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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]

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 skins (e‐skins), which are mechanically compliant with human skin, are regarded as ideal electronic devices for noninvasive human–machine interaction and wearable devices. In order to fully mimic human skin, e‐skins should possess reliable mechanical properties and be able to resist external environmental factors like heat, cold, desiccation, and bacteria, while perceiving multiple external stimuli, such as temperature, humidity, and strain. Here, a transparent, mechanically robust, environmentally stable, versatile natural skin‐derived organohydrogel (NSD‐Gel) is nanoengineered through the integration of betaine, silver nanoparticles, and sodium chloride in a glycerol/water binary solvent. The transparent NSD‐Gel e‐skin exhibits outstanding tensile strength (7.33 MPa), puncture resistance, moisture retention, self‐regeneration, and antibacterial properties. Additionally, the NSD‐Gel e‐skin possesses enhanced cold/heat resistance and stimuli‐responsive characteristics that effectively sense environmental temperature and humidity changes, as well as physiological human body motion signals. In vitro and in vivo experiments show that the NSD‐Gel e‐skin confers desired biocompatibility and tissue protective properties even in extremely harsh environments (−196 °C to 100 °C). The NSD‐Gel e‐skin has great potential for applications in multidimensional wearable electronic devices, human‐machine interfaces, and artificial intelligence, generating a versatile platform for the development of high‐performance e‐skins with on‐demand properties. [ABSTRACT FROM AUTHOR]

In recent years, with the rapid development of flexible electronic devices, researchers have a great interest in the research of electronic skin (e-skin). Traditional e-skin, which is made of rigid integrated circuit chips, not only limits the overall flexibility, but also consumes a lot of power and poses certain security risks to the human body. In this paper, a wireless passive e-skin is designed based on the surface acoustic wave sensor (SAWS) of lithium niobate piezoelectric film. The e-skin has the advantages of small size, high precision, low power consumption, and good flexibility. With the multi-sensing function of stress, temperature, and sweat ion concentration, etc., the newly designed e-skin is a sensor platform for a wide range of external stimuli, and the measurement results can be directly presented in frequency. In order to explore the characteristic parameters and various application scenarios of the SAWS, finite element analysis is carried out using the simulation software; the relationship between the SAWS and various influencing factors is explored, and the related performance curve is obtained. These simulation results provide important reference and experimental guidance for the design and preparation of SAW e-skin. [ABSTRACT FROM AUTHOR]

MXene materials have the metallic conductivity of transition metal carbides. Among them, Ti3C2TX with an accordion structure has great application prospects in the field of wearable devices. However, flexible wearable electronic devices face the problem of single function in practical application. Therefore, it is particularly important to study a flexible sensor with multiple functions for electronic skin. In this work, the near-field electrohydrodynamic printing (NFEP) method was proposed to prepare the composite thin film with a micro/nanofiber structure on the flexible substrate using a solution of poly(vinylidene fluoride)/MXene nanosheet/reduced graphene oxide (PMR) nanocomposites as the printing solution. A dual-mode flexible sensor for electronic skin based on the PMR nanocomposite thin film was fabricated. The flexible sensor had the detection capability of the piezoresistive mode and the piezoelectric mode. In the piezoresistive mode, the sensitivity was 29.27 kPa−1 and the response/recovery time was 36/55 ms. In the piezoelectric mode, the sensitivity was 8.84 kPa−1 and the response time was 18.2 ms. Under the synergy of the dual modes, functions that cannot be achieved by a single mode sensor can be accomplished. In the process of detecting the pressure or deformation of the object, more information is obtained, which broadens the application range of the flexible sensor. The experimental results show that the dual-mode flexible sensor has great potential in human motion monitoring and wearable electronic device applications. [ABSTRACT FROM AUTHOR]

Highlights: Hydrogel demonstrates superior merits of strain (1586%), self-adhesion (113 kPa for pigskin), high conductivity and transparency (92%). The wearable sensors with a gauge factor up to 18.54, wide pressure sensing range (0–600 kPa) enable the detecting, quantifying, and monitoring of human activities. The hydrogels were developed as electronic skin, high output stretchable CTA-TENGs and explored using as wearable keyboards for human-machine interaction. To date, hydrogels have gained increasing attentions as a flexible conductive material in fabricating soft electronics. However, it remains a big challenge to integrate multiple functions into one gel that can be used widely under various conditions. Herein, a kind of multifunctional hydrogel with a combination of desirable characteristics, including remarkable transparency, high conductivity, ultra-stretchability, toughness, good fatigue resistance, and strong adhesive ability is presented, which was facilely fabricated through multiple noncovalent crosslinking strategy. The resultant versatile sensors are able to detect both weak and large deformations, which owns a low detection limit of 0.1% strain, high stretchability up to 1586%, ultrahigh sensitivity with a gauge factor up to 18.54, as well as wide pressure sensing range (0–600 kPa). Meanwhile, the fabrication of conductive hydrogel-based sensors is demonstrated for various soft electronic devices, including a flexible human–machine interactive system, the soft tactile switch, an integrated electronic skin for unprecedented nonplanar visualized pressure sensing, and the stretchable triboelectric nanogenerators with excellent biomechanical energy harvesting ability. This work opens up a simple route for multifunctional hydrogel and promises the practical application of soft and self-powered wearable electronics in various complex scenes. [ABSTRACT FROM AUTHOR]

Electronic skin (E‐skin) is widely used in bionic prosthesis, soft robotics, and wearable electronic devices. Waterproof and breathable membranes that provide a high level of protection and comfort are promising core materials for meeting the pressing demand for E‐skin. However, creating such materials exhibiting waterproofness, breathability, and ease of fabrication has proven to be a great challenge. In this paper, waterproof, breathable Modal‐based knitted fabric E‐skin is proposed by using a simple, low‐cost three‐step process including the graphene oxide (GO) loading, GO‐reducing, and polydimethylsiloxane loading. The prepared E‐skin is insensitive to common liquids in daily life including water, tea, milk, and coffee, showing superior waterproof capability. The breathability is also tested with a water vapor transmission rate of ≈13.6 mg cm−2 h−1. Besides, this E‐skin can achieve reliable human motion monitoring. The authors believe this E‐skin can provide a reliable principle for further design and development of waterproof and breathable electronic skin. [ABSTRACT FROM AUTHOR]

Development of stretchable solar cells to accommodate large strain without sacrificing the power conversion efficiency is challenging. This study presents a novel approach to manufacture highly stretchable solar cell arrays, which can be integrated into wearable medical devices to operate under challenging environments. Overcoming the limitations of rigid metal wires, liquid metal wires are employed to connect single crystal silicon solar cells, ensuring both high conversion efficiency and exceptional stretchability (up to 100%). The manufacturing process introduces embedding electrospinning films into elastic silicone substrates to create a tight bond between rigid solar cells and stretchable substrates with programmable strain capabilities. Notably, a stretchable interconnect wire is efficiently fabricated using the semi-liquid metal template printing technique and demonstrates remarkable conductivity (up to 6 × 106 S/m). Individual structural unit of solar cell presents an impressive tensile rate of 200%, and endures up to 5000 cycles of tensile testing. The overall solar cell array exhibits outstanding adaptability to extensive bending and twisting, with a mere 0.1% short-circuit current reduction in its maximum stretched state. The stretchable photovoltaic device is successfully employed in creating self-powered electronic skin for continuous real-time monitoring of parameters, showcasing its valuable potential in wearable medical electronic devices and comprehensive sports health monitoring. • A novel approach to manufacture highly stretchable solar cell arrays is developed. • A programmable strain substrate offers stable connections between rigid components and stretchable liquid metal wires. • A self-powered electronic skin is proposed showing its application as wearable medical electronic devices. [ABSTRACT FROM AUTHOR]

With the rapid advances in wearable technology, several excellent strain sensors have been developed. Recent strain sensors have met various requirements, such as mechanical applicability, rapid responsiveness, and high sensitivity. Nevertheless, the processing technology, wearing comfort, and safety of strain sensors, which have received inadequate attention, have greatly hindered their commercial development and large‐scale use. Through mature electrospinning and screen‐printing, a high‐performance, safe, comfortable, waterproof, breathable, economical, and reliable wearable strain sensor is simply and quickly prepared. This strain sensor has excellent repeatability and stability with remarkable sensitivity (maximum gauge factor = 520), a broad working strain range (500%), and an ultrafast response time (100 ms). Notably, the mechanical properties of the proposed strain sensor are similar to those of natural skin, making the sensor a good match to the skin. Additionally, the strain sensor has incomparable biofriendly, enabling long‐term harmless contact with the skin. To the best of the authors' knowledge, this is the first report on the optimization of flexible electronic equipment in terms of the manufacturing process, sensing performance, and wearing experience. The results of this study have important implications for the development and practical application of flexible electronics. [ABSTRACT FROM AUTHOR]

Electronic skin (e-skin) has brought us great convenience and revolutionized our way of life. However, due to physical or chemical aging and damage, they will inevitably be degraded gradually with practical operation. The emergence of self-healing materials enables e-skins to achieve repairment of cracks and restoration of mechanical function by themselves, meeting the requirements of the era for building durable and self-healing electronic devices. This work reviews the current development of self-healing e-skins with various application scenarios, including motion sensor, human–machine interaction and soft robots. The new application fields and present challenges are discussed; meanwhile, thinkable strategies and prospects of future potential applications are conferenced. [ABSTRACT FROM AUTHOR]

Photochromic hydrogels have promising prospects in areas such as wearable device, information encryption technology, optoelectronic display technology, and electronic skin. However, there are strict requirements for the properties of photochromic hydrogels in practical engineering applications, especially in some extreme application environments. The preparation of photochromic hydrogels with high transparency, high toughness, fast response, colour reversibility, excellent electrical conductivity, and anti-freezing property remains a challenge. In this study, a novel photochromic hydrogel (PAAm/SA/NaCl-Mo 7) was prepared by loading ammonium molybdate (Mo 7) and sodium chloride (NaCl) into a dual-network hydrogel of polyacrylamide (PAAm) and sodium alginate (SA) using a simple one-pot method. PAAm/SA/NaCl-Mo 7 hydrogel has excellent conductivity (175.9 S/cm), water retention capacity and anti-freezing properties, which can work normally at a low temperature of −28.4 °C. In addition, the prepared PAAm/SA/NaCl-Mo 7 hydrogel exhibits fast response (<15 s), high transparency (>70 %), good toughness (maximum elongation up to 1500 %), good cyclic compression properties at high compressive strains (60 %), good biocompatibility (78.5 %), stable reversible discolouration and excellent sensing properties, which can be used for photoelectric display, information storage and motion monitoring. This work provides a new inspiration for the development of flexible electronic skin devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Device–body interface is significant for acquiring high quality bio‐signals, preventing skin‐irritation, and minimizing the motion artifacts. However, low breathability of the typical substrate used in a flexible electronic device usually deteriorates the stability of device–body interface, which is imperative for long‐term application but commonly disregarded. In paper, a directional sweat transport and breathable electrode with three‐layer sandwiched structure is reported. The top hydrophilic hydrolyzed‐polyacrylonitrile (HPAN) layer and middle hydrophobic thermoplastic‐polyurethane (TPU) layer form Janus structure; and the bottom layer is an electrode layer of Ag nanowires (AgNWs). This dedicatedly designed electrode can transport sweat from skin to the top HPAN layer, while keeping low noise electrocardiogram (ECG) signal detection. In the trial of ECG monitoring, the results show that the electrode can achieve reliable recording with high signal noise rate (SNR) both in calm state (10.5 dB) and sweaty state (10.1 dB) with sweat tolerance. No allergy or obvious SNR degeneration is observed when utilizing the electrode owing to the effective sweat transport away from the device–body interface rather than accumulation. Finally, the application of the anti‐sweat accumulating electrode in wearable electronics is demonstrated. [ABSTRACT FROM AUTHOR]

Flexible conductive materials and flexible electronic devices are driving the development of the next generation of cutting‐edge wearable electronics. However, the existing hydrogel‐based flexible conductive materials have limited tensile capacity, low toughness, and poor anti‐fatigue performance, resulting in narrow sensing area and insufficient durability. In this paper, a conductive nanocomposite hydrogel with high ductility, toughness, and fatigue resistance is prepared by combining silver coated copper (Ag@Cu) nanoparticles with gelatin followed by one‐step immersion in sodium sulfate (Na2SO4) solution. The salting‐out of gelatin in Na2SO4 solution greatly improve the mechanical properties of this gelatin‐based hydrogel. The uniform distribution of Ag@Cu nanoparticles inside the whole hydrogel endow the composite hydrogel with excellent electrical conductivity (1.35 S m−1). In addition, it displayed high and stable tensile strain sensitivity over a wide strain range (gauge factor = 2.08). Therefore, the Ag@Cu‐Gel hydrogel is sensitive and stable enough to be successfully utilized as flexible wearable sensor for detecting human motion signals in real time, such as bending of human joints, swallowing, and throat vocalization. Furthermore, this hydrogel is also suitable for application as electronic skin for bionic robots. The above results demonstrate the promising application of Ag@Cu‐Gel hydrogel for wearable electronics. [ABSTRACT FROM AUTHOR]

Triboelectric electronic skins (E‐skins) can be used as primary interactive devices for human–machine interfaces (HMIs). However, devices for seamless on‐skin operations must be soft and deformable, and attachable to and compatible with the skin. In this paper, a substrate‐free, skin‐compatible, skin‐attachable, mechanically deformable, and self‐powered E‐tattoo sticker consisting of carbon nanotubes (CNTs) and silk nanofibers (SNFs) is presented. The E‐tattoo can be imperceptibly tattooed on the skin and removed with water. When the device touches naked skin, triboelectric signals are generated. Because of the micro‐to‐nano hierarchical pores (with high surface‐to‐volume ratios), contact‐induced electrification generates a power density of ≈6 mW m−2 and pressure sensitivity of ≈0.069 kPa−1. The power generated on the tattooed skin can activate small electronic devices. Moreover, whole‐body joint movements can be monitored and tactile movements can be mapped by reading the generated electrical signals. The presented E‐tattoo system can promote the development of flexible energy and sensor systems for self‐powered, energy‐autonomous, imperceptible E‐skin devices for HMIs and artificial intelligent robotics and prostheses. [ABSTRACT FROM AUTHOR]

High‐performance biodegradable electronic devices are being investigated to address the global electronic waste problem. In this work, a fully biodegradable ferroelectric nanogenerator‐driven skin sensor with ultrasensitive bimodal sensing capability based on edible porcine skin gelatine is demonstrated. The microstructure and molecular engineering of gelatine induces polarization confinement that gives rise the ferroelectric properties, resulting in a piezoelectric coefficient (d33) of ≈24 pC N−1 and pyroelectric coefficient of ≈13 µC m−2K−1, which are 6 and 11.8 times higher, respectively, than those of the conventional planar gelatine. The ferroelectric gelatine skin sensor has exceptionally high pressure sensitivity (≈41 mV Pa−1) and the lowest detection limit of pressure (≈0.005 Pa) and temperature (≈0.04 K) ever reported for ferroelectric sensors. In proof‐of‐concept tests, this device is able to sense the spatially resolved pressure, temperature, and surface texture of an unknown object, demonstrating potential for robotic skins and wearable electronics with zero waste footprint. [ABSTRACT FROM AUTHOR]

The realization of liquid metal‐based wearable systems will be a milestone toward high‐performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal‐based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre‐inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as "bricks" and strain‐sensitive Ag film as "mortar" is developed, which breaks the long‐standing sensitivity bottleneck of liquid metal‐based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal‐based strain sensors rival the state‐of‐art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut‐through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid‐metal paths and create crack‐free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal‐based electronic skins, and reveals a pathway for sensor development via crack engineering. [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]

Compliance sensation is a unique feature of the human skin that electronic devices could not mimic via compact and thin formfactor devices. Due to the complex nature of the sensing mechanism, up to now, only high-precision or bulky handheld devices have been used to measure compliance of materials. This also prevents the development of electronic skin that is fully capable of mimicking human skin. Here, we developed a thin sensor that consists of a strain sensor coupled to a pressure sensor and is capable of identifying compliance of touched materials. The sensor can be easily integrated into robotic systems due to its small form factor. Results showed that the sensor is capable of classifying compliance of materials with high sensitivity allowing materials with various compliance to be identified. We integrated the sensor to a robotic finger to demonstrate the capability of the sensor for robotics. Further, the arrayed sensor configuration allows a compliance mapping which can enable humanlike sensations to robotic systems when grasping objects composed of multiple materials of varying compliance. These highly tunable sensors enable robotic systems to handle more advanced and complicated tasks such as classifying touched materials. [ABSTRACT FROM AUTHOR]

Human machine interface (HMI) devices, which can convert human motions to electrical signals to control/charge electronic devices, have attracted tremendous attention from the engineering and science fields. Herein, the high output voltage from a nonpiezoelectric meso‐poly(lactic acid) (meso‐PLA) electret‐based triboelectric nanogenerator (NG) is combined with the relatively high current from a double‐layered poly(l‐lactic acid) (PLLA)‐based piezoelectric nanogenerator (PENG) for an E‐skin (electronic skin) (HMI) device application. The hybrid NG with a cantilever structure can generate an output voltage of 70 V and a current of 25 µA at the resonance frequency of 19.7 Hz and a tip load of 4.71 g. Moreover, the output power of the hybrid NG reaches 0.31 mW, which is 11% higher than that from the PLLA‐based PENG. Furthermore, it is demonstrated that the PLA‐based hybrid NG can be used to turn a light‐emitting diode light on and off through an energy management circuit during a bending test. Finally, it is demonstrated that the PLA‐based woven E‐skin device can generate the output signals of 35 V (Voc) and 1 µA (Isc) during an elbow bending test. The advantages of biocompatible, ease of fabrication, and relatively high output power in the hybrid NG device show great promise for future E‐skin applications. [ABSTRACT FROM AUTHOR]

Flexible piezoresistive sensors hold a great potential with broad application spectrum in human-computer interaction and wearable electronic devices. Inspired by human touch sensation architecture, we report a new type of flexible piezoresistive sensor with ultrawide sensing range and highrobustness by engineering biomimetic structure and carbon black (CB)/MXene/SR/fiber nanocomposites. The facile fabrication processes, piezoresistive sensing mechanism, and performance of the device are comprehensively investigated. The sensor provides a high sensitivity of 2.18 kPa−1, ultrawide linear sensing range of 0.1–1700 kPa, fast response time (∼100 ms), and reliable durability (>5000 cycles). Furthermore, the developed flexible devices have been effectively implemented as electronic skin, demonstrating potential functions in manipulator soft grabbing and human movement monitoring. Such architecture paves the way for great application in the fields of healthcare, human–machine interface, and extremely large pressure monitoring. [ABSTRACT FROM AUTHOR]

Abstract: Electronic skin (E‐skin) imitates human skin by converting external stimuli into electrical signals. E‐skin requires high flexibility and a high level of device integration. Unlike conventional E‐skin creation methods, a highly sensitive pressure sensor matrix (100 pixels cm−2) made of position‐registered elastic conductive microparticles (MPs) is created. The MPs form a Schottky junction with the bottom electrode and the current through the junction is sensitive to external pressure, forming a simple one‐selector two‐terminal device array. The Schottky junction eliminates the electrical cross talks between the sensor pixels consisting of 64 MPs in each. The flexible pressure sensor matrix is used as an artificial fingertip for Braille reading and as an electronic scale based on detailed force distribution. This work opens up the possibility that assembled MPs, which have been a long‐standing research topic in academia, can be used to make practical electronic devices. [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]

This letter reports on an electronic device that can work as a tactile force sensor with a high spatial resolution and sensitivity. It integrates a thin-film piezoelectric sensor with a thin-film transistor (TFT) to form a dual-gate force-sensitive TFT. The piezoelectric sensor acts as a top-sensing terminal, which is charge-gated. An analytical model of the device is given to elaborate how the output current varies with the applied force, and a numerical study is conducted to evaluate its sensitivity, noise, and dynamic range. The integrated sensor can be potentially pixelated to form a high-resolution tactile sensor array, promising for electronic skin applications. [ABSTRACT FROM PUBLISHER]

In this paper we present a new optical, flexible pressure sensor that can be applied as smart skin to a robot or to consumer electronic devices. We describe a mechano-optical transduction principle that can allow the encoding of information related to an externally applied mechanical stimulus, e.g., contact, pressure and shape of contact. The physical embodiment that we present in this work is an electronic skin consisting of eight infrared emitters and eight photo-detectors coupled together and embedded in a planar PDMS waveguide of 5.5 cm diameter. When a contact occurs on the sensing area, the optical signals reaching the peripheral detectors experience a loss because of the Frustrated Total Internal Reflection and deformation of the material. The light signal is converted to electrical signal through an electronic system and a reconstruction algorithm running on a computer reconstructs the pressure map. Pilot experiments are performed to validate the tactile sensing principle by applying external pressures up to 160 kPa. Moreover, the capabilities of the electronic skin to detect contact pressure at multiple subsequent positions, as well as its function on curved surfaces, are validated. A weight sensitivity of 0.193 gr-1 was recorded, thus making the electronic skin suitable to detect pressures in the order of few grams. [ABSTRACT FROM AUTHOR]

Soft biomimetic electronic devices primarily comprise an electronic skin (e-skin) capable of implementing various wearable/implantable applications such as soft human–machine interfaces, epidermal healthcare systems, and neuroprosthetics owing to its high mechanical flexibility, tissue conformability, and multifunctionality. The conformal contact of the e-skin with living tissues enables more precise analyses of physiological signals, even in the long term, as compared to rigid electronic devices. In this regard, e-skin can be considered as a promising formfactor for developing highly sensitive and transparent pressure sensors. Specifically, to minimize the modulus mismatch at the biotic–abiotic interface, transparent-conductive hydrogels have been used as electrodes with exceptional pressing durability. However, critical issues such as dehydration and low compatibility with elastomers remain a challenge. In this paper, we propose a skin-like transparent polymer-hydrogel hybrid pressure sensor (HPS) with microstructures based on the polyacrylamide/sodium-alginate hydrogel and p-PVDF-HFP-DBP polymer. The encapsulated HPS achieves conformal contact with skin due to its intrinsically stretchable, highly transparent, widely sensitive, and anti-dehydrative properties. We believe that the HPS is a promising candidate for a robust transparent epidermal stretchable-skin device. [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]

A sensitive polydimethylsiloxane (PDMS) based wearable piezoresistive sensor based on Ag nanoparticles@multi-walled carbon nanotubes nanocomposite (AgCNT) films prepared by a simple, green, cost-effective, and easy to industrially scalable approach of tip-sonication with spray process was proposed for the application in human motion detecting. • A green, cost-effective, and easy to scalable approach of tip-sonication with spray process is used to synthesize AgNP@MWCNT aqueous solution. • The simple device assembly technology for biocompatitive AgNP@MWCNT based wearable sensor can be scalable. • Decoration of AgNPs on MWCNTs pushes the wearable sensor to have improved sensing performances. • Finger movement recognition is sampled by testing the exceptional resistance change, exhibiting its practicality. Fabricating flexible/stretchable physical sensors has emerged as a topic of interest owing to the huge market demand for wearable medical devices and electronic skins for the regular and continuous monitoring of human health information. Herein, we report a green and efficient strategy for constructing a sensitive polydimethylsiloxane-derived wearable piezoresistive sensor, based on silver nanoparticle (AgNP)@multi-walled carbon nanotube (CNT) nanocomposite films. The developed sensing material exhibits good flexibility and electrical conductivity because of the interfacial effect between AgNPs and CNTs, leading to excellent sensing performances with good sensitivity, fast response time, low operating voltage, and mechanical stability, as measured under different pressure loading, bending angle, and percentage elongation conditions. In addition, finger movement recognition is sampled by testing the exceptional resistance change, and its practicality was further proven. Thus, the developed material has potential for application in wearable electronics. Notably, the entire sensor fabrication process is low-cost, environment-friendly, scalable, and industrially available, which is beneficial for industrial applications. [ABSTRACT FROM AUTHOR]

Self-powered flexible sensors play an increasingly important role in wearable and even implantable electronic devices. Silk protein is an ideal material for flexible sensors because of its terrific biocompatibility and controllable degradation rate. Here, we overcome the problem of mechanical flexibility and poor electrical conductivity of proteins, and develop a highly transparent, biocompatible, full-degradable and flexible triboelectric nanogenerator (Bio-TENG) for energy harvesting and wireless sensing. First, the mechanical flexibility of the silk protein film is greatly enhanced by the mesoscopic functionalization of regenerated silk fibroin (RSF) via adding glycerol and polyurethane (PU). Second, hollow silver nanofibers are constructed on the silk film to form an air-permeable, stretchable, biocompatible and degradable thin layer and utilized as friction electrode. The obtained Bio-TENG demonstrates high transparency (83% by one Ag gird layer), stretchability (Ɛ = 520%) and an instantaneous peak power density of 0.8 W m−2 that can drive wearable electronics. Besides, the Bio-TENG can work as artificial electronic skin for touch/pressure perception, and also for wirelessly controlling Internet of Things as a switch. • Conductive and ultrastretchable (520%) silk protein film was prepared. • Hollow silver nanofibers were constructed on silk film to enhance conductivity. • Bio-TENG was air permeable, biocompatible, stretchable and degradable. • Bio-TENG was applied for energy harvesting and wirelessly controlling Internet of Things. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors with high sensitivity, broad working range, and good scalability are highly desired for the next generation of wearable electronic devices. However, manufacturing of such pressure sensors still remains challenging. A large‐area compliant and cost‐effective process to fabricate high‐performance pressure sensors via a combination of mesh‐molded periodic microstructures and printed side‐by‐side electrodes is presented. The sensors exhibit low operating voltage (1 V), high sensitivity (20.9 kPa−1), low detection limit (7.4 Pa), fast response/recovery time (23/18 ms), and excellent reliability (over 10 000 cycles). More importantly, they exhibit ultra‐broad working range (7.4–1 000 000 Pa), high tunability, large‐scale production feasibility, and significant advantage in format miniaturization and creating sensor arrays with self‐defined patterns. The versatility of these devices is demonstrated in various human activity monitoring and spatial pressure mapping as electronic skins. Furthermore, utilizing printing methods, a flexible smart insole with a high level of integration for both foot pressure and temperature mapping is demonstrated. The scalable and cost‐effective manufacturing along with the good comprehensive performance of the pressure sensors makes them very attractive for future development of wearable smart devices and human–machine interfaces. [ABSTRACT FROM AUTHOR]

Soft and conformable electronics are emerging rapidly and is envisioned as the future of next-generation electronic devices where devices can be readily deployed in various environments, such as on-body, on-skin or as a biomedical implant. Modern day electronics require electrical conductors as the fundamental building block for stretchable electronic devices and systems. In this review, we will study the various strategies and methods of designing and fabricating materials which are conductive, stretchable and self-healable, and explore relevant applications such as flexible and stretchable sensors, electrodes and energy harvesters. [ABSTRACT FROM AUTHOR]

Capacitive strain sensors could become an important component of electronic skin (E‐skin) due to their low hysteresis and high linearity. However, to fully mimic the functionality of human skin, a capacitive strain sensor should be stretchable and self‐healable. The development of such a sensor is limited by electrode materials which generally lack self‐healability and/or stretchability. A highly stretchable and self‐healing MXene (Ti3C2Tx)/polyvinyl alcohol (PVA) hydrogel electrode is developed for use in capacitive strain sensors for E‐skin. The incorporation of MXene into the PVA enhances the conductivity and self‐healability of the hydrogel. The electrode exhibits high stretchability at break (≈1200%) and instantaneous self healing (healing time ≈ 0.15 s). A capacitive sensor based on these electrodes shows high linearity, up to 200%, low hysteresis, a sensitivity of ≈0.40, and good mechanical durability (a 5.8% reduction in relative capacitance change after 10 000 cycles). Moreover, this sensor maintains its performance after a self‐healing test, proving its potential for the monitoring of human motion. [ABSTRACT FROM AUTHOR]

A tactile sensor is an indispensable component for electronic skin, mimicking the sensing function of organism skin. Various sensing materials and microstructures have been adopted in the fabrication of tactile sensors. Herein, we propose a highly sensitive flexible tactile sensor composed of nanocomposites with pyramid and irregularly rough microstructures and implement a comparison of piezoresistive properties of nanocomposites with varying weight proportions of multi-wall nanotubes and carbon black particles. In addition to the simple and low-cost fabrication method, the tactile sensor can reach high sensitivity of 3.2 kPa−1 in the range of <1 kPa and fast dynamic response of 217 ms (loading) and 81 ms (recovery) at 40 kPa pressure. Moreover, body movement monitoring applications have been carried out utilizing the flexible tactile sensor. A sound monitoring application further indicates the potential for applications in electronic skin, human–computer interaction, and physiological detection. [ABSTRACT FROM AUTHOR]