Multicomponent supramolecular hydrogels composed of cationic phenylalanine derivatives and anionic amino acids

Supramolecular hydrogels composed of self-assembled fluorenylmethoxycarbonyl phenylalanine (Fmoc-Phe) derivatives have been the focus of intense study as novel materials for biological applications that include drug delivery, tissue engineering, and regenerative medicine. Cationic Fmoc-Phe derivatives functionalized with diaminopropane (Fmoc-Phe-DAP) have been shown to undergo self-assembly and hydrogelation upon an increase in solution ionic strength by the addition of inorganic salts that provide cation-shielding counterions. Further, the identity of the inorganic salts modifies the assembly morphology and emergent viscoelastic properties of the resulting materials. Herein, we report multicomponent hydrogels composed of Fmoc-Phe-DAP derivatives in which hydrogelation is promoted by the addition of anionic amino acids, monosodium aspartate or monosodium glutamate. Aspartate and glutamate salts both support supramolecular gelation of Fmoc-Phe-DAP derivatives, although only the glutamate gels remain stable over periods longer than one hour. The assemblies formed by Fmoc-Phe-DAP derivatives in the presence of aspartate and glutamate are morphologically distinct relative to those formed in the presence of sodium chloride. The viscoelastic properties of stable glutamate/Fmoc-Phe-DAP derivative hydrogels are sensitive to the ratios of glutamate to Fmoc-Phe-DAP derivative, with increased concentrations of glutamate corresponding to higher viscoelastic strength. These multicomponent systems demonstrate that comixing unfunctionalized amino acids with self-assembling Fmoc-Phe-DAP derivatives is yet another effective method to modify the emergent properties of the resulting materials.