Self-adhesive, biodegradable silk-based dry electrodes for epidermal electrophysiological monitoring

Abstract Epidermal flexible devices can continuously and real-time record the electrical potential changes from human skin, which is essential for chronic disease diagnosis and smart health monitoring. However, it remains challenging to fabricate high-performance epidermal dry electrodes with excellent self-adhesive while maintaining excellent biodegradability as well as high mechanical performance and low contact impedance. Herein, we fabricate an epidermal dry electrode with high mechanical performance, low contact impedance and excellent self-adhesive by coating polypyrrole (Ppy) conductive layer and calcium (Ca)-modified SF adhesive layer on acid-modified silk (AM-SF)/cellulose nanocrystals (CNC) films. The AM-SF could effectively promote the absorption and intercalation of Ppy into the SF network, endowing the tight integration between the Ppy conductive layer and the AM-SF/CNC films and improving the conductivity of Ppy@AM-SF/CNC films. On the other side, the Ca ions in the Ca-modified SF adhesive layer capture water molecules from the atmosphere and result in a much higher flowability to allow conformal contact between Ca-modified SF and the human skin, leading to significantly low skin-electrode impedance. As a proof-of-concept, the Ppy@AM-SF/CNC electrodes are employed for both electrocardiography (ECG) and electromyography (EMG) recording. Interestingly, this electrode allows detaching from the skin by simple water rinsing to reduce skin-damage for people. Moreover, the Ppy@AM-SF/CNC electrodes possess excellent enzymatic degradability without leaving hazardous substances. This work offers a unique prospective for developing next-generation wearable healthcare devices in the era of personalized healthcare.