Triple physical cross-linking cellulose nanofibers-based poly(ionic liquid) hydrogel as wearable multifunctional sensors.

A novel triple physical cross-linking poly(ionic liquid) hydrogel, composed of poly(acrylamide-co-dodecyl methacrylate-co-1-vinyl-3-methyluracil-imidazolium chloride)/cellulose nanofibers-Ca (PADV/CNFs-Ca), was synthesized through micellar-copolymerization followed by a solvent-soaked procedure. The synergistic interactions in polymer network (i.e. the hydrophobic association of dodecyl methacrylate moiety in surfactant micelles, the hydrogen bondings between imidazolium monomer segments and other monomer segments in polymers, and the ionic coordination between Ca and -COO on cellulose nanofibers surface) endowed the hydrogel with excellent mechanical properties, including high strength (754 kPa of tensile strength and 1905 kPa of compressive strength), outstanding stretchability (1963 %), elastic modulus (56.5 kPa) and remarkable mechanical durability (200 cycles with 500 % deformations and 100 cycles at 50 % compression strain). Besides, this hydrogel exhibited other advantages, such as satisfied conductivity (28.7 mS/cm), high strain/pressure/temperature-sensitive behavior, precise and stable signal transmission, varying degrees of antibacterial activity, and biocompatibility. Owing to the exceptional comprehensive performance, the hydrogel was then assembled as a multifunctional sensor to monitor the joint motion, vocal cord vibration, tactile sensation and body temperature with remarkable sensitivity in real time. This work offered a new strategy for the fabrication of durable, biocompatible, antibacterial and conductive materials for wearable multifunctional electronic devices.