Stretchable Triboelectric Self‐Powered Sweat Sensor Fabricated from Self‐Healing Nanocellulose Hydrogels

Wearable sensor technologies are essential to the realization of personalized medicine through continuously monitoring an individual's state of health. Sampling human sweat, which is rich in physiological information, could enable non-invasive monitoring. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate analysis of the physiological state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is critical and requires full system integration to ensure the accuracy of measurements. Here we present a mechanically flexible and fully integrated (that is, no external analysis is needed) sensor array for multiplexed in situ perspiration analysis, which simultaneously and selectively measures sweat metabolites (such as glucose and lactate) and electrolytes (such as sodium and potassium ions), as well as the skin temperature (to calibrate the response of the sensors). Our work bridges the technological gap between signal transduction, conditioning (amplification and filtering), processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin with silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. This application could not have been realized using either of these technologies alone owing to their respective inherent limitations. The wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor physical activities, and to make a real-time assessment of the physiological state of the subjects. This platform enables a wide range of personalized diagnostic and physiological monitoring applications.

A review on the principles, novel applications and perspectives of triboelectric nanogenerators as power sources and as self-powered sensors.

Pressure sensitivity and mechanical self-healing are two vital functions of the human skin. A flexible and electrically conducting material that can sense mechanical forces and yet be able to self-heal repeatably can be of use in emerging fields such as soft robotics and biomimetic prostheses, but combining all these properties together remains a challenging task. Here, we describe a composite material composed of a supramolecular organic polymer with embedded nickel nanostructured microparticles, which shows mechanical and electrical self-healing properties at ambient conditions. We also show that our material is pressure- and flexion-sensitive, and therefore suitable for electronic skin applications. The electrical conductivity can be tuned by varying the amount of nickel particles and can reach values as high as 40 S cm(-1). On rupture, the initial conductivity is repeatably restored with ∼90% efficiency after 15 s healing time, and the mechanical properties are completely restored after ∼10 min. The composite resistance varies inversely with applied flexion and tactile forces. These results demonstrate that natural skin's repeatable self-healing capability can be mimicked in conductive and piezoresistive materials, thus potentially expanding the scope of applications of current electronic skin systems.