Magnesium based implants for functional bone tissue regeneration – A review

Magnesium (Mg) has emerged as one of the third-generation biomaterials for regeneration and support of functional bone tissue. Mg is a better choice over permanent implants such as titanium, stainless steel, cobalt-chrome as magnesium is biodegradable and does not require a second surgery for its removal after bone tissue recovery. It also reduces the risk of stress shielding as its elastic modulus is closer to human bone in comparison to permanent implants and other biodegradable metallic implants based on Iron and Zinc. Most importantly, Mg is osteoconductive thus stimulates new bone formation and possess anti-bacterial properties hence reducing the risk of failure due to infection. Despite its advantages, a major concern with pure Mg is its rapid bio-corrosion in presence of body fluids due to which the mechanical integrity of the implant deteriorates before healing of the tissue is complete. Mechanical properties of Mg-based implants can be enhanced by mechanical processing, alloying, and topology optimization. To reduce the corrosion/degradation rate, Mg has been alloyed with metals, reinforced with ceramics, and surface coatings have been applied so that the degradation rate of Mg-based implant matches with that of healing rate of bone tissue. The present review discusses the effect of alloying elements and reinforcing ceramics on microstructure, mechanical, and corrosion properties of Mg-based orthopedic implants. In addition, the biocompatibility of Mg-based alloys, composites, and coatings applied on Mg implants has been highlighted. Further, different methods of fabricating porous implants have been highlighted as making the implant porous facilitates the growth of new bone tissue through the pores.