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Borkar S, Baumli P, Vance T, Sharma E, Shi X, Wu JY, Yao G, Myung D, Fuller GG. Elucidating the roles of electrolytes and hydrogen bonding in the dewetting dynamics of the tear film. Proc Natl Acad Sci U S A 2024; 121:e2407501121. [PMID: 39042697 PMCID: PMC11295001 DOI: 10.1073/pnas.2407501121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2024] [Accepted: 06/24/2024] [Indexed: 07/25/2024] Open
Abstract
This study explores the impact of electrostatic interactions and hydrogen bonding on tear film stability, a crucial factor for ocular surface health. While mucosal and meibomian layers have been extensively studied, the role of electrolytes in the aqueous phase remains unclear. Dry eye syndrome, characterized by insufficient tear quantity or quality, is associated with hyperosmolality, making electrolyte composition an important factor that might impact tear stability. Using a model buffer solution on a silica glass dome, we simulated physiologically relevant tear film conditions. Sodium chloride alone induced premature dewetting through salt crystal nucleation. In contrast, trace amounts of solutes with hydroxyl groups (sodium phosphate dibasic, potassium phosphate monobasic, and glucose) exhibited intriguing phenomena: quasi-stable films, solutal Marangoni-driven fluid influx increasing film thickness, and viscous fingering due to Saffman-Taylor instability. These observations are rationalized by the association of salt solutions with increased surface tension and the propensity of hydroxyl-group-containing solutes to engage in significant hydrogen bonding, altering local viscosity. This creates a viscosity contrast between the bulk buffer solution and the film region. Moreover, these solutes shield the glass dome, counteracting sodium chloride crystallization. These insights not only advance our understanding of tear film mechanics but also pave the way for predictive diagnostics in dry eye syndrome, offering a robust platform for personalized medical interventions based on individual tear film composition.
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Affiliation(s)
- Suraj Borkar
- Department of Chemical Engineering, Stanford University, Stanford, CA94305
| | - Philipp Baumli
- Alcon Research, Limited Liability Company, Fort Worth, TX76134
| | - Travis Vance
- Department of Chemical Engineering, Stanford University, Stanford, CA94305
| | - Ekta Sharma
- Department of Chemical Engineering, Stanford University, Stanford, CA94305
| | - Xinfeng Shi
- Alcon Research, Limited Liability Company, Fort Worth, TX76134
| | - James Y. Wu
- Alcon Research, Limited Liability Company, Fort Worth, TX76134
| | - George Yao
- Alcon Research, Limited Liability Company, Fort Worth, TX76134
| | - David Myung
- Department of Chemical Engineering, Stanford University, Stanford, CA94305
- Spencer Center for Vision Research, Byers Eye Institute, Department of Ophthalmology, Stanford University School of Medicine, Palo Alto, CA94303
| | - Gerald G. Fuller
- Department of Chemical Engineering, Stanford University, Stanford, CA94305
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Baumli P, Liu C, Bekčić A, Fuller GG. The Role of Membrane-Tethered Mucins in Axial Epithelial Adhesion in Controlled Normal Stress Environments. Adv Biol (Weinh) 2023; 7:e2300043. [PMID: 37271859 DOI: 10.1002/adbi.202300043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 05/08/2023] [Indexed: 06/06/2023]
Abstract
The collective adhesive behavior of epithelial cell layers mediated by complex macromolecular fluid environments plays a vital role in many biological processes. Mucins, a family of highly glycosylated proteins, are known to lubricate cell-on-cell contacts in the shear direction. However, the role of mucins mediating axial epithelial adhesion in the direction perpendicular to the plane of the cell sheet has received less attention. This article subjects cell-on-cell layers of live ocular epithelia that express mucins on their apical surfaces to compression/decompression cycles and tensile loading using a customized instrument. In addition to providing compressive moduli of native cell-on-cell layers, it is found that the mucin layer between the epithelia acts as a soft cushion between the epithelial cell layers. Decompression experiments reveal mucin layers act as soft, nonlinear springs in the axial direction. The cell-on-cell layers withstand decompression before fracturing by a cohesive failure within the mucin layer. When mucin deficiency is induced via a protease treatment, it is found that the axial adhesion between the cell layers is increased. The findings which correlate changes in biological factors with changes in mechanical properties might be of interest to challenges in ophthalmology, vision care, and mucus research.
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Affiliation(s)
- Philipp Baumli
- Department of Chemical Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Chunzi Liu
- Department of Chemical Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Aleksandar Bekčić
- Department of Chemical Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Gerald G Fuller
- Department of Chemical Engineering, Stanford University, Stanford, CA, 94305, USA
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Cui KW, Myung DJ, Fuller GG. Tear Film Stability as a Function of Tunable Mucin Concentration Attached to Supported Lipid Bilayers. J Phys Chem B 2022; 126:6338-6344. [PMID: 35972346 PMCID: PMC9421887 DOI: 10.1021/acs.jpcb.2c04154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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In this work, we describe the development of a tunable,
acellular in vitro model of the mucin layer of the
human tear film.
First, supported lipid bilayers (SLBs) comprised of the phospholipid
DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) and
biotinyl cap PE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(cap
biotinyl)) are created on the surface of a glass dome with radius
of curvature comparable to the human eye. Next, biotinylated bovine
submaxillary mucins (BSM) are tethered onto the SLB using streptavidin
protein. The mucin presentation can be tuned by altering the concentration
of biotinylated BSM, which we confirm using fluorescence microscopy.
Due to the optically smooth surface that results, this model is compatible
with interferometry for monitoring film thickness. Below a certain
level of mucin coverage, we observe short model tear film breakup
times, mimicking a deficiency in membrane-associated mucins. In contrast,
the breakup time is significantly delayed for SLBs with high mucin
coverage. Because no differences in mobility or wettability were observed,
we hypothesize that higher mucin coverage provides a thicker hydrated
layer that can protect against external disturbances to thin film
stability. This advance paves the way for a more physiological, interferometry-based in vitro model for investigating tear film breakup.
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Affiliation(s)
- Kiara W Cui
- Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - David J Myung
- Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States.,Byers Eye Institute at the School of Medicine, Stanford, California 94305, United States
| | - Gerald G Fuller
- Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States
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Madl AC, Liu C, Cirera-Salinas D, Fuller GG, Myung D. A Mucin-Deficient Ocular Surface Mimetic Platform for Interrogating Drug Effects on Biolubrication, Antiadhesion Properties, and Barrier Functionality. ACS APPLIED MATERIALS & INTERFACES 2022; 14:18016-18030. [PMID: 35416028 PMCID: PMC9052192 DOI: 10.1021/acsami.1c22280] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 03/03/2022] [Indexed: 05/14/2023]
Abstract
Dry eye disease (DED) affects more than 100 million people worldwide, causing significant patient discomfort and imposing a multi-billion-dollar burden on global health care systems. In DED patients, the natural biolubrication process that facilitates pain-free blinking goes awry due to an imbalance of lipids, aqueous medium, and mucins in the tear film, resulting in ocular surface damage. Identifying strategies to reduce adhesion and shear stresses between the ocular surface and the conjunctival cells lining the inside of the eyelid during blink cycles is a promising approach to improve the signs and symptoms of DED. However, current preclinical models for screening ocular lubricants rely on scarce, heterogeneous tissue samples or model substrates that do not capture the complex biochemical and biophysical cues present at the ocular surface. To recapitulate the hierarchical architecture and phenotype of the ocular interface for preclinical drug screening, we developed an in vitro mucin-deficient DED model platform that mimics the complexity of the ocular interface and investigated its utility in biolubrication, antiadhesion, and barrier protection studies using recombinant human lubricin, a promising investigational therapy for DED. The biomimetic platform recapitulated the pathological changes in biolubrication, adhesion, and barrier functionality often observed in mucin-deficient DED patients and demonstrated that recombinant human lubricin can reverse the damage induced by mucin loss in a dose- and conformation-dependent manner. Taken together, these results highlight the potential of the platform─and recombinant human lubricin─in advancing the standard of care for mucin-deficient DED patients.
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Affiliation(s)
- Amy C. Madl
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - Chunzi Liu
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - Daniel Cirera-Salinas
- Biologics
Analytical Research and Development, Novartis
Pharma AG, Basel 4002, Switzerland
| | - Gerald G. Fuller
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - David Myung
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
- Byers
Eye Institute, Stanford University School
of Medicine, Palo Alto, California 94303, United States
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