Mg-based biodegradable alloys for orthopedic implants - A review

Traditional metallic biomaterials for orthopedic implants require materials exhibiting excellent corrosion resistance in human body. Recently, implants made of biodegradable metallic materials are thought to be potential for orthopedic implant applications as they can circumvent revision surgeries. These implants are considered as the third generation implants as they are expected to provide adequate mechanical strength to support the bone during restoration; have excellent in vivo biocompatibility and controlled degradation rate. These implants would degrade within the body after completing its mission without leaving any residues within the body. Biocompatible elements like Mg, Fe and Zn and their alloys have been considered for bone implant applications due to their biodegradability. Amongst these, Mg alloys are preferred due its high specific strength, low elastic modulus that are close to human bone and low density minimizing the risk of stress shielding. However, Mg alloys have fast degradation rate in biological fluids leading to the release of hydrogen which would lead to premature failure of implants. This paper reviews the research efforts towards the development of Mg-based biodegradable alloys for orthopedic implants. Concepts followed in designing Mg-based biodegradable alloys, the mechanical properties of developed Mg-based alloys, degradation mechanism of Mg-based alloys and the efforts to reduce the degradation rate, and status of Mg-based alloys in orthopedic applications are compiled along with the existing problems and future research directions