The influence of the incorporation of cholesterol and water on the particle size, bilayer thickness, melting behavior, and relative sucrose ester composition of reversed vesicles

The influence of the incorporation of cholesterol and water on the particle size, bilayer thickness, melting behavior, and relative sucrose ester composition of reversed vesicles was studied. Reversed vesicles (RVs) were prepared of sucrose ester in silicon oil by sonication. The RVs were characterized by polarized light microscopy, laser diffraction, high-performance liquid chromatography, small angle X-ray scattering (SAXS), and differential scanning calorimetry. The particle size distributions of the studied dispersions were bimodal with peaks at 5 and 0.4 μm. There was no significant difference in the sucrose ester composition of these two size categories of RVs. The incorporation of cholesterol and water had no effect on the size distribution of the RVs. The SAXS results showed that the RVs prepared without cholesterol and water consisted of bilayers with fully interdigitated alkyl chains. The incorporation of high concentrations of cholesterol caused a phase separation within the bilayers. The incorporation of water also resulted in a phase separation within the bilayers but at a lower cholesterol concentration. The presence of two different size classes of RVs in one RVs dispersion and the phase separation within the bilayers of certain compositions can have consequences for the application of RVs. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:588–598, 2001