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J.D. Clapper, R.F. Mullins, S.R. Russell, C.A. Guymon; Characterization of Nano–Structured Polymers for Fabricating and Ocular Microvascular Stent . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4080.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Central retinal vein occlusions often lead to severe visual loss. Development of collateral vessels has been suggested to reduce the risk of CRVO–associated neo–vascular glaucoma. In order to facilitate the development of a retinal venous to choroidal micro–vascular stent, we evaluated a common biocompatible polymer system to characterize the variations of network swelling, elastic modulus, and diffusional transport that may be enhanced or controlled by utilizing nano–structured templates. Methods:Two lyotropic liquid crystalline (LLC) templates were used as a scaffold within the polymer network of photopolymerized polyethylene glycol diacrylate (PEGDA). For comparison, a non–templated, random orientation network was also evaluated. PEGDA–catalyst mixtures randomly oriented, or formed on a cubic micellar or tubular hexagonal scaffold, were evaluated for the degree of swelling in normal saline, for the compressive modulus relationship, and for small solute release utilizing acetylsalicylic acid (ASA, MW 180.2). The nano–structure of the randomly oriented polymer, and the LLC templated polymer structure were characterized utilizing polarized light microscopy to allow the measured physical properties to be correlated with the polymer network architecture. Results: Utilizing randomly oriented and LLC templated PEGDA matricies, we observed that the degree of swelling in the material is 190%, 250% and 350% of its dry weight for randomly oriented, cubic micellar and tubular hexagonal structures, respectively. The elastic compressive modulus of the fully hydrated polymer is 2KPa, 3KPa and 1KPa for randomly oriented, cubic micellar and tubular hexagonal structures, respectively. Diffusional small molecule release, assessed by incorporating ASA, resulted in a half life difference of 28 hr, 116 hr, and 74 hr between randomly oriented, cubic micellar, and tubular hexagonal architectures. Conclusions:We have demonstrated that LLC templates can be used to order the structure of a PEGDA polymer network and modify their swelling, structural, and permeability characteristics. Based on the results of this initial study, the PEGDA material that is templated with cubic micellar structure domonstrates properties that best fit the desired design paramteres of the ocular stent. The desired parameters of the stent include minimal swelling, good mechanical stability, and the slow release of angiogenic solutes. We are currently evaluating the cellular responses to these polymer structures in cell culture.
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