Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.

We report on the facile fabrication of a stretchable array of highly sensitive pressure sensors. The proposed pressure sensor consists of the top layer of Au-deposited polydimethylsiloxane (PDMS) micropillars and the bottom layer of conductive polyaniline nanofibers on a polyethylene terephthalate substrate. The sensors are operated by the changes in contact resistance between Au-coated micropillars and polyaniline according to the varying pressure. The fabricated pressure sensor exhibits a sensitivity of 2.0 kPa(-1) in the pressure range below 0.22 kPa, a low detection limit of 15 Pa, a fast response time of 50 ms, and high stability over 10000 cycles of pressure loading/unloading with a low operating voltage of 1.0 V. The sensor is also capable of noninvasively detecting human-pulse waveforms from carotid and radial artery. A 5 × 5 array of the pressure sensors on the deformable substrate, which consists of PDMS islands for sensors and the mixed thin film of PDMS and Ecoflex with embedded liquid metal interconnections, shows stable sensing of pressure under biaxial stretching by 15%. The strain distribution obtained by the finite element method confirms that the maximum strain applied to the pressure sensor in the strain-suppressed region is less than 0.04% under a 15% biaxial strain of the unit module. This work demonstrates the potential application of our proposed stretchable pressure sensor array for wearable and artificial electronic skin devices.

A stretchable polyaniline nanofiber temperature sensor array with an active matrix consisting of single-walled carbon nanotube thin-film transistors is demonstrated. The integrated temperature sensor array gives mechanical stability under biaxial stretching of 30%, and the resultant spatial temperature mapping does not show any mechanical or electrical degradation.

This paper introduces a liquid-metal integrated system that combines soft electronics materials and engineering designs with advanced near-field-communication (NFC) functionality for human motion sensing. All of the active components, that is, strain sensor, antenna and interconnections, in this device are made of liquid metal, and the device has unique gel-like characteristics and stretchability. Patterning procedures based on selective wetting properties of the reduced GaInSn enable a skin-attachable, miniaturized layout, in which the diameter of the device is less than 2 cm. Electromechanical characterization of the strain sensor and antenna reveals their behaviors under large uniaxial tensile and compressive strains, as well as more complex modes of deformation. Demonstrations of these devices involve their use in monitoring various human motions in a purely wireless fashion; examples include wrist flexion, movements of the vocal cord and finger motion. This simple platform has potential for use in human-machine interfaces for prosthetic control and other applications. NPG Asia Materials (2017) 9, e443; doi:10.1038/am.2017.189; published online 27 October 2017 INTRODUCTION Skin-mounted, deformable devices capable of sensing various signals such as strain, pressure and temperature can be used in a variety of applications ranging from health monitoring systems and personal diagnostics to human-machine interfaces. 1 Advanced concepts in stretchable materials and mechanics principles form the basis for devices that can gently laminate onto the soft and curvilinear surfaces of human skin or conformally wrap onto internal organs of the body. 2-5 Gallium-based liquid metals are highly suitable candidates for such applications due to their unlimited deformability while maintaining excellent metallic conductivity. The use of gallium-based liquid-metal alloys confined in elastomeric enclosures provides intrinsically stretchable properties that maintain bulk electrical conductivity with high stretchability. 6 Additionally, unlike mercury, gallium is safe to use in ambient environment due to its low vapor pressure. 7,8 By taking full advantage of the deformability and nontoxicity of the liquid metal, many research groups have utilized liquid metal for wearable

As part of increased efforts to develop wearable healthcare devices for monitoring and managing physiological and metabolic information, stretchable electrochemical sweat sensors have been investigated. In this study, we report on the fabrication of a stretchable and skin-attachable electrochemical sensor for detecting glucose and pH in sweat. A patterned stretchable electrode was fabricated via layer-by-layer deposition of carbon nanotubes (CNTs) on top of patterned Au nanosheets (AuNS) prepared by filtration onto stretchable substrate. For the detection of glucose and pH, CoWO/CNT and polyaniline/CNT nanocomposites were coated onto the CNT-AuNS electrodes, respectively. A reference electrode was prepared via chlorination of silver nanowires. Encapsulation of the stretchable sensor with sticky silbione led to a skin-attachable sweat sensor. Our sensor showed high performance with sensitivities of 10.89 μA mM cm and 71.44 mV pH for glucose and pH, respectively, with mechanical stability up to 30% stretching and air stability for 10 days. The sensor also showed good adhesion even to wet skin, allowing the detection of glucose and pH in sweat from running while being attached onto the skin. This work suggests the application of our stretchable and skin-attachable electrochemical sensor to health management as a high-performance healthcare wearable device.

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In this study, we demonstrate the fabrication of a highly sensitive flexible temperature sensor with a bioinspired octopus-mimicking adhesive. A resistor-type temperature sensor consisting of a composite of poly(N-isopropylacrylamide) (pNIPAM)-temperature sensitive hydrogel, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and carbon nanotubes exhibits a very high thermal sensitivity of 2.6%·°C between 25 and 40 °C so that the change in skin temperature of 0.5 °C can be accurately detected. At the same time, the polydimethylsiloxane adhesive layer of octopus-mimicking rim structure coated with pNIPAM is fabricated through the formation of a single mold by utilizing undercut phenomenon in photolithography. The fabricated sensor shows stable and reproducible detection of skin temperature under repeated attachment/detachment cycles onto skin without any skin irritation for a long time. This work suggests a high potential application of our skin-attachable temperature sensor to wearable devices for medical and health-care monitoring.

offering comfort to the user. Wearable electronics can be integrated into common textiles or be directly attached onto human skin to perform various functions, for instance, measuring pulses, sensing toxins in the environment, analyzing bodily fluids such as sweat, injecting medication, and informing the user of such activities. Aside from their biomedical purposes, wearable electronics with touchpads and displays, and smart functions, including Internet communication and facial and sound recognition, can also be developed to benefit and assist with daily activities. In addition to functionality, flexibility and stretchability are desired attributes of the components of wearable electronics so that the electronics can exhibit mechanical stability against deformation due to human motions without a deterioration in performance. Many flexible/stretchable devices were developed for integration into wearable devices such as various sensors including bio-signal [1-3] and environmental sensors, [4,5] solar cells, [6,7] energy harvesters, [8] antennas, [9,10] and radio frequency identification (RFID) tags. [11] Moreover, together with other flexible/ stretchable devices, energy storage devices used for powering the active devices on wearable electronics should also be able to withstand deformation. The energy storage devices built for wearable electronics should meet specific criteria, such as having a small size and high efficiency, and being flexible, lightweight, and biocompatible. [12,13] Among the various energy storage devices, supercapacitors are considered one of the most promising candidates in wearable electronics. Rechargeable metal-ion batteries such as lithium-ion batteries (LIBs) have been widely used as energy storage devices in commercial applications owing to their large energy density. Compared to the batteries, supercapacitors have simpler structures, faster charge-discharge time, higher power density of ≈10 kW kg −1 , and longer cycle life over 100 000 cycles. Owing to supercapacitors' uncomplicated architecture, their miniaturization has been extensively studied, resulting in micro-supercapacitors (MSCs). An MSC is a supercapacitor whose total device area is on the square millimeter or centimeter scale, and/or a supercapacitor with a thickness of <10 µm. [14] Materials with a high surface area such as foamstructured materials or nanocarbon-based materials can be utilized to reduce the size and weight of a supercapacitor and to With the miniaturization of personal wearable electronics, considerable effort has been expended to develop high-performance flexible/stretchable energy storage devices for powering integrated active devices. Supercapacitors can fulfill this role owing to their simple structures, high power density, and cyclic stability. Moreover, a high electrochemical performance can be achieved with flexible/stretchable supercapacitors, whose applications can be expanded through the introduction of additional novel functionalities. Here, recent advances in and future prospects for flexible/s...