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Alysha Spadafora, Myrto Koroyannaki, Heather Sheardown; The Impact of Densely Grafted Phosphorylcholine on Surface Modified Model Silicone Hydrogel Lenses. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3069.
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© ARVO (1962-2015); The Authors (2016-present)
In contact lens wear, oxygen permeability through the lens matrix is important for corneal health. Silicone hydrogel lenses enable increased gas permeability by incorporation of siloxanes. However, the high surface-activity of these groups can impart hydrophobicity to the lens surface, decreasing wettability and increasing bio fouling. This study focuses on the surface modification of silicone hydrogels by incorporation of 2-methacryoyloxyethyl phosphorylcholine (MPC), chosen to provide a bio interface between the lens and ocular surface due to its unique biomimetic structure and anti-fouling properties. This work highlights the potential of a novel densely grafted MPC-based polymer to improve surface characteristics of silicone hydrogels.
Model silicone hydrogels incorporated 2-hydroxyethyl methacrylate (HEMA) and 3-[tris(trimethylsilyloxy)silyl]propyl methacrylate (TRIS) (90:10 wt%). Poly(2(2-bromoisobutyryloxy-ethyl methacrylate)-graft-poly(2-methacryloyloxyethyl phosphorylcholine p(BIBEM)-g-p(MPC), of varying chain lengths was sequentially grafted from the lens surface by surface-initiated atom transfer radical polymerization. Gel Permeation Chromatography and NMR were used to assess MW, chain length, and polydispersity indexes. Surfaces were analyzed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS). Wettability was measured by sessile drop and equilibrium water content (EWC) as well as dehydration were determined gravimetrically.
ATR-FTIR confirmed surface modifications, with MPC modified lenses showing a decreased peak at 850 cm-1 (Si-CH3 group), displaying a potential to mask hydrophobic silicone surface domains. XPS indicated an increase in percentage of expected surface elements. For MPC modified lenses, a substantial decrease in contact angle up to 84.2 % ± 5.8 (p<0.0001) was observed when compared to unmodified lenses, suggesting improved surface wettability. Modified lenses also demonstrated EWC values suitable for overnight wear and a decreased dehydration rate compared to unmodified materials.
MPC modification may improve surface wettability and decrease rate of dehydration compared to unmodified lenses. Future studies will focus on quantitation of adhered characteristic tear film proteins and the effect of varying chain length and grafting density on surface properties.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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