Sustainable Antibacterial Surface of Transparent PMMA Membranes with α-ZrP Nanosheets Adsorbing Tetraalkylammonium Ions.

We fabricated composite membranes containing inorganic nanosheets (NSs) and polymers and demonstrated their outstanding antibacterial performance against several opportunistic pathogens. Layered α-zirconium phosphate [Zr(HPO), α-ZrP] as a pristine compound of NS was exfoliated by ion-exchanging protons in the interlayer space of α-ZrP with bulky tetraalkylammonium ions (TRA: R = butyl, hexyl, and octyl). During the exfoliation process, TRA was electrostatically adsorbed onto α-ZrP NS with a negative surface charge (ZrP-TRA-NS). The produced PMMA membrane including α-ZrP NS (PM-ZrP-TRA-NS) was optically transparent and prohibited bacterial growth, and the effect was stronger for Gram-positive than Gram-negative . The antibacterial activity of PM-ZrP-TRA-NS was based on physical damage induced by both 2D ceramic NSs and sharp alkyl chains of TRA. Despite the inherent flexibility of alkyl chains, when adsorbed onto the NSs, they can act in a manner that effectively pierces the bacterial cell wall. The piercing force of TRA was greater for the longer alkyl chains (TBA < THA < TOA). Focusing on the difference in the cell wall structure between these bacteria, the growth of Gram-positive with loose peptidoglycan layers as an outer membrane could be easily inhibited by contact with the composite film. In contrast, Gram-negative bacteria , surrounded by a relatively dense outer cell wall composed of peptidoglycan and lipopolysaccharide layers, could not be damaged easily. In this study, the antibacterial mechanism of PM-ZrP-TRA-NS membranes was elucidated, and their usefulness as antimicrobial coatings for existing solid surfaces was demonstrated.