Control of the surface modification of liposomes by poly(ethylene glycol)-lipids with different hydrophilic-hydrophobic balances

Liposomes of which the surface was modified with poly(ethylene glycol) (PEG) chains are used to prevent aggregation and fusion and to prolong blood circulation. PEG-lipids were immobilized onto the surface of liposomes by simply adding their aqueous dispersions to the liposome dispersions. However, they dissociated from the liposomes by dilution of the mixed dispersions because they were incorporated into the liposomes in an equilibrium state. For the tight immobilization of the PEG-lipids with the long PEG chain onto the liposome surface, an increased number of alkyl chains is necessary.