Photo-induced hydrophilicity enhances initial cell behavior and early bone apposition

Objective: The anatase form of titanium dioxide (TiO₂) exhibits photo‐induced hydrophilicity when it is irradiated with ultraviolet (UV) light. In the present study, the effect of photo‐induced hydrophilicity on initial cell behavior and bone formation was evaluated. Materials and methods: Plasma source ion implantation method and post‐annealing were employed for coating the anatase form of TiO₂ to the surface of the titanium disk and implant. Half of the disks and implants were illuminated with UV for 24 h beforehand, whereas the other halves were blinded and used as controls. Photo‐induced hydrophilicity was confirmed by a static wettability assay. The effects of this hydrophilicity on cell behavior were evaluated by means of cell attachment, proliferation and morphology using pluripotent mesenchymal precursor C2C12 cells. Thereafter, bone formation around the hydrophilic implant inserted in the rabbit tibia was confirmed histomorphometrically. Results: The water contact angle of the photo‐induced hydrophilic disk decreased markedly from 43.5° to 0.5°. Cell attachment and proliferation on this hydrophilic disk showed significant improvement. The cell morphology on this hydrophilic disk was extremely flattened, with an elongation of the lamellipodia, whereas a round/spherical morphology was observed on the control disk. The photo‐induced hydrophilic implant enhanced the bone formation with the bone‐to‐metal contact of 28.2% after 2 weeks of healing (control: 17.97%). Conclusion: The photo‐induced hydrophilic surface used in the current study improves the initial cell reactions and enhances early bone apposition to the implant.