Investigations into the adsorption of liquid crystal nanostructured particles to bio-relevant surfaces

Liquid crystal nanostructured matrices, such as the bicontinuous cubic (V2) and reverse hexagonal (H2) nanostructures, are self-assembled phases of certain amphiphiles that can be dispersed using stabilizing agents into submicron sized particles, termed cubosomes and hexosomes respectively. The size and internal nanostructure of these particles means they have potential for use for the delivery active ingredients to surfaces. However a greater understanding of the structure of particles and their behavior at interfaces must be obtained to realise such an application. Obtaining such an understanding was the underlying aim of this thesis. There are a number of properties which will influence the applicability of liquid crystal nanostructured particles to deliver active ingredients to interfaces. The relationship between the particles and the stabiliser used to produce them is one of these properties, as the stabiliser is believed to have a major influence on the adsorption of the particles. The stabiliser most commonly used to produce cubosomes and hexosomes, Pluronic F127, was found to associate irreversibly with both the internal and external interfaces of cubosomes. The amount of F127 associated with the particles was observed to be highly dependent on the lipid composition and nanostructure of the particles. The transfer of material between the particles and an interface will also influence the use, as such transfer could result in changes to nanostructure and ultimately delivery properties. The transfer of material between liquid crystal nanostructured particles and other lipid particles, used as a model for a lipid-based surface such as a leaf or skin, was observed and found to occur due to compositional ripening via a micelle-mediated mechanism, and the transfer was found to be dependent on the lipid composition and nanostructure of the particles. It was also observed that lipid was not transferred between liquid crystal nanostructured particles and the triglyceride tristearin, often employed as a model leaf surface, which suggests the transfer of material may not readily occur in an agricultural setting. The adsorption of the particles to surfaces, what influences adsorption and how the adsorption influences the nanostructure of the particles will also influence their use as active ingredient delivery agents. The adsorption of liquid crystal nanostructured particles was observed to be influenced by lipid composition and nanostructure, which was attributed to the influence that these properties have on the association of F127 with the particles, which in turn influences adsorption as F127 plays a significant role in adsorption of the particles. It was also determined that in most cases liquid crystal nanostructure is not influenced by adsorption of the particles to interfaces, suggesting that the particles may be used to deliver active ingredients to interfaces. Overall, the findings of this thesis indicate that these particles do have potential to be used for such an application, however the lipid composition and nanostructure of the particles must be carefully chosen for the surface in which their application is intended.