Liposome

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A liposome is a small artificial vesicle, spherical in shape, having at least one lipid bilayer.^[2] Due to their hydrophobicity and/or hydrophilicity, biocompatibility, particle size and many other properties,^[2] liposomes can be used as drug delivery vehicles for administration of pharmaceutical drugs and nutrients,^[3] such as lipid nanoparticles in mRNA vaccines, and DNA vaccines. Liposomes can be prepared by disrupting biological membranes (such as by sonication).

Liposomes are most often composed of phospholipids,^[4] especially phosphatidylcholine, and cholesterol,^[2] but may also include other lipids, such as those found in egg and phosphatidylethanolamine, as long as they are compatible with lipid bilayer structure.^[5] A liposome design may employ surface ligands for attaching to desired cells or tissues.^[1]

Based on vesicle structure, there are seven main categories for liposomes: multilamellar large (MLV), oligolamellar (OLV), small unilamellar (SUV), medium-sized unilamellar (MUV), large unilamellar (LUV), giant unilamellar (GUV) and multivesicular vesicles (MVV).^[6] The major types of liposomes are the multilamellar vesicle (MLV, with several lamellar phase lipid bilayers), the small unilamellar liposome vesicle (SUV, with one lipid bilayer), the large unilamellar vesicle (LUV), and the cochleate vesicle. A less desirable form is multivesicular liposomes in which one vesicle contains one or more smaller vesicles.

Liposomes should not be confused with lysosomes, or with micelles and reverse micelles.^[8] In contrast to liposomes, micelles typically contain a monolayer of fatty acids or surfactants.^[9]