Biodegradable magnesium implants: From material development to clinical translation

Abstract

Next-generation biodegradable implants aim to provide temporary mechanical support while safely resorbing once healing is complete, thereby eliminating long-term complications associated with permanent fixation devices. Magnesium-based alloys have emerged as the leading biodegradable metallic candidates for this purpose, yet their clinical translation depends on achieving controlled degradation that matches bone healing kinetics. This review traces the evolution of orthopaedic implant materials from permanent metals to biodegradable systems and critically compares Mg-, Zn-, and Fe-based alloys in terms of mechanical performance, degradation behaviour, and biological response. Current evidence indicates that biomedical magnesium alloys can routinely achieve yield strengths of approximately 200–300 MPa, with elastic moduli closer to cortical bone than conventional permanent metallic implants, enabling mechanically reliable temporary fixation. Among biodegradable metals, magnesium is the most clinically advanced system, while zinc- and iron-based alloys remain limited by mechanical and degradation constraints. Advances in alloying with physiologically tolerated elements such as Zn, Ca, Mn, and Si, combined with grain refinement through thermomechanical processing and interfacial stabilisation through bioactive coatings, have significantly improved the predictability of magnesium degradation under physiological conditions. Despite these advances, key challenges remain, including variability in in vivo corrosion behaviour, hydrogen evolution, and inter-patient differences in healing response. Emerging biological evidence indicates that magnesium ions and corrosion products can actively support osteogenesis when degradation is appropriately regulated, whereas rapid or localised corrosion may be detrimental. Overall, magnesium-based alloys represent the most clinically advanced and validated biodegradable metallic system currently applied in orthopaedic implants, with further progress dependent on integrating materials design, processing, surface engineering, and biologically aligned evaluation approaches to enable safe and reliable long-term clinical adoption.