Bio-inspired catechol conjugation converts water-insoluble chitosan into a highly water-soluble, adhesive chitosan derivative for hydrogels and LbL assembly

Abstract

This report describes a simple method to prepare water-soluble chitosan derivative by conjugation of an enediol group, catechol. Chitosan functionalized with a catechol-containing compound, 3,4-dihydroxyhydrocinnamic acid, by a carbodiimide coupling method resulted in chitosan–catechol conjugates. This one-step chemical modification of high-molecular-weight chitosan (approximately 100 kDa) dramatically increased the water solubility of the chitosan derivative to 60 mg mL⁻¹ at pH 7.0. The degree of catechol conjugation was found critical in determining the solubility. The chitosan–catechol conjugates are not only water-soluble but are adhesive, due to the intrinsic adhesive properties of catechol. Also, the water-soluble chitosan derivative allows one to directly form chitosan hydrogel in neutral buffer solutions. The utility of both the water solubility and the adhesive property of the chitosan–catechol was demonstrated by the effective layer-by-layer assembly on substrates. The water-soluble chitosan–catechol is expected to be useful in many areas of surface functionalization, drug delivery, tissue engineering, and tissue adhesives.