Wearable smart textiles for long-term electrocardiography monitoring : a review

The continuous and long-term measurement and monitoring of physiological signals such as electrocardiography (ECG) are very important for the early detection and treatment of heart disorders at an early stage prior to a serious condition occurring. The increasing demand for the continuous monitoring of the ECG signal needs the rapid development of wearable electronic technology. During wearable ECG monitoring, the electrodes are the main components that affect the signal quality and comfort of the user. This review assesses the application of textile electrodes for ECG monitoring from the fundamentals to the latest developments and prospects for their future fate. The fabrication techniques of textile electrodes and their performance in terms of skin–electrode contact impedance, motion artifacts and signal quality are also reviewed and discussed. Textile electrodes can be fabricated by integrating thin metal fiber during the manufacturing stage of textile products or by coating textiles with conductive materials like metal inks, carbon mate-rials, or conductive polymers. The review also discusses how textile electrodes for ECG function via direct skin contact or via a non-contact capacitive coupling. Finally, the current intensive and promising research towards finding textile-based ECG electrodes with better comfort and signal quality in the fields of textile, material, medical and electrical engineering are presented as a perspective

Highly Sensitive Soft Foam Sensors for Wearable Applications

Due to people’s increasing desire for body health monitoring, the needs of knowing humans’ body parameters and transferring them to analyzable and understandable signals become increasingly attractive and significant. The present body-sign measurement devices are still bulky medical devices used in settings such as clinics or hospitals, which are accurate, but expensive and cannot achieve the personalization of usage targets and the monitoring of real-time body parameters. Many commercial wearable devices can provide some of the body indexes, such as the smartwatch providing the pulse/heartbeat information, but cannot give accurate and reliable data, and the data could be influenced by the user’s movement and the loose wearing habit, either. In this way, developing next-generation wearable devices combining good wearable experience and accuracy is gathering increasing attention. The aim of this study is to develop a high-performance pressure/strain sensor with the requirements of comfortable to wear, and having great electromechanical behaviour to convert the physiological signal to an analyzable signal

Challenges in Design and Fabrication of Flexible/Stretchable Carbon- and Textile-Based Wearable Sensors for Health Monitoring: A Critical Review

To demonstrate the wearable flexible/stretchable health-monitoring sensor, it is necessary to develop advanced functional materials and fabrication technologies. Among the various developed materials and fabrication processes for wearable sensors, carbon-based materials and textile-based configurations are considered as promising approaches due to their outstanding characteristics such as high conductivity, lightweight, high mechanical properties, wearability, and biocompatibility. Despite these advantages, in order to realize practical wearable applications, electrical and mechanical performances such as sensitivity, stability, and long-term use are still not satisfied. Accordingly, in this review, we describe recent advances in process technologies to fabricate advanced carbon-based materials and textile-based sensors, followed by their applications such as human activity and electrophysiological sensors. Furthermore, we discuss the remaining challenges for both carbon- and textile-based wearable sensors and then suggest effective strategies to realize the wearable sensors in health monitoring

Flexible surface electrodes targeting biopotential signals from forearm muscles for control of prosthetic hands: Part 1 - Characterisation of semg electrodes

This study is Part 1 of two studies which investigate the use of various flexible surface sensors as an alternative to the gold standard Ag/AgCl surface electromyography (sEMG) electrodes in identifying movement intention from a user during common hand gestures. Three conductive textiles, two commercial conductive elastomers and one E-skin elastomer produced on site were tested as biopotential electrodes to establish the efficacy of each in gathering movement intention from the human brain at the level of the muscle. Testing was performed in vivo on two participants across three hand gestures, with results demonstrating that sEMG electrodes made from a commercially sourced conductive fabric can outperform the traditional Ag/AgCl sEMG electrodes, obtaining substantially larger peak and RMS measurements. Given the disadvantages of Ag/AgCl electrodes over long usage periods, namely their tendency to dry out and significant skin preparation, resulting in variable impedances and skin irritation respectively, the incorporation of flexible surface EMG electrodes in hand prosthetic control systems would increase functionality of the prosthetic devices, consequently increasing the quality of life of prosthetic hand users

Entwicklung einer berührungslosen EEG-Mütze mittels kapazitiver Elektroden

Non-contact capacitive electrodes for bioelectric diagnostics provide an interesting alternative to classical galvanically coupled electrodes. Such a low cost diagnostic system can be applied without preparation time and in mobile wireless environments. For even higher user comfort textile capacitive electrodes are preferable. In this work, a comprehensive model for the electronic noise properties and frequency dependent responses of PCB-based, as well as textile non-contact capacitive electrodes, is presented. A thorough study of the influence of the electrical components on the resulting noise properties of these electrodes, is provided by independently measuring the corresponding noise spectra. The most important low frequency noise source of capacitive electrode is the necessary high input bias resistance. By comparing the noise measurements with the theoretical noise model of the electrode, it is concluded that the surface of the electrode contributes to an additional 1/f-power noise. It is also found that the highest possible coupling capacitance is most favorable for low noise behavior. Therefore, we implemented electrodes with electrically conducting fabric surfaces. With these electrodes, it is possible to enlarge the surface of the electrode while simultaneously maintaining a small distance between the body and the electrode over the whole surface area, thus maximizing the capacitance. We also show that the use of textile capacitive electrodes, reduces the noise considerably. Furthermore, this thesis describes the construction of a capacitive non-contact textile electroencephalography measuring hat (cEEG hat) with seven measuring channels. This hat benefits from the low noise characteristics of the integrated developed textile capacitive electrodes. The measured noise spectrum of this cEEG hat shows low noise characteristics at low frequencies. This fulfills many requirements for measuring brain signals. The implemented cEEG hat is comfortable to wear during very long measurements and even during sleep periods. In contrast to common methods, the cEEG hat provides a possibility of measuring EEG signal during sleep outside laboratories and in the comfort of home. EEG sleep measurements shown in this work, are recorded inside a normal apartment. The possibility of brain computer interface application is also shown by measuring steady state visually evoked potentials (SSVEP) at different frequencies.Berührungslose, kapazitive Elektroden für bioelekrische Untersuchungen stellen eine interessante Alternative zu klassischen galvanisch gekoppelten Elektroden dar. Ein solches preisgünstiges Diagnosesystem kann ohne lange Vorbereitungszeit und in mobilen Umgebungen eingesetzt werden. Für gesteigerten Tragekomfort sind textile Elektroden von Vorteil. In dieser Arbeit wird eine umfassende Beschreibung der elektronischen Rauscheigenschaften und des frequenzabhängigen Verhaltens von sowohl platinenbasierten, als auch textilen kapazitiven Elektroden vorgestellt. Die Einflüsse aller elektronischen Komponenten auf die resultierenden Rauscheigenschaften werden durch Messungen der entsprechenden Rauschspektren untersucht. Die wichtigste niederfrequente Rauschquelle kapazitiver Elektroden stellt der notwendige und zugleich hohe Bias-Eingangswiderstand dar. Durch Vergleich der gemessenen Rauschspektren mit dem theoretischen Modell wird die Oberfläche der Elektroden als eine zusätzliche 1/f-Rauschquelle identifiziert. Dabei ist die größtmögliche Kopplungskapazität vorteilhaft für ein niedriges Rauschen. Deshalb setzen wir im Folgenden Elektroden aus elektrisch leitfähigen Textilien ein. Mit diesen Elektroden ist es möglich, die Oberfläche der Elektrode unter gleichzeitiger Beibehaltung eines kleinen Abstandes zum Körper zu vergrößern. Dies maximiert wiederum die Kapazität. Wir zeigen zudem, dass die Verwendung textiler kapazitiver Elektroden die Rauscheigenschaften deutlich verbessert. Desweiteren wird in dieser Arbeit die Konstruktion eines kapazitiven, berührungslosen EEG-Helmes (cEEG-Mütze) mit sieben Kanälen beschrieben. Dieser Helm profitiert von den guten Rauscheigenschaften der zuvor entwickelten und hier integrierten textilen Elektroden. Die gemessenen Rauschspektren zeigen ein niedriges Rauschen im unteren Frequenzbereich. Dies erfüllt viele Voraussetzungen für die Messung von Gehirnsignalen. Die erstellte cEEG-Mütze lässt sich während langer Messzeiten und Schlafperioden angenehm tragen. Im Gegensatz zu herkömmlichen Methoden ermöglicht sie Messungen außerhalb von Laboratorien und im gewohnten Umfeld. Alle in dieser Arbeit gezeigten Schlafmessungen wurden in einer normalen Wohnung aufgezeichnet. Außerdem wird die Einsatzmöglichkeit für sogenannte ”Gehirn-Computer-Schnittstellen” anhand der Messung von ”steady state visually evoked potentials” (SSVEP) Signalen bei verschiedenen Frequenzen demonstriert

Conception, development and evaluation of polymer-based screen-printed textile electrodes for biopotential monitoring

Wearable technologies represent the new frontier of vital signs monitoring in different applications, from fitness to health. With the progressive miniaturization of the electronic components, enabling the implementation of portable and hand-held acquisition and recording devices, the research focus has shifted toward the development of effective and unobtrusive textile electrodes. This work deals with the study, development and characterization of organic-polymer-based electrodes for biopotentials. After an overview of the main materials and fabrication technologies presented so far in the scientific literature, the possibility to use these electrodes as an alternative to the Ag/AgCl disposable gelled electrodes usually adopted in clinical practice was tested. For this purpose, several textile electrode realization techniques were studied and optimized, in order to create electrodes with adequate features to detect two fundamental physiological signals: the electrocardiogram (ECG) and the electromyogram (EMG). The electrodes were obtained by depositing on the fabric the organic bio-compatible polymer poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) with three deposition procedures: dipcoating, ink-jet printing and screen printing. The physical\u2013chemical properties of the polymer solution were varied for each procedure to obtain an optimal and reproducible result. For what concerns the ECG signal, the research activity focused on screen-printed textile electrodes and their performance was first assessed by benchtop measurements and then by human trials. The first tests demonstrated that, by adding solid or liquid electrolytes the electrodes, the largest part of the characteristics required by the ANSI/AAMI EC12:2000 standard for gelled ECG electrodes can be achieved. Tests performed in different conditions showed that the skin contact impedance and the ECG morphological features are highly similar to those obtainable with disposable gelled Ag/AgCl electrodes (\u3c1 > 0.99). A trial with ten subjects revealed also the capability of the proposed electrodes to accurately capture with clinical instruments an ECG morphology with performance comparable to off-the-shelf disposable electrodes. Furthermore, the proposed textile electrodes preserve their electrical properties and functionality even after several mild washing cycles, while they suffered physical stretching. Similar tests were performed on screen-printed textile electrodes fabricated in two different sizes to test them as EMG sensors, with and without electrolytes. After a series of controlled acquisitions performed by electro-stimulating the muscles in order to analyze the waveform morphologu of the M-wave, the statistical analysis showed a high similarity in terms of rms of the noise and electrode-skin impedance between conventional and textile electrodes with the addition of solid hydrogel and saline solution. Furthermore, the M-wave recorded on the tibialis anterior muscle during the stimulation of the peroneal nerve was comparatively analyzed between conventional and textile electrodes. The comparison provided an R2 value higher than 97% in all measurement conditions. These results opened their use in smart garments for real application scenarios and for this purpose were developed a couple of smart shirts able to detect the EGC and the EMG signal. The results indicated that this approach could be adopted in the future for the development of smart garments able to comfortably detect physiological signals