CaCl2-Enhanced Interpenetrating Polymer Network Hydrogels with Stable Freeze Resistance and Sensing Durability Performance.
Hydrogels are attractive for flexible electronics and wearable sensors, yet their performance is severely limited at subzero temperatures due to ice crystallization, dehydration, and mechanical embrittlement. Here, we report a CaCl2-enhanced double-network (DN) hydrogel (BNP-x) that integrates excellent anti-freezing, mechanical, and adhesive properties with reliable strain-sensing capabilities. The hydrogel combines a covalently crosslinked P(NIPAm-co-HEA) network and an ionically coordinated poly(acrylic acid) network, in which Ca2+ ions regulate water states and suppress ice formation. The optimized BNP-6 hydrogel exhibits excellent low-temperature performance, maintaining a tensile strength of 0.16 MPa and an elongation at break of ∼849% at -30 °C with minimal mass loss and stable properties over repeated freeze-thaw cycles. Owing to the synergistic DN structure and mobile Ca2+ ions, BNP-6 retains high ionic conductivity (44.1 mS cm-1 at -10 °C), representing only a 17.9% decrease compared to its room-temperature value. Moreover, the hydrogel demonstrates stable adhesion, rapid strain response, and reliable sensing performance under subzero conditions-even during cyclic deformation and self-healing processes-highlighting its potential for robust low-temperature wearable electronics and bioelectronic interfaces operating in harsh environments.