Design of sterically stabilized liposomes

Liposomes have been considered as almost universal carriers for drugs and diagnostic agents, as they being biodegradable non toxic and are able to accommodate both hydrophilic and hydrophobic agents. A major hurdle towards in vivo utilization of liposomes is their prompt by the cells of the RES. Typically, prolonged circulation of the liposomes is achieved using poly(ethylene glycol) (PEG) covalently connected to a lipid residue which is incorporated into the liposome bilayer. The polymer chains create a repulsive barrier around liposomes, which reduces the interactions with blood components and consequently increases the blood circulation time. At a certain critical content referred to as saturation limit, which depends on lipid composition and PEG-molecular weight, the PEG-lipids induce a transition from bilayers to a micellar phase