Pressure-sensitive electronic skin composed of a hierarchical structural array exhibits outstanding linear and high sensitivity in the pressure range exerted by gentle touch. By virtue of monolayer graphene acting as electrode material, this device can be operated with low voltage. Especially, its high transparency enables an accurate placement of the device on the target position when it is used for health monitoring.

Human skin imperfectly discriminates between pressure and temperature stimuli under mixed stimulation, and exhibits nonlinear sensitivity to each stimulus. Despite great advances in the field of electronic skin (E-skin), the limitations of human skin have not previously been overcome. For the first time, the development of a stimulus-discriminating and linearly sensitive bimodal E-skin that can simultaneously detect and discriminate pressure and temperature stimuli in real time is reported. By introducing a novel device design and using a temperature-independent material, near-perfect stimulus discriminability is realized. In addition, the hierarchical contact behavior of the surface-wrinkled microstructure and the optimally reduced graphene oxide in the E-skin contribute to linear sensitivity to applied pressure/temperature stimuli over wide intensity range. The E-skin exhibits a linear and high pressure sensitivity of 0.7 kPa up to 25 kPa. Its operation is also robust and exhibits fast response to pressure stimulus within 50 ms. In the case of temperature stimulus, the E-skin shows a linear and reproducible temperature coefficient of resistance of 0.83% K in the temperature range 22-70 °C and fast response to temperature change within 100 ms. In addition, two types of stimuli are simultaneously detected and discriminated in real time by only impedance measurements.

Flexible and skin-attachable vibration sensors have been studied for use as wearable voice-recognition electronics. However, the development of vibration sensors to recognize the human voice accurately with a flat frequency response, a high sensitivity, and a flexible/conformable form factor has proved a major challenge. Here, we present an ultrathin, conformable, and vibration-responsive electronic skin that detects skin acceleration, which is highly and linearly correlated with voice pressure. This device consists of a crosslinked ultrathin polymer film and a hole-patterned diaphragm structure, and senses voices quantitatively with an outstanding sensitivity of 5.5 V Pa −1 over the voice frequency range. Moreover, this ultrathin device (<5 μm) exhibits superior skin conformity, which enables exact voice recognition because it eliminates vibrational distortion on rough and curved skin surfaces. Our device is suitable for several promising voice-recognition applications, such as security authentication, remote control systems and vocal healthcare.

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Recently, some researchers have incorporated a sweat-collecting system into sweat sensors for sweat collection and transportation. [6] The sweat-absorbing layers that have been tested include paper [7] and rayon; [2a] however, these collection layers have no directionality in sweat transportation and are therefore not appropriate for continuous monitoring of freshly generated sweat in the sensing area. An alternative is a microfluidics channel system; [8] however, such a system can cause contamination of the sample by allowing old and new sweat to mix by diffusion within the channel. Such devices also have low sweatcollection efficiency because the channel must be filled to fill the sensing area. [9] In all cases, the directionality and the sweatcollecting efficiency are insufficient.In the present study, we demonstrate a sweat-collecting patch with directional sweat transportation and high sweat-collection efficiency, enabling fast and continuous monitoring of sweat by a sensor. The collecting component of the patch consists of channels with a narrow superhydrophilic wedge-shaped pattern within superhydrophobic bounds on a hierarchical microstructured/ nanostructured surface and a sweat reservoir that can be combined with a sweat sensor. The wedge-shaped wettability patterns were inspired by spines of cacti; they are narrow at the perimeter of the patch and gradually widen toward the junction with the sensing area at the center. The Laplace pressure is centripetal because of a combination of geometric structure and the difference between the surface energies of the superhydrophobic and superhydrophilic components. As a result, the sweat is transported spontaneously irrespective of gravity even when the substrate is aligned vertically. The patch transports the sweat almost without leaving it inside the channel and thereby concentrates the sweat from a large area of the skin onto the sensing area. The wedge-shaped wettability-patterned channel has greater sweat-collection efficiency than a conventional microfluidics channel and enables doubling of the speed of sweat collection. In an on-body test, the patch with a sensor responded to biochemicals within 5 min of its wearer beginning to exercise. By accelerating the circulation rate of sweat, the patch reduces the time that sweat remains in the sensing area and, by providing freshly generated sweat to it, enables the continuous sensor-based monitoring of changes in sweat biochemicals as blood changes.A sweat sensor is expected to be the most appropriate wearable device for noninvasive healthcare monitoring. However, the practical use of sweat sensors is impeded by irregular and low sweat secretion rates. Here, a sweatcollecting patch that can collect sweat efficiently for fast and continuous healthcare monitoring is demonstrated. The patch uses cactus-spine-inspired wedge-shaped wettability-patterned channels on a hierarchical microstructured/nanostructured surface. The channel shape, in combination with the superhydrophobic/superhydrophilic surface materials, ...