Flame-retardant, flexible, and breathable smart humidity sensing fabrics based on hydrogels for respiratory monitoring and non-contact sensing

Smart sensing fabrics are becoming increasingly attractive in the emerging wearable areas of medical and military so far. Here, for the first time, we present a smart humidity sensing fabric (SHSF) based on a moisture-sensitive polyacrylamide hydrogel for respiratory monitoring and non-contact sensing. Fabricated by in situ cross-linking of the hydrogel precursors on the fibers of the fabric, the flexible SHSF shows excellent sensitivity, outstanding flame retardance, air permeability, water retention capacity, and stability after treatment with lithium bromide solution. Specifically, its conductance increases more than 311 times as humidity increased from 11% to 98%. Besides, the humidity sensor features good repeatability and the ability to work normally under folding due to its flexible nature. As a clothing material, hydrogel–fabric composite exhibits 4.3 times the burning time compared to cotton fabric, illustrating better flame retardance. The SHSF is used to monitor human breathing and non-contact finger approaching in real time, demonstrating its flexibility in practical applications. This work provides strategies for preparing high-performance, flame-retardant SHSF for emerging wearable electronic devices.