Surface properties and exponential stress relaxations of mammalian meibum films.
The surface properties of meibomian secretion (MGS), the major constituent of the tear film (TF) lipid layer, are of key importance for TF stability. The interfacial properties of canine, cMGS, and feline, fMGS, meibum films were studied using a Langmuir surface balance. These species were selected because they have blinking frequency and TF stability similar to those of humans. The sample's performance during dynamic area changes was evaluated by surface pressure (π)-area (A) isocycles and the layer structure was monitored with Brewster angle microscopy. The films' dilatational rheology was probed via the stress-relaxation technique. The animal MGS showed similar behavior both between each other and with human MGS (studied previously). They form reversible, non-collapsible, multilayer thick films. The relaxations of canine, feline, and human MGS films were well described by double exponential decay reflecting the presence of two processes: (1) fast elastic process, with characteristic time τ < 10 s and (2) slow viscous process, with τ > 100 s-emphasizing the meibum layers viscoelasticity. The temperature decrease from 35 to 25 °C resulted in decreased thickness and lateral expansion of all MGS layers accompanied with increase of the π/A hysteresis and of the elastic process contribution to π relaxation transients. Thus, MGS films of mammals with similar blinking frequency and TF stability have similar surface properties and stress relaxations unaltered by the interspecies MGS compositional variations. Such knowledge may impact the selection of animal mimics of human MGS and on a better understanding of lipid classes' impact on meibum functionality.
Department of Cytology, Histology and Embryology, Faculty of Biology, St. Kliment Ohridski University of Sofia, Sofia, Bulgaria.
Petar
P
Eftimov
Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Norihiko
N
Yokoi
R. Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Vesselin
V
Tonchev
Department of Optics and Spectroscopy, Faculty of Physics, St. Kliment Ohridski University of Sofia, Sofia, Bulgaria.
Yana
Y
Nencheva
Department of Optics and Spectroscopy, Faculty of Physics, St. Kliment Ohridski University of Sofia, Sofia, Bulgaria. ggeorg@phys.uni-sofia.bg.
Georgi As
GA
Georgiev
D000818:Animals; D002415:Cats; D004285:Dogs; D004548:Elasticity; D005136:Eye Proteins / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008537:Meibomian Glands / Q000737:chemistry* / Q000378:metabolism; D011312:Pressure; D012212:Rheology; D013045:Species Specificity; D013314:Stress, Mechanical; D013666:Tears / Q000737:chemistry*; D014783:Viscosity
D005136:Eye Proteins; D008055:Lipids
Canine and feline meibum; Dilatational rheology; Dry eye syndrome; Langmuir surface balance; Stress-relaxation