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Andrew Hoteling, William Nichols, Harmon Patricia, Conlon Shawn, Daniel Hook, Ivan Nuñez, Joseph Hoff, Orlando Cabarcos; Characterization of Bulk PVP Content of samfilcon A Silicone Hydrogel Lenses. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6095.
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© ARVO (1962-2015); The Authors (2016-present)
A novel silicone hydrogel lens material, samfilcon A was designed to polymerize in two time resolved phases with the methacrylate based monomers polymerizing first followed by NVP conversion to high molecular weight PVP. Several studies were conducted using a range of analytical techniques to characterize and quantitate the PVP content of samfilcon A.
The reaction of samfilcon A was monitored using Photo Differential Scanning Calorimetry (Photo-DSC), Gas Chromatography with a Flame Ionization Detector (GC-FID), and high resolution/accurate mass (HR/AM) Liquid Chromatography-Mass Spectrometry (LC-MS). GC-FID and LC-MS provided time dependent consumption of individual monomers, as well as formation of PVP polymer. Gel Permeation Chromatography (GPC) was used to measure the molecular weight distribution of iso-propanol (IPA) lens extracts. FTIR, NMR, and ASAP high resolution mass spectrometry were used to characterize fractions collected from GPC to characterize the high molecular weight polymer. PVP concentration of the IPA lens extracts was measured using a gas-phase pyrolysis MS methodology. PVP content of bulk lens material was measured using an off-line pyrolysis methodology.
GPC analysis of IPA extracts of samfilcon A and senofilcon A showed that a polymer on the order of >100KDa was extracted out of each lens material. Characterization of GPC fractions with FTIR, NMR, and MS showed that the high MW polymer was consistent with PVP. Quantitation of PVP in bulk lens material showed that the PVP content of samfilcon A was > 4X that of senofilcon A. Quantitation of PVP in IPA lens extracts of fully processed lenses showed that the PVP extracted out of samfilcon A lenses represented only 10 % of the total PVP in the bulk of the lens. Therefore, the majority of the PVP formed in-situ during lens curing remains in the lens even after the harsh IPA extraction conditions.
The data presented supports the proposed dual phase polymerization in the curing of samfilcon A lenses, which results in the formation of high molecular weight PVP that is incorporated in the lens matrix.
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