Epithelium‐Inspired, Ultrahigh‐Toughness, Ultralow‐Hysteresis, and Highly Compressible Polymer Hydrogels as Self‐Powered, Visual, and Underwater Strain Sensors

Developing high-toughness, low-hysteresis, and highly compressible polymer hydrogels as wearable strain sensors with superior detection ranges, durability, and signal accuracy is still a grand challenge due to contradictory characteristics. Herein, inspired by epithelial tissue, an epithelium-like structure hydrogel with cell-like particles (PLTAV) is synthesized from a water-in-oil high internal phase emulsion. During loading-unloading processes, the hydrophilic cell-like particles can deform reversibly and be cyclically divided into small-sized particles and aggregated, thereby dissipating more energy. Therefore, the PLTAV hydrogel with high water content (90.4 wt%) has superior stretchability (1368%), ultrahigh toughness (2.64 MJ·m^-3), ultralow hysteresis (4.7%, ε = 300%), and ultrahigh compressibility (99.9%). Subsequently, choline chloride and sorbitol are introduced into the PLTAV hydrogel (PLTAV-SC). The as-prepared PLTAV-SC hydrogel exhibits improved freezing resistance, enhanced stretchability (2021%) and toughness (6.10 MJ·m^-3), and retained low hysteresis and ultrahigh compressibility. Benefiting from the cell-like particles composed of polymers with ionic structural units and the difference in ionic mobilities, these hydrogels can act as self-powered strain sensors with high sensitivities. Meanwhile, they can also be used as high-performance visual and resistance-type strain sensors. Additionally, these sensors can be further constructed as underwater strain sensors for detecting underwater human/animal motion, water flow velocity, and water depth.