Antibacterial Functionalization of Ti-based Biomaterials Based on the Understanding of the Inactivation Mechanisms of Bacteria via Photocatalytic Activity of Titanium Oxide: Visible-light Responsive Reaction of Titanium Oxide Coating

Dental implants are made by Ti and its alloys because of their excellent mechanical property, corrosion resistance, and biocompatibility. Since the dental implant is a transdermal device, it is exposed to bacteria in the oral cavity. For the long-term survival of dental implants, antibacterial activity is also required. In this manuscript, the antibacterial surface treatment of dental implants was reviewed. Among the antibacterial treatment of Ti dental implants, the photocatalytic activity of titanium dioxide (TiO₂) was focused and the inactivation mechanisms of bacteria via photocatalytic TiO₂, visible-light responsive mechanisms of TiO₂, and development of visible-light responsive TiO₂ layers by the thermal oxidation of Ti-Au alloys were introduced. Au was introduced into the TiO₂ layers on Ti-Au alloys after the oxidation in air and existed as both metallic Au nanoparticles and dissolved Au³⁺ ions. The TiO₂ layers containing Au exhibited visible-light photocatalytic activity against Escherichia coli. These visible-light activities were attributed to the surface plasmon resonance of metallic Au nanoparticles and the decrease in bandgap energy caused by dissolved Au³⁺ ions. The formation of hydroxyl radicals observed under visible-light irradiation is attributable to antibacterial activity.