Interfacial Properties of Lipid Liquid Crystalline Nanoparticles

Abstract: Lipid liquid crystalline nanoparticles are studied for their potential as biocompatible carriers for pharmaceutical, food and cosmetic applications. Their potential as delivery vehicles is due to their nanometer size, their controllable structure and physical properties and their large carrying capacity of a wide range of molecules. This study concerns the interaction of lipid liquid crystalline nanoparticles (i) at solid/liquid interfaces, (ii) at model membranes and (iii) with peptides. (i) The adsorption behavior of cubic phase nanoparticles based on glycerol monooleate (GMO) at the solid/liquid interface is highly dependent on the surface properties. At hydrophilic surfaces, the interactions are weak and the interfacial layer consists of patches of intact nanoparticles. The surface coverage is also affected by the solution conditions and particle size, and adsorption is observed only when the electrostatic interactions are screened. The adsorption mechanism involves two competing adsorption processes: the rapid adsorption of the residual free molecules of the stabilizing polymer and the adsorption of intact nanoparticles in the gaps left at the surface. The interactions with hydrophobic surfaces, on the other hand, are strong and attractive, leading to a collapse of the internal structure of the particle. This leads to a monolayer-type of structure at hydrophobic surfaces. (ii) The interaction between GMO-based cubic phase nanoparticles and dioleoylphosphatidylcholine (DOPC) bilayers is a dynamic process. The particles initially adsorb at the bilayer surface. Interfacial exchange occurs, where GMO is delivered into the bilayer and DOPC is extracted by the nanoparticles. A subsequent release of the nanoparticles is observed, which is attributed to a local phase separation at the interface. Studies of interactions with bilayers of different coverage and with vesicles at different DOPC:GMO ratios have revealed structural changes of the GMO cubic structure, with a transition from the cubic phase to a lamellar structure upon lipid mixing. (iii) A case study of the interactions of liquid crystalline nanoparticles formed from soya phosphatidylcholine and glycerol dioleate with two different peptides has shown that the use of the carrier increases the in vivo circulation time of the peptides. Therefore applications of the delivery system represent an interesting alternative to chemical modifications of in vivo sensitive therapeutically interesting peptides.