Ultrasoft, adhesive, pH-tunable hydrogel based on in situ functionalized laser-induced graphene for through-hair concurrent biosensing

This work reports a printable, ultrasoft, highly stretchable, adhesive, breathable hydrogel engineered that is radically tuned by controlling the precursor pH level for simultaneous biosignal monitoring. The hydrogel based on porous laser-induced graphene composites synthesized using in situ laser reduction with polydopamine and tannic acid exhibits ultrasmall Young's modulus of 1.08 kilopascal, super high stretchability of ~8000%, and desirable conductivity and adhesive strength for through-hair signal monitoring even in the presence of sweat. The excellent skin conformability of the hydrogel provides the resulting electrodes with low skin contact impedance at both wet and dry conditions, a high signal-to-noise ratio, and motion artifact-free monitoring of electrophysiological signals. Combined with electrodermal activity and strain sensing from the facile patterning/printing of the reusable and storable gel, the proof-of-concept demonstration of the device platform is showcased for anxiety monitoring and nerve rehabilitation studies.