Development of a New Preparation Method of Liposomes Using Supercritical Carbon Dioxide

Abstract

A new method, the supercritical reverse phase evaporation method, for the preparation of liposomes in one step using supercritical carbon dioxide without any organic solvent toxic to the human body has been developed. This method allowed aqueous dispersions of liposomes to be obtained through emulsion formation by introduction of a given amount of water into a homogeneous mixture of supercritical carbon dioxide/l-α-dipalmitoylphosphatidylcholine/ethanol with sufficient stirring and subsequent pressure reduction. Transmission electron microscopy observations using the freeze-replica method on the obtained vesicles revealed that most of them are large unilamellar liposomes with diameters of 0.1−1.2 μm. The trapping efficiency of the liposomes examined with the d-(+)-glucose indicated more than 5 times higher trapping efficiency for the water-soluble solute than that of multilamellar vesicles prepared by the Bangham method. The trapping efficiency for cholesterol, an oil-soluble substance, of the liposomes was 63%. These results showed that the supercritical reverse phase evaporation method is an excellent technique that permits one-step preparation of large unilamellar liposomes with a high trapping efficiency for both water-soluble and oil-soluble substances.