Emerging magnesium-based biomaterials for orthopedic implantation

Orthopedic implants, such as those made of stainless steel, cobalt (Co)-based alloys and titanium (Ti) alloys, are commonly used to stabilize, protect, improve, replace or regenerate damaged musculoskeletal tissues both anatomically and functionally in millions of bone injury patients. The biggest drawback of these metallic biomaterials is their non-degradability in the body environment. Magnesium (Mg) and magnesium-based alloys are a new generation of degradable implant materials that have attracted great attention in the past 10 years. There are several advantages of magnesium-based alloys for orthopedic application over other metallic biomaterials. First, magnesium is an essential element for many biological activities, including enzymatic reactions, the formation of apatite and bone cell adsorption. Second, their mechanical properties, including density, elastic modulus and compressive yield strength, are much closer to those of natural bone, and, therefore, they can avoid the stress-shielding effect. Third, magnesium alloys can eliminate the necessity of a second surgery to remove permanent bone implants. Recent results show that alloying of magnesium with aluminum (Al), zinc (Zn), calcium (Ca), zirconium (Zr), yttrium (Y) and rare-earth elements can significantly improve its corrosion resistance and mechanical strength. This paper reviews and compares the mechanical properties, corrosion resistance and biocompatibility of currently researched magnesium-based alloys for use in medical implant applications.