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 microm. 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.

Stable reversed vesicles in oil: characterization studies and encapsulation of model compounds.

The formation of reversed sucrose ester vesicles in silicon oil and mixtures of silicon oil and isopropyl palmitate was studied. The vesicles were characterized by polarized light microscopy, freeze-fracture electron microscopy, and differential scanning calorimetry. Furthermore the ability to encapsulate p-aminobenzoic acid and cholesterol in such vesicles was studied. The vesicles were multilamellar and had sizes up to several micrometers. The vesicles agglomerated but did not show fusion for at least 2 years when stored at room temperature in glass vials. The encapsulation efficiency of both p-aminobenzoic acid and cholesterol strongly depended on the oil phase in which the vesicles were prepared. Reversed sucrose ester vesicles in silicon oil encapsulated nearly 100% of the amount of p-aminobenzoic acid or cholesterol present in the dispersion. These compounds were encapsulated in different compartments of the vesicles. Reversed sucrose ester vesicles offer new perspectives regarding the development of novel pharmaceutical dosage forms.