Biofilm development on carbon nanotube/polymer nanocomposites

Biofilms have the potential to form on polymer nanocomposites containing carbon nanotubes (CNT/PNCs) when they come into contact with microorganisms in aqueous environments post-consumer use. In this study we explored the effect that CNT/PNC surface characteristics have on biofilm development, as compared to the unmodified polymer, under drip flow and static conditions. Specifically, we examined biofilm formation on CNT/PNCs where CNTs are initially present below the PNC surface but accumulate as a result of polymer biodegradation and where CNTs are initially present at the PNC surface. CNT/PNCs composed of oxidized multi-wall CNTs and poly- -caprolactone (PCL), a biodegradable polymer, were prepared and exposed to Pseudomonas aeruginosa ; biofilm development was monitored using LIVE/DEAD staining. As prepared, CNTs were absent at the CNT/PCL surface, giving rise to an initially benign CNT/PCL-microbial interaction, analogous to that observed on PCL. As biofilm development progressed, however, PCL biodegradation caused CNTs to accumulate at the surface leading to an antimicrobial effect and eventually a full (2% w/w CNT) or partial dead (0.5% w/w CNT) layer of microorganisms. At later stages, active biofilm formation occurred on top of a protective layer of dead microorganisms indicating that biofilm growth on CNT/PCL nanocomposites was delayed, but not inhibited. CNTs also accumulated at CNT/PCL surfaces as a result of a simulated weathering process and these surfaces exhibited immediate cytotoxicity. However, "live-on-dead" biofilm formation was still ultimately observed. Qualitatively similar trends of biofilm development were observed under drip flow and static conditions although the structure and rates of biofilm formation differed. Carbon nanotube/polymer nanocomposite surfaces impact biofilm development through the cytotoxic effect of exposed carbon nanotubes on microorganisms.