Effect of photofunctionalization on the aged titanium by using ultraviolet light: Hg-vapor versus light-emitting diode-based irradiation

Ultraviolet C (UVC) mercury-vapor lamps have effectively achieved the decontamination of hydrocarbons and antimicrobial effects on dental implants. This study aimed to compare the effectiveness of photofunctionalization technologies on titanium surface by using two different UVC light sources, mercury-vapor (Hg-vapor, λ = 254 nm) and light-emitting diode (LED, λ = 275 nm) radiators. By exposing aged titanium surface to two UVC light sources, the effect on osseointegration and bacteria and the relevant mechanism was investigated. Results indicated that irradiation with UVC light source on aged titanium surface decreased carbon atom concentration, changed surface from hydrophobic to hydrophilic, consumed oxygen, formed reactive oxygen species, and altered surface potential. Additionally, irradiated groups had increased protein adsorption, changed protein structure, promoted in vitro biomineralization, and significantly enhanced the functions of human bone marrow mesenchymal stem cells. Irradiated groups also had significantly higher bone volume/tissue volume and bone-implant contact after 4-week healing by placing titanium implant in rat maxilla. UV-irradiated titanium surfaces manifested inhibiting facultative anaerobes such as Staphylococcus aureus and Escherichia coli but promoting anaerobes such as Porphyromonas gingivalis . The changes of the physicochemical properties and bioactivities of titanium surface were in a radiation energy-dependent manner. UVC-LED radiator showed similar photofunctionalization abilities as Hg-vapor radiator at similar radiation energies. Therefore, combining with its no mercury, compact design, faster start-up time, and stable output, UVC-LED radiator has the potential to be an alternative source of Hg-vapor for UV-photofunctionalization procedure.