Review of the Effects of Rare Earth Element Additions to Magnesium Alloys on Biocompatibility: An Evaluation from Mechanical, Corrosion, and Biological Perspectives

Abstract Rare earth elements (REE), the subject of this study, have become a growing focus of interest in biomaterials research in recent years, particularly in magnesium (Mg) and high-entropy alloys (HEA). These studies demonstrate that the addition of REE’s can significantly improve the microstructure of Mg alloys and, consequently, their mechanical properties, corrosion resistance and biocompatibility. For this reason, a large number of studies conducted in recent years have sought to understand the effects of REE additions on the mechanical properties, corrosion behaviour and biological responses of magnesium alloys. In this review, the effects of rare-earth element additions on the biocompatibility of magnesium alloys have been comprehensively examined in light of recent studies, and current developments and future research directions have been discussed using the review method. This comprehensive review systematically evaluates the effects of REE additions on the microstructural evolution, corrosion behaviour, mechanical performance and biocompatibility of magnesium alloys. An analysis of the latest studies indicates that Mg -REE alloying leads to significant grain refinement, the formation of stable intermetallic phases and an increase in corrosion resistance through the development of more protective surface films; these changes result in increased mechanical strength and more favourable biological responses, including improved cell viability and reduced cytotoxicity. Furthermore, this review highlights that Mg–REE alloys are promising candidates for biodegradable implant applications. Overall, Mg–REE alloys are promising candidates for biodegradable implant applications, as they combine enhanced mechanical integrity, controlled degradation and improved biocompatibility. However, despite these advantages, it has been concluded that further research is required to determine the long-term biological interactions and optimised alloy compositions; future research should therefore focus on in vivo performance and the development of alloy systems optimised for clinical use.