Electrochemical behaviour and bioactivity of self-organized TiO2 nanotube arrays on Ti-6Al-4V in Hanks’ solution for biomedical applications

In the present work, the formation of self-organized titanium oxide nanotube layer by anodic oxidation on titanium alloy Ti-6Al-4V and its influence on growth of apatite on Ti-6Al-4V is reported. Anodization was carried out in sulfuric acid and hydrofluoric acid containing electrolyte and the anodized surface was characterized by micro-Raman, XRD and FESEM. The corrosion behavior of the anodized sample was investigated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in simulated body fluid (Hanks’ solution). The influence of TiO2 nano tubes on the growth of apatite on the anodized sample was investigated by immersion in Hanks’ solution for 1 and 7 days. The investigations show that the native oxide on the sample is replaced by self assembled nanotube array by anodization. The anodic oxide consist both anatase and rutile. After vacuum annealing at 600 °C, intensity of rutile peak increased. FESEM of samples annealed at 450 °C show tubular morphology whereas those annealed at 600 °C show collapse of nano tubes. Corrosion resistance of the anodized sample was comparable with that of the untreated samples. Electrochemical impedance data of the substrate was fitted with two time constant equivalent circuit and that of anodized samples with three time constant equivalent circuit. FESEM images of immersed samples show that the growth of apatite is more with larger sized deposits on anodized surface as compared to that on the untreated substrate. XPS investigation of immersed sample shows presences of calcium, phosphorous and oxygen in hydroxide/phosphate form on the anodized sample.