Research on Biodegradable Mg-Zn-Gd Alloys for Potential Orthopedic Implants: In Vitro and in Vivo Evaluations

Various kinds of biodegradable Mg alloys have been developed in recent years due to their appropriate mechanical properties, biodegradation, and good biocompatibility. In this study, Mg-2.0Zn-xGd alloys (x = 0.5, 1.0, 1.5, and 2.0 wt %) were prepared. Hot extrusion was applied in order to refine the microstructure and improve the degradation resistance. The microstructure, mechanical properties, and in vitro degradation behavior of Mg-2.0Zn-xGd alloys were investigated first. The as-extruded Mg-2.0Zn-1.0Gd alloy exhibits excellent mechanical properties (UTS 338 MPa, YS 284 MPa, elongation 24%) and low in vitro degradation rate (0.24 mm/year) with uniform degradation morphology, and then, this alloy was selected for further assessments. The cytotoxicity of as-extruded Mg-2.0Zn-1.0Gd alloy to MC3T3-E1 cell is found to be grade 0-1, indicating good biocompatibility. The in vivo experiment shows that the in vivo degradation rate of this alloy is about 0.31 mm/y after 30 days implantation in cranial defect of Sprague-Dawley rats. All of these indicate a promising prospect of Mg-2.0Zn-1.0Gd alloy as biodegradable applications, especially as orthopedic implants.