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D. L. Leiske, B. Meckes, H. A. Ketelson, G. G. Fuller; Investigation of an Amphiphilic Block Copolymer to Prevent Contact Lens Fouling. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5646.
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© ARVO (1962-2015); The Authors (2016-present)
Silicone hydrogel contact lenses are susceptible to lipid and protein fouling. A need exists to improve prevention and removal of such deposits. The interfacial properties of an amphiphilic block copolymer and representative tear film materials were explored to evaluate the potential of the copolymer in preventing and removing contact lens deposits.
A series of block copolymers were obtained with systematically varied ratios of hydrophobic:hydrophilic block length. An air-water interface was used to model the interface between the tear film and a silicone hydrogel contact lens. The air interface enables the measurement of surface pressure and interfacial rheology in real time. Interactions between the block copolymers and DPPC, cholesterol and lysozyme were investigated.
At 0.5 ppm, the block copolymer with the longest hydrophobic block raised the surface pressure to 35 mN/m under a cholesterol monolayer compared to 22 mN/m at a bare interface and 25 mN/m under DPPC. The surface pressures of the shortest hydrophobic block measured 25 and 14 mN/m under cholesterol and air. This suggests that block copolymer adsorption is enhanced by hydrophobic interactions. The block copolymer was "squeezed out" of DPPC monolayers at high surface pressures as evidenced by the expansion isotherm. After three hours lysozyme adsorbed to a bare interface to a surface pressure of 5 mN/m and formed a strong gel with an interfacial complex viscosity of 1.1 mN-s/m. When the block copolymers were premixed with lysozyme they adsorbed to the interface within seconds and prevented the protein from gelling (interfacial complex viscosity of 0.009 mN-s/m) for up to three hours.
The rapid adsorption of the block copolymer to the interface compared to lysozyme indicates that it would also adsorb quickly to a silicone hydrogel contact lens surface and prevent protein and lipid fouling by steric hindrance. The dramatic absence of interfacial viscoelastic properties of the block copolymer compared to the strong gel formed by lysozyme and tear film lipids exhibit the potential of this material in maintaining surface lubricity and clear vision.
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