Liposome

Scheme of a liposome formed by phospholipids in an aqueous solution.

Liposomes are composite structures made of phospholipids and may contain small amounts of other molecules. Though liposomes can vary in size from low micrometer range to tens of micrometers, unilamellar liposomes, as pictured here, are typically in the lower size range with various targeting ligands attached to their surface allowing for their surface-attachment and accumulation in pathological areas for treatment of disease.

A liposome is a small artificial vesicle, spherical in shape, having at least one lipid bilayer. Due to their hydrophobicity and/or hydrophilicity, biocompatibility, particle size and many other properties, liposomes can be used as drug delivery vehicles for administration of pharmaceutical drugs and nutrients, such as lipid nanoparticles in mRNA vaccines, and DNA vaccines. Liposomes can be prepared by disrupting biological membranes (such as by sonication). A nanoliposome or nanoliposomal vehicle is a liposome in the nanoscale; in other words, it is a kind of nanocarrier involved in the processes of nanoencapsulation and nanodelivery. Another kind of lipid-based nanocarrier similar to the nanoliposome is the nanocochleate; however, whilst nanoliposomes have a roughly spherical shape, a nanocochleate has a cylindrical (cigar-like) microstructure created by spirally rolled bilayers in which drugs (e.g., hydrophobic and hydrophilic biomolecules) are nanoincapsulated.

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

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). 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.

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)).

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