Liposome-encapsulated alginate: controlled hydrogel particle formation and release.

Large unilamellar liposomes of dipalmitoyl phosphatidylcholine have been employed as reaction sites for calcium alginate gelation. Encapsulation of sodium alginate was accomplished by extrusion of phospholipid dispersions through polycarbonate filter of uniform pore size followed by incubation with high concentrations of calcium chloride. The diffusion of calcium into the liposome interior resulted in alginate gelatin within the liposome. Detergent treatment of the liposomes resulted in solubilization of the lipid bilayer with subsequent release of the alginate beads which were measured by laser light scattering and electron microscopy. The release profiles of both the liposomes with entrapped alginate beads and the alginate beads (released by detergent treatment of the liposomes) were determined using cytochrome-c as a marker for release. The release profiles show a rapid release of cytochrome-c over the first 2 for both preparations with slower subsequent release rates for the liposomes with encapsulated alginate beads. The similar early profile may be due to the release of cytochrome-c from bound calcium alginate adsorbed to the outer leaflet of the liposome. This is also supported by calorimetric results which indicate a marked reduction in the enthalpy of the main gel to liquid crystalline phase transition of multilamellar and large unilamellar dispersions of the lipid. This method results in the fabrication of easily controlled, unimodal submicron hydrogel particles which may be used for controlled-release applications.