Liposomes preparation using a supercritical fluid assisted continuous process

• A new supercritical assisted process for liposomes production is proposed.
• Liposome suspensions with diameters ranging between 120 and 300 nm are obtained.
• An interpretation of liposome formation mechanism is attempted.

Liposomes are formed by phospholipids that spontaneously generate bilayers vesicles as a consequence of their interactions with water; they can be very efficient drug carriers, capable to preserve the activity and/or improve the safety of several therapeutic molecules. In this paper, a new continuous supercritical fluid process, named Supercritical Assisted Liposome formation (SuperLip), is proposed to prepare liposomes of controlled submicrometric size. In this process, water droplets are produced by atomization inside an high pressure vessel, filled with an expanded liquid mixture formed by phospholipids/ethanol/carbon dioxide (CO2). These droplets are rapidly surrounded by a lipid layer, forming a w/CO2 emulsion and liposomes (w/w emulsion) are formed when they fall in the water pool located at the bottom of the vessel. Experiments have been performed varying process operating parameters like pressure, temperature and flow rate ratio between CO2 and ethanol, producing liposomes of different size and distribution ranging between 130 ± 62 and 294 ± 144 nm. The results demonstrated that atomized liquid droplets are transformed efficiently into submicronic liposomes as a consequence of the spontaneous organization of the vesicles on the fly in the high pressure vessel.Drug encapsulation feasibility tests were also performed using bovine serum albumin (BSA), used as a model protein. High encapsulation efficiencies (85–90%) were obtained, confirming that the active compound contained in the atomized water phase was efficiently entrapped in the formed vesicles.