Preparation and Characterization of pH-Sensitive Vesicles Made of Cholesteryl Hemisuccinate

pH-sensitive vesicles are designed to promote efficient release of entrapped agents in response to low pH. In this study, such vesicles were prepared from cholesteryl hemisuccinate (CHEMS) in Tris-HCl buffer. Vesicles prepared by this direct hydration method had a small particle size of 74.1 nm based on intensity of Gaussian and a size of 65.8 nm based on volume of Gaussian. The mean zeta potential was about –73mV, indicating that the vesicle system was stable. Entrapment efficiency for calcein by these vesicles was measured at 37 ± 2.36%, which is higher than that by phospholipid MLVs. These calcein loaded vesicles exhibited excellent stability at pH 7.4 and underwent rapid destabilization upon acidification as showed by calcein release. However these vesicles were unstable in Fetal Bovine Serum (FBS). Optimization of formulation might improve their stability in serum.