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Yuchen Huo, Scott S. Perry, Howard A. Ketelson; Surface versus Bulk Absorption of a Diblock Copolymer on/in Silicone Hydrogels. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6103.
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© ARVO (1962-2015); The Authors (2016-present)
The interaction between ethylene oxide-block-butylene oxide (EOBO) copolymer and the surfaces of four silicone hydrogel (SH) contact lenses PureVision® (PV), O2OPTIX® (O2), ACUVUE® Oasys® (AO), and Biofinity® (BF) was investigated using angle-resolved X-ray photoelectron spectroscopy (AR-XPS) following treatment in test solutions containing various concentrations of EOBO. The nature of this interaction was further understood by quantifying the amount of eluted EOBO from each lens following the same treatment using ultra performance liquid chromatography (UPLC).
Lenses were treated with solutions containing various concentrations of EOBO. For a given lens type and a specific concentration level, identical paired samples were prepared. The first sample was subjected to an elution study involving UPLC. The second sample, analyzed using XPS, was prepared through a vacuum drying procedure, in which the hydrogel is taken from a fully hydrated state directly to an ultraclean, ultrahigh vacuum environment. Upon changing the angle between the sample and the XPS analyzer, chemical compositions corresponding to uppermost 10 nm of the surface were probed for each sample.
The elution study revealed large disparity in the amount of EOBO uptake by different samples following each solution treatment. For samples subjected to the most concentrated solution treatment, the amount of EOBO recovered (in μg) from the lenses was ranked as the following, from the highest to the lowest, PV (151.77), BF (140.24), AO (77.96), and O2 (7.21). The XPS results, however, suggested that the amount of EOBO retained on the surface of the lenses demonstrated a largely different trend. For example, AO and BF displayed trivial amount of signal at binding energy characteristic to the EO blocks, whereas O2 and PV showed clear EO signature as a result of being present on the surface.
The disparity between the elution and XPS results highlights the difference in the interaction mechanism of the EOBO copolymer with different lenses. For lenses such as O2OPTIX®, this interaction is predominantly bound to the surface; for ACUVUE® OASYS®, however, EOBO was preferentially absorbed by the bulk.
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