Protein repellent polyurethane-urea surfaces by chemical grafting of hydroxyl-terminated poly(ethylene oxide): effects of protein size and charge

The objective of this work was to elucidate the mechanism of protein repellency by surfaces grafted with poly(ethylene oxide) (PEO). Surfaces were prepared by chemical grafting to polyurethane-urea films. Free isocyanate groups were first introduced into the surface and then reacted with hydroxyl-terminated PEO. The chain length of the grafted PEO was varied from 3 to 113 ethylene oxide units. Based on XPS analysis the grafting density was assessed as moderate. Protein adsorption from isotonic buffer at pH 7.4 was studied by radiolabeling methods. The effects of protein size (MW 14 to 440kDa) and isoelectric point (4.3 to 11.1) were investigated. For a given protein, the level of adsorption decreased with increasing PEO chain length, reaching a lower limit at a PEO MW of 2000. Adsorption levels on surfaces with 5000 and 2000 MW grafts were similar. On most of the surfaces, there was no clear effect of protein size or isoelectric point on the ability of any of these PEO surfaces to inhibit protein adsorption. It may be that higher grafting densities leading to the brush configuration of PEO would be required before protein discrimination based on size would become evident.