Protein Adsorption To Chemisorbed Polyethylene Oxide Thin Films

Abstract

A major area of biomaterials research is the development of surfaces that reduce or eliminate non-specific protein adsorption. End-tethered PEO has been shown to reduce protein and cell interactions at the tissue-material interface; the effects of polymer chain length, chain density and end-group chemistry are not yet completely understood. To date, there have been few detailed, systematic studies that have attempted to elucidate the effect of end-tethered PEO conformation, surface chain density, molecular weight (MW) and end-group chemistry on protein adsorption at the solid-liquid interface. In the research described in this thesis PEOs of varying molecular weight (600, 750, 2000 and 5000 MW) and terminal functional group (-OH, -OCH3) were thiolated and chemisorbed to gold coated silicon wafers for the purpose of characterizing film thickness and surface chain density for direct correlation to protein adsorption behaviour. Tethered chain density was varied by manipulating PEO solubility and chemisorption time, which in principle, should allow for variable, controlled surface chain density from low to very high values. PEO layers were characterized using water contact angles, X-ray photoelectron spectroscopy (XPS), self-nulling ellipsometry and neutron reflectometry (NR). The adsorption of two proteins having widely different molecular weights was examined using radiolabeling and ellipsometry to ascertain the effectiveness of these surfaces in resisting protein adsorption and to provide information about the nature of protein interactions with end-tethered PEO surfaces. These experiments were carried out using single or binary protein solutions in buffer. Adsorption from plasma was also investigated: (1) by Western Blot analysis of the proteins eluted after plasma contact; (2) via experiments using radiolabeled fibrinogen.