Mussel byssus-inspired gallol-enriched chitosan hydrogel fibers with strong adhesive properties

The byssus of marine mussels, which exhibits a strong adhesion to rocks in seawater, is an important target for biomimetics. The underwater adhesion of the byssus to rocks relies on mussel foot proteins (Mfps), which contain 3,4-dihydroxyphenyl-L-alanine with a catechol group and lysine with an amino group that act cooperatively. In this study, Mfps-inspired hydrogel fibers were designed by combining a gallol group with chitosan. A chitosan-gallic acid (CS-GA) conjugate was synthesized by grafting GA onto CS, and CS-GA hydrogel fibers were prepared by simple needle spinning of a concentrated CS-GA solution into a neutral or weakly basic buffer solution. Furthermore, the self-crosslinking mechanism, swelling and self-healing behaviors, adhesive properties, and tensile properties of the CS-GA gel fibers were investigated according to the solution pH. The Schiff base (reversible covalent bonding) and Michael addition (irreversible covalent bonding) reactions were dominant at pH 7.4 and 8.5, respectively. Moreover, the CS-GA hydrogel fibers exhibited high adhesive strength under wet conditions owing to the residual amino groups. The tensile strength of the fibers formed in a coagulation bath with a Fe3+-added buffer was augmented owing to the formation of metal coordination bonds. The biomimetic CS-GA hydrogel fibers have great prospects for various applications.