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Elizabeth Drolle, Zoya Leonenko, Lakshman Subbaraman, Lyndon William Jones; Nanoscale Comparison of Meibum and an In Vitro Lipid Model. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2250.
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© ARVO (1962-2015); The Authors (2016-present)
Meibum is a highly complex mix of lipids, whose characteristics can be studied in vitro by using a model mixture containing 6 lipids (cholesterol, cholesteryl oleate, oleic acid, oleic acid methyl ester, triolein and phosphatidylcholine; 6L), which are reflective of the amphiphilic and non-polar constituents of human meibum. Nanoscale surface characteristics and the surface potential of this 6L stock and collected human meibum from normal participants were examined and compared using appropriate imaging methods.
Thin films of each mixture were deposited on mica substrates using the Langmuir-Blodgett trough by depositing lipids in chloroform onto a nanopure water subphase of the trough, followed by vertical deposition on mica at a pressure of 5-10mN/m. Samples were then affixed to a metallic substrate and imaged using atomic force microscopy (AFM) to visualize the topography and Kelvin probe force microscopy (KPFM) to observe the differences in surface potential.
Topography images showed that the 6L and meibum behaved similarly. Both lipid mixtures formed thin film patches on the surface of the substrate, with large aggregates atop (Fig.1). The overall average roughness of 6L was 5.3 ± 0.3 nm (nimage=8), with aggregate sizes ranging from 41 to 153 nm in height. The range in surface potential was 33.0 - 125.9 mV. The overall average roughness of meibum was 21.5 ± 3.1 nm; aggregates had a size range of 170 to 459 nm in height (nimage=6) and surface potential ranged from 15.9 to 76.1 mV.
This study allowed for the visualization of lipids from human meibum and a 6L stock analogue, deposited on a solid substrate. It was shown that the two samples behaved similarly. This study is the first to investigate the surface potential characteristics of meibum and an in vitro meibum model. KPFM was used to simultaneously measure the differences in surface potential of the samples while analyzing the topography. For both 6L and meibum, it was shown that the areas of difference in surface potential corresponded to features visualized in the topography images, suggesting that the lipids themselves are sources of differences in surface potential. This could be an important determinant of the interaction of charged particles with the tear film and with deposits on contact lenses.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Fig1: Comparison of Surface Potential and Topography Features between Six Lipid Stock and Meibum samples
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