Study of the degradation behavior and the biocompatibility of Mg–0.8Ca alloy for orthopedic implant applications

Mg–Ca alloys have recently attracted great attention towards the research in the field of orthopedic biodegradable implants. This study presents an in vitro degradation assessment of Mg–0.8Ca (0.8 wt. % of Ca) alloy in Hank's balanced salt solution (HBSS). Immersion, hydrogen evolution and electrochemical behavior was studied as well as the cytotoxicity of the degradation products. Morphology and phase composition of the corrosion products were studied using SEM, EDX and XRD techniques. Degradation in HBSS resulted in the formation of the needle-shaped carbonated hydroxyapatite which was similar to the biological apatite in the human bone. Degradation kinetics showed that Mg–0.8Ca alloy had approximately 3-fold faster degradation rate than the pure Mg (1.08 ± 0.38 mm/year for Mg–0.8Ca and 0.35 ± 0.17 mm/year for pure Mg), as observed in two independent experiments. Both, pure Mg and Mg–0.8Ca alloy were biocompatible, generating no cytotoxic degradation products against human-derived HEK 293 cells. Thus, the Mg–0.8Ca alloy was found to be a promising biodegradable implant in terms of bioactivity and compatibility with human cell lines. Depending on the application of the implant and the estimated healing time of the bone, the desired degradation rate of an implant can be controlled by the Mg–Ca composition of such alloys.