Effect of Solvent and Cholesterol on Liposome Production by the Reverse-Phase Evaporation (RPE) Method

Liposomal drug delivery is a promising approach for delivering therapeutics effectively. While most liposomes are designed to be nanometer-sized for efficient cellular uptake, micron-sized liposomes are gaining interest due to their larger drug-loading capacity. When combined with macroscale structures, such as implants and hydrogels, they offer prolonged therapeutic delivery. This study investigates how solvents affect the production of micron-sized liposomes, with or without cholesterol, using the reverse-phase evaporation (RPE) method. Although the RPE method is established for producing micron-sized liposomes, the influence of solvents on liposome size and uniformity is not well understood. The study explores whether controlling the size of inverse micelles, an intermediate product, through the use of different organic solvents affects the final liposome size. Three solvents─diethyl ether, methanol, and acetone─were tested for their effect on the formation of inverse micelles and liposomes and their sizes. Results showed that without cholesterol, diethyl ether produced uniform inverse micelles, leading to mostly nanosized liposomes. Methanol and acetone resulted in phase separation, preventing uniform liposome formation, although some micron-sized liposomes appeared. The acetone sample yielded mostly oil droplets. The results showed that forming inverse micelles lead to nanosized liposomes. With cholesterol, phase separation was dominant in methanol, but micron-sized liposomes still formed. Across all cases, cholesterol reduced the liposome size. The findings reveal that inverse micelles are not always reliable predictors of the final liposome size and that the RPE method is highly sensitive to solvent polarity and lipid-solvent interactions. Overall, the findings of this study provide valuable insights into how the choice of solvent and lipid composition can influence the production of liposomes via the RPE method. These insights are critical for optimizing liposome production and influencing future designs of liposomal drug delivery systems.