“Low Impedance, Durable, Self-Adhesive Hydrogel Epidermal Electrodes for Electrophysiology”

Thesis lab: Chuan Wang (WashU Electrical & Systems Engineering)

Abstract: Traditional electrodes used for electrophysiology recording, characterized by their hard, dry, and inanimate nature, are fundamentally mismatched with the soft, moist, and bioactive characteristics of biological tissues, leading to suboptimal skin-electrode interfaces. Hydrogel materials, mirroring the high water content and biocompatibility of biological tissues, emerge as promising candidates for epidermal electronic materials due to their adjustable physicochemical properties. However, challenges such as inadequate electrical conductivity, elevated skin impedance, unreliable adhesion in moist conditions, and performance decline from dehydration have significantly restricted the efficacy and applicability of hydrogel-based electrodes. In this thesis, we report a high-performance hydrogel epidermal electrode patch for electrophysiology signal recording and mechanical stimuli sensing applications. By integrating a polar solvent, PEDOT particles are clustered and realigned into extended chains to enhance charge transfer. KCl salt ions, serving as conductive agents, merge with the polyacrylamide crosslinked network to establish an interpenetrating polymer network (IPN), achieving superior electrical conductivity and reduced skin impedance. The hydrogel epidermal electrodes, fortified with catechol-rich tannic acid and an innovative suction cup design inspired by octopus tentacles, exhibit exceptional skin adherence across diverse conditions. The incorporation of glycerol and a sealed hydrogel layer with the same mechanical properties as the hydrogel skin electrodes further solidifies the stability and functionality of the electrodes. This hydrogel epidermal electrode patch holds promising potential for capturing human electrophysiological signals, enabling high signal-to-noise ratio, high fidelity, durable and stable recordings in electrocardiograms and electromyograms without the need for external fixatives, and maintaining functionality in humid and submerged environments. In addition, this study provides insight into the potential of hydrogel epidermal electrodes as mechanical sensors, expanding their range of applications.

For inquiries contact Aaron Beagle at abeagle@wustl.edu.