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

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.