Antibacterial properties of nanostructured surfaces via the selfassembly of block copolymers: (I) Effects of surface interactions

Here we report synergistic nanostructured surfaces combining bactericidal and bacteria releasing properties against Escherichia coli (E. coli, a Gram-negative bacterium) and Listeria monocytogenes (L. monocytogenes, a Gram-positive bacterium). In order for the surface to emerge the dual functionalities, it is important to optimize the surface morphology and interaction. We use polystyrene-block-poly(methyl methacrylate) (PS-block-PMMA) diblock copolymers and fabricate vertically oriented cylindrical PS structures on silicon substrates (“PS-nanopillars”). To improve the biocompatibility of the PS nanopillars, a very thin layer (~ 3 nm-thick) of titanium oxide (TiO₂) was deposited by using atomic layer deposition (“TiO₂ nanopillars”). The results demonstrate that the TiO₂ nanopillars exhibit further improved bactericidal and bacteria releasing properties against E. coli, and the dual properties also emerge against L. monocytogenes. To understand the mechanisms associated with the surface interaction of the nanopillars, coarse-grained molecular dynamics simulations of a lipid bilayer (as a simplified model for E. coli) in contact with a substrate containing cylindrical pillars with different bacterium/substrate interactions are also performed. The detailed mechanism underlying the multifaceted property of the nanosurfaces will be discussed.