Target Liposome to a Particular Tissue

            Liposome is a hollow spherical bilayer, formed when polar lipids agitated in an aqueous medium. Basically, they are colloidal with vesicular structures based on phospholipid bilayers. Their structures depend on the developing procedure and choices of bilayer components. Their length can varied from 20 nm and as large as 190 nm in diameter. The liposomes can be unilamellar, only one bilayer surrounds an aqueous core or multilamellar, where several bilayers concentrically tilting around an aqueous core. Besides that, the choice of bilayer components determines the rigidity and the charge of the bilayer. For example, saturated phospholipids with long acyl chains such as dipalmitoylphosphatidylcholine form a rigid, rather impermeable bilayer structure, while the unsaturated phosphatidylcholine species from natural sources such as egg or soy bean phosphatidylcholine provide more permeable and less stable bilayers. Either positively or negatively charged lipids will resulted in the liposome's surface charge. The advantage of liposome is that liposome surfaces can be readily modified by attaching polyethylene glycol (PEG) molecules to the bilayer, the circulation time of liposomes in the blood stream is significantly increased. On the other hand, homing molecules can be attached to liposome bilayers to make these structures target site specific. Parameters that determine the fate of liposomes on the shelf and in vivo are size, lamellarity, bilayer rigidity, charge and bilayer surface modifications. .
             Liposomes are mainly used as transporters for drugs and antigens as they can used for different purposes. Firstly, they can direct a drug to a certain target. Besides, liposomes can extend the duration of drug exposure, acting as a slow release reservoir. This has been demonstrated in a number of studies, for example with the antimalarial drug chloroquine or the radical scavenger superoxide dismutase (Oussoren et al.