Preparation of Drug Liposomes by Reverse-Phase Evaporation
Liposomes display increased therapies for a series of biomedical application by stabilizing loaded payloads, overcoming shortcomings to cellular and tissue uptake, and enhancing biodistribution of payloads to target sites in vivo. The Bangham method or thin lipid film hydration technology was the first described method for constructing liposomes. The drawbacks of this method involve sonicator contact with the liposomes, and risk of high-temperature exposure may lead to phospholipid/drug damage and deceased encapsulation. A generally adopted preparative alternative is the reverse-phase evaporation technique that tends to form inverted micelles or water-in-oil emulsions. The water phase carries the drug, and organic phase is made up of the lipids for forming the liposome bilayer. The lipid mixture is dissolved in solvents, and the lipid solvents are evaporated. Formed lipid film after evaporation is redissolved in an organic phase. Under reduced pressure condition, the organic solvent can be slowly evaporated, initially resulting in the conversion of the dispersion into a viscous gel and finally generating an aqueous suspension containing the liposomes. Similar to other preparation methods, the size of liposome generated by reverse-phase evaporation technique needs to be reduced by multiple extrusions through a polycarbonate membrane. The number of extrusion cycles and the size of polycarbonate membrane pore influence the degree of size reduction and the final particle size and distribution. This paper summarized the preparation procedure and formation principle of various payload-loaded liposomes by reverse-phase evaporation technique.