Surface Gel Layers Reduce Shear Stress and Damage of Corneal Epithelial Cells

Abstract

Soft contact lenses are medical devices made from aqueous polymeric gels that are worn on the eye to correct refractive errors. These devices interrupt the natural contact pairing between the cornea and the eyelid and create two interfaces comprised of a synthetic material and the epithelia-contact lens surfaces versus (1) the cornea and (2) the eyelid conjunctiva. The cellular responses to friction and shear stress are thought to contribute to contact lens discomfort. This study performs direct contact shear experiments using in vitro biotribological experiments using a microtribometer equipped with a hydrogel membrane probe. Sections from commercial contact lenses are held in place on a spherically capped membrane probe during reciprocating sliding experiments against confluent monolayers of living human telomerase-immortalized corneal epithelial cells (hTCEpi). The contact lenses were loaded against the cell monolayers to physiological contact pressures between 400 and 1300 Pa under an applied load of 200 µN. The reciprocating distance was 3 mm, at a sliding speed of 1 mm/s, and the maximum duration of sliding was 1000 cycles. Five commercially available lenses (somofilcon A, stenfilcon A, etafilcon A, verofilcon A, and delefilcon A) were used to evaluate the cell layer responses to aqueous gels of differing composition, surface modulus, and lubricity. Cell damage was measured via propidium iodide staining and in situ fluorescence microscopy. The shear stresses varied from 16 ± 2 Pa (delefilcon A and verofilcon A) to 86 ± 12 Pa (stenfilcon A), and cell damage increased with increasing shear stress and increasing sliding duration. The two lens materials that have high water content surface gel layers (delefilcon A and verofilcon A) showed distinctly lower measures of cell damage as compared to the other lenses. Surface gel layers with a large polymer mesh size and high water content are shown to be an effective approach to lower the contact pressure, lower the friction coefficient, and thereby lower the shear stress and cell damage.

Controlling the Friction of Gels by Regulating Interfacial Oxygen During Polymerization

“…Moreover, creating a lens with a slippery front side and comparatively higher friction on the reverse side could, for example, help keeping the lens position during a blink of the eye. Since the method enables surfaces to be created with small differences in friction, the friction values on both sides of the lens could be kept low enough to avoid applying excessive shear to the corneal epithelium [35,36].…”

Evaluation of the Lubricating Effect of Hyaluronic Acid on Contact Lenses Using a Pendulum-Type Friction Tester Under Mimicking Physiological Conditions

“…Several studies have measured the friction of CLs. 6,7,16,17 We recently developed a pendulum-type friction tester for CLs, which is a modification of a friction tester for artificial joints. 18 In the current study, we measured the friction of a commercially available silicone hydrogel SCL using a range of HA concentrations to evaluate the effect of its lubrication property using the newly modified pendulum-type friction tester.…”

Nanoscaled Morphology and Mechanical Properties of a Biomimetic Polymer Surface on a Silicone Hydrogel Contact Lens

“…40 However, the coefficient of friction between the conventional silicone hydrogel contact lens and the cornea is reported to be in the range from 0.04 to 0.08. 41 As the coefficient of friction of human corneal tissue is reported to be 0.015 ± 0.09 in a tear-like fluid in phosphatebuffered saline, 42 it is clear that the PMPC-modified silicone hydrogel contact lens possesses a sufficiently low coefficient of friction against the cornea tissue.…”

“…The lubrication mechanism on the PMPC-modified surface has also been analyzed, and it has been shown that the hydrated PMPC layer provides fluid lubrication. , The coefficient of friction when sliding between the hydrogel and the human cornea is 0.03 . However, the coefficient of friction between the conventional silicone hydrogel contact lens and the cornea is reported to be in the range from 0.04 to 0.08 . As the coefficient of friction of human corneal tissue is reported to be 0.015 ± 0.09 in a tear-like fluid in phosphate-buffered saline, it is clear that the PMPC-modified silicone hydrogel contact lens possesses a sufficiently low coefficient of friction against the cornea tissue.…”