Lyophilized liposomes prepared by a modified reversed-phase evaporation method.

Abstract

A modification of the reversed-phase evaporation method (modified REV method) was developed for the preparation of lyophilized unilamellar liposomes. The encapsulation efficiencies of the liposomes after a dehydration (lyophilization) -rehydration procedure were satisfactorily high, and the liposome sizes were maintained nearly constant throughout the procedure. These results are different from those obtained with liposome samples prepared by the reversed-phase evaporation method. In the latter case, marked enlargement of liposome size and extensive leakage from liposomes were observed. The small amount of residual ether in the modified REV liposomes keeps the lipid membranes fluid even at freezing temperature. The fluidity is considered to play an important role in the protection of liposomes against aggregation, fusion and leakage.