Abstract
Factors such as lipid composition and liposome size, which affect the stability of liposomes during the freeze-drying process, were investigated. The addition of 9 mol% of charged lipids to egg-phosphatidylcholine (eggPC) had little effect on liposome stability. The addition of cholesterol decreased the retention percentage (R%) of entrapped calcein and increased the size of liposomes after freeze-drying. Destabilization occurred in the gel state of eggPC/cholesterol binary system. In liposome systems prepared using the extrusion technique, the R% decreased through freeze-drying as their size increased. Similar damage to liposomes was observed only by hyperosmotic shock : Considerable leakage occurred for large liposomes when the medium was changed from hyperosmotic to isotonic. Consequently, liposome leakage by freeze-drying likely occurs at the rehydration process.
