posted on 2023-01-05, 06:16authored byDaniel Salatto, Zhixing Huang, Peter Todd Benziger, Jan-Michael Y. Carrillo, Yashasvi Bajaj, Aiden Gauer, Leonidas Tsapatsaris, Bobby G. Sumpter, Ruipeng Li, Mikihito Takenaka, Wei Yin, David G. Thanassi, Maya Endoh, Tadanori Koga
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 (TiO2) (“TiO2 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.