Templating effects of lyotropic liquid crystals in the encapsulation of amyloid fibrils and their stimuli-responsive magnetic behavior

Abstract

The relationship between the symmetry of inverted lyotropic liquid crystals (LLC), used as hosting complex fluid, and amyloid fibrils, confined within the LLC matrix, was studied with the aim of exploiting the LLC water reservoirs for encapsulation of large protein aggregates. We used β-lactoglobulin (βlg) fibrils as a model system for high aspect ratio amyloid fibrils and encapsulated them into three different types of LLC mesophases composed of glycerol monolinoleate, with or without linoleic acid and water, yielding respectively lamellar, inverse bicontinuous cubic and inverse columnar hexagonal symmetries. The impact of fibrils confinement within the LLC on their secondary structure and spatial organization was studied by combining small angle X-ray scattering (SAXS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy (AFM) techniques. FTIR indicated that the βlg fibrils were incorporated within the aqueous layers of the lamellar phase while in the cubic and hexagonal structures they were mostly located at the lipid–water interface, along the channels. Furthermore, each mesophase affected the assembly of the amyloid fibers in accordance with the nature of the space group of the LLC structure considered. The two-dimensional order parameter of the fibrils, which was calculated on the basis of AFM images, revealed mainly random orientation distribution of the fibrils when these were confined within the lamellar and cubic phases, which can be understood by the orientation degeneracy of the fibrils in a 2D confinement and by the isotropic nature of the cubic phases. On the contrary, the fibers exhibited nearly perfect orientation when confined within the columnar hexagonal phase as a consequence of the unidirectional orientation of the LLC and the high aspect ratio of the fibrils. These trends were further exploited to induce orientation of the LLC by decorating the encapsulated amyloid fibrils with magnetic nanoparticles capable to respond to an external magnetic field stimulus: a coupling of the orientation of the nanoparticle-decorated amyloid fibrils and that of the LLC mesophase was demonstrated by small angle neutron scattering under the application of a constant magnetic field.