Effects of magnesium alloy corrosion on biological response-Perspectives of metal-cell interaction

Mg alloys are biodegradable metals widely used in orthopedic and cardiovascular applications because Mg ions are essential trace elements known to induce angiogenesis and osteogenesis. The corrosion behavior of Mg alloys is usually assessed both in vitro and in vivo; however, the inconsistency between in vitro and in vivo results cannot predict the clinical outcome, giving challenges in designing and fabricating biomaterials. Thus, the systematical understanding of the biological performance of Mg is the key foundation by studying the bio-interaction between metals and cells. Like all metals, Mg corrosion involves the oxidation of the metal and the reduction of oxidizing species like water and oxygen. While OH- and H2 are recognized as the byproducts of reduction reactions, reactive intermediate species (RIS) are often neglected. Numerous reduction reactions can occur in biology, depending on the presence of immune cells and redox-based biomolecules. Furthermore, the reduction can significantly change the cell/tis-sue response near the metal surface, depending on the corrosion rate. Hence, Mg corrosion is a complex, multi-factor phenomenon based on solution-chemistry parameters and metal-cell/ metal-biomolecule interactions, among many. Therefore, this review paper discusses the elec-trochemical and biological factors affecting the corrosion of Mg. Metal corrosion affects biology, and biology affects metal corrosion.