and antibacterial properties are low, which limits their medical application. Therefore, to improve these challenges in this study, HAp + 15 wt% TiO2 + 5 wt% Ag nanocomposite coating was applied on Ti6Al4V/TiO2 substrate by sol-gel dip method and sintered at 550 ◦C. The TiO2 layer was pre-formed on the Ti6Al4V substrate using the gel-sol process. The results showed that the nanocomposite was synthesized correctly, and the particle size was in range of 40–90 nm. The evaluation of the coatings developed showed that TiO2/HAp + 15 wt% TiO2 + 5 wt% Ag coating had higher adhesion strength (20.5 MPa), hardness (5.2 GPa), and elastic modulus (110.6 GPa) than pure hydroxyapatite coatings. The results of polarization test showed that nanocomposite coating TiO2/HAp + 15 wt% TiO2 + 5 wt% Ag has the lowest corrosion current density (0.22 μA/cm2). Also, this coating has the largest semicircular diameter in Nyquist curves, which indicates the improved corrosion resistance of this coating compared to other coatings.The inhibition zone diameter for this coating is 21 mm and kills 98.9% of E. coli bacteria. The MTT assay results showed that human MG63 cells in contact with HAp/TiO2/Ag nanocomposite coating had the highest biocompatibility (98.8% of cells survived). Therefore, the development of TiO2/HAp + 15 wt% TiO2 + 5 wt% Ag nanocomposite coating on Ti6Al4V/TiO2 substrate significantly increases the mechanical properties, corrosion resistance, antibacterial activity, and biocompatibility properties of hydroxyapatite coatings
