Biomaterials requirements blood compatibility

Implantation materials, which are in direct contact with blood, have to meet a particularly large range of requirements bio- and blood compatibility, mechanical strength against blood pressure, impermeability to the blood and its constituents, and sterilizability. In addition, the healing process that takes place on the inner and the outer surface of the artificial vessel is very different. The inner surface of the biomaterial should not stimulate adhesion of cellular blood components but should be covered with endothelial cells, whereas the outer surface of the prosthesis should be wrapped with connective tissue. 

The in vitro study of the hemocompatibility of biomaterials requires the consideration of many parameters, static or dynamic contact, flow rate, wall shear rate, form of biomaterial to be tested, pathway to consider (platelet adhesion, platelet activation, complement activation, contact phase activation etc..) and duration of contact(39). It has previously been demonstrated t t hemodynamic circumstances play a significant role in determining localization, growth and fiagmentation of thrombi and platelet adhesion in vivo, and that flow rate controls platelet transport to a surface and their adhesion (40). This evidence is siqtpoited by observed differences in platelet activity predominance in venous and arterial flow (41). Qearly, defining the blood compatibility of a material is a conqrromise between a number of these factors. 

X Biomaterials has reiterated the need for the development of blood-compatible materials since progress in this field is a condition for advances in the application of cardiocirculatory-assist devices and other procedures which require continuous or intermittent handling of blood (I). For example, the task force has specifically identified the development of small-diameter blood vessel prostheses and chronic blood access catheters as priority applications of blood-compatible materials. Both of these devices are used in low-flow situations where red thrombus formation (i.e., intrinsic clotting system activation) predominates (2). 

Biomaterials have played a vital role in the treatment of cardiovascular diseases, examples of applications including heart valve prostheses, vascular grafts, stents, indwelling catheters, ventricular assist devices, total implantable artificial heart, pacemakers, automatic internal cardioverter defibrillator, intraaortic balloon pump, and more. A key requirement for materials in cardiovascular applications, particularly blood-contacting devices, is blood compatibility, that is, nonthrombogenic. Additional requirements include mechanical and surface properties that are application specific. Surveying the field of polymers used in cardiovascular applications reveals that PUs, polyethylene terephthalate (PET), and expanded PTFE (ePTFE) are the most commonly used. This section will review each of the three polymers followed by a brief introduction of other emerging polymers for use in the cardiovascular area. 

A specific demand for a biomaterial surface is its compatibility with organ specific ceUs, which leads to the approach to cell seeding before implantation. Therefore, implants for blood contact may be durably covered with a monolayer of endothelial cells. Thus, a suitable interface between the synthetic carrier material and the individual cells is required [132]. For this reason, a concept based on covalent coupling of ceU adhesion promoters, like fibronectin or the pen-tapeptide GRGDS belonging to the endothelial cell binding domain of fibronectin, at the biomaterial surface is pursued. To achieve this the base polymer has... 

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