Skin‐Like Stretchable Fuel Cell Based on Gold‐Nanowire‐Impregnated Porous Polymer Scaffolds

Skin‐like energy devices can be conformally attached to the human body, which are highly desirable to power soft wearable electronics in the future. Here, a skin‐like stretchable fuel cell based on ultrathin gold nanowires (AuNWs) and polymerized high internal phase emulsions (polyHIPEs) scaffolds is demonstrated. The polyHIPEs can offer a high porosity of 80% yet with an overall thickness comparable to human skin. Upon impregnation with electronic inks containing ultrathin (2 nm in diameter) and ultrahigh aspect‐ratio (>10 000) gold nanowires, skin‐like strain‐insensitive stretchable electrodes are successfully fabricated. With such designed strain‐insensitive electrodes, a stretchable fuel cell is fabricated by using AuNWs@polyHIPEs, platinum (Pt)‐modified AuNWs@polyHIPEs, and ethanol as the anode, cathode, and fuel, respectively. The resulting epidermal fuel cell can be patterned and transferred onto skin as “tattoos” yet can offer a high power density of 280 µW cm^?2 and a high durability (>90% performance retention under stretching, compression, and twisting). The results presented here demonstrate that this skin‐thin, porous, yet stretchable electrode is essentially multifunctional, simultaneously serving as a current collector, an electrocatalyst, and a fuel host, indicating potential applications to power future soft wearable 2.0 electronics for remote healthcare and soft robotics.     

A Highly Stretchable Transparent Self‐Powered Triboelectric Tactile Sensor with Metallized Nanofibers for Wearable Electronics

Recently, the quest for new highly stretchable transparent tactile sensors with large‐scale integration and rapid response time continues to be a great impetus to research efforts to expand the promising applications in human–machine interactions, artificial electronic skins, and smart wearable equipment. Here, a self‐powered, highly stretchable, and transparent triboelectric tactile sensor with patterned Ag‐nanofiber electrodes for detecting and spatially mapping trajectory profiles is reported. The Ag‐nanofiber electrodes demonstrate high transparency (>70%), low sheet resistance (1.68–11.1 Ω □^?1), excellent stretchability, and stability (>100% strain). Based on the electrode patterning and device design, an 8 × 8 triboelectric sensor matrix is fabricated, which works well under high strain owing to the effect of the electrostatic induction. Using cross‐locating technology, the device can execute more rapid tactile mapping, with a response time of 70 ms. In addition, the object being detected can be made from any commonly used materials or can even be human hands, indicating that this device has widespread potential in tactile sensing and touchpad technology applications.     

Transparent,stretchable, and rapid-response humidity sensor for body-attachable wearable electronics

Stretchable and conformal humidity sensors that can be attached to the human body for continuously monitoring the humidity of the environment around the human body or the moisture level of the human skin can play an important role in electronic skin and personal healthcare applications.However,most stretchable humidity sensors are based on the geometric engineering of non-stretchable components and only a few detailed studies are available on stretchable humidity sensors under applied mechanical deformations.In this paper,we propose a transparent,stretchable humidity sensor with a simple fabrication process,having intrinsically stretchable components that provide high stretchability,sensitivity,and stability along with fast response and relaxation time.Composed of reduced graphene oxide-polyurethane composites and an elastomeric conductive electrode,this device exhibits impressive response and relaxation time as fast as 3.5 and 7 s,respectively.The responsivity and the response and relaxation time of the device in the presence of humidity remain almost unchanged under stretching up to a strain of 60％ and after 10,000 stretching cycles at a 40％ strain.Further,these stretchable humidity sensors can be easily and conformally attached to a finger for monitoring the humidity levels of the environment around the human body,wet objects,or human skin.     

Design of Novel Wearable,Stretchable, and Waterproof Cable‐Type Supercapacitors Based on High‐Performance Nickel Cobalt Sulfide‐Coated Etching‐Annealed Yarn Electrodes

Rapid advances in functional electronics bring tremendous demands on innovation toward effective designs of device structures. Yarn supercapacitors (SCs) show advantages of flexibility, knittability, and small size, and can be integrated into various electronic devices with low cost and high efficiency for energy storage. In this work, functionalized stainless steel yarns are developed to support active materials of positive and negative electrodes, which not only enhance capacitance of both electrodes but can also be designed into stretchable configurations. The as‐made asymmetric yarn SCs show a high energy density of 0.0487 mWh cm^?2 (10.19 mWh cm^?3) at a power density of 0.553 mW cm^?2 (129.1 mW cm^?3) and a specific capacitance of 127.2 mF cm^?2 under an operating voltage window of 1.7 V. The fabricated SC is then made into a stretchable configuration by a prestraining‐then‐releasing approach using polydimethylsiloxane (PDMS) tube, and its electrochemical performance can be well maintained when stretching up to a high strain of 100%. Moreover, the stretchable cable‐type SCs are stably workable under water‐immersed condition. The method opens up new ways for fabricating flexible, stretchable, and waterproof devices.     

Stretchable Triboelectric–Photonic Smart Skin for Tactile and Gesture Sensing

Smart skin is expected to be stretchable and tactile for bionic robots as the medium with the ambient environment. Here, a stretchable triboelectric–photonic smart skin (STPS) is reported that enables multidimensional tactile and gesture sensing for a robotic hand. With a grating‐structured metal film as the bioinspired skin stripe, the STPS exhibits a tunable aggregation‐induced emission in a lateral tensile range of 0–160%. Moreover, the STPS can be used as a triboelectric nanogenerator for vertical pressure sensing with a maximum sensitivity of 34 mV Pa^?1. The pressure sensing characteristics can remain stable in different stretching conditions, which demonstrates a synchronous and independent sensing property for external stimuli with great durability. By integrating on a robotic hand as a conformal covering, the STPS shows multidimensional mechanical sensing abilities for external touch and different gestures with joints bending. This work has first demonstrated a triboelectric–photonic coupled multifunctional sensing terminal, which may have great applications in human–machine interaction, soft robots, and artificial intelligence.     

Metal Deposition on a Self‐Generated Microfibril Network to Fabricate Stretchable Tactile Sensors Providing Analog Position Information

Stretchable conductors and sensors have attracted great attention for use in electronic skin and healthcare monitoring. Despite the development of many stretchable conductors, there are still very few studies that utilize the conventional methods making electrodes and circuits used in current industry. A method is proposed to fabricate a stretchable electrode pattern and a stretchable tactile sensor by simply depositing linear metal lines through a mask on a stretchable substrate. A method is developed of a self‐generating microfibril network on the surface of stretchable block copolymer substrates. The formation mechanism of the microfibril network is studied with finite element method simulations. Metals (Au and Ag nanowires) are deposited directly on the substrate through a patterned mask. This study shows that strain‐insensitive circuit and strain‐sensitive sensor can be fabricated in a controlled way by adjusting the thickness of the deposited metal, which makes it easy to fabricate a tactile sensor by metal deposition. Also, by using the characteristic that the sensor has different sensitivity depending on the line pattern width, a novel sensor structure simultaneously providing analog‐type position information and pressure value is proposed.     

Fatigue Resistant Aerogel/Hydrogel Nanostructured Hybrid for Highly Sensitive and Ultrabroad Pressure Sensing

Achieving high sensitivity over a broad pressure range remains a great challenge in designing piezoresistive pressure sensors due to the irreconcilable requirements in structural deformability against extremely high pressures and piezoresistive sensitivity to very low pressures. This work proposes a hybrid aerogel/hydrogel sensor by integrating a nanotube structured polypyrrole aerogel with a polyacrylamide (PAAm) hydrogel. The aerogel is composed of durable twined polypyrrole nanotubes fabricated through a sacrificial templating approach. Its electromechanical performance can be regulated by controlling the thickness of the tube shell. A thicker shell enhances the charge mobility between tube walls and thus expedites current responses, making it highly sensitive in detecting low pressure. Moreover, a nucleotide-doped PAAm hydrogel with a reversible noncovalent interaction network is harnessed as the flexible substrate to assemble the aerogel/hydrogel hybrid sensor and overcome sensing saturation under extreme pressures. This highly stretchable and self-healable hybrid polymer sensor exhibits linear response with high sensitivity (S_min > 1.1 kPa^?1), ultrabroad sensing range (0.12–≈400 kPa), and stable sensing performance over 10 000 cycles at the pressure of 150 kPa, making it an ideal sensing device to monitor pressures from human physiological signals to significant stress exerted by vehicles.     

A Highly Stretchable and Real‐Time Healable Supercapacitor

In addition to a high specific capacitance, a large stretchability and self‐healing properties are also essential to improve the practicality and reliability of supercapacitors in portable and wearable electronics. However, the integration of multiple functions into one device remains challenging. Here, the construction of a highly stretchable and real‐time omni‐healable supercapacitor is demonstrated by sandwiching the polypyrrole‐incorporated gold nanoparticle/carbon nanotube (CNT)/poly(acrylamide) (GCP@PPy) hydrogel electrodes with a CNT‐free GCP (GP) hydrogel as the electrolyte and chemically soldering an Ag nanowire film to the hydrogel electrode as the current collector. The newly developed dynamic metal‐thiolate (M‐SR, M = Au, Ag) bond‐induced integrated configuration, with an intrinsically powerful electrode and electrolyte, enables the assembled supercapacitor to deliver an areal capacitance of 885 mF cm^?2 and an energy density of 123 µWh cm^?2, which are among the highest‐reported values for stretchable supercapacitors. Notably, the device exhibits a superhigh stretching strain of 800%, rapid optical healing capability, and significant real‐time healability during the charge–discharge process. The exceptional performance combined with the facile assembly method confirms this multifunctional device as the best performer among all the flexible supercapacitors reported to date.     

A High Aspect Ratio Serpentine Structure for Use As a Strain‐Insensitive,Stretchable Transparent Conductor

The development of strain‐insensitive stretchable transparent conductors (TCs) is essential for manufacturing stretchable electronics. Despite recent progress, achieving a high optoelectronic performance under applied strain of 50% continues to present a significant challenge in this research field. Herein, an ultratall and ultrathin high aspect ratio serpentine metal structure is described that exhibits a remarkable stretching ability (the resistance remains constant under applied strain of 100%) and simultaneously provides an excellent transparent conducting performance (with a sheet resistance of 7.6 Ω ^?1 and a transmittance of 90.5%). It is demonstrated that the highly stretchable transparent conducting properties can be attributed to the high aspect ratio feature. A high aspect ratio (aspect ratio of 17–367) structure permits facile deformation of the serpentine structure with in‐plane motion, leading to a high stretching ability. In addition, this structural feature avoids the classic tradeoff between optical transmittance and electrical conductance, providing a high electrical conductance without decreasing the optical transmittance. The practical utility of these devices is tested by using these TCs as stretchable interconnectors among LEDs or in wearable VOC gas sensors.     

On‐Skin Triboelectric Nanogenerator and Self‐Powered Sensor with Ultrathin Thickness and High Stretchability

Researchers have devoted a lot of efforts on pursuing light weight and high flexibility for the wearable electronics, which also requires the related energy harvesting devices to have ultrathin thickness and high stretchability. Hence, an elastic triboelectric nanogenerator (TENG) is proposed that can serve as the second skin on human body. The total thickness of this TENG is about 102 µm and the device can work durably under a strain of 100%. The carbon grease is painted on the surface of elastomer film to work as stretchable electrode and thus the fine geometry control of the electrode can be achieved. This elastic TENG can even work on the human fingers without disturbing body movement. The open‐circuit voltage and short‐circuit current from the device with a contact area of 9 cm² can reach 115 V and 3 µA, respectively. Two kinds of self‐powered sensor systems with optimized identification strategies are also designed to demonstrate the application possibility of this elastic TENG. The superior characteristics of ultrathin thickness, high stretchability, and fine geometry control of this TENG can promote many potential applications in the field of wearable self‐powered sensory system, electronics skin, artificial muscles, and soft robotics.     

Printable Superelastic Conductors with Extreme Stretchability and Robust Cycling Endurance Enabled by Liquid‐Metal Particles

Stretchable conductors are vital and indispensable components in soft electronic systems. The development for stretchable conductors has been highly motivated with different approaches established to address the dilemma in the conductivity and stretchability trade‐offs to some extent. Here, a new strategy to achieve superelastic conductors with high conductivity and stable electrical performance under stretching is reported. It is demonstrated that by electrically anchoring conductive fillers with eutectic gallium indium particles (EGaInPs), significant improvement in stretchability and durability can be achieved in stretchable conductors. Different from the strategy of modulating the chemical interactions between the conductive fillers and host polymers, the EGaInPs provide dynamic and robust electrical anchors between the conductive fillers. A superelastic conductor which can achieve a high stretchability with 1000% strain at initial conductivity of 8331 S cm^?1 and excellent cycling durability with about eight times resistance change (compared to the initial resistance at 0% strain before stretching) after reversibly stretching to 800% strain for 10 000 times is demonstrated. Applications of the superelastic conductor in an interactive soft touch device and a stretchable light‐emitting system are also demonstrated, featuring its promising applications in soft robotics or soft and interactive human–machine interfaces.     

A Biodegradable and Stretchable Protein‐Based Sensor as Artificial Electronic Skin for Human Motion Detection

Due to the natural biodegradability and biocompatibility, silk fibroin (SF) is one of the ideal platforms for on‐skin and implantable electronic devices. However, the development of SF‐based electronics is still at a preliminary stage due to the SF film intrinsic brittleness as well as the solubility in water, which prevent the fabrication of SF‐based electronics through traditional techniques. In this article, a flexible and stretchable silver nanofibers (Ag NFs)/SF based electrode is synthesized through water‐free procedures, which demonstrates outstanding performance, i.e., low sheet resistance (10.5 Ω sq^?1), high transmittance (>90%), excellent stability even after bending cycles >2200 times, and good extensibility (>60% stretching). In addition, on the basis of such advanced (Ag NFs)/SF electrode, a flexible and tactile sensor is further fabricated, which can simultaneously detect pressure and strain signals with a large monitoring window (35 Pa–700 kPa). Besides, this sensor is air‐permeable and inflammation‐free, so that it can be directly laminated onto human skins for long‐term health monitoring. Considering the biodegradable and skin‐comfortable features, this sensor may become promising to find potential applications in on‐skin or implantable health‐monitoring devices.     

Surface Strain Redistribution on Structured Microfibers to Enhance Sensitivity of Fiber‐Shaped Stretchable Strain Sensors

Fiber‐shaped stretchable strain sensors with small testing areas can be directly woven into textiles. This paves the way for the design of integrated wearable devices capable of obtaining real‐time mechanical feedback for various applications. However, for a simple fiber that undergoes uniform strain distribution during deformation, it is still a big challenge to obtain high sensitivity. Herein, a new strategy, surface strain redistribution, is reported to significantly enhance the sensitivity of fiber‐shaped stretchable strain sensors. A new method of transient thermal curing is used to achieve the large‐scale fabrication of modified elastic microfibers with intrinsic microbeads. The proposed strategy is independent of the active materials utilized and can be universally applied for various active materials. The strategy used here will shift the vision of the sensitivity enhancement method from the active materials design to the mechanical design of the elastic substrate, and the proposed strategy can also be applied to nonfiber‐shaped stretchable strain sensors.     

Stretchable Organometal‐Halide‐Perovskite Quantum‐Dot Light‐Emitting Diodes

Stretchable light‐emitting diodes (LEDs) and electroluminescent capacitors have been reported to potentially bring new opportunities to wearable electronics; however, these devices lack in efficiency and/or stretchability. Here, a stretchable organometal‐halide‐perovskite quantum‐dot LED with both high efficiency and mechanical compliancy is demonstrated. The hybrid device employs an ultrathin (<3 µm) LED structure conformed on a surface‐wrinkled elastomer substrate. Its luminescent efficiency is up to 9.2 cd A^?1, which is 70% higher than a control diode fabricated on the rigid indium tin oxide/glass substrate. Mechanical deformations up to 50% tensile strain do not induce significant loss of the electroluminescent property. The device can survive 1000 stretch–release cycles of 20% tensile strain with small fluctuations in electroluminescent performance.     

Bath Electrospinning of Continuous and Scalable Multifunctional MXene‐Infiltrated Nanoyarns

Electroactive yarns that are stretchable are desired for many electronic textile applications, including energy storage, soft robotics, and sensing. However, using current methods to produce these yarns, achieving high loadings of electroactive materials and simultaneously demonstrating stretchability is a critical challenge. Here, a one‐step bath electrospinning technique is developed to effectively capture Ti₃C₂T_x MXene flakes throughout continuous nylon and polyurethane (PU) nanofiber yarns (nanoyarns). With up to ≈90 wt% MXene loading, the resulting MXene/nylon nanoyarns demonstrate high electrical conductivity (up to 1195 S cm^?1). By varying the flake size and MXene concentration, nanoyarns achieve stretchability of up to 43% (MXene/nylon) and 263% (MXene/PU). MXene/nylon nanoyarn electrodes offer high specific capacitance in saturated LiClO₄ electrolyte (440 F cm^?3 at 5 mV s^?1), with a wide voltage window of 1.25 V and high rate capability (72% between 5 and 500 mV s^?1). As strain sensors, MXene/PU yarns demonstrate a wide sensing range (60% under cyclic stretching), high sensitivity (gauge factor of ≈17 in the range of 20–50% strain), and low drift. Utilizing the stretchability of polymer nanofibers and the electrical and electrochemical properties of MXene, MXene‐based nanoyarns demonstrate potential in a wide range of applications, including stretchable electronics and body movement monitoring.     

Highly Sensitive and Stretchable Resistive Strain Sensors Based on Microstructured Metal Nanowire/Elastomer Composite Films

High sensitivity and high stretchability are two conflicting characteristics that are difficult to achieve simultaneously in elastic strain sensors. A highly sensitive and stretchable strain sensor comprising a microstructured metal nanowire (mNW)/elastomer composite film is presented. The surface structure is easily prepared by combining an mNW coating and soft‐lithographic replication processes in a simple and reproducible manner. The densely packed microprism‐array architecture of the composite film leads to a large morphological change in the mNW percolation network by efficiently concentrating the strain in the valley regions upon stretching. Meanwhile, the percolation network comprising mNWs with a high aspect ratio is stable enough to prevent electrical failure, even under high strains. This enables the sensor to simultaneously satisfy high sensitivity (gauge factor ≈81 at >130% strain) and high stretchability (150%) while ensuring long‐term reliability (10 000 cycles at 150% strain). The sensor can also detect strain induced by bending and pressure, thus demonstrating its potential as a versatile sensing tool. The sensor is successfully utilized to monitor a wide range of human motions in real time. Furthermore, the unique sensing mechanism is easily extended to detect more complex multiaxial strains by optimizing the surface morphology of the device.     

Microtopography‐Guided Conductive Patterns of Liquid‐Driven Graphene Nanoplatelet Networks for Stretchable and Skin‐Conformal Sensor Array

Flexible thin‐film sensors have been developed for practical uses in invasive or noninvasive cost‐effective healthcare devices, which requires high sensitivity, stretchability, biocompatibility, skin/organ‐conformity, and often transparency. Graphene nanoplatelets can be spontaneously assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates via a convective Marangoni force in a highly controlled manner. Based on this versatile graphene assembled film preparation, a thin, stretchable and skin‐conformal sensor array (144 pixels) is fabricated having microtopography‐guided, graphene‐based, conductive patterns embedded without any complicated processes. The electrically controlled sensor array for mapping spatial distributions (144 pixels) shows high sensitivity (maximum gauge factor ≈1697), skin‐like stretchability (<48%), high cyclic stability or durability (over 10⁵ cycles), and the signal amplification (≈5.25 times) via structure‐assisted intimate‐contacts between the device and rough skin. Furthermore, given the thin‐film programmable architecture and mechanical deformability of the sensor, a human skin‐conformal sensor is demonstrated with a wireless transmitter for expeditious diagnosis of cardiovascular and cardiac illnesses, which is capable of monitoring various amplified pulse‐waveforms and evolved into a mechanical/thermal‐sensitive electric rubber‐balloon and an electronic blood‐vessel. The microtopography‐guided and self‐assembled conductive patterns offer highly promising methodology and tool for next‐generation biomedical devices and various flexible/stretchable (wearable) devices.     

A Freestanding Stretchable and Multifunctional Transistor with Intrinsic Self‐Healing Properties of all Device Components

A flexible and stretchable field‐effect transistor (FET) is an essential element in a number of modern electronics. To realize the potential of this device in harsh real‐world conditions and to extend its application spectrum, new functionalities are needed to be introduced into the device. Here, solution‐processable elements based on carbon nanotubes that empower flexible and stretchable FET with high hole‐mobility (µ_h ≈ 10 cm² V^?1 s^?1) and relatively low operating voltages (<8 V) and that retain self‐healing properties of all FET components are reported. The device has repeatable intrinsic and autonomic self‐healing ability, namely without use of any external trigger, enabling the restoration of its electrical and mechanical properties, both after microscale damage or complete cut of the device—for example by a scissor. The device can be repeatedly stretched for >200 cycles of up to 50% strain without a significant loss in its electrical properties. The device is applicable in the form of a ≈3 µm thick freestanding skin tattoo and has multifunctional sensing properties, such as detection of temperature and humidity. With this unprecedented biomimetic transistor, highly sustainable and reliable soft electronic applications can be introduced.     

Multiscale Hierarchical Design of a Flexible Piezoresistive Pressure Sensor with High Sensitivity and Wide Linearity Range

Flexible piezoresistive pressure sensors have been attracting wide attention for applications in health monitoring and human‐machine interfaces because of their simple device structure and easy‐readout signals. For practical applications, flexible pressure sensors with both high sensitivity and wide linearity range are highly desirable. Herein, a simple and low‐cost method for the fabrication of a flexible piezoresistive pressure sensor with a hierarchical structure over large areas is presented. The piezoresistive pressure sensor consists of arrays of microscale papillae with nanoscale roughness produced by replicating the lotus leaf's surface and spray‐coating of graphene ink. Finite element analysis (FEA) shows that the hierarchical structure governs the deformation behavior and pressure distribution at the contact interface, leading to a quick and steady increase in contact area with loads. As a result, the piezoresistive pressure sensor demonstrates a high sensitivity of 1.2 kPa⁻¹ and a wide linearity range from 0 to 25 kPa. The flexible pressure sensor is applied for sensitive monitoring of small vibrations, including wrist pulse and acoustic waves. Moreover, a piezoresistive pressure sensor array is fabricated for mapping the spatial distribution of pressure. These results highlight the potential applications of the flexible piezoresistive pressure sensor for health monitoring and electronic skin.     

Kirigami‐Inspired Nanoconfined Polymer Conducting Nanosheets with 2000% Stretchability

Stretchable conductors are essential components of wearable electronics. However, such materials typically sacrifice their electronic conductivity to achieve mechanical stretchability and elasticity. Here, the nanoconfinement and air/water interfacial assembly is explored to grow freestanding mechanical endurance conducting polymer nanosheets that can be stretched up to 2000% with simultaneously high electrical conductivity, inspired by kirigami. Such stretchable conductors show remarkable electronic and mechanical reversibility and reproducibility under more than 1000 cycle durability tests with 2000% deformability, which can be accurately predicted using finite element modeling. The conductivity of nanoconfined freestanding conductor nanosheets increases by three orders of magnitude from 2.2 × 10^?3 to 4.002 S cm^?1 is shown, due to the charge‐transfer complex formation between polymer chain and halogen, while the electrical conductance of the stretchable kirigami nanosheets can be maintained over the entire strain regime. The nanoconfined polymer nanosheets can also act as a sensor capable of sensing the pressure with high durability and real‐time monitoring.