Effect of Mineral-Oil Addition on Film Stability of Polar Lipid Constituents Derived from Meibum

Abstract

We studied the effects of mineral oil (MO) on the properties and structure of a spread monolayer of polar lipid constituents in meibum, by performing cyclic lateral compression-expansion experiments using a Langmuir trough. A meibum sample without nonpolar lipids (meibumΔnonpolar-lipid) was prepared by removing the nonpolar lipids from biological meibum extruded from rabbit eyelids and spread on a water surface for measuring the cyclic surface pressure (π)–film area (A) isotherms with in situ observation of the film morphology using a Brewster angle microscope. The meibumΔnonpolar-lipid formed a homogeneous fluid monolayer and underwent collapse upon compression. The π–A isotherm shifted to a smaller area upon repeating the compression–expansion cycles. These observations contrasted those obtained for meibum previously, which may have resulted from the absence of nonpolar lipids. The recovery of the film stability against the lateral compression–expansion cycles was analyzed by adding MO as a nonpolar compound to the film system. A spread film of 1:1 mixture (by weight) could recover the high reversibility of the π–A isotherms during the repeated compression and expansion processes.