Temperature- and Salt-Concentration-Triggered Antibacterial Activity of Nanopillar Hydrogels and Their Bacterial Detachment

The skin is the largest organ of the body, and wounds caused by trauma, surgery, and extensive burns are a source of bacterial infection and pose a significant public health concern. Additionally, the excessive use of antibiotics for bacterial infections significantly reduces the susceptibility of bacterial strains to treatment, ultimately leading to the emergence of antimicrobial resistance (AMR). A dressing protects the wound, adsorbs exudate, shortens the inflammatory process, and promotes healing. Recently, natural or bioinspired surfaces covered with nanopillars have been reported to exhibit antibacterial properties by physically destroying bacterial cells, thereby circumventing the challenges posed by traditional antibacterial agents. These antibacterial nanopillars were also shown to be effective against bacteria that display AMR, but they did not increase bacterial drug resistance. However, it was found that dead bacteria and debris easily accumulate on the nanostructures, degrading their antibacterial properties and ultimately eliminating the germicidal performance of the surface. In this study, gold was deposited on the surface of poly(vinyl alcohol) (PVA)/poly(methacrylic acid) (poly(MAAc)) nanopillars; the nanopillars were modified by temperature-responsive poly(N-isopropylacrylamide) (poly(NIPAAm)) with a thiol group (–SH) at the chain end by utilizing the interaction between –SH groups and gold. Owing to the modification with poly(NIPAAm)-SH, the surface properties of the modified nanopillars were controlled by changing the temperature and salt concentration. At temperatures above the cloud point (CP), the poly(NIPAAm)-SH on the nanopillar surface became hydrophobic, capturing bacteria and exhibiting antibacterial properties. By contrast, at temperatures below the CP, the poly(NIPAAm)-SH on the nanopillar surface became hydrophilic, enabling the removal of the adsorbed bacteria.