Preparation and Characterization of Liposomal Nanovesicles Using Supercritical Carbon Dioxide Expansion-Depressurization of Phospholipid Suspension (SEDPS)

Liposomal nanovesicles (LN) were produced utilizing the supercritical carbon dioxide expansion-depressurization of phospholipid suspension (SEDPS) process via two depressurization protocols. The effects of pressure (60–300 bar), depressurization rate (10– 120 bar/min) and depressurization protocol on the vesicle size, polydispersity index (PdI), morphology and storage stability of LN were investigated. The volumetric expansion of water in equilibrium with high pressure CO2 (1–300 bar) at temperatures of 40, 50, 60°C was also evaluated. Particle size of LN decreased at elevated pressures for depressurization protocols (I) and (II). Transmission electron microscopy images displayed unilamellar spherical or nearspherical nanovesicles and higher pressure could be favorable for the formation of more symmetrical and spherical particle. LN remained stable for up to 8 and 6 weeks ( 5% increase in size) for depressurization protocols (I) and (II), respectively. The relative volumetric expansion of water in equilibrium with high pressure CO2 was up to 14.7%, 12.3% and 10.2% at 40°C, 50°C and 60°C, respectively. INTRODUCTION Liposomal nanovesicles (LN) are unilamellar structures composed of amphipathic phospholipids surrounding aqueous compartments. Due to the amphipathicity of its structure, LN allow encapsulation of hydrophilic and hydrophobic compounds. Hydrophilic components are entrapped within the aqueous core whereas lipophilic materials are incorporated into the phospholipid bilayer [1]. Through encapsulation, drugs, nutraceuticals and bioactives can be protected from unfavorable conditions such as pH, hydrolysis or enzymatic attack in the gastrointestinal tract to improve their stability and bioavailability [2]. Plus, the dispersibility of poorly water soluble components is enhanced. LN show great potential in pharmaceutical industry and have drawn much attention for food and nutritional applications [3]. Although considered promising for a number of applications, LN confronts various challenges in their preparation. Conventional preparation methods of LN, including thin film hydration (TFH), ethanol injection and reverse phase evaporation usually lead to organic solvent residues, high energy cost, heterogeneous size distribution and low reproducibility. Present supercritical carbon dioxide preparation methods for LN preparation include the rapid expansion of supercritical solution into a liquid solvent (RESOLV), supercritical reverse phase evaporation (SCRPE) and depressurization of expanded liquid organic solution (DELOS). Some of these techniques involve poor solubility of phospholipids in CO2, high CO2 consumption, relatively large size of LN and the use of surfactant and organic solvent. Thus, an alternative method, which can yield high quality LN and overcome these drawbacks is needed. In this study, a single step process via SC-CO2 expansion-depressurization of phospholipid suspension (SEDPS), which is free of surfactants other than phospholipids and