Fluorine-incorporated TiO₂ nanotopography enhances adhesion and differentiation through ERK/CREB pathway

This study compared the topography of different titanium surface structures (TiO₂ nanotube and grain) with similar elemental compositions (TiO2 and fluorine [F]) on the Ti surface. High magnification indicated that the surfaces of the control and etching groups were similar to each other in a flat, smooth form. The group anodized for 1 h was observed with TiO₂ nanotubes organized very neatly and regularly. In the group anodized for 30 min after etching, uneven wave and nanopore structures were observed. In addition, MTT assay showed that the F of the surface did not adversely affect cell viability, and the initial cell adhesion was increased in the 2.8% F-incorporated TiO₂ nanograin. At the edge of adherent cells, filopodia were observed in spreading form on the surfaces of the anodizing and two-step processing groups, and they were observed in a branch shape in the control and etching groups. Moreover, cell adhesion molecule and osteogenesis marker expression was increased at the F-incorporated TiO₂ nanostructure. In addition, it was found that the expression of p-extracellular signal-regulated kinase (ERK) and p-cAMP response element-binding protein (CREB) increased in the TiO₂ nanograin with the nanopore surface compared to the micro rough and nanotube surfaces relative to the osteogenic-related gene expression patterns. As a result, this study confirmed that the topographic structure of the surface is more affected by osteogenic differentiation than the pore size and that differentiation by specific surface composition components is by CREB. Thus, the synergy effect of osteogenic differentiation was confirmed by the simultaneous activation of CREB/ERK.