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The sense of touch and perception of hand motion form an essential part of the somatic sensory system. Although piezoelectric sensors demonstrate high sensitivity and linearity, they are traditionally not employed for electronic skins because of their limited stretchability. Here, a printed, skin‐conformal, electronic system consisting of stretchable piezoelectric pressure sensors and carbon nanotube strain gauges capable of identifying tactile sensations and joint movements on the hand is introduced. The pressure sensor demonstrates both high sensitivity (19.9 mV kPa−1) and linearity (0.1–1000 kPa) while being reliably stretchable to above 15%. To complement the pressure sensing functionality, a strain gauge is fabricated in a rapid stamp printing process and designed to demonstrate excellent mechanical reliability with up to 70% strain and high sensitivity (36.5‐gauge factor). These sensors can seamlessly conform to numerous anatomical regions and cover wide areas of the skin, making them ideal for deployment in an electronic skin. Finally, the sensors are integrated with a flexible microelectronic device to demonstrate their functionality in human touch and prosthetic hand applications. [ABSTRACT FROM AUTHOR]

This study presents a novel transparent, sensitive electronic skin (S-TENG) using a frictional nanogenerator for energy harvesting and physiological motion monitoring. Featuring thermally treated PVDF fiber membranes and silver nanowire electrodes, the e-skin boasts 80% transparency, high sensitivity (detecting 0.13 g touch), stability, and breathability. It generates 301 V and 2.7 µA under 8N force, achieving 306 mW/m2 power density. S-TENG holds promise for self-powered wearables and health training applications, representing a significant step in e-skin innovation. [Display omitted] Against the backdrop of advancements in modern multifunctional wearable electronics, there is a growing demand for simple, sustainable, and portable electronic skin (e-skin), posing significant challenges. This study aims to delineate the development of a straightforward, transparent, highly sensitive, and high power-density electronic skin based on a triboelectric nanogenerator(S-TENG), designed for harvesting human body energy and real-time monitoring of the physiological motion status. Our e-skin incorporates thermally treated polyvinylidene fluoride (PVDF) fiber membranes as the contact layer and a film of silver nanowires as the conductive electrodes. The resulting contact-separation type e-skin exhibits an impressive transparency of 80 %, along with a nice sensitivity value, capable of detecting a light touch from a 0.13 g sponge and demonstrating good working stability and breathability. Leveraging the triboelectric effect, our e-skin generates an open-circuit voltage of 301 V and a short-circuit current of 2.7 μA under an extrinsic force of 8 N over an interaction area of 4 × 4 cm2, achieving a power density up to 306 mW/m2. With its signal processing circuitry, the integrated S-TENG showcases nice energy harvesting and signal transmission capabilities. Accordingly, we contend that S-TENG has potential applications in energy capture and real-time human motion state monitoring. This research is anticipated to blaze a novel and practical trail for self-powered wearable devices and personalized health rehabilitation training regimens. [ABSTRACT FROM AUTHOR]

For the need of direct contact with the skin, electronic skins (E‐skins) should not only fulfill electric functions, but also ensure comfort during wearing, including permeability, waterproofness, and easy removal. Herein, the study has developed a self‐adhesive, detach‐on‐demand, breathable, and waterproof E‐skin (PDSC) for motion sensing and wearable comfort by electrospinning styrene‐isoprene block copolymer rubber with carbon black nanosheets as the sensing layer and liner copolymers of N, N‐dimethylacrylamide, n‐octadecyl acrylate and lauryl methacrylate as the adhesive layer. The high elasticity and microfiber network structure endow the PDSC with good sensitivity and high linearity for strain sensing. The hydrophobic and crystallizable adhesive layer ensures robust, waterproof, and detaching‐on‐demand skin adhesion. Meanwhile, the fiber structure enables the PDSC good air and water permeability. The integration of electric and wearable functions endows the PDSC with great potential for motion sensing during human activities as both the sensing and wearable performances. [ABSTRACT FROM AUTHOR]

Flexible electronic skin (e-skin) can enable robots to have sensory forms similar to human skin, enhancing their ability to obtain more information from touch. The non-invasive nature of electrical impedance tomography (EIT) technology allows electrodes to be arranged only at the edges of the skin, ensuring the stretchability and elasticity of the skin's interior. However, the image quality reconstructed by EIT technology has deteriorated in multi-touch identification, where it is challenging to clearly reflect the number of touchpoints and accurately size the touch areas. This paper proposed an EIT-based flexible tactile sensor that employs self-made hydrogel material as the primary sensing medium. The sensor's structure, fabrication process, and tactile imaging principle were elaborated. To improve the quality of image reconstruction, the fast iterative shrinkage-thresholding algorithm (FISTA) was embedded into the EIDORS toolkit. The performances of the e-skin in aspects of assessing the touching area, quantitative force sensing and multi-touch identification were examined. Results showed that the mean intersection over union (MIoU) of the reconstructed images was improved up to 0.84, and the tactile position can be accurately imaged in the case of the number of the touchpoints up to seven (larger than two to four touchpoints in existing studies), proving that the combination of the proposed sensor and imaging algorithm has high sensitivity and accuracy in multi-touch tactile sensing. The presented e-skin shows potential promise for the application in complex human–robot interaction (HRI) environments, such as prosthetics and wearable devices. [ABSTRACT FROM AUTHOR]

Only microstructures are used to improve the sensitivity of iontronic pressure sensors. By modulating the compressive modulus, a breakthrough in the sensitivity of the iontronic pressure sensor is achieved. Furthermore, it allows for programmatic tailoring of sensor performance according to the requirements of different applications. Such a new strategy pushes the sensitivity up to a record‐high of 25 548.24 kPa−1 and expands the linear pressure range from 15 to 127 kPa. Additionally, the sensor demonstrates excellent mechanical stability over 10 000 compression‐release cycles. Based on this, a well‐controlled robotic hand that precisely tracks the pressure behavior inside a balloon to autonomously regulate the gripping angle is developed. This paves the way for the application of iontronic pressure sensors in precise sensing scenarios. [ABSTRACT FROM AUTHOR]

Visible light is an important energy source for all living organisms on Earth. Given the importance of visible light, visible light sensors have attracted widespread interest from scientists. With the rapid development of wearable devices, the sensors used in them need to be flexible, stretchable, and lightweight. Herein, an intelligent electrolyte based on spiropyran (SP) that responds to visible light is developed. The reversible change rate in the electrical resistance of an SP/FeCl3·6H2O methyl cyanide (MeCN) aqueous solution under visible light irradiation is as high as 19.26%. Additionally, flexible and conductive fibrous visible light sensors with a core‐sheath structure are prepared using an SP/FeCl3·6H2O MeCN aqueous solution and silicon rubber hollow fibers as the core and outer layers, respectively. These fibrous visible light sensors are then woven into fabrics with multiple functions, such as sensing and locating visible light, reversible photochromism, and thermal management. The fibrous visible light sensors and fabrics prepared in this study have broad development prospects and application potential in the fields of fashion, smart textiles, flexible conductive fibers, flexible fibrous sensors, electronic skins, and wearable devices. [ABSTRACT FROM AUTHOR]

Copyright of Micronanoelectronic Technology is the property of Micronanoelectronic Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Electronic skin is a novel type of flexible and wearable sensor that mimics human skin perception， exhibiting characteristics such as lightweight， softness， and flexibility. It has the capability to convert external stimuli into diverse output signals， showing substantial potential in health monitoring and human-computer interaction. This article provides a comprehensive review from the perspective of intelligent materials for constructing electronic skin， focusing on commonly used substrates， conductive fillers， and their geometric structures. It discusses the requirements for biocompatibility， adhesion， self-healing， and self-powering performance of electronic skin based on the complex environmental conditions it faces in applications. It points out that in the research process， there are still issues such as poor comprehensive perception of human skin， complex and expensive fabrication processes， and delayed response to sensory signals. By optimizing materials and structures to enhance the basic performance of electronic skin， the development trend is to build outstanding performance， multifunctionality， and simultaneous detection of various external stimuli. Electronic skin shows great potential in medical diagnosis， soft robotics， smart prosthetics， and human-machine interaction.

Mechanical metamaterials (MMs) receive widespread attention due to their unprecedented mechanical properties. However, in the next‐generation MMs, the cognitive function of information processing can be realized while maintaining superior mechanical properties. Herein, a mechanical metamaterial‐based self‐powered electronic skin (e‐skin) with multimodal fusion perception capability and shape memory reconfigurability is proposed. Benefiting from an MM skeleton and its analytical model, e‐skin realizes biomimetic nonlinear mechanical behavior and mechanical reconfigurability to imitate target biotissues. Its integrated perovskite‐based elastic sensors enable high‐precision collection of physiological movements and auditory, tactile, and precontact distance signals. Further, by imitating the integration and interaction functions in biological multisensory neural networks, the system achieves advanced cognitive functions of acquiring, identifying, and integrating information across modalities. Applications of e‐skin are demonstrated in motion monitoring, speech recognition, and somatosensory game operation. These capabilities can be applied to cross‐modal perception robot systems based on multisensory neural networks. [ABSTRACT FROM AUTHOR]

Biomimetic electronic skins (e‐skins) are widely used in wearables, smart prosthesis and soft robotics. However, multimodal e‐skins, especially those based on hydrogels, face multiple challenges for practical applications, involving multi‐sensing signal mutual interference, low breathability and stretchability. Here, a breathable and stretchable multimodal e‐skin with a multilayer film microstructure is developed to achieve self‐calibrated sensing of any two of three stimuli: strain, temperature, and humidity, with minimal crosstalk. Hydrogel fibers with different shapes are designed for strain and temperature sensing modules, and the hydrogel film is developed as a humidity sensing module. The multimodal e‐skin exhibits impressive sensing performance, including a low strain detection limit (0.03%), strain linearity (R2 = 0.990), high‐temperature sensitivity (1.77%/°C), and a wide humidity detection range (33–98% RH). Interestingly, due to the directional anisotropy in strain sensitivity of different shaped fibers, the e‐skin realizes self‐calibrated detection of strain and temperature in different directions. By introducing porous elastomer encapsulation membranes, the breathability and wearing comfort of the e‐skin are attained, while the high stretchability (100% strain) is maintained. Furthermore, a personalized human‐machine interaction system is created by integrating the e‐skin with a wireless circuit to realize real‐time and wireless gesture recognition, physiological signals monitoring, and smart prosthesis. [ABSTRACT FROM AUTHOR]

Wearable and self‐healing soft electronics have led to a significant emphasis on their potential in creating versatile, conformable, and sustainable electronic modules. Among conductive additives, Liquid metals (LMs), combining both solid and liquid characteristics, have gained widespread attention due to their versatile physical, chemical, and electrical properties as well as self‐healing capability, biocompatibility, and recyclability. The fluidity of LMs facilitates adaptability to various experimental conditions and components for specific applications. Moreover, the oxide shell on LMs exhibits strong compatibility with surface functionalization and polymerization processes, enhancing the development of reliable composite materials. Herein, an in‐depth analysis of the fundamental properties and characteristics of LMs while addressing their current drawbacks, such as unpredictable reactivity and poor surface stability, is presented. To harness the advantages of LMs, their integration is extensively discussed with polymeric materials through various grafting strategies, leading to the development of macromolecular composites with exceptional softness, solubility, surface functionalization, and versatility. Furthermore, the applications of LMs within LM‐elastomer composites, particularly focusing on their relevance in specific fields such as flexible electronics, are investigated. Finally, LMs' future prospects are emphasized by highlighting their compatibility with self‐healing polymers, thereby providing pathways for major breakthroughs of LMs based devices. [ABSTRACT FROM AUTHOR]

Haptic perception of softness is a unique feature of the human skin that relies on the concurrent measurements of the lateral deformation and compression of the skin during object manipulation. This is challenging to implement in robotics because of combined requirements in sensing modalities, skin format, robotic structures, and synthetic materials. A soft sensory skin supporting distributed and bimodal mechanical sensing over large surface area and suitable for robotic hand manipulation is reported. Resistive pressure and strain sensors are prepared with spray‐coated liquid metal films embedded in a silicone matrix. Object softness is computed through a calibrated model based on both sensor response curves and the stiffness of the carrier robot. The soft sensory skin enables localization and discrimination of softness that promise interesting future implementation for robotic palpation or precise teleoperation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The emergence of cutting‐edge cross‐disciplines has motivated the rapid development of wearable technology and flexible electronics. The flexibility and tunable properties of organic materials enable organic flexible electronics to adapt to complex surface deformations and achieve sensitive detection of physiological signals. The cost‐effectiveness of organic materials in mass production offers additional possibilities for the practical and commercialization of e‐skin technology. However, how to ensure stability and long‐term reliability while maintaining a highly sensitive, flexible, and stretchable is a challenge for e‐skins. In this review, the research progress and development trend of e‐skin is systematically summarized, especially the latest breakthroughs and innovations in the frontier of organic flexible electronics, and systematically review the applications of e‐skin in sensors, physiological monitoring, and energy supply. In addition, the review further discusses the prospects and current challenges for the application of organic flexible electronics in e‐skin, which provides a one‐stop reference for the development of e‐skin. [ABSTRACT FROM AUTHOR]

Neurological electronic skin (E-skin) can process and transmit information in a distributed manner that achieves effective stimuli perception, holding great promise in neuroprosthetics and soft robotics. Neurological E-skin with multifunctional perception abilities can enable robots to precisely interact with the complex surrounding environment. However, current neurological E-skins that possess tactile, thermal, and visual perception abilities are usually prepared with rigid materials, bringing difficulties in realizing biologically synapse-like softness. Here, we report a soft multifunctional neurological E-skin (SMNE) comprised of a poly(3-hexylthiophene) (P3HT) nanofiber polymer semiconductor-based stretchable synaptic transistor and multiple soft artificial sensory receptors, which is capable of effectively perceiving force, thermal, and light stimuli. The stretchable synaptic transistor can convert electrical signals into transient channel currents analogous to the biological excitatory postsynaptic currents. And it also possesses both short-term and long-term synaptic plasticity that mimics the human memory system. By integrating a stretchable triboelectric nanogenerator, a soft thermoelectric device, and an elastic photodetector as artificial receptors, we further developed an SMNE that enables the robot to make precise actions in response to various surrounding stimuli. Compared with traditional neurological E-skin, our SMNE can maintain the softness and adaptability of biological synapses while perceiving multiple stimuli including force, temperature, and light. This SMNE could promote the advancement of E-skins for intelligent robot applications. [ABSTRACT FROM AUTHOR]

The development of electronic skin with dual stealth functionality is crucial for enabling devices to operate effectively in dynamic electromagnetic environments, thereby facilitating intelligent electromagnetic protection for autonomous perception. However, achieving compatibility between terahertz (THz) and infrared (IR) stealth technologies remains largely unexplored due to their inherent contradictions. Herein, inspired by natural corals, a novel coral‐like multi‐scale composite foam (CMSF) was proposed that ingeniously reconciles these contradictions. The design capitalizes on the conductive network and heat insulation properties of the foam skeleton, the loss effects and low infrared emission of metal particles, and the infrared transparency of magneto‐optical materials. This approach leads to the realization of a THz‐IR bi‐stealth electronic skin concept. The CMSF exhibits a maximum reflection loss of 84.8 dB in the terahertz band, while its infrared stealth capability ensures environmental adaptability under varying temperatures. Furthermore, the electronic skin exhibits exceptional sensitivity and reliability as a wearable device for perceiving environmental changes. This advanced material, combining multispectral stealth with sensing capabilities, holds immense potential for applications ranging from camouflage technology to smart wearables. [ABSTRACT FROM AUTHOR]

The field of electronic skin has received considerable attention due to its extensive potential applications in areas including tactile sensing and health monitoring. With the development of electronic skin devices, electronic skin can be attached to the surface of human skin for long-term health monitoring, which makes comfort an essential factor that cannot be ignored in the design of electronic skin. Therefore, this paper proposes an assessment method for evaluating the comfort of electronic skin based on neurodynamic analysis. The holistic analysis framework encompasses the mechanical model of the skin, the modified Hodgkin–Huxley model for the transduction of stimuli, and the gate control theory for the modulation and perception of pain sensation. The complete process, from mechanical stimulus to the generation of pain perception, is demonstrated. Furthermore, the influence of different factors on pain perception is investigated. Sensation and comfort diagrams are provided to assess the mechanical comfort of electronic skin. The comfort assessment method proposed in this paper provides a theoretical basis when assessing the comfort of electronic skin. [ABSTRACT FROM AUTHOR]

In recent years, wearable e-skin has emerged as a prominent technology with a wide range of applications in healthcare, health surveillance, human–machine interface, and virtual reality. Inspired by the properties of human skin, arrayed wearable e-skin is a novel technology that offers multifunctional sensing capabilities. It can detect and quantify various stimuli, mimicking the human somatosensory system, and record a wide range of physical and physiological parameters in real time. By combining flexible electronic device units with a data acquisition system, specific functional sensors can be distributed in targeted areas to achieve high sensitivity, resolution, adjustable sensing range, and large-area expandability. This review provides a comprehensive overview of recent advances in wearable e-skin technology, including its development status, types of applications, power supply methods, and prospects for future development. The emphasis of current research is on enhancing the sensitivity and stability of sensors, improving the comfort and reliability of wearable devices, and developing intelligent data processing and application algorithms. This review aims to serve as a scientific reference for the intelligent development of wearable e-skin technology. [ABSTRACT FROM AUTHOR]

Visible light is an important energy source for all living organisms on Earth. Given the importance of visible light, visible light sensors have attracted widespread interest from scientists. With the rapid development of wearable devices, the sensors used in them need to be flexible, stretchable, and lightweight. Herein, an intelligent electrolyte based on spiropyran (SP) that responds to visible light is developed. The reversible change rate in the electrical resistance of an SP/FeCl3·6H2O methyl cyanide (MeCN) aqueous solution under visible light irradiation is as high as 19.26%. Additionally, flexible and conductive fibrous visible light sensors with a core‐sheath structure are prepared using an SP/FeCl3·6H2O MeCN aqueous solution and silicon rubber hollow fibers as the core and outer layers, respectively. These fibrous visible light sensors are then woven into fabrics with multiple functions, such as sensing and locating visible light, reversible photochromism, and thermal management. The fibrous visible light sensors and fabrics prepared in this study have broad development prospects and application potential in the fields of fashion, smart textiles, flexible conductive fibers, flexible fibrous sensors, electronic skins, and wearable devices.

Abstract Only microstructures are used to improve the sensitivity of iontronic pressure sensors. By modulating the compressive modulus, a breakthrough in the sensitivity of the iontronic pressure sensor is achieved. Furthermore, it allows for programmatic tailoring of sensor performance according to the requirements of different applications. Such a new strategy pushes the sensitivity up to a record‐high of 25 548.24 kPa−1 and expands the linear pressure range from 15 to 127 kPa. Additionally, the sensor demonstrates excellent mechanical stability over 10 000 compression‐release cycles. Based on this, a well‐controlled robotic hand that precisely tracks the pressure behavior inside a balloon to autonomously regulate the gripping angle is developed. This paves the way for the application of iontronic pressure sensors in precise sensing scenarios.

Abstract For the need of direct contact with the skin, electronic skins (E‐skins) should not only fulfill electric functions, but also ensure comfort during wearing, including permeability, waterproofness, and easy removal. Herein, the study has developed a self‐adhesive, detach‐on‐demand, breathable, and waterproof E‐skin (PDSC) for motion sensing and wearable comfort by electrospinning styrene‐isoprene block copolymer rubber with carbon black nanosheets as the sensing layer and liner copolymers of N, N‐dimethylacrylamide, n‐octadecyl acrylate and lauryl methacrylate as the adhesive layer. The high elasticity and microfiber network structure endow the PDSC with good sensitivity and high linearity for strain sensing. The hydrophobic and crystallizable adhesive layer ensures robust, waterproof, and detaching‐on‐demand skin adhesion. Meanwhile, the fiber structure enables the PDSC good air and water permeability. The integration of electric and wearable functions endows the PDSC with great potential for motion sensing during human activities as both the sensing and wearable performances.

Real-time monitoring of human health can be significantly improved by designing novel electronic skin (E-skin) platforms that mimic the characteristics and sensitivity of human skin. A high-quality E-skin platform that can simultaneously monitor multiple physiological and metabolic biomarkers without introducing skin discomfort or irritation is an unmet medical need. Conventional E-skins are either monofunctional or made from elastomeric films that do not include key synergistic features of natural skin, such as multi-sensing, breathability, and thermal management capabilities in a single patch. Herein, a biocompatible and biodegradable E-skin patch based on flexible gelatin methacryloyl aerogel (FGA) for non-invasive and continuous monitoring of multiple biomarkers of interest is engineered and demonstrated. Taking advantage of cryogenic temperature treatment and slow polymerization, FGA is fabricated with a highly interconnected porous structure that displays good flexibility, passive-cooling capabilities, and ultra-lightweight properties that make it comfortable to wear for long periods of time. It also provides numerous permeable capillary channels for thermal-moisture transfer, ensuring its excellent breathability. Therefore, the engineered FGA-based E-skin can simultaneously monitor body temperature, hydration, and biopotentials via electrophysiological sensors and detect glucose, lactate, and alcohol levels via electrochemical sensors. This work offers a previously unexplored materials strategy for next-generation E-skin platforms with superior practicality.

Electronic skin (E‐skin) that can mimic the flexibility and stretchability of human skin with sensing capabilities, holds transformative potential in robotics, wearable technology, and healthcare. However, developing E‐skin poses significant challenges such as creating durable materials with skin‐like flexibility, integrating biosensing abilities, and using advanced fabrication techniques for wearable or implantable applications. To overcome these hurdles, a 3D‐printed electronic skin utilizing a novel class of nanoengineered hydrogels with tunable electronic and thermal biosensing capabilities is fabricated. This methodology takes advantage of the shear–thinning behavior in hydrogel precursors, allowing to construct intricate 2D and 3D electronic structures. The elasticity of skin using triple crosslinking in a robust fungal exopolysaccharide, and pullulan is simulated, while defect‐rich 2D molybdenum disulfide (MoS2) nanoassemblies ensure high electrical conductivity. The addition of polydopamine nanoparticles enhances adhesion to wet tissue. The hydrogel exhibits outstanding flexibility, stretchability, adhesion, moldability, and electrical conductivity. A distinctive feature of this technology is the precise detection of dynamic changes in strain, pressure, and temperature. As a human motion tracker, phonatory‐recognition platform, flexible touchpad, and thermometer, this technology represents a breakthrough in flexible wearable skins and holds transformative potential for the future of robotics and human‐machine interfaces. [ABSTRACT FROM AUTHOR]

In the context of an aging population and escalating work pressures, cardiovascular diseases pose increasing health risks. Electrocardiogram (ECG) monitoring presents a preventive tool, but conventional devices often compromise comfort. This study proposes an approach using Ag NW/TPU composites for flexible and breathable epidermal electronics. In this new structure, TPU fibers are used to support Ag NWs/TPU nanocomposites. The TPU fiber-reinforced Ag NW/TPU (TFRAT) nanocomposites exhibit excellent conductivity, stretchability, and electromechanical durability. The composite ensures high steam permeability, maintaining stable electrical performance after washing cycles. Employing this technology, a flexible ECG detection system is developed, augmented with a convolutional neural network (CNN) for automated signal analysis. The experimental results demonstrate the system's reliability in capturing physiological signals. Additionally, a CNN model trained on ECG data achieves over 99% accuracy in diagnosing arrhythmias. This study presents TFRAT as a promising solution for wearable electronics, offering both comfort and functionality in long-term epidermal applications, with implications for healthcare and beyond. [ABSTRACT FROM AUTHOR]

The interfacial design of the electronic skins (E‐skins), which are increasingly crucial in areas like exercise monitoring, healthcare, etc., has a great impact on wearability and functions. The adhesion between E‐skin and human skin serves as the foundation for various functionalities. In addition to robust adhesion strength, detaching‐on‐demand, and waterproof abilities are also important for long‐time wearing and comfort detachment after use. Here, self‐adhesive, detach‐on‐demand, and waterproof hydrophobic E‐skins (PBIA) by copolymerization of acrylates with conductive ionic liquid and adhesive components as the strain sensor and triboelectric nanogenerator (TENG) is developed. The strong van der Waals self‐adhesion (shear adhesion of ≈574 kPa, peeling adhesion of ≈110 N m−1), and waterproof abilities under immersing, flushing, and penetrating situations enable the E‐skin to realize stable and long‐time monitoring for body motions in both the resistance sensing and TENG modes. Meanwhile, the easy detach‐on‐demand ability of van der Waals adhesion (574 to 35 kPa and 110 to 7 N m−1) guarantees the easy and comfortable detachment of PBIA after use, avoiding pain or injury to the skin. The adhesion strategy of PBIA can be expanded to other kinds of E‐skins and accelerate the pace of practical applications of E‐skins. [ABSTRACT FROM AUTHOR]

Neurofeedback training based on brain rhythm is appealing for both cognitive neuroscience and disorder treatment. However, electrodes that can integrate dual functions of recording and feedback without signal compromise still lack. Herein, an anisotropic cellulose carbon sponge (CCS) electrode by tailoring conductivity through the temperature that has the dual ability to record electrophysiological signals and sense pressures as feedback is developed. The electrode is fabricated via a gradient temperature annealing on CCS, which involves lower (300 °C) and higher (1000 °C) temperature treatments, namely CCS‐LT and CCS‐HT. CCS‐LT exhibits perpendicular resilience to the alignment direction of CCS, and CCS‐HT possesses lower sheet resistance (≈13 Ω sq−1) parallel to the alignment direction. As a pressure sensor, CCS‐LT can achieve excellent sensitivity (1.04 kPa−1), fast response time (27 ms), and reliable stability for 1000 cycles. CCS‐HT can serve as skin electrodes for electrophysiological sensing. The anisotropic functionality of annealed CCS allows it to be used in one sensing and regulation closed‐loop system driven by nerves, achieving accurate acquisition of human brain rhythm and machine movement information simultaneously. This not only helps rapid tracking of brain activity but also facilitates feedback regulation to enhance human brain function, having great potential applications in neurofeedback and disease rehabilitation. [ABSTRACT FROM AUTHOR]

On‐skin electronics can be conformably deployed on body for health monitoring, assisted living, and human/computer interfaces. However, developing corresponding energy devices is a critical challenge. Herein, a permeable and stretchable multifunctional liquid‐metal electronic skin that can generate electricity by recovering ambient electromagnetic pollution (from surrounding electrical appliances) and biomechanical energy (from body movements) is presented for epidermal energy and self‐powered sensing applications. To the best of the authors' knowledge, this is the first demonstration that a breathable on‐skin device can convert ambient electromagnetic pollution into useful electricity. The device is constructed using two stretchable microfibrous films sandwiching self‐organized mesh‐like and wrinkled liquid‐metal that affords electricity via induced electrification (±9.3 V, ±1.7 µA; 60 Hz) and triboelectricity (205.6 V, ±2.3 µA; 4 Hz). Its applicability in powering electronic devices is demonstrated. Moreover, it can serve as an epidermal self‐powered sensor for continuously monitoring whole‐body physiological signals and motions of the eyelids, face, throat, chest, and limbs, thus demonstrating its potential to remotely collect clinical and biomechanical information. Finally, it is used as an interface in diverse system‐level applications. These results shed light on new directions in on‐skin energy and sensing, enabling to usher electronics toward untethered and diversified applications. [ABSTRACT FROM AUTHOR]

Electronic skin based on nanomaterials has great potential for material detection and health monitoring. This paper first outlines the current development of physical sensors for electronic skin based on nanomaterials. Secondly, according to the different kinds of propagation signals, it reviews the research on physical sensors based on different nanomaterials sensing. Strain signals, temperature signals and electrophysiological signals are the main types of nanomaterials transduction. It discusses the different mechanisms, research processes and advantages of the different ways of constituting physical sensors after sensing signals. In particular, it reviews the comparison of nanomaterials constituting sensors with conventional approaches and innovations in the performance of advanced electronic skin sensors. According to the technologies used in them, it reviews the particularities of each study in detail. It analytically summarizes their application in electronic skin as a novel bionic monitoring element. Finally, it also summarizes and proposes future directions for the development of electronic skins composed of physical sensors based on nanomaterials. [ABSTRACT FROM AUTHOR]

Advances in biomimetic triboelectric nanogenerators (TENGs) have significant implications for electronic skin (e-skin) and human–machine interaction (HMI). Emphasizing the need to mimic complex functionalities of natural systems, particularly human skin, TENGs leverage triboelectricity and electrostatic induction to bridge the gap in traditional electronic devices' responsiveness and adaptability. The exploration begins with an overview of TENGs' operational principles and modes, transitioning into structural and material biomimicry inspired by plant and animal models, proteins, fibers, and hydrogels. Key applications in tactile sensing, motion sensing, and intelligent control within e-skins and HMI systems are highlighted, showcasing TENGs' potential in revolutionizing wearable technologies and robotic systems. This review also addresses the challenges in performance enhancement, scalability, and system integration of TENGs. It points to future research directions, including optimizing energy conversion efficiency, discovering new materials, and employing micro-nanostructuring techniques for enhanced triboelectric charges and energy conversion. The scalability and cost-effectiveness of TENG production, pivotal for mainstream application, are discussed along with the need for versatile integration with various electronic systems. The review underlines the significance of making bioinspired TENGs more accessible and applicable in everyday technology, focusing on compatibility, user comfort, and durability. Conclusively, it underscores the role of bioinspired TENGs in advancing wearable technology and interactive systems, indicating a bright future for these innovations in practical applications. [ABSTRACT FROM AUTHOR]

Highlights An ultraconformable skin-like integrated wireless charging micro-supercapacitor (IWC-MSC) could be wireless charged to store electricity into high capacitive micro-supercapacitors (11.39 F cm−3), and fits well with human surface. Building blocks of IWC-MSC skin are all evaporated by liquid precursor, and each part of the device attached firmly benefitting from the liquid permeation, forming a compact and all-in-one configuration. The electrode thickness easily regulated varying from 11.7 to 112.5 μm by controlling the volume of electrode solution precursor.

Advances in biomimetic triboelectric nanogenerators (TENGs) have significant implications for electronic skin (e-skin) and human–machine interaction (HMI). Emphasizing the need to mimic complex functionalities of natural systems, particularly human skin, TENGs leverage triboelectricity and electrostatic induction to bridge the gap in traditional electronic devices’ responsiveness and adaptability. The exploration begins with an overview of TENGs’ operational principles and modes, transitioning into structural and material biomimicry inspired by plant and animal models, proteins, fibers, and hydrogels. Key applications in tactile sensing, motion sensing, and intelligent control within e-skins and HMI systems are highlighted, showcasing TENGs’ potential in revolutionizing wearable technologies and robotic systems. This review also addresses the challenges in performance enhancement, scalability, and system integration of TENGs. It points to future research directions, including optimizing energy conversion efficiency, discovering new materials, and employing micro-nanostructuring techniques for enhanced triboelectric charges and energy conversion. The scalability and cost-effectiveness of TENG production, pivotal for mainstream application, are discussed along with the need for versatile integration with various electronic systems. The review underlines the significance of making bioinspired TENGs more accessible and applicable in everyday technology, focusing on compatibility, user comfort, and durability. Conclusively, it underscores the role of bioinspired TENGs in advancing wearable technology and interactive systems, indicating a bright future for these innovations in practical applications.

Flexible pressure sensors have attracted wide attention due to their applications to electronic skin, health monitoring, and human-machine interaction. However, the tradeoff between their high sensitivity and wide response range remains a challenge. Inspired by human skin, we select commercial silicon carbide sandpaper as a template to fabricate carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite film with a hierarchical structured surface (h-CNT/PDMS) through solution blending and blade coating and then assemble the h-CNT/PDMS composite film with interdigitated electrodes and polyurethane (PU) scotch tape to obtain an h-CNT/PDMS-based flexible pressure sensor. Based on in-situ optical images and finite element analysis, the significant compressive contact effect between the hierarchical structured surface of h-CNT/PDMS and the interdigitated electrode leads to enhanced pressure sensitivity and a wider response range (0.1661 ​kPa−1, 0.4574 ​kPa−1 and 0.0989 ​kPa−1 in the pressure range of 0–18 ​kPa, 18–133 ​kPa and 133–300 ​kPa) compared with planar CNT/PDMS composite film (0.0066 ​kPa−1 in the pressure range of 0–240 ​kPa). The prepared pressure sensor displays rapid response/recovery time, excellent stability, durability, and stable response to different loading modes (bending and torsion). In addition, our pressure sensor can be utilized to accurately monitor and discriminate various stimuli ranging from human motions to pressure magnitude and spatial distribution. This study supplies important guidance for the fabrication of flexible pressure sensors with superior sensing performance in next-generation wearable electronic devices.

Flexible electronic skin (e-skin) can enable robots to have sensory forms similar to human skin, enhancing their ability to obtain more information from touch. The non-invasive nature of electrical impedance tomography (EIT) technology allows electrodes to be arranged only at the edges of the skin, ensuring the stretchability and elasticity of the skin’s interior. However, the image quality reconstructed by EIT technology has deteriorated in multi-touch identification, where it is challenging to clearly reflect the number of touchpoints and accurately size the touch areas. This paper proposed an EIT-based flexible tactile sensor that employs self-made hydrogel material as the primary sensing medium. The sensor’s structure, fabrication process, and tactile imaging principle were elaborated. To improve the quality of image reconstruction, the fast iterative shrinkage-thresholding algorithm (FISTA) was embedded into the EIDORS toolkit. The performances of the e-skin in aspects of assessing the touching area, quantitative force sensing and multi-touch identification were examined. Results showed that the mean intersection over union (MIoU) of the reconstructed images was improved up to 0.84, and the tactile position can be accurately imaged in the case of the number of the touchpoints up to seven (larger than two to four touchpoints in existing studies), proving that the combination of the proposed sensor and imaging algorithm has high sensitivity and accuracy in multi-touch tactile sensing. The presented e-skin shows potential promise for the application in complex human–robot interaction (HRI) environments, such as prosthetics and wearable devices.

Polyvinyl alcohol (PVA) hydrogel is favored by researchers due to its good biocompatibility, high mechanical strength, low friction coefficient, and suitable water content. The widely distributed hydroxyl side chains on the PVA molecule allow the hydrogels to be branched with various functional groups. By improving the synthesis method and changing the hydrogel structure, PVA-based hydrogels can obtain excellent cytocompatibility, flexibility, electrical conductivity, viscoelasticity, and antimicrobial properties, representing a good candidate for articular cartilage restoration, electronic skin, wound dressing, and other fields. This review introduces various preparation methods of PVA-based hydrogels and their wide applications in the biomedical field. [ABSTRACT FROM AUTHOR]

Highlights: An ultraconformable skin-like integrated wireless charging micro-supercapacitor (IWC-MSC) could be wireless charged to store electricity into high capacitive micro-supercapacitors (11.39 F cm−3), and fits well with human surface. Building blocks of IWC-MSC skin are all evaporated by liquid precursor, and each part of the device attached firmly benefitting from the liquid permeation, forming a compact and all-in-one configuration. The electrode thickness easily regulated varying from 11.7 to 112.5 μm by controlling the volume of electrode solution precursor. Conformable and wireless charging energy storage devices play important roles in enabling the fast development of wearable, non-contact soft electronics. However, current wireless charging power sources are still restricted by limited flexural angles and fragile connection of components, resulting in the failure expression of performance and constraining their further applications in health monitoring wearables and moveable artificial limbs. Herein, we present an ultracompatible skin-like integrated wireless charging micro-supercapacitor, which building blocks (including electrolyte, electrode and substrate) are all evaporated by liquid precursor. Owing to the infiltration and permeation of the liquid, each part of the integrated device attached firmly with each other, forming a compact and all-in-one configuration. In addition, benefitting from the controllable volume of electrode solution precursor, the electrode thickness is easily regulated varying from 11.7 to 112.5 μm. This prepared thin IWC-MSC skin can fit well with curving human body, and could be wireless charged to store electricity into high capacitive micro-supercapacitors (11.39 F cm−3) of the integrated device. We believe this work will shed light on the construction of skin-attachable electronics and irregular sensing microrobots. [ABSTRACT FROM AUTHOR]

Human skin comprises multiple hierarchical layers that perform various functions such as protection, sensing, and structural support. Developing electronic skin (E‐skin) with similar properties has broad implications in health monitoring, prosthetics, and soft robotics. While previous efforts have predominantly concentrated on sensory capabilities, this study introduces a hierarchical polymer system that not only structurally resembles the epidermis‐dermis bilayer structure of skin but also encompasses sensing functions. The system comprises a polymeric hydrogel, representing the "dermis", and a superimposed nanoporous polymer film, forming the "epidermis". Within the film, interconnected nanoparticles mimic the arrangement of interlocked corneocytes within the epidermis. The fabrication process employs a robust in situ interfacial precipitation polymerization of specific water‐soluble monomers that become insoluble during polymerization. This process yields a hybrid layer establishing a durable interface between the film and hydrogel. Beyond the structural mimicry, this hierarchical structure offers functionalities resembling human skin, which includes (1) water loss protection of hydrogel by tailoring the hydrophobicity of the upper polymer film; (2) tactile sensing capability via self‐powered triboelectric nanogenerators; (3) built‐in gold nanowire‐based resistive sensor toward temperature and pressure sensing. This hierarchical polymeric approach represents a potent strategy to replicate both the structure and functions of human skin in synthetic designs. [ABSTRACT FROM AUTHOR]

To realize flexible pressure sensors with high sensitivity, surface‐textured soft films have often been adopted and the contact area can vary significantly depending on the applied pressure. However, the contact area modulation realized in such a way is subject to a limited dynamic range, and its infinitesimal zero‐pressure contact area raises concerns regarding durability. Herein, a flexible pressure sensor made of a texturing‐free piezocapacitive layer based on ion‐polymer networks is proposed. In this scheme, ion infiltration leads to electrical‐double‐layer modulation that gradually varies over a wide range of applied pressures. The proposed flexible pressure sensors with the optimal ion concentration are shown to exhibit both excellent mechanical durability and linear responses with high sensitivity over a wide pressure range up to 1 MPa. With the simple fabrication route, high performance, and reliability, the proposed approach may open up a new avenue for skin‐like pressure sensors ideal for many emerging applications. [ABSTRACT FROM AUTHOR]

Flexible tactile sensors with multifunctional sensing functions have attracted much attention due to their wide applications in artificial limbs, intelligent robots, human‐machine interfaces, and health monitoring devices. Here, a multifunctional flexible tactile sensor based on resistive effect for simultaneous sensing of pressure and temperature is reported. The sensor features a simple design with patterned metal film on a soft substrate with cavities and protrusions. The decoupling of pressure and temperature sensing is achieved by the reasonable arrangement of metal layers in the patterned metal film. Systematically experimental and numerical studies are carried out to reveal the multifunctional sensing mechanism and show that the proposed sensor exhibits good linearity, fast response, high stability, good mechanical flexibility, and good microfabrication compatibility. Demonstrations of the multifunctional flexible tactile sensor to monitor touch, breathing, pulse and objects grabbing/releasing in various application scenarios involving coupled temperature/pressure stimuli illustrate its excellent capability of measuring pressure and temperature simultaneously. These results offer an effective tool for multifunctional sensing of pressure and temperature and create engineering opportunities for applications of wearable health monitoring and human‐machine interfaces. [ABSTRACT FROM AUTHOR]

The emerging field of flexible tactile sensing systems, equipped with multi-physical tactile sensing capabilities, holds vast potential across diverse domains such as medical monitoring, robotics, and human–computer interaction. In response to the prevailing challenges associated with the limited integration and sensitivity of flexible tactile sensors, this paper introduces a versatile tactile sensing system capable of concurrently monitoring temperature and pressure. The temperature sensor employs carbon nanotube/graphene conductive paste as its sensitive material, while the pressure sensor integrates an ionic gel containing boron nitride as its sensitive layer. Through the application of cost-effective screen printing technology, we have successfully manufactured a flexible dual-mode sensor with exceptional performance, featuring high sensitivity (804.27 kPa − 1 ), a broad response range (50 kPa), rapid response time (17 ms), and relaxation time (34 ms), alongside exceptional durability over 5000 cycles. Furthermore, the resistance temperature coefficient of the sensor within the temperature range of 12.5 °C to 93.7 °C is −0.17% °C−1. The designed flexible dual-mode tactile sensing system enables the real-time detection of pressure and temperature information, presenting an innovative approach to electronic skin with multi-physical tactile sensing capabilities. [ABSTRACT FROM AUTHOR]

Developing electronic skins (e‐skins) that are comparable to or even beyond human tactile perception holds significant importance in advancing the process of intellectualization. In this context, a machine‐learning‐motivated micropyramid array bimodal (MAB) e‐skin based on capacitive sensing is reported, which enables spatial mapping applications based on bimodal sensing (proximity and pressure) implemented via fringing and iontronic effects, such as contactless measurement of 3D objects and contact recognition of Braille letters. Benefiting from the iontronic effect and single‐micropyramid structure, the MAB e‐skin in pressure mode yields impressive features: a maximum sensitivity of 655.3 kPa−1 (below 0.5 kPa), a linear sensitivity of 327.9 kPa−1 (0.5–15 kPa), and an ultralow limit of detection of 0.2 Pa. With the assistance of multilayer perceptron and convolutional neural network, the MAB e‐skin can accurately perceive 6 materials and 10 surface shapes based on the training and learning using the collected datasets from proximity and pressure modes, thus allowing it to achieve the precise perception of different objects within one proximity‐pressure cycle. The development of this MAB e‐skin opens a new avenue for robotic skin and the expansion of advanced applications. [ABSTRACT FROM AUTHOR]

Flexible electronic sensors have recently garnered significant attention in the areas of soft robotics, artificial intelligence, and biomedical devices. The chemical processing of cellulose presents significant challenges due to the intricate nature of cellulosic biopolymer networks, cellulose type I crystal structure, and extensive non-covalent interactions among molecules. Cellulose is not readily meltable and is insoluble in common solvents, however, through proper physical treatment or chemical modification, its derivatives can be effectively dispersed or dissolved in solvents. This paper provides (1) a brief overview of the structural characteristics of cellulose, (2) the advantages and disadvantages of three solvents, and (3) various key roles played by cellulose nanomaterials in the field of sensor technology. Furthermore, it addresses complexities and obstacles associated with cellulose and biomaterials, as well as their potential applications in healthcare and implantable sensing areas. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth discussion of the development of electronic skin (e-skin) devices for transdermal drug delivery (TDD) for skin health management. E-skin devices, grounded in flexible conductive polymers, demonstrate immense potential as a versatile platform for TDD due to the adaptable properties factors. The integration of sensors and electronic components into e-skin devices seamlessly allows for real-time monitoring of skin health parameters, such as temperature, hydration, and pH levels. Additionally, e-skin devices can also realize the prospect of targeted and controlled drug delivery through the utilization of iontophoresis. This paper explores the current state-of-the-art in e-skin technology, emphasizing its applications in TDD and skin disease management. Furthermore, the paper outlines the prospective directions and prevailing challenges in this rapidly evolving domain. [ABSTRACT FROM AUTHOR]

Electronic skin and flexible wearable devices have attracted tremendous attention in the fields of human-machine interaction, energy storage, and intelligent robots. As a prevailing flexible pressure sensor with high performance, the piezoresistive sensor is believed to be one of the fundamental components of intelligent tactile skin. Furthermore, graphene can be used as a building block for highly flexible and wearable piezoresistive sensors owing to its light weight, high electrical conductivity, and excellent mechanical. This review provides a comprehensive summary of recent advances in graphene-based piezoresistive sensors, which we systematically classify as various configurations including one-dimensional fiber, two-dimensional thin film, and three-dimensional foam geometries, followed by examples of practical applications for health monitoring, human motion sensing, multifunctional sensing, and system integration. We also present the sensing mechanisms and evaluation parameters of piezoresistive sensors. This review delivers broad insights on existing graphene-based piezoresistive sensors and challenges for the future generation of high-performance, multifunctional sensors in various applications.

Abstract Human-machine interface has been considered as a prominent technology for numerous smart applications due to their direct communication between humans and machines. In particular, wearable electronic skins with a free form factor have received a lot of attention due to their excellent adherence to rough and wrinkled surfaces such as human skin and internal organs. However, most of the e-skins reported to date have some disadvantages in terms of mechanical instability and accumulation of by-products at the interface between the human skin and the device. Here, we report a mechanically stable e-skin via a newly designed pattern named the “eyes.” The ingeniously designed pattern of the eyes allowed mechanical stress and strain to be dissipated more effectively than other previously reported patterns. E-skin permeability of by-product was experimentally confirmed through sweat removal tests, showing superior sweat permeability compared to conventional e-skins. Finally, the real-time monitoring of the body temperature was carried out using our resistive-type thermometer in the e-skin.

Wearable piezoresistive sensors are being developed as electronic skins (E-skin) for broad applications in human physiological monitoring and soft robotics. Tactile sensors with sufficient sensitivities, durability, and large dynamic ranges are required to replicate this critical component of the somatosensory system. Multiple micro/nanostructures, materials, and sensing modalities have been reported to address this need. However, a trade-off arises between device performance and device complexity. Inspired by the microstructure of the spinosum at the dermo epidermal junction in skin, a low-cost, scalable, and high-performance piezoresistive sensor is developed with high sensitivity (0.144 kPa-1 ), extensive sensing range ( 0.1-15 kPa), fast response time (less than 150 ms), and excellent long-term stability (over 1000 cycles). Furthermore, the piezoresistive functionality of the device is realized via a flexible transparent electrode (FTE) using a highly stable reduced graphene oxide self-wrapped copper nanowire network. The developed nanowire-based spinosum microstructured FTEs are amenable to wearable electronics applications.

Background: Devices that mimic the functions of human skin are known as “electronic skin,” and they must have characteristics like high sensitivity, a wide dynamic range, high spatial homogeneity, cheap cost, wide area easy processing, and the ability to distinguish between diverse external inputs. Methods: This study introduces a novel approach, termed microfluidic droplet-based emulsion self-assembly (DMESA), for fabricating 3D microstructured elastomer layers using polydimethylsiloxane (PDMS). The method aims to produce accurate capacitive pressure sensors suitable for electronic skin (e-skin) applications. The DMESA method facilitates the creation of uniform-sized spherical micropores dispersed across a significant area without requiring a template, ensuring excellent spatial homogeneity. Results: Micropore size adjustment, ranging from 100 to 600 μm, allows for customization of pressure sensor sensitivity. The active layer of the capacitive pressure sensor is formed by the three-dimensional elastomer itself. Experimental results demonstrate the outstanding performance of the DMESA approach. It offers simplicity in processing, the ability to adjust performance parameters, excellent spatial homogeneity, and the capability to differentiate varied inputs. Capacitive pressure sensors fabricated using this method exhibit high sensitivity and dynamic amplitude, making them promising candidates for various e-skin applications. Conclusion: The DMESA method presents a highly promising solution for fabricating 3D microstructured elastomer layers for capacitive pressure sensors in e-skin technology. Its simplicity, performance adjustability, spatial homogeneity, and sensitivity to different inputs make it suitable for a wide range of electronic skin applications.

The field of electronic skin has received considerable attention due to its extensive potential applications in areas including tactile sensing and health monitoring. With the development of electronic skin devices, electronic skin can be attached to the surface of human skin for long-term health monitoring, which makes comfort an essential factor that cannot be ignored in the design of electronic skin. Therefore, this paper proposes an assessment method for evaluating the comfort of electronic skin based on neurodynamic analysis. The holistic analysis framework encompasses the mechanical model of the skin, the modified Hodgkin–Huxley model for the transduction of stimuli, and the gate control theory for the modulation and perception of pain sensation. The complete process, from mechanical stimulus to the generation of pain perception, is demonstrated. Furthermore, the influence of different factors on pain perception is investigated. Sensation and comfort diagrams are provided to assess the mechanical comfort of electronic skin. The comfort assessment method proposed in this paper provides a theoretical basis when assessing the comfort of electronic skin.