(373g) Self-Assembly and Gelation of Peptide Hydrogels Investigated with Diffusing-Wave Spectroscopy

Self-assembled peptide hydrogels are of interest for drug delivery and tissue engineering applications where, for example, biocompatible hydrogels could be used as an artificial cellular scaffold for tissue regeneration in wounds.  Applications such as these require control over both the rate of gel formation and the final gel stiffness.   Recently, gels formed from racemic mixtures of MAX1, a 20 amino acid long synthetic peptide, and its enantiomer, DMAX1, were found to assemble more rapidly and possess an equilibrated storage modulus four times as large as those containing either pure enantiomer, revealing a convenient parameter to rationally design hydrogels from self-assembling peptides.  In this talk, we present progress towards a molecular and network level understanding of this phenomena.  The viscoelastic properties of the gels are measured using diffusing wave spectroscopy (DWS).  Simultaneous photon counting and multispeckle DWS techniques are used to measure the dynamics with lag times over eight orders of magnitude.  This enables characterization of the kinetics of gelation along with the final viscoelastic properties of the gel.  The measured plateau modulus is in agreement with that found from bulk rheology, and the results provide the first direct microrheological measurements of semiflexible polymer mechanics in MAX1 systems.  Using a theoretical model and material parameters determined from complimentary, independent measurements, the persistence length and bending modulus of the peptide filaments are determined directly from the DWS experiment.  The results provide new insights into the fabrication of hydrogel networks with tunable properties using peptide assemblies.