PHOTOCROSSLINKED HYDROGELS BASED ON COPOLYMERS OF POLY(ETHYLENE GLYCOL) AND LYSINE

A group of new, water-soluble poly (ether-urethane) s, derived from poly (ethylene glycol) and the amino acid L-lysine, provide pendent carboxylic acid groups along the polymer backbone at regular intervals. The carboxylic acid groups were utilized for the attachment of acrylate and methacrylate pendent chains (hydroxyethyl acrylate, hydroxyethyl methacrylate, aminoethyl methacrylate, and aminoethyl methacrylamide), leading to functionalized polymers. The pendent chains were attached via ester and/or amide bonds having different degrees of hydrolytic stability. The attachment reactions proceeded with high yields (up to 95%). The functionalized polymers were subsequently photopolymerized (UV irradiation) to obtain crosslinked hydrogels. Crosslinked membranes with the highest degree of mechanical strength were obtained when the crosslinking reaction was performed in dioxane with benzoin methyl ether (0.1 wt %) as the initiator. The crystallinity, thermomechanical properties, and hydrolytic stability of the crosslinked membranes were studied. All membranes were transparent and highly swellable (equilibrium water content: 64-88%). The tensile strength in the swollen state ranged from 0.15 to 1.09 MPa. Under physiological conditions (phosphate buffered water, 0.1 M, pH 7.4, 37-degrees-C) the hydrolytic stability of the hydrogels varied depending on the bonds used in the attachment of the acrylate pendent chains: Hydrogels with hydroxyethyl acrylate pendent chains dissolved within 30 days, while hydrogels containing aminoethyl methacrylamide pendent chains remained unchanged throughout a 30 day period. Using high molecular weight FITC-dextrans as model compounds, complete release from the swollen hydrogels required between 60 and 150 h. Overall, the evaluation of poly (ethylene glycol) -lysine derived, photocrosslinked hydrogels indicated that these materials provide a range of potentially useful (C) 1994 John Wiley & Sons, Inc.