| Textile electrodes have received much attention in the last ten years. As the growing aging population, cardiovascular diseases have been the top diseases of death among elderly people, even found in younger people, which have become a medical and economic burden to the whole society. Cardiovascular diseases is chronic, accumulative and unpredictable, conventional periodic fitness checkup can hardly found this kind of diseases in advance, the prevail method in abroad is long-term ECG monitoring. However, the traditional disposal metal plate electrodes are not suitable for long-term health monitoring because the electrodes are stuck to skin using hydrogel to improve skin-electrode interfacial contact. The hydrogel has adverse effect on electrode performance when it is dehydrated, as well as causing skin allergy or inflammation in long-term application. As a potential alternative to traditional metal plate electrodes, textile electrodes don’t have these disadvantages which are superior in its flexible structure, comfortable feeling, good air and moisture penetration ability, as well as dry application without gel, thus less prone to skin problems in long-term application. Additionally, textile electrodes are washable, reusable and easy integrated into garments for wearable health monitoring. These advantages will undoubtedly promote more application areas for textile electrodes as well as influential social impact in the future. Although textile electrodes is a newly emerge research area, it became a hottest research topic in the scientific community showing its academic importance. Using textile structures to fabric biopotential monitoring electrodes came up only in last ten more years, which is a multidisciplinary subject involving material science, physics, chemistry, electronics, biology, mechanics and so on. In recent years, textile electrodes has been enthusiastically investigated in developed countries and regions, such as Europe, American, Japan, South Korea and Taiwan, while the research in China is still at its early stage. The state-of-the-art textile electrodes can detect perfect ECG signal when the subject is in static state, while the signal may be contaminated by noise from body movement usually called motion artifacts. Actually, motion artifacts are common phenomenon among physiological measurements which have been extensively studied in traditional metal plate electrode. From the study, we know that motion artifacts in ECG signal mainly originated from the skin-electrode interfacial instability and skin deformation induced potentials. Whereas, compared with traditional metal plate electrodes, motion artifacts in textile electrodes have their own characteristics as the differences in structure and application methods. Textile electrodes are flexible and no gel presents at the skin-electrode interface, the contact area is easily affected by fabric deformation and skin-electrode relative slippage during body movement. So motion artifacts in textile electrodes are much more complicated than traditional metal plate electrodes, especially the noise from skin-electrode interfacial instability which is the main concern of this study. The methodology in our study is through the investigation of skin-electrode mechanical interaction to determine the influence of textile structure and electrode movement on motion artifacts, thus to analyze the mechanism of motion artifacts. According to the above described method, the following wok has been done in the past few years,(1) Fabrication of textile electrodes and evaluation of the static performance. In this study, silver coated multifilament was used to fabricate textile electrodes. To improve fiber surface electrochemical properties e.g. polarization impedance and electric stability, the fiber surface was chlorided in0.9%NaCl solution using electrochemical method, the silver at working electrode was decomposed and reacted with chlorine ionic to deposit silver chloride (AgCl) on fiber surface. The processing parameters include electric voltage and treating time which affect surface microstructure and impedance of electrodes. These parameters were optimized and the treated fibers were fabricated into textile electrodes using woven, knitting and embroidery techniques. Electrical performance such as impedance and open circuit potentials of different structural electrodes were tested, ECG signal were also measured to verify the functionality of these electrodes. (2) Analysis of skin-electrode mechanical interaction. Understanding the electrode-skin mechanical interaction in dynamic state is crucial to study the motion artifacts of textile electrodes. In this study, skin-electrode mechanical interaction is defined as two independent movements:in-plane movement parallel to skin and vertical compression to skin. A special designed electrode with integrated optical displacement sensor was used to determine electrode moving speed during various body movement. The electrode-skin compression is indicated by skin-electrode contact pressure which is measured by a thin film pressure sensor at specific body locations. Electrode-skin relative moving speed and their pressure variation were analyzed which can be a useful reference for the dynamic evaluation of textile electrodes. Additionally, ECGs during different body movements were measured to analyze the influence of boy movement on ECG signal.(3) Evaluation of the motion artifacts of textile electrodes. From previous studies, we know that the influential effect of boy movement on motion artifacts of ECG signals which need to be objectively evaluated. However, physiological conditions varied greatly from subject to subject, even within subject at different times, making the experimental results inconvincible and unrepeatable, so a dynamic measurement equipment was developed. The equipment consists five parts:skin simulator, motion controller, data acquisition unit, electrolyte circulation apparatus and computer program. When testing, electrolyte circulation apparatus pumps 0.9%NaCl solution through skin simulator, electrodes held by motion controller move on skin simulator, data acquisition unit records various signals such as electrode pressure, electrode open circuit potential, skin-electrode interfacial impedance. These signals were analyzed to quantify motion artifacts induced by electrode pressure and moving speed.(4) Study the mechanism of motion artifacts of textile electrodes. Motion artifacts are directly related to skin-electrode mechanical interaction which has been demonstrated in previous in-vivo measurement (2) and simulated evaluation (3). To study the mechanism of motion artifacts from skin-electrode interaction, an equivalent circuit model of skin-electrode interface was built whose parameters can be determined by analyzing interfacial impedance. From simulated study, we know that electrode pressure has obvious effect on interfacial impedance while electrode moving speed has least. We assume that the motion artifacts are attributed to interfacial capacitance. Through theoretical calculation using open circuit potential and model parameters, the assumption were verified by simulated study and in-vivo measurement. |
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