Highly Stretchable\nand Fluorescent Visualizable Thermoplastic\nPolyurethane/Tetraphenylethylene Plied Yarn Strain Sensor with Heterogeneous\nand Cracked Structure for Human Health Monitoring

Abstract

Smart wearable technology has been more and more widely\nused in\nmonitoring and prewarning of human health and safety, while flexible\nyarn-based strain sensors have attracted extensive research interest\ndue to their ability to withstand greater external strain and their\nsignificant application potential in real-time monitoring of human\nmotion and health signals. Although several strain sensors based on\nyarn structures have been reported, it remains challenging to strike\na balance between high sensitivity and wide strain ranges. At the\nsame time, visual signal sensing is expected to be used in strain\nsensors thanks to its intuitiveness. In this work, thermoplastic polyurethane\n(TPU) and tetraphenylethylene (TPE) were wet-spun to fabricate flexible\nfluorescent fibers used as the substrate of the sensor, followed by\nthe drop addition of polydimethylsiloxane (PDMS) beads and curing\nto produce a heterogeneous structure, which were further twisted into\na plied yarn. Finally, a visualizable flexible yarn strain sensor\nbased on solidified liquid beads and crack structure was obtained\nby loading polydopamine (PDA) and polypyrrole (PPy) in situ. The sensor\nexhibited high sensitivity (the GF value was 58.9 at the strain range\nof 143–184%), a wide working strain range (0–184%),\na low monitoring limit (<0.1%), a fast response (58.82 ms), reliable\nresponses at different frequencies, and excellent cycle durability\n(over 2000 cycles). At the same time, the yarn strain sensor also\nhad excellent photothermal characteristics and a fluorescence crack\nvisualization effect. These attractive advantages enabled yarn strain\nsensors to accurately monitor various human activities, showing great\napplication potential in health monitoring, personalized medical diagnosis,\nand other aspects.