A comparative study of niosomes (non-ionic surfactant vesicles) and liposomes : their stability in biological environments
Submicron sized vesicles consisting of single and double chain non-ionic surfactant mixtures were prepared by simple dispersion of surfactant dissolved in aqueous medium, or alternatively, injecting the surfactant dissolved in organic solvent into the aqueous phase. Drug entrapment values were measured by using a fluorescent marker, 5,6- Carboxyfluorescein, and drug release characteristics were evaluated in biological media (serum and plasma) as a function of surfactant composition and in the presence or absence of cholesterol. Surface charge measurements, zeta-potential, as a function of pH, gel electrophoresis and immunoblotting (ELISA) were performed in order to measure the interaction of components of the biological fluid with the prepared vesicles. It was found that all vesicles carried a negative charge and rapidly bound plasma protein, which included albumin and immunoglobulin G, thus affecting the latency of the entrapped marker. Uptake and degradation of niosomes (non-ionic surfactant vesicles) in a living, unicellular, eukaryotic micro-organism was also investigated. It was found that the rate of release of contents depended on the composition of the vesicles and was a function of enzymatic degradation within these organisms rather than an intracellular PH effect of the digestive organelle. An identical protocol was carried out with the well- characterised liposome system and their inherent stabilities under a variety of conditions directly compared with niosomes.