Ultrastretchable, Self-Adhesive and conductive MXene nanocomposite hydrogel for body-surface temperature distinguishing and electrophysiological signal monitoring

Epidermal sensors capable of monitoring various physical signals are vital in wearable healthcare applications. MXene-based conductive hydrogels have become promising candidates as skin-attachable sensors for these purposes. However, due to the easy oxidation and weak combination of MXene nanosheets with network matrix, it remains challenging to construct a mechanically tough, highly conductive and skin-conformal hydrogel for reliable signal recording (especially weak electrophysiological signals). Herein, a new conductive MXene-based hydrogel is fabricated through introducing silk fibroin (SF)-modified MXene (MXene-SF) into polyacrylamide (PAM) network. It is demonstrated that the encapsulation of SF on MXene surfaces greatly improves its stability, and meanwhile induces the formation of multiple noncovalent interactions between MXene-SF and PAM chains. The resulting hydrogel exhibits high stretchability (1560 %), remarkable toughness (165 kJ/m 3 ), high conductivity (0.25 S/m) and self-adhesion. This hydrogel is high-sensitive in a large strain range for detecting various human motions. Especially, the high conformal adhesion and low interface impedance make the hydrogel bioelectrodes precisely monitor weak electrophysiological signals (e.g. electromyogram and electrooculogram), successfully achieving sign language translation and eye tracking. Additionally, the hydrogel has great thermosensitive capacities for body temperature monitoring. This study provides a general strategy for designing MXene-based hydrogels with tailored functionalities as flexible electronics.