(715d) Equilibrium Structure and Dynamics of Peptide-Based Molecular Gels

Aromatic short peptide derivative molecules can form rigid gels (G' > 10⁵ Pa) at very low volume fractions (< 1%) due to highly specific anisotropic interactions that result in the self-assembly of molecules into space-filling fibrous networks, featuring characteristic gel-like mechanical properties. These systems are seeing potential applications in cell culture, tissue engineering, and drug delivery, but differ from typical biopolymer networks that are commonly used in these areas, as the molecules interact predominantly through hydrogen bonding and π-π stacking, and in an absence of covalent bonds. We explore a model molecular gel, formed by mixing a solution of Fmoc-diphenylalanine (Fmoc-FF) in dimethyl sulfoxide (DMSO) with water. Using optical, scattering, and rheological techniques, we study the gel structure, as well as the kinetics and dynamics of gel formation and aging. We find that the aging process of these gels is associated with a tendency of the system to reach a steady state through the structure evolving into an increasingly uniform network, which is correlated with an increase in relaxation times and growth of the elastic modulus to a plateau value. Further, we demonstrate that the gels are mechanically and thermally reversible, and hypothesize that the system is in equilibrium in its fibrous network state. The observations provide experimental evidence for simulations of aggregation of valence-limited “patchy” particles published in the literature, which suggest that an equilibrium gel can be formed at low volume fractions without an intervening phase separation.