Earliest Stage of the Tetrahedral Nanochannel Formation in Cubosome Particles from Unilamellar Nanovesicles

Abstract

Studies of nonequilibrium lipid polymorphism at the nanoscale contribute to the in-depth understanding of the structural pathways for formation of aqueous channels and emerging of channels-network ordering in liquid-crystalline (LC) nanovehicles. We present experimental structural evidence for the smallest tetrahedral-type lipid membrane aggregate, which involves completely formed nanochannels and occurs as an early intermediate state during the bilayer vesicle-to-cubosome particle transition. Nanovehicles are generated from a self-assembled lipid mixture and studied by means of high-resolution cryogenic transmission electron microscopy (cryo-TEM) and synchrotron radiation small-angle X-ray scattering (SAXS). The investigated lipid membrane composition allows for the stabilization of long-lived intermediates throughout the unilamellar vesicle-to-cubosome nanoparticle (NP) transformation at ambient temperature. The observed small cubosomic particles, with well-defined water channels, appear to be precursors of larger cubic membrane structures, thus confirming the theoretical modeling of nanochannel-network growth in diamond-type cubic lipid particles. The reported structural findings, highlighting that bilayer vesicle membrane packing and fusion are required for nanochanneled cubosome particle formation, are anticipated to advance the engineering of small lipid NPs with controllable channels for biomolecular loading and release.

Steric Stabilizers for Cubic Phase Lyotropic Liquid Crystal Nanodispersions (Cubosomes)

“…To date only a few PEGylated lipids have been published as effective stabilizers for cubosomes (Fig. 8) [38,88,[197][198][199][200]202,[204][205][206]208]. The lipid anchors of these PEGylated lipids are explored in greater detail below.…”

“…The use of PEGylated phospholipids as a steric stabilizer for cubic nanostructured particles was reported by Angelov et al [204], Johnsson and Edwards [200], Zeng et al [205], and Koynova et al [197,198]. Angelov et al reported cubic nanostructured particles from aqueous dispersions of GMO and cis-5,8,11,14,17-eicosapentaenoic acid (20:5, EPA) in water, with 1,2-dioleoylphosphatidylethanolamine-PEG (DOPE-PEG 2000 ) as the steric stabilizer [204].…”

“…Angelov et al reported cubic nanostructured particles from aqueous dispersions of GMO and cis-5,8,11,14,17-eicosapentaenoic acid (20:5, EPA) in water, with 1,2-dioleoylphosphatidylethanolamine-PEG (DOPE-PEG 2000 ) as the steric stabilizer [204].…”

“…Although several PEGylated lipid stabilizers with different PEG lengths have been identified, the most frequently used PEG length in PEGylated lipid stabilizers is 45 PEG units (i.e., PEG 2000 ) [88,200,204,205]. The use of PEG 2000 was initiated for liposome stabilization, whereby the use of PEG 2000 hindered aggregation of lipid nanostructured particles under physiological conditions [88,[212][213][214].…”

Effect of fullerene on the dispersibility of nanostructured lipid particles and encapsulation in sterically stabilized emulsions

“…Resulting dispersions are analogous to classical oil-in-water (o/w) emulsions but the oil phase, in this case, is replaced by a lipid selfassembly ( Figure 1). Structural organization of lipid self-assemblies in the bulk (non-dispersed form) and emulsions (dispersed form) is usually determined using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) techniques [23][24][25]. Depending on the type of internal selfassembly, the nanostructured emulsions are recognized as cubosomes for cubic nanostructures, hexosomes for hexagonal nanostructures and so on [15,[26][27][28].…”