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 Omega 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. (C) 2016 Published by Elsevier B.V.