Formation and Physicochemical Properties of Liposomes Using a Supercritical Reverse Phase Evaporation Method

L-a-dipalmitoylphosphatidylcholine (DPPC) liposomes were prepared using supercritical reverse phase evaporation (scRPE) method. The effects of phospholipid structure, preparation pressure, and amount of ethanol on their physicochemical properties were examined using measurements of trapping efficiency, cloud point measurements, dynamic light scattering, and osmotic water transport studies. The maximum trapping efficiency of DPPC liposomes prepared by the scRPE method were 22.5 %. The phase behavior of DPPC/ethanol/CO2 mixture before introducing water strongly influenced their physicochemical properties. The sizes of liposomes prepared at pressures below 200 Bar seem to be larger than those prepared at > 200 Bar. The minimum ethanol concentration to obtain water in CO2 emulsion at 200 bar is 6.8 wt% which corresponds well to the optimum ethanol concentration to obtain large unilamellar vesicles with the highest trapping efficiency. On the other hand, Multilamellar vesicles (MLV) seem to be formed when the ethanol concentration added to the system is less than 4.5 wt%. The scRPE method makes it possible to control the physicochemical properties of liposomes like particle size, size distribution, trapping efficiency and lamellarity in a single step.