Coassembling Peptide-Based Biomaterials: Effects of Pairing Equal and Unequal Chain Length Oligopeptides

We have previously developed shear-responsive hydrogels assembled from mutually attractive but self-repulsive oligopeptide modules. To explore the mechanism of material assembly, we designed and synthesized a quartet of oligopeptides. The peptide quartet contains two positively charged modules 10 and 15 amino acid residues long and two negatively charged modules 10 and 15 amino acid residues long. Each positive module can pair with one negative module and hence there are four potential pairings, two of equal chain length (blunt-ended pairs) and two of unequal chain length (sticky-ended pairs). Viscoelastic properties and structural features of the hydrogels assembled from these oligo-peptide pairs were evaluated by dynamic rheometry and small-angle X-ray scattering (SAXS) techniques, respectively. It was found that the sticky ends provide no advantage in terms of mechanical properties of the hydrogels. Instead, the hydrogel assembled from the 10:10 peptide pair forms the strongest gel. These results are consistent with a cross-β structural model in which β-strands are stacked against each other in a parallel fashion to form nanofibers, the axes of which are perpendicular to individual β-strands. The optimal chain length of oligopeptide modules for such nanofiber network assembly is around 10 amino acid residues.