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With the development of wearable devices, the application of non-invasive wearable devices to monitor sweat in real time is the most important for human health. Here, a paper-based microfluidic chip for monitoring of sweat loss during exercise is proposed. Highly absorbent rice paper is selected as the paper-based material, and the capillary action of the paper base is used to actively adsorb sweat, and it can be used repeatedly. As the electrode material, the conductive cloth has good tensile properties and bending resistance, which ensures that the change of resistance is caused by the amount of sweat entering. Other materials of the chip are highly hydrophobic, ensuring that all sweat will be absorbed by the paper base. The sweat volume monitored by the microfluidic chip in real time is 0.5μl-225μl. Compared with rigid electrodes and wet electrodes, the application of flexible electrodes allows the chip to fit well with the skin, the ECG waveform is clearer and has greater amplitude, and the EMG is smoother and has a greater signal-to-noise ratio. [Display omitted] • With the development of wearable devices, non-invasive wearable devices have developed into a hot spot. • Here, a paper-based microfluidic chip for monitoring of sweat loss during exercise is proposed. • The high bending properties of the chip ensure that the resistance change is caused by the amount of sweat. • Use hydrophobic materials to ensure that sweat is absorbed by the paper base, and monitor the sweat volume of 0.5μl-225μl. • The flexible electrode makes the chip fit well with the skin, the ECG waveform is clearer, and the EMG is smoother. [ABSTRACT FROM AUTHOR]

Flexible sensors are an important part of flexible electronic devices, and its application often relies on external power sources. However, traditional commercial batteries require repeated charging, lack of flexibility and potential leakage of electrolyte contamination, which seriously hinder the wearable smart electronic devices' develop of comfortable and portable integration. To overcome this key challenge. This paper combines energy harvesting technology, distributed energy storage devices and flexible electronics. This proposes a modular layout of friction nanogenerator (TENG), miniature solid-state supercapacitor (MSSC) and strain sensor. Three of modular components are constructed on a thermoplastic polyamide film. The basic conductive network is prepared through screen printing technique and graphene multiwall carbon nanotubes (G-MWCNTs) conductive inks. The TENG module is used to collect low-frequency and high-entropy mechanical energy from the surrounding environment for conversion into AC electrical energy. The MSSC module is used to store the electrical energy generated by the TENG and to continuously power the back-end flexible electronics. The strain sensor module has an asymmetric interlaced double-arc snake rib conductive structure inspired by the spotted snake. It enables multi-dimensional strain detection and ultra-sensitive sensing performance. Finally, as a concept proof, the prepared TENG, MSSC and strain sensors are composed to form a self-powered multimode distributed flexible sensing device. It can be used for human health monitoring in the areas of knuckle, elbow, hip and heel nodes. [Display omitted] • This proposes a modular layout of friction nanogenerator (TENG), miniature solid-state supercapacitor (MSSC) and strain sensor. The TENG outputs a maximum voltage of 15.36 V, a shortage current of 0.57 μA and a transferred charge of 5.70 nC. MSSC has a high area ratio capacitance of 7.09 mF cm-2. Capacitance retention up to 96.68% after 5000 volt-amp cycles. The strain sensor uses only 0.1061nW of power at a 0.001 V operating voltage. • The strain sensor module has an asymmetric interlaced double-arc snake rib conductive structure inspired by the spotted snake. It enables multi-dimensional strain detection and ultra-sensitive sensing performance. The sensor proposed in this paper achieves strain gauge factor (GF) of 6300.75 and 435% wide sensing range response. [ABSTRACT FROM AUTHOR]

Flexible electrodes are usually well-matched to the substrate as the core component of flexible electronics technology. However, when large deformation occurs, the conductive layer of flexible electrodes can mechanically fracture due to insufficient mechanical properties, leading to the failure of flexible electronic devices. Improving the mechanical properties of flexible electrodes is essential for the development of flexible electronics. Herein, a flexible electrode with a serpentine shape tetra-chiral structure is designed and fabricated via screen-printed process based on existing tetra-chiral structure. The research demonstrates that the serpentine tetra-chiral structure can improve the mechanical properties of the flexible electrode and the maximum tensile stress is reduced by 87.19 % relative to existing tetra-chiral structure. The flexible electrode is still conductive when the strain of that is 70 %, and the resistance is only 5 Ω and 4.4 Ω, respectively, at a bending angle of 180° and following 1000 times fold cycles. In addition, the flexible electrodes fabricated in this paper are utilized to realize the collection of ECG signals and pulse signals, showing greater potential in biological signal monitoring. The strategy proposed here is expected to maintain electrodes' original functions under repeated use and complex deformation. [Display omitted] • An electrode with a serpentine four-chiral structure is proposed, which shows excellent performance in detecting physiological signals. [ABSTRACT FROM AUTHOR]