The interfacial viscoelastic properties and structures of human and animal Meibomian lipids

Leiske, Danielle L.; Raju, Shiwani R.; Ketelson, Howard A.; Millar, Thomas J.; Fuller, Gerald G.

doi:10.1016/j.exer.2010.02.004

Cited by 60 publications

(58 citation statements)

References 28 publications

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“…Understanding the mechanics of viscoelastic interfaces is critical to a number of applications, including the use of food additives and stabilizers [2], medicine, physiology and pharmaceuticals [50,51]. Although static surface tension measurements are sufficient to characterize the interfacial properties of surfactant-free solutions with clean interfaces, accurate descriptions of solutions or dispersions containing surface active molecules with dynamically evolving interfaces necessitate correct accounting of the mass and momentum transport processes occurring at the interface [52].…”

Section: (B) Interfacial Dynamicsmentioning

confidence: 99%

Power-law rheology in the bulk and at the interface: quasi-properties and fractional constitutive equations

2013

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Consumer products, such as foods, contain numerous polymeric and particulate additives that play critical roles in maintaining their stability, quality and function. The resulting materials exhibit complex bulk and interfacial rheological responses, and often display a distinctive power-law response under standard rheometric deformations. These power laws are not conveniently described using conventional rheological models, without the introduction of a large number of relaxation modes. We present a constitutive framework using fractional derivatives to model the power-law responses often observed experimentally. We first revisit the concept of quasiproperties and their connection to the fractional Maxwell model (FMM). Using Scott-Blair's original data, we demonstrate the ability of the FMM to capture the power-law response of 'highly anomalous' materials. We extend the FMM to describe the viscoelastic interfaces formed by bovine serum albumin and solutions of a common food stabilizer, Acacia gum. Fractional calculus allows us to model and compactly describe the measured frequency response of these interfaces in terms of their quasiproperties. Finally, we demonstrate the predictive ability of the FMM to quantitatively capture the behaviour of complex viscoelastic interfaces by combining the measured quasi-properties with the equation of motion for a complex fluid interface to describe the damped inertio-elastic oscillations that are observed experimentally.

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Section: (B) Interfacial Dynamicsmentioning

confidence: 99%

Power-law rheology in the bulk and at the interface: quasi-properties and fractional constitutive equations

2013

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“…In Fig. 3, we report examples of dynamic surface pressure as a function of film-thickness curves called isocycles [9][10][11]. As seen from this figure, a maximum surface pressure of 50 ± 2 mN/m was subject-independent; however, the shape of iso-cycles varied between human tear-lipid samples collected from two individuals.…”

Section: Resultsmentioning

confidence: 94%

“…The interactions between tear-lipid films and tearaqueous constituents (e.g., natural tear proteins, or ingredients added in topical ophthalmic medications or lens care solutions) are important and may influence overall tear-film stability [8][9][10]. It has been established that the tear-lipid layer plays a crucial role in tear-film stabilization, and surface physical properties such as interfacial elasticity and viscosity of tear-lipid films are the key factors determining thin-film stability [11][12][13]. Tear-film instability and ultimately film ruptures can cause ocular surface irritation or inflammation and dry eye symptoms.…”

Section: Introductionmentioning

confidence: 99%

Lens-care-solution-induced alterations in dynamic interfacial properties of human tear-lipid films

Svitova

Lin

2014

Contact Lens and Anterior Eye

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a b s t r a c tPurpose: To evaluate the influence of lens care solutions (LCS) on interfacial dynamics and rheological properties of human tear-lipid films. Methods: Tear lipids were extracted from Schirmer strips collected from 6 healthy subjects. Sessile bubble tensiometry was used to study interfacial properties at 22• C. Lipids were deposited on an air bubble immersed into electrolytes solution to form 90 ± 20 nm films. Lipid films were subjected to expansioncompression cycles for dynamic interfacial properties and to step-strain relaxations for assessments of rheological properties.were injected into optical chamber and equilibrated for 2 h without or with lipid films. Dynamic interfacial properties of films were measured. Then electrolyte solution was pumped through chamber and properties of films were re-evaluated. Results: Equilibrium surface tension (EST), elasticity modulus (E), and relaxation times ( ) of tear lipids were 22 ± 2.1 mN/m, 10.7-14.8 mN/m, and 80-150 s, respectively. EST for LCS was 45.3 ± 0.8 for CC, 40.3 ± 0.8 for BT, 33.4 ± 1.0 for PM, and 30.1 ± 0.8 mN/m for RL. E for LCS varied within 0.5-6.7 mN/m, and varied from 49 to 68 ± 5 s. For mixed lipids + LCS films, EST remained unchanged whereas E and were reduced for all LCS types. Exposure to PM and RL noticeably altered the shape of lipid-film iso-cycles. These changes persisted after LCS washout. Conclusions: Some components of LCS bind irreversibly to lipid films and make them less viscous and less elastic. These findings suggest the possibility of tear-film destabilization upon LCS exposure.

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“…2). From the in vivo studies using HRCM, 25 it appears that this also is the case in the tears as illustrated by Figure 6 in the study of KingSmith et al 26 Superficial to the surfactant layer is a collecting layer that comprises mainly hydrophobic molecules, but can recruit surfactant molecules if required from the surfactant layer when they are squeezed out. Its role is to bundle up (denature and entrap) any exotic molecules entering the surfactant layer.…”

Section: Discussionmentioning

confidence: 99%

“…Our group and others have measured surface pressures, and correlated these data with composition and appearance of films of meibomian lipids. 2,3,[20][21][22][23][24][25] Recently, a technique has been developed to observe the lipid layer in vivo using a high resolution microscope; the original monochrome camera recently has been replaced with a color camera, so the method will be referred to as a high resolution color microscopy (HRCM). 26 Many of the micrographs of in vivo lipid films have an appearance similar to those seen from micrographs of meibomian lipid films spread in vitro on a Langmuir trough.…”

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confidence: 99%

Analysis of Comparison of Human Meibomian Lipid Films and Mixtures with Cholesteryl Esters In Vitro Films using High Resolution Color Microscopy

Millar

King‐Smith

2012

Invest. Ophthalmol. Vis. Sci.

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PURPOSE. The lipid layer of the tears has been studied in vivo using high resolution color microscopy (HRCM). The purpose of these experiments was to gain further insight into the structure of the lipid layer by applying HRCM to in vitro meibomian lipid films.METHODS. Films of human meibomian lipids, cholesteryl nervonate, cholesteryl palmitate, or their mixtures, were spread on a Langmuir trough. Changes to the films were monitored using HRCM as the films were compressed to different surface pressures. The penetration of albumin into a meibomian lipid film also was studied.RESULTS. Small amounts of meibomian lipids at low pressures formed very thin films estimated to be 5.2 nm thick. Compression caused spots to appear in the films. At higher concentrations, micro lenses were a feature of the film. Cholesteryl nervonate formed a multilayered oil slick that did not change with surface pressure. Cholesteryl palmitate formed a stiff film that collapsed at high compression. Mixtures of cholesteryl nervonate and meibomian lipids showed that they mixed to increase surface pressures above that of the individual components. HRCM also allowed albumin to be seen penetrating the meibomian lipid film.CONCLUSIONS. HRCM combined with in vitro surface pressure measurements using a Langmuir trough is useful for modeling meibomian lipid films. The films often resemble the appearance of the lipid layer of in vivo films. The data indicate that the lipid layer might be modeled best as a duplex film containing an array of liquid crystals. (Invest Ophthalmol Vis Sci. 2012; 53:4710-4719) DOI:10.1167/iovs.12-10022 T he seminal work of Holly and his co-workers 1-6 signalled the beginnings of trying to understand the physical properties of the tear film in relationship to its chemical components. At that time, the lipid layer was perceived as just a blanket preventing evaporation, 7 but Holly began to investigate the role of meibomian lipids in spreading of the tear film across the ocular surface and stabilising the film. This led to a model involving lipids and then a mucin lipid mixture spread from the lid margins across the ocular surface upon eye opening. 2,3 Since this time, to understand further the structure of the lipid layer, a great deal of effort has been placed on determining the composition of meibomian lipids from humans and animals. [8][9][10][11][12][13][14][15][16][17][18][19] The analysis from several groups now suggests a composition of mainly cholesteryl and wax esters (~80%), triglycerides (~3%), and omega hydroxy acyl fatty acids (~5%). [8][9][10][11][12][13][14][15][16][17][18][19] Although the major portion being wax and cholesteryl esters is consistent across the literature, the ratios vary considerably from 13-68% for wax esters and 8-67% for cholesteryl esters. The latest analyses indicate that cholesteryl esters increase with age 18 and wax esters in human meibum estimates are around 40%.19 From their own analysis of meibomian lipid composition, McCulley and Shine proposed a model that described the major lipi...

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The interfacial viscoelastic properties and structures of human and animal Meibomian lipids

Cited by 60 publications

References 28 publications

Power-law rheology in the bulk and at the interface: quasi-properties and fractional constitutive equations

Power-law rheology in the bulk and at the interface: quasi-properties and fractional constitutive equations

Lens-care-solution-induced alterations in dynamic interfacial properties of human tear-lipid films

Analysis of Comparison of Human Meibomian Lipid Films and Mixtures with Cholesteryl Esters In Vitro Films using High Resolution Color Microscopy

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