"Deep Eutectic Solvent-in-Water" Hydrogels Enable High-Performance Flexible Strain Sensors for Electronic Skin with a Wide Operating Temperature Range

A"deep eutectic solvent-in-water" hydrogelwith a wide range of operating temperatures was prepared using theLs-Fe3+ dynamic redox system, showing great potentialas an electronic skin. Conductivehydrogels have become one of the hot topics in flexiblestrain sensors owing to excellent biocompatibility, attractive mechanicalflexibilities, and conductive properties. However, the time-consumingpreparation of hydrogels and their unsuitable properties limit theirapplication in low-temperature environment and high temperatures.Here, a new class of "deep eutectic solvent-in-water"hydrogels (DIWHs) is reported for the first time through a one-stepgelation process in situ without solvent displacement, fabricatedby combining a hydrogel with deep eutectic solvent (DES). The DIWHis constructed using a dynamic oxidation and coordination system composedof sodium lignosulfonate (Ls) and Fe3+. The effect of DESand the optimal mass ratio of water and DES on the hydrogel propertieswas synthetically investigated. The addition of DES not only shortensthe polymerization time to 8 s and enhances the mechanical propertiesof the hydrogel but also provides some unique properties. For example,the addition of DES gives the gels greater self-healing ability andantibacterial properties. When the mass ratio of water to DES was1:3, excellent antifreezing and antidrying properties were impartedto the gel, and the elasticity of the hydrogel was maintained evenat -80 & DEG;C or stored at 60 & DEG;C for 7 days. Furthermore,the hydrogel exhibited strong interfacial adhesion to natural andsynthetic materials (up to 60 kPa on glass) due to the presence ofLs with a catechol structure. In conclusion, this work stimulatesmore interest in the sustainable and high-value utilization of DESand fully demonstrates the advantages of this new easy-to-preparecoacervation gel for sensing.