Gelation kinetics of β-hairpin peptide hydrogel networks

The gelation kinetics of self- assembled hydrogels consisting of the,- 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,- 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,- 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 beta-sheet formation as measured by CD. Values of the mean- residue ellipticity at 216 nm between - 10 x 10(3) and - 12 x 10(3) deg dmol(-1) cm(2) 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.