The enhanced characteristics of osteoblast adhesion to photofunctionalized nanoscale TiO2 layers on biomaterials surfaces

Recently, UV photofunctionalization of titanium has been shown to be effective in enhancing osteogenic environment around this functional surface, in particular for the use of endosseous implants. However, the underlying mechanism remains unknown and its potential application to other tissue engineering materials has never been explored. We determined whether adhesion of a single osteoblast is enhanced on UV-treated nano-thin TiO2 layer with virtually no surface roughness or topographical features. Rat bone marrow-derived osteoblasts were cultured on UV-treated or untreated 200-nm thick TiO2 sputter-coated glass plates. After an incubation of 3 h, the mean critical shear force required to initiate detachment of a single osteoblast was determined to be 1280 ± 430 nN on UV-treated TiO2 surfaces, which was 2.5-fold greater than the force required on untreated TiO2 surfaces. The total energy required to complete the detachment was 37.0 ± 23.2 pJ on UV-treated surfaces, 3.5-fold greater than that required on untreated surfaces. Such substantial increases in single cell adhesion were also observed for osteoblasts cultured for 24 h. Osteoblasts on UV-treated TiO2 surfaces were larger and characterized with increased levels of vinculin expression and focal contact formation. However, the density of vinculin or focal contact was not influenced by UV treatment. In contrast, both total expression and density of actin fibers increased on UV-treated surfaces. Thin layer TiO2 coating and UV treatment of Co–Cr alloy and PTFE membrane synergistically resulted in a significant increase in the ability of cell attachment and osteoblastic production of alkaline phosphatase. These results indicated that the adhesive nature of a single osteoblast is substantially enhanced on UV-treated TiO2 surfaces, providing the first evidence showing that each individual cell attached to these surfaces is substantially more resistant to exogenous load potentially from blood and fluid flow and mechanical force in the initial stage of in vivo biological environment. This enhanced osteoblast adhesion was supported synergistically but disproportionately by enhancement in focal adhesion and cytoskeletal developments. Also, this study demonstrated that UV treatment is effective on nano-thin TiO2 depositioned onto non-Ti materials to enhance their bioactivity, providing a basis for TiO2-mediated photofunctionalization of biomaterials, a new method of developing functional biomaterials.