Porous vitalium-base nano-composite for bone replacement: Fabrication, mechanical, and in vitro biological properties

Porous nano-composites were successfully prepared on addition of 58S bioactive glass to Co-base alloy with porosities of 37.2-58.8% by the combination of milling, space-holder and powder metallurgy techniques. The results of X-ray diffraction analysis showed that induced strain during milling of the Co-base alloy powder and also isothermal heat treatment during sintering process led to HCP↔FCC phase transformation which affected mechanical properties of the samples during compression test. Field emission scanning electron microscopy images showed that despite the remaining 58S powder in nanometer size in the composite, there were micro-particles due to sintering at high temperature which led to two different apatite morphologies after immersion in simulated body fluid. Calculated elastic modulus and 0.2% proof strength from stress-strain curves of compression tests were in the range of 2.2-8.3GPa and 34-198MPa, respectively. In particular, the mechanical properties of sample with 37.2% were found to be similar to those of human cortical bone. Apatite formation which was identified by scanning electron microscopy (SEM), pH meter and Fourier-transform infrared spectroscopy (FTIR) analysis showed that it could successfully convert bioinert Co-base alloy to bioactive type by adding 58S bioglass nano-particles. SEM images of cell cultured on the porous nano-composite with 37.2% porosity showed that cells properly grew on the surface and inside the micro and macro-pores.