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A novel type of lipid vesicles, propylene glycol-embodying liposomes or PG-liposomes, composed of phospholipid, propylene glycol and water, is introduced. The new lipid vesicles were developed and investigated as carriers for skin delivery of the model drug, cinchocaine base. PG-liposomes showed high entrapment efficiency and were stable for at least one month of storage at 5 +/- 1 degree C. Preliminary in-vivo skin deposition studies, carried out using albino rabbit dorsal skin, showed that PG-liposomes were superior to traditional liposomes, deformable liposomes and ethosomes, suggesting that PG-liposomes, introduced in the current work, are promising carriers for skin delivery of drugs.

We revisited the vesicle-to-micelle transformation in phosphatidylcholine-cholate mixtures paying special attention to the lipid bilayer curvature effects. For this purpose, we prepared unilamellar vesicles with different starting sizes (2r(v)=45-120nm). We then studied mixtures of the unilamellar vesicles (1-8mmol kg(-1)) and sodium cholate (0-11.75mmolkg(-1)) by static and dynamic light scattering. The transformation generally comprises at least two, largely parallel phenomena; one increases and the other decreases the average mixed aggregate size. In our view, cholate first induces bilayer fluctuations that lead to vesicle asphericity, and then to lipid bilayer poration followed by sealing/reformation (or fusion). The cholate-containing mixed bilayers, whether in vesicular or open form, project thread-like protrusions with surfactant enriched ends even before complete bilayer solubilisation. Increasing cholate concentration promotes detachment of such protrusions (i.e. mixed micelles formation), in parallel to further softening/destabilising of mixed amphipat bilayers over a broad range of concentrations. Vesicles ultimately fragment into mixed thread-like micelles. Higher cholate relative concentrations yield shorter thread-like mixed micelles. Most noteworthy, the cholate-induced bilayer fluctuations, the propensity for large aggregate formation, the transformation kinetics, and the cholate concentration ensuring complete lipid solubilisation all depend on the starting mean vesicle size. The smallest tested vesicles (2r(v)=45nm), with the highest bilayer curvature, require ~30% less cholate for complete solubilisation than the largest tested vesicles (2r(v)=120nm).