New Method for Bonding Poly (Ethylene Oxide) Peo to Surfaces
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ABSTRACT A new method has been developed for the covalent attachment of poly(ethylene oxide) to various polymeric surfaces for use in biomedical applications. Methacrylic acid (MA) monomer was first grafted to low-density polyethylene (LDPE) or polystyrene (PS) sheets by placing them in a solution of 10-20% (v/v) methacrylic acid in water followed by electron beam irradiation of 2-4 megarads. The methacrylic acid was grafted to the surface and polymerized, resulting in the polymer surface being extremely hydrophilic. The MA-treated samples were placed in a solution of PEO in water (MW 8000 - lx106 g/mol, concentration 0.05-15 % w/v), where the PEO strongly hydrogen bonds to the MA on the surface. The pieces were either rinsed with water (monolayer formation) or drained of excess solution (multilayer formation), then placed under the electron beam for a dose of 2 megarads to graft the PEO to the MA-treated surface. The grafted PEO was stable on the surface, unable to be removed despite extensive washing with water, soaking in basic solution (which would break the hydrogen bonding of the PEO with the acid), or scraping of excess hydrogel from the surface. The monolayer thickness was found to have no dependence on the molecular weight or concentration of the PEO in solution, nor did it have any dependence on the time that the MA-treated samples were soaking in the PEO solution before the second irradiation. This indicates that the PEO molecules immediately lie flat on the surface with few loops or tails, with no exchange taking place after the initial adsorption. All surfaces were analyzed using X-ray photoelectron spectroscopy (XPS), with high resolution carbon Is scans being the principle means of MA and PEO detection in the top 50 angstroms of the surface.
INTRODUCTION Poly(ethylene oxide) is unique among polymers concerning its properties when applied to the biomedical applications.' Unlike any other polymer, PEO is completely bland in a biological environment. Proteins and cells to not adhere to it, nor does it cause any adverse biological reactions such as blood clotting or the activation of the immune system. It is the ideal material for blood contacting applications. For PEO to be used in such a capacity, it must be done in conjunction with another polymer, since PEO is water soluble, and in pure form (i.e., a crosslinked hydrogel) it is not very mechanically strong. In recent years, much has been done in trying to engineer a purely PEO surface, either by end-linking linear PEO to a surface through specific chemistry 2,3 or by creating block copolymer networks or interpenetrating networks. 4-6 Although some success has been achieved, a method has yet to be developed whereby the resulting surface is only PEO as seen by biological molecules. The study presented here may be the solution to this problem. One method for the grafting of polymers or monomers is through irradiation using an electron beam. Under an electron beam, radicals are created whereby monomers can polymerize, polymers or monomers can graft to a
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