Gelation Kinetics of β-Hairpin Peptide Hydrogel Networks

Abstract

The gelation kinetics of self-assembled hydrogels consisting of the β-hairpin peptide MAX1 are investigated using microrheology and far-UV circular dichroism (CD) spectroscopy. The intramolecular folding of this peptide is engineered to control its self-assembly into β-sheet-rich hydrogels. When the peptide is unfolded, it does not self-assemble, and aqueous solutions have the viscosity of water. Folding and consequent self-assembly are triggered by changes in pH, temperature, or ionic strength. This folding and self-assembly mechanism allows temporal control of the material formation. CD spectroscopy shows that the kinetics of β-sheet structure formation occurs in a concentration-dependent manner but does not provide information on the kinetics of network assembly. Here, multiple particle tracking is used to define exact gelation times as a function of peptide concentration. This allows an empirical relationship to be established between the rheologically defined gelation time and the onset of β-sheet formation as measured by CD. Values of the mean-residue ellipticity at 216 nm between −10 × 103 and −12 × 103 deg dmol-1 cm2 coincide with the formation of a percolating gel. Critically, this empirical relationship allows one to identify the gel time solely from spectroscopic measurements, greatly facilitating the establishment of peptide sequence material−function relationships.