Clot-promoting surfaces

Vroman. L, Adams A.I, Fischer. G. C, Munoz. P.C and Stanford. M, Proteins, plasma and blood in narrow spaces of clot promoting surfaces, Adv. Ghent. Ser., 199,266-276 (1982). 

Proteins, Plasma, and Blood in Narrow Spaces of Clot-Promoting Surfaces... 

A partially or completely occlusive clot forms on top of the raptured plaque. Exposure of collagen and tissue factor induce platelet adhesion and activation, which promote release of adenosine diphosphate and thromboxane A2 from platelets. These produce vasoconstriction and potentiate platelet activation. A change in the conformation of the glycoprotein (GP) Ilb/IIIa surface receptors of platelets occurs that cross-links platelets to each... 

The most widely studied synthetic polymers for blood contact applications are polyether urethane ureas ( Biomer (Ethicon)). These materials have been used in artificial hearts, as coatings for lead wires in pacemakers, have been used and are being considered for blood vessel prostheses. The success of these materials is believed to be due to preferential adsorption of albumin rather than globulin or fibrinogen which promote a clotting response. However, these materials are hydrophobic and questions of long-term effectiveness are unresolved. Particularly, these materials may shed emboli or may be susceptible to surface calcification. Thus, it may be desirable to have synthetic polymers which are hydrophilic and better resemble blood vessels [475]. 

As a result of the contact of blood with none-ndothelial surfaces, several humoral and cellular systems can be activated. Exposure of blood proteins and cells to blood contacting medical devices can activate plasma proteolytic systems (coagulation (blood clotting system), fibrinolysis (process by which clot is broken down), complement cascade (a system of soluble proteins involved in microbiocidal activity and the release of inflammatory components), Kallekrein-kinin and contact systems) and at least three cellular elements (leukocytes, endothelial cells, and platelets). Contrary to the normal situations whereby these mechanisms are localized and intended to promote wound healing, activation of these systems by medical devices can result in nonlocalized systemic reactions. The preclinical and clinical assessments of hemocompatibility are designed to minimize modification of these systems. 

The adsorption of proteins on the surface of glass is well known in many areas of biochemistry (l.- 3) For example, blood clotting is promoted on glass surfaces, and siliconization is used to minimize this effect. Clotting starts when factor XII is activated by the anionic charge of the silanol groups on the glass surface (4-5). 

Heparin, a natural protein, is an important constituent of blood and contributes to blood clotting. When circulatory assist devices were first proposed, it was found that the artificial surfaces promoted unnatural thrombosis. An important proposed solution to the problem involved grafting heparin to the surfaces of the materials involved, including such polymers as poly(vinyl chloride) and poly(dimethyl siloxane) (Artificial Heart Program, 1968 Lyman, 1966 Sears, 1965). 

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