Dynamic Antimicrobial Poly(disulfide) Coatings Exfoliate Biofilms On-Demand via Triggered Depolymerization

Bacterial biofilms are notoriously problematic in applications ranging from biomedical implants to fouling of ship hulls. Cationic, amphiphilic antibacterial surface coatings can delay the onset of biofilm formation by killing microbes on-contact, but they lose effectiveness over time due to non-specific binding of biomass and subsequent biofilm formation atop the fouled surface. Harsh physical or mechanical treatment methods are then required to forcibly expel the accumulated biomass and regenerate a clean surface. Here, we develop a simple, dynamically reversible method of polymer surface coating that enables both chemical killing on-contact, as well as on-demand mechanical delamination of surface-bound biofilms by triggered depolymerization of the underlying antimicrobial coating layer. Specifically, we synthesized antimicrobial polymer derivatives based on the cyclic dithiolane, α-lipoic acid, which can undergo dynamic and reversible polymerization into polydisulfides functionalized with biocidal quaternary ammonium salt groups. These coatings kill >99.9% of S. aureus cells, repeatedly for 15 cycles without loss of activity, for moderate microbial challenge (~10^5 CFU/mL, 1 hr) but they ultimately foul under more intense challenges (~10^7 CFU/mL, 5 days). The attached biofilms are then ultimately exfoliated from the polymer surface by UV-triggered degradation of the poly(disulfide) coating in an aqueous solution at neutral pH. This work provides a new and simple strategy for antimicrobial coatings that can both kill bacteria on-contact for extended timescales, followed by triggered biofilm removal under mild conditions.