STERILE FILTRATION OF LIPOSOMES - RETENTION OF ENCAPSULATED CARBOXYFLUORESCEIN

Multilamellar Vesicles incorporating carboxyfluorescein (CF) were calibrated through polycarbonate membranes of 0.1, 0.2 or 0.4 mu m pore size. After removal of unencapsulated material, the vesicles were passed through 0.2 mu m sterilizing filters constituted of polycarbonate, cellulose acetate or polyvinylidene fluorure (PVDF). The liposomes were readily filtered without significant change in the vesicle size and loss of phospholipids. The leakage of encapsulated material was only slight, lower than 5% in all cases, except for vesicles of 300 nm sterilized through polycarbonate membranes of 0.2 mu m pore size. However, the same preparation was easily passed through 0.2 mu m acetate cellulose membranes without significant leakage of the incorporated dye. In spite of the small size of the liposomes, trapping efficiencies up to 33% were achieved, depending on the vesicle mean diameter, lipid concentration, bilayer composition and inclusion of freeze-thawing cycles.