Anti‐Swelling, Self‐Adhesive, and Conductive Hydrogel for Amphibious Strain Sensors

ABSTRACT Hydrogel‐based amphibious sensors have drawn much attention but have faced challenges like obvious swelling, decline in conductivity and sensing performances, and poor adhesion when immersed in water. To address these challenges, conductive hydrogels with swelling resistance, strong adhesion, and long‐term stability were developed. Firstly, an anti‐swelling and conductive matrix was constructed by using polyvinyl alcohol (PVA), sodium alginate (SA), and calcium ions (Ca 2+ ) through freezing–thawing repeats and immersion strategies. Subsequently, a gelatin‐tannic acid adhesive layer was coated on the bottom to achieve the Janus structure. Even after immersing in water for 28 days, this hydrogel still showed excellent swelling resistance (with a swelling ratio of 1.8%, a tensile stress of 227 kPa, an elongation at break of 223%, an electrical conductivity of 3.2 S/m, and a gauge factor of 1.2). In addition, the J‐PSC hydrogel exhibited strong adhesion to various materials (wood, iron, glass, plastic, and skin) both in air and underwater. Therefore, an amphibious strain sensor based on this Janus hydrogel was obtained, which could enable underwater communications through Morse code. This work provides new insights into the fabrication of conductive hydrogels, holding great promise for a broad range of applications like wearable sensors, bioelectrodes, and soft robotics in aquatic environments.