Assessment of microstructure, biocompatibility and in-vitro biodegradation of a biomedical Mg-Hydroxyapatite composite for bone tissue engineering

In the present study, an Mg-based biomedical composite is fabricated by addition of Hydroxyapatite bioactive nanoparticles into a substrate of bioabsorbable WE43 Mg alloy using multi pass friction stir processing (FSP). The findings indicate that applying 6 passes of FSP leads to a decrease of grain size by over 93%, crushing and redistribution of secondary phase particles within the Mg matrix, improved homogeneity of Hydroxyapatite bioactive particles and a reduction in their agglomeration. In vitro Biodegradation tests prove that as the number of FSP passes increases, the weight loss of fabricated bio-composites and biodegradation rate in simulated body fluid (SBF) decrease. Bioactivity of Mg-based bio-composites is assessed by in vitro immersion in SBF for 28 days. Biomineralization process shows that all fabricated Mg-Hydroxyapatite bio-composites exhibit bone-like apatite forming ability, and cauliflower-shaped Hydroxyapatite crystals form on their surface. Moreover, increasing the uniformity of Hydroxyapatite particles stimulates formation of cauliflower-shaped Hydroxyapatite denser crystals, which improves biocompatibility of bio-composites. Biocompatibility of fabricated bio-composites is also evaluated by MTT assay and DAPI staining. Mg-HA-6P demonstrates the highest number of healthy flattened spindle shaped L-929 fibroblast cells with 83.36% cell viability after 5 days of incubation compared to other samples. Increasing number of FSP passes causes high bioactivity, low biodegradation rate and homogeneous distribution of Hydroxyapatite particles, which in turn improve the viability of L-929 fibroblast cells. Furthermore, with the addition of Hydroxyapatite particles and an increase in the number of FSP passes, the yield strength values of the samples increase, reaching 212 MPa and 226 MPa for the Mg–6P and Mg–6P-HA samples, respectively.