Introduction to Liposomes

A liposome is a tiny bubble (vesicle), made out of the same material as a cell membrane.Liposomes can be filled with substances such as vitamins, nutrients and even drugs and are used to protect and deliver these substances where they need to be delivered, into the cell and the body!

Membranes are usually made of phospholipids, which are molecules that have a head group and a tail group. The head is attracted to water, and the tail, which is made of a long hydrocarbon chain, is repelled by water.Liposomes have the ability to carry either water of fat-soluble payloads, which makes the an ideal delivery system. In nature, phospholipids are found in stable membranescomposed of two layers (a bilayer). In the presence of water, the heads are attracted to water and line up to form a surface facing the water. The tails are repelled by water, and line up to form a surface away from the water. In a cell, one layer of heads faces outside of the cell, attracted to the water in the environment. Another layer of heads faces inside the cell, attracted by the water inside the cell. The hydrocarbon tails of one layer face the hydrocarbontails of the other layer, and the combined structure forms a bilayer.

 

When membrane phospholipids are disrupted, they can reassemble themselves into tiny spheres, smaller than a normal cell, either as bilayers or monolayers. The bilayer structures are liposomes. The monolayerstructures are called micelles.

The lipids in the plasma membrane arechiefly phospholipids like phosphatidylethanolamine and phosphatidylcholine. Phospholipids are amphiphilic with the hydrocarbon tail of the molecule beinghydrophobic; its polar head hydrophilic. As the plasma membrane faces waterysolutions on both sides, its phospholipids accommodate this by forming a phospholipid bilayer with the hydrophobic tails facing each other.

The name liposome is derived from two Greek words:'Lipos' meaning fat and 'Soma' meaning body. A liposome can be formed at a variety of sizes as uni-lamellar or multi-lamellar construction, and its name relates to its structural building blocks, phospholipids, and not to its size.In contrast, the term Nanosome does relate to size and was coined in the early1990s to denote special liposomes in the low nanometer range; liposome and Nanosome are not synonyms. A liposome does not necessarily have lipophobiccontents, such as water, although it usually does.Liposomes were first described by British haematologist Dr Alec D Bangham FRS in 1961 (published 1964), at the Babraham Institute, in Cambridge. They were discovered when Bangham and R. W. Horne were testing the institute's new electron microscope by adding negative stain to dryphospholipids. The resemblance to the plasmalemma was obvious, and the microscope pictures served as the first real evidence for the cell membrane being a bilayer lipid structure.