Cytocompatibility, biofilm assembly and corrosion behavior of Mg-HAP composites processed by extrusion.

In this work the cytocompatibility of pure magnesium and Mg-xHAP composites (x=5, 10 and 15wt%) fabricated by powder metallurgy routes has been investigated. The materials were produced from raw HAP powders with particle mean sizes of 6µm (S-xHAP) or 25µm (L-xHAP). The biocompatibility study has been performed for MC3T3 cells (osteoblasts/osteoclasts) and L929 fibroblasts. The results indicate that S-Mg (pure magnesium), S-10HAP and L-10HAP composites are the materials with the best biocompatibility. The ability of S. aureus bacteria to assemble biofilms was also evaluated. Biofilm formation assays showed that these materials are not particular prone to colonization and biofilm assembly is strain dependent. The corrosion resistance of S-Mg, S-10HAP and L-10HAP materials immersed in the media used for the cells culture has also been analyzed. Different trends in the corrosion resistance have been found: S-Mg and S-10HAP show a very high resistance to corrosion whereas the corrosion of L-10HAP steadily increases with time.

Processing and mechanical characteristics of magnesium-hydroxyapatite metal matrix biocomposites.

Magnesium/hydroxyapatite composites were produced by conventional extrusion and their mechanical behavior studied under uniaxial compression at room temperature. The results evidence the capability of the HA for strengthening the Mg material, lowering its microstructural anisotropy and inhibiting deformation twinning. They also reveal that the ECAP processing is effective for improving the grain structure and reducing the crystallographic texture of these composites, giving rise to a significant enhancement of their yield strength and microhardness although the ultimate compressive stress worsens. The analysis of the strain hardening rate of the flow curves demonstrates that the HA addition and the ECAP processing are also effective in inhibiting non-basal dislocation slip.

Mechanical properties and corrosion behavior of Mg-HAP composites.

Mg and Mg-HAP composites containing 5, 10 and 15 wt% of hydroxyapatite have been produced following a powder metallurgy route that consists of mixing raw powders and consolidation by extrusion. The microstructure, texture, mechanical behavior and resistance to corrosion under a PBS solution have been studied. Addition of HAP increases the microhardness of the composites, however the yield strength under compression slightly decreases. Texture analyses reveal a fiber texture for pure Mg that is weakened increasing the HAP fraction. This texture promotes twinning and softening of Mg and Mg-5HAP during the initial deformation stages. Mg-10HAP and Mg-15HAP present a strain-hardening dependence showing no softening. The volume fraction of HAP particles weakens the texture and favors the activation of secondary slip systems. Corrosion experiments in PBS solution have shown that Mg-5HAP exhibits the best resistance to corrosion. Texture and porosity appear to be the main material features controlling the corrosion rates of Mg-HAP composites under the present conditions.

Effect of highly dispersed yttria addition on thermal stability of hydroxyapatite.

The capability of the colloidal method to produce yttria (Y(2)O(3)) dispersed hydroxyapatite (HA) has been investigated as an alternative method to the conventional method of mechanical mixing and sintering for developing HA-based materials that could exhibit controllable and enhanced functional properties. A water based colloidal route to produce HA materials with highly dispersed Y(2)O(3) has been applied, and the effect of 10 wt.% Y(2)O(3) addition to HA investigated by thermal analysis, X-ray diffraction and Fourier transform infrared spectroscopy. These measurements evidence a remarkable effect of this Y(2)O(3) addition on decomposition mechanisms of synthetic HA. Results show that incorporation of Y(2)O(3) as dispersed second phase is beneficial because it hinders the decomposition mechanisms of HA into calcium phosphates. This retardation will allow the control of the sintering conditions for developing HA implants with improved properties. Besides, substitution of Ca(2+) with Y(3+) ions appears to promote the formation of OH(-) vacancies, which could improve the conductive properties of HA favorable to osseointegration.