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John Pruitt, Yongxing Qiu, Sibichen Thekveli, Rick Hart; Surface Characterization of a Water Gradient Silicone Hydrogel Contact Lens (delefilcon A). Invest. Ophthalmol. Vis. Sci. 2012;53(14):6107.
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© ARVO (1962-2015); The Authors (2016-present)
A water gradient silicone hydrogel contact lens recently introduced in Europe provides substantially different properties at the lens surface compared to the lens core. Multiple analytical techniques were utilized to characterize the core, surface, and water gradient properties of DAILIES® TOTAL1® (delefilcon A) contact lenses.
Lenses were cross-sectioned to measure the transition from the core of the lens to the surface. The hydrated cross sections were placed on edge and imaged using atomic force microscopy (AFM). The surface thickness and the local compression modulus were measured along a line from the core to the outer surface. Dried contact lens cross sections were also imaged by both SEM and AFM to compare the dry vs. wet surface thickness to measure the surface water content. Gravimetric water content analysis was conducted on separately prepared samples consisting of only the high water content surface hydrogel material or the core silicone hydrogel material.
A total surface thickness of 5.9 ± 0.8 microns was measured using AFM of hydrated lens cross sections including a transition zone of 1-2 microns and an outer surface layer of 4-5 microns. The surface layer was characterized by a lower compression modulus than the core of the lens with a modulus gradient detectable in the transition zone. Gravimetric analysis of a separately prepared sample of the surface hydrogel material revealed a water content of 84.6% compared to a core water content of 33 ± 2%. The surface thickness of a vacuum dried lens cross section was measured at 1.2 microns, only 20% of the hydrated surface thickness and consistent with an average water content in the surface layer of approximately 80%. SEM images of freeze-dried lens samples revealed a porous surface structure as expected due to the high water content.
Delefilcon A contact lenses are composed of a core silicone hydrogel material consisting of approximately 33% water which transitions to an outer surface layer containing approximately 80% water. The surface is also characterized by a lower compression modulus compared to the core of the lens. This unique water gradient technology resulting in high oxygen transmission with a lubricious surface represents the next generation of contact lenses.
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