Gel Electrodes Research Articles

Modeling the Design Characteristics of Woven Textile Electrodes for long-Term ECG Monitoring.

An electrocardiograph records the periodic voltage generated by the heart over time. There is growing demand to continuously monitor the ECG for proactive health care and human performance optimization. To meet this demand, new conductive textile electrodes are being developed which offer an attractive alternative to adhesive gel electrodes but they come with their own challenges. The key challenge with textile electrodes is that the relationship between the manufacturing parameters and the ECG measurement is not well understood, making design an iterative process without the ability to prospectively develop woven electrodes with optimized performance. Here we address this challenge by applying the traditional skin-electrode interface circuit model to woven electrodes by constructing a parameterized model of the ECG system. Then the unknown parameters of the system are solved for with an iterative MATLAB optimizer using measured data captured with the woven electrodes. The results of this novel analysis confirm that yarn conductivity and total conductive area reduce skin electrode impedance. The results also indicate that electrode skin pressure and moisture require further investigation. By closing this gap in development, textile electrodes can be better designed and manufactured to meet the demands of long-term ECG capture.

Effect of Gel Electrolyte, Paste and Electrode on the Efficiency of Dye-Sensitized Solar Cell using Schiff Base Dye Compound

The low cost and ease of production have led to widespread adoption of dye-sensitized solar cells (DSSCs). Therefore, this study aims to synthesize Schiff base compounds from salicylaldehyde and ethylenediamine as a sensitizer in DSSC. The Shiff base compound was synthesized using the condensation method with mol ratio of 1:1 and the results showed yellow crystals with a yield of 81.14%. Furthermore, the UV-Vis spectrometer analysis showed that the Schiff base compound has bathochromic shift with a maximum wavelength change from 324 and 328 nm to 335 nm with transition n→π, while the IR spectrum at wavenumber of 1610 cm-1 indicated the presence of an azomethine group (–C=N–). The TG-DTA analysis showed a mass loss stage of the Schiff base molecule at 97.2% in the temperature range of 180-300 ºC. Based on UV-Vis, IR and TG-DTA data, the synthesized Schiff base has the potential to be used as a sensitizer in DSSC. The fabrication was then carried out using two variations of semiconductor namely TiO2 and ZnO, three variations of PEG gel electrolyte with 0.05 M, 0.1 M and 0.15 M, as well as three counter electrodes including graphite from a pencil, candle flame and a combination of both. Based on the results, DSSC based on TiO2 semiconductor with 0.15 M PEG gel electrolyte and candle flame counter electrode produced the highest efficiency of 0.29 % with maximum voltage (Vmax) of 370 mV and maximum current strength (Imax) of 0.8 mA.

Interfacial Roughness Enhanced Gel/Elastomer Interfacial Bonding Enables Robust and Stretchable Triboelectric Nanogenerator for Reliable Energy Harvesting.

Gel-based triboelectric nanogenerator (TENG) has demonstrated promising potentials in stretchable electronics owing to gel electrodes' intrinsic softness, stretchability, and conductivity. However, delamination between gel and elastomer layers in deformations remains a considerable challenge for gel-based TENG, which most often induces structure failure. Herein, gels are regarded as adhesives and further effectively enhances interfacial bonding strength by a rough interface in adhesives' view, which exploits gels' liquid-to-solid transformation. This method just needs surface roughness of elastomer, which avoids chemical modification. Moreover, this method is effective to both organogel with good stickiness and hydrogel with weak stickiness, demonstrating wide applicability to different gels. Owing to the tough gel/elastomer interfacial bonding, TENG-Rough largely solves delamination problem under various deformations and the corresponding output performances of TENG-Rough are also maintained, implying a robust stretchable TENG device for reliable energy harvesting. This work demonstrates a general and facile method to enhance interfacial bonding in an adhesives' way, which provides a view for addressing delamination problem in gel-based TENGs and other kinds of gel-based devices.

Stretching-insensitive stretchable and biocompatible triboelectric nanogenerators using plasticized PVC gel and graphene electrode for body-integrated touch sensor

Triboelectric nanogenerators (TENG) can generate strong electrical signals even with low frequencies and weak forces, thus research has been conducted to use them as wearable, body-attachable, and body-embeddable devices using biomechanical energies. For this reason, the TENG components, such as dielectric materials and electrodes, should be stretchable. A stretchable and biocompatible single electrode TENG based on plasticized polyvinyl chloride (PVC) gel with a graphene electrode is fabricated. PVC gel is a suitable stretchable TENG dielectric material owing to its high stretchability, dielectric constant, and tribo-negative properties, and graphene is a highly conductive electrode. Graphene and PVC gel-based stretchable and biocompatible TENGs display excellent electrical outputs (48 V, 2.5 μA, and 0.49 W/m2). The electrical resistance range of the electrode which does not affect the TENG output performance, and a stretching-insensitive TENG with approximately 50% stretching rate is successfully demonstrated through this study. In addition, both PVC gel and graphene are biocompatible. These stretching-insensitive and biocompatible TENGs may be used as a self-powered touch sensor that can be integrated into the human body.

A stretchable, self-healing and semi-transparent nanogenerator for energy harvesting and sensing

Triboelectric nanogenerators (TENGs) with an ability to harvest mechanical energy from natural and human activities, have shown tremendous potential to realise self-powered electronic devices and sensors. However, in order for optimum utilization of biomechanical energy, TENGs need to have body or tissue mimicking properties without compromising performance. Herein, a new hydrogel based all-soft, self-healing and stretchable TENG is introduced which exhibits outstanding power generation capability surpassing existing competitors. This unique TENG is realized by using gold nanoparticles doped semi-transparent hydrogel as an electrode and Ecoflex as the triboelectric layer which integrates multifunctional properties including rapid self-healing in < 2 min, 900% stretchability, high conductivity, transparency and excellent biocompatibility with human dermal fibroblasts. The use of a gel electrode with both ionic and electronic conductivities underlines the importance of gold nanoparticles in enhancing the performance of soft TENGs. A 5 cm2 device exhibits a prodigious power density of 1680 mWm−2 with an energy conversion efficiency of ≈ 26%, which is the highest achieved so far in contemporary hydrogel based TENGs. The moldable components allow easy fabrication of devices with tunable shapes and sizes that conforms to the human body and can power multiple electrical devices directly from body movements thus opening up possibilities for next generation self-powered wearable or implanted devices.

Multi-walled carbon nanotubes derived graphene nanoribbons for high performance supercapacitor applications

This study delineates the supercapacitive performance of multi-walled carbon nanotubes derived nanoribbons. Acid-processed carbon nanotubes were exfoliated and reduced with microwaves to yield high quality graphene nanoribbons (GNRs). Morphological and spectroscopic investigations revealed the successful preparation of graphene nanoribbons from carbon nanotubes. The three electrode system configuration with microwave exfoliated graphene nanoribbons (MWGNRs) based working electrode and H2SO4-PVA gel electrolyte has shown high specific capacitance of 404 F/g at 2 mVs−1 scan rate. This three electrode configuration showed 97.3% of initial capacitance retention after 10,000 cycles, which proves good cycle stability and retention capability of the MWGNRs based electrode with gel electrolyte. A supercapacitive device with MWGNRs based electrodes and 1 M H2SO4 –PVA gel electrolyte was fabricated and tested, which also showed high supercapacitive performance. MWGNRs have more number of reactive edges and high specific surface area as compared to pristine carbon nanotubes and therefore exhibit high specific capacitance. The proposed method is highly scalable and can pave a way to develop high performance low cost supercapacitors.

Breathable, Flexible, Transparent, Hydrophobic, and Biotic Sustainable Electrodes for Heating and Biopotential Signal Measurement Applications

Pressure to reduce the global amount of e‐waste has increased in recent years. The optimal use of natural resources is a demanding area especially due to the overabundance of the use of resources and challenges with after‐life disposal. Herein, an easy method is developed to fabricate an improved version of leaf skeleton‐based biodegradable, transparent, flexible, and hydrophobic electrodes. A fractal‐like rubber leaf skeleton is used as the substrate, physical vapor deposited Au interlayer to promote adhesion, and uniform deposition of overlayer silver nanowires. The fabricated surfaces present a high level of electrical stability, optical transparency, hydrophobicity, and robust mechanical properties. The prepared electrodes demonstrate a comparable level of optical transmittance to the virgin leaf skeleton. The mechanical sturdiness of the electrodes is verified by 1k bending cycles. To demonstrate the functionality of these hybrid biotic conductive network (HBCN) electrodes, their performance is evaluated as flexible transparent heating elements and as biosignal measurement electrodes. The heater can reach a temperature of 140 °C with only 2.5 V in ≈5 s and Ag nanowire loading of ≈160 μg cm−2. Likewise, electrocardiogram (ECG) and electromyogram (EMG) signals are successfully obtained from the electrodes without using any electrode gel or other electrolytes.

Comparison of two Wireless Electromyography Sensor Module Designs using wet electrodes and dry electrodes at the time of Sitting motion to stand

One of the biosignals used to identify muscle signals in humans is electromyography. Electromyography signals are frequently utilized as input and are designed to aid in post-stroke therapy recovery or to assist people with disabilities. This phenomena has led to the development of numerous electromyography module sensor designs for use in support of various research-based applications. In this study, an electromyography sensor module without an electrode cable is compared to an electromyography sensor module that uses gel electrodes, plate electrodes, electrode cables, and other electrode technologies. A function generator is used to test each module, and the correlation value is sought to determine the connection between the two modules under consideration. Later, the findings of this study served as the foundation for other studies. Researchers also wish to explore the possibility of developing an electromyography sensor module by altering the wireless EMG sensor module's structure and design. Whereas this study can subsequently be extremely helpful to improve the standing of the Health Poltekkes Kemenkes Surabaya.

Flexible and Zwitterionic Fluorinated Hydrogel Scaffold with High Fluorine Content for Noninvasive 19 F Magnetic Resonance Imaging under Ultrahigh Scanning Resolution.

The imaging of hydrogel scaffolds by 19 F magnetic resonance imaging (MRI) represents an attractive tool for straightforward and noninvasive monitoring of their morphology and in vivo fate. However, their further applications are significantly limited by a dilemma of insufficient signal resolution with low 19 F content, and/or hydrophobic aggregation of fluorine moieties-induced signal attenuation with high 19 F content. Herein, a novel label-free fluorinated hydrogel (PFCB) is fabricated with high fluorine content to realize noninvasive monitoring through 19 F MRI under ultrahigh scanning resolution (1 mm of scanning thickness). The integration of a zwitterionic unit into each fluorine moiety completely overcame the hydrophobic aggregation-induced signal attenuation, manifesting as high 19 F content and imaging performance. Importantly, 3D reconstruction of the PFCB hydrogel in vivo can be facilely and accurately performed with background free signals, providing detailed biological information of the implanted hydrogel. Additionally, PFCB hydrogel showed adjustable and high mechanical performance, and exhibited minimum foreign body reaction after implantation. As a proof of concept, PFCB hydrogel could be further applied as gel electrodes and wireless flexible sensors for healthcare monitoring. Overall, such label-free fluorinated PFCB hydrogel is an ideal flexible scaffold for eventual clinical applications integrating 19 F MRI-guided unequivocally 3D reconstruction and healthcare monitoring.

The new wireless EEG device Mentalab Explore is a valid and reliable system for the measurement of resting state EEG spectral features

Technological advancements in neuroscience have provided many conveniences to scientists, researchers, and consumers. The emerging electroencephalography (EEG) devices are good examples for it. The objective of this study was to investigate the validity and reliability of a new wireless EEG device Mentalab Explore for resting-state EEG (rsEEG) recordings in eyes open and eyes closed conditions. Twenty-three healthy subjects were recruited for the study. The subjects visited the laboratory on two occasions. On the first day, both devices were used to record rsEEG data, and after 24 h, only the Mentalab Explore was used to record rsEEG for test–retest reliability analysis. We compared the alpha peak frequency, suppression, and mean power between the two devices. Intraclass correlation coefficient was calculated for test–retest reliability analysis. Power spectral density (PSD) was calculated using Welch method. The PSD (eyes closed p < 0.0001; eyes open p = 0.01–0.0001), alpha peak frequency (p < 0.0001), and alpha suppression (p = 0.002–0.0001) from the two EEG devices as well as the test–retest results from the Mentalab device were significantly correlated. There were no significant differences in alpha peak frequency or suppression between the clinical-grade and the new devices for O1 and O2 channels in eyes-closed condition. The two measurements completed ∼24 h apart using the Mentalab system were similar for all the variables. We showed that the consumer-grade Mentalab Explore with gel electrodes is a reliable and valid EEG recording device for rsEEG spectral features.

Ultrapermeable and Wet-Adhesive Monolayer Porous Film for Stretchable Epidermal Electrode.

Noninvasive electrophysiological signal monitoring is significant for health care and scientific research. The simultaneous achievement of wet adhesion, stretchability, breathability, and low contact impedance is highly recommended in the epidermal electrode but still challenging. In this work, a monolayer porous film electrode with a pore size and wall thickness of less than ∼10 μm is fabricated via the breath figure method (BFM) and metal sputtering, and it was subsequently applied using epidermal electrophysiological monitoring. The ultrahigh permeability is comparable to the naked skin because the through holes of the monolayer porous film match well with the pores on human skin. The stretchability of 50% is realized with the combination of Au microcrack and the monolayer porous structure. The wet adhesion of 0.17 N/cm is established on the chemical bonding between the electrode and the epidermis. The contact impedance is comparable with the gold standard Ag/AgCl gel electrode, especially after sweating. Stable and precise electrophysiological signals are measured. Especially, the perspiration resistance of the monolayer porous film outperforms that of the gel electrode. The monolayer porous structure provides a new avenue to improve the breathability of the epidermal electronics.

Effect of Electrode Morphology on Performance of Ionic Actuators Based on Vat Photopolymerized Membranes.

Bucky gel electrodes are composed of morphology-determining polyvinylidene difluoride (PVDF) filled with carbon nanotubes (CNT). The electrodes are commonly fabricated via the casting of a CNT dispersion containing PVDF and ionic liquid. In this study, several pore-forming additives such as polyethylene glycol (PEG), dibutyl phthalate (DBP), and the common ionic liquid BMIMBF4 were used to control the morphology of the bucky gel electrodes. The crystalline phase type and content of PVDF in the electrodes were determined by FT-IR and DSC, respectively. SEM revealed a sponge-like structure in the case of the use of BMIMBF4 and a spherulite structure if PEG and DBP were used as additives. A strong influence of morphology on the anisotropic increase in the volume of electrodes upon impregnation with electrolyte was observed. The PEG-based electrode elongated more than the others, while the BMIMBF4-based electrode thickened to a greater extent. Ionic actuators were fabricated to experimentally reveal the effect of electrode morphology on their electromechanical efficiency. A high-precision vat photopolymerization technique was used to fabricate identical ionic membranes and minimize their influence on the properties of the actuators. The electrodes were characterized by the same porosity and electrical capacitance, while the actuators differ significantly in performance. As a result, a simple method of using pore-forming additives made it possible to increase the maximum deformation of bucky gel ionic actuators by 1.5 times by changing the morphology of the electrodes.

(Digital Presentation) A Low-Modulus, Soft and Stretchable Wearable Electrocardiography Sensor-System Patch

Electrocardiography (ECG) is a primary tool for diagnosis of various types of disease and disorders such as arrhythmias, coronary heart disease, heart attack, mental disorders, etc. Reliable wearable ECG devices can be a valuable tool in early diagnosis and effective treatment of such disease and disorders. Convention wearable ECG sensor-systems are rigid, bulky, expensive, and the recorded ECG signals using these wearable devices lack required accuracy for medical diagnosis mainly due to motion artifacts that is originated from slippage of sensors on skin and/or instable interface between the soft sensor and the rigid electronic circuits.Here, we report a low-modulus, soft and stretchable wearable electrocardiography (ECG) sensor-system patch which enables continuous and long-term recording of ECG signals with minimal motion artifacts. This system consists of two reusable, detachable-attachable patches: sensor patch and circuit patch, as shown in Figure 1a. The reusable multi-wall carbon nanotube (MWCNT) based sensor patch is fabricated on stretchable elastomer substrate by our developed cost and time-effective method. Reusable, front-end and wireless circuit patch is made by integration of the off-the-shelf integrated circuit components with three-dimensional (3D) stretchable-deformable interconnects (SDI). SDIs are 3D springs of liquid metal (EGaIn). Unlike other reported liquid metal based interconnects, SDI has been designed in 3D form to increase the stretchability and make it low-modulus and robust to deformations in all directions. The stretchability of SDI structure is beyond 500% (the limit of our measurement system) without any negligible change in electrical resistivity of the interconnects. With less than 1% change in the resistance of SDIs after 50,000 cycles of applied tensile strain of 200%, the SDI structure ensures reliable stretchability and durability of the circuit patch for long-term electrocardiography.The sensor patch is soft, stretchable and it is fabricated using a low-cost scalable method. This soft and stretchable ECG sensor-system shows comparable performance with respect to medical grade Ag/AgCl wet gel electrodes. Our CNT-PDMS sensors shows low electrode-skin interface impedance and low susceptibility to motion artifact which similar of it in medical grade Ag/AgCl wet gel sensors (Fig. 1b). Further, it is waterproof, reusable and comfortable to wear.The circuit patch includes a rechargeable battery and ECG signals is wirelessly sent to a personal device such as cellphone, tablet and laptop through Bluetooth low energy (BLE) and it is displayed in real-time (Fig. 1c) Our developed sensor-system is a multi-use platform which can be applied for the detection of EMG, EEG or EOG signals. Figure 1

Simplified Attachable EEG Revealed Child Development Dependent Neurofeedback Brain Acute Activities in Comparison with Visual Numerical Discrimination Task and Resting.

The development of an easy-to-attach electroencephalograph (EEG) would enable its frequent use for the assessment of neurodevelopment and clinical monitoring. In this study, we designed a two-channel EEG headband measurement device that could be used safely and was easily attachable and removable without the need for restraint or electrode paste or gel. Next, we explored the use of this device for neurofeedback applications relevant to education or neurocognitive development. We developed a prototype visual neurofeedback game in which the size of a familiar local mascot changes in the PC display depending on the user’s brain wave activity. We tested this application at a local children’s play event. Children at the event were invited to experience the game and, upon agreement, were provided with an explanation of the game and support in attaching the EEG device. The game began with a consecutive number visual discrimination task which was followed by an open-eye resting condition and then a neurofeedback task. Preliminary linear regression analyses by the least-squares method of the acquired EEG and age data in 30 participants from 5 to 20 years old suggested an age-dependent left brain lateralization of beta waves at the neurofeedback stage (p = 0.052) and of alpha waves at the open-eye resting stage (p = 0.044) with potential involvement of other wave bands. These results require further validation.

Highly breathable, surface-hydrophobic and wet-adhesive silk based epidermal electrode for long-term electrophysiological monitoring

Epidermal electrodes for long-term electrophysiological signals monitoring have great potentials in bioelectronics such as health monitoring, disease diagnosis, and human-machine interaction. However, it still remains challenges for epidermal electrodes with simultaneously high breathability, surface self-cleaning, and robust skin-adhesion, which may cause skin discomfort, loosing adhesion, and misleading signals during long-term using. In this work, based on the soft and wet-adhesive silk fibroin nanofibers membrane, we report a novel three-layer all-nanofiber-based polytetrafluoroethylene (PTFE)/silver nanowires (Ag NWs)/silk fibroin nanofibers membrane (Silk NFs) fabric electrode. This hierarchical porous structure endows the fabric with thinness (∼10 μm), high conductivity (∼3.58 Ω/sq), high breathability (51.5 mm/s, water vapor transmission rate (WVTR) = 2553 g m−2 d−1 at 35 °C), wet skin-adhesion (13 N/m on wet skin), and surface hydrophobicity (contact angle of 142.3°). As a result, it can be conformally attached to the skin with no skin irritation and prevent sweat accumulation and immersion. Furthermore, compared to the commercial Ag/AgCl gel electrodes, the as-prepared fabric electrode in this work provides a better skin-electrode interface, so that the obtained electrochemical signals in exercise have higher signal qualities with equivalent signal strength and lower signal noise. Therefore, this fabric electrode may further promote the development of epidermal electrode in real-time long-term use.

Conducting polymer host–guest hydrogels with bicontinuous electron/ion transport for boosted thickness–independent supercapacitance

The development of conducting polymer hydrogels with 3D ordering and hierarchical geometry is urgent yet challenging for the design of electrochemical/electronic systems with combined features of hydrogel structures and pseudocapacitive organic materials. Herein, a host–guest hybrid gel electrode that is composed of a polypyrrole (PPy) aerogel and its skeleton-surface-constrained Fe3+-coordinated poly(acrylic acid) (Fe-PAA) hydrogel is fabricated, which can readily work as a highly elastic and self-healable electrode for an all-gel-state supercapacitor with thickness-independent capacitive performance. An interfacial polymerization approach by restraining oxidative nucleation and promoting secondary growth reactions is presented for preparing the pseudocapacitive PPy aerogel as a host component with good elasticity. Upon an impregnation with the ionically conductive and self-healable Fe-PAA hydrogel as a guest component, the resultant PPy aerogel-hosting hydrogels (PAHH) exhibit a remarkable thickness-independent supercapacitance owing to the enhanced electron/ion transport kinetics induced by a bicontinuous electron/ion-conducting network. A proof-of-concept all-solid-state supercapacitor based on the host–guest hybrid electrodes demonstrates a remarkable remarkably high areal capacitance of 2033 mF cm−2 and extremely steady retention undergoing a 60 % compression deformation and cutting damage with high self-healing performance. The host–guest geometry design for the development of bicontinuous electron/ion conductive transport in conducting polymer-based electrodes might boost unprecedented electron and ion transport in high-mass-loading thick electrodes for smart energy storage devices.

Highly Conductive and Underwater Stable Ionic Skin for All‐Day Epidermal Biopotential Monitoring

AbstractEpidermal biopotential monitoring is an essential part of wearable healthcare. For 24 × 7 h detection of electrophysiological signals, commercialized gel electrodes cannot satisfy the demands, in particular for monitoring in humidity or underwater. Epidermal electrodes that can be stable and operated underwater are required. Here, a highly conductive and optically camouflaged ionic skin for epidermal biopotential monitoring under aquatic circumstances is designed. There is a fluorine‐dipole interaction system consisting of fluorine‐rich segment in the polyurethane backbone and fluorine‐cation bonded 1‐ethyl‐3‐methylimidazolium bis(trifluoromethyl‐sulfonyl) imide ([EMIM]+ [TFSI]−) ion pairs distributed in the polymer matrix. Benefitting from the fluorine‐cation interaction, the ionic skin gains remarkable ionic conductivity (1.04 × 10−3 S cm−1), high optical transmittance (92%), and improved mechanical strength (3.1 MPa of Young's modulus). Via cations caught by fluorine‐rich segments, its ionic conductivity can keep stable even by rinsing or fierce washing in water. The epidermal electrode based on such ionic skin can accurately measure a variety of electrophysiological signals undboth atmospheric and aquatic environments, exhibiting robust and excellent signal quality. As the first demonstration of ionic skin‐based electrophysiological electrodes, the ionic skin paves a new way for all‐day wearable healthcare.

Fabrication of Textile-Based Dry Electrode and Analysis of Its Surface EMG Signal for Applying Smart Wear.

Ag/AgCl hydrogel electrodes, which are wet electrodes, are generally used to acquire bio-signals non-invasively. Research concerning dry electrodes is ongoing due to the following limitations of wet electrodes: (1) skin irritation and disease when attached for a long time; (2) poor adhesion due to sweat; and (3) considerable cost due to disposable use. Accordingly, electrodes in film, embroidery, and knit forms were manufactured from conductive sheets and conductive yarns, which are typical textile-type dry electrode materials, using different manufacturing methods and conditions. The prepared electrodes were conducted to measure the morphology, surface resistance, skin-electrode impedance, EMG signal acquisition, and analysis. The conductive sheet type electrode exhibited a similar skin-impedance, noise, and muscle activation signal amplitude to the Ag/AgCl gel electrode due to the excellent adhesion and shape stabilization. Embroidery electrodes were manufactured based on two-dimension lock stitch (Em_LS) and three-dimension moss-stitch (Em_MS). More stable EMG signal acquisition than Em_LS was possible when manufactured with Em_MS. The knit electrode was manufactured with the typical structures of plain, purl, and interlock. Although it was possible to acquire EMG signals, considerable noise was generated as the shape and size of the electrodes were changed due to the stretch characteristics of the knit structure. Finally, the applicability of the textile-type dry electrode was confirmed by combining it with a wearable device. More stable and accurate EMG signal acquirement will be possible through more precise parameter control in the future.

Stretchable and Self-Adhesive PEDOT:PSS Blend with High Sweat Tolerance as Conformal Biopotential Dry Electrodes.

Dry epidermal electrodes that can always form conformal contact with skin can be used for continuous long-term biopotential monitoring, which can provide vital information for disease diagnosis and rehabilitation. But, this application has been limited by the poor contact of dry electrodes on wet skin. Herein, we report a biocompatible fully organic dry electrode that can form conformal contact with both dry and wet skin even during physical movement. The dry electrodes are prepared by drop casting an aqueous solution consisting of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(vinyl alcohol) (PVA), tannic acid (TA), and ethylene glycol (EG). The electrodes can exhibit a conductivity of 122 S cm-1 and a mechanical stretchability of 54%. Moreover, they are self-adhesive to not only dry skin but also wet skin. As a result, they can exhibit a lower contact impedance to skin than commercial Ag/AgCl gel electrodes on both dry and sweat skins. They can be used as dry epidermal electrodes to accurately detect biopotential signals including electrocardiogram (ECG) and electromyogram (EMG) on both dry and wet skins for the users at rest or during physical movement. This is the first time to demonstrate dry epidermal electrodes self-adhesive to wet skin for accurate biopotential detection.

Assembly of symmetric supercapacitor based on alginate hydrogel electrolyte and polyaniline modified electrodes

Biopolymer-based hydrogel electrolytes can be described as alternative materials for supercapacitors due to their good ionic conductivity, no liquid leakage, and no toxicity, allowing the construction of flexible devices. This work reports the preparation of alginate gels crosslinked with Ca2+, H+, and a combination of Ca2+ and H+, for use as electrolytes in a symmetric supercapacitor with polyaniline (PANI) films as electrodes. Results indicated that the gel formed with both Ca2+ and H+ showed to be the most appropriate for supercapacitor development for presenting the better electrochemical performance of PANI electrodes, higher values of ionic conductivity and capacitance, also presenting good cycling stability. The symmetrical supercapacitor assembled with the alginate gel and conventional PANI electrodes provided a specific capacitance of 15.08 F g−1 at 0.05 mA cm−2 and exhibited good cycling stability with 92% capacitance retention after 1100 cycles. Three supercapacitor devices fabricated with 3D printing were connected in series and used to power a red LED.