Entrapment of platelet

Denudation of collagen Entrapment of platelets in collagen fibers... 

Arterial thrombosis. The formation of an aggregate of blood factors (thrombus), primarily platelets and fibrin, with entrapment of cellular elements in the arteries. Arthritis. Inflammation of a joint. 

High shear rate (arterial) flow conditions promote thrombi composed largely of platelets such deposits are called white thrombi. Low shear rate (venous) flow conditions promote thrombi composed of red cells and platelets entrapped in a fibrin mesh, referred to as red thrombi. Sometimes, a smooth layer of fibrin also may be deposited. Embolization of the white or red thrombi may produce ischemia and infarction in distal circulatory beds. 

The first event that generally occurs after blood contacts a polymer surface is the formation of a protein layer at the blood-polymer interface (1). The formation of this protein layer is followed by the adherence of platelets, fibrin, and possibly leukocytes (2). Further deposition with entrapment of erythrocytes and other formed elements in a fibrin network constitutes thrombus formation. The growth of the thrombus eventually results in partial or total blockage of the lumen unless the thrombus is sheared off or otherwise released from the surface as an embolus (3). Emboli can travel downstream, lodge in vital organs, and cause infarction of tissues. The degree to which the polymer surface promotes thrombus formation and embolization, hemolysis, and protein denaturation determines its usefulness as a biomaterial (4). 

The platelets subsequently release adenosine diphosphate (ADP) which results in the cohesion of additional platelets thus forming the nucleus around which fibrin is formed (by activation of the intrinsic coagulation system). Entrapment of red and white blood cells follows and a full-blown throndOus results. 

Cellular Carriers. Erythrocytes, leukocytes, platelets, islets, hepatocytes, and fibroblasts have all been suggested as potential carriers for drugs and biological substances. They can be used to provide slow release of entrapped drugs in the circulatory system, to deliver drugs to a specific site in the body, as cellular transplants to provide missing enzymes and hormones (in... 

Desai and Hubbell (34) have entrapped PEO chains to the surface by partially dissolving the base polymer in a suitable solvent Poly(ethylene terephthalate) (PET) with entrapped PEO (Mol. Wt 18,5(X)) decreased albumin adsorption by 80% and platelet adhesion by more than 95% as compared to the control PET. In addition, the adhesion of Staphylococcus epidermidis. Staphylococcus aureus, and Pseudomonas aeruginosa was r uced by 70-95% on PEO-modified PET compared to control PET... 

The barrier properties of the PCL-based composites were investigated. The transport properties, sorption and diffusion, were measured by a microgravimetric method . The studied model permeants were methylene chloride and water vapour for which the zero concentration diffusion coefficient Dq was determined. The presence of clay (hydrophilic platelets) in the composite gives rise to specific sites on which water molecules can be entrapped and immobilized, thus the water sorption increases on increasing the clay content, particularly for microcomposites containing Cloisite Na It was found out that the microcomposites as well as the intercalated nanocomposites have diffusion parameters for water vapour very near to those of pure PCL. 

Figure 1. Reaction of blood to different surfaces a) natural blood vessel wall consisting of endothelium (E) and subendo-thelial connective tissue (CT) shows no thrombogenic reaction to flowing blood, b) rough surfaced porous polymers entrap and clot blood as it flows past. Fibrinogen in blood precipitates as fibrin entrapping the blood cells, c) smooth surfaced polymers form small platelet aggregates at the interface with the blood, which embolize into the blood stream.

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