Evaluating Textile Electrodes for Transcutaneous Electrical Nerve Stimulation: Performance and Viability, 2021-2023

Over recent decades, wearable electronics have introduced successful bio-medical products to the commercial market, including real-time monitoring, symptom diagnosis, stimulation therapy, and rehabilitation. Hydrogel electrodes are commonly used in such devices, for data acquisition or electrical intervention. However, they are not a comfortable option for long-term applications and can trigger allergic reactions. Furthermore, it has been demonstrated that most water-based electrolytes, such as pure water, saline and conductive gel, gradually evaporate, resulting in signal degradation for long-term use. The electrode properties become particularly important in applications where moderate amount of electrical current is injected to the body, as in transcutaneous electrical nerve stimulation (TENS). To this end, a promising alternative is seen in conductive textile-based, dry electrodes.
However, there is not sufficient evidence investigating viable alternative electrolytes for electrical stimulation involving human subject participation and controlled measurement. The aim of this work is to determine the possibility of TENS using textile electrodes to ensure stable performance over both short and long-term timescales. This was achieved by simultaneous EMG measurements to validate the efficacy of our electrode setup. The stimulation electrode prototypes used in the study comprised a knit conductive fabric, a soft insulating filling, an underlying layer of insulating fabric, and a pair of metal connectors. The EMG measurement is done using standard hydrogel electrodes. All the textile electrode prototypes used in this study have identical dimensions of 50 mm × 50 mm to match the size of typical CE certified hydrogel electrodes. A FDA approved Constant Current Stimulator (Digitimer DS-07A) was used for stimulation.
Four healthy volunteers – one female (25 years old), and three males (28, 32, and 35 years old) – participated in this experiment. All experimental protocols were approved by the Informatics Research Ethics Committee, University of Edinburgh, and all participants gave written informed consent before the start of the trial.