The effect of annealing temperatures on surface properties, hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well-ordered TiO2 nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH4F and 10 wt% H2O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 degrees C, while rutile formation was observed at 600 degrees C. Disintegration of the nanotubes was observed at 600 degrees C and the structure vanished completely at 750 degrees C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as-formed nanotubes. The growth of hydroxyapatite on the different TiO2 nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO2 nanotubes annealed at 600 degrees C. Copyright (C) 2010 John Wiley & Sons, Ltd.