Preparation and properties of vesicles (niosomes) of sorbitan monoesters (Span 20, 40, 60 and 80) and a sorbitan triester (Span 85)

Abstract Formation of multilamellar vesicles (niosomes) of a series of sorbitan monoesters (Span 20, 40, 60 and 80) and a sorbitan trioleate (Span 85) has been studied using a mechanical shaking technique without sonication. 5(6)-Carboxyfluorescein (CF) was used as a model solute to investigate entrapment efficiency and release. For Span 80, cholesterol and dicetyl phosphate (DCP) in the molar ratio 47.5:47.5:5.0, entrapment efficiency increased linearly with increasing concentration of lipid. Entrapment efficiency per mmol lipid, however, was constant at about 34%, independent of the lipid concentration. Entrapment efficiency increased with increasing cholesterol content when vesicles were prepared by changing the molar ratio of non-ionic surfactant to cholesterol. Most efficient entrapment of CF occurred with Span 60 (HLB 4.7). Mean size of the un-sonicated niosomes showed a regular increase with increasing HLB from Span 85 (HLB 1.8) to Span (HLB 8.6). The release rate of CF from vesicles depended on the surfactant used in the preparation of the vesicles.