Self-Sorting in Supramolecular Peptide Amphiphile Nanostructures

Soft materials in nature, such as the extracellular matrix and the actin filaments and microtubules found in the cytoskeleton, are often composed of mixtures of molecules that co-assemble into functional multicomponent networks through precise control of supramolecular interactions. Creating synthetic materials with ordered structures which mimic complex natural fibrous networks that self-sort into individual populations offers a valuable approach to designing novel multi-functional tissue scaffolds for regenerative medicine. We recently reported that supramolecular twisted nanostructures formed from peptide amphiphile (PA) molecules exhibit different supramolecular chirality depending on the intermolecular hydrogen bonding, which is determined by the amino acid sequences used. Here, we demonstrate that PAs can be designed to self-sort into either separate nanostructures or co-assemble within the same nanostructures by mixing PAs of different peptide sequences that vary in their β-sheet strength but have the same electrostatics. We use atomic force microscopy (AFM) to reveal the nanoscale morphology of the assemblies, and confocal laser scanning microscopy (CLSM) to determine the distribution of fluorescently labelled PA monomers between nanostructures. By correlating the two imaging modalities on the same region of the samples, we show that the multicomponent PA mixtures can co-assemble or self-sort based on the supramolecular twist of the assemblies: when PAs that form left-handed nanostructures are mixed with PAs that form right-handed nanostructures, the two components self-sort. However, a PA that forms both left- and right-handed nanostructures can co-assemble with either PA to different extents. Our results demonstrate that the driving force for the self-sorting reported here is determined by the enthalpic penalty of the torsion required to change the twist of a peptide in a β-sheet and is controlled by the internal hydrogen bonding sequence.