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Juan Manuel Urueña, Angela A Pitenis, Tristan Hormel, Tapamoy Bhattacharjee, Samantha L Marshall, Samuel M Hart, Kyle D Schulze, Thomas E Angelini, W Gregory Sawyer; In Vitro Hydrogel Friction Experiments on Corneal Cells. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3095.
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© ARVO (1962-2015); The Authors (2016-present)
The tear film and health of the epithelia in the eye are important for both lubricity and comfort. The extent of tear film disruption due to contact lens use is difficult to measure in vivo, and determining the shear stresses imparted by the lens represents an even greater challenge. This study examines the effects of shear stress on human corneal epithelial cells (hTCEpi) by sliding a hydrogel probe against a hTCEpi monolayer for 24 hours while monitoring mucin production and cell viability with in situ fluorescence microscopy.
Cells were incubated in a culture dish with Keratinocyte Growth Media (KGM-Gold™) growth media and grown to confluence. Cells bodies were stained with CellTrace™ Calcein Red-Orange. Mucins produced by hTCEpi cells were dyed with Concanavalin A Alexa Fluor® 488 Conjugate. A hydrogel spherical shell probe (7.5 wt.% acrylamide, 0.3 wt.% bisacrylamide) was loaded against the cells to 200 µN and achieved average contact pressures below 1 kPa, which were maintained over 10,000 reciprocating cycles (3 mm stroke length, 1 mm/s sliding velocity). Tribological experiments were performed at 37±0.2°C, 5% CO2, and 80% RH. Fluorescence microscopy monitored cell viability and mucin production in situ.
Over 10,000 reciprocating cycles, the normal force (Fn) was Fn = 218.6±20.3 µN, the friction force (Ff) was Ff = 12.8±3.2 µN, and the friction coefficient (Ff/Fn) was µ = 0.058 ±0.008. Average contact pressure was measured to be approximately 1 kPa and the frictional shear stress was therefore approximately 60 Pa. A live/dead assay performed at the conclusion of the experiment (ReadyProbes® Cell Viability Imaging Kit [Blue/Green]) revealed that less than 0.2% of hTCEpi cells died during sliding. The intensity of fluorescently tagged mucin increased over time during sliding.
A monolayer of hTCEpi cells was cultured, fluorescently tagged, and subjected to 10,000 reciprocating cycles at physiologically-relevant conditions. Cell damage after 10,000 cycles was not significant (0.2%) and mucin production continued to increase during testing. These results demonstrate that corneal epithelial cells can endure prolonged frictional interactions with hydrogels if they are subject to sufficiently low shear stress throughout this process. This principle may serve as a guideline for new contact lens design.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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