Chapter 2: Surface Properties of Liposomes Depending on Their Composition

Abstract Since the discovery of liposomes in the middle of the 20th century, much attention has been focused on their physicochemical properties and on the liposome design from their potential value as drug carriers in drug delivery systems. Also, from a biological interest, liposomes have been studied as biomimetic cells, since biological membrane is composed of lipids, proteins, and carbohydrates. In this chapter, lipid compositions, shapes of lipids, diversity, and distribution in biological membranes will be discussed in terms of their functions. Physicochemical properties of liposomes, such as hydration of lipid headgroup, size, osmotic effects, and surface charges, which affect the stability and loading efficacy of drugs in liposomes, will be discussed. The modification of liposome surfaces with glycolipids and hydrophilic polymers stabilizes the liposomes and increases the loading efficiency of drugs. By the modification of liposome surfaces with polyethylene glycol (PEG), the circulation time of liposomes after being administered to blood is prolonged, since PEGylated liposomes have an ability to escape from the uptake by reticuloendothelial system. Liposomes, the surfaces of which are modified by hydrophilic polymers, have been studied as injectable drug carriers for passive targeting of anticancer drugs to cancer tissue. In addition, positively charged liposomes have recently been studied as DNA transfection agents.