Controlling the surface antimicrobial efficacy of anionic block polymers via film thickness

As the global threat of infectious diseases continues to grow due to antimicrobial resistance, novel and non-targeting prevention strategies must be identified and their inactivation mechanisms understood. Upon hydration, styrenic pentablock polymers possessing a partially sulfonated midblock can effectively kill (99.9999+% in most cases) a wide range of contagious pathogens after relatively short exposure times (on the order of minutes) due to the formation of a highly acidic surface contact layer. Here, we demonstrate for a bacterial exemplar that the inactivation efficacy and contact-layer pH of one such anionic block polymer with a constant degree of sulfonation (52 mol%) likewise depend on polymer film thickness, which dictates the proton reservoir available for surface acidification. Our results reveal that the minimum film thickness needed for the polymer to attain the highest inactivation level of ampicillin-resistant Escherichia coli after an exposure time of 2 min is about 65 μm. Interestingly, the calculated proton partition coefficient between the microbial suspension and polymer film reaches a maximum at this thickness and decreases for thicker films, suggesting that proton transport within thick films becomes additionally affected by one or more molecular-level processes within the polymer.