Effects of oligoethylene oxide monoalkyl(aryl) alcohol ether grafting on the surface properties and blood compatibility of a polyurethane

A series of oligoethylene oxide monoalkyl(aryl) alcohol ethers was grafted on to the backbone of a polytetramethylene oxide (PTMO)-based polyurethane, in an attempt to improve its biocompatibility. Each polyurethane contained a different pendant chain grafted to the urethane nitrogen atoms. The grafted chains consisted of various short lengths of hydrophillic oligomeric poly(ethylene oxide) (PEO) spacer segments and alkyl/aryl hydrophobic terminal groups. By using the 1H-NMR (nuclear magnetic resonance) technique, the extent of grafting was found to range from 7 to 12 mol% substitution of the urethane hydrogen groups. The surface properties of these materials were evaluated using high-vacuum, air-equilibrated and water-equilibrated methods. X-ray photoelectron spectroscopy (XPS) and static and dynamic contact angle experiments were performed. XPS showed that all of the grafted polyurethane surfaces contained higher ratios of C1s to O1s than the base polyurethane. These C:O contents correlate with the C:O ratios of the grafted chains. Dynamic contact angle analysis showed larger contact angle hysteresis for the grafted polyurethanes. The grafted polyurethanes generally exhibit lower complement activation, measured by an in vitro assay for C3a. A canine ex vivo arteriovenous series shunt was used to monitor platelet and fibrinogen deposition on these polymers. The incorporation of short ethylene oxide spacer segments with terminal C18 linear alkyl chains resulted in an improved short-term (up to 15 min) blood compatibility compared to the underivatized polyurethane. At longer blood contact times, all the grafted polyurethanes were more thrombogenic than the base polyurethane. In addition, there was no observable correlation between the material surface properties and the blood contact response.