Immobilization of liposomes on hydrophobically modified polymer gel particles in batch mode interaction

Abstract

Immobilization of liposomal phospholipids onto Sephacryl S-1000 gels that were chemically conjugated with hydrophobic alkyl moieties, octyl, dodecyl and hexadecyl, was examined in batch mode interaction. Compared with the octyl gel, the dodecyl and the hexadecyl gels were found to immobilize the three to four times more phospholipids with the less hydrophobic moieties. The encapsulation of a water-soluble marker, with other evidences, suggests that the majority of the immobilized phospholipids maintained liposomal morphology. As the lipid of the interacting liposomes, egg yolk phosphatidylcholine (eggPC), 1,2-dimyristoylphosphatidylcholine (DMPC) and a mixture of DMPC and 1,2-dimyristamido-1,2-deoxyphosphatidylcholine were examined. At 22°C, DMPC liposomes showed higher extent of immobilization than at 37°C but not eggPC liposomes, suggesting that the phase of liposomal membrane could have influence on the immobilization. Exchange between the immobilized liposomes and free ones was found to be small, less than 3%. The gel that had been first interacted with liposomes to apparent saturation could further immobilize the newly added liposomes. The rate of this second immobilization was similar to that of the slow adsorption process; the both could be based on the same mechanism, possibly involving rearrangement of the immobilized liposomes on the gel as proposed by Lundahl. As had been observed in the flow mode, the immobilization had preference for smaller liposomes. In application of the system in batch mode, the size distributions of the immobilized liposomes and of those left in the supernatant may differ from that of the originally added liposomes.