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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: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Hemocompatibility can be conferred on a biomaterial by covering this material with a monolayer of endothelial cells. The endothelial cell is an epithelial cell of mesenchymal origin, that features a specific phenotype with homotypic intercellular interactions and with specialized cell-matrix interactions. These interactions are mandatory to the normal barrier function and the non-thrombogenicity of the endothelial monolayer and are maintained in vivo at shear stresses ranging from 10-5 to 10-3 N cm-2. The endothelial monolayer grafted on a biomaterial should meet similar requirements. We have constructed a rotating disc device to investigate the effects of differential shear stresses on cell-cell and cell-matrix interactions in a monolayer of endothelial cells grafted on a disc-shaped biomaterial. The range of shear stresses that are being applied by the device vary from 0–10-4 N cm-2 to 0–2×10-3 N cm-2. In a series of experiments with discs of plasma discharge treated polycarbonate (PC) that are coated with fibronectin, it has been shown that a monolayer of endothelial cells grafted on these discs starts to lose intercellular contacts and cell-fibronectin interactions at shear stresses of 10-4 N cm-2. Coating of the PC discs with a complex extracellular matrix, synthesized by arterial smooth muscle cells in culture, prior to endothelial cell seeding results in the formation of a monolayer, which retains its integrity at shear stresses up to 2×10-3 N cm-2.
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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: 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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  • 4
    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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  • 5
    ISSN: 0021-9304
    Keywords: polyurethane ; phosphorylcholine ; protein adsorption ; phospholipid adsorption ; ellipsometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In a previous report we demonstrated that the blood compatibility of poly(ether urethane) (PEU) was improved by grafting phosphorylcholine (PC) groups on the surface. The improved blood compatibility was indicated by decreased platelet adsorption/activation and reduced thrombin formation at the polymer surface in experiments in which the surfaces were contacted with platelet-rich plasma in vitro. In the present study, we investigated the effect of grafted PC groups at a PEU surface on protein and phospholipid adsorption. Adsorption of human fibrinogen (Fg), human serum albumin (Alb), human high-molecular-weight kininogen (HMWK), and dioleoyl phosphatidylcholine (DOPC) vesicles was measured by ellipsometry. For this purpose, thin PEU films were cast on silicon wafers. The polymer film was photochemically modified with a PC-containing aryl azide. The presence of PC groups on the polymer surface was demonstrated by ESCA (Electron Spectroscopy for Chemical Analysis). The hydrophilicity of the polymer surface increased by the surface modification, as indicated by a decrease of the contact angle from 59° before to 43° after modification. Our data show that the presence of PC groups has little effect on the adsorption of proteins to a PEU surface. The highest adsorption was observed for Fg (0.49 μg/cm2 on PC-modified PEU and 0.50 μg/cm2 on PEU), followed by HMWK (0.28 μg/cm2 on both PC-modified PEU and PEU), and Alb (0.16 μg/cm2 on PC-modified PEU and 0.18 μg/cm2 on PEU). Protein adsorption was further studied on a “biomembrane-like” DOPC bilayer formed on hydrophilic silicon. We found no protein adsorption on this DOPC bilayer. The adsorption of small unilamellar DOPC vesicles on the polymer surfaces amounted to about 0.06 μg/cm2 (corresponding to circa 30% of monolayer coverage) and was similar for PC-modified PEU and PEU. Despite this partial surface coverage, preadsorbed DOPC on the polymer surface diminished the subsequent adsorption of proteins considerably. These results show that the mere presence of phosphorylcholine groups on a PEU surface is insufficient to suppress protein adsorption. The highly ordered structure of natural phospholipid bilayers seems to be required to suppress protein adsorption effectively. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 195-203, 1998
    Additional Material: 5 Ill.
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  • 6
    ISSN: 0304-4165
    Keywords: (Bovine) ; Factor Va ; Phospholipid-protein interaction ; Protein C ; Subunit interaction
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
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  • 7
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
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  • 8
    Publication Date: 2011-05-04
    Description: The posttranslational modification of therapeutic proteins with terminal sialic acids is one means of improving their circulating half-life, thereby improving their efficiency. We have developed a two-step in vitro enzymatic modification of glycoproteins, which has previously only been achieved by chemical means [Gregoriadis G, Jain S, Papaioannou I, Laing P (2005) Int J Pharm 300:125–130). This two-step procedure uses the Campylobacter jejuni Cst-II α2,8-sialyltransferase to provide a primer on N-linked glycans, followed by polysialylation using the Neisseria meningitidis α2,8-polysialyltransferase. Here, we have demonstrated the ability of this system to modify three glycoproteins with varying N-linked glycan compositions: the human therapeutic proteins alpha-1-antitrypsin (A1AT) and factor IX, as well as bovine fetuin. The chain length of the polysialic acid addition was optimized by controlling reaction conditions. After demonstrating the ability of this system to modify a variety of proteins, the effect of polysialylation on the activity and serum half-life of A1AT was examined. The polysialylation of A1AT did not adversely affect its in vitro inhibition activity against human neutrophil elastase. The polysialylation of A1AT resulted in a significantly improved pharmacokinetic profile when the modified proteins were injected into CD-1 mice. Together, these results suggest that polysialylated A1AT may be useful for improved augmentation therapy for patients with a deficiency in this protein and that this modification may be applied to other therapeutic proteins.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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