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The use of beta-tricalcium phosphate (β-TCP) ceramic as a bioresorbable bone substitute is limited to non-load-bearing sites by the material׳s brittleness and low bending strength. In the present work, new biocompatible β-TCP-based composites with improved mechanical properties were developed via reinforcing the ceramic matrix with 30 vol% of a biodegradable iron–magnesium metallic phase. β-TCP-15Fe15Mg and β-TCP-24Fe6Mg (vol%) composites were fabricated using a combination of high energy attrition milling, cold sintering/high pressure consolidation of powders at room temperature and annealing at 400 °C. The materials synthesized had a hierarchical nanocomposite structure with a nanocrystalline β-TCP matrix toughened by a finely dispersed nanoscale metallic phase (largely Mg) alongside micron-scale metallic reinforcements (largely Fe). Both compositions exhibited high strength characteristics; in bending, they were about 3-fold stronger than β-TCP reinforced with 30 vol% PLA polymer. Immersion in Ringer׳s solution for 4 weeks resulted in formation of corrosion products on the specimens׳ surface, a few percent weight loss and about 50% decrease in bending strength. In vitro studies of β-TCP-15Fe15Mg composite with human osteoblast monocultures and human osteoblast–endothelial cell co-cultures indicated that the composition was biocompatible for the growth and survival of both cell types and cells exhibited tissue-specific markers for bone formation and angiogenesis, respectively. [ABSTRACT FROM AUTHOR]

A modified particulate leaching method for fabrication of strong calcium phosphate–polymer composite scaffolds with improved pore interconnectivity is reported. The scaffolds were produced by mixing precompacted composite granules (β-TCP with 40vol% PLA) of different size and density with salt particles followed by high pressure consolidation (at room temperature or 120°C) and porogen dissolution. The scaffolds' compressive strength and Darcy's permeability were found to be inversely related and to be strongly dependent on the processing parameters. The use of precompacted granules instead of the loose β-TCP–PLA powder allowed us to increase permeability by three orders of magnitude while maintaining load bearing characteristics. Scaffolds with 50% porosity prepared from large (300–420μm) composite granules of β-TCP–40vol% PLA and salt porogen particles of comparable size exhibited the best combination of compressive strength (4–6MPa) and permeability (1.3–1.6×10−10 m2) falling within the range of trabecular bone. [ABSTRACT FROM AUTHOR]

Abstract: Bone tissue regeneration in load-bearing regions of the body requires high-strength porous scaffolds capable of supporting angiogenesis and osteogenesis. 70% porous Nitinol (NiTi) scaffolds with a regular 3-D architecture resembling trabecular bone were produced from Ni foams using an original reactive vapor infiltration technique. The “trabecular Nitinol” scaffolds possessed a high compressive strength of 79MPa and high permeability of 6.9×10−6 cm2. The scaffolds were further modified to produce a near Ni-free surface layer and evaluated in terms of Ni ion release and human mesenchymal stem cell (hMSC) proliferation (AlamarBlue), differentiation (alkaline phosphatase activity, ALP) and mineralization (Alizarin Red S staining). Scanning electron microscopy was employed to qualitatively corroborate the results. hMSCs were able to adhere and proliferate on both as-produced and surface-modified trabecular NiTi scaffolds, to acquire an osteoblastic phenotype and produce a mineralized extracellular matrix. Both ALP activity and mineralization were increased on porous scaffolds compared to control polystyrene plates. Experiments in a model coculture system of microvascular endothelial cells and hMSCs demonstrated the formation of prevascular structures in trabecular NiTi scaffolds. These data suggest that load-bearing trabecular Nitinol scaffolds could be effective in regenerating damaged or lost bone tissue. [Copyright &y& Elsevier]

Abstract: Highly dense bioresorbable Ca-deficient HA–PLA (CDHA–PLA) and β-TCP–PLA nanocomposite materials with high (up to 80vol%) contents of the calcium phosphate (CaP) phase and homogeneous phase distribution were prepared via attrition milling followed by high pressure consolidation at ambient temperature. The microstructure and mechanical properties of the materials obtained were studied as a function of milling time and PLA amount. Attrition milling resulted in disintegration of β-TCP powder agglomerates down to 50–150nm, disintegration of CDHA agglomerates and refinement of 15×150nm2 CDHA nanoparticles to a size of 8×20nm2, and in a uniform distribution of the polymer component. Very high compressive strengths up to 400MPa and high bending strengths up to 70MPa were obtained. For both β-TCP and CDHA-based nanocomposites, the strength characteristics increased with milling time and decreased with increasing PLA content. For CDHA-based nanocomposites, attrition milling resulted in decrease of ductility while for β-TCP-40vol% PLA the ductility increased. The observed behavior may be a result of formation of homogeneous, relatively thick (tens of nanometers), ductile PLA layers in β-TCP—PLA nanocomposites, but very thin (several nanometers) PLA layers in attrition milled CDHA–PLA nanocomposites. Degradation of compressive and bending strength in aqueous solutions was observed for all the studied CaP–PLA nanocomposites. [Copyright &y& Elsevier]

Abstract: Densification of pure nanocrystalline MgO powder with 10nm particle size by hot-pressing was investigated in the temperature range 700–800°C, applied pressure range 100–200MPa, and for durations of up to 240min. It was shown that significant densification under the pressure begins above 440°C. Densities higher than 99.5% with grain size of 73nm were achieved at 790°C and 150MPa for a 30min duration. Remarkable densification from 90 to 99.5% was observed by temperature change from 700 to 790°C, for which the grain size was doubled only. The final grain size decreased with increasing the applied pressure. Higher shrinkage rates and cumulative shrinkages were recorded by the application of pressure at 550°C rather than from room temperature. The temperature at which the pressure was applied is crucial in determining the maximum shrinkage rate in the nanocrystalline compacts. This effect was related to the morphological changes of the particles caused by plastic deformation at lower temperatures. Analysis of the densification rate and its comparison to the literature data was in agreement with Coble creep, where self-diffusion of Mg2+ cations along the grain boundaries acts as a main densification mechanism. [Copyright &y& Elsevier]