Highly adhesive, washable and stretchable on-skin electrodes based on polydopamine and silk fibroin for ambulatory electrocardiography sensing

Ambulatory electrocardiography (ECG) is used to realize the diagnostics of coronary heart disease. On-skin electrodes are employed for ambulatory ECG sensing through conformable contact with the arbitrarily shaped moving skin. However, the low skin-adhesion of electrodes limits their application in long-term ambulatory ECG sensing. For example, for the current on-skin electrodes, the low shear viscosity of sweat on the skin decreases the skin-adhesion, leading to their slipping and even falling off. Herein, highly adhesive and washable on-skin electrodes were achieved by combining stretchable Au nanofilms with hybrid materials composed of polydopamine and silk fibroin (SF). The strong interaction of polydopamine with water enhanced the adhesion energy of these electrodes by decreasing the Young's modulus of the SF gel and increasing the contact area between electrodes and skin. Additionally, the microcrack structure of Au nanofilms provided good conductivity upon stretching. Remarkably, our electrodes could be easily removed on washing and had low impedance due to the existence of hydrophilic SF and Ca2+. To demonstrate the application of these electrodes for perceiving accurate and reliable signals, they were pasted on the skin to record long-term and high-quality ECG signals for the diagnosis of heart disease.