A\nDouble-Layer Polyurethane\nElectrospun Membrane with\nDirectional Sweat Transport Ability for Use as a Soft Strain Sensor

Wearable\nelectronics for long-term monitoring of physiological\nsignals should be capable of removing sweat generated during daily\nmotion, which significantly impacts signal stability, human comfort,\nand safety of the electronics. In this study, we developed a double-layer\npolyurethane (PU) membrane with sweat-directional transport ability\nthat can be applied for monitoring strain signals. The PU membrane\nwas composed of a hydrophilic, conductive layer and a relatively hydrophobic\nlayer. The double-layer PU composite membrane exhibited varied pore\nsize and opposite hydrophilicity on its two sides, enabling the spontaneous\npumping of sweat from the hydrophobic side to the hydrophilic side,\ni.e., the directional transport of sweat. The membrane can be used\nas a strain sensor to monitor motion strain over a broad working range\nof 0% to 250% with high sensitivity (GF = 4.11). The sensor can also\ndetect simple human movements even under sweating conditions. We believe\nthat the strategy demonstrated here will provide new insights into\nthe design of next-generation strain sensors.