Preparation of liposomes using supercritical carbon dioxide technology: Effects of phospholipids and sterols

• Liposomes were prepared using a supercritical carbon dioxide method.
• The effects of compositional parameters on liposome preparation were investigated.
• Soy lecithin (25 mM) with ketocholestanol (20%) at 50 °C was chosen as optimal condition.
• Phytosterol shows possibility (smaller size and PdI in liposomes) to replace cholesterol.
• SC-CO2 method demonstrated superior preparation of liposomes over traditional TFH.

Liposomes were prepared utilizing a supercritical carbon dioxide (SC-CO2) process. A phospholipid suspension was first equilibrated with CO2 at 300 bar and then depressurized at a constant pressure and rate. The effects of phospholipid concentration, phospholipid type, sterol concentration and sterol type on particle size, uniformity, zeta potential and morphology were investigated. With increasing soy lecithin concentration (5–30 mM) at 50 °C, the smallest particle size of liposomes (146.1 ± 0.8 nm) was obtained at 30 mM with the polydispersity index (PdI) of 0.398 ± 0.008. Increased phospholipid concentration was favorable for the formation of smaller size vesicles with higher uniformity. Longer chain length of fatty acids in pure phospholipids resulted in a larger particle size with more spherical shape while a phospholipid with unsaturated fatty acyl chains resulted in increased asymmetry. With elevated β-sitosterol concentration (10%–50%), particle size and PdI increased to 245.5 ± 7.14 nm and 0.514 ± 0.018, respectively, with decreased absolute zeta potential. 6-Ketocholestanol showed the smallest diameter and PdI of liposomes with the most spherical shape among all sterol types tested. Soy lecithin exhibited the highest stability of vesicular systems due to its highest absolute zeta potential (− 58.3 ± 2.17 mV) among all the phospholipid types. The SC-CO2 method demonstrated superior characteristics of liposomes over traditional thin film hydration method for a smaller size and PdI as well as enhanced intactness without leakage. It might offer a promising way to reduce usage of sterol in liposome formulations while eliminating organic solvent usage.