All-in-one, gas-permeable, ultrathin, flexible, and self-adhesive epidermal electrode for biopotential recording and muscle theranostics

Epidermal electronics have attracted extensive attention owing to their potential in personal healthcare and human–machine interactions (HMIs). However, their low conductivity and poor ability to conform to the human skin impede their practical application. Herein, a multifunctional flexible dry epidermal electrode for biopotential recording and muscle thermotherapy was developed based a conductive polymer (poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT:PSS)). PEDOT:PSS was modified using poly(vinyl alcohol) (PVA) with hydrophobic groups. The electrode is able to self-adhere to human skin through a hydrophobic interaction with the skin. Moreover, the hydrophilic groups can absorb the humidity under the skin and move it by the hydrophobic groups, which allows the electrode exhibits good gas-permeability. The ultrathin electrode conforms well to the topography of the human skin and, thus, can form a stable and intimate interface with it, resulting in a low electrode–skin contact impedance that allows the recording of biopotentials with high quality. Moreover, the electrode exhibits rapid Joule heating performance at a low voltage (up to 53.8 °C in 12 s at 1.5 V), which is suitable for the electrothermal therapy of muscle. On-body measurements confirm that our electrode could detect muscle fatigue via electromyography (EMG) and perform electrothermal therapy to relieve muscle fatigue. This study offers an efficient method for developing all-in-one wearable flexible epidermal electrode for biopotential recording and muscle theranostics.