Hofmeister Effect-Driven Mussel-Inspired Hydrogel with Tunable Mechanics for Flexible Sensors

Inspired by the adhesive proteins of mussels, we developed a dual-network hydrogel with robust adhesion and tunable mechanical properties for wearable sensors. A catechol-functionalized polymer (PAA-<i>g</i>-Dopa) was synthesized by grafting L-DOPA onto a poly(acrylic acid) backbone, introducing catechol groups capable of dynamic interfacial bonding. This adhesive component was copolymerized with acrylamide (AM) and poly(vinyl alcohol) (PVA) to fabricate a tough, stretchable, and highly adhesive PVA-DOPA hydrogel. The PVA-DOPA hydrogel adhered strongly to a wide variety of substrates, regardless of their surface energy, through synergistic noncovalent interactions. Incorporation of PVA endowed the hydrogel with ion-responsive mechanical tunability via the Hofmeister effect, enabling reversible modulation of stiffness and elasticity. The optimized hydrogel also exhibited excellent stretchability, high toughness, and repeatable adhesion, maintaining structural integrity under large deformations. Furthermore, integration into wearable devices demonstrated its ability to monitor real-time human motion from different joints (e.g., elbow and finger) with high sensitivity and stability. Novelty, it can transmit information and recognize sign language via Morse code. This study offers a versatile design approach for multifunctional hydrogels that combine strong adhesion, mechanical adaptability, and biocompatibility, paving the way for their application in next-generation epidermal electronics, soft robotics, and biointegrated devices.