Iodine-immobilized hydrophobically modified chitosan coatings for antibacterial surface applications

Hydrophobically modified chitosan (HMCS) was prepared via reductive amination of chitosan with dodecyl aldehyde to introduce long alkyl chains onto the amino groups. Owing to chitosan's excellent film-forming properties, uniform HMCS coatings were readily fabricated on solid substrates. The hydrophobic modification imparted intrinsic antibacterial activity against Escherichia coli, attributed to enhanced membrane interactions induced by the grafted alkyl chains. The modified polymer matrix also exhibited increased affinity for iodine, enabling efficient incorporation of iodine from either ethanolic iodine tincture or aqueous I₂-KI solutions. Compared with unmodified chitosan coatings, HMCS coatings demonstrated significantly higher iodine-loading capacity. The iodine-loaded HMCS coatings exhibited markedly enhanced antibacterial activity against both Gram-negative E. coli and Gram-positive Staphylococcus aureus after 2 h of exposure. The improved antimicrobial performance is attributed to the synergistic effect of contact-mediated membrane disruption by hydrophobic alkyl chains and sustained bactericidal action through controlled iodine release. These findings highlight the role of hydrophobic modification in regulating iodine stabilization and antimicrobial efficacy in chitosan-based coatings.