PREPARATION AND CHARACTERIZATION OF NONIONIC SURFACTANT VESICLES

Nonionic surfactant vesicles (NSVs) were prepared from polyoxyethylene alkyl ether surfactants (C(n)EO(m)) and sugar ester surfactants. The relationship between the hydrophilic-lipophilic balance (HLB), gel-liq uid transition temperature (T-c) of the surfactants, and vesicle forma tion was examined. For spontaneous vesicle formation both an HLB betwe en 7.5 and 10.5 and a T-c below the experimental temperature were nece ssary. Surfactants with a suitable HLB, but with a high T-c, were able to form vesicles upon sonication. Cholesterol (CHOL) encapsulation fa cilitated vesicle formation. The minimum amount of cholesterol necessa ry to form vesicles and the maximum amount that could be encapsulated were related to the HLB and the T-c. Addition of cholesterol and dicet ylphosphate decreased the size of NSVs, Cholesterol decreased the floa ting and increased the sedimentation behavior of vesicles. Dicetylphos phate stabilized the suspensions and minimized the aggregation behavio r of sugar ester vesicles. The capacity of the NSVs to encapsulate car boxyfluorescein and triamcinolone acetonide was not influenced by the physical state of the bilayers. Heating C(n)EO(m) vesicles without cho lesterol to 40 degrees C or higher resulted in an increase in size, in contrast to vesicles with a CHOL/SURF molar ratio of 0.67. This is pr obably the explanation for the decrease in size with increasing CHOL c ontent in the NSVs. (C) 1996 Academic Press, Inc.