Advances in Fe-based bone implants: Accelerated degradation, cytocompatibility and osteogenesis

Degradable iron (Fe)–based alloys and composites have attracted increasing attention as promising materials for bone implants. These alloys exhibit sufficient mechanical strength to provide reliable support during implantation and gradually degrade in parallel with bone tissue healing. This review thoroughly investigates recent advances in degradable Fe-based bone implant materials, primarily focusing on degradability, biocompatibility, and mechanical properties. Specifically, supported by example studies, the following five strategies to accelerate the degradation of Fe were explored: (i) alloying, which lowers electrode potential and generates second phases that promote microgalvanic corrosion; (ii) reinforcing Fe with bioceramics, as Fe–bioceramic composites can introduce surface defects, release hydrogen ions, produce corrosive chloride ions and generate gaseous products that function as expansion agents to crack the dense surface layer; (iii) surface engineering; (iv) micro- and nanostructuring, including heterostructuring, nanolaminating, core-shell structuring; and (v) magnetization. The mechanisms of strengthening through solid-solution hardening and grain refinement, as well as the reduction of elastic modulus via the introduction of porous structures to achieve bone-mimicking mechanical properties, were discussed. Furthermore, the incorporation of manganese, copper, hydroxyapatite, tricalcium phosphate and biphasic calcium phosphate was systematically assessed with respect to cytocompatibility, osteogenesis and in vivo biosafety. Finally, additional animal studies, including histological staining of the main organs and blood chemistry analysis after implantation, were proposed to accelerate the translation of the alloys towards clinical applications in orthopedics. By integrating these strategic advancements and critically evaluating their biological outcomes, this study provides a comprehensive framework that not only reviews current knowledge but also highlights underexplored synergies for next-generation Fe-based implants.