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Ananth V Iyer, Aziza Sahin; Polymerizable silicone compatibilizers for silicone hydrogels. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6096.
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© ARVO (1962-2015); The Authors (2016-present)
Silicone hydrogels are important contact lens materials for promoting corneal health by enabling higher oxygen permeability. They, however, suffer from the drawback of having higher lipid deposition than conventional hydrogels which can negatively affect clarity and end of day comfort. A polymerizable zwitterionic silicone (ZiSi) monomer was incorporated into silicone hydrogel formulations to improve wettability and minimize the hydrophobic domains with the intent of reducing lipid adsorption. The effect of this zwitterionic silicone monomer in silicone hydrogel formulations on clarity, oxygen permeability, equilibrium water content and size of hydrophobic domains was investigated.
Silicone hydrogels were prepared using a formulation containing 2-20 wt% zwitterionic silicone monomer (ZiSi), 3-[tris(trimethylsiloxy)silyl]propyl methacrylate (TRIS), and N,N-dimethylacrylamide (DMA) as monomers with 1.0 wt% crosslinker (EGDMA) and 0.5 wt% thermal initiator azobisisobutyronitrile (AIBN) followed by curing at 90°C for 1h. The oxygen permeability of the silicone hydrogel films were measured on a MOCON unit using a modified Coulometric method as referenced in ISO 18369-4:2006. Equilibrium water content (EWC) was determined gravimetrically per the standard - ISO 18369-4:2006 Ophthalmic Optics—Contact lenses—Part 4: Physicochemical properties of contact lens materials. Clarity of hydrogel films are reported as a qualitative comparison. Size of hydrophobic domain in hydrated hydrogel films were characterized using a qualitative lipophilic dye test as described in literature (Jacob, J. et al Visualizing hydrophobic domains in silicone hydrogel lenses with Sudan IV. Invest Ophthalmol Vis Sci. 2012;53(7):3473-3480). Relative staining was determined by visual inspection.
Table 1 below lists the Clarity, Dk, and EWC for representative hydrogel films.
Silicone hydrogel films made with zwitterionic silicone monomer have comparable oxygen permeability (Dk) and equilibrium water content (EWC) while maintaining clarity and mechanical stability to control films. The addition of zwitterionic silicone monomer to the silicone hydrogel formulation did not seem to have a detrimental effect on the silicone hydrogel properties, while resisting any significant dye staining by the lipophilic dye used in this study.
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