PDMS tri-block copolymers bearing quaternary ammonium salts for epidermal antimicrobial agents: Synthesis, surface adsorption and non-skin penetration

Quaternary ammonium salts are widely used as epidermal and topical antimicrobial agents in medical treatments due to their broad activity, excellent performance and ready availability. However, their epidermal application has revealed many noticeable disadvantages, including short-term functionality, environmental toxicity, rapid antimicrobial resistance and skin penetration. Here, a series of tri-block copolymers grafted with dimethylaminopropyl benzyl chloride and based on a polydimethylsiloxane (PDMS) backbone, referred to as PDMS-b-(PDMS-g-BC)-g-PDMS, were prepared with well-controlled chain length and cationic grafting content. The quaternary ammonium salt-containing polymers were effective antimicrobial agents against epidermal pathogenic microbes, such as E. coli, S. albus and C. albicans. By incorporating hydrophilic and antimicrobial quaternary ammonium salt groups into the hydrophobic PDMS backbones, the amphiphilic tri-block copolymers were water-soluble but capable of assembling onto different surfaces, driven by electrostatic attraction or hydrophobic repulsion, which yielded long-term functionality on the surface. Moreover, the enlarged molecular size prevented penetration though full-thickness rat skins. These findings suggest a promising application of polymeric quaternary ammonium salts with hydrophobic moieties as epidermal antimicrobial agents.