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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]

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]

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 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]

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]

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]

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]

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]

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]

The conformal integration of the electronic skin on the non‐developable surface is in great demand for the comprehensive tactile sensing of robotics and prosthetics. However, the current techniques still encounter obstacles in achieving conformal integration of film‐like electronic skin on non‐developable surfaces with substantial curvatures for contact pressure detection and tactile mapping. In this paper, by utilizing the 3D printing technology to prepare the 3D electrode array in the structural component following its surface curvature, and covering it with a molded functional shell to form the pressure sensitive iontronic interface, a device is proposed to achieve high‐sensitive pressure detection and high‐fidelity tactile mapping on a complicated non‐developable surface, called structural electronic skin (SES). The SES is prepared in a 3D printed fingertip with 46 tactile sensing units distributed on its curved surface, achieving the integration of both structural and tactile functions in a single component. By integrating the smart fingertip into a dexterous hand, a series of demonstrations are presented to show the dead‐zone free pressure detection and tactile mapping with high sensitivity, for instance, 2D pulse wave monitoring and robotic injection in a medical robot, object recognition and compliant control in a smart prosthesis. [ABSTRACT FROM AUTHOR]

As key interfaces for the disabled, optimal prosthetics should elicit natural sensations of skin touch or proprioception, by unambiguously delivering the multimodal signals acquired by the prosthetics to the nervous system, which still remains challenging. Here, a bioinspired temperature‐pressure electronic skin with decoupling capability (TPD e‐skin), inspired by the high‐low modulus hierarchical structure of human skin, is developed to restore such functionality. Due to the bionic dual‐state amplifying microstructure and contact resistance modulation, the MXene TPD e‐skin exhibits high sensitivity over a wide pressure range and excellent temperature insensitivity (91.2% reduction). Additionally, the high‐low modulus structural configuration enables the pressure insensitivity of the thermistor. Furthermore, a neural model is proposed to neutrally code the temperature‐pressure signals into three types of nerve‐acceptable frequency signals, corresponding to thermoreceptors, slow‐adapting receptors, and fast‐adapting receptors. Four operational states in the time domain are also distinguished after the neural coding in the frequency domain. Besides, a brain‐like machine learning‐based fusion process for frequency signals is also constructed to analyze the frequency pattern and achieve object recognition with a high accuracy of 98.7%. The TPD neural system offers promising potential to enable advanced prosthetic devices with the capability of multimodality‐decoupling sensing and deep neural integration. [ABSTRACT FROM AUTHOR]

Electronic skins (E‐skins) capable of biomechanical/bioelectrical signal acquisition are intensively pursued for human‐centered healthcare of daily life. For practical use, it is highly desired, yet challenging, to mass‐produce E‐skins that are soft and breathable for wearing comfort, skin‐adhesive for robust signal acquisition, multi‐signal sensing for enhanced healthcare data. Herein, a scalable fabrication strategy for a bioinspired E‐skin (SPRABE‐skin) with a multi‐layered architecture is reported that integrates skin‐like softness, self‐protection, self‐adhesion, breathability, and bimodal sensing in a single patch. The fibrous thermoplastic polyurethane (TPU) scaffold endows the SPRABE‐skin with tissue‐like softness (Young's modulus of 3.36 MPa) and stretchability, good permeability to water vapor, and self‐protection against adverse loading events. A strain sensing layer composed of MXene‐carbon nanotubes@TPU (MXene‐CNT@TPU) composition exhibits ultra‐high sensitivity in a wide sensing range (gauge factor at strain of 485% reaches 63 494). An electrode layer made of MXene‐waterborne polyurethane (MXene‐WPU) provides a highly adhesive electrode‐skin interface, which enables the acquisition of biopotentials, such as electrocardiograph (ECG), electromyograph (EMG), electroencephalo‐graph (EEG), with improved fidelity even under various dynamic interferences. Finally, a SPRABE‐skin based human‐centered healthcare system is demonstrated that realizes the wireless, long‐duration, and dynamic monitoring of ECG and running activities. [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]

In this work, a capacitive flexible tactile sensor based on the composite dielectric layer with a C-type symmetrical structure is proposed to improve the sensing performance through the introduction of a precise structure. Combined with simulations and experiments, the influence of the structural characteristics of the tactile sensor on its sensitivity is investigated, the correlation between the signal output of the sensor and the loading pressure is shown for different structural parameter designs, and the structure of the sensor is optimized. Data results display that the tactile sensor proposed in this work exhibits a lower detection limit (8.6 Pa) and an ultra-wide linear sensing range (8.6–500 kPa). In addition, from the 55 ms response time of the sensor and 2000 cycles of experiments, it can be concluded that the sensor possesses good repeatability and durability, and can achieve more accurate measurement results in motion detection, soft robots, and electronic skin. [ABSTRACT FROM AUTHOR]

Wearable hydrogel sensors provide a user-friendly option for wearable electronics and align well with the existing manufacturing strategy for connecting and communicating with large numbers of Internet of Things devices. This is attributed to their components and structures, which exhibit exceptional adaptability, scalability, bio-compatibility, and self-healing properties, reminiscent of human skin. This review focuses on the recent research on principal structural elements of wearable hydrogels: toughening networks and conductive networks, highlighting the strategies for enhancing mechanical and electrical properties. Wearable hydrogel sensors are categorized for an extensive exploration of their composition, mechanism, and design approach. This review provides a comprehensive understanding of wearable hydrogels and offers guidance for the design of components and structures in order to develop high-performance wearable hydrogel sensors. [ABSTRACT FROM AUTHOR]

Bionic flexible sensors are a new type of biosensor with high sensitivity, selectivity, stability, and reliability to achieve detection in complex natural and physiological environments. They provide efficient, energy-saving and convenient applications in medical monitoring and diagnosis, environmental monitoring, and detection and identification. Combining sensor devices with flexible substrates to imitate flexible structures in living organisms, thus enabling the detection of various physiological signals, has become a hot topic of interest. In the field of human health detection, the application of bionic flexible sensors is flourishing and will evolve into patient-centric diagnosis and treatment in the future of healthcare. In this review, we provide an up-to-date overview of bionic flexible devices for human health detection applications and a comprehensive summary of the research progress and potential of flexible sensors. First, we evaluate the working mechanisms of different classes of bionic flexible sensors, describing the selection and fabrication of bionic flexible materials and their excellent electrochemical properties; then, we introduce some interesting applications for monitoring physical, electrophysiological, chemical, and biological signals according to more segmented health fields (e.g., medical diagnosis, rehabilitation assistance, and sports monitoring). We conclude with a summary of the advantages of current results and the challenges and possible future developments. [ABSTRACT FROM AUTHOR]

In recent years, extensive research has been conducted on the development of high-performance flexible tactile sensors, pursuing the next generation of highly intelligent electronics with diverse potential applications in self-powered wearable sensors, human–machine interactions, electronic skin, and soft robotics. Among the most promising materials that have emerged in this context are functional polymer composites (FPCs), which exhibit exceptional mechanical and electrical properties, enabling them to be excellent candidates for tactile sensors. Herein, this review provides a comprehensive overview of recent advances in FPCs-based tactile sensors, including the fundamental principle, the necessary property parameter, the unique device structure, and the fabrication process of different types of tactile sensors. Examples of FPCs are elaborated with a focus on miniaturization, self-healing, self-cleaning, integration, biodegradation, and neural control. Furthermore, the applications of FPC-based tactile sensors in tactile perception, human–machine interaction, and healthcare are further described. Finally, the existing limitations and technical challenges for FPCs-based tactile sensors are briefly discussed, offering potential avenues for the development of electronic products. [ABSTRACT FROM AUTHOR]

Wearable hydrogel sensors provide a user-friendly option for wearable electronics and align well with the existing manufacturing strategy for connecting and communicating with large numbers of Internet of Things devices. This is attributed to their components and structures, which exhibit exceptional adaptability, scalability, bio-compatibility, and self-healing properties, reminiscent of human skin. This review focuses on the recent research on principal structural elements of wearable hydrogels: toughening networks and conductive networks, highlighting the strategies for enhancing mechanical and electrical properties. Wearable hydrogel sensors are categorized for an extensive exploration of their composition, mechanism, and design approach. This review provides a comprehensive understanding of wearable hydrogels and offers guidance for the design of components and structures in order to develop high-performance wearable hydrogel sensors. [ABSTRACT FROM AUTHOR]

Epidermal electronics have been attracting considerable attention due to their various potential applications in human‐computer interaction and health monitoring. However, because of the lack of a self‐adhesive and stable interconnect method between epidermal electronic sensors and rigid circuit boards, there remain difficulties in detecting body signals accurately by epidermal electronic sensors in daily life. Here, a 3D helical on‐skin interconnect is first introduced for epidermal electronics sensors. Inspired by the structure of the accordion lantern, the interconnect is composed of two electrospinning polyurethane (PU) fiber films and a helical metal fiber. The helical metal fiber acts as a stable conductor with stretchability, and the PU fiber film with polydimethylsiloxane provides a self‐adhesive substrate. Mechanical simulations and tests prove that the proposed interconnect can laminate conformally and unobtrusively onto human skin with excellent electrical stability (less than 0.5% electrical resistance change upon 100% elongation). Furthermore, based on the proposed interconnect, an all‐in‐one sensor‐interconnect design is presented, which endows the epidermal electronic systems with anti‐motion interference capability. A gesture identification wristband system realized by a single all‐in‐one strain sensor is demonstrated. Besides, a wireless on‐skin system that accurately monitors dynamic 12‐lead electrocardiographic is successfully built using all‐in‐one electrodes. [ABSTRACT FROM AUTHOR]

Pressure sensors show significant potential applications in health monitoring, bio-sensing, electronic skin, and tactile perception. Consequently, tremendous research interest has been devoted to the development of high-performance pressure sensors. In this paper, recent progress on the polymer composite-based flexible pressure sensor is reviewed. The parameters of pressure sensors, including sensitivity, linear response range, detection limit, response speed, and reliability, are first introduced. Secondly, representative types of pressure sensors and relevant working principles are introduced and discussed. After that, the applications in human physiology monitoring, health monitoring, artificial skin, and self-powered smart system are listed and discussed in detail. Finally, the remaining challenges and outlook of polymer composite-based flexible sensors are summarized at the end of this review paper. This work should have some impact on the development of high-performance flexible pressure sensors. [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]

Highlights: Bioinspired directional moisture-wicking electronic skin (DMWES) was successfully realized by surface energy gradient and push–pull effect via the design of distinct hydrophobic-hydrophilic difference. The DMWES membrane showed excellent comprehensive pressure sensing performance with high sensitivity and good single-electrode triboelectric nanogenerator performance The superior pressure sensing and triboelectric performance enabled the DMWES for all-range healthcare sensing, including accurate pulse monitoring, voice recognition, and gait recognition. Electronic skins can monitor minute physiological signal variations in the human skins and represent the body's state, showing an emerging trend for alternative medical diagnostics and human–machine interfaces. In this study, we designed a bioinspired directional moisture-wicking electronic skin (DMWES) based on the construction of heterogeneous fibrous membranes and the conductive MXene/CNTs electrospraying layer. Unidirectional moisture transfer was successfully realized by surface energy gradient and push–pull effect via the design of distinct hydrophobic-hydrophilic difference, which can spontaneously absorb sweat from the skin. The DMWES membrane showed excellent comprehensive pressure sensing performance, high sensitivity (maximum sensitivity of 548.09 kPa−1), wide linear range, rapid response and recovery time. In addition, the single-electrode triboelectric nanogenerator based on the DMWES can deliver a high areal power density of 21.6 µW m−2 and good cycling stability in high pressure energy harvesting. Moreover, the superior pressure sensing and triboelectric performance enabled the DMWES for all-range healthcare sensing, including accurate pulse monitoring, voice recognition, and gait recognition. This work will help to boost the development of the next-generation breathable electronic skins in the applications of AI, human–machine interaction, and soft robots. [ABSTRACT FROM AUTHOR]

Electronic skin (e‐skin) is facing new challenges owing to the development of artificial intelligence. Among the existing working modes, triboelectric‐based e‐skin (TES) can convert mechanical energy into electrical energy and can be used as a sensor to directly output an electrical signal without additional power supply. Therefore, with the advantages of self‐powering, low cost, and wide application of materials, TES provides a new concept for developing e‐skin and has been extensively studied. Starting from TES, this review describes the working principle and application of triboelectric nanogenerators (TENGs) in e‐skin. Existing materials for TES can be mainly divided into fiber textiles, gels, liquid‐based materials, and degradable materials. Therefore, the material section is divided into four chapters to describe the properties of each material. As for the structure of TES, the transition from single‐channel to multi‐channel for the multifunctionalization of TES is described, and the various links required for a TES‐based closed‐loop system are introduced. Based on these advanced units, the recent progress as well as the current challenges and future development prospects of TES are reviewed. [ABSTRACT FROM AUTHOR]

Flexible sensors are the essential foundations of pressure sensing, microcomputer sensing systems, and wearable devices. The flexible tactile sensor can sense stimuli by converting external forces into electrical signals. The electrical signals are transmitted to a computer processing system for analysis, realizing real-time health monitoring and human motion detection. According to the working mechanism, tactile sensors are mainly divided into four types—piezoresistive, capacitive, piezoelectric, and triboelectric tactile sensors. Conventional silicon-based tactile sensors are often inadequate for flexible electronics due to their limited mechanical flexibility. In comparison, polymeric nanocomposites are flexible and stretchable, which makes them excellent candidates for flexible and wearable tactile sensors. Among the promising polymers, conjugated polymers (CPs), due to their unique chemical structures and electronic properties that contribute to their high electrical and mechanical conductivity, show great potential for flexible sensors and wearable devices. In this paper, we first introduce the parameters of pressure sensors. Then, we describe the operating principles of resistive, capacitive, piezoelectric, and triboelectric sensors, and review the pressure sensors based on conjugated polymer nanocomposites that were reported in recent years. After that, we introduce the performance characteristics of flexible sensors, regarding their applications in healthcare, human motion monitoring, electronic skin, wearable devices, and artificial intelligence. In addition, we summarize and compare the performances of conjugated polymer nanocomposite-based pressure sensors that were reported in recent years. Finally, we summarize the challenges and future directions of conjugated polymer nanocomposite-based sensors. [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]

Recent advancement in wearable and robot-assisted healthcare technology gives rise to the demand for smart interfaces that allow more efficient human-machine interaction. In this paper, a hydrogel-based soft sensor for subtle touch detection is proposed. Adopting the working principle of a biomedical imaging technology known as electrical impedance tomography (EIT), the sensor produces images that display the electrical conductivity distribution of its sensitive region to enable touch detection. The sensor was made from a natural gelatin hydrogel whose electrical conductivity is considerably less than that of human skin. The low conductivity of the sensor enabled a touch-detection mechanism based on a novel short-circuiting approach, which resulted in the reconstructed images being predominantly affected by the electrical contact between the sensor and fingertips, rather than the conventionally used piezoresistive response of the sensing material. The experimental results indicated that the proposed sensor was promising for detecting subtle contacts without the necessity of exerting a noticeable force on the sensor. [ABSTRACT FROM AUTHOR]

Electronic skin (e-skin) has attracted tremendous interest due to its diverse potential applications, including in physiological signal detection, health monitoring, and artificial throats. However, the major drawbacks of traditional e-skin are the weak adhesion of substrates, incompatibility between sensitivity and stretchability, and its single function. These shortcomings limit the application of e-skin and increase the complexity of its multifunctional integration. Herein, the synergistic network of crosslinked SWCNTs within and between multilayered graphene layers was directly drip coated onto the PU thin film with self-adhesion to fabricate versatile e-skin. The excellent mechanical properties of prepared e-skin arise from the sufficient conductive paths guaranteed by SWCNTs in small and large deformation under various strains. The prepared e-skin exhibits a low detection limit, as small as 0.5% strain, and compatibility between sensitivity and stretchability with a gauge factor (GF) of 964 at a strain of 0–30%, and 2743 at a strain of 30–60%. In physiological signals detection application, the e-skin demonstrates the detection of subtle motions, such as artery pulse and blinking, as well as large body motions, such as knee joint bending, elbow movement, and neck movement. In artificial throat application, the e-skin integrates sound recognition and sound emitting and shows clear and distinct responses between different throat muscle movements and different words for sound signal acquisition and recognition, in conjunction with superior sound emission performance with a sound spectrum response of 71 dB (f = 12.5 kHz). Overall, the presented comprehensive study of novel materials, structures, properties, and mechanisms offers promising potential in physiological signals detection and artificial throat applications. [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]

Advances in stretchable and flexible sensors are responding to the emerging demand of wearable and portable smart electronics. A core component of these electronics are tactile sensing devices which detect external stimuli and obtain in-time information from the surroundings. A fusion of electronics, physics and materials science, tactile sensors have great potential in robots, biomedicine, flexible interactive devices, and several other applications. By integrating with a flexible polymer matrix conductive materials (nanometals, carbon nanomaterials, conducting polymers, etc.), which are either embedded in the matrix or surface-coated or sandwiched between films, the resulting conductive polymer-based composites are promising for flexible tactile sensors. This review summarizes recent advances across different types of tactile sensors, including piezoresistive, capacitive, piezoelectric, and triboelectric. Examples are highlighted on how the combination of new materials, unique structure designs, and novel fabrication methods can advance the progress of tactile sensors. Enhanced sensing performance and mechanical properties can be realized by integrating nanomaterials into polymer substrates. This review provides guidelines for further selection of polymer-based materials and design of tactile sensors. [ABSTRACT FROM AUTHOR]

Multimodal force identification by electronic skin (E‐skin) provides comprehensive and precise tactile information that can enhance elaborated functions of fine tactile discrimination, robotic manipulation, and gesture recognition. However, it remains a great challenge to realize such complicated functions from a highly simplified E‐skin sensing system. Here, mimicking the multi‐mechanoreceptor synergistic effect in human skin, a simple, thin, soft, intelligent tactile sensor composed of an asymmetrically arrangement of strain sensing units array for multimodal tactile information decoding is reported. The E‐skin type tactile sensor exhibits good performance with excellent sensitivity for shear force (2.5 N–1), vertical force (0.11 kPa–1), that enables 3D force refactoring, as well as accurate recognition of sliding force for direction tracking. Another unique feature of the E‐skin type tactile sensor is the side force screen effect, that allows the tactile sensor to yield great accuracy and a gauge factor of 1492 in strain measuring. Furthermore, integration of the sensors into E‐skin array offers the capability of capturing dynamic and real‐time stress distribution on the hand in various conditions. This work provides a new route for complex force‐sensing from the simple structure and shows great potential in robotics, human‐machine interface, and virtual reality/augmented reality (VR/AR). [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]

Highlights: This work reviews the development of breathable electronic skins (e-skins) for daily physiological signal monitoring in recent years. The design methods, preparation processes, and performances of typical breathable e-skin electrodes, breathable e-skin sensors, and breathable e-skin systems developed these years are systematically introduced and discussed. This review analyzes the challenges that breathable e-skins may face in daily health monitoring and puts forward the possible development directions of breathable e-skins.With the aging of society and the increase in people’s concern for personal health, long-term physiological signal monitoring in daily life is in demand. In recent years, electronic skin (e-skin) for daily health monitoring applications has achieved rapid development due to its advantages in high-quality physiological signals monitoring and suitability for system integrations. Among them, the breathable e-skin has developed rapidly in recent years because it adapts to the long-term and high-comfort wear requirements of monitoring physiological signals in daily life. In this review, the recent achievements of breathable e-skins for daily physiological monitoring are systematically introduced and discussed. By dividing them into breathable e-skin electrodes, breathable e-skin sensors, and breathable e-skin systems, we sort out their design ideas, manufacturing processes, performances, and applications and show their advantages in long-term physiological signal monitoring in daily life. In addition, the development directions and challenges of the breathable e-skin are discussed and prospected. [ABSTRACT FROM AUTHOR]

Highlights: A bioinspired MXene-based user-interactive electronic skin (e-skin) for digital and visual dual-signal sensing was designed and fabricated. The MXene-based e-skin exhibited an excellent electromechanical sensing performance and realized the real-time monitoring of human activities, such as handwriting, drinking, walking, and speaking. Benefiting from the outstanding Joule-heating performance of MXene-based film, the e-skin with thermochromic pigments could realize a wider range and dynamic coloration for passive displays and visual recognition of various human motions.User-interactive electronic skin (e-skin) that could convert mechanical stimuli into distinguishable outputs displays tremendous potential for wearable devices and health care applications. However, the existing devices have the disadvantages such as complex integration procedure and lack of the intuitive signal display function. Here, we present a bioinspired user-interactive e-skin, which is simple in structure and can synchronously achieve digital electrical response and optical visualization upon external mechanical stimulus. The e-skin comprises a conductive layer with a carbon nanotubes/cellulose nanofibers/MXene nanohybrid network featuring remarkable electromechanical behaviors, and a stretchable elastomer layer, which is composed of silicone rubber and thermochromic pigments. Furthermore, the conductive nanohybrid network with outstanding Joule heating performance can generate controllable thermal energy under voltage input and then achieve the dynamic coloration of silicone-based elastomer. Especially, such an innovative fusion strategy of digital data and visual images enables the e-skin to monitor human activities with evermore intuition and accuracy. The simple design philosophy and reliable operation of the demonstrated e-skin are expected to provide an ideal platform for next-generation flexible electronics. [ABSTRACT FROM AUTHOR]

Neuromorphic skin is an emerging electronic skin that demonstrates sensory, memory, learning, and motor responses in a neuromorphic way by using advanced artificial synaptic devices that emulate the biological nervous system and its neural plasticity. Many types of artificial synapses that emulate brain‐inspired computing have been developed and are being integrated in electronic skin to demonstrate artificial sensory and motor nervous systems. The neuromorphic skin, which operates using voltage spikes thereof, precisely mimics the energy‐efficient information processing of biological nervous system in the brain and body and enables the implementation of power‐ and time‐efficient cognitive sensors and computing, biomimetic robotics and electronics, and biocompatible neuroprosthetics. Here, biological synapses and emerging artificial synapses are introduced, and recent research is reviewed on neuromorphic skins that use artificial synapses for sensing, memory, learning, and motor systems. Finally, the outlook and challenges to be addressed are provided for future advanced neuromorphic skin in which all neuromorphic parts are integrated with brain‐inspired computing and bioinspired robotics. [ABSTRACT FROM AUTHOR]

Silicone elastomer composites with piezoelectric properties, conferred by incorporated polyimide copolymers, with pressure sensors similar to human skin and kinetic energy harvester capabilities, were developed as thin film (<100 micron thick) layered architecture. They are based on polymer materials which can be produced in industrial amounts and are scalable for large areas (m2). The piezoelectric properties of the tested materials were determined using a dynamic mode of piezoelectric force microscopy. These composite materials bring together polydimethylsiloxane polymers with customized poly(siloxane-imide) copolymers (2–20 wt% relative to siloxanes), with siloxane segments inserted into the structure to ensure the compatibility of the components. The morphology of the materials as free-standing films was studied by SEM and AFM, revealing separated phases for higher polyimide concentration (10, 20 wt%). The composites show dielectric behavior with a low loss (<10−1) and a relative permittivity superior (3–4) to pure siloxane within a 0.1–106 Hz range. The composite in the form of a thin film can generate up to 750 mV under contact with a 30 g steel ball dropped from 10 cm high. This capability to convert a pressure signal into a direct current for the tested device has potential for applications in self-powered sensors and kinetic energy-harvesting applications. Furthermore, the materials preserve the known electromechanical properties of pure polysiloxane, with lateral strain actuation values of up to 6.2% at 28.9 V/μm. [ABSTRACT FROM AUTHOR]

Recent advances in scalable fabrication methods based on printing technologies have improved the yield and lowered the cost of manufacturing epidermal sensors. However, modern technologies still require expensive multi‐bio‐ink raw materials. A laser‐centric fabrication method that realizes a cost‐effective, scalable, and streamlined fabrication process with easily used material and equipment is reported. The fabricated epidermal patch can quickly respond to the demands of personalized models. Here, the epidermal sensor patch is applied to continuous monitoring of the human cardiopulmonary system. The sensor performs conventional bio‐signal monitoring but is also extendible to other monitoring forms. The patch provides enhanced functions through its gas‐permeable and skin‐adhesive microporous layer and its stretchable, conformal, and biocompatible multimodal sensing layer. The utility of the proposed sensor patch in clinical diagnosis in a mobile healthcare environment is demonstrated in multiple bio‐signal‐morphology analyses. [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]

To uncover the effects of preparation process on material properties represents an important advance in the translational application of composites in intelligent biomedicine. Here, we investigated how preparation temperature interferes with the biocompatible composite integrating piezoresistivity and mechanical flexibility. By thermomechanical blending, the composite from poly(ε-caprolactone) (PCL) and nanocarbon black (nanoCB) obtained electric conductivity, whilst single-axial drawing re-distributed the nanoCB in PCL matrix. The drawing at a temperature declined from 55 to 25 °C resulted in the elastic strain of PCL/nanoCB composite increasing from ~5 to ~30 % and elastic limitation increasing from ~15 to ~55 MPa. Meanwhile, the composite drawing at 25 °C demonstrated improved piezoresistive response (a sensitivity of ~16 at 10% strain) in sensing external loading. This work provides insights into how preparation temperature influences the composite structure and electromechanical properties. The method can be applied to engineer biocompatible electronics for intelligent biomedicine. [ABSTRACT FROM AUTHOR]

Flexible electronic skin has tactile perception similar to human skin, and has been widely used in the field of human-computer interaction. The flexible electronic skin is designed and fabricated using poly-vinylidene fluoride (PVDF), reduced graphene oxide (rGO), and room temperature vulcanised (RTV) silicone rubber. Performed tests reveal that RTV silicone rubber has good piezoelectric properties and can increase the output voltage of the electronic skin. The effect of the number and spacer thickness of PVDF/rGO films on the voltage are studied, and the optimal structure is determined accordingly. Obtained results show that the proposed electronic skin has a wider linear working range at low frequencies, the peak voltage reaches 8.80 V. Meanwhile, good flexibility and high sensitivity are obtained, which can realise the measurement of static and dynamic pressures. The proposed electronic skin is used to monitor and identify the muscle activity caused by pulse and breathing. [ABSTRACT FROM AUTHOR]

Electronic skin (e‐skin) is widely studied for its ability to detect physiological information and provide feedback through electrical signals. Biocompatible stimulus‐responsive DNA‐based hydrogels exhibit high sensitivity, which makes them outstanding candidates for biomedical applications. However, several disadvantages, such as weak mechanical properties, expensive manufacturing costs, cumbersome double chain design, and difficulty obtaining bulk size, seriously limit their practical application. Based on the double network (DN) strategy, a universal, low‐cost, and high‐toughness deoxyribonucleic acid/poly(N‐hydroxyethyl acrylamide) (DNA/pHEAA) DN hydrogel is designed. The transparent hydrogel shows tensile stress/strain of 0.96 ± 0.043 MPa/2537.55 ± 23.24%, rapid self‐recovery ability (peak stress/energy dissipation recovery rate of 99.72%/95.38% after 30 s resting), excellent fatigue resistance (peak stress/energy dissipation retention rate of 91.08%/81.05% after 100 loading‐unloading cycles with strain of 50%), reversible adhesive ability (≈45 KPa), and good biocompatibility. Thus, the DNA/pHEAA DN hydrogel can be used as an e‐skin. Sensing signals are displayed on a smartphone as images sent through wireless technology; the images change with the collected signals, achieving motion detection. The universal and low‐cost design of stimulus‐responsive DNA‐based hydrogels with high toughness, excellent self‐recovery, and anti‐fatigue performance is expected to promote their application in the biomedical field. [ABSTRACT FROM AUTHOR]

Flexible electronic technology is one of the research hotspots, and numerous wearable devices have been widely used in our daily life. As an important part of wearable devices, flexible sensors can effectively detect various stimuli related to specific environments or biological species, having a very bright development prospect. Therefore, there has been lots of studies devoted to developing high-performance flexible pressure sensors. In addition to developing a variety of materials with excellent performances, the microstructure designs of materials can also effectively improve the performances of sensors, which has brought new ideas to scientists and attracted their attention increasingly. This paper will summarize the flexible pressure sensors based on material microstructure designs in recent years. The paper will mainly discuss the processing methods and characteristics of various sensors with different microstructures, and compare the advantages, disadvantages, and application scenarios of them. At the same time, the main application fields of flexible pressure sensors based on microstructure designs will be listed, and their future development and challenges will be discussed. [ABSTRACT FROM AUTHOR]

In this work, we developed a novel method to prepare a hydrogel‐based electronic skin by self‐assembling cross‐linking. The conductive hydrogel (named PGRS) integrates multiple properties. The hydrogel has good moisture retention (70 °C, 14 days), adhesion, and high elongation (2799 %). When the hydrogel is damaged externally, it can repair itself without external stimulation. The hydrogel adheres to the skin surface and monitors large strain movements, such as finger joints, wrist joints, elbow joints, head lowering and head lifting. It can also detect small movements, such as drinking and talking. It is used as an adhesive in liquid nitrogen (−196 °C). PGRS conductive hydrogel with multiple synergistic functions. It has great potential in the direction of flexible electronic skin. It indicates that PGRS conductive hydrogels have highly prospective applications in wearable devices. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors are essential components for wearable smart devices and intelligent systems. Significant progress has been made in this area, reporting on excellent sensor performance and fascinating sensor functionalities. Nevertheless, geometrical and morphological engineering of pressure sensors is usually neglected, which, however, is significant for practical application. Here, we present a digitized manufacturing methodology to construct a new class of iontronic pressure sensors with optionally defined configurations and widely modulated performance. These pressure sensors are composed of self-defined electrode patterns prepared by a screen printing method and highly tunable pressure-sensitive microstructures fabricated using 3D printed templates. Importantly, the iontronic pressure sensors employ an iontronic capacitive sensing mechanism based on mechanically regulating the electrical double layer at the electrolyte/electrode interfaces. The resultant pressure sensors exhibit high sensitivity (58 kPa−1), fast response/recovery time (45 ms/75 ms), low detectability (6.64 Pa), and good repeatability (2000 cycles). Moreover, our pressure sensors show remarkable tunability and adaptability in device configuration and performance, which is challenging to achieve via conventional manufacturing processes. The promising applications of these iontronic pressure sensors in monitoring various human physiological activities, fabricating flexible electronic skin, and resolving the force variation during manipulation of an object with a robotic hand are successfully demonstrated. [ABSTRACT FROM AUTHOR]

The paper describes the semi-automatised calibration procedure of an electronic skin comprising screen-printed graphene-based sensors intended to be used for robotic applications. The variability of sensitivity and load characteristics among sensors makes the practical use of the e-skin extremely difficult. As the number of active elements forming the e-skin increases, this problem becomes more significant. The article describes the calibration procedure of multiple e-skin array sensors whose parameters are not homogeneous. We describe how an industrial robot equipped with a reference force sensor can be used to automatise the e-skin calibration procedure. The proposed methodology facilitates, speeds up, and increases the repeatability of the e-skin calibration. Finally, for the chosen example of a nonhomogeneous sensor matrix, we provide details of the data preprocessing, the sensor modelling process, and a discussion of the obtained results. [ABSTRACT FROM AUTHOR]