Biocompatibility and Anti-microbial Properties of Silver Modified Amorphous Carbon Films

Infection due microbes on implant surfaces has a strong influence on healing and long term viability of dental implants. The prevention and control of biofilms can be achieved by reducing the bacterial adhesion on the surface. The coating of medical devices with silver, or the addition of silver nanoparticles, are two possible ways to prevent device-associated infections. On the other hand, amorphous carbon films, in its different forms and compositions, have been studied as beneficial surface modification for implant materials. However, the bacterial adhesion on these films by oral bacteria in comparison to standard surfaces (Ti and SS) has been seen to be relatively high. In the oral cavity, the microbial ecology is complex and consists of hundreds of bacterial species, and therefore it is recommendable to study bacteria adhesion using various strains. In this work, we tested the biocompatibility and the anti-microbial properties of amorphous carbon films with the addition of silver nanoparticles. The a-C:Ag films were deposited by co-sputtering in an Argon plasma using a target made of graphite with a small piece of pure silver. Biocompatibility tests were performed using osteoblast-like cells (MG63) and included: cell proliferation, alkaline phosphatase specific activity and OPG. The bacterial adhesion test was evaluated after 1, 3 and 7 days of incubation. We used nine oral bacteria strains: Aggregatibacter actinomycetemcomitans serotype b, Actinomyces israelii, Campylobacter rectus, Eikenella corrodens, Fusobacterium nucleatum ss nucleatum, Parvimonas micra, Porphyromonas gingivalis, Prevotella intermedia and Streptococcus sanguinis. The effect of including silver in the a-C films was studied by X-ray Diffraction, Energy Dispersive spectroscopy, Scanning Electron Microscopy. The results showed that the films had silver nanoparticles (40-60 nm) uniformly distributed in the carbon matrix. The silver was crystalline with a maximum content of around 6 at%. The biological tests showed that a-C:Ag films had good biocompatibility properties, allowing the osteoblast to proliferate and produced osteogenic local factors. Concerning the antimicrobial properties of the a-C:Ag films, we did not observe an effect of the silver particles on bacterial adherence after 1 and 3 days of incubation; however, a significant reduction was observed after 7 days, compared to the a-C, Ti films or the bare SS substrate, suggesting that silver nanoparticles have a time-dependent antimicrobial effect.