One of the concerns today's societies face is the development of resistant pathogenic microorganisms. The need to tackle this problem has driven the development of innovative antimicrobial materials capable of killing or inhibiting the growth of microorganisms. The present study investigates the dependence of the antimicrobial activity and solubility properties on the hydrophilicity/hydrophobicity ratio of antimicrobial coatings based on quaternary ammonium compounds. In this line, suitable hydrophilic and hydrophobic structural units were selected for synthesizing the antimicrobial copolymers poly(4-vinylbenzyl dimethyldodecylammonium chloride-co-acrylic acid), P(VBCDDA-co-AA20) and poly(dodecyltrimethylammonium 4-styrene sulfonate-co-glycidyl methacrylate), P(SSAmC12-co-GMA20), bearing an alkyl chain of 12 carbons either through covalent bonding or through electrostatic interaction. The cross-linking reaction of the carboxylic group of acrylic acid (AA) with the epoxide group of glycidyl methacrylate (GMA) of these two series of reactive antimicrobial copolymers was explored in blends, obtained through solution casting after curing at various temperatures. The release of the final products in pure water and NaCl 1 M solutions (as analyzed by gravimetry and total organic carbon, TOC/total nitrogen, TN analyses), could be controlled by the coating composition. The cross-linked polymeric membranes of composition 60/40 w/w % ratios led to 97.8 and 99.7% mortality for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively, whereas the coating 20/80 w/w % resulted in 96.6 and 99.8% cell reduction. Despite the decrease in hydrophobicity (from a 16- to a 12-carbon alkyl chain), the new materials maintained the killing efficacy, while at the same time resulting in increased release to the aqueous solution.
Keywords: antimicrobial materials; carboxyl groups; cross-linking reaction; epoxy groups; polymeric coatings; quaternary ammonium compounds.