Drug delivery systems,second edition Figure 1.1 Schematic of a bilayer vesicle or liposome.(From Pharmaceutical Techology,Conf. Proc.,The Latest Developments in Drug Delivery Systems,Oct.1985.With permission.) Bilayer Vesicle Internal aqueous Bilayer membrane compartment Entrapped material Figure 1.2 A micrograph view of a liposome.(Reprinted by permission of The Lipo some Company,Inc.Princeton,NI.) groups.This compartmentalization has been discussed in detail by Roerdink et al.1 C. Phospholipids A variety of phospholipids can be used to prepare liposomes.The lipid most widely used is phosphatidylcholine,2324 which has been used individually or in combination with cholesterol.Cholesterol is known to condense the 6 Drug delivery systems, second edition groups. This compartmentalization has been discussed in detail by Roerdink et al.14 C. Phospholipids A variety of phospholipids can be used to prepare liposomes. The lipid most widely used is phosphatidylcholine,23,24 which has been used individually or in combination with cholesterol. Cholesterol is known to condense the Figure 1.1 Schematic of a bilayer vesicle or liposome. (From Pharmaceutical Technology, Conf. Proc., The Latest Developments in Drug Delivery Systems, Oct. 1985. With permission.) Figure 1.2 A micrograph view of a liposome. (Reprinted by permission of The Lipo￾some Company, Inc., Princeton, NJ.)