Enhanced Antibacterial Capability and Corrosion Resistance of Ti6Al4V Implant Coated with ZrO2/Organosilica Nanocomposite Sol-Gel Films

Abstract

Ti6Al4V is one of the most commonly used biomaterials in orthopedic applications due to its interesting mechanical properties, corrosion resistance and reasonable biocompatibility, which derive from a compact, thin, and chemically stable oxide film that spontaneously develops on these materials surface able to minimize ion release. Despite these advantages, a post-operative serious and unresolved problem leading to the failure of the implant is the appearance of implant-associated infections. For this reason, the ability to control microbial adhesion is of importance in healthcare, particularly in modern surgery where postoperative implant associated infections are still an unresolved and serious complication. As a proof of concept, we have assessed the antibacterial behaviour of Ti6Al4V surfaces modified by organic-inorganic hybrid sol-gel films with different loading of ZrO2 nanoparticles. The starting organosilica sol was prepared using a mixture of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethyl orthosilicate (TMOS). Tetrabutoxyzirconium (TBZ) was used as precursor of ZrO2 nanoparticles. Sol-gel films with variable contents of TBZ (0.2—1.0 wt.%) have been tested. The thermal stability of the resulting sol-gel films was studied by using thermal analysis (TG/DTG). Structural characterization of the films was carried out using Attenuated Total Reflectance Fourier transformer Infrared spectroscopy (ATR-FTIR). Surface morphology and composition of coated samples have been analized by Optical and Scanning Electron Microscopy coupled with Energy Dispersive X-ray (OM and SEM/EDX) both before and after the corrosion tests were carried out. The evaluation of the barrier properties on the films and corrosion behaviour of the Ti6Al4V were carried out using Global and Local Electrochemical Impedance Spectroscopy (EIS/LEIS) during immersion in a simulated body fluid (SBF). Regarding bacterial adhesion, two representative strains of the vast majority of nosocomial infections related to orthopedic implants, i.e., Staphylococcus aureus and Staphylococcus epidermidis, were used. Optical and scanning electron microscopies observations have shown the formation of a uniform, homogeneous, crack free and highly adherent protective film on the Ti6Al4V substrates. The electrochemical studies and bacterial adhesion assessments have shown that the incorporation of ZrO2 in MAPTMS/TMOS matrix of the sol-gel films enhance their corrosion protection behaviour and antibacterial capability. Studies on the optimization of the sol-gel formulation to obtain the films with the best antibacterial capability without compromising their good corrosion resistance using different ZrO2 doses are in progress. Acknowledgments The authors would like to acknowledge financial support from the Ministry of Economy of Spain (MAT2015-65445-C2-1-R and MAT2015-63974-C4-3 Projects). M-ERA.NET PCIN-2016-146; Spanish “Junta de Extremadura” and FEDER for the projects IB16117, TE-0016-18 and GR15089