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Self-assembled monolayers of alkylsiloxanes supported on polydimethyl siloxane (PDMS) rubber were used as model systems to study the relation between blood compatibility and surface chemistry. The inner lumen of PDMS tubes was first treated with an oxygen plasma. The resultant oxidized surfaces were postderivatized by reacting them with alkyltrichlorosilanes to form the monolayer films. The chemical properties of the monolayers were controlled by varying the head-group chemical compositions. Surface derivatization was verified using variable-angle X-ray photoelectron spectroscopy (XPS or ESCA). Blood compatibility was evaluated using a canine ex vivo arteriovenous series shunt model. Surfaces grafted with hydrophobic head-groups as -CH3 and -CF3 had significantly lower platelet and fibrinogen deposition than the surfaces composed of hydrophilic groups such as -CO2CH3, -(CH2CH2O)3COCH3, and -(OCH2CH2)3OH.

Polyetherurethanes (PEUs) based on polytetramethylene oxide (PTMO) as the polyol, and derivatized with propyl sulfonate functionality, have previously been shown to possess antithrombotic properties. In this article, the bulk physical properties of sulfonated and nonsulfonated polyurethanes containing either polyethylene oxide (PEO) or PTMO as the soft segment are studied. The in vitro shape-change of platelets in contact with these surfaces, and their ex vivo blood-contacting response are also investigated. It was found that PEO-base was physically weaker than PTMO-base, which is attributed to a lower degree or phase separation in the former. In the dry state, sulfonation enhanced the physical properties for PTMO-containing polyurethane (PTMO-SO3-0.20), but weakened the PEO-containing polyurethane (PEO-SO3-0.15). In vitro platelet spreading studies showed the lowest degree of platelet spreading and also the lowest platelet density on PEO-base, while platelet spreading and density on the other three materials and polyethylene (PE) was greater. The thromboresistance of these materials was evaluated using a canine arteriovenous series shunt ex vivo. It was determined that PTMO-SO3-0.20 was the least thrombogenic, followed by both PEO-base and PEO-SO3-0.15, and that PTMO-base was the most thrombogenic.

Polyurethanes based upon polytetramethylene oxide (PTMO) as the polyol and derivatized with propyl sulfonate functionality pendant from the urethane nitrogen have previously been shown to possess good blood-contacting properties. Other investigators have shown that sulfonated polyurethanes containing polyethylene oxide (PEO) as the soft segment are much more thrombogenic than those containing PTMO as the soft segment. In this article, the surface properties of sulfonated polyurethanes based upon either PTMO or PEO are compared. Dynamic contact angle measurements show a significant decrease in the receding angles of the sulfonated PTMO-containing polyurethane as compared to its nonsulfonated precursor polymer. No significant difference is seen between the receding contact angles of either the sulfonated PEO-based polyurethane or its nonsulfonated analog. Variable-angle electron spectroscopy for chemical analysis (ESCA) studies of sulfonated PTMO-based polyurethane performed at room temperature show that there is a significant decrease in sulfur content at the surface. In contrast, the sulfonated PEO-based polyurethane showed little change in sulfur content with take-off angle. Finally, ESCA studies of freeze-dried surfaces show a significant increase in sulfur near the surface of the sulfonated PTMO-based polymer as compared to vacuum-dried samples but show no such increase for the sulfonated PEO-based polyurethane. It is suggested that the ability of the sulfonate functionality to be expressed at the surface may explain the observed differences in blood compatibility between the sulfonated polyurethanes based upon polyols of varying hydrophilicity.

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