Synergistic effect of crystalline phase on protein adsorption and cell behaviors on TiO 2 nanotubes

The objective of this study is to explore the structure–property relationships of TiO2 nanotubes (TNTs) with different crystalline phases that link to protein adsorption and cell responses. Given the formation of intact rutile nanotubular structures by furnace annealing is challenge, a combination of furnace annealing and flame annealing is employed for the preparation of rutile TNTs. TNTs with pure anatase phase and mixed anatase/rutile phases are obtained by simple furnace annealing of amorphous TNTs. Results show that BSA and FBS adsorptions are greatly enhanced on rutile TNTs, whereas no discernable difference on other crystalline phases. Rutile TNTs also present highest adsorption of fibronectin and collagen which are diminished on anatase and dual anatase–rutile phases. Interestingly, however, there is no significant difference in cell proliferation or differentiation on TNTs with different crystallites. Scrutinization of the surface properties involved in protein adsorption and cell activities, a synergistic effect of surface charge, hydroxyl groups, and roughness is found on protein adsorption which further regulates cell behaviors. Those findings provide a better understanding of the structure–property relationships of titanium-based biomaterials.