Antithrombogenicity

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. 

PDMS-co-PS has been proposed to have the antithrombogenicity. PDMS-PEO-heparin has been synthesized to achieve better blood compatibility. Silicone-PC copolymers are always used as blood oxygenation, dialysis, and microelectrode membranes. 

Another metabolite of arachidonic acid is prostacyclin (PGI2). As with TxA2, PGI2 is produced continuously. Synthesized by vascular smooth muscle and endothelial cells, with the endothelium as the predominant source, PGI2 mediates effects that are opposite to those of TxA2. Prostacyclin causes vasodilation and inhibits platelet aggregation and, as a result, makes an important contribution to the antithrombogenic nature of the vascular wall. 

Merrill, E. W., Salzman, E. W., Lipps, B. J., Jr., Gilliland, E. R., Austen, W. G., and Joison, J., Antithrombogenic cellulose membranes for blood dialysis. Transactions—American Society for Artificial Internal Organs 12, 139-150 (1966). 

A new material with good antithrombogenic properties, suitable as biomedical material which assures the endothelialization of the inner surface of a polyurethane tube to imitate the inner wall of a natural blood vessel has been synthesized by blending PVA with polycarbonate urethane)(PCU) [229],... 

Chitosan is produced from the deacetylation of chitin. Chitosan is employed in the food industry. It is a hemostatic from which blood anticoagulants and antithrombogenic have been formed. It is often sold as a body fat-reducing agent or to be taken along with food to encapsulate fat particles. 

T. Okano, T. Aoyagi, K. Kataoka, K. Abe, Y. Sakurai, M. Shimada, I. Shinohara, Hydrophilic-hydrophobic microdomains surfaces having an ability to suppress platelet adhesion and their in vitro antithrombogenicity, J. Biomed. Mater. Res. 20 (1986) 919-927. 

The most important structural features of these SPUs are the microphase-separated (or microdomain) structures which are formed in their molecular assembly systems. In 1972, Lyman [5] suggested that the antithrombogenic property of his PEUU may be brought about by its microarchitectural effect. In the same year (1972), Imai and Masuhara [6,7] reported that micro-heterogeneous surface structure was responsible for its antithrombogenicity. 

As for the effect of anionic group, there are a number of reports dealing with the antithrombogenic behavior of sulfonate-modified surfaces of segmented polyurethane (SPU). An interesting feature of the adsorptive behavior of fibrinogen on these material surfaces will be discussed in Sect. 4.1. 

To improve the biomedical properties of SPUs, a number of attempts have so far been proposed. In particular, surface modifications by mobile, hydrophilic polyethylene glycol) (PEG) chains were extensively studied, and some of them proved to give fairly good results in terms of the antithrombogenicity. Nevertheless, as discussed in Sect. 3.1, the effect of PEG chains tethered onto the SPU surface should be carefully evaluated in detail with regard to clinical application as well as to fundamental considerations. 

Certain bioflavonoids may play a preventive role against cardiovascular diseases. Some citrus and other bioflavonoids have been demonstrated to reduce serum cholesterol levels and to affect fatty acid metabolism (70,71,72). The strong antiadhesive action on red cells and platelets of highly methoxylated flavones such as nobiletin, which also demonstrates antithrombogenic activity (73), indicates an important role in blood rheology and tissue perfusion. The antiadhesive action may indicate a preventive role in atherosclerosis since there is evidence that reduced perfusion of the vascular wall may interact with serum lipids to promote atherogenesis (74). 

As a class, PPs are considered active as antioxidant, antithrombogenic, and anti-inflammatory compounds. Many of them show an in vitro activity as scavengers of a wide range of RS, and also show inhibition of cycloxygenase and lipoxygenase (59,60), xantine oxidase (61), metalloproteases (62), and angiotensin II converting enzyme (63). All these activities are... 

Herrmann R, Schmidmaier G, Markl B, et al. Antithrombogenic coating of stents using a biodegradable drug delivery technol-ogy. Thromb Haemost 1999 82(1)51-57. 

Dextran-coupled surfaces give rise to thrombus formation to a lesser extent than the virgin hydrophobic surface. Although antithrombogenicity of the modified surfaces should be further estimated with more effective methods in vitro as well as... 

Blood-compatible polymer materials are required to inhibit both platelet adhesion and coagulation just as the endothelial on the polymer surface. It is known that there are many investigations in the design and the synthesis of socalled antithrombogenic materials. The immobilization of biologically active substances such as heparin [74, 75], urokinase [76], and prostaglandins [77-81] is one of the practical approaches. 

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