It is a great challenge for traditional hydrogel-based sensors to be effective underwater due to unsatisfactory water resistance and insufficient wet adhesion. Herein, a tough supramolecular hydrogel aiming at underwater sensing is prepared by the modification of hydrophilic poly­(acrylic acid) (PAA) with a small amount of hydrophobic lauryl methacrylate (LMA) in the presence of high concentrations of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Owing to the synergistic effects of the electrostatic interactions and hydrophobic associations of CTAB with the P­(AA-co-LMA) copolymer, the hydrogel with a water content of approximately 58.5 wt % demonstrates outstanding anti-swelling feature, superior tensile strength (≈1.6 MPa), large stretchability (>900%), rapid room-temperature self-recovery (≈3 min at 100% strain), and robust wet adhesion to diverse substrates. Moreover, the strain sensor based on the hydrogel displays keen sensitivity in a sensing range of 0–900% (gauge factor is 0.42, 3.44, 5.44, and 7.39 in the strain range of 0–100, 100–300, 300–500, and 500–900%, respectively) and pronounced stability both in air and underwater. Additionally, the hydrogel can be easily recycled by dissolving in anhydrous ethanol. This work provides a facile strategy to fabricate eco-friendly, tough supramolecular hydrogels for underwater sensing.

Conductive hydrogels are ideal candidate materials for flexible sensors, but the integration of satisfactory mechanical performances with high conductivity to meet the requirements for practical applications remains a challenge. Herein, a tough ionically conductive polyacrylamide (PAAm)/carboxymethyl chitosan (CMCs) double‐network (DN) hydrogel is fabricated via in situ polymerization of acrylamide in CMCs aqueous solution, followed by ferric chloride (FeCl3) solution immersing. The PAAm/CMCs‐Fe3+ DN hydrogel demonstrates satisfactory mechanical properties, including sufficient tensile strength (~440 kPa), prominent stretchability (~715%), high toughness (~1658 kJ m−3), and excellent fatigue resistance, as well as superb conductivity up to 3.1 S m−1. Moreover, the ionically conductive DN hydrogel‐based sensors exhibit high sensitivity in a broad strain window (0%–700%) and can accurately, and repeatedly monitor the motions of body joints, such as finger and wrist, exhibiting great potential in applications of flexible sensors.

As a promising functional material, conductive hydrogel has attracted extensive attention, especially in flexible sensor field. Despite the recent developments, current hydrogels still experience several issues, such as limited stretchability, lack of self‐recovery and self‐healing capability, and insufficient self‐adhesion. Herein, dual cross‐linked (DC) poly (AA‐co‐LMA)SDS/Fe3+ hydrogels are fabricated subtly on the basis of ionic coordination interactions and the poly (AA‐co‐LMA)SDS hydrophobic association networks, which may provide one plausible routine to compensate the mentioned drawback of hydrogels. The hydrophobic association and ionic coordination networks work synergistically to endow the hydrogels remarkable stretchability (>1200%), high‐fracture strength (≈ 820 kPa), and excellent self‐healing capability. In addition, the DC hydrogel‐based strain sensors displayed a broad sensing range (0 ∼ 900%), conspicuous sensitivity (strain 0% ∼ 200%, gauge factor = 0.53; strain 200% ∼ 500%, gauge factor = 1.23; strain 500% ∼ 900%, gauge factor = 2.09), and pronounced durability. What's more, the self‐adhesive feature ensures the strain sensor always forming a good conformal contact with the skin during human movements and displaying remarkable bidirectional detection capability.