1,721,037 research outputs found
An Enhanced Bioactive Glass Composition with Improved Thermal Stability and Sinterability
No full textThe development of new bioactive glasses (BGs) with enhanced bioactivity and improved resistance to crystallization is crucial for overcoming the main challenges faced by commercial BGs. Most shaping processes require thermal treatments, which can induce partial crystallization, negatively impacting the biological and mechanical properties of the final product. In this study, we present a novel bioactive glass composition, S53P4_MSK, produced by a melt-quench route. This novel composition includes magnesium and strontium, known for their therapeutic effects, and potassium, recognized for improving the thermal properties of bioactive glasses. The thermal properties were investigated through differential thermal analysis, heating microscopy and sintering tests from 600 degrees C to 900 degrees C. These characterizations, combined with X-ray diffraction analysis, demonstrated the high sinterability without crystallization of S53P4_MSK, effectively mitigating related issues. The mechanical properties-elastic modulus, hardness and fracture toughness-were evaluated on the sintered sample by micro-indentation, showing high elastic modulus and hardness. The bioactivity of the novel BG was assessed following Kokubo's protocol and confirmed by scanning electron microscopy, X-ray energy dispersive spectroscopy, and Raman spectroscopy. The novel bioactive glass composition has shown high sinterability without crystallization at 700 degrees C, along with good mechanical properties and bioactivity
Fabrication of 45S5 bioactive glass-polycaprolactone composite scaffolds
No full text45S5 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
Experimental and computational analyses of lead zirconate titanate reinforced glass matrix composites for structural applications
No full textThe mechanical reliability of glass matrix composites depends on the properties of the composite constituents, e.g. matrix and reinforcement. In many cases, microstructural variables, such as the volume fraction of the reinforcing secondary phase, the crystallographic anisotropy of the involved materials, and the physical coupling between the underlying thermodynamic fields, influences the macroscopic mechanical behaviour, in particular fracture toughness. In this paper, the mechanical properties of lead silicate glass matrix composites reinforced with 30wt% lead zirconate titanate (PZT) ferroelectric particles were studied. The samples were fabricated by hot pressing, and characterized by means of SEM, X-ray diffraction, DTA, and Vickers' indentation techniques. For this material, the stress fields at the tip of an advancing crack should be able to re-orient the ferroelectric domains in the PZT inclusions, inducing local crack-arrest, thus contributing to an increase of the macroscopic fracture toughness. Microstructural effects, such as crack-particle interactions were analysed using a FEM-based numerical approach. A good agreement between predicted crack propagation patterns and those obtained experimentally by the indentation technique was found. Numerical and experimental results suggest that traditional toughening mechanisms such as crack deflection, thermal cooling residual stresses, and load-transfer toughening are not active in the studied glass/PZT composites
Production of Bioglass® 45S5 - Polycaprolactone composite scaffolds via salt-leaching
No full textPolycaprolactone (PCL)-Bioglass (R) 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 alteratio
A new hydroxyapatite-based biocomposite for bone replacement
Full text linkSince 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 degrees C divided by 1300 degrees 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 degrees C), thanks to the employment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5 Bioglass (R). 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 (R) having the same HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferatio
Surface Analysis of Ti-Alloy Micro-Grooved 12/14 Tapers Assembled to Non-Sleeved and Sleeved Ceramic Heads: A Comparative Study of Retrieved Hip Prostheses
Full text linkTi6Al4V titanium alloy (Ti-alloy) sleeved ceramic heads have become widely used in revision surgery when the hip stem is left in situ. This solution guarantees a new junction between the bore of the ceramic head and the Ti-alloy sleeve, regardless of any possible, slight surface damage to the Ti-alloy taper of the stem. However, this solution introduces an additional Ti-alloy/Ti-alloy interface pairing, which is potentially susceptible to mechanically assisted crevice corrosion. This study evaluated both qualitatively and quantitatively the damage that occurred in vivo on Ti-alloy micro-grooved 12/14 tapers of (i) primary implants with non-sleeved ceramic heads (Group 1), (ii) secondary implants with non-sleeved ceramic heads (Group 2), and (iii) secondary implants with sleeved ceramic heads (Group 3). A total of 45 explants—15 for each group, including short-, medium- and long-neck heads—underwent optical evaluation for surface damage (Goldberg scoring), surface roughness analysis, and SEM/EDX analysis. The Goldberg scores did not reveal different patterns in the tapers’ surface damage; surface damage was classified as absent or mild (surface damage score ≤2) in 94%, another 94%, and 92% of the analysed regions for Group 1, Group 2, and Group 3, respectively. Small but significant differences in morphological changes occurred in the tapers of the three groups: reductions no greater than a few percentage points in median values of roughness parameters were found in Group 1 and Group 2, while negligible changes were found in Group 3. SEM/EDX analysis revealed little (i.e., a slight increase in the oxygen content) to undetectable changes in the chemical composition on the Ti-alloy surface independently of the group. These results suggest that the Ti-alloy/Ti-alloy sleeve/taper junction is only mildly susceptible to mechanically assisted crevice corrosion. Assembling a sleeved ceramic head, with variable neck lengths up to a “long-neck”, to a Ti-alloy micro-grooved 12/14 taper of a stem left in situ does not seem to increase the risk of revision due to trunnionosis, as long as junction stability (i.e., the proper seating of the sleeved ceramic head on the 12/14 taper) is achieved intraoperatively
A new bioactive glass with extremely high crystallization temperature and outstanding biological performance
No full textIn this work, a new bioactive glass was designed, prepared by means of a melt-quenching route and characterized in terms of both thermal properties and biological performance. The main objective was to obtain a novel product with high temperature of crystallization in view of possible thermal treatments, as well as remarkable biological responsiveness. Thermal behavior was investigated by heating microscopy, differential thermal analysis (DTA) and sintering tests. The glass displayed a very high crystallization temperature and the samples remained completely amorphous after sintering. Bioactivity was evaluated by means of Simulated Body Fluid (SBF) assay, which is a widely used method to preliminary investigate samples' reactivity in vitro; the glass showed a strong apatite forming ability. Additionally, in order to exclude cytotoxic effects, biocompatibility was verified according to ISO standard 10993. Finally, the biological potential of the new glass was tested by using an innovative 3D cellular model, that mimicked the potential clinical application of a given biomaterial. Human bone marrow mesenchymal stem cells (BM-MSCs) were employed to study the performance of bioactive glass granules in such 3D cellular model. The results showed that the bioactive glass supported human BM-MSCs adhesion, colonization and bone differentiation. Thus, this new bioactive glass looks particularly promising for orthopedic applications, bone tissue engineering and regenerative medicine, especially when a thermal treatment is necessary for the production of specific devices
Post-deposition laser treatment of plasma sprayed titanic-hydroxyapatite functionally graded coatings
No full textThe viability of a high power diode laser source as effective post-deposition treatment technique of functionally graded titanic-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 -4 mm 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 titanic-HA graded one, plasma-sprayed under the same conditions, to perform a comparative evaluation. The microstructural characterization by scanning electron microscopy, X-ray diffraction and the local mechanical investigation by Vickers micro-indentations proved that the degree of crystallinity of HA at the outermost layers of the graded coating could be improved without significantly altering the compositional and functional gradient. Furthermore, the properties of the pure HA coating, as-sprayed and laser treated, were found to be substantially less advantageous than those of the titanic-HA functionally graded coating (higher microstructural defectiveness; inferior degree of crystallinity of HA at the working surface; lower Vickers hardness), thus confirming the beneficial effect of the compositional gradient. (C) 2009 Elsevier Ltd. All rights reserved
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