Ultrathin Hydrogel Biosensor with Controllable Self-Adhesion Properties for Electrophysiology Measurement

Hydrogel has recently been utilized to develop health monitoring sensors and devices such as bioelectrodes. Owing to their good electrical conductivity, ultra-softness, and self-adhesion, current hydrogel sensors have found their application in electroencephalogram (EEG), electromyogram (EMG), and electrocardiogram (ECG) recording. However, the highly adhesive hydrogels are hard to peel off from the surface of the skin after laminating it and they are susceptible to losing the water content and unfavorable changes in the electrical conductivity and mechanical softness. Here we report an ultrathin hydrogel-based sensor with controllable self-adhesion properties that can fully conform to the skin and perform reliably for an extended period. An ultrathin, conformable biosensor with a thickness of less than 10 μm is fabricated based on gelatin-acrylamide-polypyrrole hydrogel, where the sol-gel transition of the gelatin is utilized to control the modulus and adhesion force. The ultralow thickness and good stretchability of the gelatin-acrylamide-polypyrrole hydrogel contribute to a seamless interface between the biosensor and human skin, which is desired in wearable devices for high-quality bio-signal acquisitions such as electrocardiography (ECG) and electromyography (EMG).