Fabrication of Ag and Ta co-doped amorphous calcium phosphate coating films by radiofrequency magnetron sputtering and their antibacterial activity

Coating of amorphous calcium phosphate (ACP) on titanium (Ti) implants is a promising technique for enhancing bone-forming ability because of its dissolution in vivo. Surgical site infection is one of the serious complications associated with implant devices. In order to achieve both the antibacterial properties and bone-forming ability on the surface of Ti implants, Ag-doped ACP coating films were fabricated. The ACP coating film is expected to work as a carrier of Ag. Ta was added to suppress the dissolution rate of the Ag-ACP coating films, which expands its potential applications. Ag and Ta co-doped ACP coating films were fabricated on Ti substrates by radiofrequency (RF) magnetron sputtering. The sputtering targets were hot-pressed sintered compacts with the same Ag concentration of 10 mol% and varying Ta concentration (0, 0.8, and 8.0 mol%), while the RF power was changed from 8 to 50 W. With increasing RF power, Ag concentration in the coating films decreased. The fabricated ACP coating films were dense and smooth, with their constituent elements (P, Ca, Ag, and Ta) distributed homogeneously along the depth direction. In addition, Ag existed as ions in the ACP regardless of Ta concentration. We clarified for the first time that the dissolution of Ag-containing ACP coating films in solution was suppressed by a Ta addition. Antibacterial activity was obtained from the release of Ag⁺ ions through continuous dissolution of Ag and Ta co-doped ACP coating films.