Article

Skin Conformal Polymer Electrodes for Clinical ECG and EEG Recordings

Authors:
  • Innovative Sensor Technology IST AG
If you want to read the PDF, try requesting it from the authors.

Abstract

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.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Textile dry electrode Band Ref: [12,19,34,35,37] Ref: [68,72,85,88,90,99,100] Ref: [111,115,117,119,123,126,129,130,135,138,139,140,141,142] Adhesive film Ref: [16,18,20,21,22,23,24,33,38,40,41,43,55,58,59,61,62,63,109,147] Ref: [70,74,77,81,82,83,84,87,89,95,101,102,103,105,106,107] Ref: [112,113,114,122,124,125,131,132,134,143,161] Adhesives Ref: [13,36,37,44,54,56,65] \ Ref: [118] Self-adhesive Ref: [14,15,39,162,163] Ref: [73,108] \ Integration with clothes \ \ Ref: [120,121,127,133] PPy: Lower electrochemical stability flexible bioelectric dry electrodes will become more and more abundant, and the bioelectric dry electrodes with excellent performance and easy operation will bring new opportunities for long-term wearable health monitoring systems. ...
... ECG[69,70,71,72,73,76,77,81,82,83,84,87,89,90,91,94,97,99,100,102,104,105,107,108,109]; EMG[71,81,83,84,88,90,95,103,104,105,106]; EEG[68,71,74,75,76,77,78,79,80,85,86,87,90,92,95,96,97,98,99,101,104,109]; EOG[91,97,104] ...
... ECG[69,70,71,72,73,76,77,81,82,83,84,87,89,90,91,94,97,99,100,102,104,105,107,108,109]; EMG[71,81,83,84,88,90,95,103,104,105,106]; EEG[68,71,74,75,76,77,78,79,80,85,86,87,90,92,95,96,97,98,99,101,104,109]; EOG[91,97,104] ...
Article
The surface bioelectric sensors in contact with human skin is a key component of Long-term wearable health monitoring systems (LWHMs), bioelectric signals generated by living cells or tissues are closely related to the health status of the human body, and bioelectric sensors are used to record such signals. Compared to conventional Ag/AgCl wet electrodes, surface bioelectric dry electrodes (SBDEs) offer significant advantages in terms of ease of use, biocompatibility and long-term stability. Therefore, the research focus has shifted to the study of dry electrodes, which can be used without gels. This paper provides a detailed overview of the research progress of SBDEs and a comprehensive introduction to their measurement principles, different types of SBDEs (flat film dry electrodes, surface micro/nano-structured dry electrodes and textile dry electrodes) and evaluation test methods, analyzes the advantages and disadvantages of SBDEs and their prospects, and provides some inspiration for the development of high-performance SBDEs.
... [31][32][33] Up to now, there are two types of ECG monitoring devices based on the electrode number: single-lead ECG and multiple-lead ECG (ranging from 2 to 12 leads) as shown in Table S1. [34][35][36][37][38][39][40][41] Commercialized wearable singlelead ECG devices, which could provide accurate heart rate (HR) measurement, 31 are already a mature technology in the market, such as fitness trackers and smartwatches. 42 However, those devices could not provide convincing medical information and professional disease diagnosis apart from the HR monitoring. ...
... As shown in Table S2, the high conductivity, strong adhesive strength, and low Young's modulus compared to other electrodes have been reported for ECG recording, indicating the superior property of the organohydrogel patch for long-term recording of high-quality ECG signal. [38][39][40][41] The organohydrogel patch (diameter, 3 cm) is elaborated by photo-triggered gelation of SBMA, AAc, gelatin, and CaCl 2 in a binary solvent of glycerol and water for the formation of ionic polymer skeleton with a close Young's modulus to the human skin ( Figure S3). Figure 3A shows that the organohydrogel patch displays a higher electrical conductivity (electrical resistance:~6.5 kΩ), which is significantly lower than that of the traditional, commercial patches (resistance,~45 kΩ; LT-302, Shanghai LITU Medical Appliances Co., Ltd.), owing to the presence of the abundant ions within organohydrogel network for the formation of continuous ion mobility pathway. In addition to its high and sustained conductivity, the organohydrogel patch is also imparted with strong interfacial adhesion. ...
Article
Full-text available
Cardiovascular diseases (CVDs) are fatal chronic diseases, where electrocardiography (ECG) monitoring could be a prominent solution for early diagnosis. In spite of available commercialized, multilead ECG devices, bulky formats, discontinuous monitoring, and no safety alarm system significantly limit their practical applications. Herein, we present a soft, and stretchable, three‐lead ECG device allowing continuous monitoring and wireless transmission of ECG signals. A newly developed organohydrogel patch with a strong adhesive ability (~9.9 kPa) and higher conductivity (~6.5 kΩ) is applied for high‐quality ECG signals collection. With a long operation duration (6.5 h) and wireless transmission distance (20.9 m), it could fulfill most of the daily applications. Machine learning algorithms and the graphical user interface are used for real‐time ECG monitoring and cardiac abnormalities diagnosis. The vibratory flexible actuator, which is triggered by cardiac abnormalities that need immediate medical treatment, is also integrated as a warning system for the user. As a newly reported stretchable multi‐lead ECG device for long‐term ECG signal monitoring, there is a high potential for improving users' life quality with the high‐risk population of CVDs. In this manuscript, we developed a stretchable, three‐lead electrocardiography (ECG) device based on self‐developed organohydrogel patches with strong adhesion and high conductivity for continuously monitoring human ECG signals. A safety warning system based on a mechanical vibration actuator is built up inside the ECG device as an indicator of the seriousness of the cardiovascular diseases, which could remind users to take proper actions.
... With increasing research in the field of bioelectricity, electrophysiology equipment, such as neural electrodes [1], electrocardiogram (ECG) electrodes [2], electroencephalogram (EEG) electrodes [3], and electronic skins [4], has been gaining extensive attention. Since these instruments directly come into contact with human tissues, they must exhibit high safety, biocompatibility, and skin adhesion as well as low impedances [2,5]. ...
... With increasing research in the field of bioelectricity, electrophysiology equipment, such as neural electrodes [1], electrocardiogram (ECG) electrodes [2], electroencephalogram (EEG) electrodes [3], and electronic skins [4], has been gaining extensive attention. Since these instruments directly come into contact with human tissues, they must exhibit high safety, biocompatibility, and skin adhesion as well as low impedances [2,5]. Conductive-gelbased Ag/AgCl wet electrodes are commonly used for the detection of electrophysiological signals owing to the ability of the conductive gel to reduce the impedance, allowing conformal contact between human skin and electrodes [6,7]. ...
Article
Graphene has shown immense potential for applications in monitoring scalp electroencephalogram (EEG) signals. However, the radial head shape, high-resistance scalp cuticle, and hair prevent graphene from contacting skin, resulting in high contact impedances and low signal-to-noise ratios (SNRs) in EEG signals. Therefore, B and N co-doped vertical graphene (BNVG) electrodes are synthesized to improve the skin affinity and sweat adsorption capacity. X-ray photoelectron spectroscopy results show that the series of BNVG electrodes comprise B-doping contents of 1.25–9.85 at% and N-doping contents of 1.12–6.48 at%. A systematic analysis of the effects of B and N atom contents on the real-time scalp-contact resistances, EEG correlation coefficients between BNVG and Ag/AgCl electrodes, and SNRs of the EEG signals are conducted. The BNVG electrode comprising 4.47 at% B and 3.18 at% N is determined as the optimum electrode for scalp EEG signal acquisition. Furthermore, an EEG cap assembled with 19 optimized BNVG electrodes records spontaneous and evoked EEG signals. The BNVG-based EEG cap used with sweat or aqueous NaCl solution is confirmed to be advantageous and can be applied to clinical and brain-computer interface systems.
... However, due to the highly resistive SC, dry electrodes generally do not exhibit good EII compared to wet electrodes [6,7]. Various new materials and structures have been proposed to improve the electrode-skin contact, but the trade-off is the large electrode volume or footprint [3][4][5][8][9][10]. ...
... Consequently, the characterization of EII should also consider the contact area. An impedance normalized according to area (kΩ cm 2 ) can better reflect the electrode performance [9,33]. For long-term applications, flexible microneedle electrodes fitting a curved body surface provide a better tolerance to patient activity. ...
Article
Full-text available
Highlights Polyimide-based flexible microneedle array (PI-MNA) electrodes realize high electrical/mechanical performance and are compatible with wearable wireless recording systems. The normalized electrode–skin interface impedance (EII) of the PI-MNA electrodes reaches 0.98 kΩ cm ² at 1 kHz and 1.50 kΩ cm ² at 10 Hz, approximately 1/250 of clinical standard electrodes. This is the first report on the clinical study of microneedle electrodes. The PI-MNA electrodes are applied to clinical long-term continuous monitoring for polysomnography. Abstract Microneedle array (MNA) electrodes are an effective solution to achieve high-quality surface biopotential recording without the coordination of conductive gel and are thus very suitable for long-term wearable applications. Existing schemes are limited by flexibility, biosafety, and manufacturing costs, which create large barriers for wider applications. Here, we present a novel flexible MNA electrode that can simultaneously achieve flexibility of the substrate to fit a curved body surface, robustness of microneedles to penetrate the skin without fracture, and a simplified process to allow mass production. The compatibility with wearable wireless systems and the short preparation time of the electrodes significantly improves the comfort and convenience of electrophysiological recording. The normalized electrode–skin contact impedance reaches 0.98 kΩ cm ² at 1 kHz and 1.50 kΩ cm ² at 10 Hz, a record low value compared to previous reports and approximately 1/250 of the standard electrodes. The morphology, biosafety, and electrical/mechanical properties are fully characterized, and wearable recordings with a high signal-to-noise ratio and low motion artifacts are realized. The first reported clinical study of microneedle electrodes for surface electrophysiological monitoring was conducted in tens of healthy and sleep-disordered subjects with 44 nights of recording (over 8 h per night), providing substantial evidence that the electrodes can be leveraged to substitute for clinical standard electrodes.
... e idea of developing a resultant membrane-like substance that acts as sensors and feels like the skin is a novel approach to developing biosensors [33]. e invention of a Gecko-based dry adhesive with conductive capability offers favorable outcomes for monitoring biosignals from the wearer's skin in real time through highactivity periods [34]. Table 1 illustrates the different smart cloth products that are designed and marketed by different brands for various applications. ...
... In the fashion industry, the supply chain plays a crucial role, as it provides the flow of goods and services that are required to transform raw materials into the final product. e real-time monitoring and tracking of the supply chain are required in the fashion, as it empowers to visualize the activities that are carried out from beginning to end. Figure 7 illustrates the IoT-assisted traceability architecture that is proposed by [34] for the fashion supply chain; this architecture comprises the following six stages: create, read, communicate, aggregate, consult/trace, and analyze. Under create a stage, the production of textile goods along with the integration of sensors and tags allows to trace in the supply chain. ...
Article
Full-text available
The Sustainable Development Goals of the United Nations prioritize sustainability by 2030. The fashion industry is one most substantial manufacturing industries that generate an economy of 3 trillion dollars and contributes to 2% of the world’s gross domestic product. In addition to this, the fashion industry must focus on social and environmental concerns, where it should create fashionable products to promote sustainable consumption and production. Sustainable consumption and production can be achieved with the establishment of resilient infrastructure with innovation. The resilient infrastructure with innovation is realized by the integration of digital technologies such as the Internet of Things (IoT), artificial intelligence (AI), blockchain, augmented reality (AR), and virtual reality (VR). With this motivation, this study explored the different studies that implemented these technologies in the fashion industry for smart cloth (health), supply chain, circular economy, dress recommendation system, fashion trend forecasting, health prediction, and virtual and augmented based shopping experience. Along with the progress of these technologies in the fashion industry, the study also discussed limitations and provided recommendations such as wide adoption of blockchain in fashion supply chain; advancement in energy storage for smart cloth; integration of IoT, AI, and edge computing; and smart clothing-based framework for rescue operation for future enhancement.
... Generally, a higher skin-contact impedance leads to an increased impedance mismatch that reduces common-mode rejection and, hence the SNR (signal to noise ratio) [31,32]. Therefore, it is important to decrease and control the impedance to manufacture an electrode for bio-signals. ...
Article
Full-text available
The interest in wearable devices has expanded to measurement devices for building IoT-based mobile healthcare systems and sensing bio-signal data through clothing. Surface electromyography, called sEMG, is one of the most popular bio-signals that can be applied to health monitoring systems. In general, gel-based (Ag/AgCl) electrodes are mainly used, but there are problems, such as skin irritation due to long-time wearing, deterioration of adhesion to the skin due to moisture or sweat, and low applicability to clothes. Hence, research on dry electrodes as a replacement is increasing. Accordingly, in this study, a textile-based electrode was produced with a range of electrode shapes, and areas were embroidered with conductive yarn using an embroidery technique in the clothing manufacturing process. The electrode was applied to EMG smart clothing for fitness, and the EMG signal detection performance was analyzed. The electrode shape was manufactured using the circle and wave type. The wave-type electrode was more morphologically stable than the circle-type electrode by up to 30% strain, and the electrode shape was maintained as the embroidered area increased. Skin-electrode impedance analysis confirmed that the embroidered area with conductive yarn affected the skin contact area, and the impedance decreased with increasing area. For sEMG performance analysis, the rectus femoris was selected as a target muscle, and the sEMG parameters were analyzed. The wave-type sample showed higher EMG signal strength than the circle-type. In particular, the electrode with three lines showed better performance than the fill-type electrode. These performances operated without noise, even with a commercial device. Therefore, it is expected to be applicable to the manufacture of electromyography smart clothing based on embroidered electrodes in the future.
... Inspired by nature, many bionic flexible devices for different applications have been developed, such as electronic skin [32], wearable sensors [33], and flexible electrodes [34]. By mimicking human and biological structures, a variety of ECG electrodes with excellent performance, including better skin adhesion, low skin contact impedance, and high stability, have been proposed [35][36][37][38][39]. ...
Article
Full-text available
With the rapidly aging society and increased concern for personal cardiovascular health, novel, flexible electrodes suitable for electrocardiogram (ECG) signal monitoring are in demand. Based on the excellent electrical and mechanical properties of graphene and the rapid development of graphene device fabrication technologies, graphene-based ECG electrodes have recently attracted much attention, and many flexible graphene electrodes with excellent performance have been developed. To understand the current research progress of graphene-based ECG electrodes and help researchers clarify current development conditions and directions, we systematically review the recent advances in graphene-based flexible ECG electrodes. Graphene electrodes are classified as bionic, fabric-based, biodegradable, laser-induced/scribed, modified-graphene, sponge-like, invasive, etc., based on their design concept, structural characteristics, preparation methods, and material properties. Moreover, some categories are further divided into dry or wet electrodes. Then, their performance, including electrode–skin impedance, signal-to-noise ratio, skin compatibility, and stability, is analyzed. Finally, we discuss possible development directions of graphene ECG electrodes and share our views.
... Electrochemical impedance was used by many researchers to analyze and evaluate dry electrode performance. 41 In this study, electrochemical impedance spectroscopy was measured on an electrochemical workstation (CHI660D, Shanghai Chenhua Instrument Co., Ltd., China). The electrochemical impedance of the electrode−electrolyte interface and the electrode−skin interface was measured to analyze the electrochemical behavior, respectively. ...
... 13−16 Since material properties of such devices are matched with those of human tissues and organs, their sensing and therapy performance as well as long-term biocompatibility in vivo will be improved over those of conventional bulky and rigid devices. 17−19 Specifically, these soft electronic devices can be conformally integrated with the human body, 20,21 which minimize the impedance and maximize the signal-to-noise ratio, 22,23 and thus, they can capture various biosignals from target sites and translate them into electrical signals efficiently ( Figure 1A). 24,25 In addition, such devices supply power to the biointegrated devices ( Figure 1B), store the recorded data ( Figure 1C), visualize the collected biosignals ( Figure 1D), and apply feedback therapeutic stimulations ( Figure 1E). ...
Article
Full-text available
Recent advances in nanostructured materials and unconventional device designs have transformed the bioelectronics from a rigid and bulky form into a soft and ultrathin form and brought enormous advantages to the bioelectronics. For example, mechanical deformability of the soft bioelectronics and thus its conformal contact onto soft curved organs such as brain, heart, and skin have allowed researchers to measure high-quality biosignals, deliver real-time feedback treatments, and lower long-term side-effects in vivo. Here, we review various materials, fabrication methods, and device strategies for flexible and stretchable electronics, especially focusing on soft biointegrated electronics using nanomaterials and their composites. First, we summarize top-down material processing and bottom-up synthesis methods of various nanomaterials. Next, we discuss state-of-the-art technologies for intrinsically stretchable nanocomposites composed of nanostructured materials incorporated in elastomers or hydrogels. We also briefly discuss unconventional device design strategies for soft bioelectronics. Then individual device components for soft bioelectronics, such as biosensing, data storage, display, therapeutic stimulation, and power supply devices, are introduced. Afterward, representative application examples of the soft bioelectronics are described. A brief summary with a discussion on remaining challenges concludes the review.
... This conformal contact minimizes the gaps between the skin and the electrodes, which allows the tattoo-like electrode to have low electrode-skin impedance comparable to the commercial electrode without using wet electrolytes. In addition, it is very effective in reducing motion artifacts to minimize the inconsistent gaps that are induced by human motion or external vibration [41][42][43][44] . Not only the electrode but also the connector is another reason for the motion artifacts. ...
Article
Full-text available
Human nonverbal communication tools are very ambiguous and difficult to transfer to machines or artificial intelligence (AI). If the AI understands the mental state behind a user’s decision, it can learn more appropriate decisions even in unclear situations. We introduce the Brain–AI Closed-Loop System (BACLoS), a wireless interaction platform that enables human brain wave analysis and transfers results to AI to verify and enhance AI decision-making. We developed a wireless earbud-like electroencephalography (EEG) measurement device, combined with tattoo-like electrodes and connectors, which enables continuous recording of high-quality EEG signals, especially the error-related potential (ErrP). The sensor measures the ErrP signals, which reflects the human cognitive consequences of an unpredicted machine response. The AI corrects or reinforces decisions depending on the presence or absence of the ErrP signals, which is determined by deep learning classification of the received EEG data. We demonstrate the BACLoS for AI-based machines, including autonomous driving vehicles, maze solvers, and assistant interfaces.
... Textile-electrodes have been already proposed for various EEG recording applications [23], such as monitoring newborns [25] and brain-computer interfaces [26]. Recently, self-adhesive microstructure textile-electrodes have been developed for electrocardiography and EEG recordings and for measuring micro-and macro-level EEG sleep features [27], [28]. Despite the promising results, it is still unclear how forehead EEG signals acquired with textile-electrodes correspond to standard EEG and EOG signal derivations recommended by the American Academy of Sleep Medicine [13]. ...
Article
Full-text available
The current clinically used electroencephalography (EEG) sensors are not self-applicable. This complicates the recording of the brain’s electrical activity in unattended home polysomnography (PSG). When EEG is not recorded, the sleep architecture cannot be accurately determined, which decreases the accuracy of home-based diagnosis of sleep disorders. The aim of this study was to compare the technical performance of forehead EEG signals recorded with FocusBand, an easily applicable textile electrode headband, to that recorded using clinical EEG and electrooculography (EOG) electrodes. Overnight unattended recordings were conducted at participants’ (n=10) homes. Signals were recorded using a portable Nox A1 PSG device. The FocusBand’s forehead EEG (Fp1-Fp2) signals contained features that are visible at both, the standard EEG and EOG signals. The FocusBand’s EEG signal amplitudes were significantly lower compared to standard EEG (F4-M1; average difference 98%) and EOG (E1-M2; average difference 29%) signals during all sleep stages. Despite the amplitude difference, forehead EEG signals displayed typical EEG characteristics related to certain sleep stages. However, the frequency content of the FocusBand-based signals was more similar to that of the standard EOG signals than that of standard EEG signals. The majority of the artifacts seen in the FocusBand signals were related to a loosened headband. High differences in the frequency content of the compared signals were also found during wakefulness, suggesting susceptibility of the textile electrodes to electrode movement artifacts. This study demonstrates that the forehead biopotential signals recorded using an easily attachable textile electrode headband could be useful in home-based sleep recordings.
... Thus, this would cause skin irritation and significant decays of the signal-to-noise ratio of biosignals, respectively. Instead, the fabrication of dry-type electrodes was intensively investigated using a thin metal [4][5][6][7], a carbon nanotube (CNT) [8][9][10][11], polymer-metal particle composites [12], graphene [13][14][15][16][17] and conductive polymers, such as poly (3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) [18][19][20]. ...
Article
Full-text available
To increase the human lifespan, healthcare monitoring devices that diagnose diseases and check body conditions have attracted considerable interest. Commercial AgCl-based wet electrodes with the advantages of high conductivity and strong adaptability to human skin are considered the most frequently used electrode material for healthcare monitoring. However, commercial AgCl-based wet electrodes, when exposed for a long period, cause an evaporation of organic solvents, which could reduce the signal-to-noise ratio of biosignals and stimulate human skin. In this context, we demonstrate a dry electrode for a poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS)-based blended polymer electrode using a combination of PEDOT:PSS, waterborne polyurethane (WPU) and ethylene glycol (EG) that could be reused for a long period of time to detect electrocardiography (ECG) and electromyography (EMG). Both ECG and EMG are reliably detected by the wireless real-time monitoring system. In particular, the proposed dry electrode detects biosignals without deterioration for over 2 weeks. Additionally, a double layer of a polyimide (PI) substrate and fluorinated polymer CYTOP induces the strong waterproof characteristics of external liquids for the proposed dry electrodes, having a low surface energy of 14.49 mN/m. In addition, the proposed electrode has excellent degradability in water; it dissolves in hot water at 60 °C.
... Additionally, according to studies [121,122], subjects prefer noninvasive systems for their medical diagnosis and treatment despite having low-quality signals. Therefore, the non-invasive EEG systems are the most commonly used in BCI-assisted stroke rehabilitation systems that are based on either gel [123][124][125] or dry electrodes [126,127]. However, the current EEG systems [128][129][130][131] are heavy, bulky, and contain rigid hardware components, hence, not suitable for longterm mobile EEG monitoring on a daily basis. ...
Article
Full-text available
Objective: Stroke is one of the most common neural disorders, which causes physical disabilities and motor impairments among its survivors. Several technologies have been developed for providing stroke rehabilitation and to assist the survivors in performing their daily life activities. Currently, the use of flexible technology (FT) for stroke rehabilitation systems is on a rise that allows the development of more compact and lightweight wearable systems, which stroke survivors can easily use for long-term activities. Approach: For stroke applications, FT mainly includes the "flexible/stretchable electronics", "e-textile (electronic textile)" and "soft robotics". Thus, a thorough literature review has been performed to report the practical implementation of FT for post-stroke application. Main results: In this review, the highlights of the advancement of FT in stroke rehabilitation systems are dealt with. Such systems mainly involve the "biosignal acquisition unit", "rehabilitation devices" and "assistive systems". In terms of biosignals acquisition, electroencephalography (EEG) and electromyography (EMG) are comprehensively described. For rehabilitation/assistive systems, the application of functional electrical stimulation (FES) and robotics units (exoskeleton, orthosis, etc.) have been explained. Significance: This is the first review article that compiles the different studies regarding flexible technology based post-stroke systems. Furthermore, the technological advantages, limitations, and possible future implications are also discussed to help improve and advance the flexible systems for the betterment of the stroke community.
... Grasshopper-inspired microstructured electrodes made of silver microparticles (AgNPs) mixed with PDMS fabricated on a microstructured wafer have low skin-contact impedance and can be applied directly to the skin without skin preparation or external pressure. 32 Inspired by the suction mechanism of octopus suckers, octopus-like polymer masters patterned polyurethane (PU)/multiwalled nanotubes (MWNTs)/silver flakes composite can increase the adhesion between electrodes and skin, and these types of electrodes can make conformal contact even with rough and moist human skin and can withstand bending and twisting conditions. 33 However, these bioinspired approaches typically require a more sophisticated fabrication process to make the mold masters through photolithography and etching processes. ...
Article
Full-text available
Soft electronic devices and sensors have shown great potential for wearable and ambulatory electrophysiologic signal monitoring applications due to their light weight, ability to conform to human skin, and improved wearing comfort, and they may replace the conventional rigid electrodes and bulky recording devices widely used nowadays in clinical settings. Herein, we report an elastomeric sponge electrode that offers greatly reduced electrode-skin contact impedance, an improved signal-to-noise ratio (SNR), and is ideally suited for long-term and motion-artifact-tolerant recording of high-quality biopotential signals. The sponge electrode utilizes a porous polydimethylsiloxane sponge made from a sacrificial template of sugar cubes, and it is subsequently coated with a poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) conductive polymer using a simple dip-coating process. The sponge electrode contains numerous micropores that greatly increase the skin-electrode contact area and help lower the contact impedance by a factor of 5.25 or 6.7 compared to planar PEDOT:PSS electrodes or gold-standard Ag/AgCl electrodes, respectively. The lowering of contact impedance resulted in high-quality electrocardiogram (ECG) and electromyogram (EMG) recordings with improved SNR. Furthermore, the porous structure also allows the sponge electrode to hold significantly more conductive gel compared to conventional planar electrodes, thereby allowing them to be used for long recording sessions with minimal signal degradation. The conductive gel absorbed into the micropores also serves as a buffer layer to help mitigate motion artifacts, which is crucial for recording on ambulatory patients. Lastly, to demonstrate its feasibility and potential for clinical usage, we have shown that the sponge electrode can be used to monitor uterine contraction activities from a patient in labor. With its low-cost fabrication, softness, and ability to record high SNR biopotential signals, the sponge electrode is a promising platform for long-term wearable health monitoring applications.
... 为了改善收集脑电信号的质量, 苏黎世联邦理工学院的 Janos Vörös 教授 [63] 提出了一种基于导电的 软微柱聚合物电极, 实现脑电信号高质量采集. 该电极主要由 15mm 直径的导电底座以及 12 个软微柱构 成, 并采用仿生蚱蜢脚结构进行设计, 加强电极与皮肤表面的范德华作用力, 在测试者具有浓密毛发的 情况下, 仍然可以与头皮完美贴合, 进而监测脑电信号的 α 波活性. ...
... As dehydration and skin irritation occur after the long-term use of gel electrodes 13,14 , dry electrodes have emerged as promising alternatives. Many efforts have been devoted to improving the performance of dry electrodes in case of exercise and sweating respectively [15][16][17][18][19][20][21][22][23] . a. ...
Article
Full-text available
Electrophysiological monitoring under strenuous exercise by using stretchable dry electrodes is vital for healthcare monitoring, prosthetic control, human−machine interfaces and other biomedical applications. However, the existing dry electrodes are not applicable to the strenuous exercise situation that always involves both fast moving and profuse sweating. Herein, we present a nano-thick porous stretchable dry electrode system with high stretchability and water permeability. The system attaches conformably to the skin and stretches with it under Van der Waals forces even at sweating conditions, allowing the detection of electromyogram when moving with an acceleration of 10 g at a sweating rate of 2.8 mg cm−2 min−1. It is also capable of acquiring electrocardiogram and electroencephalogram signals. The strategy proposed would enable the biomedical studies and related applications with the requirement of stably recording electrophysiological signals under strenuous exercise scenarios.
... Wet electrodes made of silver/silver chloride (Ag/AgCl) are currently used for conventional ECG testing [6]. Conducting gel is used in these electrodes to minimize skin-electrode contact impedance between the electrode and the skin's stratum corneum (SC) layer [7,8]. Although these electrodes have a low contact impedance and good signal quality for short-term monitoring, they have several drawbacks and limitations for long-term monitoring. ...
Article
Biopotential signals are extremely useful in assessing organ function and diagnosing diseases. This study proposes a highly flexible, conductive, antibacterial, and self-adhesive silver nanorods (AgNRs) embedded polydimethylsiloxane (PDMS) dry electrode for long-term electrocardiogram (ECG) monitoring with portable instrumentation. We use a unique glancing angle deposition method to fabricate AgNRs and embedded them in a biocompatible PDMS matrix. These electrodes do not cause skin irritation even after several hours of use and work efficiently without skin preparation. These AgNRs-PDMS electrodes have an electrical resistivity of 10⁻⁷ Ω-m and a skin contact impedance of 93.9 ± 0.7 kΩ to 6.2 ± 3.7 kΩ for frequencies ranging from 40 Hz to 1 kHz, which is around 18% less than most conventional Ag/AgCl wet electrodes. The fabricated electrodes have a signal-to-noise ratio of 12 dB, comparable to that of a conventional Ag/AgCl electrode. A signal acquisition circuit is designed to detect ECG signals combined with proposed dry electrodes and a wireless monitoring device. Finally, real-time ECG signals are displayed on a mobile phone via an Android application. These AgNRs-PDMS dry electrodes, in combination with the portable wireless device, may be used in future clinical studies that require real-time and long-term ECG monitoring.
... In addition, further multidisciplinary improvements aimed at enhancing the stability, comfort, and performance of dry electrodes are needed. Alternatively, materials-based approaches for epidermal electronics 110,127 and noncontact capacitive electrodes 128,129 have been explored to develop EEG systems with enhanced wearability. However, despite the advantages provided by these technologies, the majority of consumer-grade wEEG platforms that have reached the market rely on the use of dry and semi-dry electrodes. ...
Article
Full-text available
Brain–computer interfaces (BCIs) provide bidirectional communication between the brain and output devices that translate user intent into function. Among the different brain imaging techniques used to operate BCIs, electroencephalography (EEG) constitutes the preferred method of choice, owing to its relative low cost, ease of use, high temporal resolution, and noninvasiveness. In recent years, significant progress in wearable technologies and computational intelligence has greatly enhanced the performance and capabilities of EEG-based BCIs (eBCIs) and propelled their migration out of the laboratory and into real-world environments. This rapid translation constitutes a paradigm shift in human–machine interaction that will deeply transform different industries in the near future, including healthcare and wellbeing, entertainment, security, education, and marketing. In this contribution, the state-of-the-art in wearable biosensing is reviewed, focusing on the development of novel electrode interfaces for long term and noninvasive EEG monitoring. Commercially available EEG platforms are surveyed, and a comparative analysis is presented based on the benefits and limitations they provide for eBCI development. Emerging applications in neuroscientific research and future trends related to the widespread implementation of eBCIs for medical and nonmedical uses are discussed. Finally, a commentary on the ethical, social, and legal concerns associated with this increasingly ubiquitous technology is provided, as well as general recommendations to address key issues related to mainstream consumer adoption.
... In recent years, conducting polymers such as poly (3,4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT: PSS) have been used as the dry electrode of the ECG sensor after inserting silver/silver chloride (Ag/AgCl) into the conducting polymer matrix to improve the interface with the skin 17 . In addition, self-adhesive electrodes for the sensor were designed using extra soft or microstructurally patterned polymers [18][19][20][21][22][23] . Moreover, printing patterned dry electrodes on stretchable polymers has been reported to improve adhesion to the skin 24 . ...
Article
Full-text available
In this study, based on inspiration drawn from origami and the suction mechanism of leeches, a dry electrode is developed for reliable blood pressure (BP) monitoring. The leech-inspired suction mechanism generated a local soft vacuum facilitating appropriate contact with the human skin. Subsequently, an electrocardiogram (ECG) sensor, termed a leech-inspired origami (LIO) sensor, was constructed using the developed dry electrode. The LIO with a sensing robot system ensures reliable ECG signals with a signal-to-noise ratio of 21.7 ± 0.56 dB. From the paired detection of ECG and photoplethysmography (PPG) through human–robot interaction, BP monitoring was demonstrated. The average difference of the systolic BP between that estimated by the sensing robot and that monitored by the sphygmomanometer was 0.03 mmHg, indicating the reliable BP monitoring ability of the sensing robot. The LIO sensing system inspired by origami and leech behaviors makes BP sensing tools feasible, which in turn would further the development of a remote healthcare monitoring robotic system.
Article
Thin dry electrodes are promising components in wearable healthcare devices. Assessing the condition of the human body by monitoring biopotentials facilitates the early diagnosis of diseases as well as their prevention, treatment, and therapy. Existing clinical-use electrodes have limited wearable-device usage because they use gels, require preparation steps, and are uncomfortable to wear. While dry electrodes can improve these issues and have demonstrated performance on par with gel-based electrodes, providing advantages in mobile and wearable applications; the materials and fabrication methods used are not yet at the level of disposable gel electrodes for low-cost mass manufacturing and wide adoption. Here, a low-cost manufacturing process for thin dry electrodes with a conductive micro-pyramidal array is presented for large-scale on-skin wearable applications. The electrode is fabricated using micromolding techniques in conjunction with solution processes in order to guarantee ease of fabrication, high device yield, and the possibility of mass production compatible with current semiconductor production processes. Fabricated using a conductive paste and an epoxy resin that are both biocompatible, the developed micro-pyramidal array electrode operates in a conformal, non-invasive manner, with low skin irritation, which ensures improved comfort for brief or extended use. The operation of the developed electrode was examined by analyzing electrode-skin-electrode impedance, electroencephalography, electrocardiography, and electromyography signals and comparing them with those measured simultaneously using gel electrodes.
Article
Recent advances in telemedicine and personalized healthcare have motivated new developments in wearable technologies targeting continuous monitoring of biosignals. Common limitations of wearables for continuous monitoring include durability and breathability of their biopotential electrodes. This paper tackles this challenge by proposing flexible, breathable, and washable dry textile electrodes made of conductive elastomeric filaments (CEFs). First, candidate CEF fibers are characterized. Using an industrial knitting machine, CEF fibers are then directly knitted into textile electrodes. To assess their performance in more realistic circumstances, smart garments with textile electrodes are knitted. Electrocardiograms (ECGs) are acquired using an underwear garment and electrooculograms (EOGs) are acquired using a headband. ECGs and EOGs with textile electrodes are found to have comparable fidelity to that of the gold standard gel electrodes. CEF electrodes are also resistant to repeated wash and dry cycles (30×) and continue to acquire high‐fidelity biosignals. Smart underwear garments are also used to perform continuous ECG measurements in five participants over 24 h of unrestricted daily activities. Results demonstrate the success of these garments in performing high fidelity continuous ECG monitoring. Collectively, these results present CEF electrodes as a promising scalable solution to the challenges of wearable technologies for long‐term continuous electrophysiological monitoring applications. Conductive elastomeric filaments (CEFs) can be directly knitted into durable, flexible, and breathable textile electrodes using industrial‐scale knitting machines. Smart knitted garments with CEF electrodes are resistant to repetitive wash and dry cycles and are able to provide high fidelity electrocardiograms (ECGs) and electrooculograms. Tests of continuous 24 h ECG recording demonstrate the capability of CEF electrodes for long‐term monitoring applications.
Article
Full-text available
Hierarchically interactive 3D-porous soft carbon nanofibers (CNFs) have great potential for wearable bioelectronic interfaces, yet 90% of CNFs are derived from expensive polyacrylonitrile associated with complex production methods. Here, another cost-effective fluoropolymer, poly(1,1-difluoroethylene) (PDFE), is introduced to investigate its transition chemistry and structural evolution over laser-induced carbonization (LIC). The impregnation of Ti3C2Tx-MXene followed by dehydrofluorination is believed to be crucial to enhance the β-phase and reinforce PDFE-based nanofibers. It is explored that the β-phase of the dehydrofluorinated MXene-PDFE nanofibers is converted into an sp²-hybridized hexagonal graphitic structure by cyclization/cross-linking decomposition during LIC. Remarkably, this approach generates laser-induced hierarchical CNFs (LIHCNFs) with a high carbon yield (54.77%), conductivity (sheet resistance = 4 Ω sq⁻¹), and stability over 500 bending/releasing cycles (at 10% bending range). Using LIHCNFs, a skin-compatible breathable and reusable electronic-tattoo is engineered for monitoring long-term biopotentials and human–machine interfaces for operating home electronics. The LIHCNFs-tattoo with high breathability (≈14 mg cm⁻² h⁻¹) forms compliant contact with human skin, resulting in low electrode-skin impedance (23.59 kΩ cm²) and low-noise biopotential signals (signal-to-noise ratio, SNR = 41 dB). This finding offers a complementary polymer precursor and carbonization method to produce CNFs with proper structural features and designs for multifunctional biointerfaces.
Article
Wearable devices offer a revolutionary approach to ambulatory electrocardiography (ECG) for cardiovascular disease diagnosis. Herein, an adhesive, highly stretchable and conformal (ASC) patch for long‐term ambulatory ECG monitoring is presented. The ASC patch is designed with a “three‐bridge” structure to provide inhomogeneous strain distribution during stretching. Meanwhile, the electrical stability is achieved by stretchable liquid metal interconnects at the domain experiencing larger strain. Moreover, the long‐term usability can be attained by an adhesive layer made of polydopamine/polyacrylamide glycerol–water hydrogel, maintaining good adhesiveness and stretchability for more than two weeks. Altogether, the patch can successfully measure stable high‐quality ECG signals in relaxed, stretched, or underwater conditions. Enhanced mechanical and electrical properties exhibited by our ASC patch confer superior skin‐device interface on either dry or wet conditions than that of current electrodes. The hydrogel‐based patch displays conformal deformation along with the stretched skin. This work provides a scalable prototype for multilead wearable ECG devices and promises new opportunities for medical applications in soft electronics. An adhesive, highly stretchable, and soft patch is developed for long‐term ambulatory electrocardiography (ECG) monitoring. The designed “three‐bridge” structure provides inhomogeneous strain distribution to maintain resistance and adhesion stability during stretching. The long‐term usability is attained by an adhesive glycerol–water hydrogel. The patch can successfully measure stable high‐quality ECG signals in relaxed, stretched, or underwater conditions.
Article
Bio-adhesive and ion-conductive hydrogels are of great significance in the field of bioelectric monitoring, but many challenges remain for practical applications in complex conditions and underwater environments. Here, we report a bioelectrical electrode based on ion-conductive gel with excellent water-resistant, underwater adhesion, and swelling resistance for application in the aquatic environment. Especially, the gel electrode exhibits extremely low impedance (<10 Ω) at physiologically relevant frequencies, long-term electrical and structural stability in the aqueous environment. The static noise (19 uV) and dynamic noise (30 uV) it generating are much lower than the current bioelectrodes and commercial gel electrodes. It can effectively reduce the influence of motion artifacts and obtain real-time high-quality electrocardiogram and electromyography signals underwater. Therefore, it shows great potential in long-term motion-robust underwater bioelectric monitoring.
Article
Full-text available
Electrocardiogram (ECG) monitoring is vital for diagnosing cardiac rhythm and rate disorders. Wearable ECG sensor system are promising alternatives to conventional, in-hospital healthcare systems. In this study, a wearable and semi-disposable ECG system is developed based on the self-adhesive ECG sensor patch. The patch is designed with two sensor electrodes on the silicon adhesive film. By using the silicon based conductive paste with cobweb structure, highly conductive and stretchable electrodes can be achieved. This design also enables the sensor patch to be fabricated using large area coating process and strongly adhered to the skin surface with low electrode-to-skin impedance. The conductive magnets are introduced for electrical connection between the ECG sensor patch and the readout circuit board. The two connected magnets show stable electrical performance under large dynamic tension loading. The use of conductive magnets also enables easy integration and reusability of the circuit boards with batteries to the ECG sensor patch. The developed ECG sensor system was worn on a volunteer for real-time test. The results show that the circuit boards with batteries can be reused by the magnetic connection design and the quality of the measured signal will not be affected after normal activities.
Article
Full-text available
Motor imagery offers an excellent opportunity as a stimulus-free paradigm for brain–machine interfaces. Conventional electroencephalography (EEG) for motor imagery requires a hair cap with multiple wired electrodes and messy gels, causing motion artifacts. Here, a wireless scalp electronic system with virtual reality for real-time, continuous classification of motor imagery brain signals is introduced. This low-profile, portable system integrates imperceptible microneedle electrodes and soft wireless circuits. Virtual reality addresses subject variance in detectable EEG response to motor imagery by providing clear, consistent visuals and instant biofeedback. The wearable soft system offers advantageous contact surface area and reduced electrode impedance density, resulting in significantly enhanced EEG signals and classification accuracy. The combination with convolutional neural network-machine learning provides a real-time, continuous motor imagery-based brain–machine interface. With four human subjects, the scalp electronic system offers a high classification accuracy (93.22 ± 1.33% for four classes), allowing wireless, real-time control of a virtual reality game.
Article
Tattoo electronics is one of the emerging technologies in skin compliant biosensing. The growing interest in their large application in health monitoring raises several interrogations on how these sensors interface with the skin. In this paper, the bioimpedance at the interface of the skin and ultra‐conformable tattoo electrodes made of conducting polymers are focused on. The electrochemical characteristics of these electrodes differ from traditional gelled Ag/AgCl electrodes. The modeling of equivalent circuits in different skin‐electrode configurations proposes the explanation of the biopotentials transduction mechanism. The strong agreement between the circuit model and experimental values reveals the capacitive coupling of conducting polymer tattoo electrodes where circuit's values reflect the electrodes’ and skin physical characteristics. Additional studies underline an enhanced signal stability in inter/intra‐subject evaluations using dry tattoos beneficial for broad long‐term recordings. This study provides a comprehensive explanation of the skin/tattoo electrode interface model. The understanding of this interface is essential when designing next generation wearable biomonitoring devices using imperceptible interfaces. Tattoo electrodes are dry sensors that provide outstanding conformability to the skin thanks to their ultralow thickness. These electrodes interact with the skin via capacitive coupling where the upper layers act as a dielectric. Tattoos made of conducting polymer poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) display great mechanical stability and a long‐term performance in detecting biopotentials from the skin despite their considerably large impedance.
Article
To date, brain-computer interfaces (BCIs) have proved to play a key role in many medical applications, for example, the rehabilitation of stroke patients. For post-stroke rehabilitation, the BCIs require the EEG electrodes to precisely translate the brain signals of patients into intended movements of the paralyzed limb for months. However, the gold standard silver/silver-chloride electrodes cannot satisfy the requirements for long-term stability and preparation-free recording capability in wearable EEG devices, thus limiting the versatility of EEG in wearable BCI applications over time outside the rehabilitation center. Here, we design a long-term stable and low electrode-skin interfacial impedance conductive polymer-hydrogel EEG electrode that maintains a lower impedance value than gel-based electrodes for 29 days. With this technology, EEG-based long-term and wearable BCIs could be realized in the near future. To demonstrate this, our designed electrode is applied for a wireless single-channel EEG device that detects changes in alpha rhythms in eye-open/eye-close conditions. In addition, we validate that the designed electrodes could capture oscillatory rhythms in motor imagery protocols as well as low-frequency time-locked event-related potentials from healthy subjects, with better performance than gel-based electrodes. Finally, we demonstrate the use of the designed electrode in online BCI-based functional electrical stimulation, which could be used for post-stroke rehabilitation.
Article
Electronic tattoo has great potential application in mobile health. Fully conformal contact between E-tattoo and skin is critical for reliable monitoring. In this paper, we reported a substrate-free, ultra-conformable PEDOT: PSS (3,4-ethylenedioxythiophene):poly(styrene-sulfonate) E-tattoo achieved by interface energy regulation on skin. The controllable gel/dry electrode mutual transformation property of PEDOT: PSS was carefully studied and reported. Then a novel transfer approach was studied to transfer thin, substrate-free PEDOT: PSS E-tattoo onto skin. Meanwhile, PEDOT: PSS E-tattoo was gelled, then dried directly on skin, regulating its bending energy, contact area, and interface adhesion energy with skin. Through this method, the critical thickness of the after-transformation dry E-tattoo that could form fully conformal contact with skin was increased by 4 times. The electrode-skin interface impedance and ECG measurement performance of the reported E-tattoo were on par with commercial Ag/AgCl gel electrodes, while offering superior comfort and reliability. The substrate-free, ultra-conformable PEDOT: PSS E-tattoo could be applied as sensing electrode for reliable monitoring in mobile health.
Article
Long‐term and highly sensitive electrophysiological signal detection is the primary issue for wearable health monitoring. The critical issues of pre‐gelled wet electrodes as conventional approaches are limited conductivity and low adhesivity owing to the dependence of moisture concentration. Along this line, this paper presents a biocompatible, mechanically robust, water degradable, and intrinsically conductive organic composite dry film electrode based on poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), hydroxyethyl cellulose, and dopamine. The effects on PEDOT:PSS structure transition are studied systematically according to the combination of each component with various analytical methods including morphological, chemical, electrical, and mechanical characterization. The proposed film exhibits high conductivity (292 S m–1) and robust mechano‐electrical stability (only 8% of resistance change under 110 of fully flat‐bended cycles) owing to the weak but synergetic interactions between the components. Furthermore, low noise, clear signal, and long‐term stability for a wireless electrocardiogram and electromyogram signal sensing is achieved using the proposed dry electrode. Intrinsically conductive dry electrode for long‐term and sensitive electrophysiological bio signal sensing is demonstrated through organic composite film. The synergistic effects of combining organic components to improve mechano‐electrical properties are systematically investigated. The proposed eco‐friendly organic electrode shows clear and stable ECG and EMG signals with a continuous wireless sensing system.
Article
Full-text available
Robust and controllable wet attachment like tree frog toe pads attracts worldwide attention owing to potential applications in wet climbing robots, medical devices, and wearable sensors. Instead of conventional uniform pillars, nonuniform pillar arrays with features of inclination and gradients are discovered as typical structures on tree frog toe pads, whereas their effects on wet friction have been ignored. Micro‐nano in situ observation demonstrates that such a nonuniform pillar surface brings about unique multi‐dimensional self‐splitting behaviors in interfacial liquid films and contact stress distribution to enhance the wet attachment. The self‐splitting of the interfacial liquid film breaks the thick large area liquid film into an immense number of more uniform and robust tiny thin liquid bridges. Furthermore, the contact stress is redistributed by the inclined and gradient pillar array with contact stress self‐splitting, where the peak normal separating stress decreases ≈91% and lateral stress transmission increases ≈63%. Such contact stress self‐splitting further improves the liquid film self‐splitting by forming sturdy thin liquid films even under a larger load, which generates more robust capillarity with enhanced strong friction. Finally, theoretical models are built for the multi‐dimensional self‐splitting enhanced wet attachment, and applications in robotic and medical fields are performed to validate its feasibility.
Article
We propose to explore teeth-clenching-based target selection in Augmented Reality (AR), as the subtlety in the interaction can be beneficial to applications occupying the user's hand or that are sensitive to social norms. To support the investigation, we implemented an EMG-based teeth-clenching detection system (ClenchClick), where we adopted customized thresholds for different users. We first explored and compared the potential interaction design leveraging head movements and teeth clenching in combination. We finalized the interaction to take the form of a Point-and-Click manner with clenches as the confirmation mechanism. We evaluated the taskload and performance of ClenchClick by comparing it with two baseline methods in target selection tasks. Results showed that ClenchClick outperformed hand gestures in workload, physical load, accuracy and speed, and outperformed dwell in work load and temporal load. Lastly, through user studies, we demonstrated the advantage of ClenchClick in real-world tasks, including efficient and accurate hands-free target selection, natural and unobtrusive interaction in public, and robust head gesture input.
Article
Conformal contact with skin is a critical requirement for wearable electronics in medical healthcare, artificial electronics, and human–computer interfaces. Tattoo‐like electronics exploiting water‐dissolvable polymers have been introduced to directly transfer electronics to the skin increasing conformality and adhesion. However, water‐dissolvable polymers cannot be anchored on the skin while maintaining electrical properties because water‐based sweat can destroy the polymer substrate. In this study, we present a transparent and skin‐attachable electrode (TSE) composed of highly conductive silver nanowires and biocompatible polyurethane composite using surface redissolution by ethanol. The TSE can be fabricated into various patterns by a simple fabrication method and firmly mounted on the skin. There was no reddishness or residue on the attached spot after detachment. Additionally, the TSE showed low mechanical modulus of 225 kPa and an optical transmittance of ≈70% at 550 nm. Stable and conformal contact with the skin leads to effective body motion sensing and sensitive electrophysiological signal acquisition due to the low electrical interfacial impedance. Highly conductive silver nanowires and biocompatible polyurethane composite can be exploited as transparent and skin‐attachable electrode (TSE) using surface redissolution by ethanol. The TSE has no side effect on the skin such as reddishness or polymer residue. Stable and conformal contact with the skin leads to effective body motion sensing and sensitive electrophysiological signal acquisition due to the low electrical interfacial impedance.
Article
Full-text available
Recently, bioelectronic devices extensively researched and developed through the convergence of flexible biocompatible materials and electronics design that enables more precise diagnostics and therapeutics in human health care and opens up the potential to expand into various fields, such as clinical medicine and biomedical research. To establish an accurate and stable bidirectional bio‐interface, protection against the external environment and high mechanical deformation is essential for wearable bioelectronic devices. In the case of implantable bioelectronics, special encapsulation materials and optimized mechanical designs and configurations that provide electronic stability and functionality are required for accommodating various organ properties, lifespans, and functions in the biofluid environment. Here, this study introduces recent developments of ultra‐thin encapsulations with novel materials that can preserve or even improve the electrical performance of wearable and implantable bio‐integrated electronics by supporting safety and stability for protection from destruction and contamination as well as optimizing the use of bioelectronic systems in physiological environments. In addition, a summary of the materials, methods, and characteristics of the most widely used encapsulation technologies is introduced, thereby providing a strategic selection of appropriate choices of recently developed flexible bioelectronics.
Article
The detection and conversion of physiological responses to electrical signals in long-term and dynamic measurement conditions are essential for the operation of health monitoring systems and human-computer interaction devices. An important challenge in tracking these bioelectrical signals is the electrodes with both high tracking quality and patient comfort. Here, a 3D textile electrode inspired by embroidery technique with 1D composite yarns is proposed that contains the mixture of reduced graphene oxide (RGO), sericin and water-retention polymer. The water retaining material and fluffy structure enables these textile electrodes to have conformal contact with skin and reduced contact impedance for a multiple-biosignal measurement. Porous construction of the knitted electrode further brings comfort to users due to the soft tactile formation and the breathable property. Unambiguous analyses of electromyography (EMG) and electrocardiogram (ECG) signals have been conducted experimentally as demos for potential clinical applications. Further, an ambulatory ECG monitoring for heart rate variability (HRV) test is carried out on volunteers under running motions as well as long-term tests. Continuous and high-fidelity signals are successfully achieved, despite the active motion and sweat conditions. As such, the proposed textile electrode could be applicable for the wearable bioelectrical signal acquisitions for a broad range of applications.
Article
Stable adhesion and comfort for long‐term use are the main challenges currently limiting wearable in real‐time health monitoring, especially in disturbed state such as exercise and sweating. Here, A biomimetic microneedles‐based adhesive electrode is designed, which utilizes the mechanical locking of the microneedle array and the adhesion property of the mimic tree frog foot pad microstructures on the rough and wet substrate to synergistically enhance the stable adhesion performance of electrode on the skin surface. This adhesion‐mechanical locking synergistic enhancement effect of the electrode through experiments is verified; the synergistic enhancement mechanism of the electrode is analyzed, and successfully electrocardiograph and electromyogram on human body skin is monitored. The electrode presented here provides a new path to solve the problem of stable signal acquisition under the condition of sweating and exercise, and realizing comfortable, low‐noise, and continuous health monitoring. This work focuses on the integration of multiple attachment mechanisms into electrodes, and the analysis of the attachment gain effect achieved by the multimechanisms strategy of bioinspired adhesive material and microneedles. It provides a promising pathway to solve the problem of stable signal acquisition during exercising activities and sweat conditions, realizing smooth and comfortable bioelectrical signal monitoring of the body.
Article
The growing demand for efficient home healthcare applications for brain disorder diagnostics and treatment has inspired the development of wearable devices for monitoring brain activity. However, flexible probes that have improved biocompatibility for wearable devices are markedly affected by noise due to contact interface issues. In this study, a stretchable (≤1500% strain) and transparent (over 85% transmittance) biocompatible electrode that steadily adheres to skin is developed to fabricate an imperceptible sheet‐type device that wirelessly records electroencephalograms (EEGs). The multifunctional characteristic of the electrode results from the double‐network structure in an elastomer/conductive additive blend on a metal‐nanowire‐based track, which contributed to EEG monitoring with ultralow noise (≈0.14 µV noise floor) and sleep‐stage classification. Furthermore, the optical transparency enabled camera‐based photoplethysmography to detect pulse waves and blood oxygen saturation without interfering with the light path, which is a crucial factor in realizing a remote healthcare system. The developed skin‐like transparent sensor sheet represents the ultimate imperceptible probe in terms of wearability and invisibility, delivering the most sought‐after performance in biometrics, as it combines low noise, high stretchability, and transparency. Integrated system for the remote recording of electroencephalography and photoplethysmography offers the possibility of stress‐free point‐of‐care assessment for sleep quality and brain diseases.
Article
On‐skin healthcare patch‐type devices have great technological challenges in monitoring the full‐day activities and wearing for multiple days without detachment. These challenges can be overcome when the sensor is air‐permeable but waterproofing. This study presents a light‐weight highly stable and stretchable Au electrode that was fabricated by sputtering on an imidized nanofiber mat. The contact surface of the electrode is hydro‐wetting and the outer surface of the electrode is hydrophobic, so that the porous electrode simultaneously has excellent sweat permeability and waterproofing capability. The electrode is applied to electrocardiogram (ECG) sensor for monitoring the cardiac signals for 5 consecutive days without detaching while doing various full‐day activities such as relaxing, exercising, showering, and sleeping. This study suggests a modular setup of the electrodes and the cardiac signal processing unit for activating the device when cardiac monitoring is required. This article is protected by copyright. All rights reserved
Article
Flexible bioelectric dry electrodes are an important part of long-term medical healthcare monitoring systems. In this study, a new method is proposed for the preparation of dry electrodes with micronanopillar arrays structured by designing dimensionally tunable anodized aluminum oxide (AAO) templates, by which polyaniline/thermoplastic polyurethane single-layer micronanopillar array structured dry electrodes (PANI/TPU-SE) and polyaniline/thermoplastic polyurethane double-layer micronanopillar array structured dry electrodes (PANI/TPU-DE) are prepared. Compared with the planar structure, the micronanopillar array structure can reduce the contact gap between the electrode and skin and increase the contact area, thus exhibiting lower contact impedance and higher signal quality. At 0.1 Hz, the impedances of the wet electrode, PANI/TPU-DE300, PANI/TPU-SE10, and planar structure electrodes are 269.5 kΩ, 375.5 kΩ, 398.1 kΩ, and 2.257 MΩ, respectively, and the impedance value for PANI/TPU-DE300 is smaller than that for PANI/TPU-SE10 and closer to that for the wet electrode. In addition, because the surface of the micronanostructure can conform to the human skin, about 210.7% increase in the peel strength of double-layer structure electrodes compared to flat structure electrodes, it shows a low baseline drift in the dynamic ECG measurement, and the signal-to-noise ratio in the walking state can reach 21.33 ± 5.4775 dB. Therefore, the prepared bioelectric dry electrode has a wide application prospect in the fields of wearable medical monitoring.
Article
Next generation textile‐based wearable sensing systems will require flexibility and strength to maintain capabilities over a wide range of deformations. However, current material sets used for textile‐based skin contacting electrodes lack these key properties, which hinder applications such as electrophysiological sensing. In this work, we present a facile spray coating approach to integrate liquid metal nanoparticle systems into textile form factors for conformal, flexible and robust electrodes. The liquid metal system employs functionalized liquid metal nanoparticles that provide a simple “peel‐off to activate” means of imparting conductivity. The spray coating approach combined with our functionalized liquid metal system enables the creation of long‐term reusable textile‐integrated liquid metal electrodes (TILEs). Although the TILEs are dry electrodes by nature, they show equal skin‐electrode impedances and sensing capabilities with improved wearability compared to commercial wet electrodes. Biocompatibility of TILEs in an in‐vivo skin environment was demonstrated, while providing improved sensing performance compared to previously reported textile‐based dry electrodes. The “spray on dry – behave like wet” characteristics of TILEs opens opportunities for textile‐based wearable health monitoring, haptics, and augmented/virtual reality (AR/VR) applications that require the use of flexible and conformable dry electrodes. This article is protected by copyright. All rights reserved
Article
Full-text available
The electroencephalogram (EEG) is considered to be a promising method for studying brain disorders. Because of its non-invasive nature, subjects take a lower risk compared to some other invasive methods, while the systems record the brain signal. With the technological advancement of neural and material engineering, we are in the process of achieving continuous monitoring of neural activity through wearable EEG. In this article, we first give a brief introduction to EEG bands, circuits, wired/ wireless EEG systems, and analysis algorithms. Then, we review the most recent advances in the interfaces used for EEG recordings, focusing on hydrogel-based EEG electrodes. Specifically, the advances for important figures of merit for EEG electrodes are reviewed. Finally, we summarize the potential medical application of wearable EEG systems.
Article
Recent advances in scalable fabrication methods based on printing technologies have improved the yield and lowered the cost of manufacturing epidermal sensors. However, modern technologies still require expensive multi‐bio‐ink raw materials. A laser‐centric fabrication method that realizes a cost‐effective, scalable, and streamlined fabrication process with easily used material and equipment is reported. The fabricated epidermal patch can quickly respond to the demands of personalized models. Here, the epidermal sensor patch is applied to continuous monitoring of the human cardiopulmonary system. The sensor performs conventional bio‐signal monitoring but is also extendible to other monitoring forms. The patch provides enhanced functions through its gas‐permeable and skin‐adhesive microporous layer and its stretchable, conformal, and biocompatible multimodal sensing layer. The utility of the proposed sensor patch in clinical diagnosis in a mobile healthcare environment is demonstrated in multiple bio‐signal‐morphology analyses. Here, a scalable‐streamlined fabrication process of a laser‐centric epidermal sensor patch utilizing a single fabrication equipment, CO2 laser, and a single‐conductive material, porous graphene, is demonstrated for multimodal bio‐signal sensing. The fabricated sensor patch is ideal to achieve a clinical‐grade vital signal acquisition such as the electrical and mechano‐acoustic signals of heart muscle movement simultaneously.
Article
Recent technological innovations in wearable electronics offer possibilities to perform real‐time monitoring of electrophysiological parameters, such as ECG, EMG, and EEG. To achieve accurate and long‐term electrophysiological measurement, great signs of progress have been made in the skin–electrode interfacial problems; nevertheless, the challenges related to sweat have not been fully resolved. Excessive sweat between human skin and the electrode usually fails to achieve a conformal and intact contact, and the nonconductive barriers will lead to a high skin–electrode impedance. Inspired by the structure of liquid directional movement in nature, a Janus gold nanowires/nitrocellulose (AuNWs/NC) electrophysiological electrode with conical micropores is developed to solve interfacial problems caused by sweat. The Janus AuNWs/NC electrodes spontaneously wick sweat from the AuNW side to the NC side, thus keeping intimate skin–electrode contact and low interfacial impedance to ensure a high‐fidelity signal during the long‐term monitoring. By integrating Janus AuNWs/NC electrode with circuit modules and advanced algorithms, a real‐time visualization system is developed for muscle activity intensity. This system is applied to precisely evaluate the muscle controllability and assess the muscle balance ability, which presents great potentials for health monitoring, sports training, and the areas of human–computer interaction. A Janus gold nanowires/nitrocellulose electrophysiological electrode is developed to solve interfacial problems caused by sweat. The Janus electrodes spontaneously wick sweat from the skin–electrode interface, thus keeping intimate skin–electrode contact and low interfacial impedance. The sweat‐wicking electrode is then applied to evaluate muscle controllability and balance ability, which may show great potentials in sports training.
Article
Full-text available
A low interfacial contact resistance is a challenge in polymer nanocomposites based on conductive nanomaterials for high-performance wearable electrode applications. Herein, a polydimethylsiloxane (PDMS)-based flexible nanocomposite incorporating high-conductivity 1D single-walled...
Article
Stable ambulatory electrophysiological sensing is widely utilized for smart e‐healthcare monitoring, clinical diagnosis of cardiovascular diseases, treatment of neurological diseases, and intelligent human‐machine interaction. As the favorable signal interaction platform of electrophysiological sensing, the conformal property of on‐skin electrodes is an extremely crucial factor that can affect the stability of long‐term ambulatory electrophysiological sensing. From the perspective of materials, to realize conformal contact between electrodes and skin for stable sensing, highly conformal polymers are strongly demanding and attracting ever‐growing attention. In this review, we focused on the recent progress of highly conformal polymers for ambulatory electrophysiological sensing, including their synthetic methods, conformal property, and potential applications. Specifically, three main types of highly conformal polymers for stable long‐term electrophysiological signals monitoring were proposed, including nature silk fibroin based conformal polymers, marine mussels bio‐inspired conformal polymers, and other conformal polymers such as zwitterionic polymers and polyacrylamide. Furthermore, the future challenges and opportunities of preparing highly conformal polymers for on‐skin electrodes were also highlighted. This article is protected by copyright. All rights reserved
Article
Noninvasive, wearable brain-computer interfaces (BCI) find limited use due to their obtrusive nature and low information. Currently available portable BCI systems are limited by device rigidity, bulky form factors, and gel-based skin-contact electrodes – and therefore more prone to noise and motion artifacts. Here, we introduce virtual reality (VR)-enabled split-eye asynchronous stimulus (SEAS) allowing a target to present different stimuli to either eye. This results in unique asynchronous stimulus patterns measurable with as few as four EEG electrodes, as demonstrated with improved wireless soft electronics for portable BCI. This VR-embedded SEAS paradigm demonstrates potential for improved throughput with a greater number of unique stimuli. A wearable soft platform featuring dry needle electrodes and shielded stretchable interconnects enables high throughput decoding of steady-state visually evoked potentials (SSVEP) for a text spelling interface. A combination of skin-conformal electrodes and soft materials offers high-quality recordings of SSVEP with minimal motion artifacts, validated by comparing the performance with a conventional wearable system. A deep-learning algorithm provides real-time classification, with an accuracy of 78.93% for 0.8 s and 91.73% for 2 s with 33 classes from nine human subjects, allowing for a successful demonstration of VR text spelling and navigation of a real-world environment. With as few as only four data recording channels, the system demonstrates a highly competitive information transfer rate (243.6 bit/min). Collectively, the VR-enabled soft system offers unique advantages in wireless, real-time monitoring of brain signals for portable BCI, neurological rehabilitation, and disease diagnosis.
Article
Full-text available
A class of ferromagnetic, folded, soft composite material for skin-interfaced electrodes with releasable interfaces to stretchable, wireless electronic measurement systems is introduced. These electrodes establish intimate, adhesive contacts to the skin, in dimensionally stable formats compatible with multiple days of continuous operation, with several key advantages over conventional hydrogel-based alternatives. The reported studies focus on aspects ranging from ferromagnetic and mechanical behavior of the materials systems, to electrical properties associated with their skin interface, to system-level integration for advanced electrophysiological monitoring applications. The work combines experimental measurement and theoretical modeling to establish the key design considerations. These concepts have potential uses across a diverse set of skin-integrated electronic technologies.
Article
Full-text available
Conventional gel electrodes are widely used for biopotential measurements, despite important drawbacks such as skin irritation, long set-up time and uncomfortable removal. Recently introduced dry electrodes with rigid metal pins overcome most of these problems; however, their rigidity causes discomfort and pain. This paper presents dry electrodes offering high user comfort, since they are fabricated from EPDM rubber containing various additives for optimum conductivity, flexibility and ease of fabrication. The electrode impedance is measured on phantoms and human skin. After optimization of the polymer composition, the skin-electrode impedance is only ~10 times larger than that of gel electrodes. Therefore, these electrodes are directly capable of recording strong biopotential signals such as ECG while for low-amplitude signals such as EEG, the electrodes need to be coupled with an active circuit. EEG recordings using active polymer electrodes connected to a clinical EEG system show very promising results: alpha waves can be clearly observed when subjects close their eyes, and correlation and coherence analyses reveal high similarity between dry and gel electrode signals. Moreover, all subjects reported that our polymer electrodes did not cause discomfort. Hence, the polymer-based dry electrodes are promising alternatives to either rigid dry electrodes or conventional gel electrodes.
Article
Full-text available
We proposed new electrodes that are applicable for electrocardiogram (ECG) monitoring under freshwater- and saltwater-immersion conditions. Our proposed electrodes are made of graphite pencil lead (GPL), a general-purpose writing pencil. We have fabricated two types of electrode: a pencil lead solid type (PLS) electrode and a pencil lead powder type (PLP) electrode. In order to assess the qualities of the PLS and PLP electrodes, we compared their performance with that of a commercial Ag/AgCl electrode, under a total of seven different conditions: dry, freshwater immersion with/without movement, post-freshwater wet condition, saltwater immersion with/without movement, and post-saltwater wet condition. In both dry and post-freshwater wet conditions, all ECG-recorded PQRST waves were clearly discernible, with all types of electrodes, Ag/AgCl, PLS, and PLP. On the other hand, under the freshwater- and saltwater-immersion conditions with/without movement, as well as post-saltwater wet conditions, we found that the proposed PLS and PLP electrodes provided better ECG waveform quality, with significant statistical differences compared with the quality provided by Ag/AgCl electrodes.
Article
Full-text available
Long-term, continuous, and unsupervised tracking of physiological data is becoming increasingly attractive for health/wellness monitoring and ailment treatment. Nanomaterials have recently attracted extensive attention as building blocks for flexible/stretchable conductors and are thus promising candidates for electrophysiological electrodes. Here we provide a review on nanomaterial-enabled dry electrodes for electrophysiological sensing, focusing on electrocardiography (ECG). The dry electrodes can be classified into contact surface electrodes, contact-penetrating electrodes, and noncontact capacitive electrodes. Different types of electrodes including their corresponding equivalent electrode–skin interface models and the sources of the noise are first introduced, followed by a review on recent developments of dry ECG electrodes based on various nanomaterials, including metallic nanowires, metallic nanoparticles, carbon nanotubes, and graphene. Their fabrication processes and performances in terms of electrode–skin impedance, signal-to-noise ratio, resistance to motion artifacts, skin compatibility, and long-term stability are discussed.
Article
Full-text available
We present wearable dry electrodes made of silver nanowires for electrophysiological sensing such as electrocardiography and electromyography. The dry electrodes perform as well as the Ag/AgCl wet electrodes when the subject is resting and show fewer motion artifacts, but without the electrolytic gel. The nanowire electrodes show no signs of skin irritation, which is desirable for long-term health monitoring.
Article
Full-text available
For the long-time monitoring of electrocardiograms, electrodes must be skin-friendly and non-irritating, but in addition they must deliver leads without artifacts even if the skin is dry and the body is moving. Today's adhesive conducting gel electrodes are not suitable for such applications. We have developed an embroidered textile electrode from polyethylene terephthalate yarn which is plasma-coated with silver for electrical conductivity and with an ultra-thin titanium layer on top for passivation. Two of these electrodes are embedded into a breast belt. They are moisturized with a very low amount of water vapor from an integrated reservoir. The combination of silver, titanium and water vapor results in an excellent electrode chemistry. With this belt the long-time monitoring of electrocardiography (ECG) is possible at rest as well as when the patient is moving.
Article
Full-text available
Patterned structures of flexible, stretchable, electrically conductive materials on soft substrates could lead to novel electronic devices with unique mechanical properties allowing them to bend, fold, stretch or conform to their environment. For the last decade, research on improving the stretchability of circuits on elastomeric substrates has made significant progresses but designing printed circuit assemblies on elastomers remains challenging. Here we present a simple, cost-effective, cleanroom-free process to produce large scale soft electronic hardware where standard surface-mounted electrical components were directly bonded onto all-elastomeric printed circuit boards, or soft PCBs. Ag-PDMS tracks were stencil printed onto a PDMS substrate and soft PCBs were made by bonding the top and bottom layers together and filling punched holes with Ag-PDMS to create vias. Silver epoxy was used to bond commercial electrical components and no mechanical failure was observed after hundreds of stretching cycles. We also demonstrate the fabrication of a stretchable clock generator.
Article
Full-text available
Adhesion of biological systems has recently received much research attention: the survival of organisms ranging from single cells and mussels to insects, spiders and geckos relies crucially on their mechanical interaction with their environments. For spiders, lizards and possible other 'dry' adhesive systems, explanations for adhesion are based on van der Waals interaction, and the adhesion of single-contact elements has been described by the classical Johnson-Kendall-Roberts (JKR) model derived for spherical contacts. However, real biological contacts display a variety of shapes and only rarely resemble a hemisphere. Here, we theoretically assess the influence of various contact shapes on the pull-off force for single contacts as well as their scaling potential in contact arrays. It is concluded that other shapes, such as a toroidal contact geometry, should lead to better attachment; such geometries are observed in our microscopic investigations of hair-tip shapes in beetles and flies.
Article
Full-text available
The superlative adhesive properties of some biological attachment systems, such as those of geckos, spiders, and insects, have inspired researchers from different fields (e.g. biology, physics and engineering) to conceive and design man-made microstructured surfaces that might mimic their performance. Among the several proposed designs, very recently mushroom-shaped adhesive microstructures have drawn the interest of scientists and engineers, because experiments have proved their superiority compared to other micro-and nano-structures. In this article, we explain theoretically the physical mechanism behind the enhanced adhesion of such microstructures, and provide for the first time a useful tool to predict adhesive performance depending on the geometry, mechanical properties of the material, and energy of adhesion. Our theoretical predictions are strongly supported by the available experimental data. The present study can streamline the optimisation of adhesive microstructures for industrial applications.
Article
Full-text available
We report a novel electrode material for the detection of human bio-potentials using carbon nanofibre ( CNF) arrays functionalized with silver/silver chloride ( Ag-AgCl) core-shell nanoparticles. The CNFs are protected against detachment using a thin polymer film, which firmly secures the fibres to the substrate surface. The core-shell Ag-AgCl nanoparticles on the CNF surfaces clearly enhance transduction in ionic media as shown by cyclic voltammetry and impedance spectroscopy. We infer that these functionalized CNF arrays can be utilized as dry electrophysiological sensors for bio-potential monitoring applications.
Article
Full-text available
Recent demand and interest in wireless, mobile-based healthcare has driven significant interest towards developing alternative biopotential electrodes for patient physiological monitoring. The conventional wet adhesive Ag/AgCl electrodes used almost universally in clinical applications today provide an excellent signal but are cumbersome and irritating for mobile use. While electrodes that operate without gels, adhesives and even skin contact have been known for many decades, they have yet to achieve any acceptance for medical use. In addition, detailed knowledge and comparisons between different electrodes are not well known in the literature. In this paper, we explore the use of dry/noncontact electrodes for clinical use by first explaining the electrical models for dry, insulated and noncontact electrodes and show the performance limits, along with measured data. The theory and data show that the common practice of minimizing electrode resistance may not always be necessary and actually lead to increased noise depending on coupling capacitance. Theoretical analysis is followed by an extensive review of the latest dry electrode developments in the literature. The paper concludes with highlighting some of the novel systems that dry electrode technology has enabled for cardiac and neural monitoring followed by a discussion of the current challenges and a roadmap going forward.
Article
Full-text available
Breaking the skin when applying scalp electroencephalographic (EEG) electrodes creates the risk of infection from blood-born pathogens such as HIV, Hepatitis-C, and Creutzfeldt-Jacob Disease. Modern engineering principles suggest that excellent EEG signals can be collected with high scalp impedance ( approximately 40 kOmega) without scalp abrasion. The present study was designed to evaluate the effect of electrode-scalp impedance on EEG data quality. The first section of the paper reviews electrophysiological recording with modern high input-impedance differential amplifiers and subject isolation, and explains how scalp-electrode impedance influences EEG signal amplitude and power line noise. The second section of the paper presents an experimental study of EEG data quality as a function of scalp-electrode impedance for the standard frequency bands in EEG and event-related potential (ERP) recordings and for 60 Hz noise. There was no significant amplitude change in any EEG frequency bands as scalp-electrode impedance increased from less than 10 kOmega (abraded skin) to 40 kOmega (intact skin). 60 Hz was nearly independent of impedance mismatch, suggesting that capacitively coupled noise appearing differentially across mismatched electrode impedances did not contribute substantially to the observed 60 Hz noise levels. With modern high input-impedance amplifiers and accurate digital filters for power line noise, high-quality EEG can be recorded without skin abrasion.
Article
Stretchable electronic devices hold the potential to revolutionize noninvasive healthcare diagnostics and treatments. Current clinical healthcare technologies are of limited use in ambulatory, long-term settings. A new class of epidermal electronics is designed to conform closely to and with the irregular shape of the human body is emerging, providing an improved functional interface even during motion, while being imperceptible to the user. This review discusses challenges associated with long-term interactions between electronic devices and the skin without interfering with its regulatory and protective function. We report on the current state of the art of monitoring devices for the detection of temperature, motion, biopotentials or biomarkers alongside therapeutic approaches for thermal treatment or drug delivery. In particular, focus is brought on the long-term application of such devices with the associated challenges in terms of materials, wearability, communication and energy supply. With a number of obstacles left to tackle, epidermal stretchable electronics represents a powerful tool in the rising field of personalized medicine. © 2017 International Journal of Automation and Smart Technology.
Article
Here we propose a concept of conductive dry adhesives (CDA) combining a gecko-inspired hierarchical structure and an elastomeric carbon nanocomposite. To complement the poor electrical percolation of 1D carbon nanotube (CNT) networks in an elastomeric matrix at a low filler content (~1 wt%), a higher dimensional carbon material (i.e., carbon black, nano graphite, and graphene nanopowder) is added into the mixture as an aid filler. The co-doped graphene and CNT in the composite show the lowest volume resistance (~100 Ohm∙cm) at an optimized filler ratio (1 : 9, total filler content: 1 wt%) through a synergetic effect in electrical percolation. With an optimized conductive elastomer, gecko-inspired high-aspect-ratio (>3) microstructures over large-area (~4 in2) are successfully replicated from intaglio patterned molds without collapse. The resultant CDA pad shows high normal adhesion force (~1.3 N/cm2) even on rough human-skin and excellent cyclic property for repeatable use over 30 times without degradation of adhesion force, which cannot be achieved by commercial wet adhesives. The body-attachable CDA can be used as a metal-free, all-in-one component for measuring bio-signals under daily activity conditions (i.e., underwater, movements) because of its superior conformality and water-repellent characteristic.
Article
We have developed hydrophobic electrodes that provide all morphological waveforms without distortion of an ECG signal for both dry and water-immersed conditions. Our electrode is comprised of a mixture of carbon black powder (CB) and polydimethylsiloxane (PDMS). For feasibility testing of the CB/PDMS electrodes, various tests were performed. One of the tests included evaluation of the electrode-to-skin contact impedance for different diameters, thicknesses, and different pressure levels. As expected, the larger the diameter of the electrodes, the lower the impedance and the difference between the large sized CB/PDMS and the similarly-sized Ag/AgCl hydrogel electrodes was at most 200 kΩ, in favor of the latter. Performance comparison of CB/PDMS electrodes to Ag/AgCl hydrogel electrodes was carried out in three different scenarios: a dry surface, water immersion, and postwater immersion conditions. In the dry condition, no statistical differences were found for both the temporal and spectral indices of the heart rate variability analysis between the CB/PDMS and Ag/AgCl hydrogel (p > 0.05) electrodes. During water immersion, there was significant ECG amplitude reduction with CB/PDMS electrodes when compared to wet Ag/AgCl electrodes kept dry by their waterproof adhesive tape, but the reduction was not severe enough to obscure the readability of the recordings, and all morphological waveforms of the ECG signal were discernible even when motion artifacts were introduced. When water did not penetrate tape-wrapped Ag/AgCl electrodes, high fidelity ECG signals were observed. However, when water penetrated the Ag/AgCl electrodes, the signal quality degraded to the point where ECG morphological waveforms were not discernible.
Article
Modulus-tunable composite micropillars are presented by combining replica molding and selective inking for skin adhesive patch in "ubiquitous"-health diagnostic devices. Inspired from hierarchical hairs in the gecko's toe pad, a simple method is presented to form composite polydimethylsiloxane (PDMS) micropillars that are highly adhesive (∼1.8 N cm(-2) ) and mechanically robust (∼30 cycles).
Article
Nature has developed reversibly adhesive surfaces whose stickiness has attracted much research attention over the last decade. The central lesson from nature is that “patterned” or “fibrillar” surfaces can produce higher adhesion forces to flat and rough substrates than smooth surfaces. This paper critically examines the principles behind fibrillar adhesion from a contact mechanics perspective, where much progress has been made in recent years. The benefits derived from “contact splitting” into fibrils are separated into extrinsic/intrinsic contributions from fibril deformation, adaptability to rough surfaces, size effects due to surface-to-volume ratio, uniformity of stress distribution, and defect-controlled adhesion. Another section covers essential considerations for reliable and reproducible adhesion testing, where better standardization is still required. It is argued that, in view of the large number of parameters, a thorough understanding of adhesion effects is required to enable the fabrication of reliable adhesive surfaces based on biological examples.
Article
Inspired by biological attachment systems, micropatterned elastomeric surfaces with pillars of different heights (between 2.5 and 80 microm) and radii (between 2.5 and 25 microm) were fabricated. Their adhesion properties were systematically tested and compared with flat controls. Micropatterned surfaces with aspect ratios above 0.5 were found to be more compliant than flat surfaces. The adhesion significantly increases with decreasing pillar radius and increasing aspect ratio of the patterned features. A preload dependence of the adhesion force has been identified and demonstrated to be crucial for obtaining adhesives with tunable adherence.
New Dev. Biomed. Eng
  • L. Tchvialeva
  • H. Zeng
  • I. Markhvida
  • D. I. McLean
  • H. Lui
  • T. K. Lee
  • H Han
  • A M Reichmuth
  • A F Renz
  • F Stauffer
  • M Thielen
  • J Voros
H. Han, A. M. Reichmuth, A. F. Renz, F. Stauffer, M. Thielen, J. Voros, Int. J. Autom. Smart Technol. 2017, 7, 37.
  • Y M Chi
  • T.-P Jung
  • G Cauwenberghs
Y. M. Chi, T.-P. Jung, G. Cauwenberghs, IEEE Rev. Biomed. Eng. 2010, 3, 106.
  • D.-H Kim
  • J.-H Ahn
  • W M Choi
  • H.-S Kim
  • T.-H Kim
  • J Song
  • Y Y Huang
  • Z Liu
  • C Lu
  • J A Rogers
D.-H. Kim, J.-H. Ahn, W. M. Choi, H.-S. Kim, T.-H. Kim, J. Song, Y. Y. Huang, Z. Liu, C. Lu, J. A. Rogers, Nature 2008, 320, 507.
  • K I Jang
  • H N Jung
  • J W Lee
  • S Xu
  • Y H Liu
  • Y Ma
  • J W Jeong
  • Y M Song
  • J Kim
  • B H Kim
  • A Banks
  • J W Kwak
  • Y Yang
  • D Shi
  • Z Wei
  • X Feng
  • U Paik
  • Y Huang
  • R Ghaffari
  • J A Rogers
K. I. Jang, H. N. Jung, J. W. Lee, S. Xu, Y. H. Liu, Y. Ma, J. W. Jeong, Y. M. Song, J. Kim, B. H. Kim, A. Banks, J. W. Kwak, Y. Yang, D. Shi, Z. Wei, X. Feng, U. Paik, Y. Huang, R. Ghaffari, J. A. Rogers, Adv. Funct. Mater. 2016, 26, 7281.
  • Y H Chen
  • M Op De Beeck
  • L Vanderheyden
  • E Carrette
  • V Mihajlović
  • K Vanstreels
  • B Grundlehner
  • S Gadeyne
  • P Boon
  • C Van Hoof
Y. H. Chen, M. Op de Beeck, L. Vanderheyden, E. Carrette, V. Mihajlović, K. Vanstreels, B. Grundlehner, S. Gadeyne, P. Boon, C. van Hoof, Sensors 2014, 14, 23758.
  • M Kamperman
  • E Kroner
  • A Campo
  • R M Mcmeeking
  • E Arzt
M. Kamperman, E. Kroner, A. Del Campo, R. M. McMeeking, E. Arzt, Adv. Eng. Mater. 2010, 12, 335.
  • G Carbone
  • E Pierro
  • S N Gorb
G. Carbone, E. Pierro, S. N. Gorb, Soft Matter 2011, 7, 5545.
  • P C P Watts
  • S J Henley
  • E Mendoza
  • S R P Silva
  • J K Irvine
  • E T Mcadams
P. C. P. Watts, S. J. Henley, E. Mendoza, S. R. P. Silva, J. K. Irvine, E. T. McAdams, Nanotechnology 2007, 18, 205502.
  • R Spolenak
  • S Gorb
  • H Gao
  • E Arzt
R. Spolenak, S. Gorb, H. Gao, E. Arzt, Proc. R. Soc. London, Ser. A 2005, 461, 305.
  • W G Bae
  • D Kim
  • M K Kwak
  • L Ha
  • S M Kang
  • K Y Suh
W. G. Bae, D. Kim, M. K. Kwak, L. Ha, S. M. Kang, K. Y. Suh, Adv. Healthcare Mater. 2013, 2, 109.
  • A Larmagnac
  • S Eggenberger
  • H Janossy
A. Larmagnac, S. Eggenberger, H. Janossy, J. Vörös, Sci. Rep. 2014, 4, 7254.