Corrosion and biocompatibility improvement of magnesium-based alloys as bone implant materials: a review

Magnesium (Mg) or its alloys are widely tested as potential orthopedic implants, particularly as biodegradable alloys for fracture fixation due to their mechanical properties are close to those of bone. Currently, available Mg or its alloys are confronted with challenges in passing regulatory biosafety tests prior to clinical trials due to its fast degradation and associated degradation products. The degradation of Mg is accompanied by the release of Mg ions, the rise of pH and osmolality in surrounding environments. According to the standard of ISO 10993 Part 13, the pH value shall be appropriate to the site of intended use maintaining in an appropriate range. Approaches to overcome these challenges include the selection of adequate alloying elements, proper surface treatment techniques and control of the degradation rate of Mg or its alloys developed as orthopedic implants. To date, Mg or its alloy-based bone implants have not yet been widely used in clinical applications as medical implants. This review critically summarized published methods to improve the corrosion resistance of Mg and its alloys. The current progress on in vitro cytotoxicity and in vivo biocompatibility properties of these metals was also reviewed. This review aimed to provide a reference for further research and development (R&D) of biodegradable Mg and its alloys with regard to the evaluation of their corrosion process and biocompatibility and facilitation of their translation to clinical applications.