Bio-Inspired Polymer Thin Films with Non-Close-Packed Nanopillars for Enhanced Bactericidal and Antireflective Properties

The perpetual health and safety concerns caused by bacterial adhesion on surfaces demand the development of next-generation antibacterial materials. Inspired by bactericidal surfaces on cicada wings with protrusive nanostructures, which induce mechanical rupture of adhered bacterial membranes without antibacterial, chemical treatments, analogous structures have been fabricated on various synthetic materials to achieve such mechanical bactericidal efficacy. Herein, we developed a series of protrusive nanopillars on hard silicon (Si) substrates and soft poly(ethylene glycol) diacrylate (PEGDA) thin films by colloidal lithography. We first investigated the correlation of interpillar distance and bactericidal efficacy against a model Gram-negative bacterium, Escherichia coli, using Si surfaces with different nanopillar number densities. We demonstrated that the bactericidal efficacy increased with decreasing nanopillar number density, which occurred when the average interpillar distance was smaller than the cell size. The bactericidal efficacy decreases when the average interpillar distance becomes larger than the comparable size of bacteria. We then designed PEGDA thin films with optimized bactericidal nanopillar density to improve their antibacterial and antireflective performance. The results indicate that the surface nanostructure plays a critical role in dictating antibacterial performance, regardless of the material type. This work provides insight into the understanding of physical interactions between nanostructured surfaces and bacterial cells as well as practical solutions for the development of antibacterial polymer surfaces for the application of optical lenses or screen displays to prevent public pathogenic infections.