Supercritical CO2 assisted liposomes formation: Optimization of the lipidic layer for an efficient hydrophilic drug loading

Liposomes are natural vesicles generally based on phosphatidylcholine (PC). The optimization of the lipid bilayer composition with the addition of little percentages of natural lipids is still at early stage due to the difficulties experienced by classical liposome formation processes, mainly, in reproducibility and encapsulation efficiency. Supercritical assisted liposome formation (SuperLip) has demonstrated that these limitations can be overcome. Therefore, in this work, this process has been tested to produce liposomes of controlled nanometric diameter and the effect of water solution flow rate on drug encapsulation efficiency was investigated. The addition of cholesterol (Chol) or phosphatidylethanolamine (PE) was also studied to gain the control on the release rate of the drug entrapped in liposomes. Theophylline was selected as the model hydrophilic drug. Using SuperLip process, PC/Chol and PC/PE liposomes were successfully produced with nanometric mean diameters down to 200nm. Optimization of both lipid composition and SuperLip operative parameters allowed to obtain theophylline encapsulation efficiencies up to 98%. Drug release kinetics were affected by liposome composition, in particular, the addiction of Chol and PE allowed to slow down theophylline release rate. These results confirmed the possibility of producing liposomes with a complex architecture of the lipid membrane using the SuperLip process.