title: Sebum/Meibum Surface Film Interactions and Phase Transitional Differences.
abstract: Sebum may contribute to the composition of the tear film lipid layer naturally or as a contaminant artifact from collection. The aims of this study were to determine: if sebum changes the rheology of meibum surface films; if the resonance near 5.2 ppm in the 1H-NMR spectra of sebum is due to squalene (SQ); and if sebum or SQ, a major component of sebum, interacts with human meibum.
  
  
  
  Human meibum was collected from the lid margin with a platinum spatula. Human sebum was collected using lipid absorbent tape. Langmuir trough technology was used to measure the rheology of surface films. Infrared spectroscopy was used to measure lipid conformation and phase transitions. We used 1H-NMR to measure composition and confirm the primary structure of SQ.
  
  
  
  The NMR resonance near 5.2 ppm in the spectra of human sebum was from SQ which composed 28 mole percent of sebum. Both sebum and SQ lowered the lipid order of meibum. Sebum expanded meibum films at lower concentrations and condensed meibum films at higher concentrations. Sebum caused meibum to be more stable at higher pressures (greater maximum surface pressure).
  
  
  
  Physiological levels of sebum would be expected to expand or fluidize meibum making it spread better and be more surface active (qualities beneficial for tear film stability). Sebum would also be expected to stabilize the tear film lipid layer, which may allow it to withstand the high shear pressure of a blink.
authors.affiliation: School of Medicine Western Sydney University, Penrith, New South Wales, Australia.
authors.forename: Poonam
authors.initials: P
authors.lastname: Mudgil
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States.
authors.forename: Douglas
authors.initials: D
authors.lastname: Borchman
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States.
authors.forename: Dylan
authors.initials: D
authors.lastname: Gerlach
authors.affiliation: Department of Chemistry, University of Louisville, Louisville, Kentucky, United States.
authors.forename: Marta C
authors.initials: MC
authors.lastname: Yappert
mesh_terms: D002648:Child; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008537:Meibomian Glands / Q000737:chemistry*; D008875:Middle Aged; D044367:Phase Transition; D012629:Sebum / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D013666:Tears / Q000737:chemistry*