**1. Introduction**

Liposomes are vesicular arrangements composed of one or more phospholipid bilayers surrounding an aqueous core. Liposomes were discovered almost six decades ago. Due to its versatility, liposomes are now analyzed for their applicability both in laboratory techniques and in medical studies. Its interest lies in its ability to traverse cell membranes and to transport certain types of molecules to defined places in the human body.

Liposomes can carry both hydrophilic and hydrophobic molecules. The preparation of the liposomes results in different properties for these systems. There are several factors involved in the preparation of liposomes that can modify their structures. Due to its biological compatibility, nonimmunogenicity, greater solubility of chemotherapeutic agents, and its ability to encapsulate a wide variety of drugs, the supply of drugs using liposomes has meant a great advance. The purpose of this book is to focus on recent developments in liposomes. The chapters selected in this book are contributions from invited researchers with long experience in different areas of research. This book offers expert and updated reviews of the field of liposomes.

## **2. Brief history of liposomes**

Liposomes were discovered in 1961 by Alec Bangham, a British scientist who studied blood coagulation. Bangham and RW Horne were testing the new electron microscope of the Agricultural Research Council Institute of Animal Physiology, Babraham, Cambridge, England, when they observed for the first time applying the negative staining technique for the study of the structures of the lipid phase that the dispersions of lecithin contained spherulites composed of concentric sheets [1]. These images served as the first evidence that the cell membrane was a two-layered lipid structure. The width of the lipid layer was estimated at 44 Å. Preparations of phosphatidylcholine-cholesterol of equal molar ratios were described as basically the same as phosphatidylcholine alone.

A year later, in a Cambridge pub, Weissmann in a discussion with Bangham called these structures "liposomes" in honor of the lysosome, a simple organelle whose latency linked to the structure could be interrupted with detergents and streptolysins. [2], and that his laboratory had been studying: liposomes can be easily distinguished from micelles and hexagonal lipid phases by transmission electron microscopy by negative staining [3].
