Sustainable metallic biomaterials for orthopaedic implants: a comprehensive review of biodegradable and conventional metals

The selection of biomaterial is crucial for the long-term success of implants. Materials that perform an adequate function and reduce negative biological responses should be taken. Due to their good mechanical strength, stainless steel, titanium, and Co-based alloys have been utilized for implant purposes; however, their permanent nature and very low corrosion rates may lead to long-term clinical complications. Researchers are looking for biomaterials that combine suitable mechanical properties with controlled and uniform degradation behavior. In the last decade, magnesium and iron-based alloys have been seen as a good alternative and examined as promising biodegradable metals for implant applications. However, their excessively rapid corrosion (Mg) or extremely slow degradation (Fe) imposes significant limitations on their clinical applicability. In recent times, zinc-based alloys have been seen as new materials that will challenge magnesium and iron-based alloys. Zn2+ ions released from zinc metal corrosion play a crucial role in bone metabolism, enzymatic activity, and cellular proliferation. However, the low mechanical strength and limited ductility of pure zinc restrict its direct utilization in load-bearing implants. Therefore, the fabrication of high-strength and ductile zinc-based alloys while maintaining biocompatibility and suitable corrosion rate remains a main research challenge. This article critically assesses and compares the mechanical properties, corrosion behavior, and biocompatibility of magnesium-, zinc-, and titanium-based alloys, and inspects the impact of advanced fabrication methods, particularly additive manufacturing, on microstructure evolution and implant performance.