Ultra-stretchable, super-tough, and highly stable ion-doped hydrogel for advanced robotic applications and human motion sensing

Hydrogel-based sensors are recognized as key players in revolutionizing robotic applications, healthcare monitoring, and the development of artificial skins. However, the primary challenge hindering the commercial adoption of hydrogel-based sensors is their lack of high stability, which arises from the high water content within the hydrogel structure, leading to freezing at subzero temperatures and drying issues if the protective layer is compromised. These factors result in a significant decline in the benefits offered by aqueous gel electrolytes, particularly in terms of mechanical properties and conductivity, which are crucial for flexible wearable electronics. Previous reports have highlighted several disadvantages associated with using cryoprotectant co-solvents and lower mechanical properties for ion-doped anti-freezing hydrogel sensors. In this study, the design and optimization of a photocrosslinkable ionic hydrogel utilizing silk methacrylate as a novel natural crosslinker are presented. This innovative hydrogel demonstrates significantly enhanced mechanical properties, including stretchability (>1825%), tensile strength (2.49 MPa), toughness (9.85 MJ m^–3), and resilience (4% hysteresis), compared to its non-ion-doped counterpart. Additionally, this hydrogel exhibits exceptional nonfreezing behavior down to −85°C, anti-drying properties with functional stability up to 2.5 years, and a signal drift of only 5.35% over 2450 cycles, whereas the control variant, resembling commonly reported hydrogels, exhibits a signal drift of 149.8%. The successful application of the developed hydrogel in advanced robotics, combined with the pioneering demonstration of combinatorial commanding using a single sensor, could potentially revolutionize sensor design, elevating it to the next level and benefiting various fields.