Structure-Based Design of Dual Bactericidal and Bacteria-Releasing Nanosurfaces

Abstract

Here, we report synergistic nanostructured surfaces combining bactericidal and bacteria-releasing properties. A polystyrene-block-poly(methyl methacrylate) (PS-block-PMMA) diblock copolymer is used to fabricate vertically oriented cylindrical PS structures ("PS nanopillars") on silicon substrates. The results demonstrate that the PS nanopillars (with a height of about 10 nm, size of about 50 nm, and spacing of about 70 nm) exhibit highly effective bactericidal and bacteria-releasing properties ("dual properties") against Escherichia coli for at least 36 h of immersion in an E. coli solution. Interestingly, the PS nanopillars coated with a thin layer (≈3 nm thick) of titanium oxide (TiO 2 ) ("TiO 2 nanopillars") show much improved dual properties against E. coli (a Gram-negative bacterium) compared to the PS nanopillars. Moreover, the dual properties emerge against Listeria monocytogenes (a Gram-positive bacterium). To understand the mechanisms underlying the multifaceted property of the nanopillars, coarse-grained molecular dynamics (MD) simulations of a lipid bilayer (as a simplified model for E. coli) in contact with a substrate containing hexagonally packed hydrophilic nanopillars were performed. The MD results demonstrate that when the bacterium−substrate interaction is strong, the lipid heads adsorb onto the nanopillar surfaces, conforming the shape of a lipid bilayer to the structure/curvature of nanopillars and generating high stress concentrations within the membrane (i.e., the driving force for rupture) at the edge of the nanopillars. Membrane rupture begins with the formation of pores between nanopillars (i.e., bactericidal activity) and ultimately leads to the membrane withdrawal from the nanopillar surface (i.e., bacteria-releasing activity). In the case of Gram-positive bacteria, the adhesion area to the pillar surface is limited due to the inherent stiffness of the bacteria, creating higher stress concentrations within a bacterial cell wall. The present study provides insight into the mechanism underlying the "adhesion-mediated" multifaceted property of nanosurfaces, which is crucial for the development of next-generation antibacterial surface coatings for relevant medical applications.

Cell Adhesion, Elasticity, and Rupture Forces Guide Microbial Cell Death on Nanostructured Antimicrobial Titanium Surfaces

“…Moreover, there are inherent differences that need to be accepted between the experiments: (1) In the CLSM analysis, there is no applied force, meaning that the bacteria and fungi naturally equilibrate. The 16 h of microbial exposure was chosen to get a global view of the systems and to align with previous studies in the literature. ,,,,, (2) The SCFM interrogates one microbe at a time with technical replicates, so observation is of single-cell level detail, which needs to be assessed with more universal techniques, like CLSM. (3) An external force must be applied in the AFM experiment, which is missing in the CLSM.…”

“…The 16 h of microbial exposure was chosen to get a global view of the systems and to align with previous studies in the literature. 16,17,19,21,33,120 (2) The SCFM interrogates one microbe at a time with technical replicates, so observation is of single-cell level detail, which needs to be assessed with more universal techniques, like CLSM. (3) An external force must be applied in the AFM experiment, which is missing in the CLSM.…”

Laser‐Textured Surfaces: A Way to Control Biofilm Formation?

“…Such a synergetic surface design combining a bactericidal effect with bacteria-releasing properties was explored by Salatto et al for nanopillar-covered surfaces -inspired by the anti-bacterial wings of cicada. [151] The authors also presented Molecular Dynamics (MD) simulations revealing that when the bacterium−substrate interaction is strong, the lipid heads of the bacterial cell membrane strongly adsorb at the hydrophilic nanopillar surfaces. This can eventually conform the lipid bi-layer membrane to the curved structure of nanopillars, while locally generating high mechanical stress within the cell membrane as the driving force for its rupture.…”

Black silicon spacing effect on bactericidal efficacy against gram-positive bacteria

“…Previous studies on mechanically bactericidal nanostructures have focused on non-uniform and irregular nanostructures in cicada wings and black silicon. Such randomness complicates the analysis of how specific changes in surface morphology affect bactericidal efficacy [48][49][50]. These nanoneedles are tested against Staphylococcus epidermidis (S. epidermidis), which consists of cocci approximately 500-1000 nm in diameter, arranged in clusters [51,52].…”