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Charles W Scales, Sam Popwell, Brian Pall, Bart Johnson, Thomas Maggio; Sticky Business: How Cross-Linker Content Can Have a Profound Effect on the Adhesiveness of Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3094.
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© ARVO (1962-2015); The Authors (2016-present)
The use of cross-linker to modulate the adhesive properties of polymeric materials, including hydrogels, is commonly employed in various industries to modulate material adhesiveness, depending on the application. Typically, materials with lower cross-link densities exhibit higher adhesiveness to surfaces, while materials with higher cross-link densities can exhibit a dis-adhesive effect. Degree of cross-linking also impacts the muco-adhesiveness of a material. Herein, two methodologies were employed to measure the adhesion of silicone hydrogel formulations (within senofilcon contact lens materials) with increasing levels of cross-linker content.
Two measurements of contact lens adhesion were employed to demonstrate differences in adhesion between materials. The first utilized a lap-shear adhesive test, in which two lenses (from the same material) were pressed against one another with a specified normal force Fn across a fixed area. The two lens surfaces were then pulled apart (laterally) and the force required to do so is measured. Alternatively, the amount of time required for a contact lens to be released from its front-curve mold has been used to assess the adhesive strength of silicone hydrogel materials. Ultimately, these methods may be good surrogates for assessing the muco-adhesion of contact lenses.
Four senofilcon-material derived lens formulations with increasing cross-linker contents were tested. Both methodologies showed that senofilcon A (i.e. the lens with the most cross-linker) had the least adhesion (1.6±0.13 kPa, 14.3±1.8 sec), while the experimental, senofilcon-derived lens with the least cross-linker showed the greatest adhesion (2.7±0.22 kPa, 29.0±2.20 sec). Senofilcon-based experimental lenses with intermediate levels of cross-linker showed intermediate levels of adhesion.
Through two different methodologies, the adhesiveness of a series of senofilcon formulations with increasing levels of cross-linker has been measured. Both methods demonstrate that modulating the cross-linker content of a silicone hydrogel impacts its adhesive properties, which may have an impact on lens tribology, a property that has been correlated with contact lens comfort/discomfort.
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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