PHYTOSTEROL STABILIZED EMULSIONS (LIQUID CRYSTALS, DRUG DELIVERY, MESOMORPHIC, CONTROLLED RELEASE, COMPLEXATION, SURFACE CHEMISTRY)

Mechanisms operative in the stabilization of certain phytosterol stabilized emulsions have been reported. The behavior of a soyasterol, Generol 122, in the presence of an amphoteric surfactant, Deriphat 160C (sodium lauriminodipropionate), has been studied. Interfacial complexation of Generol 122 serving as a cosurfactant with the amphiphilic Deriphat 160C, has been proposed from NMR, IR and DSC studies. This intermolecular complex at the interface reaches an apparent maximum stability during a short period of continued structure build-up and would be expected to be responsible for facilitating emulsification and providing a barrier to coalescence. Interfacial tensions between an oil phase containing Generol 122 and a water phase containing Deriphat 160C were found to be very low. Studies by polarized light microscopy showed emulsions formulated with phytosterols and Deriphat 160C to be birefringent in nature.;Data obtained from conductivity and rheologic studies utilizing non-destructive short heating-cooling-heating cycles, and from DSC indicated that formulations containing 4% Deriphat 160C are stable as compared to systems containing 1, 2, 3, and 5% Deriphat 160C. Comparisons of a model formulation containing phytosterols with alternative formulations containing various nonionic and ionic surfactants revealed that the phytosterol-containing formulations have the smallest particle size, indicating a rather low interfacial free energy. In addition, drug delivery studies have indicated that Generol 122 concentration is a factor in the rate determining step in the release of the model drug salicylic acid from systems containing Deriphat 160C and water.;Such association complexes appear to form liquid crystalline phases at the oil-water interfaces and are the actual emulsion stabilizing component. A ternary phase diagram of Generol 122:Deriphat 160C:water was constructed and the presence of various liquid crystalline phases has been demonstrated. The formation of structures similar to multilamellar vesicles and the presence of an o/w emulsion has been shown by freeze-fracture electron microscopy. Also, the presence of a lamellar like structure in the model emulsions has been suggested by small angle x-ray diffraction studies. The stabilized emulsions exhibit a moderate degree of thixotropy. The yield value, obtained from rheologic data suggests a basic gel-like structure for those emulsions with high degree of structure and thermodynamic stability.