Characterization And Applications Of Liposomes Microencapsulated By A Novel Supercritical Fluid Process

Abstract

A novel supercritical fluid (SCF) process, composed of SCF extraction, rapid expansion of a supercritical solution, and vacuum-driven cargo loading based on the Bernoulli principle, was successfully developed for liposomal microencapsulation. It aimed to be a non-toxic and continuous process based on the flow-through design and without usage of any organic solvent. Soy lecithin and cholesterol in a 10:1 mass ratio were dissolved in SC-CO2 at 20 ± 0.5 MPa and 60 oC. The phospholipids/cholesterol-laden SC-CO2 was then passed through a 1000-micron nozzle and immediately mixed with the cargo solution to form liposomes. Liposome size, zeta potential, and encapsulation efficiency (EE) were characterized as functions of the operating parameters. The results showed that the average liposome size varied from 400-500 nm to 9001200 nm when the pressure was increased from 8.27 to 16.55 MPa. For the liposomal microencapsulation of 0.2 M glucose solution, it was found that the highest EE of 31.6 % was reached at 12.41 MPa, 90 oC, and 0.25 ml/second of cargo loading rate. Under a confocal laser scanning microscope, the large unilamellar vesicles (LUVs) and multivesicular vesicles (MVVs) accounted for a majority of the liposomal emulsion produced by this novel SCF technique. Simultaneous microencapsulation of hydrophilic and lipophilic compounds in the integrated liposomes were also conducted for versatile applications of this novel SCF process. The liposomal microencapsulation was run via a 1000-micron jetting nozzle at 12.41 MPa, 90 oC, and 0.25 ml/second of the cargo loading rate. Vitamins C and E were used as model hydrophilic and lipophilic compounds, respectively, for characterization and storage-stability evaluation of the SCF-based liposomes. The average vesicle size of vitamins C and E microencapsulated liposomes was 951.02 nm with a zeta potential of -51.87 mV. The EE for vitamin C was 32.97 %, and EE for vitamin E was 99.32 %. During 20 days of storage at 4 oC, the EEs were found to slightly decrease by 1.76 % and 0.88 %, for vitamins C and E, respectively. The simultaneous microencapsulation of hydrophilic and lipophilic compounds in the liposomes was successfully demonstrated using this SCF process.