Surfaces, blood contacting

The studies on the chemical synthesis of 0-acyl chitins were followed by studies on their biocompatibihty, and hence their potential use as materials for blood contacting surfaces has been investigated by measuring, inter... 

Interactions of blood, or more precisely of plasma macromolecules and blood cells with the vessel wall, should the latter be natural or artificial, depend upon several parameters the mechanical properties of the vascular conduit, on the one hand, the morphology and the physical and chemical characteristics of the blood-contacting surface on the other. 

It will be later proposed that an ideal blood-contacting surface would be one on which endothelial cells could adhere and grow normally to create a complete endothelium endowed with the physiological functions of such tissue. But the correct expression of such physiological functions requires normal blood flow conditions. And the correlation of thrombosis with regions of disturbed flow suggests that shear stress may alter the production of endothelial cell-derived products and directly affect endothelial cell function. 

The slower intrinsic mechanism first described in 1964 47,548 consists of a cascade involving six proteases (Fig. 12-17, left side). Again, autocatalytic cycles are present in the activation by Xlla of both prekallikrein and XII and in activation by thrombin of factors XI and VIII. This intrinsic pathway is initiated by the serine protease proenzymes prekallikrein and factor XII together with the accessory protein high-molecular-mass-H- kininigen. 49 Activation occurs when blood contacts surfaces such as glass or kaolin (a clay). 47,548,550 Factor XI can also be activated by thrombin. Heredity absence of factor XI leads to bleeding problems, especially... 

The increased longevities of animal implantations have caused unforeseen problems at the blood contacting surfaces. Increased mechanical and surface degradation of polymers employed as flexing components in... 

FTIR spectroscopy has proven to be particularly useful in gaining an understanding of the biocompatibility phenomenon. It is believed [746, 841, 856, 857] that protein adsorption is the initial step in the interaction of blood with implanted biomaterials, followed by adhesion of cells and subsequent tissue attachment. This implies that the substrate surface characteristics influence the process, which was confirmed by ATR studies of albumin adsorption on calcium phosphate bioceramics and titanium [763] and segmented polyurethane [764], albumin and fibrinogen on acetylated and unmodified cellulose [765, 766], poly(acrylic acid)-mucin bioadhesion [767], polyurethane-blood contact surfaces [768], and other proteins on poly(ester)urethane [769], polystyrene [767, 771] and poly(octadecyl methacrylate) [771] and by IRRAS study of adsorption of proteins on Cu [858]. Another branch of IR spectroscopic studies of protein adsorption relates to microbial adhesion (Section 7.8.3). 

The blood-contacting surface of oxygenators has also been modified with the MPC polymer, PMD, with the aim of reducing platelet activation during blood circulation (Sorin Prim02X , Synthesis ). The porous hollow fiber polypropylene membranes that contact the blood were coated with the PMD. ° As the affinity of the dodecyl group on the substrate was strong, and... 

Because the variables affecting cardiovascular device responses are sufficiently numerous and complex, those properties of blood-contacting surfaces which would be desirable to minimize adverse reactions cannot, in most instances, be predicted with confidence. The choice of material is usually constrained by mechanical property considerations and by variable requirements for material durability and chemical stability. Cardiovascular device engineering must therefore be guided by previous experience in successful clinical applications. 

Figure 11.13 Fibrous polyurethane vascular prosthesis. Upper SEM pictures are morphology of the vascular prosthesis prepared with SPU/PMBU polymer alloy by electrospun procedure. Lower SEM pictures are the blood-contacting surface of the vascular prosthesis after 4 h blood circulating.

As previously described, device failure has fiequently occurred as a result of both thrombosis and calcification. PUR valve caldficafion occurs on the blood-contacting surfaces of these devices, and in general results firam calcified thrombus (Bezuidenhout et al., 2015). This is caused in part by the lack of an intact endothelium on device surfaces, with resulting thromboembohc activity. 

Another approach utilizes the grafting of the sulfate-containing polysaccharide heparin onto the blood-contacting surface. This material prevents coagulation and concomitant thrombosis. The strong anionic character of heparin enables it to bond ionically to cationic surfaces. The heparin is slowly released into the bloodstream. During this release process, the concentration of heparin near the surface is sufficiently high to prevent the formation of a thrombus for several days. Unfortunately, after this period of time, the release rate decreases. Thus, this approach is only suitable for use in short-term devices. 

A new approach involves growing of living cells on the blood-contacting surface. Bone marrow cells (112) and endothelial cell monolayers (113) both contribute to nonthrombogenicity. 

The protein composition and distribution on the blood contacting surface of MPC copolymers from human plasma has been determined by radioimmunoassay and an immunogold labeling technique (8). In Fig. 5, proteins existed on the plasma contacting surface after 60 min contact with poly(MPC-co-BMA) and glass were determined by radioimmunoassay. On all materials, not only major components of plasma pro-... 

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