Adaptively resettable microfluidic patch for sweat rate and electrolytes detection.

Skin-interfaced microfluidic patch has become a reliable device for sweat collection and analysis. However, the intractable problems of emptying the microchannel for reuse, and the channel's volumetric capacity limited by the size of the patch, directly hinder the practical application of sweat sensors. Herein, we report an adaptively resettable microfluidic sweat patch (Art-Sweat patch) capable of continuously monitoring both sweat rate (0.2-4.0 µL min-1) and total ionic charge concentration (10-200 mmol L-1). We develop a platform with a vertical and horizontal microchannel combined strategy, enabling repeatedly filling sweat and emptying the microchannel for autonomously resetting and detecting. The variation in the emptied volume is designed to be adaptively identified by the sensor, resulting in enhanced stability and an enlarged volumetric capacity of over 300 µL. By integrating with self-designed wireless transmission modules, the proposed Art-Sweat patch shows product-level wearability and high performance in monitoring variations in regional sweat rate and concentration for hydration status assessment.

Perspiration permeable, textile embeddable microfluidic sweat sensor.

Epidermal microfluidic devices are continuously being developed for efficient sweat collection and sweat rate detection. However, most microfluidic designs ignore the use of airtight/adhesive substrate will block the natural perspiration of the covered sweat pores, which will seriously affect normal sweat production and long-term wearable comfort. Herein, we present a Janus textile-embedded microfluidic sensor platform with high breathability and directional sweat permeability for synchronous sweat rate and total electrolyte concentration detection. The device consists of a hollowed-out serpentine microchannel with interdigital electrodes and Janus textile. The dual-mode signal of the sweat rate (0.2-4.0 µL min-1) and total ionic charge concentration (10-200 mmol L-1) can be obtained synchronously by decoupling conductance step signals generated when sweat flows through alternating interdigitated spokes at equal intervals in the microchannel. Meanwhile, the hollowed-out microchannel structure significantly reduces the coverage area of the sensor on the skin, and the Janus textile-embedded device ensures a comfortable skin/device interface (fewer sweat pores are blocked) and improves breathability (503.15 g m-2 d-1) and sweat permeability (directional liquid transportation) during long-term monitoring. This device is washable and reusable, which shows the potential to integrate with clothing and smart textile, and thus facilitate the practicality of wearable sweat sensors for personalized healthcare.

An unconventional vertical fluidic-controlled wearable platform for synchronously detecting sweat rate and electrolyte concentration.

Epidermal microfluidic devices with long microchannels have been developed for continuous sweat analysis, which are crucial to assess personal hydration status and underlying health conditions. However, the flow resistance in long channels and the ionic concentration variation significantly affect the accuracy of both the sweat rate and electrolyte concentration measurements. Herein, we present a novel fluidic-controlled wearable platform for synchronously dropwise-detecting the sweat rate and total electrolyte concentration. The unconventional platform consisting of a vertically shortened channel, a pair of embedded electrodes and an absorption layer, is designed to minimize the flow resistance and transform sweat fluidics into uniform micro-droplets for chronological and dropwise detection. Real-time sweat conductance is decoupled from a square-wave-like curve, where the sweat rate and electrolyte concentration can be derived from the interval time and peak value, respectively. Flexible and wearable band devices are demonstrated to show their potential application for hydration status assessment during exercises.

All-Nanofiber-Based Janus Epidermal Electrode with Directional Sweat Permeability for Artifact-Free Biopotential Monitoring.

Epidermal electronics have been developed with gas/sweat permeability for long-term wearable electrophysiological monitoring. However, the state-of-the-art breathable epidermal electronics ignore the sweat accumulation and immersion at the skin/device interface, resulting in serious degradation of the interfacial conformality and adhesion, leading to signal artifacts with unstable and inaccurate biopotential measurements. Here, the authors present an all-nanofiber-based Janus epidermal electrode endowed with directional sweat transport properties for artifact-free biopotential monitoring. The designed Janus multilayered membrane (≈15 µm) of superhydrophilic-hydrolyzed-polyacrylonitrile (HPAN)/polyurethane (PU)/Ag nanowire (AgNW) can quickly (less than 5 s) drive sweat away from the skin/electrode interface while resisting its penetration in the reverse direction. Along with the medical adhesive (MA)-reinforced junction-nodes, the adhesion strength among the heterogeneous interfaces can be greatly enhanced for robust mechanical-electrical stability. Therefore, their measured on-body electromyography (EMG) and electrocardiography (ECG) signals are free of sweat artifacts with negligible degradation and baseline drift compared to commercial Ag/AgCl gel electrodes and hydrophilic textile electrodes. This work paves a way to design novel directional-sweat-permeable epidermal electronics that can be conformally attached under sweaty conditions for long-term biopotential monitoring and shows the potential to apply epidermal electronics to many challenging conditions.

Flexible Capacitive Tactile Sensor Based on Micropatterned Dielectric Layer.

Flexible tactile sensors are considered as an effective way to realize the sense of touch, which can perform the synchronized interactions with surrounding environment. Here, the utilization of bionic microstructures on natural lotus leaves is demonstrated to design and fabricate new-type of high-performance flexible capacitive tactile sensors. Taking advantage of unique surface micropattern of lotus leave as the template for electrodes and using polystyrene microspheres as the dielectric layer, the proposed devices present stable and high sensing performance, such as high sensitivity (0.815 kPa-1 ), wide dynamic response range (from 0 to 50 N), and fast response time (≈38 ms). In addition, the flexible capacitive sensor is not only applicable to pressure (touch of a single hair), but also to bending and stretching forces. The results indicate that the proposed capacitive tactile sensor is a promising candidate for the future applications in electronic skins, wearable robotics, and biomedical devices.

Exfoliation at the liquid/air interface to assemble reduced graphene oxide ultrathin films for a flexible noncontact sensing device.

Reduced graphene oxide ultrathin films are fabricated by a reproducible exfoliation method at the liquid/air interface, and they show high transparency, tunable sheet resistance, uniform electric conductivity, and structural homogeneity over a large area. A flexible relative humidity sensing matrix is demonstrated and it is shown to be excellent for close proximity sensing without touching it. This method opens up a novel avenue for future human-machine interaction applications.

Silk-molded flexible, ultrasensitive, and highly stable electronic skin for monitoring human physiological signals.

Flexible and transparent E-skin devices are achieved by combining silk-molded micro-patterned polydimethylsiloxane (PDMS) with single-walled carbon nanotube (SWNT) ultrathin films. The E-skin sensing device demonstrates superior sensitivity, a very low detectable pressure limit, a fast response time, and a high stability for the detection of superslight pressures, which may broaden their potential use as cost-effective wearable electronics for healthcare applications.