In this study, high performance hydrogels with strong underwater adhesion were constructed through a "mussel feet-rock" inspired strategy, in which a random copolymer containing side-chain positive charges and catechol groups (PMD) simulated the adhesive proteins of mussel, and poly(acrylic acid) (PAA) mimicked the rocky surface. PMD and PAA chains could noncovalently cross-link together through hydrogen bonding, charge interaction, and chain entanglement. Catechol groups further provide the hydrogel strong adhesion ability. Taking advantage of this strategy, the obtained PAA/PMD hydrogels featured the best stretchability among reported hydrogels and intensive repeatable adhesion behavior, and further exhibited unusual wet-enhanced tensile and shear strength together with durable underwater adhesion. These findings are valuable for the development of musselinspired adhesives and high performance hydrogels.

Dynamically crosslinked supramolecular networks have emerged in the last decades as extremely stretchable and self-healing materials thanks to the energy dissipation in weak and reversible interactions. Stretchable materials with tunable properties represent an effort to develop a charming class of smart devices. Once stretched, however, these materials' properties are usually fixed due to strain-induced crystallization (SIC), hindering their practical applications. Here, photoinduced contraction smart fibers and photoswitchable adhesives are generated from a dynamic supramolecular gel network, the SIC in which can be disrupted by UV irradiation to release the prestored strain energy. The dynamic sliding of azo-bridged bipedal host molecules along the polymer chains renders the extreme stretchability of supramolecular gel under stretching forces. The oriented crystalline microdomains or crystallites through SIC upon stretching serve as physical crosslinks to store the contractile energy of fibers and improve the adhesion force of adhesives, and then are disoriented induced by trans-to-cis isomerization of azobenzene mesogens to release the prestored strain energy, resulting in such contraction of fibers and reduction of adhesion strength of adhesives. This work provides inspiration for exploring the structure-property relationship of supramolecular networks and transforming their clear potential to fabricate more remarkable synthetic smart materials.

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