Formulation design, production and characterisation of solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) for the encapsulation of a model hydrophobic active.

Lipid nanoparticles have been widely investigated for their use as either carriers for poorly water soluble actives or as (Pickering) emulsion stabilisers. Recent studies have suggested that the fabrication of lipid nanostructures that can display both these performances concurrently, can enable the development of liquid formulations for multi-active encapsulation and release. Understanding the effects of different formulation variables on the microstructural attributes that underline both these functionalities is crucial in developing such lipid nanostructures. In this study, two types of lipid-based nanoparticles, solid lipid nanoparticles and nanostructured lipid carriers, were fabricated using varying formulation parameters, namely type of solid lipid, concentration of liquid lipid and type/concentration of surface active species. The impact of these formulation parameters on the size, thermal properties, encapsulation efficiency, loading capacity and long-term storage stability of the developed lipid systems, was studied. Preliminary lipid screening and processing conditions studies, focused on creating a suitable lipid host matrix of appropriate dimensions that could enable the high loading of a model hydrophobic active (curcumin). Informed by this, selected lipid nanostructures were then produced. These were characterised by encapsulation efficiency and loading capacity values as high as 99% and 5%, respectively, and particle dimensions within the desirable size range (100-200 nm) required to enable Pickering functionality. Compatibility between the lipid matrix components, and liquid lipid/active addition were shown to greatly influence the polymorphism/crystallinity of the fabricated particles, with the latter demonstrating a liquid lipid concentration-dependent behaviour. Successful long-term storage stability of up to 28 weeks was confirmed for certain formulations.