Morphological and mechanical variations in E. coli induced by PMMA nanostructures patterned via electron beam lithography: An atomic force microscopy study

Nanostructured antibacterial surfaces have recently gained significant interest for their ability to mechanically disrupt bacterial cells and reduce populations. This study presents an efficient method for fabricating PMMA nanostructures using Electron Beam Lithography, focusing on nanograting and nanopillar arrays with pitches ranging from 160 to 200 nm. Atomic Force Microscopy was employed to characterize these structures. The antibacterial efficacy was assessed against Escherichia coli revealing a significant reduction in bacterial adhesion, grown on the nanostructures compared to the flat PMMA surfaces, with the nanopillars showing a more pronounced effect (about 85 %) compared to the nanogratings (75 %). The bacteria exhibited significant shape changes and damage, indicative of severe cellular disruption. Detailed AFM analysis confirmed notable morphological changes, including reduced major axis length, decreased surface area, and increased roughness, probably due to membrane rupture. Nanomechanical studies on the cell surface revealed changes in E. coli Young's modulus and adhesion forces, further demonstrating that nanostructures play a role. The Young's modulus of E.coli changes from (1.5 f 0.2) MPa on flat PMMA (control) to (0.7 f 0.1) MPa on nanograting with a pitch of 160 nm (lower pitch) and (0.5 f 0.1) MPa on nanopillars with a pitch of 200 nm (higher pitch). Similarly, the adhesion forces of bacteria grown on flat PMMA were (1.8 f 0.1) nN while they increased to (7.2 f 0.1) nN and (14.8 f 1.4) nN for lower-pitch nanogratings and higher-pitch nanopillars, respectively. These findings highlight the potential of nanostructured surfaces as advanced antibacterial materials.