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N. Ravi, H. Aliyar, P. Hamilton; Novel Copolymer Compositions with High Refractive Index and Low Modulus as Lens Substitute Materials . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1727.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Age–related changes in the viscoelasticity of the lens have been implicated to be one of the primary causes of lenticular presbyopia. In our effort to develop materials for validation of mechanical properties, we previously reported a hydrogel material with reversible disulfide bonds (ARVO #243, 2003). These hydrogel materials exhibited moduli of 0.27 Kpa to 1.16 KPa covering the range of the natural lens. Usually the refractive index scales linearly with polymer composition while the modulus scales exponentially (2.4–3.0). Thus in an ideal hydrogel, it is almost impossible to have a material with high refractive index and low modulus. In this abstract, we report a novel copolymer formulation, in which non–ideal network is formed by increasing the network defects. Methods: Acrylamide (AAm) and bisacryloylcystamine (BAC) (4 acrylic mole %) were copolymerized to obtain hydrogels containing disulfide (–SS–) bonds. The reduction of –SS– bonds followed by precipitation of the copolymer solution in methanol yielded water soluble copolymers containing thiol (–SH) groups. The non–ideal copolymer network was formed by oxidation of thiol groups at varying concentrations of the copolymer during the re–gelling stage. The mechanical properties of hydrogels (in cyclindrical shape) were determined by compression between parallel plates using a dynamic mechanical analyzer (DMA 7e, Perkin Elmer, Norwalk, Connecticut, USA). The refractive index of the composite materials were determined using Abbe refractometer (ATAGO’s Abbe refractometer 1T/4T, Kirkland, WA, USA). Results: We successfully identified copolymeric formulations in which network defects could be modulated. This has enabled us to develop materials whose refractive index increased with network defects while the modulus actually decreased. The refractive index ranged from 1.346 to 1.422 and the moduli from 0.418 to 0.606 KPa as shown in the graph below. View OriginalDownload SlideView OriginalDownload Slide Conclusions: The non–ideal copolymeric network exhibited low modulus with high refractive index values which have potential for use as lens substitute materials.
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