An Investigation into Some Effective Factors on Encapsulation Efficiency of Alpha-Tocopherol in MLVs and the Release Profile from the Corresponding Liposomal Gel.
Seyed Alireza Mortazavi
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Vitamin E (α-tocopherol) is a natural antioxidant very useful for preventing the harmful effects of UV sun rays as skin aging and cancers. In this study, different MLV formulations were made using egg lecithin and varying molar ratios of α-tocopherol and/or cholesterol, and their encapsulation efficiencies were determined. The best liposomal product was incorporated into a carbomer 980 gel. The resulting preparation was then studied with regard to the rheology and release profile using r(2) values and Korsmeyer-Peppas equation. The encapsulation efficiency was dramatically decreased when using α-tocopherol at molar ratios of 1:10 or more, which is suggested to be due to the defect in regular linear structure of the bilayer membrane. Addition of cholesterol to formulations caused a decrease in encapsulation efficiency directly related to its molar ratio, which is due to the condensation of the bilayer membrane as well as competition of cholesterol with α-tocopherol. The liposomal gel showed a yield value of 78.5 ± 1.8 Pa and a plastic viscosity of 27.35 ± 2.3 cp. The release showed a two-phase pattern with the zero-order model being the best fitted model for the first phase. However, the "n" and r(2) values suggested a minor contribution of Higuchi model due to some diffusion of α-tocopherol from the outermost bilayers of the MLVs to the gel. The second phase showed a non-Fickian release indicating a more prominent role for diffusion. This combinational release profile provides a high initial concentration of α-tocopherol followed by a slow release throughout a 10 h period.