Phytic acid-mediated polyacrylamide/chitosan/cellulose nanocrystal/PEDOT:PSS composite hydrogels with ion-electron dual conductive pathways for wearable flexible biosensors

Conductive hydrogels are widely used in flexible sensors for health monitoring. However, current hydrogel sensors face some sustainability challenges, such as unstable conductivity, poor freeze tolerance, rapid dehydration under ambient conditions and limited functionality, significantly hindering their applications. To address these issues, in this study, biomass-derived chitosan (CS) and cellulose nanocrystals (CNC) were incorporated as the primary biological macromolecules into a polyacrylamide (PAM)/2-acrylamido-2-methylpropanesulfonic acid (AMPS) polymer network system. By further introducing phytic acid (PA) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), the PAM/AMPS/CS/CNC/PA/PEDOT:PSS conductive hydrogel was successfully fabricated. The elongation at break and tensile strength of the hydrogel reached 2362.38% and 126.52 kPa, respectively. The H⁺ ions released from PA and the π-π conjugated structure of PEDOT:PSS constructed an ion-electron hybrid conduction mechanism, endowing the hydrogel with an exceptional electrical conductivity of 2.49 S m^-1 and a high sensitivity (gauge factor: 6.04). The strong hydrogen bonding between PA and H₂O molecules effectively inhibited the crystallization and evaporation of water molecules, imparting antifreeze performance to the hydrogel. Even at -20 °C, the hydrogel maintained good toughness (1582% elongation) and electrical conductivity (1.64 S m^-1). Furthermore, the hydrogel demonstrated remarkable self-adhesion, self-healing, antibacterial, and water retention properties. The ultra-stretchable, self-adhesive PA-based anti-freezing and antibacterial conductive hydrogels, built upon the natural polysaccharides CS and CNC, bring great prospects for flexible electronics.