A “bird nest” bioinspired strategy deployed for inducing cellulose gelation without concomitant dissolution

Albeit the abundance, renewability, and biodegradability of the polymer known as cellulose, the insolubility and poor dispersibility in most common organic solvents make it incredibly difficult to facilitate conversion into hydrogels without concomitant dissolution. It is known that Swift family birds construct strong and sturdy nests with saliva that acts to bind fibers and twigs. Inspired by this charming hierarchical architecture, protonated carboxymethyl cellulose and cellulose were exploited as “saliva” and “twigs,” respectively, and by a combination of freeze–thaw treatments, cellulose hydrogels can be successfully induced without pre-dissolution representing a striking advancement over what is currently known or predicted. The gel materials displayed considerable increases in storage modulus, viscoelastic behaviors, and thermal stability as the cellulose content increases and exhibited unique omniphilic behaviors. Moreover, this bioinspired strategy is much more universal than originally surmised as found by the gelation of bamboo fibers (additionally containing lignin and hemicellulose), illustrative of the versatility. As a bio-inspired strategy, the current work is the first report on a straightforward, simple, green, yet effective gelation protocol to prepare cellulose-based soft materials.