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Mohinder M Merchea, Katarzyna A Wygladacz, Daniel Hook; Comparative Surface Smoothness Durability of a Novel Silicone Hydrogel Material. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6063.
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© ARVO (1962-2015); The Authors (2016-present)
Surface durability of a novel SiHy material was compared to commercially available contact lens materials. Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) were used to evaluate the morphology, roughness, and atomic composition for a) new and b) after 15 or 30 rub/rinse cycles for samfilcon A, senofilcon A, comfilcon A, and lotrafilcon B contact lenses.
Lens wear was simulated with rub/rinse cycles (30 cycles for samfilcon A, comfilcon A, and lotrafilcon B; 15 cycles for senofilcon A) with renu Fresh Multipurpose Solution. The morphology and surface roughness for new and rub/rinsed lenses were evaluated by AFM (tapping in air). Elemental compositions of all examined new and rub/rinsed lenses were evaluated in dry state by XPS.
AFM and XPS showed surface durability of samfilcon A with mean roughness of RMS= 2.6±0.5nm that was not affected by simulated wear (RMS= 3.0±1.0nm). Carbon, oxygen, nitrogen, and silicon detected on new samfilcon A (C1s = 68.5±1.1%, O1s = 17.4±0.8%, N1s = 4.4±0.5%, Si2p = 9.8±0.6%) and the elemental composition was unchanged after rub/rinse (C1s= 68.4±0.8%, O1s= 17.7±0.7%, N1s= 4.2±0.4%, Si2p= 9.8±0.5%). Surface roughness increased slightly for new senofilcon A lenses after rub/rinse cycles, RMS= 2.3±0.3nm and RMS= 4.3±1.6nm respectively. Randomly distributed rough and tall domains (up to 500nm) were detected on the surface of new comfilcon A lenses, which left pockets on the lens surface after rub/rinse. Differences in the carbon and nitrogen surface chemistry between new and rub/rinsed lenses were also found by XPS. The plasma coated lotrafilcon B contact lenses were the most altered by the 30 cycles of rub/rinse. The plasma coating showed numerous cracks on the surface, resulting in higher concentration of silicon being detected on rub/rinsed lenses (new lens up to 0.3%, rub/rinsed lens up to 3.3%). RMS value calculated for rub/rinsed lotrafilcon B lenses (RMS= 9.4±5.2nm) was higher compared to the new lenses (RMS= 3.9±2.0nm).
samfilcon A demonstrated more surface durability among the silicone hydrogels tested. No significant change in surface morphology, roughness, and elemental composition were found after simulating 1 month of wear. lotrafilcon B and comfilcon A were the most impacted materials by the 30 rub/rinse cycles.
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