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Bacteria are mechanically resistant biological structures that can sustain physical stress. Experimental data, however, have shown that high-aspect-ratio nanopillars deform bacterial cells upon contact. If the deformation is sufficiently large, it lyses the bacterial cell wall, ultimately leading to cell death. This has prompted a novel strategy, known as mechano-bactericide technology, to fabricate antibacterial surfaces. Although adhesion forces were originally proposed as the driving force for mechano-bactericidal action, it has been recently shown that external forces, such as capillary forces arising from an air-water interface at bacterial surfaces, produce sufficient loads to rapidly kill bacteria on nanopillars. This discovery highlights the need to theoretically examine how bacteria respond to external loads and to ascertain the key factors. In this study, we developed a finite element model approximating bacteria as elastic shells filled with cytoplasmic fluid brought into contact with an individual nanopillar or nanopillar array. This model elucidates that bacterial killing caused by external forces on nanopillars is influenced by surface topography and cell biomechanical variables, including the density and arrangement of nanopillars, in addition to the cell wall thickness and elastic modulus. Considering that surface topography is an important design parameter, we performed experiments using nanopillar arrays with precisely controlled nanopillar diameters and spacing. Consistent with model predictions, these demonstrate that nanopillars with a larger spacing increase bacterial susceptibility to mechanical puncture. The results provide salient insights into mechano-bactericidal activity and identify key design parameters for implementing this technology.

Nanopillars have been shown to mechanically damage bacteria, suggesting a promising strategy for future antibacterial surfaces. However, the mechanisms underlying this phenomena remain unclear, which ultimately limits translational potential toward real-world applications. Using real-time and end-point analysis techniques, we demonstrate that in contrast to initial expectations, bacteria on multiple hydrophilic "mechano-bactericidal" surfaces remained viable unless exposed to a moving air-liquid interface, which caused considerable cell death. Reasoning that normal forces arising from surface tension may underlie this mechano-bactericidal activity, we developed computational and experimental models to estimate, manipulate, and recreate the impact of these forces. Our experiments together demonstrate that a critical level of external force acting on cells attached to nanopillar surfaces can rapidly deform and rupture bacteria. These studies provide fundamental physical insight into how nanopillar surfaces can serve as effective antibacterial materials and suggest use-conditions under which such nanotechnology approaches may provide practical value.