Sol-Gel TiO2 and ZrO2-Nanocomposite Thin Films for Enhancing in Vitro Biocompatibility and Bio-Corrosion Resistance of Ti6Al4V Orthopaedic Implants

Abstract

The aim of this work has been to study the effect of TiO2 and ZrO2-silane sol-gel coatings on the corrosion resistance and biocompatibility of Ti6Al4V biomedical alloys. The sol used for coating was an aqueous solution containing 3-methacryloxypropyltrimethoxysilane (MAPTMS), tetramethoxysilane (TMOS) and titanium tetrabutoxide (TBT) or zirconium tetrabutoxide (ZBT). A system without tetrabutoxides was used as reference. The effect of the addition of different amounts of TiO2 or ZrO2 precursors on the thermal stability of the prepared organic-inorganic hybrids was investigated by using thermal analysis (TG/DTG). Structural characterization of the coatings was carried out using Attenuated Total Reflectance Fourier Transformer Infrared Spectroscopy (ATR-FTIR). Contact angle measurements were used to study the hydrophilicity of the coatings. The thickness of the resulting sol-gel coatings was measured by using a profilometer. Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) were applied to study the surface morphology and composition of the MAPTMS/TMOS/TiO2 and MAPTMS/TMOS/ZrO2 coatings. Global and Local electrochemical Impedance Spectroscopies (EIS and LEIS) and potentiodynamic polarization measurements during immersion in Dulbecco’s Phosphate Buffered Saline with MgCl2 and CaCl2 (PBS) were carried out to evaluate the barrier properties on the coatings. In vitro bioactivity was assessed by soaking the nanocomposite coatings at 36.5ºC up to 14 days in the Kokubo’s simulated body fluid (SBF; pH 7.4). After applying the soaking tests the samples were removed from the SBF, rinsed with ddH2O and dried at room temperature and submitted to analysis by XRD, SEM and EDX. In parallel studies the biocompatibility of these sol-gel coatings has been evaluated. In this way protein adsorption was studied using fibrinogen as a representative protein. Adsorbed protein was determined by applying the Bradford method and ATR-FTIR after immersion the sol-gel thin films in fibrinogen. In summary SEM observations of these coatings showed the formation of a uniform, homogeneous, crack free and highly adherent protective film on the substrates. The electrochemical techniques indicated that the incorporation of TiO2 and ZrO2 nanoparticles in the MAPTMS-TMOS matrix improved the corrosion protection properties of the organic-inorganic hybrid coatings. SEM/EDX analyses showed bone-like precipitates after 14 days of immersion in SBF. XRD detected trace amounts of Ca and P in these precipitates but it was not possible to determine conclusively their nature. The in vitro biocompatibility studies confirmed that these sol-gel thin films can be good candidates to develop coatings for Ti6Al4V orthopaedic implants. Acknowledges: This work was supported by the Ministry of Economy and Competitiveness of Spain (Projects MAT2012-38541-C02-02, MAT2012-30854 and MAT2015-65445-C2-1-R).