Sweat-inspired cone-beaked waterbirds drain flexible electrophysiological electrodes in a directional manner. Courtesy of Hu Chuan’s team
Flexible electrophysiological electrodes are used for weight balancing training and shooting muscle precision control training. Courtesy of Hu Chuan’s team
Inspired by skin perspiration and water-oriented transmission in nature, Professor Hu Chuan’s team at the Institute of Semiconductors of Guangdong Academy of Sciences has made important progress in the research direction of bionic perspiration bioelectrodes. The research was recently published in Advanced Materials Technologies.
The latest technological innovations in wearable electronics offer the possibility of real-time monitoring of electrophysiological parameters such as ECG, EMG and EEG. As a bridge between the biological world and the information world, electrophysiological electrodes convert the ion signals of biological tissues into electrical signals. To achieve accurate and long-term electrophysiological measurements, the ideal electrode should have the following characteristics: excellent biocompatibility, conformal adhesion, user-friendliness, long-term stability, and low skin-electrode impedance to guarantee signal sensitivity and reliability. Much progress has been made in the problems associated with the skin-electrode interface, but the challenges associated with sweat have not yet been fully addressed.
Perspiration is a way for humans to regulate body temperature, when the electrodes are attached to the skin for a period of time, sweat will form a thin layer of water at the skin interface, which acts as an electrolyte. However, in the case of more sweating, on the one hand, the excessively thick sweat layer makes the interface impedance of the electrode-skin increase sharply, resulting in a poor signal acquisition effect; on the other hand, the adhesion between the electrode and the skin is seriously weakened due to the lubrication effect of sweat, resulting in the electrode and the skin sliding relatively to produce a serious motion pseudo-difference. Breathable fabric electrodes are known to mitigate these effects to some extent, but the ability of fabric electrodes to wick away is too laborious when the wearer is in the case of excessive sweating, such as strenuous exercise or high temperature environments.
The directional transmission of water is a universal phenomenon in nature. For example, water birds transport water droplets in a directional manner through the opening and closing action of the tapered beak, which can be explained by the Laplace pressure gradient. Inspired by skin perspiration and the phenomenon of water-directed transport in nature, Hu Chuan’s team developed a Janus gold nanowire/nitrocellulose (AuNWs/NC) electrophysiological electrode with tapered micropores to address the interface problems caused by sweat. Under the action of laplace pressure differential caused by the asymmetrical structure of the tapered pore and the wettability gradient within the well, the Janus AuNWs/NC electrode spontaneously sucks sweat from the AuNWs side to the NC side, thus maintaining close contact and low interfacial impedance of the skin electrode to ensure high-fidelity signals during long-term monitoring.
A series of experiments have proved that the ECG and EMG signals collected by the non-perspiration-wicking electrode with more sweat at the electrode-skin interface are severely distorted. The bionic perspiration electrode collects high-fidelity ECG and EMG signals even when the skin at the site under test is sweating profusely. Therefore, this bionic perspiration electrode can solve the interface problem caused by skin sweating and improve the recording quality of electrophysiological signals during long-term wear and exercise.
Hu Chuan’s team also integrated non-porous electrodes with circuit modules, advanced algorithms and human-machine interfaces to develop a muscle activity intensity visualization system based on EMG signals. The EMG monitoring system can be applied to accurately assess the control and balance of specific muscle groups and has been initially validated in the training of shooting and weightlifting sports. In addition to this, the system has great potential in terms of rehabilitation and sports training.
The study proposes a new solution to the skin interface problem of the next generation of skin wearable electronic devices.
The research work is supported by the National Natural Science Foundation of China, the Guangdong Provincial Key Area R&D Program Project, and the Guangdong Academy of Sciences’ Action Special Fund Project for Building a First-class Research Institution in China. (Source: China Science Daily, Zhu Hanbin, Yin Shuhui)
Related paper information:https://doi.org/10.1002/admt.202200040