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Tatyana F Svitova, Meng C Lin; Thick Human Tear Lipid Films: Effect of Lipids Interaction with Model Tear Proteins on Interfacial Properties.. Invest. Ophthalmol. Vis. Sci. 2014;55(13):41.
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© ARVO (1962-2015); The Authors (2016-present)
To study and quantify the effects of model tear proteins (MTP) on interfacial dynamics and rheological properties of human tear lipids extracted from Schirmer strips (SSL).
SSL samples were collected from 8 healthy subjects. Sessile bubble tensiometry was used to study interfacial properties of SSL, MTP, and mixed film (SSL+MTP) at 35° C. SSL was deposited on an air bubble to form 90±20 nm-thick films. SSL films were subjected to expansion-compression cycles; the film area changed from ~5 to 50 mm2. MTP solutions (Hen Egg Lysozyme (HEL), final concentration (FC) =2 mg/ml, Human Serum Albumin (HSA), FC=0.2 mg/ml, Bovine Submaxillary Mucin (BSM), FC= 0.15 mg/ml, or their mixture with FC=2.35 mg/ml total) was injected into a cell and equilibrated without or with SSL film for up to 24 hours. Dynamic interfacial properties of films were assessed. MTE was then pumped through the cell to remove MTP from bulk and SSL dynamic properties were re-evaluated.
Equilibrium surface tension (EST), elasticity modulus (E), and relaxation times (τ) of SSL alone were 22±2.1 mN/m, 10.7-14.8 mN/m, and 90-170 s, respectively. EST for proteins was 45.3±1.5 for HEL, 40.4±0.5 for HSA, and 36.7±1.3 mN/m for BSM. The range of E for proteins was 12.5 -18.5 mN/m; τ was 433-525 s. For mixed SSL+MTP films, EST remained unchanged. E for SSL+MTP mixed films was 5-7 mN/m lower than for SSL; τ increased to 250-360 s. MTP altered the shape of surface pressure vs. film thickness (π-h) iso-cycles and film compressibility. HSA produced minor changes, whereas BSM and HEL changed SSL properties more notably. For SSL alone the maximum surface pressure πmax was attained at h ∼50 nm; in the presence of BSM πmax was attained at h ∼ 20 nm. HEL shifted πmax toward higher h, to ∼70 nm. These changes persisted after proteins were washed out.
Model proteins adsorb and bind irreversibly to thick SSL films and change interfacial properties of SSL films and the range of maximum surface pressure. BSM alone or mixed with other MTP is found to be most active at lipid-water interface, implying its likely role in tear film stabilization.
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