Bioactive and electrochemical characterization of TiO2 nanotubes on titanium via anodic oxidation

The selection of bioactive and electrochemically stable materials for implants having effective corrosion resistance during long-term use in the body is essential. In this study, the bioactive and electrochemical properties of titanium implant materials with a nanotube surface treatment and various types of post-treatments were examined. Two types of amorphous TiO₂ nanotubes were grown homogeneously on the surface: one with a larger diameter (approximately 85 nm) and one with a smaller diameter (approximately 50 nm). Amorphous TiO₂ nanotubes were partially crystallized to anatase and rutile by heat treatment at 500 °C for 2 h. The corrosion potential (E_corr) of the heat-treated sample (HT) had a novel value of 0.102 V due to the stable TiO₂ crystal phase compared to the −0.106 V observed in the anodic oxidation sample (AN). The corrosion current density (I_corr) ranged from 0.20 to 0.64 μA/cm² according to the post-treatment conditions. However, at 0.6 V, where a passive layer had formed, the corrosion resistance of the HT was approximately ten times that of the AN and untreated (UT) samples. After evaluating the hydroxyapatite (HA)-forming ability by immersion in a simulated body fluid (SBF) solution, the CP process induced the adsorption of Ca and P onto HT. A comparison of the time-dependent amount of Ca and P adsorption showed that Ca adsorption plays a role in determining the rate at which hydroxyapatite (HA) is formed. For the induction of HA formation, a level of Ca adsorption above a critical level is required.