Comparative study between microporous and nanoporous TiO₂ layer produced by the electrochemical anodization process on the Ti6Al4V alloy

ABSTRACT

In recent years, techniques aimed at superficial modification of materials used for implants in bone replacement and/or reconstitution have been increasingly improved in order to enhance their osteoinductive and osteoconductive properties, improving their osteointegration. In this work, the surface of the Ti6Al4V alloy was modified through the anodic oxidation electrochemical process in order to change the morphology of its natural layer of titanium dioxide (TiO₂). Two different types of TiO₂ films, with microporous (MP) and nanoporous (NP) characteristics, were produced in order to be evaluated morphologically and biologically. The MP films were obtained from anodizing with H₃PO₄ electrolyte (1.0 mol/L), applying 174 V DC potential, during 5 minutes; and the NP films were produced from anodizing with C₆H₈O₇ electrolyte (0.1 mol/L) + NaF (0.5% w/w), applying 20 V DC potential, during 90 minutes. The morphological and chemical characterization was performed by Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM / EDS), X Ray Diffraction (XRD) and X Ray Fluorescence (XRF). The MPs reached an approximately average diameter of 0.49 µm, randomly distributed on the substrate and the NPs got an average diameter of 73 nm, aligned like parallel nanotubular structures to each other. The NP layer showed to be rougher than the MP. Both films obtained hydrophilic characteristics when measuring the contact angle. After the Simulated Body Fluid (SBF) test, depositions of Ca and P on both films were identified, which may sign the apatite formation on the surface. The MPs and NPs showed evidence of not being cytotoxic through the agar diffusion and macrodilution assays with the resazurin test; the cell adhesion, evaluated with bacterial strain, was morphologically more favorable on the nanoporous surface.

Keywords
Anodic oxidation; microporous; nanoporous; Ti6Al4V; TiO₂ layer