High-toughness multifunctional conductive hydrogel fibers via microfluidic spinning for flexible strain sensor

Flexible conductive hydrogel fibers have captured considerable attention in wearable electronic devices due to the remarkable flexibility and heightened sensitivity. However, seldom attention has been directed towards the flexible conductive hydrogel fibers that integrate remarkable strength, stretchability, anti-freezing property and wide linear sensing range. Herein, the TEMPO-oxidized cellulose nanofibers-carbon nanotubes/poly(vinyl alcohol)-sodium alginate-tannic acid (TOCNs-CNTs/PVA-SA-TA, TCG) hydrogel fibers are fabricated through the facile microfluidic spinning. TA enhances the mechanical toughness of TCG by establishing richer hydrogen bonds with the double network structure constructed by PVA and SA. TOCNs not only contribute to the homogeneous dispersion of CNTs to form connected conductive networks, but also act as nano-reinforcement to strengthen the matrix. The as-prepared fibers exhibit excellent mechanical properties, including a tensile strength of 8.06 MPa and a strain at break of 438 %. Furthermore, the fibers demonstrate remarkable electrical conductivity (1.57 S m⁻¹) and anti-freezing performance at temperature below −20℃. The sensors based on TCG successfully detect human motions due to the wide detection range (0–250 %), high sensitivity (gauge factor = 2.49 at 250 % strain), fast response time (120 ms) and excellent fatigue resistance (500 cycles), substantiating a great potential for application in flexible wearable devices.