Bactericidal and Antifouling Coatings with the “Killing–Repelling–Killing” Triple Function Based on Cationic Copolymers with Structure Conversion and Capsaicin Analogue Release

The capsaicin analogue <i>N</i>-(4-hydroxy-3-methoxybenzyl) acrylamide (HMBA) was linked with polylauryl methacrylate-<i>b</i>-poly(2-(<i>N</i>,<i>N</i>-dimethylamino)ethyl methacrylate) (PLMA-<i>b</i>-PDMAEMA) via a quaternization reaction with 4-(acrylamidomethyl)-2-methoxyphenyl 2-chloroacetate (AAMPCA). The amphiphilic copolymers were capable of transforming its structure in response to the solvent change from aprotic to protic, which was verified by the ¹H NMR spectrum. The resulting cationic copolymers underwent a hydrolysis process in water, yielding zwitterionic groups on surfaces. Meanwhile, the bactericidal reagent HMBA was released. It was proved that the hydrolysis rate of the copolymers accelerated with higher temperature, higher pH value, and higher hydrophilic block units. And the controllable, sustainable release of HMBA was achieved with copolymer-mediated hydrolysis. Protein-repellent and bactericidal tests on the surface of the coating proved that antifouling and bactericidal performances of the coating correlated to the structure conversion abilities of the corresponding copolymer. The dynamic monitoring of <i>Escherichia coli</i> adhesion in 3 h evidenced the antifouling and bactericidal process of copolymers with different block ratios and concentrations. The coating incorporated with 3% PLMA₁₂₀-<i>b</i>-(PDMAEMA-AAMPCA)₁₂₀ in polylactic acid base materials showed an adhesion ratio of <i>E. coli</i> less than 1% within 1 h, and the survival ratio of the adhered bacteria is <1%, suggesting its rapid speed and high efficiency in "bacterial repelling and killing". Also, the PLMA₁₂₀-<i>b</i>-(PDMAEMA-AAMPCA)₁₂₀ copolymer demonstrated enhanced bactericidal ability compared with the mixture of cationic poly(laruyl methacrylate)₁₂₀-<i>b</i>-poly(carboxybetaine methacrylate ester)₁₂₀ (PLMA₁₂₀-<i>b</i>-PCBMAE₁₂₀) and free HMBA. The lowest minimal inhibitory concentration was 0.078 mg/mL against <i>Staphylococcus aureus</i> and 0.312 mg/mL against <i>E. coli</i>, respectively.