Hydrogels have three-dimensional network structures that have been widely applied owing to their high water content, excellent biocompatibility, and physicochemical properties. Compared with conventional hydrogels, sprayable hydrogels exhibit excellent temporal and spatial controllability. Biomass materials offer easy accessibility, biocompatibility, biodegradability, and other physicochemical properties that are extensively used in the formation of sprayable hydrogels. In situ formed biomass-based sprayable hydrogels are realized by chemical or physical crosslinking. Rapid spray filming, in situ drug delivery, high permeability, and flexible portability enable biomass-based sprayable hydrogels to show great potential for topical drug delivery, wound healing, and other applications. This review describes in detail the status of research on the preparation and application of biomass-based sprayable hydrogels and suggests prospects for their future development.

Cellulose nanofibers (CNF) are considered to be a potential substrate of energy material for energy storage devices due to the foldable, lightweight, recyclable and environmentally friendly feature. However, the energy materials tend to distribute unevenly or fall off from CNF easily, resulting in the decrease of the devices’ overall performance. Here, for the first time, we used quaternized chitosan (QCS) as stabilizer and adhesive to in situ synthesize and deposite copper sulfide nanocrystals (CuS-NCs) on CNF and further obtained the conductive paper for flexible supercapacitors. In the presence of QCS, CuS-NCs deposited in situ on CNF can be capped and stabilized by the QCS molecular chains for uniform distribution, which is conducive to the capacitive behavior and electrochemical stability of composite paper. The result shows that the specific capacitance of the composite paper was as high as 314.3 F/g at a current density of 1 A/g, a high rate capacitance of 252.6 F/g was achieved even at a high current density of 10 A/g. It reveals that the composite paper exhibited better electrochemical performance than many other CuS-based electrode materials for supercapacitor. More importantly, the composite paper performed well in various folding state without changing much electrochemical performance. Therefore, this work provides a novel strategy to in situ fabricate paper-based electrode for next- generation flexible energy-storage system.