Phase Separation of Polymerized Mixed Liposomes: Analysis of Release Behavior of Entrapped Molecules with Skeletonization

Shinji Takeoka, Hiromi Sakai, Hiroyuki Ohno,+ and Eishun Tsuchida'

Macromolecules 1991,24, 1279-1283

The mixed liposomes, composed of a polymerizable lipid, 1,2-bis(2,4-octadecadienoyl)-snglycero-3-phosphorylcholine(D ODPC), and nonpolymerizable membrane constituents, DPPC, cholesterol, and sodium didodecyl phosphate, were prepared by an extrusion method. After polymerization, onpolymerizable constituents were removed to obtain the polymerized framework of the liposome (the skeletonized liposome). The release of small molecules from the skeletonized liposomes through resulting holes was analyzed. A 5(6)-carboxyfluorescein (CF) and saccharides with various molecular weights were applied as release molecules. The molecular weight of dextran, whose retention ratio in the skeletonized liposomes is 5096, relates to the apparent size of the holes, i.e., the apparent domain size of the phase separation of a polymerized mixed liposome. The size of the holes increases with an increase in the mole fraction of nonpolymerizable lipids. This also depends on the polymerization temperature and the structure of nonpolymerizable lipids.