Bioinspired Self-Healable Polyallylamine-Based Hydrogels for Wet Adhesion: Synergistic Contributions of Catechol-Amino Functionalities and Nanosilicate

Recently, many studies have been reported on functional adhesives that are applicable in wet conditions as well as in air conditions. In this study, a novel polymer hydrogel that mimics the mussel foot proteins (Mfps) was designed as an adhesive that can adhere strongly to various substrates in wet conditions. Polyallylamine-hydrocaffeic acid (PAA-CA) conjugates were synthesized to introduce the catechol moiety into the PAA backbone. The PAA-CA hydrogels were simply prepared by controlling the pH to enable the formation of a dynamic imine bond via the Schiff base reaction without any additional cross-linking agents. Owing to its residual amino groups, the PAA-CA hydrogel showed improved adhesive strength in wet conditions, which was found to be ∼4.7 times higher than in dry conditions. In addition, dual-cross-linked PAA-CA hydrogels were prepared by the addition of laponite (LP). The synergistic effect of the dynamic imine bonds and ionic bonds of the PAA-CA/LP nanocomposite hydrogels led to improved mechanical and self-healing properties. PAA-based hydrogels have great potential for more diverse applications than those of the commercial adhesives.