An anti-swelling and wet-adhesive nanocellulose hydrogel sensor for underwater communication

Traditional hydrogel sensors face numerous challenges when applied in underwater environments, such as structural damage caused by water absorption and rapid loss of adhesion, which hinder the realization of underwater sensing. Therefore, the development of hydrogels with strong wet adhesion and anti-swelling properties is of paramount importance. In this study, a double-network hydrogel was synthesized via hydrogen bond entanglement, using a copolymer of acrylic acid (AA), tannic acid (TA), and methacrylic acid sulfonic betaine (SBMA) as the flexible chain, and polydopamine-modified cellulose nanofibers (PCNFs) as the rigid chain. The swelling rate of the PCNF/P(AA-SBMA)@TA hydrogel (PCAST hydrogel) reached only 38.90% following 15 days of swelling, indicative of its superior anti-swelling performance. This excellent anti-swelling property is ascribed to the dense cross-linked network of the PCAST hydrogel, which also shows good mechanical properties, high sensitivity with a gauge factor (GF) of 2.97, and a maximum adhesion of 47.01 kPa in wet environments. Based on these merits, the wearable sensor fabricated from this hydrogel can accurately capture signal changes both in air and underwater. When combined with Morse code, it provides protection for the safety of underwater activities. This research proposes a novel strategy for developing anti-swelling and self-adhesive wearable sensors for underwater applications, holding broad prospects in the field of intelligent sensing.