Microencapsulated liposomes for the pulsed release of biologically-active materials

Lipid vesicles (liposomes) have gained wide acceptance as potential drug carriers. This colloidal system is a supramolecular assembly of amphipathic molecules, such as phospholipids, that form a bilayer around an aqueous core. The lipid bilayer serves both as a reservoir for hydrophobic drugs and as an effective diffusion barrier to encapsulated drugs with molecular weights greater than 1,000. One problem, however, remains to be overcome before the liposomal system can achieve its usefulness as a drug carrier. Liposomes interact with components of the immune system and with plasma proteins which leads to their rapid clearance by the reticuloendothelial system. Our approach towards overcoming this problem was to entrap the drug containing liposomes in alginate microcapsules. The microencapsulated lipsome system has the advantage of preventing the uptake of liposomes into the circulation where they would be metabolized, and an efficient local delivery system is thus created.