Biodegradable metallic bone implants

Abstract

Biodegradable metals, such as Mg and Mg alloys, Fe and Fe alloys, and Zn and Zn alloys, are drawing increased attention as bone implant materials owing to their biodegradability. Among them, Mg and Mg alloys have similar densities and elastic moduli as compared to those of natural bone, but they degrade too quickly in human physiological environments, resulting in excessive release of hydrogen and premature loss of strength. Fe and Fe alloys are known for their outstanding mechanical properties, while their degradation rates are too slow to meet the requirements of bone repair. In comparison, Zn and Zn alloys have suitable degradation rates when compared with the growth rates of natural bone. However, their poor strength and ductility constrain their applications in bone repair. This review summarizes the current status of research on the use of biodegradable metals in bone implants. Their biodegradability, mechanical properties, and biocompatibility are systematically reviewed. On the basis of presentation, efforts made to improve the deficiencies of these biodegradable metals, such as alloying and heat treatment, are summarized. The problems and further directions are also put forward for biodegradable metallic bone implants.