Synthesis and Surface Modification of Double Network Hydrogel From Poly(Ethylene Glycol) and Poly(Acrylic Acid)

Abstract

Abstract: : Purpose: To design and characterize novel nanoporous hydrogel for the artificial cornea by inducing a double–network structure and to modify hydrogel surface with cell adhesion proteins to support epithelial cell adhesion. Methods: Double–network hydrogel was synthesized by a (two–step) sequential network formation technique based on the UV initiated free radical polymerization. First hydrogel network was prepared from acrylated poly(ethyleng glycol)(PEG). The precursor solution containing PEG and photoinitiator was cast in the mold and underwent gelation by UV exposure. To incorporate the second network, the PEG–based hydrogel was removed from the mold and immersed in acrylic acid solution containing photoinitiator and cross–linking agent. The swollen gel was exposed to the same UV source so that a second network was polymerized inside first network. To promote epithelial cell adhesion and proliferation on the nonadhesive double network hydrogel surface, collagen was covalently attached to hydrogel surface modified with photoreactive, bifunctional azide linker such as 5–azido–2–nitrobenzoic acid N–hydroxysuccinimide ester. Results: A range of double network was synthesized with molecular weight of PEG from 575 to 14000. It was found that the low molecular weight PEG (3400) gave rise to gels that were opaque or brittle, whereas the hydrogels made from higher molecular weight PEG (≥8000) were transparent and flexible. Equilibrium swelling study showed that water content of resultant double network hydrogel is about 80 %, which is similar with that of human cornea. The average molecular weight between crosslinks and mesh size were also determined for the further characterization of our hydrogel networks. Surface modification with collagen was confirmed by fluorescent method. Amino acid analysis revealed that more collagen was immobilized on the modified hydrogel surface than unmodified one, even though there was baseline adsorption of collagen occurring on the unmodified hydrogel. Conclusions: Double network hydrogel with the desirable characteristics of an artificial cornea was successfully synthesized from poly(ethylene glycol) and poly(acrylic acid). Physical properties of double network hydrogel could be optimized by varying several parameters such as molecular weight of PEG and concentration of monomer.

Keywords: keratoprostheses