Insights into complex nanopillar-bacteria interactions: Roles of nanotopography and bacterial surface proteins

Nanopillared surfaces have emerged as a promising strategy to combat bacterial infections on medical devices. However, the mechanisms for the specific interactions underlying nanopillar-induced rupture of the bacterial cell membrane remain speculative. In this study, we have tested three medically relevant poly(ethylene terephthalate) (PET) nanopillared-surfaces with well-defined nanotopographies against both Gram-negative and Gram-positive bacteria. Focused ion beam scanning electron microscopy (FIB-SEM) and contact mechanics analysis were utilised to understand the nanobiophysical response of the bacterial cell wall to a single nanopillar. Given their importance to bacterial adhesion, the contribution of bacterial surface proteins to nanotopography-mediated cell wall damage was also investigated. We found that, whilst the cell wall deformation was affected by the nanopillar tip diameter, the nanopillar density affected bacterial metabolic activities. Moreover, three different types of bacterial cell envelope deformation were observed, attributed to regulation of the cell wall stress by bacteria to counter the high intrinsic pressure of nanopillars exerted by bacterial surface proteins. Such influences of bacterial surface proteins on antibacterial action of nanopillars have not been previously reported. Our findings will be valuable to the design and fabrication of effective antibacterial surfaces.