Protein Adsorption to Polyethylene Oxide-Grafter Surfaces

Abstract

<p>The objective of this work was to study and gain a better understanding of the mechanisms and factors that mediate how effectively grafted polyethylene oxide chains promote protein repellency.</p> <p>A polyurethane-urea was used as a substrate to which PEO was grafted. This material was synthesised by conventional methods and characterised using water contact angles, XPS and AFM. A grafting protocol was developed based on methods found in the literature, involving the introduction of isocyanate groups into the polyurethane surface followed by reaction of amine- or hydroxyl-terminated PEO. Surfaces grafted with PEO chains of various lengths were prepared and characterised by water contact angles, XPS and AFM. The data showed that the amine-terminated polyethylene oxide gave higher PEO graft densities than the hydroxy-terminated polyethylene oxide. Direct measurements of the grafting density of PEO via radiolabeling resulted in only qualitative data due to experimental problems associated with the measurements.</p> <p>Protein adsorption studies were performed with the PEO-grafted surfaces. Several factors anticipated to have an impact on the effectiveness of the PEO-grafted surfaces in repelling proteins were examined. The levels of protein adsorption generally decreased with increasing PEO graft molecular weight. The reduction generally reached a maximum at a PEO MW of 2000. Adsorption levels on surfaces with 5000 and 200 MW grafts were usually similar. Adsorption levels on surfaces prepared with amino-terminated PEO were in agreement with the surface characterisation data that indicated higher levels of grafted PEO.</p> <p>On most of the surfaces, there was little or no effect of protein size on the ability of the PEO grafts to inhibit protein adsorption. However a surface grafted with PEO of MW 550 adsorbed smaller proteins more extensively that larger proteins. The data also showed little or no effect of protein isoelectric point on PEO surfaces with long PEO-grafts probably due to surface charge "masking" by the PEO grafts. Surfaces with shorter PEO grafts, however, showed lower levels of adsorption for the more highly charged proteins. This effect may have been due to electrostatic protein-protein repulsion as protein accumulated at the interface.</p> <p>Experiments to investigate the effect of temperature on protein replusion by the PEO-grafted surfaces showed that the properties of the proteins themselves play a large role in determining levels of adsorption and that the solution properties of PEO (inverse temperature dependence) could not explain the effects observed.</p> <p>Results of experiments using multi-protein systems showed that the PEO-grafted surfaces did not repel proteins selectively: only the total quantity of protein adsorbing to the surfaces was affected.</p>