Cold Polymerization Enables a Hybrid Hydrogel for Coupling Electronic Devices to Skin

Wearable electronic devices monitoring physiological signals from skin generate heat that can lead to skin irritation, burns, and reduced device lifespan. Current heat‐managing materials involve trade‐offs in performance, flexibility, strength, and biocompatibility. Here, we report a heat‐managing adhesive hydrogel for wearables that is simultaneously transparent to ultrasound waves, available for electronic recording, conformable to skin, durable and biocompatible. Our hydrogel integrates biomacromolecule gelatin with synthetic polyacrylamide. A cold crosslinking strategy is proposed to kinetically trap the gelatin‐acrylamide mixture in a physical gel state prior to photocrosslinking, effectively preventing otherwise phase separation and yielding a transmitted and structurally stable hybrid hydrogel. In our hydrogel, gelatin absorbs heat through gel‐sol transition, while its chemical crosslinking with polyacrylamide strengthens the material. The resulting hydrogel is an excellent coupling pad for ultrasound imaging and electroencephalogram recording, and functions as a strain sensor for monitoring human motion. This hybrid material system could be a universal material form coupling rigid devices to skin or coupling stretchable electronic devices to skin.