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C. Scholz, W. Vayaboury, V. Enzmann, D. B. Shire, J. F. Rizzo; Biocompatible Block Copolymers for Coating Sub-Retinal Prostheses. Invest. Ophthalmol. Vis. Sci. 2007;48(13):665.
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This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind. The specific purpose of this presentation is the synthesis, characterization and biocompatibility studies of derivatized block copolymers that could be used as coatings for sub-retinal prostheses. This polymeric coating is expected to form the interface between the device and the surrounding tissue and should have the potential for further chemical modification, e.g. formation of gels, attachment of prodrugs or trophic factors.
Biocompatible block copolymers were synthesized by ring-opening polymerization of N-carboxyanhydrides of protected L-lysine, L-glutamate and L-aspartate using alpha-methoxy-omega-amino poly(ethylene glycol), PEG, as macroinitiator. After deprotection in basic medium, poly(amino acid), paa, blocks were derivatized with S-acetyl hexanoic acid or cystamine dihydrochloride to introduce thiol moieties at the paa side chain ends. Molecular weight was determined by GPC, and the molecular architecture was verified by 1H NMR. Cytotoxicity, apoptosis and cell attachment/detachment studies were conducted.
Block copolymers were synthesized with varying paa block length, ranging between 10 and 200 repeat units. The molecular weight was determined by GPC and confirmed the initial PEG:paa ratio charged in the polymerization; the polydispersity index ranged between 1.05 and 1.15. NMR confirmed the chemical structure and the successful derivatization with thiol groups. The presence of thiol groups was further confirmed by coating the copolymer onto a generic gold surface. The change in surface morphology was recorded by atomic force microscopy imaging. Thiol groups readily undergo oxidation to disulfides upon drying, hence it is recommended to purify the polymer by dialysis and coat actual subretinal prostheses immediately out of this purified polymer solution, thus avoiding crosslinking by disulfide formation. For the results on biocompatibility studies, please see poster by Franco et al. in this meeting.
Our technique allows for the synthesis of PEG-b-paa block copolymers with controlled block length and terminal side chain thiol functions without the use of a metal catalyst. These block copolymer coating materials have been shown to be non-toxic and biocompatible and they readily react with noble metal surfaces.
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