Directional sweat transport window based on hydrophobic/hydrophilic Janus fabric enables continuous transfer and monitoring of sweat

• Hydrophobic/hydrophilic Janus wettability on fabric's two sides is utilized to design a directional sweat transport window. • Fiber-shaped sensing electrodes are fixed on hydrophobic side of the directional sweat transport window. • Spontaneous sweat transfer from hydrophobic to hydrophilic side reduces wear discomfort and measurement inaccuracy caused by sweat accumulation. • Such a directional sweat transport window strategy shows potential to be a platform technology for the development of advanced wearable electronics. Wearable sweat sensors are promising for non-invasive and real-time health monitoring but still confront notable challenges, such as the inaccuracy caused by sweat accumulation/evaporation in sensing area and the wear discomfort due to accumulated sweat and lack of breathability. In this work, we present an all-fabric-based sweat sensing platform based on a novel design of directional sweat transport window for continuous transfer and monitoring of sweat. The directional sweat transport window is built based on hydrophobic/hydrophilic Janus wettability on fabric's two sides, integrated in a highly hydrophobic cotton fabric, and sandwiched between hydrophilic cotton layers. Through the window, sweat collected by inner cotton layer from area in and around the window can be directionally and spontaneously transferred from hydrophobic side to hydrophilic side, even when the hydrophobic side faces downward, i.e., irrespective of gravity. The outer cotton layer serves to draw sweat away from hydrophilic side of directional sweat transport window through continuous evaporation, and thus also as reservoir for sweat residue. Fiber-shaped sensing electrodes were fixed on the hydrophobic side of directional sweat transport window. The directional sweat transport function reduces the time that the sweat remains in the sensing area, thus effectively avoiding the sweat accumulation and enhancing the sensing stability and accuracy, as well as the wear comfort. As a proof of concept, we demonstrated on-body, wireless monitoring of the sweat of a volunteer in physical exercise. Such a directional sweat transport window strategy also shows potential as a platform technology for other wearable applications.