HYDROGELS PREPARED BY ELECTRON-IRRADIATION OF POLY(ETHYLENE OXIDE) INWATER SOLUTION - UNEXPECTED DEPENDENCE OF CROSS-LINK DENSITY AND PROTEIN DIFFUSION-COEFFICIENTS ON INITIAL PEO MOLECULAR-WEIGHT

Under ionizing radiation aqueous solutions of water-soluble polymers b ecome cross-linked and form hydrogels, primarily by radiolysis of wate r-generating hydroxyl radicals which attack the polymer chains. The ch ain radicals thus formed create cross-links by coupling. In particular , hydrogels formed from poly(ethylene oxide) are of interest for biome dical applications, including those in which it is necessary to transp ort large molecules such as growth factors, in addition to nutrients, to cells attached to the surface. We sought a rapid and simple method for estimating diffusion coefficients by observing the diffusion of tw o red-coloured proteins: cytochrome C and hemoglobin of respective mol ecular weights 12 000 and 67 000. In the course of this we discovered a previously un reported effect of the primary molecular weight of the polymer, before cross-linking, on the cross-link density finally achi eved and on the diffusion coefficient of the proteins. (C) 1996 Elsevi er Science Limited.