Highly ionic conductive, elastic, and biocompatible double-network composite gel for epidermal biopotential monitoring and wearable sensing.

Soft ionic conductors are promising candidates for epidermal electrodes, flexible sensors, ionic skins, and other soft iontronic devices. However, their inadequate ionic conductivity and mechanical properties (such as toughness and adhesiveness) are still the main constraints for their wide applications in wearable bioelectronics. Herein, an all-biocompatible composite gel with a double-network (DN) strategy is proposed. Compared to the single network, introducing a double-helix structured ι-carrageenan facilitates the DN gel with greatly enhanced mechanical properties and higher ionic conductivity (16.0 mS cm). Moreover, the DN gels exhibit high transparency (>92 %), high stretchability (1660 %), and sufficient adhesion. Benefiting from the above unique features, the DN gels successfully serve as biopotential electrodes, which can dynamically monitor human electrophysiological signals with a higher signal-to-noise ratio and superior environmental stability than the commercial electrode. Additionally, they can be employed as resistive strain sensors for accurate human movement monitoring. Our multifunctional DN composite gels offer a feasible platform for on-skin bioelectronics and human-machine interactions.