Adhesive antibacterial coatings based on copolymers bearing thiazolium cationic groups and catechol moieties as robust anchors

Herein, we describe a simple approach for the preparation of antibacterial polymeric coatings based on mussel inspired catechol chemistry. A series of statistical copolymers composed of 2-(4-methylthiazol-5-yl)ethyl methacrylate (MTA) and N-(3,4-dihydroxyphenethyl) methacrylamide (DOMA) were synthesized by conventional free radical and reversible addition fragmentation chain transfer (RAFT) polymerizations. Subsequently, the thiazole groups of MTA units were quatemized with methyl and butyl iodide as alkylating agents to provide cationic copolymers with also adhesive anchoring groups of catechol. The copolymers were systematically studied to investigate the effects of composition (MTA/DOMA ratio), molecular weight and alkylating agent on adhesive and antibacterial properties. It was proved that DOMA units play a major role in the adhesion, while the antibacterial activity only decreases slightly with content of DOMA up to 32%. Remarkable, for similar MTA molar equivalent, the copolymers with higher molecular weight exhibit better antimicrobial properties in solution, whereas when they are tethered onto a surface as a coating, the copolymers with lower molecular weight showed enhanced antibacterial performance even against Gram-negative bacteria. These findings confirm that antimicrobial polymers attached onto surfaces behave in a different manner than in solution, and can be more effective as the mobility and accessibility of the cationic groups increase.