A Spray-Drying Method for Mass Production of Liposomes1

Abstract

A spray-drying method for the mass production of liposomes was developed: lipids were dissolved in a volatile organic solvent such as chloroform in which, in some cases, a core material such as mannitol was additionally suspended, and the organic solution or suspension was then spray-dried. Addition of core material particles or the use of hydrogenated lecithins increased the recovery of the lipid mixture prepared by spray-drying. Since the obtained spray-dried product was very amorphous, it could be easily hydrated with an aqueous solution, and lipid vesicles (liposomes) were spontaneously formed by agitating. These spray-dried (SD) liposomes were characterized in comparison with the traditional liposomes known as Bangham's liposomes. Incorporation of cholesterol into the SD-liposomal membrane was confirmed by differential scanning calorimetry and gel filtration chromatography. Incorporation of charged lipids was confirmed by the zeta potential of liposomes. The size distribution of the unextruded SD-liposomes was similar to that of Bangham's liposomes, and a more homogeneous size distribution could be obtained by the extrusion technique. When glucose and dextran were used as water-soluble model drugs, the encapsulation efficiency was 15—65% depending on the total lipid concentration. Increasing the practical surface area of the lipid mixture using a core material was considered to cause a noticeably high encapsulation efficiency of dextran into the SD-liposomes. This spray-drying method was found to be useful and valuable for the mass production of liposomes. © 1991, The Pharmaceutical Society of Japan. All rights reserved.