Reduction of protein adsorption by coating surfaces with polyethylene glycol (PEG) is well documented. The present work has four goals related to these previous studies: first, to develop chemistry providing densely packed, covalently bound PEG on polystyrene (PS); second, to determine the ability of these modified surfaces to reject fibrinogen; third, to compare the protein-rejecting ability of branched and linear PEGs; and fourth, to examine the utility of an ELISA-type procedure for measuring protein adsorption. It was found that PEG-epoxide could be readily coupled to amine groups of poly(ethylene imine) (PEI), which had been preadsorbed onto an oxidized PS surface. The PEG groups on branched PEGs appear to act as an excluded volume to repel proteins, similar to arguments previously raised for linear PEGs. The results of protein adsorption studies showed that fibrinogen adsorption is significantly reduced by coating polystyrene with either linear or branched PEGs of 1500 to 20,000 in molecular weight. The ELISA technique was found to be equivalent in sensitivity to radiolabeled fibrinogen for estimating adsorption levels. It is expected that PEG-coated PS will have much utility in a variety of biomedical applications.

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Previous studies have shown that certain glow discharge treated polymers strongly retain adsorbed albumin and fibrinogen. On the basis of this phenomenon, we have investigated the possibility of immobilizing antibodies on glow discharge treated surfaces for diagnostic immunoassay applications. As a model for antibody immobilization, bovine IgG was immobilized on the following polymers: polyethylene (PE), tetrafluoroethylene glow discharge treated PE (TFE/PE), poly(ethylene terephthalate) (PET), TFE/PET, poly(tetrafluoroethylene) (PTFE), ethylene glow discharge treated PET (E/PET) and hexamethyldisiloxane glow discharge treated PET (HMDS/PET). IgG was radiolabeled with 125I and immobilized by either of the following two methods: (a) physical adsorption of IgG on untreated and glow discharge treated polymers or (b) physical adsorption of albumin followed by chemical coupling of IgG to albumin by glutaraldehyde. IgG concentration as well as adsorption times were varied in order both to optimize the immobilization conditions and to investigate the adsorption and retention mechanisms. To evaluate the efficiency of the immobilization techniques, blood plasma, Tween-20, and sodium dodecyl sulfate (SDS) were used to elute the adsorbed IgG layer. We found that IgG was successfully immobilized on the fluorocarbon glow discharge treated surfaces by using either the physical adsorption or the glutaraldehyde coupling method, although the former is more efficient than the latter method.

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