Tunicate-inspired polyallylamine-based hydrogels for wet adhesion: A comparative study of catechol- and gallol-functionalities

Abstract

Hypothesis: Functional adhesives with excellent adhesive strength in wet as well as dry environments are actively studied for various applications. In particular, the adhesion mechanism of marine organisms has been imitated to achieve strong adhesion in wet environments.

Experiments: Polyallylamine (PAA) was modified with catechol groups (CA), which mimic the mussel adhesion proteins, and gallol groups (GA) found in tunicates to compare the gelation, self-healing, and adhesive properties of the modified polymers according to pH change. The effect of the Schiff base formation and antioxidant capacity exerted by polyphenolic groups were investigated by comparing the self-healing behaviors of the two hydrogels. Furthermore, the wet adhesion and antibacterial properties of the PAA-CA and PAA-GA hydrogels were evaluated in terms of the synergistic effects of the amino groups and catechol or gallol groups.

Findings: The self-crosslinkable PAA-CA and PAA-GA hydrogels showed high self-healing ability owing to these dynamic imine bonds. Furthermore, the PAA-based hydrogels showed higher adhesive strength in wet environments than in dry environments owing to the synergism between the catechol or gallol groups and amino groups. Overall, the PAA-GA hydrogels are superior to the PAA-CA ones, indicating that gallol-functionalized hydrogels have great potential as multifunctional adhesives.

Keywords: Adhesives; Catechol; Gallol; Hydrogel; Polyallylamine; Self-healing; Wet adhesion.