Detachable immobilization of liposomes on polymer gel particles.

Immobilization of liposomes on hydrophobized Sephacryl gel and controlled detachment of the liposomes from the gel were examined. The gel was chemically modified and bore octyl, hexadecyl or cholesteryl moiety via disulfide linkage as anchors to liposomal bilayer membrane. Upon interaction with the gel, egg phosphatidylcholine liposomes were successfully immobilized onto the gel. The gel with cholesteryl moiety showed 1.7 times higher liposome immobilization per anchor moiety than the gels with the alkyl moieties. The immobilization of liposomes on the gel was stable, and no significant spontaneous detachment of phospholipid or leakage of fluorescein isothiocyanate-conjugated dextran encapsulated in the immobilized liposomes was observed in 24h. Reductive cleavage of the disulfide linkage by dithiothreitol resulted in detachment of the liposomes from the gel. The majority of the detached liposomes were found encapsulating the dextran derivative, and these liposomes should have kept their structural integrity throughout the immobilization and the detachment processes. The release of the liposomes was insignificant until the ratio of the dithiothreitol to the hydrophobic anchor reached a threshold. The presence of the threshold suggests that the immobilization of liposomes should require a certain minimum number of the hydrophobic moieties anchored in the liposomal membrane. By applying the present immobilization-detachment system, preparation of liposomes encapsulating the dextran derivative without using costly gel filtration or ultracentrifugation procedure was successfully demonstrated.