Extraordinarily Sensitive and Low‐Voltage Operational Cloth‐Based Electronic Skin for Wearable Sensing and Multifunctional Integration Uses: A Tactile‐Induced Insulating‐to‐Conducting Transition

Electronic skin sensing devices are an emerging technology and have substantial demand in vast practical fields including wearable sensing, robotics, and user‐interactive interfaces. In order to imitate or even outperform the capabilities of natural skin, the keen exploration of materials, device structures, and new functions is desired. However, the very high resistance and the inadequate current switching and sensitivity of reported electronic skins hinder to further develop and explore the promising uses of the emerging sensing devices. Here, a novel resistive cloth‐based skin‐like sensor device is reported that possesses unprecedented features including ultrahigh current‐switching behavior of ≈10⁷ and giant high sensitivity of 1.04 × 10⁴–6.57 × 10⁶ kPa^?1 in a low‐pressure region of <3 kPa. Notably, both superior features can be achieved by a very low working voltage of 0.1 V. Taking these remarkable traits, the device not only exhibits excellent sensing abilities to various mechanical forces, meeting various applications required for skin‐like sensors, but also demonstrates a unique competence to facile integration with other functional devices for various purposes with ultrasensitive capabilities. Therefore, the new methodologies presented here enable to greatly enlarge and advance the development of versatile electronic skin applications.     

Screen‐Printed Soft Capacitive Sensors for Spatial Mapping of Both Positive and Negative Pressures

Soft pressure sensors are one class of the essential devices for robotics and wearable device applications. Despite the tremendous progress, sensors that can reliably detect both positive and negative pressures have not yet been demonstrated. In this paper, a soft capacitive pressure sensor, made using a convenient and low‐cost screen‐printing process that can reliably detect both positive and negative pressures from ?60 to 20 kPa, is reported. The sensor is made with an Ecoflex‐0030 dielectric layer, conductive and stretchable poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (with ionic additives) electrodes, and polydimethylsiloxane encapsulation layers. Air gaps are designed and incorporated into the dielectric layer to significantly enhance the sample deformation and pressure response especially to negative pressure. The sensor exhibits repeatable response for thousands of cycles, even under bending or stretching conditions. Lastly, to demonstrate the practical application, a 12 × 12‐pixel sensor array that can automatically measure both positive and negative pressure distributions has been reported under ?20 and 10 kPa.     

Full 3D Printing of Stretchable Piezoresistive Sensor with Hierarchical Porosity and Multimodulus Architecture

A soft piezoresistive sensor with its unique characteristics, such as human skin, light weight, and multiple functions, yields a variety of possible practical applications to skin‐attachable electronics, human–machine interfaces, and electronic skins. However, conventional filler‐matrix piezoresistive sensors often suffer from unsatisfactory sensitivity or insufficient measurement range, as well as significant cross‐correlation between out‐of‐plane pressure and in‐plane extension. Here, a stretchable piezoresistive sensor (SPS) is realized by combining a hierarchically porous sensing element with a multimodulus device architecture via a full 3D printing process. As a result, the sensor exhibits high sensitivity (5.54 kPa^?1), large measurement range (from 10 Pa to 800 kPa), limited cross‐correlation, and excellent durability. Meanwhile, benefiting from the porous structure and mechanical mismatch design, which efficiently distributes the stress away from the sensing element, the device experiences only 7% resistance change at 50% stretching. This approach is employed to rapidly program and readily manufacture stylish, all‐in‐one, functional devices for various applications, demonstrating that the technique is promising for customized stretchable electronics.     

Fingertip‐Skin‐Inspired Highly Sensitive and Multifunctional Sensor with Hierarchically Structured Conductive Graphite/Polydimethylsiloxane Foams

Fingertip skin exhibits high sensitivity in a broad pressure range, and can detect diverse stimuli, including textures, temperature, humidity, etc. Despite adopting diverse microstructures and functional materials, achieving skin sensor devices possessing high pressure sensitivity over a wide linear range and with multifunctional sensing capabilities is still challenging. Herein, inspired by the microstructures of fingertip skin, a highly sensitive skin sensor is demonstrated with a linear response over a broad pressure range and multifunctional sensing capabilities. The porous sensing layer is designed with hierarchical microstructures on the surface. By optimizing the porosity and the graphite concentration, a fabricated skin sensor device exhibits a superior sensitivity of 245 kPa^?1 over a broad linear pressure range from 5 Pa to 120 kPa. For practical application demonstrations, the sensor devices are utilized to monitor subtle wrist pulse and diverse human motions including finger bending, wrist bending, and feet movement. Furthermore, this novel sensor device demonstrates potential applications in recognizing textures and detecting environmental temperatures, thereby marking an important progress for constructing advanced electronic skin.     

Textile‐Based Wireless Pressure Sensor Array for Human‐Interactive Sensing

A textile‐based wireless pressure sensor array (WiPSA) is proposed for flexible remote tactile sensing applications. The WiPSA device is composed of a fabric spacer sandwiched by two separate layers of passive antennas and ferrite film units. Under the external pressure, the mechanical compression of the flexible fabric spacer leads to an inductance change, which can further be transduced to a detectable shift of the resonant frequency. Importantly, WiPSA integrates the ferrite film featuring an ultrahigh permeability, which effectively improves the device sensitivity and avoids the interference of conductive materials simultaneously. The device performance with a high quality factor (>35) and sensitivity (?0.19 MHz kPa^?1) within a pressure range of 0–20 kPa is demonstrated. In addition, WiPSA achieves excellent reproducibility under periodical pressures (>20 000 cycles), temperature fluctuations (15–103 °C), and humidity variations (40–99%). As a proof of concept for human‐interactive sensing, WiPSA is successfully 1) integrated with a flexible wrist band for fingertip pressure‐guided direction choices, 2) developed into a smart wireless insole to map the plantar stress distributions, and 3) embedded into a waist‐supporting belt to resolve the contact pressure between the belt and human abdomen in a remote transmitting scheme.     

Textile‐Based Flexible Tactile Force Sensor Sheet

The next generation of electronics will include human‐interactive flexible sensor sheets to monitor health. One approach is to realize practical macroscale low‐cost sensor arrays to monitor pressure distribution and health conditions without directly attaching a device onto the body. However, practical requirements such as reliability, scalability, and washability are not often discussed as most studies focus on the sensing sensitivity and validations. This study demonstrates an all textile‐based tactile force sensor sheet that covers the above requirements. By considering the device design and materials, high reliability/repeatability (≈250 000 cycles at ≈5 kPa) and washability are realized. These are important factors for practical applications for human‐interactive macroscale sensor sheets. In addition to the fundamental characteristics, pressure distribution mapping and respiration rate monitoring are confirmed by placing the sensor sheets on a bed, chair, and floor.     

E‐Skin Tactile Sensor Matrix Pixelated by Position‐Registered Conductive Microparticles Creating Pressure‐Sensitive Selectors

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

Pressure‐Driven Eu2+‐Doped BaLi2Al2Si2N6: A New Color Tunable Narrow‐Band Emission Phosphor for Spectroscopy and Pressure Sensor Applications

A series of BaLi₂Al₂Si₂N₆ (BLASN): xEu²⁺ phosphors are successfully synthesized and their crystal structure and luminescence properties under varying hydrostatic pressures are reported herein. Structure variation is analyzed using in situ high‐pressure X‐ray diffraction and Rietveld refinements. Based on decay curves and Gaussian fitting of emission spectra, the presence of two photoluminescence centers is demonstrated. BaLi₂Al₂Si₂N₆: 0.01Eu²⁺ exhibits an evident peak position shift from 532 to 567 nm with an increase in pressure to ≈20 GPa. The possible factors and mechanisms for the variations are studied in detail. At a pressure of 16 GPa, BLASN: Eu²⁺ realizes a narrow yellow emission with a full width at half maximum of ≈70 nm. The addition of BLASN: Eu²⁺ (16 GPa) to the commercial white light‐emitting diodes combination consisting of an InGaN chip, β‐SiAlON: Eu²⁺, and red K₂SiF₆:Mn⁴⁺, can increase the color gamut by ≈15%, demonstrating the promising potential of pressure‐driven BLASN: Eu²⁺ for wide‐color gamut spectroscopy applications. Moreover, the emission shifts arising from pressure variation and the distinct color changes enable its potential utility as an optical pressure sensor; the material exhibits high pressure sensitivity (dλ/dP ≈ 1.58 nm GPa^?1) with the advantage of visualization.     

Multi‐Layered,Hierarchical Fabric‐Based Tactile Sensors with High Sensitivity and Linearity in Ultrawide Pressure Range

Resistive tactile sensors based on changes in contact area have been extensively explored for a variety of applications due to their outstanding pressure sensitivity compared to conventional tactile sensors. However, the development of tactile sensors with high sensitivity in a wide pressure range still remains a major challenge due to the trade‐off between sensitivity and linear detection range. Here, a tactile sensor comprising stacked carbon nanotubes and Ni‐fabrics is presented. The hierarchical structure of the fabrics facilitates a significant increase in contact area between them under pressure. Additionally, a multi‐layered structure that can provide more contact area and distribute stress to each layer further improves the sensitivity and linearity. Given these advantages, the sensor presents high sensitivity (26.13 kPa^?1) over a wide pressure range (0.2–982 kPa), which is a significant enhancement compared with the results obtained in previous studies. The sensor also exhibits outstanding performances in terms of response time, repeatability, reproducibility, and flexibility. Furthermore, meaningful applications of the sensor, including wrist‐pulse‐signal analysis, flexible keyboards, and tactile interface, are successfully demonstrated. Based on the facile and scalable fabrication technique, the conceptually simple but powerful approach provides a promising strategy to realize next‐generation electronics.     

Stretchable,Transparent, and Self‐Patterned Hydrogel‐Based Pressure Sensor for Human Motions Detection

In this study, a binary networked conductive hydrogel is prepared using acrylamide and polyvinyl alcohol. Based on the obtained hydrogel, an ultrastretchable pressure sensor with biocompatibility and transparency is fabricated cost effectively. The hydrogel exhibits impressive stretchability (>500%) and superior transparency (>90%). Furthermore, the self‐patterned microarchitecture on the hydrogel surface is beneficial to achieve high sensitivity (0.05 kPa^?1 for 0–3.27 kPa). The hydrogel‐based pressure sensor can precisely monitor dynamic pressures (3.33, 5.02, and 6.67 kPa) with frequency‐dependent behavior. It also shows fast response (150 ms), durable stability (500 dynamic cycles), and negligible current variation (6%). Moreover, the sensor can instantly detect both tiny (phonation, airflowing, and saliva swallowing) and robust (finger and limb motions) physiological activities. This work presents insights into preparing multifunctional hydrogels for mechanosensory electronics.     

Hierarchical Ordered Dual‐Mesoporous Polypyrrole/Graphene Nanosheets as Bi‐Functional Active Materials for High‐Performance Planar Integrated System of Micro‐Supercapacitor and Gas Sensor

Planar integrated systems of micro‐supercapacitors (MSCs) and sensors are of profound importance for 3C electronics, but usually appear poor in compatibility due to the complex connections of device units with multiple mono‐functional materials. Herein, 2D hierarchical ordered dual‐mesoporous polypyrrole/graphene (DM‐PG) nanosheets are developed as bi‐functional active materials for a novel prototype planar integrated system of MSC and NH₃ sensor. Owing to effective coupling of conductive graphene and high‐sensitive pseudocapacitive polypyrrole, well‐defined dual‐mesopores of ≈7 and ≈18 nm, hierarchical mesoporous network, and large surface area of 112 m² g^?1, the resultant DM‐PG nanosheets exhibit extraordinary sensing response to NH₃ as low as 200 ppb, exceptional selectivity toward NH₃ that is much higher than other volatile organic compounds, and outstanding capacitance of 376 F g^?1 at 1 mV s^?1 for supercapacitors, simultaneously surpassing single‐mesoporous and non‐mesoporous counterparts. Importantly, the bi‐functional DM‐PG‐based MSC‐sensor integrated system represents rapid and stable response exposed to 10–40 ppm of NH₃ after only charging for 100 s, remarkable sensitivity of NH₃ detection that is close to DM‐PG‐based MSC‐free sensor, impressive flexibility with ≈82% of initial response value even at 180°, and enhanced overall compatibility, thereby holding great promise for ultrathin, miniaturized, body‐attachable, and portable detection of NH₃.     

Knittable and Washable Multifunctional MXene‐Coated Cellulose Yarns

Textile‐based electronics enable the next generation of wearable devices, which have the potential to transform the architecture of consumer electronics. Highly conductive yarns that can be manufactured using industrial‐scale processing and be washed like everyday yarns are needed to fulfill the promise and rapid growth of the smart textile industry. By coating cellulose yarns with Ti₃C₂T_x MXene, highly conductive and electroactive yarns are produced, which can be knitted into textiles using an industrial knitting machine. It is shown that yarns with MXene loading of ≈77 wt% (≈2.2 mg cm^?1) have conductivity of up to 440 S cm^?1. After washing for 45 cycles at temperatures ranging from 30 to 80 °C, MXene‐coated cotton yarns exhibit a minimal increase in resistance while maintaining constant MXene loading. The MXene‐coated cotton yarn electrode offers a specific capacitance of 759.5 mF cm^?1 at 2 mV s^?1. A fully knitted textile‐based capacitive pressure sensor is also prepared, which offers high sensitivity (gauge factor of ≈6.02), wide sensing range of up to ≈20% compression, and excellent cycling stability (2000 cycles at ≈14% compression strain). This work provides new and practical insights toward the development of platform technology that can integrate MXene in cellulose‐based yarns for textile‐based devices.     

Bioinspired Artificial Sensory Nerve Based on Nafion Memristor

Bioinspired artificial haptic neuron system has received much attention in the booming artificial intelligence industry for its broad range of high‐impact applications such as personal healthcare monitoring, electronic skins, and human–machine interfaces. An artificial haptic neuron system is designed by integrating a piezoresistive sensor and a Nafion‐based memristor for the first time in this paper. The piezoresistive sensor serves as a sensory receptor to transform mechanical stimuli into electric signals, and the Nafion‐based memristor serves as the synapse to further process the information. The pyramid‐structured sensor exhibits excellent sensitivity (6.7 × 10⁷ kPa^?1 in 1–5 kPa and 3.8 × 10⁵ kPa^?1 in 5–50 kPa) and durability (>7000 cycles), while the memristor realizes fundamental synaptic functions under low power consumption (10–200 pJ) and remains stable for over 10⁴ consecutive tests. The integrated system can detect tactile stimuli encoded with temporal information, such as the count, frequency, duration and speed of the external force. As a proof‐of‐concept, English characters recognition with high accuracy can be achieved on the system under a supervised learning method. This work shows promising potential in bioinspired sensing systems owing to the high performance, excellent durability, and simple fabrication procedure.     

Microchannel‐Confined MXene Based Flexible Piezoresistive Multifunctional Micro‐Force Sensor

Multifunctional micro‐force sensing in one device is an urgent need for the higher integration of the smaller flexible electronic device toward wearable health‐monitoring equipment, intelligent robotics, and efficient human–machine interface. Herein, a novel microchannel‐confined MXene‐based flexible piezoresistive sensor is demonstrated to simultaneously achieve multi‐types micro‐force sensing of pressure, sound, and acceleration. Benefiting from the synergistically confined effect of the fingerprint‐microstructured channel and the accordion‐microstructured MXene materials, the as‐designed sensor remarkably endows a low detection limit of 9 Pa, a high sensitivity of 99.5 kPa^?1, and a fast response time of 4 ms, as well as non‐attenuating durability over 10 000 cycles. Moreover, the fabricated sensor is multifunctionally capable of sensing sounds, micromotion, and acceleration in one device. Evidently, such a multifunctional sensing characteristic can highlight the bright prospect of the microchannel‐confined MXene‐based micro‐force sensor for the higher integration of flexible electronics.     

Porous Conductive Hybrid Composite with Superior Pressure Sensitivity and Dynamic Range

Porous conductive composites hold immense promise in flexible sensors and soft robotics due to their pressure-responsive electrical conductivity. Unlike non-porous composites whose pressure sensitivity is limited by relatively high elastic modulus, porous materials show improved pressure sensitivity owing to their lower stiffness. Despite this, existing porous composites still suffer from insufficient pressure sensitivity or narrow detection ranges, severely restricting their applications. This work presents a liquid metal hybrid filler porous composite to address these issues. Through experiment and simulation optimization, the composite exhibits a conductivity increase of five order-of-magnitude over 0–250 kPa, demonstrating a 900% higher pressure sensitivity than the best non-porous counterpart in this work. The composite maintains a highly linear response (R² of 0.999) over an exceptionally wide dynamic range up to 8.9 MPa, with a pressure sensitivity of 8.1 MPa^–1, surpassing the state-of-the-art in both pressure range and sensitivity. A proof-of-concept pressure sensor array further demonstrates the composite's excellent sensing performance, showing stable response under 100-cycle loading with a measured pressure deviation of only 1.4%, outperforming existing commercial pressure sensors in terms of sensitivity, detection range and cyclic stability. The porous material design strategy opens doors for high sensitivity pressure sensors in wearable devices, flexible electronics, and soft robotics.     

Membrane‐Based Self‐Powered Triboelectric Sensors for Pressure Change Detection and Its Uses in Security Surveillance and Healthcare Monitoring

A new membrane‐based triboelectric sensor (M‐TES) is presented as a self‐powered pressure change sensor. It generates a voltage induced by surface triboelectric charges in response to an air pressure change. Extremely high detection resolutions of 0.34 Pa and 0.16 Pa are achieved when the air pressure increases and decreases in a small region away from the ambient standard atmosphere pressure, respectively, indicating an excellent sensitivity. By integrating the M‐TES with a signal processing unit, we demonstrate practical applications of the device in sensing footsteps, respirations, and heartbeat, which suggests widespread use of the M‐TES in fields of security surveillance, chemical engineering, geography research, environment monitoring, and personal healthcare.     

Flexible pressure sensor with high sensitivity and fast response for electronic skin using near-field electrohydrodynamic direct writing

Electronic skin imitates the function of human skin. The flexible pressure sensor is an important sensor of electronic skin. Although the flexible pressure sensor has made some progress, electronic skin is still a challenging subject with good pressure resolution, high sensitivity, and fast response ability in biomedical, human motion detection, personal health monitoring, and other fields. The PEDOT:PSS/GR/SWCNTs multicomponent solution was directly written on the flexible PDMS substrate by the near-field electrohydrodynamic direct-writing method, a serpentine shaped pressure sensitive unit was prepared, which was encapsulated with the PDMS thin film, and the flexible pressure sensor was fabricated. The sensitivity of the flexible pressure sensor is about 0.39 kPa⁻¹ at 0–0.5 kPa and 1.04 kPa⁻¹ at 0.5–2.4 kPa, and the response/recovery speed is 75 ms/150 ms, respectively. The fabricated flexible pressure sensor can detect a small pressure of about 6.4 Pa. The experimental results show that the fabricated flexible pressure sensor has high sensitivity, fast response capability, and low detection limit. The flexible pressure sensor for electronic skin demonstrates good performance in the application of finger joint movement and word pronunciation recognition, which indicates that it has great potential application in human motion detection and personal health monitoring.     

High‐Sensitivity,Skin‐Attachable,and Stretchable Array of Thermo‐Responsive Suspended Gate Field‐Effect Transistors with Thermochromic Display

The fabrication of a skin‐attachable, stretchable array of high‐sensitivity temperature sensors is demonstrated. The temperature sensor consists of a single‐walled carbon nanotube field‐effect transistor with a suspended gate electrode of poly(N‐isopropylacrylamide) (PNIPAM)‐coated gold grid/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate and thermochromic leuco dye. The sensor exhibits a very high sensitivity of 6.5% °C^?1 at temperatures between 25 and 45 °C. With increasing temperature, the suspended gate electrode bends due to the deswelling of the PNIPAM, resulting in the reduction of the air gap to increase the drain current under a constant gate voltage. At the same time, the leuco dye coated on top of the transparent gate electrode changes color to visualize changes in temperature. The 4 × 6 integrated temperature sensor array integrated using liquid metal interconnections exhibits mechanical and electrical stability under 50% biaxial stretching and allows for the spatial mapping of temperature with visual color display regardless of wrist movement while attached to the skin of the wrist. This work is expected to be widely useful in the development of skin‐attachable electronics for medical and health‐care monitoring.     

Bubble‐Decorated Honeycomb‐Like Graphene Film as Ultrahigh Sensitivity Pressure Sensors

Recently, macroporous graphene monoliths (MGMs), with ultralow density and good electrical conductivity, have been considered as excellent pressure sensors due to their excellent elasticity with a rapid rate of recovery. However, MGMs can only exhibit good sensitivity when the strain is higher than 20%, which is undesirable for touch‐type pressure sensors, such as artificial skin. Here, an innovative method for the fabrication of freestanding flexible graphene film with bubbles decorated on honeycomb‐like network is demonstrated. Due to the switching effect depended on “point‐to‐point” and “point‐to‐face” contact modes, the graphene pressure sensor has an ultrahigh sensitivity of 161.6 kPa^?1 at a strain less than 4%, several hundred times higher than most previously reported pressure sensors. Moreover, the graphene pressure sensor can monitor human motions such as finger bending and pulse with a very low operating voltage of 10 mV, which is sufficiently low to allow for powering by energy‐harvesting devices, such as triboelectric generators. Therefore, the high sensitivity, low operating voltage, long cycling life, and large‐scale fabrication of the pressure sensors make it a promising candidate for manufacturing low‐cost artificial skin.     

2D Colloidal Array of Glucose‐Conjugative Conductive Microparticles for a Pressure‐Mediated Chemiresistive Sensor Platform

A platform is introduced for pressure‐mediated chemiresistive glucose sensing based on a 2D array of glucose‐conjugating silver nanowire (AgNW)‐deposited conductive microparticles (AgCMPs). Glucose‐conjugating AgCMPs, as transducers of the sensors, are fabricated by decorating the surface of monodisperse polyurethane elastomeric MPs with AgNWs by layer‐by‐layer deposition. Then, the AgNWs are covalently bonded to 4‐mercaptophenylboronic acid (4‐MPBA) to endow them with chemiresistive glucose sensing property against the applied pressure. The 4‐MPBA‐functionalized AgCMPs are positioned with high accuracy on a hole‐patterned stencil film placed between electrodes. Using this sensor system, it is shown that the current induced by the application of constant pressure to the sensor film at a given supply voltage varies linearly with the glucose concentration before and after critical glucose bridging concentration. Notably, the AgCMP‐based chemiresistive sensors could detect glucose over a wide concentration range from 0.56 × 10^?6 m to 56 × 10^?3 m with remarkable sensitivity and selectivity.