| Liposomes are phospholipid vesicles that have the potential to encapsulate therapeutic drugs and carry them through the bloodstream and to the target region. One of the properties of the liposomes that mainly contribute to their lifespan in the bloodstream is their size. In order to avoid opsonization and detection by the body's immune system, the liposome diameter should be less than 200 nm. Consequently, this study implements sonication to form small unilamellar vesicles (SUVs) and investigates how the mean diameters and size distributions of the liposomes are affected by sonication time, temperature and the lipid composition. Furthermore, the study attempted to determine the optimal conditions to form these small liposomes. There were several formulations that had mean diameters less than 200 nm after at least 25 minutes of sonication at 45 °C and above. The smallest mean diameter was 81.01 nm, which was exhibited by a formulation that consisted of 60 mol% DOPC, 10 mol% DPPC, and 30 mol% cholesterol. However, the ideal formulation could not be concluded since several exhibited similar behavior. SUVs were not formed for liposomes that did not consist of DOPC regardless of the temperature and sonication time, which was mainly caused by aggregation and rigid membrane packing.;The size distributions were also examined to provide further insight on the individual populations of liposomes. Many formulations exhibited bimodal distributions and consisted of an alpha population of SUVs and a beta population of LUVs. Before sonication, the lipid solutions were mainly a unimodal beta population consisting of liposomes larger than 1000 nm. The alpha populations were formed due to shear forces from cavitation bubbles that stretch the large liposomes until they broke into smaller ones. Future investigations are still necessary to determine an ideal formulation because many of them exhibited similar distributions as well. |
