Studies of vesicles are important to better understand the functioning of living organisms, as they have a wide range of important roles like cell-cell communication and transport of substances. They are composed of a phospholipid bilayer consisted of water and macromolecules like proteins and RNA. Lately scientists have been working on preparation of artificial vesicles or liposomes which can be used for many different purposes. One of the techniques to prepare large vesicles formed from one lipid bilayer is the extrusion technique. We used extrusion for liposomes preparation with the aim of synthesizing vesicles of different sizes, composed of three different phospholipid bilayers. For the structure of phospholipid bilayers, we used natural or synthetic surfactants which reduce the surface tension. We made vesicles from egg lecithin, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine lipid, and a mixture of the 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine lipids.
We measured the size of vesicles via dynamic light scattering and thus we were able to calculate the hydrodynamic radius of the particles with the help of measured translation diffusion coefficient (using the Stokes-Einstein equation). According to the first extrusion, all the measured sizes of the particles were too large, presumably due to the impurities in the extruder. We have repeated extrusion with the egg lecithin residues using another cleaner extruder. The vesicles were of the right size. However, with repeated extrusions of 2-dioleoyl-sn-glycero-3-phosphoethanolamine lipid, sizes of vesicles did not agree with the pore size of filters that were used for the extrusion. After another extrusion of samples that had already been extruded, the hydrodynamic radius of vesicles wase almost the same, irrespective of the filter used.
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