Antibacterial, Wash-resistant Coatings Based on Imine-grafted Catechol Isomers

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Abstract
Antibacterial coatings are needed to reduce surface contamination in clinical and textile environments, but many existing antimicrobial coatings rely on the release of biocides, creating concerns about toxicity and antimicrobial resistance, or require metal ions, harsh chemicals, and complex multi-step fabrication processes that limit practical deployment. In this study, six catechol aldehyde isomers were grafted onto bactericidal branched polyethylenimine (bPEI) using Schiff-base click chemistry to create one-component, metal-free coating solutions. Upon exposure to air and moisture, these solutions crosslinked into quinone-based networks that formed uniform films on cellulose substrates through simple dip-coating. Evaluation using colony-forming-unit counts, zone-of-inhibition assays, and ¹H NMR leachate analysis distinguished contact-killing activity from antibacterial effects caused by diffusion. All coatings exhibited low leaching, losing no more than 7.6% of their mass after aqueous exposure, while maintaining antibacterial performance after brief water and ethanol rinses. Notably, the bPEI-g-(3,5-DBA) formulation matched the strong contact-bactericidal activity of unmodified bPEI, achieving more than a three-log reduction in bacterial count. The results demonstrate that catechol substitution patterns can be used to control the balance between diffusible and surface-retained antibacterial activity, offering a versatile strategy for designing durable, wash-resistant, air-activated antibacterial coatings.