The present study concerns the formation and structure of aqueous dispersions of lipid-based lyotropic liquid crystalline phases, namely reversed types of hexagonal and bicontinious cubic phases. As stabilizer a nonionic triblock polymer proves to be efficient for dispersions of both phases. We demonstrate that these dispersions contain submicron particles with a preserved inner periodicity. The morphology and inner structure of the dispersed particles are characterized by means of SAXS (small-angle X-ray scattering) and cryo-TEM (cryo-transmission electron microscopy). The particle shape is shown to reflect the crystallinity of the lipid structure. Thus the morphology of particles from cubic phases differs from that of the ones obtained from the hexagonal phase. Furthermore, an interesting difference is found in the partitioning of the polymer in the two types of dispersions. The polymer is localized within the core as well as at the surface of the dispersed particles of the cubic phase, whereas the core of the particles from the hexagonal phase seems depleted of polymer at the same polymer concentration.

The formation of dispersed colloidal particles of a bilayer cubic phase is demonstrated and discussed in relation to the phase behavior of the components used. Examination by means of cryotransmission electron microscopy reveals submicron particles of faceted morphology, showing an inner texture compatible with the expected periodicity from the QII(P) structure.

The association structures formed by cationic liposomes and DNA-plasmids have been successfully employed as gene carriers in transfection assays. In the present study such complexes was studied by cryo-TEM (cryo-transmission electron microscopy). Cationic liposomes made up by DOPE (dioleoylphosphatidylethanolamine) and various amounts of three different cationic surfactants were investigated. The cryo-TEM analysis suggests that an excess of lipid in terms of charge, leads to entrapment of the DNA molecules between the lamellas in clusters of aggregated multilamellar structures. With increasing amounts of DNA free or loosely bound plasmids were found in the vicinity of the complexes. The importance of the choice of surfactant, as reported from many transfection assays, was not reflected in changes of the type of DNA-vesicle association. A tendency towards polymorphism of the lipid mixtures is reported and its possible implications are discussed.