Stable lotus leaf-inspired hierarchical, fluorinated polypropylene surfaces for reduced bacterial adhesion

Polypropylene (PP) is used in a wide variety of medical components, but is susceptible to bacteria surface colonization and biofilm formation, which lead to infections and inflammations. In this study, we report on the micro-/nanostructuring and surface functionalization of PP substrates through various oxygen and fluorine reactive ion etching (RIE) treatments and their effects on wettability and bacteria adhesion. We found that oxygen treatment creates a hydrophilic surface that reduces bacteria adhesion by 68.7% compared to the control, but additional nanostructuring reduces the surface's anti-biofouling properties due to increased microscale roughness and air pockets that reduce the effectiveness of the liquid barrier. We demonstrate that a fluorine etch chemistry may be utilized to create lotus leaf-inspired, low surface energy, hierarchical microstructure/nanofibrils in PP. Due to the low surface energy and hierarchical morphology, the surface exhibits lotus-leaf wetting (high contact angle ~155° and low contact angle hysteresis < 10°) where water droplets easily roll off the surface in contrast to other PP samples. The lotus leaf-inspired hierarchical, fluorinated surfaces exhibit a 99.6% reduction of E. coli cell adhesion compared to untreated PP. These surfaces demonstrate water contact angle stability over a week in contrast to hydrophilic samples, where the contact angle degrades after just a few days. These new surfaces may help reduce the spread of infections from various plastic medical components without the need for the loading of antibacterial agents that eventually deplete from the surface.