Covalent incorporation of Ag nanoparticles into TiO2 nanotubes on Ti6Al4V by molecular grafting for enhancing antibacterial effect

Silver antibacterial composite coatings were prepared on additive manufactured Ti6Al4V substrates by merging anodic oxidation, molecular grafting, and spray deposition methods. The surface microstructure, composition, elemental characteristics, and antibacterial properties of the composite coatings were obtained. When the anodizing time was varied from 0.5 to 4 h, the results revealed that the average inner diameter of TiO2 nanotubes (TNTs) increased from 19.9 nm to 78 nm and the average wall thickness decreased from 22.9 nm to 12.8 nm, concluding the optimized voltage of 40 V and anodizing time of 1 h. X-ray diffraction spectra depicted that the structure of TNTs transformed to the more stable anatase phase with a small amount of rutile phase after annealing. After molecule grafting, silanes are covalently bonding to the TNTs via amino groups and Si-O-Si networks. With the help of the covalent bonding between Ag and TNTs, the Ag+ release has been slowed down significantly from 1.127 ppm to 0.17 ppm. Bare TNTs show a certain antibacterial effect with an anti-bacterial rate of 57.5% for E. roll and of 50.1% for S. aureus. When the spraying pass for Ag deposition is 10, the prepared AgNPs embedded coatings have significantly improved the antibacterial properties, as the antibacterial efficiencies are 100% for all these silane-modified TNTs surfaces.