This review summarizes the current research status on biodegradable metals as bone implants, including their biodegradability, mechanical properties, and biocompatibility.

Iron (Fe) has been highly anticipated as a bone implant material owing to the biodegradability and excellent mechanical properties, but limited by the slow degradation and poor bioactivity. In this study, novel Fe-palladium (Pd)-bredigite biocomposites were developed by selective laser melting aiming to improve both the degradation behavior and bioactivity of Fe. The results showed that most Pd formed Pd-rich intermetallic phases (IMPs) with a nearly continuous network while the bredigite phase was distributed at the grain boundaries. In addition, a large amount of much nobler IMPs formed micro-galvanic pairs with the Fe matrix, inducing tremendous micro-galvanic corrosion. The IMPs contained a high amount of Pd2+ with a high reduction potential, which further promoted the efficiency of micro-galvanic corrosion. Moreover, the rapid degradation of bredigite also facilitated the penetration of the corrosion medium. As a result, the Fe-4Pd-5bredigite biocomposite showed a uniform degradation with a rate that is 6 times that of Fe. Furthermore, the developed Fe-Pd-bredigite biocomposites also featured excellent bioactivity, cytocompatibility, and suitable mechanical properties as characterized by the rapid apatite deposition, normal proliferation of human osteoblast-like cells (MG-63), and comparable strength and microhardness with the native bone. Overall, this study opens a new avenue for improving both the degradation and bioactivity of Fe-based composites and may facilitate their applications as biodegradable implants for tissue/organ repair.