Photofunctionalizing effects of hydroxyapatite combined with TiO₂ on bone regeneration in rabbit calvarial defects

The hydrophilicity of bone graft material generally used as a carrier can play an important role in regulating bone morphogenetic protein (BMP) expression at the bone graft site. The hydrophilicity, altering physicochemical properties, and enhancing biological capabilities, can be increased via surface modification through ultraviolet (UV) photofunctionalization and the effect on de novo osteogenesis could be further improved. Therefore, this study aimed to assess the effects of UV-irradiated TiO₂-coated hydroxyapatite (HA) in combination with rhBMP-2 on bone regeneration in rabbit calvarial defects. The hydrophilicity of HA and TiO₂-coated HA pellets was evaluated by measuring the contact angle of water droplets with UV irradiation. To compare de novo osteogenesis in rabbit calvarial defects, the rabbits were segregated into four different groups: negative control, HA, TiO₂-coated HA, and TiO₂-coated HA with UV; histomorphometric analysis and micro-computed tomography (μCT) imaging were performed after 4 and 8 weeks. In vivo analysis revealed that de novo osteogenesis occurred on the critical size defects in all groups and was significantly increased in the TiO₂-coated HA with UV group than in other groups (p < 0.05). The present results indicate that UV photofunctionalization promotes de novo osteogenesis.