Wearable fiber-based visual strain sensors with high sensitivity and excellent cyclic stability for health monitoring and thermal management

Visual strain sensors have attracted significant attention in the smart wearables field due to their ability to intuitively monitor human health and movement through color displays. However, their development is limited by restricted sensitivity over a large strain range and poor cyclic stability. The conductivity and electricity-induced heating performance can be enhanced by filling microcracks with conductive nanoparticles to increase the conductive paths. Inspired by this concept, nanocarbon powder/silver nanoparticles@carboxylic multi-walled carbon nanotubes/polyurethane (NAMP) fiber-based visual strain sensors were developed using wet spinning, in-situ polymerization, and ultrasonic impregnation techniques. The NAMP sensors exhibit high sensitivity (GF=3528), a wide strain range (0-107 %), and excellent cyclic stability (over 5000 cycles), demonstrating high reusability, stability, and durability. Meanwhile, a wide temperature range from 27.8 degrees C to 75.2 degrees C and corresponding color display changes triggered by applied voltages from 0 to 2.5 V were achieved, indicating excellent visualization performance. In addition, the integration of NAMP fibers into temperature-adjustable electrothermal fabric can be utilized for human thermal management therapy and deicing. This work provides valuable insights into the design and potential applications of intelligent fibrous sensor, paving the way for the development of wearable textiles from fibers to fabrics.