A Robust and Adhesive Hydrogel Enables Interfacial Coupling for Continuous Temperature Monitoring

Continuous temperature monitoring by flexible hydrogel-based electronics achieves rapid advances, overcoming the drawbacks of rigid and unportable thermocouples. However, an open question is whether and how the thermosensitive hydrogel designing can prevent mechanical mismatching between devices and skin-tissues and reduces interfacial failure. Herein, a versatile hydrogel-based thermistor epidermal sensor (HTES) paradigm is engineered consisting of thermosensitive and self-adhesive function layer (PEST) in tandem with a surface spraying Ag interdigital electrode. Leveraging the advantage of catechol chemistry inspired tannic acid-coated cellulose nanocrystals, the resultant PEST achieves the adhesion-cohesion equilibrium along with superior thermosensitivity. The assembled HTES thereby yields unprecedented features of superior thermosensitivity (TCR = 1.43% degrees C-1), exceptional mechanical integrity (hammering 200 cycles, current variation <9%), impressive interfacial compatibility (adhesion strength, 25 kPa), and environmental stability (thermosensation retention of 98% over 5 days). By in-situ microstructure observation, the unique geometrical synchronization of HTES with arbitrary curvilinear surfaces (e.g., sphere, cone, and saddle) stemming from elastic dissipation and discrete rupture of the adhesive fibrillar bridges is validated, affording competitive advantages than that of the state-of-the-art thermistor electronics for alleviating the interfacial deterioration, which dramatically inspires advanced HTES design strategies and paves the way for commercialization of attachable thermistor electronics.