Preparation of liposomes using supercritical carbon dioxide via depressurization of the supercritical phase

Liposomes were produced utilizing the supercritical carbon dioxide technology via depressurization of the supercritical phase and the effects of pressure, depressurization rate and temperature on liposome characteristics were investigated. The relative volumetric expansion of water upon equilibration with high pressure CO2 reached a plateau at 14.4%, 12.3% and 10.2% at 40 °C, 50 °C and 60 °C, respectively. With an increase in pressure to 300 bar, the liposomes obtained had a relatively large particle size of 523 ± 2 nm and a small polydispersity index (PdI) of 0.226 ± 0.009. Increasing depressurization rate up to 120 bar/min lowered PdI to 0.198 ± 0.016 for a relatively high homogeneity. Pressures over 200 bar yielded spherical vesicles with good uniformity and liposomes could be stored for up to 4 weeks with limited change in size (below 5%). Supercritical CO2 method displayed advantages of high stability and homogeneity for liposome preparation over conventional thin film hydration method.