Totally shape-conformable electrode/hydrogel composite for on-skin electrophysiological measurements

An Au film electrode supported by a conductive elastic film was tightly bonded on a stretchable double-network hydrogel sheet by means of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) grown from the electrode surface into the hydrogel. This electrode/hydrogel composite showed stable resistance of 35 ± 5 Ω sq⁻¹ even during successive 20% stretching because of the pre-formed, designed cracks in the Au film. The large interfacial electric double layer capacitance (9.5 ± 0.3 mF cm⁻²) of the PEDOT adhesive layer at the interface of the layered composite was found to stabilize the electrode potential against external noises, and decrease the electric impedance at the frequency of 5–500 Hz, which is the typical range of electromyographic signals. The electrical robustness and shape-conformability of the composite electrode were demonstrated by monitoring electromyographic signals of the joint of a human forefinger. In addition, it was also demonstrated that an ionic liquid-containing gel (ionogel) serves as a substrate of the composite for longer-term monitoring over 3 days on air-exposed human skin.