Modifying Ti6Al4V Implant Surfaces: Cell Responses and Corrosion Resistance of Annealed Titania Nanotubes
Grotberg, John C.
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Titanium alloy (Ti-6Al-4V) is often used in orthopedic and dental implants integrated into bone tissue. However, the negative impact of in vivo corrosion of these metallic biomedical implants still remains a complex problem in the medical field. As current surface modifications of this alloy are investigated for potential application as implant materials, it is necessary to characterize these surfaces, understand how they will perform in an in vivo-like environment, and investigate the properties of corrosion resistance under simulated physiological conditions. Surface modifications of interest included the formation of titania nanotubes by anodization, as they have shown promise in providing nanoscale topography for cellular growth as well as drug-loading capabilities, and thermal oxidation, in order to induce thickening of a compact oxide layer as well as changing the crystalline structure. Thus, the primary aim was to determine the effects of electrochemical anodization (60 V, 2h) and thermal oxidation (600° C) on the corrosive behavior of Ti-6Al-4V, with serum proteins, at physiological temperature. Anodization produced a mixture of anatase and amorphous TiO2 nanotubes, while the annealing process yielded an anatase/rutile mixture TiO2 nanotubes. The surface area was analyzed by Brunauer-Emmett-Teller method and was estimated to more than 2 orders of magnitude higher than that of polished control samples. Corrosion resistance was evaluated on the parameters of open circuit potential, corrosion potential, corrosion current density, passivation current density, polarization resistance and equivalent circuit modeling. Samples both anodized and thermally oxidized exhibited shifts of open circuit potential and corrosion potential in the positive direction, indicating a more stable nanotube layer, as well as lower corrosion current densities and passivation current densities than the smooth control. They also showed increased polarization resistance and diffusion limited charge transfer within the bulk oxide layer. However, compared to the amorphous nanotubes, the thermally oxidized nanotubes showed evidence of increased corrosion in anodic regions slightly greater than the corrosion potential, and less favorable passivation behavior. As per the findings, the treatment groups analyzed were ordered from greatest corrosion resistance to least as Anodized+Thermally Oxidized > Anodized > Smooth > Thermally Oxidized.