Low-temperature-tolerant hydrogels via a polyanionic hydration strategy for flexible sensors

Polyanionic hydration enables anti-freezing to −80 °C without small-molecule agents. • Hydrogel shows 1000% stretchability, adhesion, and >88% recovery at −40 °C. • Polyanionic framework stabilizes ions/water, yielding 0.07-4.32 S/m conductivity. • Integrated sensors reliably monitor motion and temperature even at −40 °C. The freezing behavior of hydrogels at sub-zero temperatures significantly hinders their application in flexible electronics. However, the prevalent strategy of incorporating small-molecule anti-freezing agents often results in solute leaching, which undermines the environmental durability and long-term stability of the materials. In this work, we present a polyanionic hydration-based design incorporating carboxylate and sulfonate groups into the polymer network. This approach establishes a hydration architecture with hierarchical binding energies, thereby endowing the hydrogel with intrinsic anti-freezing properties and eliminating the requirement for conventional small-molecule additives. Within this system, the polyanionic framework stabilizes water molecules via hierarchical ion-dipole interactions, which disrupt the intrinsic hydrogen-bonding network and inhibit ice nucleation and crystal growth. Consequently, no detectable freezing transition was observed for the hydrogel within the tested temperature range down to −80°C. Meanwhile, the hydrogel demonstrated an ionic conductivity of 4.32 S/m, a recovery efficiency of 90%, an elongation of 1000%, and stable adhesion. Flexible sensors integrated with this hydrogel demonstrate the capability to monitor human motion reliably even under sub-zero conditions. This strategy offers a viable approach for the design of intrinsically anti-freezing hydrogels and establishes a basis for the development of sensing devices in cold environments. Download: Download high-res image (254KB) Download: Download full-size image