Adhesive Biocomposite Electrodes on Sweaty Skin for Long-Term Continuous Electrophysiological Monitoring

Abstract

Noninvasive on-skin electrodes record the electrical potential changes from human skin, which reflect body condition and are applied for healthcare, sports management, and modern lifestyle. However, current on-skin electrodes have poor conformal properties under sweaty condition in real-life because of decreased electrode-skin adhesion with sweat film at the interface. Here, we fabricated biocomposite electrodes based on silk fibroin (SF) through interfacial polymerization, which is applicable on sweaty skin. Interfacial polymerized conductive polypyrrole (PPy) and SF are structurally interlocked and endow the whole electrode with uniform stretchability. Existence of water results in similar Young's modulus of SF to the skin and enhanced interfacial adhesion. It keeps the electrodes conformal to skin under sweaty condition and allows reliable collection of ambulatory electrophysiological signals during sports and sweating. Wearable devices with these electrodes were used to acquire continuous and stable real-time electrocardiography (ECG) signals during running for 2 h. The collected signals can provide information for sports management and are also analyzed by artificial intelligence to show their potential for intelligent human emotion monitoring. Our strategy provides opportunities to record long-term continuous electrophysiological signals in real-life conditions for various smart monitoring systems.

A Compliant Ionic Adhesive Electrode with Ultralow Bioelectronic Impedance

“…Ionic conduction in the biological system plays a central role in the transmission of vital signs and performing physiological activities, such as the transmission of nerve signals, muscle contraction, heart beating, and blood pressure control. [ 1–24 ] Highly efficiently and precisely collecting or delivering these ionic signals are of great interest in clinical neurophysiology and material science for future wisdom medical and AI device controlling. [ 1,25–30 ] Therefore, an electrode that complies with the curved biological surface and has low bioelectrical interfacial impedance (the ideal impedance of electrode‐skin system is 6–10 kΩ which is the intrinsic impedance of skin) is in demand to effectively couple the ionic fluxes in electrolytic tissues and electronic current in recording devices.…”

Conducting polymers in wearable devices

“…This would hinder affixation of electrode to skin. Using water to enhance interfacial polymerization between silk fibroin (SF) and PPy (PPy) result in stretching uniformly plus water (in sweat) enhance adhesion of patch to skin due to mechanical property match between conductive (PPy) and adhesive layer (SF) (Yang et al, 2020). Interfacial polymerization is executed using SF gel, made by formic acid solution of SF (adhesive layer), FeCl 3 (PPy polymerization initiator) and CaCl 2 (adjust mechanical property of SF gel).…”

“…(c) The highly conformal property of CAPE on the human elbow. (d) Interfacial adhesion energy of CAPE increased with increasing relative humidity from 11% to 94.6%, compared with commercial gel electrodes (adapted with permission from Yang et al, 2020)…”

“…Further incorporation with other elements such as D‐sorbitol is also reported (Spyropoulos et al, 2019). Other than PEDOT:PSS, interfacial polymerization between SF and PPy improves maximum strains up to 300% with 1.91Mpa maximum adhesion (Yang et al, 2020). 60% maximum strains with 250 kPa maximum adhesion is achieved through octopus patterned electrode moulded using Carbon black with PDMS and p3ht mixture.…”

“…Using water to enhance interfacial polymerization F I G U R E 7 (a) Logic circuit diagram and working principal of fibre-based organic electrochemical transistors when no gate voltage (up) and positive gate voltage (down) are applied; the letters S,D, and G represent the source, drain, and gate electrode, respectively. (b) Woven series arrayed fibre-based organic electrochemical transistor circuit with PPy/NFs/PA6 fibre in the wearable point-of-care applications (adapted with permission fromQing et al, 2019) between silk fibroin (SF) and PPy (PPy) result in stretching uniformly plus water (in sweat) enhance adhesion of patch to skin due to mechanical property match between conductive (PPy) and adhesive layer (SF)(Yang et al, 2020). Interfacial polymerization is executed using SF gel, made by formic acid solution of SF (adhesive layer), FeCl 3 (PPy polymerization initiator) and CaCl 2 (adjust mechanical property of SF gel).…”