Papahadjopoulos was born on 24 August 1934 in Patra, which has been one of Greece's western gates for more than 2,500 years. He obtained a BSc in chemistry from the University of Athens and a PhD in biochemistry from the University of Washington in Seattle, under D. J. Hanahan. His interest in phospholipids and their role in blood coagulation (the subject of his thesis) brought him in 1966 to A. D. Bangham's laboratory at the Institute of Animal Physiology, Babraham, Cambridgeshire, where liposomes had just been discovered. His fascination with them was to remain undiminished throughout his life.
Liposomes had originally been recognized as closed, semipermeable bilayers of phospholipids (very similar to cell membranes) that can entrap water and solutes. Some of Papahadjopoulos's work, both in Babraham, and later on at the Roswell Park Memorial Institute in Buffalo, New York state, dealt with the development of novel, reproducible methods for making liposomes of a defined vesicle-size distribution. He was thus able to study bilayer permeability to ions, which was found to reach a maximum at the liquid crystalline transition temperature of the phospholipid. This research greatly contributed to the understanding of the physical nature of liposomes (and, indirectly, of cell membrane biophysics) in terms of their structure, the stability of the bilayer and mobility of the lipids within it, their interaction with proteins, and membrane fusion. Liposome research had made the transition from art to science, and Papahadjopoulos's contribution to it was decisive.
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