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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 8 (1997), S. 747-751 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract The role of temperature and shear rate in the activation status of aggregating platelets and platelet microparticles (MPs) was investigated in a modified concentric-cylinder rotational viscometer. Whole blood anticoagulated with citrate was exposed to a range of shear rates typical of cardiopulmonary bypass circuits (0, 1000, 2000 and 4000 s-1) over four temperatures spanning hypothermic to mildly hyperthermic conditions (24, 30, 37 and 42°C) for short durations (100 s). Aliquots of blood were double-stained for CD41 (platelet GPIIb/IIIa) and CD62 (P-selectin). Platelets, platelet aggregates, MPs and red blood cell-platelet and -MP aggregates were identified by flow cytometry by acquiring only CD41-positive particles and differentiating on a plot of CD41 versus forward light scatter. The activation status of each particle was quantified by measuring CD62 expression (α-granule release). A degree of correlation between the shedding of MPs and the formation of platelet–platelet aggregates was observed for the data as a whole (r=0.85 for p〈0.01), although this trend was not observed for a shear rate of 4000 s-1. The mean expression of CD62 on both platelets and MPs was maintained at a very low level for all temperature and shear rate combinations. There was, however, a number of very highly activated MPs associated with red blood cells at high shear rates.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 8 (1997), S. 887-890 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Samples of whole blood were obtained from male volunteers and exposed to combinations of shear rates and temperatures representative of cardiopulmonary bypass (CPB) in a modified computer-controlled concentric cylinder rotational viscometer for a period of 100 s. Blood sampled from the chamber was fixed in paraformaldehyde, stained with CD41 and analysed by flow cytometry. Only platelet-positive particles were acquired, each individual cell, or aggregate of cells, identified by analysis of its fluorescence and forward light scatter characteristics. Little platelet aggregation was observed at shear rates of less than 4000 s-1 for temperatures of greater than 24°C, but large numbers of aggregates were formed at all temperatures at 4000 s-1 (p〈0.05), with more aggregates forming at 24 and 30°C than at 37 and 42°C (p〈0.05). We conclude that the process of aggregation is dependent on both temperature and shear rate. We note that a large number of platelets become involved in aggregates under conditions of temperature and shear-rate typical of CPB.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 9 (1998), S. 1-7 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract There are many medical applications which benefit from the use of soluble biomaterials, including the sustained release of drugs over a precise period of time, or temporary conduits for controlling nerve regrowth. We have manufactured a series of phosphate-based controlled release glasses (CRGs) in which the solubility could be controlled by varying the concentration of CaO and Na2O. Fibres of the CRG containing iron and cerium were placed into direct contact with human neutrophils and macrophages in tissue culture for 2.5 and 24 h respectively and the responses analysed by scanning electron microscopy (SEM) and confocal microscopy. The supernatants were analysed for the cytokine IL-1β by enzyme-linked immunosorbent assay (ELISA). Disks of CRG of various compositions were placed in contact with whole blood for 30 min and platelet adhesion assessed by SEM. Activation of platelets, granulocytes and complement were quantified by ELISA for β-thromboglobulin, elastase and iC3b. Intrinsic coagulation activation was measured by timing the clotting of recalcified plasma. Only the cerium fibre inhibited IL-1β release from macrophages. No platelet adhesion was observed to any disk composition. Three compositions containing MgO inhibited plasma clotting and showed an insignificant level of complement activation. This study has demonstrated the development of a number of compositions of CRG, which have great potential in a wide variety of biomedical applications.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 6 (1995), S. 839-843 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Cellular responses to silicone and latex were investigated using flow cytometry, to determine the cells involved in the inflammatory responses and to characterize the differences in the response between these materials, if any. A panel of 11 monoclonal antibodies were selected to cover the range of cells that could be involved in the response, each antibody being directly conjugated with fluorescein isothiocyanate (FITC). The materials were implanted subcutaneously into rats in tubular form; the tubes were sealed at one end with Silastic adhesive. Two tubes per animal were implanted, using four animals per time period for 1, 2, 5 and 7 day implantation periods. After these times the animals were sacrificed and the tubes retrieved and then spun to harvest the exudate from the lumen. This exudate was analysed using flow cytometry. Significant and reproducible differences in cell number and antibody positivity were observed between these two materials. Latex had a much larger cellular response and showed significant increases in antibody positivity that involved macrophages or granulocytes of unusual size and granularity. Overlap between antibody positivity made specific characterization difficult and led to many questions about the effect of exposure to a material and its effect on cell morphology and phenotype, particularly in the case of macrophages.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 9 (1998), S. 767-772 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract The influence of surfaces on the reactions of platelets in whole blood under laminar flow was investigated in a cone and plate viscometer. Citrated whole blood was exposed to steel, PMMA and PMMA modified with PEO at low (500 s−1) and high (4000 s−1) wall shear rates at room temperature for a period of 100 s. Treated blood samples were fixed with paraformaldehyde, stained with a monoclonal antibody for CD41 (platelet GPIIb/IIIa) conjugated with phycoerythrin and analyzed by flow cytometry. The reactions of platelets (microparticle generation and formation of platelet–platelet, platelet–red blood cell and red blood cell–microparticle aggregates) to these environments were quantified. Additionally, the size of platelet–platelet aggregates was assessed. The percentage platelet aggregation and numbers of microparticles generated were independent of surface type at any shear rate. The composition of the aggregates formed was influenced by the surface: at low and high shear rates PMMA caused the generation of platelet–platelet aggregates of the greatest size. The numbers of red blood cell–platelet and red blood cell–microparticle aggregates also varied depending on the surface. Fewer red blood cell–platelet aggregates were formed at higher shear rates, whereas the reverse was true for red blood cell–microparticle aggregates. It is concluded that these variations may help to explain the differential effects of surfaces to the induction of distant thrombotic events: microparticles may be protected from loss from the blood stream by their association with red blood cells at high shear rates. © 1998 Kluwer Academic Publishers
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 5 (1994), S. 666-670 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: A series of medical grade polymers and one non-medical grade polymer, in the form of tubes closed at one end, were implanted subcutaneously into the dorso-lumbar region of rats. The samples were retrieved after 1, 2, 5, 7 and 14 days and the exudate which formed within the lumen of the tubes analysed by flow cytometry. Positivity for each of six antibodies: CD45RO (pan leucocyte), OX42 (macrophage/monocyte), CD5 (T-lymphocyte), CD45RA (B-lymphocyte), Interleukin-2 (IL-2) receptor and Major Histocompatibility class II (MHC-II) antigen were tested. The volumes of exudates and their total cellularities varied greatly from material to material, but there was no relationship between the two. Silicone, for example, had the greatest exudate volume at all time periods, but the lowest cellularities after day 5. Large numbers of granulocytes and macrophages were observed in all materials, with smaller populations of T-lymphocytes, which also demonstrated high IL-2 receptor expression. High levels of MHC-II expression were observed and attributed mainly to the macrophage population. All materials demonstrated the very reactive nature of this type of model: a massive inflammatory reaction continuing right up to 14 days in all cases, seemingly acute in cellular composition with high immunological activity. It is concluded that flow cytometry is an extremely useful tool in probing the interaction of cells with artificial materials.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 28 (1994), S. 435-439 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The effect of material composition and shear rate on fluid-phase platelet activation was investigated using a capillary perfusion model. Citrated whole blood was perfused along the lumens of tubes constructed from silicone, PVC, Pellethane, W124 (an experimental polyetherurethane), and glass. Platelet activation was determined by measuring the increase in α-granule membrane protein P-selectin (GMP-140, CD62) and the lysosomal granule membrane protein GP-53 (CD63) on fluid-phase platelets by flow cytometry. All tubes caused an increase over the negative control in the number of P-selectin and GP-53 molecules detectable on the surface of these platelets. The activation response of platelets to changes in shear rate was also investigated. It was found that lysosomal release paralleled α-granule release in glass, but not in Pellethane, over a range of wall shear rates (100-1,000 s-1). © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 481-488 
    ISSN: 0021-9304
    Schlagwort(e): MCP-1 ; biomaterials ; flow cytometry ; macrophages ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Macrophages were elicited by the subcutaneous implantation of ultra high molecular weight polyethylene (UHMWPE) for periods of 2, 7, and 14 days in rats. Exudates of varying volumes were produced that was comprised of granulocytes, monocytes, immature and mature macrophages, and T-lymphocytes. No B-lymphocytes were observed at any time periods. Cell types were identified by their granularity and positivity to the following antibodies: leucocyte common antigen (LCA, pan leucocyte); CD11b/c (macrophage/monocyte); CD5 (T-lymphocyte); CD45RA (B-lymphocyte); HIS48 (granulocyte); ED2 (mature macrophage); and MCP-1 (monocyte chemoattractant protein 1). Monocytes isolated from control rat blood demonstrated a size slightly larger than that of granulocytes but with less granularity. Their size and granularity were followed over increasing time periods. The macrophages elicited by UHMWPE showed a similar pattern, with the exception of an apparently highly granular subpopulation with volumes similar to that of granulocytes but significantly more granular. The granular macrophage subset had a very high degree of ED2 and MCP-1 positivity, and their proportion, compared with other macrophages, was greatest at 2 days. The high MCP-1 expression was accounted for by MCP-1 molecules bound to the surface of a small proportion of macrophages that were activated. It is postulated that this subpopulation was responsible for the synthesis of the MCP-1 and could indicate a mechanism by which monocytes are attracted to the site of an implanted material. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 481-488, 1997.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
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