Bioinspired functional self-healing hydrogels from a minimalistic dipeptide building block

Abstract

Bioinspiration is of paramount importance for the innovation of novel biomaterials through nanotechnology. Short peptide-based bioinspired building blocks interact supramolecularly and produce materials where individual molecules' attributes are transferred to the bulk. Specifically, self-assembled peptide hydrogels manifest the transcendence of peptide nanotechnology into functional materials. Given their versatile applications ranging from biology to nanotechnology, developing peptide-based minimalistic supramolecular synthons is essential. In a quest to identify an efficient bioinspired hydrogelator, we conceived a modified peptide building block composed of two 9-fluorenylmethyloxycarbonyl (Fmoc) groups. We, therefore, report a hydrogelator, Fmoc–Lys(Fmoc)–Phe (Lys = lysine, Phe = phenylalanine), that produced hydrogels at a very low concentration. The peptide hydrogel exhibited self-sustaining and self-healing behavior and, intriguingly, improved mechanical properties compared to the previously reported di Fmoc-based hydrogels. Molecular dynamics simulations revealed that while the aromatic stacking among Fmoc groups drives the hydrogel's hydrophobic core formation, the Phe groups located on the surface of two adjacent hydrophobic cores bridge two adjacent cores, facilitating the branching of the fibrous aggregate. These results manifest the importance of the Phe residue in the self-assembly process. To introduce conductivity to the peptide hydrogels, their network structure was nanoengineered with edge-functionalized graphene oxide nanosheets, resulting in composite hydrogels. The dried composite hydrogels exhibited a non-linear current–voltage response with both resistive and capacitative features. The peptide and the composite hydrogels exhibited excellent selective dye adsorption capacities, demonstrating their utilization as supramolecular functional materials. Overall, the peptide hydrogels exhibit significant promise in terms of their design, self-assembly pathway, properties, and applications.