Polymers thrombogenicity

Biomaterials with Low Thrombogenicity. Poly(ethylene oxide) exhibits extraordinary inertness toward most proteins and biological macromolecules. The polymer is therefore used in bulk and surface modification of biomaterials to develop antithrombogenic surfaces for blood contacting materials. Such modified surfaces result in reduced concentrations of ceU adhesion and protein adsorption when compared to the nonmodifted surfaces. 

Sefton, M. V., Sawyer, A., Gorbet, M., Black, J. P., Cheng, E., Gemmell, C., and Pottinger-Cooper, E., Does surface chemistry affect thrombogenicity of surface modified polymers . J. Biomed. Mater. Res. 55, 447 459 (2001a). 

Hydrophobic polymer materials that slowly release N O can be used on the surface of medical devices. Many medical devices suffer from the surface adhesion of blood platelets. To minimize this thrombogenic effect, blood thinners such as heparin, coumarin, and aspirin are often used. However, systemic administration of antiplatelet agents could increase the risk of uncontrolled bleeding elsewhere in the body. In contrast, biocompatible polymer films would solve this problem [153]. It is possible to create polymeric surfaces that mimic the inner surface of a blood vessel by... 

Aggarwal R, Ireland D, Azrin M, de Bono D, Gershlik A. Reduction in thrombogenicity of cellulose polymer-coated stents by immobilisation of platelet-targeted urokinase [abstr], J Am Coll Cardiol 1997 29 353A. 

Reduced blood-polymer interaction (Filler-free silicone surface reduces thrombogenic response.)... 

Essentially all the TAH devices have used the PEUU materials (53. 54). but some other materials such as biolized poly(l,4-hexadiene) show promise (31). In the past, polysilicones, natural rubber, plasticized poly(vlnyl chloride), and other polymers were tried but were generally considered too thrombogenic or too weak. Better materials most likely will be developed in the future because much research work is in progress in the general area of cardiovascular materials. The lack of patient mobility probably poses the greatest difficulty for the present TAH devices. No doubt portable pumps will be developed, and perhaps implantable, and electrically powered devices (using rechargeable batteries) will be developed. Polymers will most likely be used in these developments as well. 

Flexible (as opposed to stiff) polymer chain ends and loops in the material interface lower the thrombogenic potential of the foreign surface. 

Table I. Relative Thrombogenicity of Vein Segments Placed on Polymer-Coated Rods...

The adsorption of plasma proteins to polymers precedes the interaction of blood cells with the surfaces, and therefore, is likely to be an important initial event in the response of blood to polymers (25, 29). At present, however, little is known about the adsorbed protein layer, even though it has been studied in some detail in recent years (30-36). Because protein adsorption from blood plasma is a competitive process, differences in the adsorbed layer on different polymer substrates could be a primary cause of differences in thrombogenicity. Previous studies of the composition of the adsorbed protein layer have employed 12oI-labeled protein added to plasma (37-39), antibody binding (34) to detect individual proteins, or electrophoretic analysis of detergent-elutable proteins (17, 33, 35). The procedure used in this study does not require the large surface areas used in previous work (35), nor does it rely on incorporation of radiolabels (36) into adsorbed protein. Instead, a staining method at least 100-fold more sensitive than these other techniques has been used. 

Therefore, in conclusion, these results indicate that an initial effect of molecular motions on thrombogenesis occurs independent of morphological order/disorder, crystallinity, and/or associated water (at the 0.01 mg bound water/mg polymer level). At higher levels of bound water (0.05 mg bound water/mg polymer), the effect of molecular motions on thrombogenesis is complexed by the presence of the bound water, as evidenced by the increased thrombogenic response. 

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