Lotus-leaf-inspired hierarchical structured surface with non-fouling and mechanical bactericidal performances

Antibiotics, a power tool to combat pathogenic bacterial infection, have experienced their inability to kill drug-resistant bacteria due to the development of antibiotic resistance. As an alternative, nanostructured, mechanical bactericidal surfaces may hold promise in killing bacteria without triggering antimicrobial resistance; however, accumulation of dead bacteria would greatly reduce their antimicrobial activity. In this study, for the first time we report a surprising discovery that the lotus leaf, well known for its superhydrophobicity, has demonstrated not only strong repelling effect against bacteria but also bactericidal activity via a cell-rupturing mechanism. Inspired by this unexpected finding, we subsequently designed and prepared a hierarchically structured surface, which was rendered superhydrophobic (water contact angle: 174 degrees; roll-off angle:< 1 degrees) upon surface perfluorination. The hierarchically structured surface has displayed remarkable synergistic antimicrobial activity against Escherichia coli: while the majority of the bacteria (> 99%) were repelled from the surface (non-fouling), those tenacious bacteria that managed to be in touch of the surface were physically killed completely. Compared to a conventional superhydrophobic surface (non-fouling to some extent, but no bacteria-killing) or a mechanical bactericidal surface (bacteria-killing but not bacteria-repelling), our new structured surface has the great advantage in maintaining long-term effectiveness in antimicrobial activity based entirely on physical mechanism.