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• A novel silk fibroin/polyacrylamide (SF/PAM) hydrogel synthesized in a CaCl 2 -ethanol–water ternary solvent was presented. • The SF/PAM hydrogels demonstrate exceptional tensile strength (800 % strain and 120 kPa stress) and compressive strength (80 % strain and 334.0 kPa stress), along with high ion conductivity (2.4 S·cm−1) and low-temperature resistance (−60 °C). • The study successfully integrates the developed hydrogels into various wearable devices, including strain sensors and capacitive electronic skin. Integrating high strength, flexibility, biocompatibility, adhesion, and freezing resistance into conductive hydrogels for developing wearable electronic devices has consistently posed significant challenges in relevant research fields. Inspired by the silk dissolution behavior, a robust, flexible, antifreezing, and conductive silk fibroin/polyacrylamide (SF/PAM) hydrogel was synthesized in a CaCl 2 -ethanol–water (Ca2+/E/W) ternary solvent via a one-pot photogelation process. The gelation of SF and AM was enhanced by the ternary solvent, attributed to the inhibitory effects of Ca2+ ions and alcohols on hydrogen bond formation. The SF/PAM hydrogels based on Ca2+/E/W exhibited desirable mechanical properties (stretching: 800 % strain and 120 kPa stress; compression: 80 % strain and 334.0 kPa stress), excellent recoverability after deformation, high ion conductivity (2.4 S·cm−1) and strain sensitivity (gauge factor: ∼2.0), and low-temperature tolerance (−60 °C). These hydrogels were assembled into various wearable electronic devices, such as strain sensors, electronic skin, and electrodes, for detecting multiple physiological parameters, including joint activities, bioelectrical signals, and subtle movements like finger and wrist rotation, heartbeat, and vocal cord vibrations, demonstrating significant potential in flexible electronic applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Applying a multi-modal sensing algorithm to a skin-like dual-channel self-powered sensor, which accurately detects real-time and continuous changes in pressure on the skin in response to variations in finger-applied force, while mitigating errors induced by temperature fluctuations. • A multimodal sensing algorithm compensating errors induced by temperature fluctuations. • Oxidation-stable metal-elastomer thermoelectric composite with a high pressure-sensitivity. • A self-powered sensor accurately detecting real-time continuous pressure changes. In the rapidly evolving field of electronic skins (e-skins), the development of self-powered sensors has emerged as a promising solution to providing continuous and reliable power sources for embedded sensors. This study introduces a novel approach that incorporates spike-shaped nickel (Ni) microparticles into a styrene-ethylene-butylene-styrene (SEBS) matrix, resulting in a thermoelectric material that functions as both an energy harvester and a pressure sensor, and a multimodal sensing algorithm designed to mitigate pressure sensing errors arising from temperature fluctuations in the thermoelectric self-powered pressure sensor. The Ni-SEBS composite, with a sensing mechanism that identifies changes in the Ni particle percolation state induced by compressive strain, exhibited a high sensitivity of 0.6234 kPa−1. Based on this composite, a dual-channel self-powered sensor was fabricated using the proposed algorithm and attached to the skin; the sensor successfully detected various forms of external pressure applied to the skin without errors due to temperature changes. [ABSTRACT FROM AUTHOR]

[Display omitted] • i-gluten avoids potential carbon emission and environmental pollution problems during its preparation and use. • i-gluten can quickly identify dangerous movements and nuances for error correction and personalized guidance in sports. • i-gluten has good mechanical, adhesive, self-healing and biological safety. Physiological declines and inadequate safeguards expose the elderly to elevated safety risks during physical activities. We here introduce the fabrication of an ionic conductive gluten (i-gluten) through the integration of ionic liquids for smart elderly care. The orchestrated interactions among ionic liquid and peptide chains within the gluten matrix engendered remarkable properties in the resultant i-gluten , including electrical conductivity, mechanical strength (tensile strength ∼ 82.6 kPa), flexibility (stretching up to 790 %) and self-healability. Moreover, the i-gluten demonstrates exceptional strain sensing capabilities across diverse scenarios, underpinned by its robust adhesion to various substrates. The i-gluten holds great promise for addressing challenges associated with elderly physical activity monitoring. The multifaceted properties of i-gluten , including its mechanical robustness, self-healing capabilities, and biocompatibility, underscore its suitability as a versatile material for real-time exercise posture assessment, personalized guidance, and injury prevention among the elderly population. Furthermore, the demonstrated biodegradability of i-gluten offers potential solutions for sustainable e-waste disposal. Collectively, these findings illuminate the potential of i-gluten as a pivotal component in the burgeoning field of wearable electronics, fostering a synergy between technological advancements and geriatric care, while also addressing environmental concerns in electronics manufacturing and disposal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Integration of two distinctly sized 2D nanosheets forms a synergistic dual 3D network. • The synergistic effect of MXOH and hBN boosts electrical conductivity and network stability. • The modified hydrogel showed mechanical and electrical self-healing properties. • It showed a linear response (0–80 kPa) in pressure sensing with minimal hysteresis. • It is employed in wearables, e.g., touchscreens and thread-based motion sensors. Next-generation wearable electronic devices rely on electronic skin for its high flexibility, wearability, and ability to monitor vital health signs. Despite these advantages, developing flexible strain sensors for full-range human activity detection remains challenging. A solution involves thread-based motion sensors seamlessly integrated into clothing. This study employs a synergistic dual three-dimensional network using hydroxyl-functionalized MXene (MXOH) and hexagonal boron nitride (hBN) to modify poly(vinyl alcohol) (PVA) hydrogels, showcasing promising advancements in wearable technology. The hydrogel, incorporating MXOH with its larger lateral size and hBN with its smaller lateral size, forms a robust 3D network that reinforces the percolation network of MXOH nanosheets. This strategic combination ensures stability in the conductive pathway, minimizing electrical hysteresis during mechanical stress. The completion of the 3D network in PVA, facilitated by hBN, significantly enhances electrical conductivity due to the ion conduction properties of hBN. Moreover, the incorporation of non-conductive hBN nanosheets amplifies overall conductivity compared to MXOH alone, contributing to network stability. Rheological tests demonstrate the pronounced impact of increasing hBN weight percentage on the storage modulus, indicating the formation of a 3D network upon percolation. Additionally, MXOH and hBN exhibit self-healing characteristics through hydrogen bonding with the PVA chain, with hBN displaying higher mobility and faster self-healing compared to MXOH. These hydrogel-based flexible sensors exhibit mechanical stability and responsiveness across a wide pressure range (0 to 80 kPa) and find versatile applications in touch screens, thread-based motion sensors, and wearable electronics, promising transformative advances in handwriting-to-digital translation and smart textile technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrospun polysaccharide-based nanofiber membrane with a 3D network structure. • Biomimetic scale-like "core-shell" nanostructured piezoresistive material. • A broadened conductive pathway by in-situ polymerization of PPy. • A broad pressure range (0.13–128.46 kPa) and a high sensitivity (52.42 kPa−1). • Huge potential applicability in remote monitoring. A nanofiber membrane is an ideal carrier for constructing a typical three-dimensional conductive network. Inspired by the biomimetic scale-like nanostructure, polysaccharide-based piezoresistive material with outstanding Joule heating performance, thermal efficiency, and high conductivity is developed, presenting a potential indicator material with the color shifting function for intelligent skin or soft robots in practical applications. The stable core-shell structure due to the in-situ polymerization of polypyrrole (PPy) on the electrospun nanofiber endows the piezoresistive sensor (s-PGG@PPy) with a broad pressure range (0.13–128.46 kPa), high sensitivity (52.42 kPa−1) and fast response time (26 ms). The free motion of π electrons along the nanofibers between carbon atoms perfectly made it an attractive candidate for real-time monitoring of human activities, including bending of fingers, wrist, knee, and facial expression. In addition, designing s-PGG@PPy is to be connected in parallel and composed of an indication function glove, which shows different brightness with finger pressure. Consequently, the reported piezoresistive sensor represents a potential for wearable bioelectronics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Investigation of self-healing polymers for electronic-skin devices. • Overview of recent self-healing polymeric electronic skin advances. • Understanding of the thermodynamic contribution for self-healing fibrous network. • Conceptualization for electrospun self-healing breathable electronic skin. The development of wearable soft electronic skins requires the production of materials with high mechanical flexibility, an inherent self-healing mechanism, and high breathability. Autonomous self-healing mechanisms have been widely investigated to produce materials that can continue operating in hostile environments or after sustaining damage. However, mimicking the functions of natural human skin requires breathability. Given the thermodynamic considerations of the self-healing process and self-healing polymers, achieving porosity in such materials is a major challenge. Electronic skins fabricated through electrospinning have mechanical flexibility, breathability, and high overall performance; however, most electrospun self-healing fibrous materials have an extrinsic healing mechanism. Therefore, the further development of intrinsic healing methods is essential for the maturation of fibrous electronic skin technology. Several challenges must be addressed before the next generation of electronic skin devices can be developed. This review aims to discuss the shortcomings of current electronic skins and suggests several paths for developing fully self-healing and breathable electronic skins for future soft robotics and human–machine interfaces. [ABSTRACT FROM AUTHOR]

[Display omitted] • Empathetic haptic skin detects complicated touch motions for emotional interactions. • Nonionic polyvinyl chloride gels with different plasticizers were fabricated. • Empathetic skin was chemically assembled by ionic conductors and a nonionic gel. • Empathetic skin measures pressure/strain via capacitance or resistance change. • Chemically assembled haptic skin shows high transparency and stretchability. Using a smart polymeric material, we design a transparent and stretchable empathetic haptic skin cushion that secretly allows a target device to understand users' emotions. The skin comprises highly transparent and stretchable conducting hydrogels and a plasticized nonionic polyvinyl chloride (PNIPVC) whose dielectric, electrical, optical, and mechanical properties are adjusted by the type, ratio, and concentration of the dual-plasticizers. Hydrogels adhere strongly to the upper and lower surfaces of the PNIPVC via covalent bonding to form durable, reliable, and sensitive empathetic skin. The skin exhibits excellent transparency and stretchability with low mechanical hysteresis. In addition, the skin senses the capacitance or resistance of the PNIPVC by varying its operating frequency, which enables the perception of various external pressures for detecting emotional touches (tapping, patting, stretching, pinching, and twisting). Thus, the skisn cushion can be used as a new tactile emotional interface system for future emotion-interactive shape-deformable materials and devices. [ABSTRACT FROM AUTHOR]

• An e-skin exhibits multifunctional sensing capabilities. • Device is sensitive to dynamic force, static contact, and thermal transduction. • PLLA side of the e-skin has good biocompatibility. • The e-skin shows a high-resolution visualized restoring function. To fully mimic the sensing function of human skin, electronic sensor is highly demanding to not only respond to various external stimuli, but also visually restore the information of the contacting object including its location, size, and texture. In this study, a skin-inspired visualized tactile sensing electronic skin (VTSES) composed of poly (vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)/thin-film transistor (TFT)/poly (l -lactide) (PLLA) arrays was present. The PVDF-TrFE layer served not only as a sensor for out-of-plane dynamic and thermal stimuli, but also as an equivalent dielectric capacitor that was coupled with the TFT array for a static response. The integrated sensor pixels with a self-designed circuit array in the TFT reproduce the processing procedure of the brain, resulting in a high-resolution visualized restoring function. The PLLA layer offered dynamic slide detection and biocompatibility for health concern. The proposed VTSES may find a wide range of applications in future artificial intelligence or human–machine interactions. [ABSTRACT FROM AUTHOR]

• Facile method for fabricating stretchable vertical graphene array; • Multifunctional perception for pressure, airflow, surface morphology and temperature; • Ultrafast responsiveness and resilience, broad pressure sensing range, high sensitivity, robust cyclability. Electronic skin (e-skin) has significant application prospects in soft robotics, prosthetics, medical monitoring, and wearable equipment. However, it remains a great challenge for e-skin to comprehensively mimic the multifunctional sensing capabilities and characteristics of human skin. Herein, vertical graphene arrays (VGA) were directly fabricated on the surface of a natural latex film using a facile method. The e-skin based on VGA combines the intrinsic properties of graphene and flexible substrates, as well as the morphological advantages of VGA, giving it multifunctional sensing capabilities similar to those of human skin. The e-skin not only exhibited multifunctional tactile perception of the pressure, airflow, and surface morphology of objects, but could also percept the difference in temperature between the detected object and the e-skin in a noncontact manner. Moreover, the sensing characteristics, including an ultrafast responsiveness (6.7 ms) and resilience (13.4 ms), a broad pressure sensing range (2.5 Pa – 1.1 MPa), a high sensitivity, and a robust cyclability, further demonstrate the similarity to that of human skin. The outstanding stretchability of the substrate endows the e-skin with an ultrabroad strain detection range (0.5%∼250%). Furthermore, the e-skin can still maintain the VGA structure, as well as the sensing capability under large tensile deformations. The facile preparation methods and excellent performance mean this e-skin is expected to be applied as a multifunctional integrated e-skin in smart flexible electronics. [ABSTRACT FROM AUTHOR]

A Super-flexible and transparent wood film/silver nanowire electrode for optical and capacitive dual-mode sensing wood-based electronic skin. This work opens new directions for directly incorporating natural wood into e-skin sensors and may offer potential applications in wearable electronics, artificial intelligence, soft robots and so on. [Display omitted] • A wood-based e-skin with instrument- and naked eye-readable characteristics. • A pyramidal microstructure polydimethlysiloxane film was used as a sensing layer. • A super-flexible transparent wood film was used as the electrodes. • The e-skin can map the spatial distribution of static and dynamic pressures. • The e-skin in luminescence exhibited a maximum sensitivity value at 1.28 kPa−1. Flexible electronic skin (e-skin) with multimode broad-range pressure sensing and high sensitivity is highly desirable for robotics, artificial intelligence and human–machine interaction applications. Most research on e-skin has focused on improving the sensitivity of sensing layers interfaced with an electronic output device, with only a limited number of studies focused on user interfaces based on a human-readable output. Moreover, naturally degradable materials are receiving increasing attention for e-skin. Herein, inspired by a bioluminescent noctiluca, a wood-based e-skin with instrument- and naked eye-readable characteristics was sandwich assembled using silver nanowires and a super-flexible transparent wood (STW) film as an electrode and a pyramidal microstructure polydimethlysiloxane film as a stimuli-responsive layer. The electrode was prepared by depositing silver nanowires on the surface of the STW film through a Meyer rod coating method. The film demonstrated outstanding performance with high transmittance (91.4%), a small curvature radius (2 mm) and excellent sheet resistance stability even after greater than 1500 bending cycles. The e-skin showed notable changes in electroluminescence from 0 to 150 kPa (where humans feel pain) and the sensitivity remains larger than 0.15 kPa−1 over the broad pressure range. The sensitivity in capacitance exhibited high sensitivity at 1.01 kPa−1 in the low-pressure regime, meanwhile, the luminescence exhibited a maximum value at 1.28 kPa−1 at medium pressure. Furthermore, the e-skin accurately mapped the spatial distribution of static and dynamic pressures through optical sensing. This work not only improves the sustainable development of materials in electrodes but also illustrates the potential of utilizing natural wood in high value-added e-skin. [ABSTRACT FROM AUTHOR]

• A single-layer microgels structure was integrated into wearable capacitive sensors. • A mechanistic insight into the generation of capacitive signals during sensing. • Its ability to detect physiological signals, bacteria, and metabolites. Flexible and wearable sensors have recently found wide applications in health monitoring and human-machine interaction. Desirable features in wearable sensors are high sensitivity and multi-targets detection capability in non-invasive manners. The sensitivity and multi-analyte detection capabilities are a function of the sensing material and sensor structures. Herein, we utilize a single-layer microgels structure integrated into a wearable capacitive sensor to realize both high sensitivity and multi-targets detections. We established a responsive sensing chain of analytes-the conformational changes of polymer chains-the morphology changes of the single-layer microgels structure-device capacitive signals. The conformational changes of microgel polymer chains due to physiological signals and metabolites in body fluids induce measurable capacitive signals generated by the sensors. This work provides mechanistic insight into a stimuli-responsive chain of analytes induced molecular conformation and thus morphology changes that induce the capacitive signal in the wearable sensors. This multipurpose sensor platform demonstrates the ability to detect bacteria such as E. coli and B. subitilis , metabolites such as uric acid in sweat, and physiological signals such as sound recognition, respiration, and pulse beat. [ABSTRACT FROM AUTHOR]

• A dual-mode electronic skin was obtained within the same sensing textile. • The textile can precisely perform temperature detection and pressure perception. • It provides a new conceptual design for the next-generation wearable devices. Flexible electronic skin is highly desired to realize the real-time tactile sensing and smart health assessment for human beings. Nevertheless, it is still a huge challenge to develop multifunctional electronic skin for human activity monitoring and body temperature detection in a single device without sensory interference. Here, a dual-mode electronic skin was obtained by vertically integrating the pressure sensing layer and temperature sensing layer within the same textile. The textile is composed of piezoelectric polyvinylidene fluoride nanofibrous membrane doped with zinc oxide nanoparticles (PVDF/ZnO NFM) and flexible thermal-resistance carbon nanofibers (CNFs). This all-in-one electronic skin textile can precisely perform pressure perception and temperature detection. For pressure sensing, a high sensitivity of 15.75 mV/kPa and 52.09 mV/kPa can be acquired within the pressure range of 4.9–25 kPa and 25–45 kPa, separately. In addition, it presents a temperature resolution of 0.381% per centigrade with a wide detection range of 25 °C to 100 °C. The electronic skin textile can perform multiple functions of ambient temperature detection, expiratory air temperature monitoring, external pressure perception, human pulse capture, and tactile spatial mapping with excellent sensing capacities. This study provides a new conceptual design for the next-generation wearable electronic skin. [ABSTRACT FROM AUTHOR]

• Designed dynamic network structure enables strong and robust PEG-PPy films. • Optimized PEG-PPy film shows both high conductivity and specific capacitance. • All-polymer ultrathin flexible supercapacitors (UF-SC) are made of PEG-PPy films. • The UF-SC exhibits high capacitance, mechanical and electrochemical robustness. Ultrathin flexible supercapacitors (UF-SCs) are highly desired for powering electronic skin devices. Most of current UF-SCs require electrochemically inactive substrates and binders to load electro-active materials, which limit the volumetric capacitance and stability of these UF-SCs. Herein, we report an all-polymer UF-SC based on conductive polypyrrole (PPy) film, which is constructed by the dynamic network formed by rigid PPy (~90 wt%) and soft polyethylene glycol (PEG, only 10 wt%) through supramolecular interactions. The network structure can effectively dissipate the destructive energy during mechanical or electrochemical deformation, making the PPy film strong and robust; and also helps to maximize the utilization of PPy, enabling the PPy film better electric conductivity and electrochemical capacitance than conventional PPy materials. After systematic optimization, we found the PEG600-PPy as the optimal electrode material, which can serve as electroactive material, current collector, and mechanical support simultaneously. Therefore, without using any substrate or current collector, these high-performance PEG600-PPy films can be directly used as electrodes for making all-polymer UF-SC. With high volumetric capacitance (547 F/cm3), outstanding mechanical and electrochemical stability, our all-polymer UF-SC (~80 μm in thickness, thinner than a piece of A4 paper) is a promising power device for electronic skin devices. [ABSTRACT FROM AUTHOR]

• Superhydrophobic conductive TPE/MWCNTs/PDMS film was fabricated at air/water interface. • The as-obtained sandwich-like film showed extreme repellency to water, salt, acid and alkali solutions. • The film is conductively sensitive and can be used as a wearable sensor in water wetted environment. Flexible and wearable sensors are of extreme importance for various practical applications in complex environments, such as electronic skin, body motion detection, etc. However, preparation of cost-effective and superhydrophobic wearable sensors with excellent flexibility, anti-corrosion, outstanding sensitivity and environmental adaptability remains challenging. Herein, a superhydrophobic flexible film is fabricated by spray-coating thermoplastic elastomer (TPE) solution on the upside of a multi-walled carbon nanotube (MWCNTs) sheet formed at the air/water interface, followed by treating the downside of MWCNTs sheet with polydimethylsiloxane (PDMS) pumped into the water. In the process, the covering of TPE on the MWCNTs made the sheet shrunk and increased the density of the conductive network. PDMS coating enhanced superhydrophobicity of the film, and binding fastness of the MWCNTs. The obtained sandwich-like TPE/MWCNTs/PDMS film had superior conductive sensitivity, large strain range (80%), fast and stable response time (60–80 ms) with great stability over 1000 stretching-relaxing cycles. Benefiting from the favorable superhydrophobic property, the fabricated film was capable of being put into liquid environment for quantifying the resistance under humid environments including moisture, acid, basic and salt conditions. It can be effectively used to measure wrist pulse and monitor various movements associated with different human body joints, such as finger, wrist, elbow. Moreover, the sensing film was able to capture the continuous signals in diverse atmosphere such as the area change of film, and the real-time stress response of drop impact. This study affords an innovative and promising track for multifunctional wearable sensors with wide applications in a harsh environment. [ABSTRACT FROM AUTHOR]

• A flexible and stretchable strain and self-powered multi-functional sensor was fabricated. • The electricity generated by temperature gradients supplies a power supply for the sensor. • The strain sensitivity was increased remarkably owing to addition of carbon nanocoils. • The sensor preliminary distinguishes strain and stimulus with different temperatures. The development of flexible and stretchable multi-functional sensors addresses the requirements for applications in fields of electronic skins, artificial intelligence, and health/structure monitoring. Here, we fabricated a novel self-powered strain-temperature dual-functional sensor based on composite films of carbon nanocoils (CNCs) and a conductive elastomeric blends of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and waterborne polyurethane (WPU). Owing to the high stretchability of helical-structured CNCs, high elasticity of WPU and multiple interfacial contacts between the conducting constitutes, the sensor exhibited a broad strain detection range of 0–50% and a high sensitivity with gauge factor (GF) of 25. Based on the Seebeck effect arising from the conducting polymer of PEDOT:PSS, the sensor-enabled both detection of temperature changes and strain deformations at a self-powered circumstance. To demonstrate its practical application as a wearable device, the senor was directly attached to the human skin. It not only detected subtle human motion and strain stimuli but also could distinguish the stimuli from either a warm or a cold objective by telling the difference in their temperature signals. This is the first time that the CNC-based composites are developed for use as a multi-functional sensing medium. Our self-powered strain-temperature dual-functional sensor demonstrates great potential in flexible devices and e-skin applications. [ABSTRACT FROM AUTHOR]

• A flexible CB/TPU foam with a pinnate-veined aligned porous structure was prepared. • The foam can both serve as a flexible strain sensor and an adsorption material. • The foam sensor has excellent sensing discernibility and high sensitivity. • The sensor exhibits superior response stability in a wide sensing range. In this paper, flexible conductive carbon black (CB)/thermoplastic polyurethane (TPU) foam (CTF) with an intriguing pinnate-veined aligned porous structure was fabricated via a unidirectional freeze-drying process. The density, porosity and average pore size of the composite foam are 0.13 g cm−3, 83.7% and 24.9 μm, respectively. CB particles are uniformly dispersed in the skeleton of the as-prepared foam, resulting in a low percolation threshold of 0.48 vol%. The CTF is capable of distinguishing different compressive strain by change of the relative resistance. Its responsive behaviors towards compressive strain present an excellent linear characteristic with a high gauge factor (GF) up to 1.55. In the piezoresistive tests, the CTF shows a fast response/relaxation time (150/150 ms), fascinating recoverability, excellent response stability within a wide workable detection range up to 80% strain (corresponding pressure of 584.4 kPa) and a superior durability (>10000 cycles), which is mainly related to the pinnate-veined aligned porous structure along the orientation direction. The CTF was then assembled as a wearable sensor to monitor various human motions such as arm bending, squatting, tiptoeing, etc., showing good detection performances. The sensor can also deal with water pollution through oil/water separation, suggesting its multifunctionality and promising prospects in complicated situations. [ABSTRACT FROM AUTHOR]