E-textiles with embedded novel dry electrodes for wearable electrotherapy applications

Abstract

Electrotherapy involves applying electrical stimulation to the nerves and/or muscles for therapeutic applications. It is a commonly used intervention for reducing pain (e.g., transcutaneous nerve stimulation (TENS)) and improving movement function (e.g., functional electrical stimulation (FES)). Although various commercial electrotherapy devices have been developed, challenges remain on the usability (e.g., comfort, ease of use), affecting user experience and adherence to treatment caused by the poor performance of existing electrodes (detailed in Section 1. Introduction).
Textiles are the most comfortable material for wearable applications due to their natural properties (e.g., lightweight, soft, and breathable). This work is to develop wearable electronic textiles (E-textiles) with dry electrodes embedded in sleeves for electrotherapy applications in knee joint pain relief using TENS, and stroke hand/arm rehabilitation using FES. The main work includes novel electrodes development, textile and electrode integration, prototype design and testing, and durability measurement and improvement.
Novel dry electrode paste formulations and fabrication processes have been investigated. Different silicone polymer materials and carbon percentages were investigated to achieve an optimised formulation which produces a soft (Shore hardness 11 HA) and conductive (26.6 Ω·m) electrode. Three electrode mixing processes (e.g., hand mixing, kitchen mixer, speed mixer) were evaluated to achieve a uniform electrode with significantly reduced voids in the cross-section as evidenced by scanning electron microscope (SEM) images. The relationship between the electrode resistivity and the pressure applied on the electrode was assessed.
The electrode paste has been used to fabricate wearable TENS electrodes for osteoarthritis (OA) knee joint pain relief. Three fabrication integration methods (weaving of conductive textile followed by electrode printing, all-printing, lamination of printed conductive tracks followed by electrode printing) were investigated to improve the stretchability and washing durability. The optimal performance was achieved by laminating sinusoidal conductive tracks followed by electrode printing which can stretch by 50% with a recovered resistance change less than 36% and survive 100 washes.
The application of the optimal e-textile has also been demonstrated in FES for stroke hand/arm rehabilitation. Considering the disability of people who have had a stroke, E-textile sleeves were designed and tested with this group to ensure usability. Bespoke electrode sleeves have been tested with three participants who have had a stroke to determine the optimal design that allows them to put on and take off the electrode sleeve independently. Hand extension has been achieved on all participants and all of them confirmed the electrode sleeve is comfortable to wear.
Although the first investigated electrode has demonstrated good conductivity and usability, it has limited pot life (~10 mins) when the components are mixed together. This limits its application in cases where the electrode cannot be processed within its limited pot life. Therefore, a novel dry electrode paste formulation with extended pot life (~3 hours) has been developed. Optimised formulation was achieved through using the combination of graphite and carbon at a ratio of 2:1 in 25 parts per hundred rubber (phr). The potential use of the electrode material has been demonstrated by fabricating a fully dispenser-printed 24-electrode array on textile which requires longer processing time. It also showcases the feasibility to develop a bespoke electrode design without needing physical screens, which allows customised designs to be made in a cost-effective and time-efficient manner.

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Identifiers

ORCID for Meijing Liu: orcid.org/0000-0001-8334-7533

ORCID for Stephen Beeby: orcid.org/0000-0002-0800-1759

ORCID for Kai Yang: orcid.org/0000-0001-7497-3911

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