Drug delivery liposome, computer artwork. This artificially-constructed, spherical vesicle possesses a selectively-permeable wall that closely resembles the membrane of a living cell. The membrane consists of a dual layer of phospholipids. Each phospholipid consists of a phosphate group head (blue) and a fatty acid tail (orange). Liposomes can be used to carry drugs or genes to target cells. This is particularly useful for highly toxic cancer drugs as it reduces unpleasant side effects.