Bilayer Composite Hydrogels for Corneal Prostheses
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BILAYER COMPOSITE HYDROGELS FOR CORNEAL PROSTHESES
Edward Perez,* Linda G. Cima," David Miller*, and Edward W. Merrill* From the *Department of Chemical Engineering, Massachusetts Institute of Technology and the lCornea Consultants, Simmons Eye Associates Abstract A two-layer composite material composed of a thin-layer of corneal tissue and a synthetic polyethylene oxide (PEO) hydrogel is described. The material is designed to provide a suitable substrate for corneal epithelial cell growth while maintaining the desirable characteristics of hydrogels, i.e. clarity, flexibility, and ability to allow diffusive flow of nutrients. The gels are synthesized via electron irradiation induced crosslinking of an aqueous solution of PEO onto a thin layer of collagenous tissue substrate. light microscopic studies indicate that the interface between the corneal tissue and PEO gel appears well adherent with no gaps in the interface. SEM studies of the material surface show an architecture similar to that of normal corneal tissue. Surface analytical techniques were used to identify amino-acids covalently bound to the gel at the gel/collagen interface after the proteinaceous material was removed. ESCA survey scans identified the presence of nitrogen on exposed gel/collagen interfaces and amino acid labelling confirmed the presence of amino acids. ATR-IR studies identifed increased absorption for the gel collagen interfaces at 1640 cm"1 and 1540 cm"1 indicative of bound amino acids. Introduction A viable prosthetic alternative to corneal transplants is needed for treatment of severely intractable cornea cases as well for cases in underdeveloped countries where human corneal tissue is unavailable. Hydrogel materials have received much attention in relation to their applicability as prosthetic corneal devices"12' 3 because of clarity, flexibility, and ability to allow diffusive flow of nutrients. Anatomically, a penetrating corneal prosthesis must be fully enclosed in the cornea with a contiguous epithelium; i.e. a contiguous epithelium must develop between the implant and host via colonization of the implant surface by epithelial cells which migrate from the host cornea. The long term objective of our work is to construct a hydrogel material possessing a surface environment conducive to corneal epithelial cell growth in addition to maintaining other desirable characteristics of hydrogels. The approach that we are taking toward a suitable hydrogel is to synthesize a composite material comprising a synthetic hydrogel covalently attached to a thin collagen matrix. This synthesis is based on the use of electron-irradiation-induced (Eli) crosslinking to crosslink a hydrogel network 4'5 onto the substrate collagenous matrix. This thin tissue layer will serve as a substrate for cell growth. We have chosen to work with polyethylene oxide (PEO) and corneal tissue to synthesize the hydrogel and matrix surface. Crosslinked PEO has previously been used in the synthesis of hydrogel materials for corneal implantation.6 These materials have shown
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