Poly(ionic liquid) functionalization: A general strategy for strong, tough, ionic conductive, and multifunctional polysaccharide hydrogels toward sensors

Ionic conductive hydrogels (ICHs) prepared from natural bioresources are promising candidates for constructing flexible electronics for both commercialization and environmental sustainability due to their intrinsic characteristics. However, simultaneous realization of high stiffness, toughness, conductivity, and multifunctionality while ensuring processing simplicity is extremely challenging. Here, a poly(ionic liquid) (PIL)-macromolecule functionalization strategy within a NaOH/urea system is proposed to construct high-performance and versatile polysaccharide-based ICHs (e.g., cellulosic ICHs). In this strategy, the elaborately designed "soft" (PIL chains) and "hard" (cellulose backbone) structures as well as the dynamic covalent and noncovalent bonds of the cross-linked networks endow the hydrogel with high mechanical strength (9.46 +/- 0.23 MPa compressive modulus), exceptional stretchability (214.3%), and toughness (3.64 +/- 0.12 MJ m-3). Ingeniously, due to the inherent conductivity, design flexibility, and functional compatibility of the PILs, the hydrogels exhibit high conductivity (6.54 +/- 0.17 mS cm-1), self-healing ability (94.5% +/- 2.0% efficiency), antibacterial properties, freezing resistance, water retention, and recyclability. Interestingly, this strategy is extended to fabricate diverse hydrogels from various polysaccharides, including agar, alginate, hyaluronic acid, and guar gum. In addition, multimodal sensing (strain, temperature, and humidity) is realized based on the stimulus-responsive characteristics of the hydrogels. This strategy opens new perspectives for the design of biomass-based hydrogels and beyond.