Hydrogel Electronic Skin Synergistically Enhanced by Multibond Crosslinking and a Negative Poisson's Ratio Structure for Human Respiration Monitoring.

Electronic skin demonstrates significant potential for wearable health monitoring and human-machine interaction. However, conventional hydrogels rarely achieve a balance of high strength, fatigue resistance, sensitivity to subtle deformations, and conformability to complex curved surfaces. They often suffer from mechanical degradation, signal drift, and insufficient interfacial adhesion under repeated loading. Here, we propose a synergistic strategy integrating multibond crosslinking reinforcement with structural configuration amplification to develop a PVA/PAA/Zr4+ ion-conductive hydrogel strain sensor featuring a re-entrant honeycomb negative Poisson's ratio structure. At the material level, PVA/PAA hydrogels are fabricated via one-pot in situ photopolymerization followed by freeze-thaw-induced crystalline crosslinking. Incorporation of Zr4+ coordination, together with a high-density hydrogen-bond network, establishes a dynamic dissipation-reconstruction mechanism, thereby markedly improving strength, toughness, and fatigue durability. Structurally, the re-entrant honeycomb geometry amplifies strain and mitigates local stress concentration through unit rotation and beam bending, enhancing low-strain signal resolution and surface adaptability. The resulting hydrogel sensor delivers a maximum tensile stress of 552.9 kPa and an elongation at break of 629.4%. It provides a broad sensing range of 0.1-200% with a 0.1% resolution and a response time of 94.2 ms while maintaining stable outputs under cyclic deformation. As application demonstrations, the hydrogel sensor enables discrimination of soft gripper bending states and grasped object sizes, conforms tightly to dynamically changing curved surfaces, and supports continuous abdominal skin-contact respiratory monitoring with clear differentiation among distinct breathing patterns. Overall, this work establishes a reliable material-structure integrated design paradigm for hydrogel-based electronic skin, promoting its development toward wearable physiological monitoring.