An Amino Acid Derived Minimalistic Supramolecular Self-Healing Nanostructured Hydrogel Exhibits Underwater Adhesion

The multifarious advantages of supramolecular materials prompt researchers to seek molecular building blocks capable of aggregating hierarchically via noncovalent interactions into nanoscale architecture, which are further organized into bulk materials with desired applications. Compared to the large volume of literature on peptide-based supramolecular materials, amino-acid-derived materials are scarcely investigated despite their minimalistic nature, ease of acquisition, and underlying propensity to self-assemble into fibrous nanostructures. To this end, we designed and synthesized an amino-acid-derived de novo building block, N,N′-difluorenylmethoxycarbonyl-l-cystine (DFC), that forms nanostructured supramolecular hydrogels with self-recovery, injectability, and self-healing properties. The self-assembly proceeds via liquid–liquid phase separation into solute-rich droplets functioning as nucleating sites, instead of the usually observed nucleation-elongation mechanism, forming spherulitic domains of nanofibers. The remarkable self-healing, self-supporting, and malleability of the bulk hydrogel, bestowed by the coacervate-like microstructures, allowed cutting, rejoining, and molding of the gel monoliths into desired shapes without solvent loss, a significant accomplishment in the milieu of supramolecular gels. Intriguingly, the hydrogel exhibited glue-like adhesion, a feat observed mostly in polymeric materials since supramolecular materials lack desired mechanical robustness. Our minimalistic bioinspired building block, DFC, synthesized from readily available precursors in a one-step reaction, exhibited water-resistant and underwater adhesion without the aid of any nanoclusters or polymer, demonstrating its potential applications as bioadhesives in wound closure or hemostasis. Therefore, we propose an elementary amino-acid-derived supramolecular material that might realize the immense functional potential of supramolecular chemistry into practical products.