Mechanical, structural, and biological evaluation of multilayer HA-Ag/TiO2/TiN/Ti coatings on Ti6Al4V obtained by magnetron sputtering for implant applications

Abstract

In the present work the surface of Ti6Al4V alloy, widely used for the fabrication of implants, was modified by incorporating a novel biocompatible and antibacterial coating composed of multiple layers of hydroxyapatite (HA) and Ag deposited on a TiO2/TiN/Ti trilayer. During the characterization of the coatings, their chemical and phase compositions were evaluated by energy dispersive X-ray spectroscopy and X-ray diffraction. Structural, topographical, and morphological studies were performed by focused ion beam, field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. Mechanical properties were determined by nano indentation and micro scratch test. Finally, the in vitro biological response was evaluated by cell viability tests with mouse mesenchymal stem cells, while bacterial viability was evaluated with Staphylococcus aureus strain. The results obtained show great chemical and compositional control, identifying HA (Ca/P close to 1.67) and anatase phases for TiO2. Additionally, an architecture composed of nanometric layers forming a HA-Ag/TiO2/TiN/Ti coating with granular morphology was obtained. The incorporation of multiple Ag layers in the HA structure led to a decrease of about 44 % in its hardness, obtaining values of up to 6.3 GPa. Meanwhile, there was a relief in the residual stresses of >50 %, which generated increases of up to 74 % in the adhesion of the coatings to the substrate The biological tests showed that biocompatible coatings with high antibacterial potential were obtained.