The cubic phases of lipids

Composite material in the sea urchin Cidaris rugosa: ordered and disordered micrometre-scale bicontinuous geometries

The sponge-like biomineralized calcite materials found in echinoderm skeletons are of interest in terms of both structure formation and biological function. Despite their crystalline atomic structure, they exhibit curved interfaces that have been related to known triply periodic minimal surfaces. Here, we investigate the endoskeleton of the sea urchin Cidaris rugosa that has long been known to form a microstructure related to the Primitive surface. Using X-ray tomography, we find that the endoskeleton is organized as a composite material consisting of domains of bicontinuous microstructures with different structural properties. We describe, for the first time, the co-occurrence of ordered single Primitive and single Diamond structures and of a disordered structure within a single skeletal plate. We show that these structures can be distinguished by structural properties including solid volume fraction, trabeculae width and, to a lesser extent, interface area and mean curvature. In doing so, we present a robust method that extracts interface areas and curvature integrals from voxelized datasets using the Steiner polynomial for parallel body volumes. We discuss these very large-scale bicontinuous structures in the context of their function, formation and evolution.

Bottom-up cubosome synthesis without organic solvents

HYPOTHESIS

Bottom-up synthesis of cubosomes is more energetically favourable than top-down approaches. However, bottom-up methods often rely on organic solvents such as ethanol as diluents, and lead to concurrent formation of liposomes. We propose using non-toxic diluents such as honey, glycerol and lactic acid for bottom-up cubosome synthesis.

EXPERIMENTS

Cubosomes were prepared using solutions of phytantriol in a range of diluents including choline chloride-glycerol, honey, lactic acid, glycerol, and ethanol. These solutions were added dropwise to water containing the stabiliser, poloxamer 407, following an established method of cubosome synthesis. The resulting structures were characterised using small-angle X-ray scattering, DLS and cryo-TEM.

FINDINGS

Cubosomes were successfully formed using a range of non-toxic diluents. This demonstrates that harmful organic solvents like ethanol are not required, and that the diluents need not be hydrotropes. Furthermore, unlike ethanol, these other diluents allowed formation of cubosomes without concurrent formation of liposomes. Given the huge potential for cubosomes in drug delivery, this new method offers a potentially useful low-cost, low-toxicity synthesis option.

Lipids from algal biomass provide new (nonlamellar) nanovectors with high carrier potentiality for natural antioxidants

Lipid mesophases are lyotropic liquid crystalline systems which differ from liposomes and other globular aggregates in dilute regimes due to their inner ordering. It is known that natural lipids enable to obtain a rich variety of nanosystems and many of them have been proposed as delivery agents for bioactive compounds. Due to their packing parameters, several classes of lipids found in natural sources are able to self-assemble into nonlamellar structures. Among lipids occurring in plants and algae, triglycerides display this tendency. In the present study we examine new nanosystems built with lipids extracted from the marine microalga Nannochloropsis sp and their use as carriers for lipophilic antioxidants. The antioxidants studied, curcumin and tocopherol were encapsulated with high rate in the carriers. The physico-chemical characterization of plain and loaded vectors showed their structure and localization site, as well as the structure-functionality relationship related to potential drug delivery. The results show that the cargo molecules play an active role in driving the interactions which characterize the overall structure of the aggregates. The systems studied showed several coexisting mesophases, the most predominant structure being of cubic symmetry.

Lipid-based mesophases as matrices for nanoscale reactions

Lipidic mesophases are versatile bioorganic materials that have been effectively employed as nanoscale matrices for membrane protein crystallization, drug delivery and as food emulsifiers over the last 30 years. In this review, the focus is upon studies that have employed non-lamellar lipid mesophases as matrices for organic, inorganic and enzymatic reactions. The ability of lipidic mesophases to incorporate hydrophilic, amphiphilic and hydrophobic molecules, together with the high interfacial area of the lipidic cubic and inverse hexagonal phases has been exploited in heterogeneous catalysis as well as for enzyme immobilization. The unique nanostructure of these mesophases is the driving force behind their ability to act as templates for synthesis, resulting in the creation of highly ordered polymeric and inorganic materials with complex geometries.

Experimental Evidence for Proposed Transformation Pathway from the Inverse Hexagonal to Inverse Diamond Cubic Phase from Oriented Lipid Samples

A macroscopically oriented inverse hexagonal phase (HII) of the lipid phytantriol in water is converted to an oriented inverse double diamond bicontinuous cubic phase (QII(D)). The initial HII phase is uniaxially oriented about the long axis of a capillary with the cylinders parallel to the capillary axis. The HII phase is converted by cooling to a QII(D) phase which is also highly oriented, where the cylindrical axis of the former phase has been converted to a ⟨110⟩ axis in the latter, as demonstrated by small-angle X-ray scattering. This epitaxial relationship allows us to discriminate between two competing proposed geometric pathways to convert HII to QII(D). Our findings also suggest a new route to highly oriented cubic phase coatings, with applications as nanomaterial templates.