TY - JOUR U1 - Zeitschriftenartikel, wissenschaftlich - begutachtet (reviewed) A1 - Georgiev, Georgi A1 - Yokoi, Norihiko A1 - Ivanova, Slavyana A1 - Tonchev, Vesselin A1 - Nencheva, Yana A1 - Krastev, Rumen T1 - Surface relaxations as a tool to distinguish the dynamic interfacial properties of films formed by normal and diseased meibomian lipids JF - Soft matter N2 - The surface properties of human meibomian lipids (MGS), the major constituent of the tear film (TF) lipid layer, are of key importance for TF stability. The dynamic interfacial properties of films by MGS from normal eyes (nMGS) and eyes with meibomian gland dysfunction (dMGS) were studied using a Langmuir surface balance. The behavior of the samples during dynamic area changes was evaluated by surface pressure–area isotherms and isocycles. The surface dilatational rheology of the films was examined in the frequency range 10−5 to 1 Hz by the stress-relaxation method. A significant difference was found, with dMGS showing slow viscosity-dominated relaxation at 10−4 to 10−3 Hz, whereas nMGS remained predominantly elastic over the whole range. A Cole–Cole plot revealed two characteristic processes contributing to the relaxation, fast (on the scale of characteristic time τ < 5 s) and slow (τ > 100 s), the latter prevailing in dMGS films. Brewster angle microscopy revealed better spreading of nMGS at the air–water interface, whereas dMGS layers were non-uniform and patchy. The distinctions in the interfacial properties of the films in vitro correlated with the accelerated degradation of meibum layer pattern at the air–tear interface and with the decreased stability of TF in vivo. These results, and also recent findings on the modest capability of meibum to suppress the evaporation of the aqueous subphase, suggest the need for a re-evaluation of the role of MGS. The probable key function of meibomian lipids might be to form viscoelastic films capable of opposing dilation of the air–tear interface. The impact of temperature on the meibum surface properties is discussed in terms of its possible effect on the normal structure of the film. Y1 - 2014 SN - 1744-683X SS - 1744-683X U6 - https://doi.org/10.1039/C4SM00758A DO - https://doi.org/10.1039/C4SM00758A VL - 10 IS - 30 SP - 5579 EP - 5588 S1 - 12 PB - Royal Society of Chemistry CY - London ER -