Organisation of self-assembling peptide nanostructures into macroscopically ordered lamella-like layers by ice crystallisation

Abstract

Bio-inspired molecular self-assembly has attracted considerable research interest as a promising route to novel nanostructured materials. Self-assembling peptides have proven particularly popular building blocks for the construction of a variety of well-defined nanostructures. There is a great interest in learning to control not only the types and properties of nanostructures, but also their precise macroscopic organisation. Here we investigate the effect of water crystallisation during freezing as a possible method for directed organisation of preformed β-sheet tapes, ribbons and fibrils and for the production of microporous materials comprising lamella-like layers. We employ a range of short, systematically designed self-assembling peptides and a wide variety of techniques including SEM, TEM, X-ray tomography, X-ray diffraction, FTIR spectroscopy and compression testing. We find that ice growth does not alter the peptide nanostructures but templates the formation of lamella-like layers of mesoscopically aligned peptide ribbons and fibrils into nematic-like domains. The lamella are macroscopically oriented into regularly spaced stacks, giving rise to rather brittle peptide aerogels. This behaviour is contrasted with that of other self-assembling networks such as surfactant rod-like micelles and the polysaccharide agar. The differences in the properties of the self-assembling network seem to prescribe the way it will behave during ice crystallisation, and whether or not it will form ordered lamella structures. This approach may lead to the preparation of well-aligned peptide nanostructures, important for high-resolution structural studies; anisotropic microporous materials comprising lamella-like layers of self-assembling peptide fibrils with incorporated protein-like bioactivity may also be useful in medical applications e.g. tissue engineering, and nanotechnology.