POLY(ETHYLENE OXIDE) GRAFTED TO SILICON SURFACES - GRAFTING DENSITY AND PROTEIN ADSORPTION

Poly(ethylene oxide) (PEO) polymer, in Linear and star form, was coval ently grafted to silicon surfaces, and the surfaces were tested for th eir ability to adsorb proteins. Linear PEG of molecular weight 3400, 1 0 000, and 20 000 g/mol and star PEO molecules were coupled via their terminal hydroxyl groups activated by tresyl chloride to aminosilane-t reated silicon wafers. The amount of PEO coupled to the surface was va ried by changing the concentration of the tresyl-PEO solution. The dry PEO thickness on the surface was measured using X-ray photoelectron s pectroscopy (XPS) and ellipsometry, from which the grafting density wa s calculated. The PEO surfaces were exposed to solutions of each of th ree proteins: cytochrome-c, albumin, and fibronectin. The degree of ad sorption of each protein was determined by XPS and ellipsometry and re corded as a function of PEO grafting density. All three proteins were found to reach zero adsorption at the highest grafting densities on al l three PEG surfaces, which for all three PEG surfaces was a PEO conte nt of 100 +/- 10 ng/cm(2). On both star PEO surfaces, albumin and fibr onectin decreased to zero adsorption at intermediate values of graftin g density, whereas cytochrome-e continued to adsorb at all grafting de nsities, although with a decreasing trend. A physical model of the sur face helped explain these protein adsorption results in terms of the s pacing and degree of overlap of grafted PEO chains.