy and the achievement of the required properties for the final metal components greatly depend on the shape of the solid phase. Powder sinterability, packing density, compressibility, mechanical behavior, reactivity and flowability, among the others, are influenced by particle shape. The present paper offers an informative overview on the role of particle shape in powder metallurgy and provides the basic definitions, qualitative shape descriptors and semi-quantitative shape factors that are essential to better understand the effect of metal particle shape in everyday industrial practice.
2018
- Proposal of a Novel Natural Biomaterial, the Scleral Ossicle, for the Development of Vascularized Bone Tissue In Vitro
[Articolo su rivista]
Checchi, Marta; Bertacchini, Jessika; Grisendi, Giulia; Smargiassi, Alberto; Sola, Antonella; Messori, Massimo; Palumbo, Carla
abstract
Recovering of significant skeletal defects could be partially abortive due to the perturbations that affect the regenerative process when defects reach a critical size, thus resulting in a non-healed bone. The current standard treatments include allografting, autografting, and other bone implant techniques. However, although they are commonly used in orthopedic surgery, these treatments have some limitations concerning their costs and their side effects such as potential infections or malunions. On this account, the need for suitable constructs to fill the gap in wide fractures is still urgent. As an innovative solution, scleral ossicles (SOs) can be put forward as natural scaffolds for bone repair. SOs are peculiar bony plates forming a ring at the scleral-corneal border of the eyeball of lower vertebrates. In the preliminary phases of the study, these ossicles were structurally and functionally characterized. The morphological characterization was performed by SEM analysis, MicroCT analysis and optical profilometry. Then, UV sterilization was carried out to obtain a clean support, without neither contaminations nor modifications of the bone architecture. Subsequently, the SO biocompatibility was tested in culture with different cell lines, focusing the attention to the differentiation capability of endothelial and osteoblastic cells on the SO surface. The results obtained by the above mentioned analysis strongly suggest that SOs can be used as bio-scaffolds for functionalization processes, useful in regenerative medicine.
2017
- Increased production of bacterial cellulose as starting point for scaled-up applications
[Articolo su rivista]
Gullo, Maria; Sola, Antonella; Zanichelli, Gabriele; Montorsi, Monia; Messori, Massimo; Giudici, Paolo
abstract
Bacterial cellulose is composed of an ultrafine nanofiber network and well-ordered structure; therefore, it offers several advantages when used as native polymer or in composite systems. In this study, a pool of 34 acetic acid bacteria strains belonging to Komagataeibacter xylinus were screened for their ability to produce bacterial cellulose. Bacterial cellulose layers of different thickness were observed for all the culture strains. A high-producing strain, which secreted more than 23 g/L of bacterial cellulose on the isolation broth during 10 days of static cultivation, was selected and tested in optimized culture conditions. In static conditions, the increase of cellulose yield and the reduction of by-products such as gluconic acid were observed. Dried bacterial cellulose obtained in the optimized broth was characterized to determine its microstructural, thermal, and mechanical properties. All the findings of this study support the use of bacterial cellulose produced by the selected strain for biomedical and food applications.
2017
- Role of magnesium oxide and strontium oxide as modifiers in silicate-based bioactive glasses: Effects on thermal behaviour, mechanical properties and in-vitro bioactivity
[Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Salvatori, Roberta; Anesi, Alexandre; Chiarini, Luigi; Cannillo, Valeria
abstract
The composition of a CaO-rich silicate bioglass (BG_Ca-Mix, in mol%: 2.3 Na2O; 2.3 K2O; 45.6 CaO; 2.6 P2O5; 47.2 SiO2) was modified by replacing a fixed 10 mol% of CaO with MgO or SrO or fifty-fifty MgO-SrO. The thermal behaviour of the modified glasses was accurately evaluated via differential thermal analysis (DTA), heating microscopy and direct sintering tests. The presence of MgO and/or SrO didn't interfere with the thermal stability of the parent glass, since all the new glasses remained completely amorphous after sintering (treatment performed at 753 °C for the glass with MgO; at 750 °C with SrO; at 759 °C with MgO and SrO). The sintered samples achieved good mechanical properties, with a Young's modulus ranging between 57.9 ± 6.7 for the MgO-SrO modified composition and 112.6 ± 8.0 GPa for the MgO-modified one. If immersed in a simulated body fluid (SBF), the modified glasses after sintering retained the strong apatite forming ability of the parent glass, in spite of the presence of MgO and/or SrO. Moreover, the sintered glasses, tested with MLO-Y4 osteocytes by means of a multi-parametrical approach, showed a good bioactivity in vitro, since neither the glasses nor their extracts caused any negative effect on cell viability or any inhibition on cell growth. The best results were achieved by the MgO-modified glasses, both BGMIX_Mg and BGMIX_MgSr, which were able to exert a strong stimulating effect on the cell growth, thus confirming the beneficial effect of MgO on the glass bioactivity.
2016
- Functionally graded materials for orthopedic applications – an update on design and manufacturing
[Articolo su rivista]
Sola, Antonella; Bellucci, Devis; Cannillo, Valeria
abstract
Functionally graded materials (FGMs) are innovative materials whose composition and/or microstructure gradually vary in space according to a designed law. As a result, also the properties gradually vary in space, so as to meet specific non-homogeneous service requirements without any abrupt interface at the macroscale. FGMs are emerging materials for orthopedic prostheses, since the functional gradient can be adapted to reproduce the local properties of the original bone, which helps to minimize the stress shielding effect and, at the same time, to reduce the shear stress between the implant and the surrounding bone tissue, two critical prerequisites for a longer lifespan of the graft. After a brief introduction to the origin of the FGM concept, the review surveys some representative examples of graded systems which are present in nature and, in particular, in the human body, with a focus on bone tissue. Then the rationale for using FGMs in orthopedic devices is discussed more in detail, taking into account both biological and biomechanical requirements. The core of the paper is dedicated to two fundamental topics, which are essential to benefit from the use of FGMs for orthopedic applications, namely (1) the computational tools for materials design and geometry optimization, and (2) the manufacturing techniques currently available to produce FGM-based grafts. This second part, in its turn, is structured to consider the production of functionally graded coatings (FGCs), of functionally graded 3D parts, and of special devices with a gradient in porosity (functionally graded scaffolds). The inspection of the literature on the argument clearly shows that the integration of design and manufacturing remains a critical step to overpass in order to achieve effective FGM-based implants.
2016
- Hydroxyapatite and tricalcium phosphate composites with bioactive glass as second phase: State of the art and current applications
[Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract
Calcium phosphates are among the most common biomaterials employed in orthopaedic and dental surgery. The efficacy of such systems as bone substitutes and bioactive coatings on metallic prostheses has been proved by several clinical studies. Among these materials, hydroxyapatite (HA) and tricalcium phosphate (TCP) play a prominent role in medical practice since the '80s. In the last years, numerous attempts to combine HA or TCP with bioactive glasses have been made. There are two main motivations for sintering calcium phosphates with a glassy phase: on the one hand, it is possible to tune the dissolution of the final system and to enhance its biological response through the synergistic combination of two bioactive phases; on the other hand, the glass acts as a sintering aid with the aim to increase the densification of the composite and thus its mechanical strength. In this sense, TCP and HA are penalized by their relatively poor fracture toughness and tensile strength compared to natural bone, which makes it impossible to use them in load-bearing applications. Moreover, the bioactivity index of pure calcium phosphates is typically lower with respect to that of many bioactive glasses. In this review, the state of the art and current applications of composites, based on HA or TCP with bioactive glass as second phase, are presented and discussed. A special emphasis is given to the processing and mechanical behaviour of these systems, together with their biological implications, as a function of the composition of the glass employed as second phase.
2015
- Bioactive glass/hydroxyapatite composites: Mechanical properties and biological evaluation
[Articolo su rivista]
Bellucci, Devis; Sola, Antonella; Anesi, Alexandre; Salvatori, Roberta; Chiarini, Luigi; Cannillo, Valeria
abstract
Bioactive glass/hydroxyapatite composites for bone tissue repair and regeneration have been produced and discussed. The use of a recently developed glass, namely BG_Ca/Mix, with its low tendency to crystallize, allowed one to sinter the samples at a relatively low temperature thus avoiding several adverse effects usually reported in the literature, such as extensive crystallization of the glassy phase, hydroxyapatite (HA) decomposition and reaction between HA and glass. The mechanical properties of the composites with 80wt.% BG_Ca/Mix and 20wt.% HA are sensibly higher than those of Bioglass® 45S5 reference samples due to the presence of HA (mechanically stronger than the 45S5 glass) and to the thermal behaviour of the BG_Ca/Mix, which is able to favour the sintering process of the composites. Biocompatibility tests, performed with murine fibroblasts BALB/3T3 and osteocites MLO-Y4 throughout a multi-parametrical approach, allow one to look with optimism to the produced composites, since both the samples themselves and their extracts do not induce negative effects in cell viability and do not cause inhibition in cell growth.
2015
- Classical Bioglass® and innovative CaO-rich bioglass powders processed by Spark Plasma Sintering: A comparative study
[Articolo su rivista]
Desogus, L.; Cuccu, A.; Montinaro, S.; Orrù, R.; Cao, G.; Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract
Densification and crystallization phenomena taking place when a recently developed CaO-rich bioactive glass and conventional 45S5 Bioglass® are processed by Spark Plasma Sintering (SPS) are examined. Fully dense and wholly amorphous products can be obtained from the new glass composition at 730 ◦ C after 2min dwell time. Moreover, temperatures equal or higher than 830◦C are needed to induce crystal- lization (- and -CaSiO3) in the parent glass. Conversely, Na6Ca3Si6O18 crystals are formed in sintered 45S5 samples produced under optimal conditions (550◦C, 2min), although the glassy character is still preserved.
Products resulting from the innovative glass powders generally display higher hardness and local elastic modulus. Devitrification also provides improvements in this system. In contrast, mechanical properties become slightly worsen when classical bioglass is processed at 600 ◦ C. This can be probably associated to the corresponding decrease in compactness which, apparently, overcomes the benefits arising from the crystallization progress.
2015
- Comparison between Suspension Plasma Sprayed and High Velocity Suspension Flame Sprayed bioactive coatings
[Articolo su rivista]
Bolelli, Giovanni; Bellucci, Devis; Cannillo, Valeria; Gadow, Rainer; Killinger, Andreas; Lusvarghi, Luca; Müller, Philipp; Sola, Antonella
abstract
This paper assesses the diverse potentialities of two different suspension spraying processes, namely High Velocity Suspension Flame Spraying (HVSFS) and Suspension Plasma Spraying (SPS), for the deposition of bioactive coatings based on hydroxyapatite and on a new, custom-made K2O–Na2O–CaO–P2O5–SiO2 bioactive glass. With both feedstock types, the HVSFS process imparts high in-flight velocities to the particles and aggregates released after solvent vaporisation, resulting in well flattened, tightly bound lamellae. The coatings, b50 μm thick and very dense, have hardness and elastic modulus values close to those of the corresponding bulk materials. They can be employed as high-quality bioactive layers on metallic implantable devices. Few days of soaking in simulated body fluid (SBF) results in the re-precipitation of a surface hydroxyapatite layer, albeit through different mechanisms. In HVSFS bioactive glass coatings, ion leaching turns the surface into a silica gel, onto which hydroxyapatite subsequently deposits. In HVSFS hydroxyapatite, the amorphous fraction is progressively dissolved and microcrystalline hydroxyapatite precipitates onto the remaining coating layer.
The SPS technique, due to the lower in-flight velocity of particles and agglomerates, always produces more po- rous, rougher layers with columnar-like growth. They are not mechanically strong, but their peculiar structure can be useful for specific, functional applications. The high surface area of porous SPS bioactive glass coatings favours ion leaching and fast dissolution in simulated body fluid (SBF); hence, it is suggested that SPS bioglass could be useful as a rapidly resorbable layer. SPS hydroxyapatite, by contrast, is more stable than the corresponding HVSFS layer, despite its porosity, because of the higher crystallinity. After the amorphous fraction is dissolved in SBF, newly formed hydroxyapatite does not constitute a surface layer but precipitates inside the pores, suggesting that a sealing pre-treatment in SBF could be a means to tune porosity and phase composition.
2015
- Composite scaffolds for controlled drug release: role of the polyurethane nanoparticles on the physical properties and cell behaviour
[Articolo su rivista]
Gentile, Piergiorgio; Bellucci, Devis; Sola, Antonella; Mattu, Clara; Cannillo, Valeria; Ciardelli, Gianluca
abstract
Localised delivery of appropriate biomolecule/drug(s) can be suitable to prevent postoperative infections and inflammation after scaffold implantation in vivo. In this study composite shell scaffolds, based on an internally produced bioactive glass and a commercial hydroxyapatite, were surface coated with a uniform polymeric layer, embedded with thermo-stable polyesterurethane (PU)-based nanoparticles (NPs), containing an anti-inflammatory drug (indomethacin; IDCM). The obtained functionalised scaffolds were subjected to physico-mechanical and biological characterisations. The results indicated that NPs incorporation into the gelatin coating of the composite scaffolds: 1) not changed significantly the micro-architecture of the scaffolds in terms of mean pore diameter and pore size distribution; 2) increased the compressive modulus; and 3) allowed to a sustained IDMC release (65-70% of the loaded-drug) within the first week of incubation in physiological solution. On the other hand, the NPs incorporation did not affect the biocompatibility of composite scaffolds, as evidenced by viability and alkaline phosphatase (ALP) activity of MG63 human osteoblast-like cells.
2015
- Consolidation of different hydroxyapatite powders by SPS: Optimization of the sintering conditions and characterization of the obtained bulk products
[Articolo su rivista]
Cuccu, A.; Montinaro, S.; Orrù, R.; Cao, G.; Bellucci, Devis; Sola, Antonella; Cannillo, Valeria
abstract
The difference in purity, particle size, microstructure, and thermo-chemical stability of three commercially available hydroxyapatite powders are found to play an important role during their consolidation using spark plasma sintering (SPS) as well as strongly affect the characteristics of the resulting sintered bodies. A fully dense material without secondary phases was obtained by SPS at 900 1C, when using the relatively small sized, with refined grains and high purity powders. The sintered product, consisting of sub-micrometer sized hydroxyapatite grains, displayed optical transparency and good mechanical properties.
In contrast, the higher temperature levels (up to 1200 1C) needed to sinter powders with larger particles, or finer ones which contain additional phases, lead to products with coarser microstructures and/or significant amount of β-TCP as a result of HAp decomposition. Optical characteristics, hardness and elastic modulus of the resulting sintered samples are correspondingly worsened.
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
- 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
- Bioactivity of thermal plasma synthesized bovine hydroxyapatite/glass ceramic composites
[Relazione in Atti di Convegno]
C. P., Yoganand; V., Selvarajan; Mahmoud, Rouabhia; Cannillo, Valeria; Sola, Antonella
abstract
Bone injuries and failures often require the inception of implant biomaterials. Research in this area is receiving increasing attention worldwide. A variety of artificial bone materials, such as metals, polymeric materials, composites and ceramics, are being explored to replace diseased bones. Calcium phosphate ceramics are currently used as biomaterials for many applications in both dentistry and orthopedics. Bioactive silicate-based glasses show a higher bioactive behaviour than calcium phosphate materials. It is very interesting to study the mixtures of HA and silicate-based glasses. In the present study; natural bovine hydroxyapatite / SiO2–CaO–MgO glass composites were produced using the Transferred arc plasma (TAP) melting method. TAP melting route is a brisk process of preparation of glass-ceramics in which the raw materials are melted in the plasma and crystallization of the melt occurs while cooling down at a much faster rate in relatively short processing times compared to the conventional methods of manufacture of glass ceramics/composites. It is well known that; one essential step to the understanding of the biological events occurring at the bone tissue/material interface is the biological investigation by in vitro tests. Cell lines are commonly used for biocompatibility tests, and are very efficient because of their reproducibility and culture facility. In this study, we report the results of a study on the response of primary cultures of human fibroblast cells to TAP melted bioactive glass ceramics.
2010
- Bioceramic scaffolds: where materials science meets life – Part I
[Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract
Tissue engineering is a new and highly multidisciplinary field. The main objective is to realize “living alternatives” for harvested tissues to be employed in reconstructive surgery. A key issue for tissue engineering is the design of scaffolds, i.e. artificial temporary structures acting as extracellular matrices to support the tissue regrowth. After a brief introduction on biomaterials, the main properties of scaffolds are reviewed, with a particular emphasis on scaffolds for bone tissue engineering, which can be used whenever a skeletal defect occurs because of trauma, diseases or degenerative pathologies. Bioceramic scaffolds have the great advantage to interact with bone tissue by forming a direct bond. Moreover, they can resorb in a predictable way, at the same rate as the bone tissue is repaired. The recent development of a new generation of scaffolds, based on the highly bioactive Bioglass®, is addressed. The realization of these structures is then explored discussing the widely used sponge replication and burning out techniques.
2010
- Bioceramic scaffolds: where materials science meets life – Part II
[Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract
2010
- Characterization and in vitro bioactivity of natural hydroxyapatite based bio-glass-ceramics synthesized by thermal plasma processing
[Articolo su rivista]
C. P., Yoganand; V., Selvarajan; Cannillo, Valeria; Sola, Antonella; E., Roumeli; O. M., Goudouri; K. M., Paraskevopoulos; Mahmoud, Rouabhia
abstract
Natural bovine hydroxyapatite/SiO2–CaO–MgO glass–ceramics were produced using the transferred arc plasma (TAP) processing method. Homogeneous mixtures of HA/25 wt% SiO2–CaO–MgO and HA/50 wt% SiO2–CaO–MgO batches obtained by dry mixing the respective compositions in a ball mill were processed in argon plasma using the TAP torch at 5 kW for 1, 2 and 3 min, respectively. The synthesized glass–ceramic samples were studied for phase composition, microstructure and bioactivity. The phase study of the synthesized glass–ceramics revealed the formation of calcium phosphate silicate with traces of calcium silicate. The structural study by SEM revealed that the prepared samples possessed smooth glassy surface morphology. The in vitro-bioactivity of the TAP synthesized glass–ceramics was examined in simulated body fluid (SBF). The SBF test results confirmed the development of crystalline carbonated apatite phase after 12 days of immersion. The cytocompatibility was evaluated through human fibroblast cell proliferation. The fibroblasts culture results showed that the sample was non- toxic and promoted cell growth.
2010
- Cristallizazione e bioattività: gli effetti del trattamento termico sui vetri bioattivi
[Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Manfredini, Tiziano; Sola, Antonella
abstract
2010
- Different approaches to produce coatings with bioactive glasses: enameling vs plasma spraying
[Articolo su rivista]
Cannillo, Valeria; Sola, Antonella
abstract
Two alternative approaches, enamelling and plasma spraying, were tested to deposit coatings made with two different bioactive glasses: the established Bioglass ® 45S5, which is considered as a term of comparison, and the experimental BioK. The strong points and weaknesses of the two methods were highlighted. From the analysed samples, it resulted that the enamelling approach works well on thermally stable substrates and creates a strong bond, characterized by a compositional gradient, with alumina substrates. However the coating thickness must be carefully controlled to limit the thermal residual stresses and the glass formulation should be designed to reduce the glass tendency to crystallize. Instead plasma spraying is suitable for any kind of substrate and is highly automatizable, but the equipment is expensive and the coatings are likely to retain some defectiveness, which makes a post-deposition thermal treatment necessary. Both enamelling and plasma spraying may induce crystallization phenomena, depending on the glass formulation. The introduction of potassium oxide in the glass composition, such as in the BioK, may be useful to hinder the crystallization.
2010
- Highly porous polycaprolactone-45S5 bioglass® scaffolds for bone tissue engineering
[Articolo su rivista]
Fabbri, Paola; Cannillo, Valeria; Sola, Antonella; A., Dorigato; F., Chiellini
abstract
Highly porous biocompatible composites made of polycaprolactone (PCL) and 45S5 Bioglass® (BG) were prepared by a solid-liquid phase separation method (SLPS). The composites were obtained with BG weight contents varying in the range 0-50%, using either dimethylcarbonate (DMC) or dioxane (DIOX) as solvent, and ethanol as extracting medium. The porosity of the scaffolds was estimated to be about 88-92%. Mechanical properties showed a dependence on the amount of BG in the composites, but also on the kind of solvent used for preparation, composites prepared with DIOX showing enhanced stress at deformation with respect to composites prepared with DMC (stress at 60% of deformation being as high as 214 ± 17 kPa for DIOX-prepared composites and 98 ± 24 kPa for DMC-prepared ones, with 50% wt/wtPCL of glass), as well as higher elastic modulus (whose value was 251 ± 32 kPa for DIOX-prepared scaffolds and 156 ± 36 kPa for DMC-prepared ones, always with 50% wt/wtPCL of glass). The ability of the composites to induce precipitation of hydroxyapatite was positively evaluated by means of immersion in simulated body fluid and the best results were achieved with high glass amounts (50% wt/wtPCL). In-vitro tests of cytotoxicity and osteoblast proliferation showed that, even if the scaffolds are to be considered non-cytotoxic, cells suffer from the scarce wettability of the composites.
2010
- Microstructure and in-vitro behaviour of a novel High Velocity Suspension Flame Sprayed (HVSFS) bioactive glass coating
[Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; Sola, Antonella; N., Stiegler
abstract
Bioactive glass coatings based on a novel SiO2-P2O5-CaO-K2O system (“Bio-K”) were deposited by the High-Velocity Suspension Flame Spraying (HVSFS) technique. Attrition-milled micrometric powder particles, dispersed in water+isopropanol, were sprayed onto Ti plates. The coatings remained entirely glassy, but the glass underwent some structural alterations during processing. After soaking in simulated body fluid (SBF), a quite uniform hydroxyapatite layer was developed on the coatings, which indicates they may have the potential to favour osseointegration of prosthetic implants.
2010
- Monte Carlo simulation of microstructure evolution in biphasic systems
[Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract
Over the past few decades, a variety of models have been proposed in order to investigate the grain growth kinetics and the development of crystallographic textures in polycrystalline materials. In particular, a full understanding of the microstructure evolution is a key issue for ceramic systems, since their mechanical or thermal behaviour is intimately related to their microstructure. Moreover, the development of appropriate simulative tools is crucial to reproduce, control and finally optimize the solid-state sintering process of ceramics. Monte Carlo simulations are particularly attractive because of their ability to reproduce the statistical behaviour of atoms and grain boundaries with time. However, Monte Carlo simulations applied to two-phase materials, such as many ceramic systems, result complex because both grain growth and diffusion processes should be taken into account. Here the Monte Carlo Potts model, which is widely used to investigate the crystallization kinetics for monophasic systems, is modified and extended to biphasic ones. The proposed model maps the microstructure onto a discrete lattice. Each lattice element contains a number representing its phase and its crystallographic orientation. The grain formation and growth are simulated by appropriate switching and reorientation attempts involving the lattice elements. The effect of temperature is also discussed.
2010
- Potassium based bioactive glass for bone tissue engineering
[Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; G., Ciardelli; P., Gentile; Sola, Antonella
abstract
A fundamental issue for the restoration of bone defects according to a tissue engineering approach is the development of highly porous bioactive scaffolds. The polymer burning out method is widely employed to fabricate bioceramic scaffolds because of its versatility, simplicity and low cost. However, the resulting scaffolds may suffer low porosity and non-interconnected pores. In the present contribution a new fabrication method is presented. Thanks to a recently developed potassium-based bioactive glass, which has the peculiarity to be sintered at a relatively low temperature (i.e. 750 C), it was possible to use sodium chloride particles as pore generating agents, which helped to maintain the shape of the struts during the entire sintering process. The salt particles can be easily removed by immersing the scaffold in water, giving place to a structure that combines high porosity (in the 70–80 vol.% range) with interconnected pores and an appreciable mechanical behaviour (Young’s modulus in the 3.4–3.7 MPa range according to compression tests).
2010
- Production of Bioglass® 45S5-Polycaprolactone composite scaffolds via salt leaching
[Articolo su rivista]
Cannillo, Valeria; F., Chiellini; Fabbri, Paola; Sola, Antonella
abstract
Polycaprolactone (PCL)-Bioglass 45S5 (45S5) composite scaffolds were produced by means of the salt- leaching technique. Various salts (NaCl, NaHCO3, and a mixture of them) were used with the aim of opti- mising the pores network; moreover several glass weight fractions and glass particle sizes were tested. The so-obtained composite scaffolds were characterized from a microstructural, mechanical and biolog- ical point of view; in particular, in view of the biomedical application of the materials, both in vitro and cytotoxicity tests were performed. The microstructure of the composite scaffolds possessed a well-devel- oped interconnected porosity, ideal for bone regeneration and vascularization. The mechanical properties of the PCL matrix were not altered by the introduction of the glass and the scaffolds ensured an easy han- dling. As regards the bioactivity, the prolonged contact of the 45S5 particles with the water used to remove the salt probably induced a reaction which promoted the development of calcite and altered the glass composition, suppressing the development of hydroxyapatite in vitro; however the response to the cytotoxicity test was promising, confirming the relevance of the PCL-45S5 composite scaffolds and justifying future efforts to improve the production technique, in order to limit the glass alteration
2010
- Shell scaffolds: a new approach towards high strength bioceramic scaffolds for bone regeneration
[Articolo su rivista]
Bellucci, Devis; Cannillo, Valeria; Sola, Antonella
abstract
A key issue for bone tissue engineering is the design of bioceramic scaffolds combining high porosity with adequate mechanical properties. Furthermore, a resistant surface is required in order to have manageable samples for both in vivo and in vitro applications. Here a new protocol that aims to give an appropriate response to these issues is developed. The realized shell scaffolds, obtained combining a modified replication technique with the usual polymer burning-out method, look rather promising mainly thanks to their manageability, porosity and permeability. In this preliminary work the developed technique is discussed, together with an overview on the structure of the realized samples.
2010
- Steel particles-porcelain stoneware composite tiles: an advanced experimental-computational approach
[Articolo su rivista]
Cannillo, Valeria; L., Esposito; G., Pellicelli; Sola, Antonella; A., Tucci
abstract
Innovative porcelain stoneware tiles with a surface layer containing 2.4wt% of stainless-steel particles were produced by the Double Charge Technology. Considering this layer as a composite material, the effects of the metal particles on the mechanical behaviour of the ceramic matrix were extensively investigated in terms of Young’s modulus, fracture toughness and flexural strength. With this aim, composite materials were prepared by using the same silicate-based ceramic matrix with increasing weight percentages of the same stainless-steel powder. The composites were accurately characterised. In particular, due to the high sintering temperature, possible changes at the interface between metal particles and ceramic matrix were thoroughly analysed by means of SEM and EDS microanalysis. To clarify the role of the observed chromium-rich interphase on the mechanical behaviour of the steel particles-stoneware composites, analytical equations were used and simulations were performed by using the Object Oriented Finite element method (OOF).
2010
- Surface modification of Al-Al2O3 composites by laser treatment
[Articolo su rivista]
Cannillo, Valeria; Sola, Antonella; M., Barletta; A., Gisario
abstract
Heat treatment of ceramic-reinforced aluminium matrix composites (AMCs) using a high-power diode laser (HPDL) was investigated.
2009
- Design of Experiments (DOE) for the Optimization of Titania–hydroxyapatite Functionally Graded Coatings
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella
abstract
Titania–hydroxyapatite functionally graded coatings were deposited on titanium alloy substrates by plasma spraying. Because it was necessary to spray together the titania and the hydroxyapatite powders to obtain the graded system, the first target of the present study was to optimize the process parameters in order to obtain a high-quality coating. A 23 Design of Experiments was applied to define the optimal values of plasma torch power, hydrogen flux, and spraying distance. This defined set of parameters (38 kW, 5 SLPM, and 90 mm, respectively) was used to spray the most promising graded coating, which was characterized and postheat treated
2009
- Effect of a Heat Treatment on the Bioactivity of Titania-Hydroxyapatite Functionally Graded Coatings
[Relazione in Atti di Convegno]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella
abstract
2009
- Effect of porosity on the elastic properties of porcelainized stoneware tiles by a multi-layered model
[Articolo su rivista]
Cannillo, Valeria; L., Esposito; E., Rambaldi; Sola, Antonella; A., Tucci
abstract
Porcelainized stoneware represents a leading product in the world market of ceramic tiles, thanks to its relevant bending strength (with respectto other classes of tiles) and extremely low water absorption: these properties derive from its really low content of residual porosity. Nevertheless,an accurate investigation of the cross section of a porcelainized stoneware tile reveals a non-uniform distribution of the residual pores through thethickness, which results in a spatial gradient of properties. Porcelainized stoneware, therefore, may be looked at as a functionally graded material.In the present research, commercial porcelainized stonewares were analysed in order to define the effect of the residual porosity and its spatialdistribution on the mechanical properties of tiles. Polished cross sections of porcelainized stoneware tiles were investigated by optical and scanningelectron microscopy in order to define the content and distribution of residual pores as a function of distance from the working surface. For eachporcelainized stoneware, the local elastic properties of the ceramic matrix were measured by a depth-sensing Vickers micro-indentation technique,then the so-obtained microstructural images and elastic properties were used to model the stoneware tile mechanical properties. In particular, thecross section of each tile was described as a multi-layered system, each layer of which was considered as a composite material formed by a ceramicmatrix and residual pores. The elastic properties of each layer were predicted by applying analytical equations derived from the theory of compositematerials and, as a new approach, by performing microstructure-based finite element simulations. In order to validate the proposed multi-layeredmodel and identify the most reliable predictive technique, the numerical results were compared with experimental data obtained by a resonancebasedmethod.
2009
- Fabrication of 45S5 bioactive glass-polycaprolactone composite scaffolds
[Relazione in Atti di Convegno]
Cannillo, V.; Fabbri, P.; Sola, A.
abstract
45S5 bioactive glass-polycaprolactone composite porous scaffolds were produced using a solution blending and salt-leaching technique. The main target was the optimisation of the fabrication parameters (such as: blending conditions; nature and amount of salt; glass weight fraction and granulometric size distribution) in order to confer a suitable porosity and composition to the composite scaffold.
2009
- Microstructural and mechanical changes by chemical ageing of glazed ceramic surfaces
[Articolo su rivista]
Cannillo, Valeria; L., Esposito; E., Rambaldi; Sola, Antonella; A., Tucci
abstract
In the present work, several ceramic tiles, characterised by different glazes, were considered in order to define the role played by the glassy and crystalline phases on the leaching mechanisms and the deterioration of the mechanical properties. The glazedworking surfaces were subjected to chemical attack by using a strong basic solution and the chemical analysis of the leached solutions was performed. Before and after the chemical attack, the glazed surfaces of the samples were analysed from both the microstructural and mechanical point of view. In this context, the microstructure was observed by SEM and analysed by X-ray diffraction. In order to define other possible changes, roughness measurements, Vickers hardness and micro-scratch tests were also performed. The results made it possible to deepen the understanding of the mechanisms of elements release caused by the chemical attack and their implications on microstructural and mechanical degradation of the working surface of glazed ceramic tiles.
2009
- Post-deposition laser treatment of plasma sprayed titania-hydroxyapatite functionally graded coatings
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella; M., Barletta
abstract
The viability of a high power diode laser source as effective post-deposition treatment technique of functionally graded titania-HA coatings was checked. In particular, several laser treatments were performed on various coatings plasma-sprayed under different conditions to verify the presence of an operative window large enough for practical purposes and, subsequently, to identify the most promising settings of the laser parameters. Laser power as low as 80-100 W and focus distance as high as -4mm were found to be the most feasible choice to improve the overall coating properties as well as to inhibit undesired secondary reactions between calcium phosphates and titania. Finally, the best set of the laser parameters were applied to a pure HA coating and to a titania-HA graded one, plasma-sprayed under the same conditions, to perform a comparative evaluation.
2009
- Potassium-based composition for a bioactive glass
[Articolo su rivista]
Cannillo, Valeria; Sola, Antonella
abstract
The increasing need for biomedical devices, required to face dysfunctions of natural tissues and organs caused by traumatic events, diseases and simple ageing, has drawn attention onto new materials, that could be able to positively interact with the human body. Among them, Bioglass1 is firmly diffused in medical practice, thanks to its high bioactivity. In particular, due to its brittleness, it is mainly applied as a coating onto tougher bionert substrates; nevertheless, its bioactivity may be altered by the crystallization phenomena that could be involved by its processing. With the aim of reducing the tendency to crystallize, a new glass composition, inspired by the 45S5 Bioglass1, was formulated by substituting the sodium oxide with potassium oxide. A parallel characterization of the new glass and the 45S5 Bioglass1 was carried out in order to define the effect of the potassium oxide on the thermal behaviour, mechanical properties and bioactivity. The results proved that the thermo-mechanical properties, as well as the in vitro response of the two glasses were comparable; however, preliminary tests to produce glass coatings by enamelling evidenced a higher stability of the new glass that, unlike the 45S5 Bioglass1, did not crystallize during processing.
2009
- Processing and characterisation of High-Velocity Suspension Flame Sprayed (HVSFS) bioactive glass coatings
[Capitolo/Saggio]
Bolelli, Giovanni; Cannillo, Valeria; R., Gadow; A., Killinger; Lusvarghi, Luca; J., Rauch; Sola, Antonella
abstract
The High-Velocity Suspension Flame Spraying (HVSFS) technique was employed in order to deposit bioactive glass coatings onto titanium substrates. Two different glass compositions were examined: the classical 45S5 Bioglass and a newly-developed SiO 2 –CaO–K 2 O–P 2 O 5 glass, labelled as "Bio-K". Suitable raw materials were melted in a furnace and fritted by casting into water. The frit was dry-milled in a porcelain jar and subsequently attrition-milled in isopropanol. The resulting micron-sized powders were dispersed in a water+isopropanol mixture, in order to prepare suitable suspensions for the HVSFS process. The deposition parameters were varied; however, all coatings were obtained by performing three consecutive torch cycles in front of the substrate. The thickness and porosity of the coatings were significantly affected by the chosen set of deposition parameters; however, in all cases, the layer produced during the third torch cycle was thicker and denser than the one produced during the first cycle. As the system temperature increases during the spraying process, the particles sprayed during the last torch cycle remain at T > Tg while they spread, so that interlamellar viscous flow sintering takes place, favouring the formation of such denser microstructure. Both coatings are entirely glassy; however, micro-Raman spectroscopy reveals that, whereas the 45S5 coating is structurally identical to the corresponding bulk glass, the "Bio-K" coating is somewhat different from the bulk one.
2009
- Role of process type and process conditions on phase content and physical properties of thermal sprayed TiO2 coatings
[Articolo su rivista]
J. R., Colmenares Angulo; Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella; S., Sampath
abstract
Thermal spray represents an advantageous technique for depositing large-area titanium dioxide coat- ings that are of interest for both traditional wear-resistant coatings as well as functional applications such as photo- induced decontamination surfaces. Numerous past studies have examined the phase evolution and properties of TiO2 coatings using different thermal spray processes or parameters. In this paper, an integrated study of thermal sprayed TiO2 was conducted with different thermal spray devices and process parameters for a single feedstock powder comprising the metastable anatase phase. The aforementioned variables are correlated with in-flight par- ticle state (particle temperature and velocity), phase evolution, and coating physical properties. The results are represented through the framework of process maps which connect process parameters with material properties. Based on the phase characterization, an initial exploration of the metastable phase evolution during thermal spray deposition of TiO2 is proposed. Furthermore, the sprayed TiO2 coat- ings show varying degrees of electrical conductivity associated with process-induced stoichiometric changes (vacancy generation) in the TiO2. The effects of these stoichiometric changes as well as extrinsic microstructural attributes (pores, cracks, interfaces), contribute to the complex electrical response of the coatings. This integrated study provides insights into the process–microstructure– property relationship with the ultimate goal of tailoring the functionality of spray deposited oxide thick films.
2008
- Cobalt doped glass for the fabrication of percolated glass-alumina functionally graded materials
[Articolo su rivista]
Cannillo, Valeria; D., Mazza; Siligardi, Cristina; Sola, Antonella
abstract
The present research was focused on the development of a new glass to produce glass–alumina FGMs. The glass formulation, belonging to theCaO–ZrO2–SiO2 system, was doped with cobalt, by adding a small molar percentage (about 0.1 mol%) of CoO, in order to obtain a blue glass,which could be useful to appreciate the final compositional gradient. The glass was accurately characterized, evaluating its thermal behaviour, itsmechanical properties, and its attitude to crystallize during a thermal treatment. Subsequently, the glass was used to produce glass–alumina FGMsvia percolation and the so obtained specimens were analysed in order to evaluate the effect of the glass infiltration. The possible development ofnew crystal phases, in particular, was tested via micro X-ray diffraction and the elastic properties gradient associated with the compositionalgradient was measured via depth-sensing Vickers microindentation.
2008
- Effects of different production techniques on glass-alumina functionally graded materials
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Siligardi, Cristina; Sola, Antonella
abstract
Glass–alumina functionally graded materials were obtained using two different methods: percolation, which was representative of naturaltransport based processes, and plasma spraying, which was representative of constructive processes. The specimens produced in this way wereinvestigated to evaluate the effect of production techniques on the final microstructure and gradient, which, in turn, govern the properties andperformances of the graded systems. Moreover, post-production heat treatments were performed in order to improve the reliability of the materialsexamined.
2008
- In-vitro behaviour of titania-hydroxyapatite functionally graded coatings
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Pierli, Fiorenza; Sola, Antonella
abstract
The in vitro behaviour of titania–hydroxyapatite graded coatings obtained by plasma sprayingwas investigated by a microstructural and mechanical point of view. To verify the bioactivity of thegraded coatings, as sprayed and after thermal treatment, in vitro tests were performed insimulated body fluid. Furthermore, since the mechanical properties of the coatings may bealtered by the immersion in simulated body fluid, the local elastic properties were measured onthe cross-section by means of a depth sensing Vickers microindentation technique beforeimmersion (reference materials) and after soaking for 1 week (short term response) and 4 weeks(long term response), separately investigating the titania and the hydroxyapatite rich zones toaccount for the compositional gradient. The results proved that the presence of titania in thecoating did not suppress the bioactivity, which, on the contrary, was inhibited by the heattreatment. However, the heat treated samples showed higher mechanical properties and reduceddissolution rates.
2008
- Production and characterization of plasma sprayed TiO2-hydroxyapatite functionally graded coatings
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Sola, Antonella
abstract
Among bioactive ceramics, hydroxyapatite (HAp) has been widely studied, especially as a coating onto metallic substrates. In clinical applications,coating delamination has been observed, close to the interface between coating and substrate. This is due to a mismatch in the thermal expansioncoefficients of HAp and titanium/titanium alloy. In order to improve the adhesion, a proper bond coat may be introduced. In this work, a functionallygraded coating TiO2–HAp, in which the composition gradually changed from TiO2 to HAp, was deposited onto Ti6Al4V substrates by atmosphericplasma spraying (APS). With the aim of defining the best spraying parameters to obtain the graded system, preliminary coatings of pure TiO2 andpure HAp were deposited by varying systematically the typical spraying conditions, such as the torch power and H2 flux. The preliminary coatingswere characterized by means of SEM, that confirmed the strong dependence of the microstructure on the torch power, and X-ray diffraction, thatshowed the significant influence exerted by the hydrogen flux on the crystallinity and thermal decomposition of HAp. The results of the preliminaryinvestigations were used to optimise the spraying conditions for the FGM deposition and, accordingly, the final graded coating was obtained andcharacterized. Post-deposition heat treatments were performed in order to improve further the graded coating and their effect on the mechanicalproperties was evaluated via Vickers micro-indentation tests. The investigation showed that, after raising the temperature, the crystallinity of HApand the Vickers hardness increased, however, at high temperature (more than 750 ◦C), the stress induced by the re-crystallization promoted thepropagation of cracks and weakened the interface.
2008
- Sintering behaviour, microstructure and mechanical properties of low-quartz content vitrified ceramics using volcanic ash
[Articolo su rivista]
Kamseu, Elie; Boccaccini, Dino Norberto; Sola, Antonella; Rizzuti, Antonino; Leonelli, Cristina; U., CHINJE MELO; N., Billong
abstract
-
2007
- Characterization of glass-alumina functionally graded coatings obtained by plasma spraying
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Siligardi, Cristina; Sola, Antonella
abstract
Glass-alumina functionally graded coatings (FGCs) were produced Via plasma spraying, a deposition technique for thick (> 10-20 mu m) coatings production, which ensures high flexibility and good reliability. The samples were obtained by building a graded glass-alumina coating onto an alumina substrate; the coatings were designed as multi-layered systems, each layer having a mean composition slightly different from the neighbouring ones. Two different compositional gradients were considered (front 100 vol.% alumina to 100 vol.% glass and from 80-20 vol.% glass to 100 vol.% glass) and several heat treatments were performed in order to improve the substrate-coating interface and induce a controlled transformation (sintering and/or crystallization) of the glassy phase. After a preliminary screening of the as-sprayed and the heat treated samples, the most interesting ones were carefully characterized, especially from a mechanical point of view. In fact, tests Such as Vickers micro-indentation allowed to appreciate the effects of the graded compositional profile and the consequences induced by thermal treatments. (c) 2006 Elsevier Ltd. All rights reserved.
2007
- Glass-alumina Functionally Graded Materials produced by plasma-spraying
[Relazione in Atti di Convegno]
Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract
The present work was focused on glass-alumina functionally graded materials. Thesamples, produced by plasma spraying, were built as multi-layered systems by depositing severallayers of slightly different composition, since their alumina and glass content was progressivelychanged. After fabricating the graded materials, several, proper characterization techniques were setup to investigate the gradient in composition, microstructure and related performances. A particularattention was paid to the observation of the graded cross sections by scanning electron microscopy,which allowed to visualize directly the graded microstructural changes. The scanning electronmicroscopy (SEM) inspection was integrated with accurate mechanical measurements, such assystematic depth-sensing Vickers microindentation tests performed on the graded cross sections.
2007
- Glass-ceramic Functionally Graded Materials produced with different methods
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract
Functionally graded materials (FGMs) are innovative composite materials characterized by a gradual spatial change in composition, microstructure and related properties. This work was focused on glass-alumina functionally graded materials, produced via percolation of molten glass into a sintered polycrystalline alumina substrate and via plasma spraying. The glass composition, belonging to the CaO-ZrO2-SiO2 system, was purposely designed in order to minimize the difference between the coefficients of thermal expansion of the constituent phases, which may induce thermal residual stresses in service or during fabrication. The ingredient materials as well as the resultant FGMs were carefully characterized. In particular, a great attention was devoted to the microstructural investigation of the penetration profile. (c) 2006 Elsevier Ltd. All rights reserved.
2007
- Prediction of the elastic properties profile in glass-alumina functionally graded materials
[Articolo su rivista]
Cannillo, Valeria; Lusvarghi, Luca; Siligardi, Cristina; Sola, Antonella
abstract
Glass-alumina functionally graded materials were obtained by percolation and alternatively by plasma spraying. The paper develops a reliable model to predict the functional gradient of the analysed systems. A finite element code, which was able to handle microstructural images, was employed to estimate the effective elastic properties along the gradient direction. The calculated values were compared with experimental data acquired by means of systematic microindentation tests. The computational approach was compared with analytical tools such as the rule of mixture. The results revealed that the elastic properties were significantly influenced by microstructural features such as the shape of the ingredient materials domains and the presence of pores at the grain boundaries. This was particularly evident in the sprayed FGMs, due to their peculiar lamellar microstructure. Even if the coating-substrate interface properties were difficult to include in the model, the numerical simulations fitted fairly well the experimental data. (c) 2006 Elsevier Ltd. All rights reserved.
2007
- Surface acoustic wave depth profiling of functionally graded material
[Articolo su rivista]
J., Goossens; P., Leclaire; X., Xu; C., Glorieux; L., Martinez; Sola, Antonella; Siligardi, Cristina; Cannillo, Valeria; T., VAN DER DONK; J. P., Celis
abstract
The potential and limitations of Rayleigh wave spectroscopy to characterize the elastic depth profileof heterogeneous functional gradient materials are investigated by comparing simulations of thesurface acoustic wave dispersion curves of different profile-spectrum pairs. This inverse problem isshown to be quite ill posed. The method is then applied to extract information on the depth structureof a glass-ceramic alumina functionally graded material from experimental data. The surfaceacoustic wave analysis suggests the presence of a uniform coating region consisting of a mixture ofAl2O3 and glass, with a sharp transition between the coating and the substrate. This is confirmed byscanning electron microscope with energy dispersive x-ray analysis.
2007
- Technological properties of celsian reinforced glass matrix composites
[Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; A., Motori; F., Patuelli; A., Saccani; Sola, Antonella
abstract
Monoclinic celsian derived from an innovative route, i.e. cation exchanged zeolites heat-treated at low temperature, was added at differentcontents (10, 20, 30 wt%) to a glass matrix, in order to improve its mechanical and electrical performances. The effect of the celsian reinforcementwas evaluated by testing several properties of the composite materials, such as the elastic modulus, abrasion resistance, flexural strength andelectrical insulation. The results so far obtained suggest that the addition of the monoclinic celsian to the glass matrix may produce low-costparticulate composites with interesting technological properties.
2006
- Analysis of crack propagation in alumina-glass functionally graded materials
[Relazione in Atti di Convegno]
Cannillo, V.; Lusvarghi, L.; Manfredini, T.; Montorsi, M.; Siligardi, C.; Sola, A.
abstract
abstract
2006
- Glass-alumina functionally graded materials: their preparation and compositional profile evaluation
[Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Siligardi, Cristina; Sola, Antonella
abstract
This work was focused on glass-alumina functionally graded materials (FGMs). For the glass phase, a proper composition was chosen belonging to the ternary system CaO-ZrO2-SiO2 and the substrate was made up of a sintered, high-purity polycrystalline alumina. Both of the ingredient materials were carefully characterized. The fabricated functionally graded materials were analysed in detail, by observing them under a scanning electron microscope (SEM) coupled with an X-ray energy dispersive spectrometer (X-EDS). The depth of penetration of the glass and the compositional profile were evaluated by means of a SEM-image elaboration. Moreover, this work applied an analytical model to predict the depth of penetration as a function of time and fabricating parameters such as temperature.
2006
- Microscale computational simulation and experimental measurement of thermal residual stresses in glass-alumina functionally graded materials
[Articolo su rivista]
Cannillo, Valeria; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella; G., DE PORTU; L., Micele; G., Pezzotti
abstract
Glass-alumina functionally graded materials are new attractive composite materials, that can achieve peculiar mechanical properties due to their gradual compositional variation. Nevertheless, the difference between the coefficients of thermal expansion of the constituent phases may result in significant thermal residual stresses in service or during fabrication. A proper (glass formulation can minimize the mismatch in thermo-mechanical properties, thus relevantly reducing the mean value of the resultant thermal stresses. However, it is a crucial requirement to evaluate the effect of microstructural discreteness and randomness oil the actual stress distribution in functionally graded materials. With this aim,a computational model which applies the finite element method at the microscale is used. The careful modelling of the real microstructural details enables to accurately predict the local stress values and distribution. In order to verify the reliability of the computational simulations, the residual thermal stresses were also experimentally measured by means of a piezo-spectroscopic technique. The comparison between the numerical and the experimental results validate the microstructure-based model.
2006
- Microstructure-based modelling and experimental investigation of crack propagation in glass-alumina functionally graded materials
[Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract
The aim of the present work was the determination of the fracture mechanisms in glass-alumina functionally graded materials (FGMs). The investigation was performed by means of a combined approach based on microscale computational simulations, which provided for an accurate modelling of the actual FGM microstructure, and experimental analysis. The numerical results proved that microstructural defects, such as pores, deeply influenced the damage evolution. On the contrary, the minimization of the mismatch in the coefficients of thermal expansion of the ingredient materials allowed to obtain low thermal residual stresses, which did not relevantly affect the crack propagation. In order to support the numerical model, microindentation tests were performed on the cross-section of FGM specimens and the experimentally observed crack paths were compared to the computationally predicted ones. (c) 2005 Elsevier Ltd. All rights reserved.
2006
- Preparation and experimental characterization of glass-alumina functionally graded materials
[Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Siligardi, Cristina; Sola, Antonella
abstract
This work aims at investigating the effects of the processing conditions on the final microstructure of glass-alumina functionally graded materials (FGMs). The ingredient materials, i.e. a polycrystalline sintered alumina and a CaO-ZrO2-SiO2 glass, were accurately characterized, since their mechanical and thermal properties may deeply influence the fabricating process and the overall FGM behaviour. The functionally graded materials were obtained by means of percolation of the molten glass into the alumina substrate. Two types of samples were considered-the Bulk FGMs, produced starting from a glass bulk, and the Powder FGMs, produced starting from a glass powder; in both cases four different heating cycles were attempted. The functionally graded materials were analysed using a SEM-EDS and a X-ray diffractometer. Great attention was devoted to the resulting microstructure; moreover the depth of penetration was measured and related to the fabricating parameters, such as time and temperature.
2005
- Experimental characterization and computational simulation of glass-alumina functionally graded surfaces
[Relazione in Atti di Convegno]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, A.
abstract
Functionally graded materials are a new and attractive class of materials incorporating an engineered spatial variation in composition and/or microstructure: this idea has immediately revealed successful since it allows to reach peculiar mechanical properties such as resistance to wear and contact damage. As a matter of fact, the final behaviour of a Functionally Graded Material is mainly influenced by its graded composition and/or microstructure. Therefore a good fabrication technique should provide a high control and reproducibility of the spatial variation in composition and/or microstructure; on the other hand, a reliable model should take into account the gradient in order to accurately predict the final behaviour of a Functionally Graded Material. The present study is focused on glass-alumina FGMs: the compositional variation, which occurs along only one direction, has been realized through percolation of a molten glass into a bulk polycrystalline alumina. The resulting Functionally Graded Coatings have been carefully characterized through Scanning Electron Microscopy, X-ray diffraction, classical mechanical tests and analysis. Moreover, their behaviour has been modeled by means of a microstructure-based FEM method. A great attention has been paid to the validation of the computational model on the basis of the experimental data. Furthermore, the experimental and the computational approaches have been combined in order to define the correlation between fabrication parameters, such as time and temperature, and resulting gradients in composition and microstructure as well as related performances. Since changes in material properties can be easily evaluated, the resulting model may be useful to simulate the material response to a given thermo-mechanical loading and to tailor the gradient as a function of the specific application.
2005
- New frontiers in engineered materials: fabrication processes and relevant applications of Functionally Graded Materials
[Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract
Functionally GradedMaterials (FGMs) are a newand attractive class ofcomposite materials,characterized by anengineered spatial variationin composition andmicrostructure. Anappropriate design of thecompositional andmicrostructural gradientensures a gradual change ofproperties andperformances, which can betailored to the assignedapplication requirements.The optimization of the finalFGM, however, isconditioned not only by theunderstanding of thecorrelation existing betweencomposition/microstructureand material behaviour, butalso by the adoption of asuitable fabricationtechnique. In the presentpaper, therefore, specialattention will be paid to theproduction of FunctionallyGraded Materials. Finally abrief overview of theirapplications will beprovided
2004
- Computational simulations for the optimisation of the mechanical properties of alumina-glass Functionally Graded Materials
[Capitolo/Saggio]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract
Functionally graded materials are finding increasing applications especially as protective coatings, due to their mechanical properties such as resistance to wear and contact damage. It is well known that the microstructure of FGMs governs the resulting global properties. Finite element simulations can be successfully used to characterize the performance of these materials, provided that the computational model is able to take into account microstructural variations along the thickness. In this work, Functionally Graded Materials obtained by percolation of a glass into a bulk polycrystalline alumina are considered and the effect of the microstructure on the overall behavior is investigated by means of a microstructure-based FEM approach. The model is validated by comparison with experimental data, and can be employed in order to optimize the design of these graded surfaces.
2004
- Computational simulations for the optimization of the mechanical properties of alumina-glass functionally graded materials
[Capitolo/Saggio]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, Antonella
abstract
Computational simulations for the optimization of the mechanical properties of alumina-glass functionally graded materials
2003
- Functionally Graded Materials: a review of fabrication processes and modelling of properties
[Articolo su rivista]
Cannillo, Valeria; Manfredini, Tiziano; Montorsi, Monia; Siligardi, Cristina; Sola, A.
abstract
Review of FGM