Micropatterned TiO2 nanotube surfaces for site-selective nucleation of hydroxyapatite from simulated body fluid

TiO2 nanotube layers can provide greatly enhanced kinetics for hydroxyapatite formation from simulated body fluid compared with smooth, compact TiO2 surfaces. In the present work we show how this contrast in reactivity can be used to create highly defined lateral microstructures where bone-like hydroxyapatite can be deposited with very high selectivity. For this we used a photolithographic approach to produce micropatterned TiO2 nanotube layers surrounded by compact oxide that were then immersed in a simulated body fluid (SBF) solution. Not only the tubular vs. flat geometry but also the finding that compact oxides created in phosphate electrolytes in particular suppress apatite deposition are crucial for a very high reactivity contrast. Overall the results show the feasibility of stimulating hydroxyapatite deposition at surface locations where needed or desired. This provides a valuable tool for biomedical device design.