Liquid Crystals in O/W Emulsions with Urea: Development and Testing

December 23, 2005 | Contact Author | By: O.D.H. Santos, F. Sacai, M. Ferrari and P.A. Rocha-Filho, Faculdade de Ciencias Farmaceuticas de Ribeirao
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Keywords: liquid crystal | lamellar phase | phase diagram | lanolin | urea | moisturizer

Abstract: Using a ternary phase diagram, the authors developed systems based on nonionic surfactants, light paraffin oil, water, and (optionally) urea. Systems in which lamellar liquid crystals formed and in which urea was an ingredient showed higher occlusive power and lower TEWL in in vitro tests.

Dispersed systems are the basis for formulations developed as vehicles for parenteral, oral, ocular and mainly topical use. Dispersed systems can assume different characteristics, from thick gels to creamy emulsions. Each formulation component exerts a specific effect, and the interactions between some constituents determine the pharmaceutical forms. Phase diagrams are a very useful methodology for studying and achieving dispersed systems. Through them, chemists can identify and characterize the association of different components in a formula and determine the best proportion of these components for a given formulation type.

Lanolin is the oily secretion from a sheep’s sebaceous glands. It is deposited on the wool fibers and serves to soften the skin during shearing and to protect against foreign elements. Chemically it is considered to be esters, diesters, hydroxyesters, acids and alcohol with a high molecular weight. Thus it is a complex wax mixture with properties that facilitate its incorporation in formulations and improve its effects (such as moisturization) in finished cosmetic topical products.

Among lanolin’s derivatives are the ethoxylated ones obtained by reacting lanolin or a derivative, such as alcohol, with ethylene oxide. The result is a hydrosoluble substance with hydrophilic surfactant capacity that maintains the emolliency, moisturizing and stabilizing activity of lanolin.