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  • 1
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Thrombus formation at an artificial surface in contact with blood is the result of the interplay of two tightly linked biological systems, namely blood platelets and blood coagulation. While initiation of the overall process is thought to originate from proenzyme-enzyme conversions at the artificial surface, propagation of the process is only possible when a suitable phospholipid surface is available. The outer leaflet of the plasma membrane of activated platelets is such a surface; it containts negatively charged phospholipids which are normally present in the inner leaflet of the membrane. An examination of the thrombogenicity of materials, therefore, should include a quantitative assay for procoagulant sites at an artificial surface. In the present study we have evaluated polymers, exposed to platelet-rich plasma, for their procoagulant properties by using two sets of assays. With the one set, markers of blood coagulation were assayed (recalcification time of platelet rich plasma and kallikrein-C1-Inhibitor complex formation) and with the other set the surfaces were analysed for platelet adherence and procoagulant sites utilising annexin V, which has a high affinity for negatively charged phopholipids. For the polymers, the fastest rate of contact activation, as determined from kallikrein-C1-Inhibitor generation, was found with polyethylene. In spite of that, the conventional partial thromboplastin time (PTT) could not reveal differences between the various materials. However, when clotting was performed with platelet-rich plasma, it was found that the polymers differed significantly in their clot promoting activities. The shortest clotting time (5 min) was found with polyethylene (PE), and polyvinyl chloride (PVC) gave the longest clotting time (10 min). These findings closely correlated with the amount of procoagulant sites generated at the platelet-rich plasma-polymer interface.
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  • 2
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Polyacrylamide-grafted polyetherurethane sheets were modified by end-point and multipoint attachment of heparin. The surface-bound heparin was firmly attached. No release of heparin activity could be detected when the surface was rinsed at a wall shear rate of 2000 s-1. Uptake of antithrombin and thrombin inactivation were investigated under well-defined flow conditions by the use of a spinning device with an attached disk-shaped heparinized surface. It is demonstrated that the rate of thrombin inactivation at the antithrombin-heparin surface equals the maximal rate of transport of thrombin toward the surface when the surface coverage of antithrombin exceeds 10 pmol/cm2. This result indicates that a higher intrinsic catalytic efficiency of a surface does not necessarily result in a higher antithrombin activity. We varied the heparin content of the surfaces between 0 and 35 μg/cm2 by increasing the number of functional groups to which heparin could be covalently attached. The uptake of antithrombin increased with the heparin content of the surface, but the stoichiometry decreased from 2 to 0.5 pmol antithrombin/μg heparin. Apparently, antithrombin could not bind to heparins buried in the poly(acrylamide) layer. The rate of thrombin inactivation at surfaces with low heparin content (2 μg/cm2) fells below the transport limit of thrombin and became proportional with the heparin content of the surface. Although the contribution of surface-bound heparin to the neutralization of fluidphase thrombin was found to be negligible compared with the effect of fluid-phase antithrombin at physiologic relevant concentrations, these heparinized surfaces markedly delayed the onset of thrombin generation in platelet-rich plasma. It is concluded that the inhibition of locally produced thrombin might contribute to the thromboresistance of the heparinized surface. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 3
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Two new polymeric materials (polymers A and B) containing covalently bound iodine were prepared. These polymers were evaluated with respect to their possible use as radiopaque implant biomaterials - that is, materials that are visible in a noninvasive manner using routine X-ray absorption imaging techniques. Polymer A is a copolymer of methyl methacrylate (MMA) and 1 (80 and 20 mol%, respectively). Polymer B was prepared from MMA, 1, and 2-hydroxyethyl methacrylate (HEMA) (mol ratio 65:20:15, respectively). Compound 1 was synthesized from 4-io-dophenol and methacryloyl chloride. The resulting polymers were characterized with GPC, DSC, NMR, and by measuring both the advancing and receding contact angles. Thrombogenicity of the polymers was determined by an in vitro thrombin generation test procedure. The maximum concentration of free thrombin was 76 ± 1 nM for polymer A, and 64 ± 3 nM for polymer B. The lag times (i.e., time onset of thrombin generation) were 392 seconds for polymer A and 553 seconds for polymer B. For PVC-T, which is known as a passive material, a lag time of 583 seconds was found. This indicates that polymer B is comparable to PVCT, and more passive than polymer A. Polymer A exhibited minor activation of platelets. Polymer B did not induce platelet activation at all. The polymers exhibited, even as fibers with a diameter of ca. 0.3 mm, good radiopacity with routine imaging X-ray techniques in the clinic. It is argued that polymers A and B - which actually represent a whole family of radiopaque polymeric biomaterials - exhibit promising properties with respect to applications as construction materials for a new generation of endovascular stents. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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