Multimodal Hydrogel Fiber Sensors with Core-Sheath Architecture for Strain, Temperature, and Flame-Resistant Applications

The porous structure and tunable mechanical modulus of hydrogels make them ideal platforms for multimodal sensing. However, existing multimodal sensors still face challenges such as material interface mismatch, signal crosstalk, and insufficient mechanical flexibility, which limit their long-term stable application. To address these issues, this study introduces a pioneering core-shell structured, wearable multimodal hydrogel fiber sensor. By combining wet spinning with a continuous coating process, a composite structure consisting of a polyvinyl alcohol (PVA)/sodium alginate (SA) hydrogel core and a conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) shell is fabricated. This design provides a composite system with enhanced mechanical properties, wide strain detection, temperature responsiveness, freeze resistance, and flame retardancy. Using a ternary deep eutectic solvent (CaCl 2 -DES) as a coagulation bath significantly improves the fiber’s flexibility and environmental adaptability, overcoming the trade-off between conductivity and mechanical toughness in traditional hydrogel sensors. The resulting fibers exhibit an ultra-high elongation at break (658%) and high tensile strength (10.21 MPa). The strain sensitivity coefficient (GF) remains as high as 31.84 across a wide strain range (>480%), with rapid response/recovery times (<0.6 s) and excellent cycling durability (>150 cycles). Additionally, the fiber sensor shows significant negative temperature coefficient characteristics (TCR = -1.22%/°C) and stability under extreme conditions (structure maintained after 24 h at -20°C). The conductive shell layer also provides effective flame retardancy. This integrated multi-performance strategy not only expands the application potential of hydrogel fibers in flexible wearable devices, medical health monitoring, and extreme environment sensing, but also offers a novel approach to the design of multimodal smart materials.