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Jessica Rex, Scott Perry, Jessie Lemp, Cecile A Maissa; Concentrations of Silicon at the Surface of Silicone Hydrogel Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6099.
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© ARVO (1962-2015); The Authors (2016-present)
The surface composition and structure of materials are known to directly influence interfacial properties. Furthermore, composition and structure within the outermost atomic layers has been observed to differ from that of the bulk material. To this end, the concentration of the constituent elements in outermost 10.0 nm of the surface of silicone hydrogel (SH) contact lenses was measured using X-ray photoelectron spectroscopy (XPS).
Eleven SH lens types (balafilcon A, lotrafilcon A, lotrafilcon B, senofilcon A, comfilcon A, samfilcon A, delefilcon A, narafilcon A, stenfilcon A, somofilcon A daily disposable (DD) and somofilcon A monthly) were prepared with a 24 hr soak in a phosphate buffer solution before vacuum drying for analysis. Integration of the photoelectron signals from all elements present and normalization by published sensitivity factors allows the calculation of % atomic concentration. By measuring photoelectron intensity as a function of off angle (55-85°), the relative presence and distribution of specific elements within the outermost 10.0 nm is captured.
For all lenses, carbon, oxygen and nitrogen were observed in varying quantities. In addition, fluorine was detected for comfilcon A. The silicon content within the outermost surface region (10.0 nm) of the test lens materials varied substantially: balafilcon A (7.7%), lotrafilcon A (1.2%), lotrafilcon B (1%), senofilcon A (8.7%), comfilcon A (13.4%), samfilcon A (5%), delefilcon A (<1%), narafilcon A (6.7%), stenfilcon A (7.9%), somofilcon A DD & Monthly (8.8%).
Lenses differed most in their surface silicon concentration, with delefilcon A and lotrafilcon A and B exhibiting the lowest silicon contents within the outermost 10.0 nm of the lens surface. Silicon has hydrophobic properties which, when found at the surface, may influence the wettability of the contact lenses and their interaction with the tear film and ocular tissues.
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