(379g) Fast Dynamics of Semiflexible Chain Networks of Self-Assembled Peptides

The cytoskeleton within cells is comprised of several biopolymers, which include actin, microtubules, and intermediate filaments. Rheological and spectroscopy techniques show that these polymer chains are semiflexible and form networks with unique viscoelastic properties, such as high storage moduli at low monomer concentrations and significant strain hardening at low strain. Recently, synthetic polymers have been developed with similar semiflexible characteristics. One example is a synthetic β-hairpin peptide analogue, MAX1, which undergoes triggered self assembly at the nanoscale to form a physically crosslinked network of fibrils with a defined cross-section. These peptides adopt a random coil conformation in aqueous solutions and are freely soluble. However, when subjected to a stimulus, such as physiological pH and ionic strength, the peptides fold into a β-hairpin, and subsequently, self-assemble to form a structurally rigid hydrogel stabilized by non-covalent cross-links. MAX8 is an alternate peptide sequence derived from MAX1, in which faster folding and self assembly kinetics are observed at the same buffer conditions, resulting in more rigid gels at the same concentration of peptide. Here, we present the first quantitative neutron spin echo (NSE) measurements of self-assembling peptide hydrogel networks to study their dynamics on the nanometer and nanosecond length and time scales. These measurements demonstrate that these self-assembled peptide fibrils can be described by the theory of semiflexible chains on these length and time scales. Alteration of peptide sequence does not affect the nanoscale dynamics, but does significantly affect the macroscopic rheology. We conjecture that the difference arises from the rate of assembly and the degree of branching, rather than a change in the fibril structure or persistence length.