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Saman Mohammadi, Maud Gorbet; Design and Development of an In Vitro Tear Replenishment System. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6109.
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© ARVO (1962-2015); The Authors (2016-present)
When testing contact lens biocompatibility, an important missing element with in vitro models of the cornea is the constant hydration of the contact lens and exchange of tear fluid that occurs in the eye. The purpose of this project was to design a novel physiologically realistic microfluidic device to mimic tear replenishment in the human eye through spraying, at physiological rates, artificial tear fluid onto the surface of the contact lens on a curved in vitro cornea model.
The microfluidics system provides a pressurized artificial tear fluid supply line controlled through a series of isolation valves and can deliver the desired amount of artificial tear fluid on the surface of the in vitro model. A micro-pump was used to pump the artificial tear fluid through Teflon (TM) tubing. Six-well inserts were curved using a stainless steel die designed to mimic the curvature and dimension of the cornea. The curved inserts with or without human corneal epithelial cells (HCEC) were transferred into the device in a sterilized environment. The excess tear fluid was pumped out from each well into a waste container. The entire device was placed in a cell incubator and tested for up to 12 hours.
The experiments on contact lenses in the absence of cells showed the device can keep the contact lens hydrated over any period of time while maintaining lens exposure to air in between tear fluid delivery, mimicking in vitro tear break-up over a contact lens. The device allowed enough air exchange within a 5% CO2 regulated incubator to maintain medium pH levels within physiological range. MTT viability studies on a curved stratified culture of immortalized corneal epithelial cells showed no significant change in cell viability with lotrafilcon A lenses. Experiments using the tear replenishment system on the in vitro model without a contact lens, showed slightly lower cell viability in the superficial layer but no significant change in overall cell viability compared to controls where no tear replenishment was applied.
Our results proved this physiologically realistic modeling of tear replenishment system can provide artificial tear fluid to a lens on a curved surface with or without a multilayer of HCEC, at flow rates and frequency similar to the human eye. This device allows mimicking in vivo conditions more closely and will contribute to a better understanding of corneal cell-lens interactions in vitro.
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