Abstract
The electrochemical behavior of polycrystalline TiO2 anatase coatings prepared by a one-step hydrothermal synthesis on commercially pure (CP) Ti grade 2 and a Ti13Nb13Zr alloy for bone implants was investigated in Hank’s solution at 37.5 °C. The aim was to verify to what extent the in-situ-grown anatase improved the behavior of the substrate in comparison to the bare substrates. Tafel-plot extrapolations from the potentiodynamic curves revealed a substantial improvement in the corrosion potentials for the anatase coatings. Moreover, the coatings grown on titanium also exhibited lower corrosion-current densities, indicating a longer survival of the implant. The results were explained by considering the effects of crystal morphology, coating thickness and porosity. Evidence for the existing porosity was obtained from corrosion and nano-indentation tests. The overall results indicated that the hydrothermally prepared anatase coatings, with the appropriate morphology and surface properties, have attractive prospects for use in medical devices, since better corrosion protection of the implant can be expected.
Highlights
A suitable combination of acceptable bulk mechanical properties and relatively good chemical stability makes titanium and its alloys the most used metals for body implants
In our previous report on hydrothermally grown anatase crystals on titanium substrates [14], we have shown that such nanostructured coatings lead to a crystal morphology and surface topography that result in hydrophilic behavior
The samples were hydrothermally treated under slightly different conditions to form different coatings: the samples Ti-A and Ti-B were prepared using different sources of titanium ions, while different times of hydrothermal treatment (HT) were used in samples Ti13Nb13Zr alloy (TNZ)-C and TNZ-D
Summary
A suitable combination of acceptable bulk mechanical properties and relatively good chemical stability makes titanium and its alloys the most used metals for body implants The inertness of these materials is due to a biocompatible passivation layer of amorphous titanium dioxide, which is naturally formed on the surface [1,2]. This is considered as a protective interlayer between the hosting tissues and the foreign implant, it is too thin (only a few nanometres) and insufficiently stable under the action of body fluids to provide full corrosion protection, so that the bulk material may undergo a slow but lasting release of metal ions in the neighboring tissues. Nano-indentation of the selected anatase coatings was carried out to determine their hardness and elastic modulus
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