Stratum Corneum‐Inspired Zwitterionic Hydrogels with Intrinsic Water Retention and Anti‐Freezing Properties for Intelligent Flexible Sensors

Abstract Hydrogels, which mimic the properties of natural tissues, are essential for flexible electronics in human‐machine interfaces (HMIs). However, traditional hydrogels suffer from dehydration, compromising stability and functionality. To address this issue, a stratum corneum‐inspired, water‐retaining hydrogel is developed using hygroscopic polymers and bound water. Three types of hydrophilic monomers (non‐ionic, mono‐ionic, and zwitterionic) are explored, with polyzwitterions, particularly N,N‐dimethyl (acrylamidopropyl) ammonium propane sulfonate (DMAAPS), forming a quasi‐hydrogel that retains the softness and flexibility of conventional hydrogels. Water acts as a plasticizer, enhancing polymer chain mobility and reducing stiffness. The DMAAPS hydrogel maintains 100% weight retention under specific humidity conditions and shows skin‐like softness across a wide humidity range. The Young's modulus increases from 54 to 118 kPa as relative humidity decreases from 80% to 40%. The absence of free water confers intrinsic anti‐freezing properties. A triple crosslinking mechanism and conductive polymers endow the hydrogel with stretchability (> 2000%), toughness, elasticity, self‐healing, and stable sensing capabilities. The hydrogel functions as an excellent flexible sensor for real‐time, sensitive detection of human motion and physiological signals. An intelligent handwriting recognition platform with high accuracy is also established using double‐channel signal collection and machine learning algorithms, offering insights for next‐generation durable, biomimetic, and smart HMIs.