Antibacterial surface design of biomedical titanium materials for orthopedic applications

Titanium (Ti) and titanium alloys have become widely used as biomedical materials in orthopedics because of their good machinability, corrosion resistance, low elastic modulus and excellent biocompatibility. However, when Ti-based implants are used for bone repair and replacement, they are easy to cause bacteria adhesion and aggregation, which leads to postoperative infection. In addition, Ti and its alloys, as bio-inert materials, cannot induce desirable tissue responses such as osseointegration after implantation, which will eventually lead to implant loosening. Postoperative bacterial infection and lack of osseointegration directly lead to the failure of implantation surgery and are not conductive to the long-term service of titanium-based implants. Recently, researchers have made many attempts to focus on the surface modification of multifunctional Ti-based implants to endow them with both antibacterial activity and simultaneous osteoinductive property. In this review, we primarily highlighted the recent progresses in the surface design of Ti implants with both antimicrobial and osteoinductive properties for orthopedic applications. First, the challenges for treating implant-associated infections were briefly introduced such as the emergence of antibiotic resistance, the formation of biofilms, and the construction of cell-selective surfaces. Some of the essential fundamentals were concisely introduced to address these emerging challenges. Next, we intended to elaborate the potential strategies of multifunctional surface design to endow good osseointegration for antibacterial Ti implants and highlighted the recent advances of the implants. We hope that this review will provide theoretical basis and technical support for the development of new Ti implant with antibacterial and osteogenic functions.