Anticoagulant polymers

These anticoagulant polymers may be divided into two major categories, namely "AT Ill-like" or "heparin-like" materials, according to their different interaction mechanisms with thrombin... 

In practice, some anticoagulation agents such as heparin or antiplatelet agents, e.g. nitric oxide (NO) are delivered to sensor sites in order to reduce the risk of thrombus formation. Nitric oxide (NO), which is a potent inhibitor of platelet adhesion and activation as well as a promoter of wound healing in tissue, has been incorporated in various polymer metrics including PVC (poly(vinyl-chloride)), PDMS (poly-dimethyl-siloxane) and PU (poly-urethanes). Those NO release polymers have been tested in animals as outer protection coatings and have shown promising effects for the analytical response characteristics of the sensor devices [137],... 

The mammalian blood anticoagulant heparin is also a carbohydrate polymer in which amino sugars (glucosamine) alternate with uronic acid residues (see... 

Pereira, M. S., Mulloy, B., and Mourao, P. A. (1999). Structure and anticoagulant activity of sulfated fucans. Comparison between the regular, repetitive, and linear fucans from echinoderms with the more heterogeneous and branched polymers from brown algae. ]. Biol. Chem. 274, 7656-7667. 

Methods for preparing heparin-containing polymeric materials by means of ionic and covalent immobilization of heparin on various polymers are surveyed. The data on the biological activity of heparin are discussed as well as the probable mechanisms of thromboresistance enhancement endowed to polymeric materials by this anticoagulant. Some approaches toward an increased efficiency of anticoagulant properties of immobilized heparin are analyzed, and the position of heparin-containing polymers among other biomedical polymers is discussed. 

The year of 1961, when Vincent Gott11 observed the inhibition of thrombus formation by immobilized heparin for the first time, was marked as the second birth date of heparin, since it was for the first time isolated from liver tissue. Its anticoagulant action was detected in 1892. Although more than 20 years have passed since Gott s publication, there is still much confusion concerning the views on the mechanism of enhanced thromboresistance of heparin-modified polymers, which greatly hinders the introduction of HCP into clinical practice. 

It seemed reasonable to anticipate that the synergism of these two features (high heparin content and stability of the resultant materials) would result in long-term thromboresistant polymers. The in vivo tests revealed, however, their extremely low thromboresistance as compared to the ionically bound heparin-containing polymers, in particular. The effect is assumed to be caused by a lack of sufficient mobility of the polymer-bound heparin molecules, which prevents the performance of the intrinsic anticoagulant properties of heparin. 

In all of the reported cases, anticoagulant activity of immobilized heparin, as was already stressed above, was less than the activity of heparin in solution, which was attributed to the low accessibility of heparin molecules for physiological substrates. Increasing the porosity of the polymer, i.e., increasing the accessibility of the immobilized heparin led to an increase in its anticoagulant activity 100). 

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