Gel-based strain/pressure sensors for underwater sensing: Sensing mechanisms, design strategies and applications

Flexible and wearable strain/pressure sensors are of extraordinary interest in underwater applications such as underwater motion monitoring and marine environmental exploration. With tunable mechanical properties, biocompatibility and multifunctional characteristics, gel can be structurally designed and network cross-linked to obtain excellent swelling resistance in underwater environments, making them one of the most promising materials for constructing strain/pressure sensors for underwater applications. However, the complex underwater environment and different application scenarios put higher demands on the sensing sensitivity and accuracy of gel sensors. In recent years, gel sensors with multifunctional underwater properties have been developed to ensure long-term stable sensing underwater. In this review we first summarized the sensing mechanism of gelbased underwater strain/pressure sensors, and then summarized the strategy for designing gel sensors with multifunctional underwater characteristics by analyzing the relationship between different functional characteristics and sensing parameters. According to the development trend in recent years, we summarized the common application fields for underwater strain/pressure gel sensors. Finally, we presented our views on the challenges of building underwater gel sensors in the future, with the expectation of providing useful insights for the design and development of next-generation underwater strain/pressure sensors.