Physical and blood-contacting properties of polyurethanes based on a sulfonic acid-containing diol chain extender.

Polyurethanes chain extended with N,N-bis (2-hydroxyethyl)-2-aminoethane-sulfonic acid (BES) were synthesized. The effect of the sulfonic acid group on the polymers' bulk, surface, and blood-contacting properties was evaluated by comparing the BES-based polymers with polyurethanes based on N-ethyldiethanolamine (EDEA). In addition, the effect of soft-segment polarity was addressed by comparing polyurethanes based on polytetramethylene oxide (PTMO) (MW = 1000) with polymers based on polyethylene oxide (PEO) (MW = 1000). The EDEA control samples had physical properties similar to a viscous fluid. The presence of the sulfonic acid group dramatically enhanced the degree of microphase separation and the mechanical strength of all the polymers. The more polar PEO soft segment resulted in polymers which were more phase mixed than the PTMO-based polyurethanes. Surface characterization studies revealed that in vacuum, all the surfaces were enriched in the polyether soft-segment phase. After 24-h equilibration in water, all the surfaces had similar surface polarities independent of the SO3H content. The canine ex vivo blood-contacting results showed that the sulfonic acid group in the PTMO-based polymers significantly reduced the number and activation of the adherent platelets. Fibrinogen deposition, however, increased with increasing sulfonic acid content. In contrast, platelet and fibrinogen deposition on the sulfonic acid-containing PEO-based polymers was greatly enhanced.

Effect of hydrophilic soft segment side chains on the surface properties and blood compatibility of segmented poly(urethaneureas).

Segmented poly(urethaneureas) with hydrophilic side chains were prepared from poly(tetramethylene oxide) (PTMO), 4,4'-diphenylmethane diisocyanate (MDI), ethylene diamine (ED) and a diol with a long hydrophilic side chain comprised of an ethylene oxide-proplene oxide copolymer. The end groups of the hydrophilic chains were either sodium sulfonate or methoxy groups. The state of microphase separation showed a small dependence on the fraction of long-chain hydrophilic diol. Surface analysis by means of static underwater contact angle and dynamic contact angle measurements revealed that the graft chains were at the aqueous interface in the hydrated state. An ex vivo A-V shunt experiment revealed that a more thrombogenic blood-material response was correlated with an increase in the concentration of polymeric hydrophilic side chain incorporation. The polyurethane containing a long chain diol with methoxy end groups exhibited a higher level of thrombogenicity than the similar polymers possessing a sulfonate terminated side chain.

Effect of carboxylate and/or sulphonate ion incorporation on the physical and blood-contacting properties of a polyetherurethane.

Propyl sulphonate and ethyl carboxylate groups were grafted on to the backbone of a polytetramethylene oxide-based polyurethane (PEU). The effects of ion type and ion content on the polymer's bulk, surface, and blood-contacting properties were evaluated. Ion incorporation disrupted the packing of the hard segment but had little effect on the overall microphase separation of the polymers. The mechanical properties of the ionomers were improved relative to the base PEU, although the carboxylate-containing ionomers were weaker than the sulphonate-containing polymers. As expected, the polymer's water absorption and surface polarity increased with increasing ion content. Dynamic and static contact angle analysis indicated that the propyl sulphonate-containing polymers were more polar than the ethyl carboxylate-containing polymers at the same ion content which is attributed to the higher ionic strength of the sulphonate ion. The carboxylate-containing polymers had no statistically significant effect on the polymer's canine ex vivo blood-contacting response. At the same ion content, propyl sulphonate incorporation significantly reduced platelet deposition for very short blood-contacting times. When both ion types were present in the polymer, the propyl sulphonate group appeared to be the primary factor determining the polymer's blood-contacting response. The polymer containing 20 mol% propyl sulphonate groups significantly reduced platelet deposition and activation while also exhibiting enhanced fibrinogen deposition.

Effect of surface hydrophilicity on ex vivo blood compatibility of segmented polyurethanes.

The relationship between surface, bulk and ex vivo blood-contacting properties of segmented polyurethanes with various polyol soft segment was investigated. The polyols used in this study were poly(ethylene oxide), poly(tetramethylene oxide), hydrogenated poly(butadiene), poly(butadiene) and poly(dimethylsiloxane). The hard segment of these segmented polyurethanes was composed of 4,4' diphenylmethane diisocyanate and 1,4 butanediol, present at 50 wt%. An experimental polyurethane, Biostable PUR, which has shown excellent biostability, was used in this study. The segmented polyurethanes based on the hydrophobic polyols such as poly(dimethylsiloxane) and hydrogenated poly(butadiene) showed distinct microphase separation between hard and soft segments. X-ray photoelectron spectroscopy revealed the surface enrichment of the hydrophobic component at the air-solid interface. Dynamic contact angle measurements indicated that the poly(dimethylsiloxane)-based segmented polyurethane possessed a hydrophobic surface in water. The poly(dimethylsiloxane)-based segmented polyurethane had the lowest platelet adhesion among the segmented polyurethanes investigated in this study, whilst the platelet deposition on the poly(ethylene oxide)-based polymer increased with time.

Physical and blood contacting characteristics of propyl sulphonate grafted Biomer.

Propyl sulphonate groups were grafted on to the backbone of Biomer, a polyetherurethaneurea, in an attempt to improve its blood-contacting properties. The bulk, surface and blood-contacting properties of this series of sulphonated polymers were evaluated. Differential scanning calorimetry and dynamic mechanical analysis indicated that propyl sulphonate incorporation increased the microphase separation of the polymers. The ultimate tensile strength was also increased with sulphonation at the expense of the polymer's extensibility. Dynamic contact angle analysis showed that, in water, the sulphonated Biomer surfaces were more polar than the Biomer sample indicating the propyl sulphonate groups were enriched at the surface. Canine ex vivo blood-contacting results showed that the incorporation of propyl sulphonate groups dramatically reduced the number and activation of platelets adherent to the polymer surface. In addition, fibrinogen deposition increased with increasing sulphonate content, despite the low level of platelet activation.

Acute and chronic canine ex vivo blood interactions with NHLBI-DTB primary reference materials.

Thrombus deposition was measured on NHLBI-DTB Primary Reference Material polyethylene (PRM-PE) and polydimethylsiloxane (PRM-SR) and their commercially available counterparts, surgical grade Intramedic polyethylene and Dow Corning Silastic. Canine blood-contacting experiments evaluating short-term (up to 60 min) and longer-term (up to 24 h) thrombus deposition were used to quantitate adherent platelets on the lumenal surface of test materials ex vivo. A similar pattern of thrombus deposition and detachment was observed for all materials in both acute and chronic blood contact. Although differences in the wall shear rates affected the absolute numbers of adherent platelets, the relative levels of thrombus deposition showed similarities between the two experiments, with the polyethylene materials as a group showing slightly less deposition than the silicone rubber materials. The PRM-PE showed the least thrombus deposition at extended exposure to blood. The PRM-SR showed the most thrombus deposition in the acute term. The overall similarity in blood compatibility and surface properties indicates the need for the inclusion of less thromboresistant and more polar reference materials.

Bulk, surface, and blood-contacting properties of polyetherurethanes modified with polyethylene oxide.

The bulk, surface, and blood-contacting properties of a series of polyether polyurethanes based on polyethylene oxide (PEO) (MW = 1450), polytetramethylene oxide (PTMO) (MW = 1000), and mixed PEO/PTMO soft segments were evaluated. The effect of varying the weight percentage of PEO, and thus the overall polarity of the mixed soft segment phase, was investigated. Two polymer blends prepared from a PTMO-based and a PEO-based polyurethane were also studied. Differential scanning calorimetry (DSC) and dynamic mechanical analysis indicated that the polyurethanes based on either the PEO or the PTMO soft segments are relatively phase mixed. The degree of phase mixing in the polymers increased with increasing weight fraction of PEO. As expected, water absorption and the hydrophilicity of the polymer increased with increasing PEO soft segment content. In vacuum, the PEO-rich polymers have a lower concentration of soft segment at the surface, possibly due to the migration of the polar PEO segments away from the polymer/vacuum interface. The blood-contacting results indicated that the higher PEO-containing polymers were more thrombogenic than the pure PTMO-based polyurethane. A threshold concentration of PEO in the polyurethane appeared to be required before the blood-contacting properties were significantly affected.

Bulk, surface and blood-contacting properties of polyether polyurethanes modified with polydimethylsiloxane macroglycols.

The bulk, surface and blood-contacting properties of a series of polyether polyurethanes, modified with three different polydimethylsiloxane (PDMS) macroglycol segments, were evaluated. The PDMS oligomers were terminated with hydroxy-tipped end groups of varying polarity. The effect of substituting the polytetramethylene oxide (PTMO) soft segment of a base polyurethane with 5 and 15 wt% of these PDMS-containing polyols was investigated. The ultimate tensile strength and elongation at break appeared to be the bulk properties most significantly affected by the addition of the PDMS-containing polyols. Underwater contact angle data indicate that the block copolymer surface became more hydrophilic with increasing PDMS content. In a vacuum, as determined from the ESCA data, the relatively non-polar PDMS soft segments preferentially oriented at the surface with increasing PDMS incorporation. Despite the variation in the surface properties, the blood compatibility of these polymers was not significantly affected by the addition of the PDMS-containing polyols.

Extraction of polyurethane block copolymers: effects on bulk and surface properties and biocompatibility.

In order to study changes occurring in polyurethane block copolymers upon solvent extraction, a base polymer containing approximately 50% polyurethane hard segment based on 4,4'-bis(p-phenyl isocyanate), 1,4-butanediol, and poly(tetramethylene oxide) of MW 1000 was synthesized. Portions of this polymer were extracted using methanol, toluene, and acetone. Multidetector gel permeation chromatography was used to characterize the effect of extraction on molecular weight and molecular weight distribution. Extraction also affected bulk and surface properties and the blood compatibility as assessed using a canine ex vivo blood-contacting experiment. Extracted materials possessed a higher molecular weight than the base polymer and had narrower molecular weight distributions. Acetone extraction resulted in the polymer with the highest ultimate tensile strength. Contrary to expectations, the surface properties and blood compatibility of the material studied were affected minimally by extraction.