**7.5 Stealth liposomes and conventional liposomes**

Liposomes become known by the mononuclear phagocytic system following contact with plasma proteins. This is solved through the use of synthetic phospholipids, particle coated with amphipathic polyethylene glycol, coating liposomes with chitin derivatives, freeze drying, polymerization, and microencapsulation of gangliosides. A stealth liposome is a sphere-shaped vesicle with a membrane that is composed of a phospholipid bilayer used to deliver drugs or genetic material to a cell.

Drug loading can be achieved through passive (if the drug is encapsulated during liposome formation) or active methods (after liposome formation). Freeze-dried (lyophilization) liposomes are formed from preformed liposomes at tremendously low pressures. Very high encapsulation efficiencies, even for macromolecules, can be achieved using this method. During dehydration, the lipid bilayers and the drug to be encapsulated into the liposomes are brought into close contact. Upon reswelling, the chances for the encapsulation of the adhered molecules are much higher. Rehydration is a very important step and it should be very carefully done. The aqueous phase should be added in very small portions with a micropipette to the dried materials. After each addition, the tube should be thoroughly vortexed.
