Fabrication of titanium-based alloys with bioactive surface oxide layer as biomedical implants: Opportunity and challenges

Titanium and its alloys have long been used as implant materials due to their outstanding mechanical properties and apparent biocompatibility. Despite this, the search for better alloys has continued to be active by researchers and industries alike, as there are still pressing issues that require attention. These include (1) a large mismatch in the elastic modulus of the implant material, which causes a stress shielding problem; (2) the release of harmful ions from Ti alloys after long-term use; (3) a low bioactivity of the Ti alloy surface, which prolongs the healing process. More research has been directed toward finding new generation Ti alloys composed of more biocompatible phases and modifying the surface of Ti alloys from naturally bio-inert to bioactive in order to circumvent the problems. This review examines recent work reported on the fabrication of Ti alloys, and based on the survey, major characteristics highlighted the importance of elastic modulus and the use of non-toxic metal elements to improve biocompatibility. In terms of surface modification of Ti alloys, numerous studies have found that a nano-scaled surface oxide layer grown on the surface is always beneficial to improving the bioactivity of Ti alloys for rapid recovery after implantation. This comprehensive review focuses on the appropriate phase and composition for new Ti alloys intended for use as biomedical implants, emphasizing both fabrication and surface modification methods.