The Cryoprotective Mechanism of Saccharides on Freezing and Freeze-Drying of Liposomes

Abstract

The cryoprotective mechanism of saccharides on the freeze-thawing and freeze-drying of liposome was studied by several methods, such as leakage of aqueous inner markar, Raman- and NMR-spectroscopy and DSC. The surface of frozen liposome was covered by a concentrated aqueous saccharide solution or glassy solid, which protects from the mechanical damage of ice crystal and the fusion of liposome. Mono-, di- and trisaccharides showed a similar protective effect per monosaccharide unit. In the course of drying, the water molecules hydrated to the polar phosphate group of lecithin were displaced by the saccharide molecules. In the liquid crystal state the lyophilized liposome was maintained and the lipid membrane was stable during the rehydration process. The liposome lyophilized with a disaccharide showed the strongest stability during the rehydration process, indicating the importance of hydrogen bonding between the phosphate group and a sugar molecule with suitable molecular size.