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Alison C. Dunn, Juan M. Uruena, Enrique Puig, Victor L. Perez, Howard A. Ketelson, W G. Sawyer; In Vivo Frictional Measurements of Lubricity on Murine Corneas. Invest. Ophthalmol. Vis. Sci. 2012;53(14):553.
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© ARVO (1962-2015); The Authors (2016-present)
To quantify the natural lubricity existing on healthy corneas by quickly performing in vivo frictional experiments on the corneas of healthy, but anesthetized, mice.
The mouse used in this study was a C57 black 6 that was anesthetized using isoflurane 2-5% mixed with air. The mouse was immobilized in a three-point stereotactic restrainer that provided continuous inhalational anesthetic during all friction testing and imaging. Post-testing, the mouse was removed from anesthesia and observed until normal activity resumed. A portable, custom reciprocating micro-tribometer with nano-positioning and 3-axis control was designed and constructed in order to apply the microscale normal forces and measure the friction force response. Motion was controlled to nanoscale positioning at sliding speeds of 250 um/s. A smooth 0.5 mm radius sphere was fixed to the force sensing flexures, and experiments were performed by varying the loads over a range of 3-5 mN. Contact pressures were computed to be between 4-5 kPa. Before and after friction testing, the mouse left eye (OS) was rinsed for 2 minutes in a fluorescein saline solution. Images were assessed for any scratching or punctate damage.
The friction coefficient in both the forward and reverse sliding directions was calculated by taking the ratio of the friction force to the applied normal force. In order to get the overall friction coefficient, the absolute values of the friction coefficient in both sliding directions were averaged. The friction coefficient on these corneas was mu=0.06, with an uncertainty below mu=0.01. Further, no detectable damage of the corneas was observed.
A portable micro-tribometer was used to run friction measurements on a living mouse eye, finding a friction coefficient of mu=0.06 under an estimated contact pressure of 4.3 kPa. This measurement produced no discernable damage to the mouse cornea as determined by stereoscopic imaging. In vivo friction measurements could provide insight as to the mechanical interactions of blinking, especially in diseased or damaged corneal states.
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