Biopotential Electrodes Research Articles

Evaluating electronic and structural properties of Au and Cu substituted AgCl electrode for application in surface electromyography

The material content of electrodes is very much important for improving the signal quality of surface electromyography (sEMG) in various environments, in particular, long-term monitoring. The electronic and structural properties of silver/silver chloride (Ag/AgCl), a popular biopotential electrode for sEMG recording, were studied under different conditions by X-ray absorption fine structure (XAFS) spectroscopy calculations. The effects of substitution of good-conducting elements (Cu and Au) on Ag coordination were tested at different temperatures as well as possible defect conditions. In the Au-substituted AgCl material, an extension of the Ag K-edge spectra was detected due to the rich quantum symmetry of Au valence level. Hence, it was determined that Au atoms bond with Cl atoms stronger than Ag atoms. Additionally, it was determined that Au atoms also changed the ionic properties of Ag atoms by losing Ag-Cl bonds.

Large‐Area Transient Conductive Films Obtained through Photonic Sintering of 2D Materials

AbstractTransient electronics that can chemically or physically disappear after a period of stable operation have been achieved through various metal and semiconductor materials. Despite excellent properties and wide availability of 2D materials and van der Waals (vdW) thin‐film electronics, transient films and devices based on them have rarely been reported, not to mention large‐area production with high throughput. Here, a photonic sintering approach is developed to achieve large‐area transient vdW films that may be used for bioresorbable devices. The approach can process 2D materials such as graphite, graphene, and transition metal sulfide, resulting in continuous films that are 10 × 10 cm2 in area and ≈60 to ≈440 nm in thickness on transient substrates. The influence of interfacial adhesion and sintering conditions to the thickness and the electrical properties of transient graphite films is investigated. In addition, the transient films can yield conductive patterns such as biopotential electrodes, interdigital electrodes, and resistor arrays using complementary metal–oxide–semiconductor (CMOS) fabrication processes or a two‐step sintering method. The photonic sintering method may eventually lead to large‐area transient electronics for innovative applications in healthcare, data security, and consumer electronics, and enrich the category of transient electronics through achievement of more printable transient vdW electronics.

Self-Adhesive, Stretchable, Biocompatible, and Conductive Nonvolatile Eutectogels as Wearable Conformal Strain and Pressure Sensors and Biopotential Electrodes for Precise Health Monitoring.

Conductive stretchable hydrogels and ionogels consisting of ionic liquids can have interesting application as wearable strain and pressure sensors and bioelectrodes due to their soft nature and high conductivity. However, hydrogels have a severe stability problem because of water evaporation, whereas ionogels are not biocompatible or even toxic. Here, we demonstrate self-adhesive, stretchable, nonvolatile, and biocompatible eutectogels that can always form conformal contact to skin even during body movement along with their application as wearable strain and pressure sensors and biopotential electrodes for precise health monitoring. The eutectogels consist of a deep eutectic solvent that has high conductivity, waterborne polyurethane that is an elastomer, and tannic acid that is an adhesive. They can have an elongation at a break of 178%, ionic conductivity of 0.22 mS/cm, and adhesion force of 12.5 N/m to skin. They can be used as conformal strain sensors to accurately monitor joint movement and breath. They can be even used as pressure sensors with a piezoresistive sensitivity of 284.4 kPa-1 to precisely detect subtle physical movements like arterial pulses, which can provide vital cardiovascular information. Moreover, the eutectogels can be used as nonvolatile conformal electrodes to monitor epidermal physiological signals, such as electrocardiogram (ECG) and electromyogram (EMG).

Selecting grounding points to reduce the interference level of the signal of high-impedance measuring channel

The study was carried out (2020) to reduce the effect of electromagnetic interference generated by a device for the formation of temperature effects based on Peltier element on a plant biopotential meter. Four variants of equipment grounding circuits are considered in the absence of a separate grounding bus for power equipment; graphs of biopotential signals are given. The type of interference that the device for the formation of temperature effects induces on the biopotential measurement channel is shown. The control unit case for the temperature-controlled stage based on Peltier element and the power cable shield for connecting Peltier element to the control unit must be grounded at a separate point from the biopotential meter. Biopotential meter electrodes should be grounded as far as possible from the control unit case and at a separate point from the grounding of the plate of the temperature-controlled stage. Recommendations are given for the grounding of high impedance input measuring devices and the power equipment emitting powerful inductive interference and causing interference in the grounding bus located in the same laboratory room, in the absence of separate grounding for power equipment. To reduce interference to an acceptable level, in addition to the selection of the grounding point, filtering is required. If the grounding point is selected incorrectly, a signal with a high level of interference is present at the filter output. The application of the proposed recommendations for grounding a device for the formation of a temperature effect based on Peltier element and a biopotential meter makes it possible to assess the response of a plant placed on the temperature-controlled stage to a temperature effect and not complicate programmed filtering of the signal received by the biopotential meter.

Fully Untethered Battery-free Biomonitoring Electronic Tattoo with Wireless Energy Harvesting

Bioelectronics stickers that interface the human epidermis and collect electrophysiological data will constitute important tools in the future of healthcare. Rapid progress is enabled by novel fabrication methods for adhesive electronics patches that are soft, stretchable and conform to the human skin. Yet, the ultimate functionality of such systems still depends on rigid components such as silicon chips and the largest rigid component on these systems is usually the battery. In this work, we demonstrate a quickly deployable, untethered, battery-free, ultrathin (~5 μm) passive “electronic tattoo” that interfaces with the human skin for acquisition and transmission of physiological data. We show that the ultrathin film adapts well with the human skin, and allows an excellent signal to noise ratio, better than the gold-standard Ag/AgCl electrodes. To supply the required energy, we rely on a wireless power transfer (WPT) system, using a printed stretchable Ag-In-Ga coil, as well as printed biopotential acquisition electrodes. The tag is interfaced with data acquisition and communication electronics. This constitutes a “data-by-request” system. By approaching the scanning device to the applied tattoo, the patient’s electrophysiological data is read and stored to the caregiver device. The WPT device can provide more than 300 mW of measured power if it is transferred over the skin or 100 mW if it is implanted under the skin. As a case study, we transferred this temporary tattoo to the human skin and interfaced it with an electrocardiogram (ECG) device, which could send the volunteer’s heartbeat rate in real-time via Bluetooth.

An Analysis of Different Biopotential Electrodes Used for Electromyography

An Analysis of Different Biopotential Electrodes Used for Electromyography

Evolution of the mechanical properties of Ti-based intermetallic thin films doped with different metals to be used as biomedical devices

This study reports the assessment of the mechanical properties of intermetallic titanium thin films, doped with different amounts of aluminium, copper, silver, and gold, aiming their use as biopotential electrodes for non-invasive physiological monitoring. The four binary thin film systems, Ti-Me (Me = Al, Cu, Ag, Au), were prepared by DC magnetron sputtering, placing different number of Me pellets on a pure Ti target. The use of a Ti-composed target gave rise to a wide range of compositions, resulting in three distinctive zones of (micro)structural features, identified in all the prepared systems. In the first zone, a Ti-rich one, the films behaved like solid solutions, developing Ti-like microstructures. As the Me/Ti atomic ratio increased, the formation of intermetallic phases played the leading role and it became possible to observe two different microstructural trends, clearly related to the Me type. This zone was identified as an intermetallic region. In the third zone, a Me-rich one, the microstructures displayed by the different films (Me/Ti > 1.0) showed to be dependent on the Ti solubility into Me. The assessment of the mechanical properties revealed an improved hardness and stiffness with the Me addition, directly related to the formation of intermetallic compounds in different degrees of crystallinity. Moreover, the adhesive strength between the substrate and the coating was higher for the films deposited in the intermetallic zone, more evident in the films prepared with Au, Cu and Ag, in this order. The hardness enhancement was especially evident for the thin films presenting microstructures typical of thin film metallic glasses (TFMGs), Ti-Au and Ti-Cu, about twice the values exhibited by the Ti-Al and Ti-Ag ones. Furthermore, the toughness of these metallic glass-like thin film systems was remarkable, more evident within the Ti-rich zone, presenting H/E ratios close to 0.1 and good elastic recoveries. In contrast, the typical columnar morphologies, combined with the brittle intermetallic structures of the Ti-Ag and Ti-Al films, proved to be less resistant to the plastic deformation (H/E ≤ 0.04), despite the improved elasticity presented by the Ag-rich films.

Embroidered electrodes for bioelectrical impedance analysis: impact of surface area and stitch parameters

Measuring electrical activity in the human body is vital in the diagnosis and monitoring of patients; thus, attention to the design of biopotential electrodes is essential. It is important that electrodes are designed accordingly by adapting to a specific device and application. By embroidering electrodes, we can tailor the electrode parameters to suit the application and integrate them into textile outfits. However, embroidered electrodes possess unwanted polarizing impedance () relative to the frequency of the current applied by the system. Dry embroidered electrodes are preferred to wet electrodes for bioelectrical impedance analysis (BIA) recordings providing stable measurements. BIA is a relatively simple and non-invasive technique that measures the resistivity of biological tissue. This research analyzes the impact of embroidery characteristics (i.e. electrode surface area, stitch type, stitch density and stitch length) on embroidered electrodes by identifying the parameters reducing for BIA in a dry and wet state. In addition, the influence of the amount of conductive thread utilised for the fabrication of the sample electrodes was studied. For dry electrodes, we identified that a larger electrode surface area, increased stitch length and stitch density reduce . Moreover, it was observed that potentially there is a threshold on the amount of conductive yarn used for the embroidered electrode. In contrary, wet electrodes displayed irregular and thus, it can be concluded that they could potentially impair BIA measurements. In essence, our findings show that embroidered electrodes can be incorporated into wearable BIA systems for health monitoring in home settings.

The effect of chlorine/argentum atomic ratios on electrochemical behaviors and signal acquisition abilities of embroidered electrodes for bio-potential signal measurement

Bio-potential dry electrode is an important part of smart garments or wearable devices for monitoring bio-potential signals. In this work, embroidered electrodes are developed by embroidering silver-plated yarns in woven fabric. Then, AgCl is electrochemically deposited on silver-plated yarns in the embroidered electrode, and the chlorine/argentum (Cl/Ag) atomic ratios can be adjusted by the chlorination time. Moreover, a novel active evaluation system of wearable bio-potential electrodes developed by our group is utilized to evaluate the performance of the embroidered electrodes, and two novel indexes (bio-potential phase shift and voltage amplitude attenuation) were presented for evaluating the performance of embroidered electrodes. Results show that the chlorination of silver-plated yarns can improve the performance of embroidered electrodes. The electrochemical behaviors and signal acquisition abilities of the embroidered electrodes can be affected by Cl/Ag atomic ratios. The embroidered electrodes with the Cl/Ag atomic ratios of 62% (E-90) have the lowest impedance (3364 ± 894 O), and their static open-circuit potential and dynamic open-circuit potential variation are all less than 7 mV. During the standard ECG signal test, E-90 shows the minimum bio-potential phase shift (0.011 s), voltage amplitude attenuation (11.768%), noise amplitude (0.025 mV), and maximum signal to noise (41 dB). The noise amplitude of human body ECG of E-90 is also the lowest (0.013 mV) and signal to noise is the maximum (40.996 dB). The embroidered electrodes have broad application prospects in long-term health-monitoring system.

Highly conformable stretchable dry electrodes based on inexpensive flex substrate for long-term biopotential (EMG/ECG) monitoring

The comfortable, long-term, accurate, and continuous biopotential monitoring is of paramount importance for biomedical applications. In this respect, dry electrodes are the way forward for the next generation of wearable health monitoring devices. However, it is still challenging to record the bioelectrical signals, i.e., electroencephalogram (EEG), electromyogram (EMG), electrocardiogram (ECG), of patients during their everyday life. It is mainly because, soft skin-like, at the same time, electrically conducting and biocompatible materials have to be integrated with electrical circuits. Dry electrodes have the potential to be integrated in this manner into a variety of wearable form factors. However, most dry electrodes are fabricated on rigid substrates, which do not possess sufficient flexibility and conformability to human skin. Novel flexible/stretchable substrates are a topic of research in the state-of-the-art literature for dry electrodes in pursuit of the wearable biopotential electrodes.In this work, a novel flexible and wearable dry electrode technology based on polydimethylsiloxane (PDMS) is presented. It has been tested for EMG and ECG signal acquisition as the proof of principle. The performance of the fabricated dry electrodes is investigated by measuring the contact impedance between the skin and the electrode. The impedance is compared with the commercially available wet Ag/AgCl electrodes. Overall the contact impedance of the dry electrodes is comparable compared to the wet Ag/AgCl in the frequency range of interest for biopotential electrodes. Experimentally received signal quality of EMG/ECG with the dry electrode is comparable to the wet electrode as well. The dry electrodes do not require any skin preparation nor conductive gels. Thanks to the extreme flexibility of our electrode, it provides more robust contact as well as less skin irritation. The provided results suggest that the presented electrodes/technology have the potential to be used in clinical health-care applications. To support this claim, long term EMG/ECG results are also provided in the manuscript.

Stretchable bio-potential electrode with self-similar serpentine structure for continuous, long-term, stable ECG recordings.

Current stretchable surface electrodes have attracted more and more attentions owing to their potential applications in the fields of biological signal monitoring, wearable human-machine interface (HMI) and Internet of Things (IoT). The paper presents that stretchable bio-potential electrode is designed with the second order self-similar serpentine structure to continuous, long-term, stable ECG signal recordings which is conformal contact with the soft skin surface. FEM and experiments have validated >30% deformability of the surface electrode with second order self-similar structure. The continuous 48h electrocardiograms (ECG) signal recording experiments have been demonstrated by the stretchable electrodes. Meanwhile, robustness and stability of ECG signal are validated by the stretchable bio-potential electrodes when the external strain is applied to the body surface. The stretchable bio-potential electrode could be integrated to biological signal monitoring and human machine interface capabilities for the future research.

Device for Evaluation of Electrical Parameters of Biopotential Electrodes

Biopotential electrodes are essential for measurements of biological signals. There are many different manufacturers and many different types of electrodes on the market. Essential parameters such as impedance, distortion and phase angle are often not disclosed by the manufacturer. This work presents a simple device that can be used to test electrical parameters of any biopotential electrodes in the frequency range of few Hz to 2 kHz. The device is based on Arduino Due and uses this board’s internal DAC and ADC for generating and sampling the measurement signal. The proposed device was used to measure electrical parameters of a brass biopotential electrode with various signal voltages and also for evaluation of four different commercially available Ag/AgCl electrodes.

Біоелектричні потенціали модрини європейської в деревостанах Кременецького горбогір'я

Досліджено біоелектричні потенціали модрини європейської, дуба звичайного, ялини європейської і сосни звичайної, які формують деревостани в різних типах лісорослинних умов Кременецького горбогір'я. Вік деревостанів становить 12–109 років. Частка модрини в їх складі змінюється в межах 1–10 одиниць. Модрина європейська в умовах суборів і сугрудів характеризується нижчими абсолютними показниками БЕП кореневої шийки, порівняно з сосною звичайною, а в умовах грудів – вищими, порівняно з дубом звичайним і ялиною європейською. Встановлені відмінності між деревними видами зберігаються упродовж дня. Відмінності між модриною і дубом за абсолютними показниками біопотенціалів посилюються у другій половині дня. У модрини в мішаних молодняках і середньовікових деревостанах абсолютні значення БЕП виявились вищими, ніж у чистих деревостанах. Встановлено три типи денних біопотенціалограм, які характеризують динаміку проходження метаболічних процесів у деревних видів у деревостанах різних лісорослинних умов та видового складу. Між біометричними показниками модельних дерев різних деревних видів і середньоденними показниками біопотенціалів переважно спостережено помірний і значний прямий кореляційний зв'язок. Більш тісною залежність денної зміни біопотенціалів виявлено від денної динаміки температури і вологості повітря, аніж від інтенсивності світла. Між вологістю повітря і біоелектричними потенціалами існує зворотний кореляційний зв'язок.

Fully printed all-polymer tattoo/textile electronics for electromyography

Driven by the ever-growing need for developing low-cost, easy-to-use, noninvasive diagnostic tools, biomedical devices that can be integrated on human skin or textiles have begun to emerge. These ‘wearable’ devices should couple electronics directly to the human skin and detect a variety of biologically relevant signals such as neuromuscular activity. In this work, we develop a simple, low-cost and customizable device to perform electromyography measurements based on electronics fabricated on tattoo paper. The electrodes are based on the conducting polymer poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) and inkjet-printed on the conformable tattoo paper. Addressing the integration challenge common to such flexible electronic devices, we connect the tattoo electrodes to the acquisition system through a textile in the form of a wristband comprising printed PEDOT:PSS contacts. While the textile wristband conforms around the ‘tattooed’ skin, it enables a reliable contact with the electrodes beneath. We show that this tattoo/textile electronics platform is able to monitor the biceps activity of the arm during muscle contractions lasting for a period of 7 h, with comparable performance to conventional biopotential electrodes and without the use of gels or expensive metallic materials. Combining the tattoo electronics with the electronic textile improves the communication of skin-like electrodes with external electronics, renders a reliable and versatile system for detecting biopotential signals critical for myoelectric prosthesis, muscle injury prevention and/or detection.

Simple fabrication method of an ultrasensitive gold micro-structured dry skin sensor for biopotential recording

Fast advancement of dry biopotential electrode has driven to the reduction of using Ag/AgCl (wet electrode). There is a necessity for development of flexible and eco-friendly micro-structured (MSE) dry biopotential electrode utilizing biodegradable and non-toxic materials for a better life and sustainable future. It is very difficult to create micro-structure without using any solvents or high-end equipment. Here, a novel micro-structured electrode coated with Ti/Au film is fabricated using a sandpaper template and is proposed for biopotential signal monitoring applications. We used sandpaper, which is recyclable and biodegradable. The proposed MSE is a flexible, stretchable, and biocompatible dry micro-structured electrode. The sheet resistance of the proposed MSE is 2.5 Ω/sq. The area of MSE was only 4 cm × 4 cm (l × w), and the sweat of the epidermis layer of human skin could be utilized as the electrolyte for the flexible MSE during the electrocardiography (ECG) and electromyography (EMG) recording. The fabricated MSE was enough thin and flexible to be well attached onto the skin. The contact impedance of the flexible MSE was stable and suitable for long-term biopotential recording. The main advantage of the electrodes is simple fabrication, which can be used in wearable electrode systems to monitor human health. The results of the experiment show that the proposed electrode can operate in dry conditions when the subject is resting, and it shows fewer motion artifacts during movement.

Development of wearable electromyogram for the physical fatigue detection during aerobic activity

Physical fatigue or muscle fatigue is a common problem that affects people who are vigorously involved in activities that require endurance movements. It becomes more complicated to measure the fatigue level when the dynamic motion of the activity is included. Therefore, this paper aims to develop a wearable device that can be used for monitoring physical fatigue condition during aerobic exercise. A 10-bit analog to digital converter (ADC) micro-controller board was used to process the data sensed by Ag/AgCl electrodes and real-time transmitted to the computer through Bluetooth's technology. The wearable was attached to the knee and connected to the biopotential electrodes for sensing the muscle movement and convert it into the electrical signal. The signal then processed by using the fourth-order Butterworth filter to filter the low-pass filter frequency and eliminate the noise signal. The results reveal that the fatigue level increased gradually based on the rating of perceived exertion (RPE), using 10-point Borg's scale, which is rated by the subject’s feeling. Both muscle's activities in lower limb rise as speed is increased, and it was also observed that the rectus femoris is functioning more than gastrocnemius due to the size of muscle fiber. Furthermore, it was established that the maximum volumetric contraction (MVC) could be used as a reference and indicator for measuring the percentage of contraction in pre-fatigue but not to fatigue induced experiment. However, this wearable device for EMG is promising to measure the muscle signal in the dynamic motion of movement. Consequently, this device is beneficial for a coach to monitor their athlete's level of exhaustion to be not over-exercise, which also can prevent severe injury.

Skin Conformal Polymer Electrodes for Clinical ECG and EEG Recordings.

Preparation-free and skin compliant biopotential electrodes with high recording quality enable wearables for future healthcare and the Internet of Humans. Here, super-soft and self-adhesive electrodes are presented for use on dry and hairy skin without skin preparation or attachment pressure. The electrodes show a skin-contact impedance of 50 kΩ cm2 at 10 Hz that is comparable to clinical standard gel electrodes and lower than existing dry electrodes. Microstructured electrodes inspired by grasshopper feet adhere repeatedly to the skin with a force of up to 0.1 N cm-2 without further attachment even during strong movement or deformation of the skin. Skin compliance and adhesive properties of the electrodes result in reduction of noise and motion artifacts superior to other dry electrodes reaching the performance of commercial gel electrodes. The signal quality is demonstrated by recording a high-fidelity electrocardiograms of a swimmer in water. Furthermore, an electrode with soft macropillars is used to detect alpha activity in the electroencephalograms from the back of the head through dense hair. Compared to gel electrodes, the soft biopotential electrodes are nearly imperceptible to the wearer and cause no skin irritations even after hours of application. The electrodes presented here could combine unobtrusive and long-term biopotential recordings with clinical-grade signal performance.

Fabrication and testing of a novel biopotential electrode array

This paper focuses on the fabrication and testing of a novel biopotential electrode array for detecting human brainwaves activity signals. A hybrid micro electro-machining process that combines spark erosion with silver deposition to create suitable taper-shaped micropillar and special discharge craters for holding the biopotential electrode in position on the human scalp is proposed. By means of controlling the secondary-electrode wear rate, the required taper-rate (T=1/7) and special surface roughness (Ra=2.9μm) on the designed biopotential electrode are successfully achieved. The trend curves of bottom wear and carbon deposition in the secondary-electrode reveal near linear increases while the residual hole-depth declines with increased machinings. This indicates that the work energy used allows a steady-state wear rate in the secondary-electrode. Silver deposition is conducted to enhance the safety, electrical conductivity of the microprobe array and being antibacterial. Clinical and experimental results demonstrate that the formed biopotential skin electrode with an array of short-tapered pillars realizes quasi-invasive light contact between cerebral cortex and the microprobe. Four brainwave activity frequency signals are confirmed with superior intensity and repeatability to those realized by present-day commercial planar electrodes. Approaches to secondary-electrode formation, traction force testing, novel microprobe formation in batch mode, work capacitance, and pulse current effects, insertion durability tests, and life expectancy tests of the secondary-electrode are all evaluated in detail.

A printed, dry electrode Frank configuration vest for ambulatory vectorcardiographic monitoring

This paper describes the design and fabrication of a screen printed network of bio-potential measurement electrodes on a garment, in this case a vest. The electrodes are placed according to the Frank configuration, which allows monitoring of the electrical behavior of the heart in three spatial orientations. The vest is designed to provide stable contact pressure on the electrodes. The electrodes are fabricated from stencil printed carbon loaded rubber and are connected by screen printed silver polymer conductive tracks to an array of vias, which form an electrical connection to the other side of the textile. The vest is tested and compared to Frank configuration recordings that were obtained using standard self-adhesive ECG electrodes. The vest was successfully used to obtain Frank configuration recordings with minimal baseline drift. The vest is fabricated using only technologies found in standard textile production lines and can be used with a reduced setup effort compared to clinical 12-lead examinations.

Design and Development of Non-Contact Bio-Potential Electrodes for Pervasive Health Monitoring Applications.

For the advent of pervasive bio-potential monitoring, it will be necessary to utilize a combination of cheap, quick to apply, low-noise electrodes and compact electronics with wireless technologies. Once available, all electrical activity resulting from the processes of the human body could be actively and constantly monitored without the need for cumbersome application and maintenance. This could significantly improve the early diagnosis of a range of different conditions in high-risk individuals, opening the possibility for new treatments and interventions as conditions develop. This paper presents the design and implementation of compact, non-contact capacitive bio-potential electrodes utilising a low impedance current-to-voltage configuration and a bootstrapped voltage follower, demonstrating results applicable to research applications for capacitive electrocardiography and capacitive electromyography. The presented electrodes use few components, have a small surface area and are capable of acquiring a range of bio-potential signals.