Electronic Skin Research Articles

Silver nanowires/waterborne polyurethane composite film based piezoresistive pressure sensor for ultrasensitive human motion monitoring

Flexible piezoresistive pressure sensors are gaining significant attention, particularly in the realm of flexible wearable electronic skin. Here, a flexible piezoresistive pressure sensor was developed with a broad sensing range and high sensitivity. We achieved this by curing polydimethylsiloxane (PDMS) on sandpaper, creating a PDMS film as the template with a micro-protrusion structure. The core sensing layer was formed using a composite of silver nanowires (AgNWs) and waterborne polyurethane (WPU) with a similar micro-protrusion structure. The sensor stands out with its exceptional sensitivity, showing a value of 1.04 × 106 kPa−1 with a wide linear range from 0 to 27 kPa. It also boasts a swift response and recovery time of 160 ms, coupled with a low detection threshold of 17 Pa. Even after undergoing more than 1000 cycles, the sensor continues to deliver stable performance. The flexible piezoresistive pressure sensor based on AgNWs/WPU composite film (AWCF) can detect small pressure changes such as pulse, swallowing, etc, which indicates that the sensor has great application potential in monitoring human movement and flexible wearable electronic skin.

Electronic Skin for Health Monitoring Systems: Properties, Functions, and Applications.

Electronic skin (e-skin), a skin-like wearable electronic device, holds great promise in the fields of telemedicine and personalized healthcare because of its good flexibility, biocompatibility, skin conformability, and sensing performance. E-skin can monitor various health indicators of the human body in real time and over the long term, including physical indicators (exercise, respiration, blood pressure, etc.) and chemical indicators (saliva, sweat, urine, etc.). In recent years, the development of various materials, analysis, and manufacturing technologies has promoted significant development of e-skin, laying the foundation for the application of next-generation wearable medical technologies and devices. Herein, the properties required for e-skin health monitoring devices to achieve long-term and precise monitoring and summarize several detectable indicators in the health monitoring field are discussed. Subsequently, the applications of integrated e-skin health monitoring systems are reviewed. Finally, current challenges and future development directions in this field are discussed. This review is expected to generate great interest and inspiration for the development and improvement of e-skin and health monitoring systems.

Design and Optimization of NR-Based Stretchable Conductive Composites Filled with MoSi2 Nanoparticles and MWCNTs: Perspectives from Experimental Characterization and Molecular Dynamics Simulations.

Stretchable conductive composites play a pivotal role in the development of personalized electronic devices, electronic skins, and artificial implant devices. This article explores the fabrication and characterization of stretchable composites based on natural rubber (NR) filled with molybdenum disilicide (MoSi2) nanoparticles and multi-walled carbon nanotubes (MWCNTs). Experimental characterization and molecular dynamics (MD) simulations are employed to investigate the static and dynamic properties of the composites, including morphology, glass transition temperature (Tg), electrical conductivity, and mechanical behavior. Results show that the addition of MoSi2 nanoparticles enhances the dispersion of MWCNTs within the NR matrix, optimizing the formation of a conductive network. Dynamic mechanical analysis (DMA) confirms the Tg reduction with the addition of MWCNTs and the influence of MoSi2 content on Tg. Mechanical testing reveals that the tensile strength increases with MoSi2 content, with an optimal ratio of 4:1 MoSi2:MWCNTs. Electrical conductivity measurements demonstrate that the MoSi2/MWCNTs/NR composites exhibit enhanced conductivity, reaching optimal values at specific filler ratios. MD simulations further support experimental findings, highlighting the role of MoSi2 in improving dispersion and mechanical properties. Overall, the study elucidates the synergistic effects of nanoparticles and nanotubes in enhancing the properties of stretchable conductive composites.

A Suspended, 3D Morphing Sensory System for Robots to Feel and Protect.

Artificial sensory systems with synergistic touch and pain perception hold substantial promise for environment interaction and human-robot communication. However, the realization of biological skin-like functional integration of sensors with sensitive touch and pain perception still remains a challenge. Here, a concept is proposed of suspended electronic skins enabling 3D deformation-mechanical contact interactions for achieving synergetic ultrasensitive touch and adjustable pain perception. The suspended sensory system can sensitively capture tiny touch stimuli as low as 0.02Pa and actively perceive pain response with reliable 5200 cycles via 3D deformation and mechanical contact mechanism, respectively. Based on the touch-pain effect, a visualized feedback demo with miniaturized sensor arrays on artificial fingers is rationally designed to give a pain perception mapping on sharp surfaces. Furthermore, the capability is shown of the suspended electronic skin serving as a safe human-robot communication interface from active and passive view through a feedback control system, demonstrating potential in bionic electronics and intelligent robotics.

Multifunctional electronic skins for ultra-sensitive strain, temperature, humidity sensing, and energy harvesting

Though gaining increasing attention in various portable and wireless electronic devices and sensors, flexible gels used in strain sensors and triboelectric nanogenerators (TENGs) still suffer from inferior mechanical properties and lack long-term stability. Herein, multifunctional electronic skins (e-skin) from oriented 2D nanosheets enhanced eutectogel were facilely fabricated via a one-step curing strategy with excellent transparency (96%), superb elasticity (1613%), toughness (17.22 MPa). Moreover, the multifunctional e-skin also exhibits temperature and humidity sensibility. Notably, the as-assembled TENG e-skin exhibits high and stable electrical output performances, including an open-circuit voltage of 224 V, short-circuit current of 7.1 μA, and short-circuit charge of 640 nC. Meanwhile, the TENG can easily light up 130 LEDs, charge capacitors to drive a calculator, and sustain a long service life (120 days). Furthermore, it can serve as a self-powered biomechanical sensor to realize the real-time monitoring of various human motions, showing application potentials in wearable electronics, human health management, and energy harvesting systems.

Intrinsically Stretchable Floating Gate Memory Transistors for Data Storage of Electronic Skin Devices.

To propel electronic skin (e-skin) to the next level by integrating artificial intelligence features with advanced sensory capabilities, it is imperative to develop stretchable memory device technology. A stretchable memory device for e-skin must offer, in particular, long-term data storage while ensuring the security of personal information under any type of deformation. However, despite the significance of these needs, technology related to stretchable memory devices remains in its infancy. Here, we report an intrinsically stretchable floating gate (FG) polymer memory transistor. The device features a dual-stimuli (optical and electrical) writing system to prevent easy erasure of recorded data. An FG comprising an intermixture of Ag nanoparticles and elastomer and with proper energy-band alignment between the semiconductor and dielectric facilitated sustainable memory performance, while achieving a high memory on/off ratio (>105) and a long retention time (106 s) with the ability to withstand 50% uniaxial or 30% biaxial strain. In addition, our memory transistor exhibited high mechanical durability over multiple stretching cycles (1000 times), along with excellent environmental stability with respect to factors such as temperature, moisture, air, and delamination. Finally, we fabricated a 7 × 7 active-matrix memory transistor array for personalized storage of e-skin data and successfully demonstrated its functionality.

An Intelligent Non-Invasive Blood Pressure Monitoring System Based on a Novel Polyvinylidene Fluoride Piezoelectric Thin Film.

Hypertension is a common cause of cardiovascular diseases, closely associated with the high mortality and disability rates of cardiovascular diseases such as stroke and coronary heart disease. Therefore, developing a comfortable and sustainable device for monitoring human pulse signals holds practical significance for the prevention and treatment of hypertension and cardiovascular diseases. PVDF flexible pressure sensors possess the characteristics of high sensitivity, good flexibility, and strong biocompatibility, thereby demonstrating extensive application potential in areas such as health monitoring, wearable devices, and electronic skins. This paper focuses on the development of a modified piezoelectric polymer and its application in an intelligent blood pressure monitoring system, demonstrating its outstanding performance and feasibility through a series of experiments. This research provides innovative material choices for the development of intelligent medical devices and offers beneficial guidance for the design and application of future intelligent health monitoring systems.

Bilayer piezoionic sensors for enhanced detection of dynamic, static, and directional forces with self-healing capabilities

Electronic skin (e-skin) aims to replicate the tactile feedback mechanism of natural skin, offering great potential across robotics, healthcare monitoring, and human-machine interfaces. Traditional e-skin systems utilize electron-based sensing through capacitance and piezoresistivity for static forces, and piezoelectricity and triboelectricity for dynamic forces. However, the former group struggles with dynamic stimuli and external power dependencies, while the latter excels in self-powering but fails in static detection. Addressing these gaps, iontronics emerges as a versatile solution, providing innovative avenues for energy harvesting, sensing, and actuation through ion redistribution in response to varied stimuli, but shows limitations in output signals and response times. We report herein the development of bilayerstructured piezoionic materials with significantly enhanced output signal and response time. The piezoionic bilayer structure not only harnesses an ion accumulation interface, leading to amplified output signals and fast response times, but also exhibits an ion-dipole interactive self-healing property. Our sensor generates a signal output of 95 mV and features a quick response time of 30 ms, with an impressive self-healing capability of ∼100%. It demonstrates the ability to accurately detect both static and dynamic forces, including specific movements like bending and vibrations, maintaining its robustness through 8000 cycles of repetitive deformation. Its utility is further proven in a practical setting with a braille reader device, highlighting its potential for incorporation into a wide array of soft, autonomous iontronic systems that require enhanced sensitivity, rapid detection capabilities, and self-sustainability.

Soft multifunctional neurological electronic skin through intrinsically stretchable synaptic transistor

Soft multifunctional neurological electronic skin through intrinsically stretchable synaptic transistor

Gyrofluid simulations of turbulence and reconnection in space plasmas

A Hamiltonian two-field gyrofluid model is used to investigate the dynamics of an electron-ion collisionless plasma subject to a strong ambient magnetic field, within a spectral range extending from the magnetohydrodynamic (MHD) scales to the electron skin depth. This model isolates Alfvén, Kinetic Alfvén and Inertial Kinetic Alfvén waves that play a central role in space plasmas, and extends standard reduced fluid models to broader ranges of the plasma parameters. Recent numerical results are reviewed, including (i) the reconnection-mediated MHD turbulence developing from the collision of counter-propagating Alfvén wave packets, (ii) the specific features of the cascade dynamics in strongly imbalanced turbulence, including a possible link between the existence of a spectral transition range and the presence of co-propagating wave interactions at sub-ion scales, for which new simulations are reported, (iii) the influence of the ion-to-electron temperature ratio in two-dimensional collisionless magnetic reconnection. The role of electron finite Larmor radius corrections is pointed out and the extension of the present model to a four-field gyrofluid model is discussed. Such an extended model accurately describes electron finite Larmor radius effects at small or moderate values of the electron beta parameter, and also retains the coupling to slow magnetosonic waves.

Avian Bone‐Inspired Super Fatigue Resistant MXene‐Based Aerogels with Human‐Like Tactile Perception for Multilevel Information Encryption Assisted by Machine Learning

AbstractDeveloping multimodal sensors with human‐like tactile perception is highly desirable for wearable devices, electronic skins (e‐skins), and human‐machine interfaces. However, realizing decoupled signal output and high‐precision measurement remains challenging. Superelastic conductive aerogels are ideal materials for fabricating multimodal sensors as they can convert pressure and temperature stimuli into different electrical signals. Herein, inspired by the microstructure of lightweight and robust avian bones, a biomimetic lamellar silica nanofiber/MXene aerogel (LSMA) sensor for decoupled pressure and temperature sensing is first developed. The avian bone‐like lamellae‐strut structure endows the ultralight LSMA with superb fatigue resistance of 99.1% height retention after 10 000 compression cycles, which is second to none in the reported MXene‐based aerogels. Meanwhile, benefiting from the advantages of the aerogel structure, the LSMA sensor integrating piezoresistive and thermoelectric effects has an ultrahigh temperature resolution of 0.07 K and the lowest pressure detection limit of 0.20 Pa in the reported pressure‐temperature sensors. The unique performance renders it a promising platform for wearable physiological monitoring and tactile e‐skin. Furthermore, an innovative multilevel encryption protection system assisted by machine learning is designed based on the LSMA sensing array as the interactive terminal. This study provides novel insights into the design and application of multimodal sensors.

Latest developments and trends in electronic skin devices

The skin, a vital medium for human-environment communication, stands as an indispensable and pivotal element in the realms of both production and daily life. As the landscape of science and technology undergoes gradual evolution and the demand for seamless human-machine interfaces continues to surge, an escalating need emerges for a counterpart to our biological skin - electronic skins (e-skins). Achieving high-performance sensing capabilities comparable to our skin has consistently posed a formidable challenge. In this article, we systematically outline fundamental strategies enabling e-skins with capabilities including strain sensing, pressure sensing, shear sensing, temperature sensing, humidity sensing, and self-healing. Subsequently, complex e-skin systems and current major applications were briefly introduced. We conclude by envisioning the future trajectory, anticipating continued advancements and transformative innovations shaping the dynamic landscape of e-skin technology. This article provides a profound insight into the current state of e-skins, potentially inspiring scholars to explore new possibilities.

Underwater sensors based on dual dynamically crosslinked hydrogels with excellent anti-swelling and adhesive properties

Hydrogel-derived flexible sensors have fascinating applications in the fields of wearable electronics and electronic skin. Nevertheless, the fabrication of underwater sensors is still restricted due to the underwater instability and the poor adhesion in an aquatic environment. In this work, a dynamic physical/chemical dual crosslinked poly (acrylic acid-co-lauryl methacrylate) and polyvinyl alcohol interpenetrating network hydrogel was successfully prepared to overcome the above issues. The as-prepared hydrogels exhibited prior stretchability (2310 % strain), good self-healing performance (83 % healing efficiency within 36 h), remarkable underwater instability (23 % of equilibrium swelling ratio), and long-term underwater adhesion (65.4 kPa of adhesive strength in water for 24 h). The as-prepared hydrogel strain sensor features excellent sensing performance (GF = 4.83) and a wide sensing range of 1%–1000 %. Due to its excellent flexibility, strong adhesion, and high strain sensitivity, the prepared hydrogel can be conveniently used for the real-time monitoring of various human movements, including pronounced joint movements and subtle muscle vibrations. Furthermore, the hydrogel-based sensor with good and stable mechanical, electrical, and adhesive properties in an aquatic environment can accomplish effective signal transmission underwater via the combination of body movement and the Morse code.

Multiscale Transfer Printing via Shape Memory Polymer with High Adhesion and Modulus Switchability.

Flexible electronics have gained significant attention as an innovative solution to meet the growing need for information collection from the human body and the environment. However, a critical challenge lies in the need for a transfer printing technique that can fabricate rigid and brittle devices on flexible organic substrates. Here, we develop a multiscale transfer printing technique using an ultraviolet-curable shape memory polymer (SMP) that serves as both the stamp and the receiver substrate. The SMP demonstrates exceptional mechanical performance with toughness at room temperature and remarkable flexibility near its glass transition temperature. The SMP material exhibits an impressive shape recovery ratio and remarkable adhesion switchability. We demonstrate robust transfer printing of diverse objects with different materials and morphologies and in situ transfer of multiscale metallic structures. In addition, the in situ fabricated transparent hyperthermia patches with embedded metal grids are demonstrated, offering potential application in the field of sensors, wearable devices, and electronic skin.

A dual function flexible sensor for independent temperature and pressure sensing

Temperature and pressure sensing are two primary goals of bionic electronic skin. In this work, we developed a dual function flexible sensor, which achieved independent temperature and pressure sensing, with easy fabrication and without complicate signal decoupling. For this sensor, two flexible films with conductively bionic microstructure on the surface are combined face to face, which were replicated from rose petal and mulberry leaf. Ti3C2Tx nanoflakes were mixed with PEDOT: PSS as conductive layer and thermoelectric layer, and the performance of which can be optimized by regulating the concentration of Ti3C2Tx. The principles for temperature and pressure sensing are thermoelectric and piezo-resistive respectively, which are isolated by structure design. The change of contact area and resistance between the two micro-structured layers upon pressure determines the pressure response of the device. The thermoelectric response in one layer realizes the temperature sensing. The metallic conductivity of Ti3C2Tx is insensitive to temperature, leading to the invariable electric response to pressure upon varied temperature. The microstructure buffers most of the pressure, which keeps the substrate unchanged and results in the independent thermoelectric response upon varied pressure. This dual function sensor shows robust and repeatable response, and exhibits great application potential in flexible electronics.

Spike timing-based coding in neuromimetic tactile system enables dynamic object classification.

Rapid processing of tactile information is essential to human haptic exploration and dexterous object manipulation. Conventional electronic skins generate frames of tactile signals upon interaction with objects. Unfortunately, they are generally ill-suited for efficient coding of temporal information and rapid feature extraction. In this work, we report a neuromorphic tactile system that uses spike timing, especially the first-spike timing, to code dynamic tactile information about touch and grasp. This strategy enables the system to seamlessly code highly dynamic information with millisecond temporal resolution on par with the biological nervous system, yielding dynamic extraction of tactile features. Upon interaction with objects, the system rapidly classifies them in the initial phase of touch and grasp, thus paving the way to fast tactile feedback desired for neuro-robotics and neuro-prosthetics.

Intrinsically stretchable phototransistors with polymer-QD-polymer multi-layered hybrid films for visible-NIR perspective electronic skin sensors

Stretchable phototransistors represent a crucial component in the development of skin-inspired optoelectronics. Although there have been significant advancements in the development of skin-like photosensitive semiconductors, technology for stretchable phototransistors that can detect a broad spectrum of wavelengths from near-infrared (NIR) to visible light is still in its early stages. This study introduces an intrinsically stretchable phototransistor employing hybrid semiconductor films consisting of polymer semiconductors (PSC) and quantum dots (QDs). The hybrid multi-layered semiconductor film (PSC/QDs/PSC) possesses wide-ranging color sensitivity from NIR to visible light, along with high photosensitivity and photoresponsivity. Furthermore, our phototransistor exhibits remarkable strain-insensitive, photo-response characteristics, maintaining performance even under 50% strain and enduring 10,000 strain cycles. Notably, the phototransistor array, featuring a distinctive dodecagon shape of source/drain electrodes, effectively responds to NIR and visible light stimuli, even when subjected to substantial areal strains of up to 38%.

Asymmetric nanofiber photothermal interactive electronic skin with triboelectric autonomous thermal perceptivity

Thermal-perceptive electronic skins (e-skin) represent an important functional interface in wearables and soft robots. Realizing an all-in-one structured nanofiber interactive e-skin with autonomous thermal perceptivity remains challenging. We demonstrated a polyurethane/(polyvinyl pyrrolidone/MXene) (PPM) bilayer nanofiber film with asymmetric structure compactness by continuous and controllable electrospinning, that achieves asymmetric optical transmittance (visible light transparency of 20∼97%, infrared transparency of 5.5∼34.1%) and photothermal actuation response, with a response rate of 0.8 mm−1 s−1 and bending curvature of 2.2 cm−1, as well as additional excellent triboelectric outputs of ∼320 V and ∼5.4 µA. We proposed a “contact-actuation-perception” strategy for instantaneous object temperature sensing based on the PPM, which can actuate under photothermal stimulation to change its contact area with the target objects at different temperatures, producing temperature-dependent distinguishable triboelectric signals for autonomous thermal perception, with sensitivity up to ∼99.6%. This work could inspire a facile strategy to realize asymmetric features in fiber materials, in which the asymmetric optical-thermal-mechanical-electrical coupling mechanism for active perception is expected to promote the development of autonomous interactive e-skins.

Mechanically programmable substrate enable highly stretchable solar cell arrays for self-powered electronic skin

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.

Advanced Dressings for Chronic Wound Management.

Wound healing, particularly for chronic wounds, presents a considerable difficulty due to differences in biochemical and cellular processes that occur in different types of wounds. Recent technological breakthroughs have notably advanced the understanding of diagnostic and therapeutic approaches to wound healing. The evolution in wound care has seen a transition from traditional textile dressings to a variety of advanced alternatives, including self-healing hydrogels, hydrofibers, foams, hydrocolloids, environment responsive dressings, growth factor-based therapy, bioengineered skin substitutes, and stem cell and gene therapy. Technological advancements, such as 3D printing and electronic skin (e-skin) therapy, contribute to the customization of wound healing. Despite these advancements, effectively managing chronic wounds remains challenging. This necessitates the development of treatments that consider performance, risk-benefit balance, and cost-effectiveness. This review discusses innovative strategies for the healing of chronic wounds. Incorporating biomarkers into advanced dressings, coupled with corresponding biosensors and drug delivery formulations, enables the theranostic approach to the treatment of chronic wounds. Furthermore, integrating advanced dressings with power sources and user interfaces like near-field communication, radio frequency identification, and Bluetooth enhances real-time monitoring and on-demand drug delivery. It also provides a thorough evaluation of the advantages, patient compliance, costs, and durability of advanced dressings, emphasizing smart formulations and their preparation methods.