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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.

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.

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 2 min dwell time. Moreover, temperatures equal or higher than 830 °C are needed to induce crystallization (α- and β-CaSiO 3 ) in the parent glass. Conversely, Na 6 Ca 3 Si 6 O 18 crystals are formed in sintered 45S5 samples produced under optimal conditions (550 °C, 2 min), 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.

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.

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.

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.

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.

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 (40 wt%) 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.

International audience; A bioactive glass topcoatwas introduced to modify the surface morphology and in-vitro reactivity of hydroxyapatite(HA) coatings for biomedical applications. With this aim, a CaO-rich bioactive glass, termed BG_Ca (wt.%: 4.7Na2O, 42.3 CaO, 6.1 P2O5, and 46.9 SiO2),was selected due to its good bioactivity and lowtendency to crystallize athigh temperature. The standardHA coatings were sprayed through atmospheric plasmaspray (APS) on steel substratesstarting from commercial powders (“APS-HA” samples). The HA coatings, in turn, were subsequentlycoated 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 andwithout the BG_Ca layer were analysed by microstructuralcharacterization and by in vitro tests in simulated body fluid (SBF). The analysis revealed an increased reactivityof the APS-HA/SPS-BG_Ca samples compared to the glass-free APS-HA coatings.© 2013 Elsevier

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.

Various bioactive glass/hydroxyapatite (HA) func-tional 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 chang-ing 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 mechani-cal reliability and apatite-forming ability in SBF. V C 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000–000, 2013.

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. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 2502–2510, 2014.

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 composites 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 composition, 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.

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 realized and discussed. The samples can be sintered at a relatively low temperature (800 °C), thanks to the employment 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.

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.

Because of their excellent bioactivity, bioactive glasses are increasingly diffused to produce biomedical devices 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 treatment to apply or sinter the glass. The exposure to high temperature 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(®). The basic goal is to understand the effect of both the original composition and the thermal treatment on the performance 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 sintering tests 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 sintering was especially striking on the BG_Ca material, whose Vickers hardness increased from 598.9 ± 46.7 HV to 1053.4 ± 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.

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®, 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 (750°C) compared with the widely studied HA/45S5 Bioglass® 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.

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.

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 Bioglass ® 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 Bioglass ® 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 Bioglass ® 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.

Glass-ceramic macroporous scaffolds are crucial for bone tissue engineering, since they act as temporary templates for cell proliferation. An ideal scaffold should combine bioactivity, high porosity, and adequate mechanical properties. Moreover, a resistant and permeable surface is required in order to have manageable samples for both in vitro and in vivo applications. The standard replication technique usually results in relatively weak scaffolds, which can be handled with difficulty because of their brittle surfaces. For this reason, alternative preparation procedures are necessary. In this work a new protocol to realize bioceramic scaffolds is presented. The resulting samples show an original structure, which matches an external resistant surface and a highly porous internal network. In particular, the external surface, which behaves like a "shell", guarantees both high permeability and manageability. The present contribution proposes a brief description of the new protocol and a general overview of the resulting scaffolds. Moreover, some preliminary data regarding the in vitro bioactivity of the new scaffolds are reported.

Heat treatment of ceramic-reinforced aluminium matrix composites (AMCs) using a high-power diode laser (HPDL) was investigated. AMCs were treated by irradiation with laser beams of different power and scanning speeds. This resulted in significant changes in the overall appearance and microstructure of the composite material. Contact gauge profilometry and combined SEM-EDXS and XRD analyses were performed to investigate the relationship between changes in the morphology and microstructure to the amount of laser energy delivered. Vickers microhardness and tribological tests were performed to identify changes in the local mechanical properties of the composite material. Laser treatment often improves the properties of AMCs, although setting of the operational parameters is crucial. In fact, small deviations in power and/or scan speed can severely damage the material, leading to deterioration of the microstructure and overall mechanical behaviour. © 2010 Elsevier Ltd. All rights reserved.

Bioactive glass coatings based on a novel SiO 2 –P 2 O 5 –CaO–K 2 O 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 rather uniform hydroxyapatite layer developed on the coatings, indicating that they may have the potential to faster osseointegration of prosthetic implants.

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.

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 relatively 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.

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.

Polycaprolactone (PCL)-Bioglass® 45S5 (45S5) composite scaffolds were produced by means of the salt-leaching technique. Various salts (NaCl, NaHCO 3 , and a mixture of them) were used with the aim of optimising 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 biological 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-developed 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 handling. 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.

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.

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, Bioglass ® 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 Bioglass ® , was formulated by substituting the sodium oxide with potassium oxide. A parallel characterization of the new glass and the 45S5 Bioglass ® 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 Bioglass ® , did not crystallize during processing.

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 glazed working 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.

Porcelainized stoneware represents a leading product in the world market of ceramic tiles, thanks to its relevant bending strength (with respect to 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 the thickness, 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 spatial distribution on the mechanical properties of tiles. Polished cross sections of porcelainized stoneware tiles were investigated by optical and scanning electron microscopy in order to define the content and distribution of residual pores as a function of distance from the working surface. For each porcelainized 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, the cross section of each tile was described as a multi-layered system, each layer of which was considered as a composite material formed by a ceramic matrix and residual pores. The elastic properties of each layer were predicted by applying analytical equations derived from the theory of composite materials and, as a new approach, by performing microstructure-based finite element simulations. In order to validate the proposed multi-layered model and identify the most reliable predictive technique, the numerical results were compared with experimental data obtained by a resonance-based method.

A complete investigation on the sintering behaviour, involving ceramic transformation, of volcanic ash is reported. Sintering and softening points, vitrification and fusion of finely ground powders of volcanic ash were obtained by hot stage microscope observation. Then, a suitable thermal cycle, which matches the better microstructure and mechanical properties, has been performed. The low quartz content of the final product, the relative high density together with the particular structural complexity of the matrix consequence of the interlocking of various crystalline phases conferred to fired volcanic ash relevant ceramic characteristics. Nucleation and microcrystallisation of pyroxene together with oxidation and cation enrichment are indicated as the main sintering mechanism of fired volcanic ash. Differently from conventional vitrified ceramics, i.e. quartz and mullite in vitreous matrix, the microstructure of the fired products presents spinel, anorthite, diopside, enstatite, pyroferrite, faya...

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 expansion coefficients of HAp and titanium/titanium alloy. In order to improve the adhesion, a proper bond coat may be introduced. In this work, a functionally graded coating TiO2–HAp, in which the composition gradually changed from TiO2 to HAp, was deposited onto Ti6Al4V substrates by atmospheric plasma spraying (APS). With the aim of defining the best spraying parameters to obtain the graded system, preliminary coatings of pure TiO2 and pure HAp were deposited by varying systematically the typical spraying conditions, such as the torch power and H2 flux. The preliminary coatings were characterized by means of SEM, that confirmed the strong dependence of the microstructure on the torch power, and X-ray diffraction, that showed the significant influence exerted by the hydrogen flux on the crystallinity and thermal decomposition of HAp. The results of the preliminary investigations were used to optimise the spraying conditions for the FGM deposition and, accordingly, the final graded coating was obtained and characterized. Post-deposition heat treatments were performed in order to improve further the graded coating and their effect on the mechanical properties was evaluated via Vickers micro-indentation tests. The investigation showed that, after raising the temperature, the crystallinity of HAp and the Vickers hardness increased, however, at high temperature (more than 750 °C), the stress induced by the re-crystallization promoted the propagation of cracks and weakened the interface.

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.

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

The present work was focused on glass-alumina functionally graded materials. The samples, produced by plasma spraying, were built as multi-layered systems by depositing several layers of slightly different composition, since their alumina and glass content was progressively changed. After fabricating the graded materials, several, proper characterization techniques were set up to investigate the gradient in composition, microstructure and related performances. A particular attention 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 electron microscopy (SEM) inspection was integrated with accurate mechanical measurements, such as systematic depth-sensing Vickers microindentation tests performed on the graded cross sections.

Glass–alumina functionally graded coatings (FGCs) were produced via plasma spraying, a deposition technique for thick (>10–20 μm) 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 (from 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.

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.

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–ZrO 2 –SiO 2 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.

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.

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.

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, The SPS technique, due to the lower in-flight velocity of particles and agglomerates, always produces more porous, 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.

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 °C, 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 °C) 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.

Enamelling is a relatively easy and inexpensive technique to produce glass coatings. In this contribution, three different low-alkaline bioactive glasses, modified with Na 2 O and/or K 2 O 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 K 2 O 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 K 2 O. However, the development of bioactive crystalline species, such as wollastonite, was beneficial, in that the new phases not only improved the local mechanical properties (in terms of Vickers microhardness, from 232.1 ± 76.8 HV for the Na 2 O-modified glass coating to 317.9 ± 48.8 for the K 2 O-modified one), but still preserved the apatite-forming ability in a simulated body fluid.

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 powders, 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 powders. 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 Mg(2+) and Sr(2+) ions.

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 hydroxyapatite coatings. The HVSFS hydroxyapatite coatings studied were dense, 27-37μm thick, with some transverse microcracks. Lamellae 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 (

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.

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.