A facile chemical process to form an ultrathin hydroxyapatite layer with a customizable silver-releasing function on a titanium implant.

Abstract

Silver-containing hydroxyapatite (Ag/HAp) layer on a bioinert material provides both bioactive and antibacterial properties; however, the Ag release duration needs to be customized to a patient's age and metabolism for minimizing the toxic effects. Herein, we present a facile chemical process to produce an ultrathin Ag/HAp layer on a Ti implant with a customized Ag-releasing profile. The process involves the following steps: preparation of a slurry-type reagent by mixing calcium phosphate powder with an aqueous AgNO₃ solution, burying a Ti substrate in the slurry, and heating the slurry in air. An HAp layer, approximately 50 nm thick, with Ag particle deposits was obtained using this process. The Ag-particle content can be varied by adjusting the concentration of AgNO₃ solution used for slurry preparation, resulting in different Ag-release profiles in a physiological solution. For instance, Ag release was retained for up to 30 days when 100 mM AgNO₃ was used, whereas the release lasted 15 days when 10 mM AgNO₃ was used. The duration of the antibacterial activity varied accordingly, but Ag-release-derived cytotoxicity was not observed irrespective of the AgNO₃ concentration. In addition, differentiation of osteoblast-like cells was facilitated owing to the formation of the HAp layer. Thus, the chemical process presented in this study allows the production-at a clinical site-of an Ag/HAp layer customized to the patient's needs.