Bio-inspired smart glass-like hydrogels with strong and switchable underwater adhesion

Smart adhesives with on-demand control are highly desirable, while creating hydrogels that combine strong, switchable underwater adhesion remains a significant challenge. Herein, we develop a novel strategy to achieve robust and tunable underwater adhesion with bio-inspired smart glass-like hydrogels. As a proof of concept, a hydrogel is simply prepared by integrating rigid poly(phenyl acrylate) segments into a poly[2-(acryloyloxy)ethyl]trimethylammonium chloride network. At room temperature, the vitrified phase-separated structure imparts the hydrogel with high mechanical strength. The adhesion is governed by a reversible transition between a soft network state and a frozen one, where the elastic modulus varies by 600-fold. The soft state conditions conformal underwater contact, allowing non-covalent interactions and mechanical interlocking to develop, while the network re-enters the frozen state, restoring cohesion and locking the established interfacial contact, thereby enabling high underwater adhesive strength on various substrates (up to 1.45 MPa), which outperforms most reported hydrogel adhesives. Notably, the adhesive performance can be reversibly switched off by returning the network to the soft state for facile detachment, allowing the material to function as a thermo-controllable gripper. Systematic evaluations validate the proposed adhesion mechanism, revealing that adhesive performance is strongly dependent on the hydrogel’s stiffness, contact condition, testing temperature, and substrate roughness. This work offers a promising strategy for designing next-generation smart adhesives with tunable and reversible performance for broad practical applications.