Microstructure controlled electrostatic and channel mediated interactions between bacterial membrane and copper and carbon surfaces

The outer membrane of Gram-negative bacteria acts as a key physical barrier against antibacterial agents. While some antibiotics traverse this barrier through porins, contact-killing metallic surfaces bypass molecular transport entirely by directly compromising membrane integrity, a process still poorly understood at the atomic scale. Here, Reactive Force-Field (ReaxFF) molecular dynamics simulations were employed to elucidate how metal and carbon surfaces modulate bacterial membrane destabilisation. Using an Escherichia coli lipid bilayer as a model, we investigated its interactions with nanocrystalline, polycrystalline and amorphous surfaces of carbon and copper as two classes of bactericidal and surface-active materials. Multi-parameter analyses of interfacial charge distribution, potential energy, bilayer thickness and two-dimensional lipid density mapping revealed distinct, substrate-specific perturbations in membrane structure and energetics. Copper surfaces produced pronounced and sustained disruption, accompanied by substantial interfacial charge accumulation of approximately 0.14 C to 0.17 C. Polycrystalline copper (PC-Cu) destabilised the membrane through localised grain-boundary-driven electrostatics, whereas nanocrystalline copper (NC-Cu) induced a more uniform but comparably severe perturbation. In contrast, nanocrystalline and polycrystalline carbon (NC-C and PC-C) operated in a low-charge regime of approximately 0.01 C and did not induce global membrane failure. Instead, they promoted localised adaptive responses characterised by the formation of discrete vertical membrane channels, enabling confined membrane–substrate contact while preserving overall bilayer integrity. Amorphous carbon (a-C) remained largely inert, exhibiting negligible charge transfer below 0.02 C and preserving bilayer structure. These findings establish that membrane stability during contact killing is governed not only by elemental composition but also by surface microstructure. The results provide new atomistic insight into contact-induced antibacterial mechanisms and offer a theoretical foundation for the rational design of antimicrobial surfaces with tunable membrane activity.