Enhanced corrosion resistance and biocompatibility of β-type Ti-25Nb-25Zr alloy by electrochemical anodization

The biocompatibility of implants is largely determined by their surface characteristics. This study presents a novel method for performing electrochemical anodization on β-type Ti-25Nb-25Zr alloy with a low elastic modulus (approximately 70 GPa). This method results in a thin hybrid layer capable of enhancing the surface characteristics of the implants. We investigated the surface topography and microstructure of the resulting Ti-25Nb-25Zr alloy. The corrosion resistance was evaluated using potentiodynamic polarization curve measurements in simulated body fluid. The cytotoxicity was evaluated according to International Organization for Standardization 10993-5 specification. Cell adhesion of human bone marrow mesenchymal stem cells on the test specimens was observed using scanning electron microscopy and fluorescence microscopy. The anodization produced a thin (approximately 40 nm-thick) hybrid oxide layer with a nanoporous outer sublayer (pore size < 15 nm) and a dense inner layer. The thin hybrid oxide layer increased the corrosion resistance of the Ti-25Nb-25Zr alloy by increasing the corrosion potential and decreasing both the corrosion rate and passive current. Ti-25Nb-25Zr alloys with and without anodization treatment were non-toxic. Surface nanotopography on the anodized Ti-25Nb-25Zr alloy enhanced protein adsorption and cell adhesion. Our results demonstrate that electrochemical anodization increases the corrosion resistance and cell adhesion of β-type Ti-25Nb-25Zr alloy while providing a lower elastic modulus suitable for implant applications.