Microneedle electrodes for electromyography

Surface electromyography (sEMG) is the measurement of the electrical activity of muscle and is extensively used in fundamental research and across many applications in health and sport. Conventional surface electrode technology can suffer from poor signal quality, particularly when used outside the laboratory, requires careful skin preparation prior to electrode application, and can be challenging when used for long-term recording. These limitations have challenged the translation of sEMG to widespread clinical application. In addition, with the advent of home healthcare, ambulatory monitoring and associated wearable technology, there is a need for new types of electrodes which can be easily applied by non-experts, and that enable high-quality measurements during day-to-day activities and long-term wear. Dry microneedle electrodes (MNEs) have been proposed as a way to overcome some of the limitations associated with conventional sEMG recording electrodes. By penetrating the outer layer of the skin, the stratum corneum, MNEs offer the potential to improve the quality and consistency of the electrode-skin interface, and the resulting sEMG signals, while maintaining stability of the electrode-tissue contact and eliminating the need for skin preparation. This article provides a review of the state-of-the-art in microneedle electrode research for sEMG applications, covering the theoretical background, fabrication methods and recording performance in studies conducted to-date. Data are presented which demonstrate the long-term stability of microneedle recording systems for EMG, their capability to reduce contact impedance and potential to improve signal to noise ratio, opening new opportunities for sEMG recording and analysis.