Bioinspired by Sandcastle Worm Glue: An Underwater Reversible Adhesive Modulated by pH Environments Based on Urushiol

The development of wet adhesives with robust and reversible adhesion to diverse substrates remains challenging. In nature, sandcastle worm glue exemplifies the successful synergy of vital adhesive components with hydrophobic elements to achieve efficient wet adhesion. Herein, a strategy taking advantage of the structural advantage of urushiol, a natural catechol derivative, is proposed to facilely prepare pH-responsive reversible wet adhesive hydrogels with a commonly used pH-responsive component, 3-(acrylamidophenyl) boronic acid (AAPBA), and a framework monomer, N-2-hydroxyethyl acrylamide (HEAA). In the resulting hydrogel, the catechol groups of urushiol form bonds with the phenyl boric acid groups from AAPBA, enabling responsive wet adhesion. Simultaneously, the hydrophobic long unsaturated alkyl side chains of urushiol (UH) facilitate hydrogel cross-linking and impart moisture-repelling properties upon adhesion. Consequently, the hydrogel demonstrated reliable and universally applicable pH-responsive reversible adhesion. Furthermore, it exhibits remarkable improvements in mechanical properties, including enhanced compressive strength, tensile strength, and elongation at break. This study may present a promising approach to the development of smart and universal wet adhesive hydrogels.