Copper-coated carbon-infiltrated carbon nanotube surfaces effectively inhibit Staphylococcus aureus and Pseudomonas aeruginosa biofilm formation

ABSTRACT Implant-associated infections caused by Staphylococcus aureus are a growing problem for healthcare systems. Implant materials that resist bacterial colonization may help reduce infection rates and severity. This research examined the effect of a copper-coated carbon-infiltrated carbon nanotube surface (Cu-CICNT). We have previously shown that CICNT without copper has an anti-biofilm effect, and copper has long been known to have anti-bacterial properties. Bacterial biofilms were grown in a droplet on the Cu-CICNT surface, and a control consisting of copper deposited on a relatively flat, non-nanotube-structured surface. The Cu-CICNT surface was highly effective at reducing biofilm formation, reducing recoverable S. aureus bacteria by 99.9999% in 12 hours (a 6.3-log reduction). This effect was confirmed in both a methicillin-resistant and a methicillin-sensitive isolate of S. aureus . The Cu-CICNT surface was also highly effective against Pseudomonas aeruginosa , resulting in a 6.9-log reduction in adherent bacteria. The Cu-CICNT surface was more effective at inhibiting biofilm formation than the flat copper-coated titanium, indicating a synergistic effect between the CICNT topography and copper. The concentration of copper ions in growth media was low after exposure to Cu-CICNT (6.2 ppm), and media with this amount of supplemented copper had only a small effect on biofilm reduction, as did conditioned media previously exposed to Cu-CICNT. Our findings suggest that the antibacterial effect is likely due to contact killing of bacteria on the textured copper surface. IMPORTANCE Orthopedic implants and devices are becoming increasingly common. Unfortunately, as their use increases, so does the prevalence of implant-associated infections. These infections are most commonly caused by the bacterium Staphylococcus aureus. S. aureus infections are particularly difficult to treat because they form biofilms resistant to antibiotics and the host immune system. In this research, we used a carbon nanotube-based surface combined with a thin film of copper to produce a surface coating that could be used on implants to prevent bacterial infection. The combination of the surface topography with the copper coating resulted in over a 6-log reduction in the number of adherent bacteria, preventing the formation of a bacterial biofilm. This reduction in adherent bacteria is likely due to the surface killing effects of the bacteria on contact. The potential applications of such a surface could help reduce infection burden, improve patient quality of life, and reduce stress on healthcare systems.