The oxidation state of Ag nanoparticles highly affects the release of Ag ions without compromising the mechanical performance and the safety of amorphous hydrogenated carbon coatings

Abstract

Antibacterial coatings play an important adjunct against hospital-acquired infections. More specifically, the use of silver nanoparticles (Ag NPs) incorporated on amorphous hydrogenated carbon (a-C:H) demonstrates a promising approach to reduce microbial contamination while maintaining excellent mechanical properties. However, their success as a long-term (e.g. years) antibacterial coating hinges on the control over Ag+ release. In this sense, if a continuous release is required, a driving force must exist to induce silver ionization. Thus, this research studies the influence of silver oxide (AgO) NPs in a-C:H film as a novel and a simple approach to activate the release of Ag+. Herein, Ag and AgO NPs were deposited on a-C:H films (with 2.8 and 2.5 at.% Ag, respectively) using low-pressure plasma. Their mechanical properties, release kinetics, and antibacterial activity were analyzed, with special attention to cell viability. Overall, a-C:H:Ag showed an increase in hardness, whereas a-C:H:AgO exhibited ameliorated mechanical properties with higher elastic deformation and wear resistance. Moreover, the coatings did not induce any cytotoxicity after 7 days. Regarding the release kinetics, a-C:H:Ag displayed a slow-release reaching a maximum of 22 μg/L, while a-C:H:AgO showed a fast continuous-release with a maximum of 148 μg/L. In this sense, a-C:H:AgO exhibited improved antibacterial activity in comparison with a-C:H:Ag. The use of AgO NPs in a-C:H film demonstrated to be a simple approach to activate the release of Ag+, without compromising the mechanical and the cytotoxic properties of the coating. These results highlight a new pathway towards coatings with lasting antibacterial and mechanical stability.