Proteins blood-polymer

The reasons for the increased platelet adhesion onto covalently-immobilized heparin-containing polymers were disclosed in the studies of the protein adsorption onto HCP i.e., as stated above, the first step of the complicated blood-polymer interaction. 

Adsorption of Blood Proteins onto Polymer Surfaces... 

The bead surface critically affects nonspecific binding, which is particularly serious in the presence of physiological fluids, e.g., human whole blood. Conventional polymeric surfaces need chemical coupling processes to immobilize functional molecules and are vulnerable to contamination originating from nonspecific adsorption of proteins that are not analytes, like albumins in blood. Polymers including ethylene glycol oligomers have been tried in an effort to... 

The adsorption of plasma proteins to polymers precedes the interaction of blood cells with the surfaces, and therefore, is likely to be an important initial event in the response of blood to polymers (25, 29). At present, however, little is known about the adsorbed protein layer, even though it has been studied in some detail in recent years (30-36). Because protein adsorption from blood plasma is a competitive process, differences in the adsorbed layer on different polymer substrates could be a primary cause of differences in thrombogenicity. Previous studies of the composition of the adsorbed protein layer have employed 12oI-labeled protein added to plasma (37-39), antibody binding (34) to detect individual proteins, or electrophoretic analysis of detergent-elutable proteins (17, 33, 35). The procedure used in this study does not require the large surface areas used in previous work (35), nor does it rely on incorporation of radiolabels (36) into adsorbed protein. Instead, a staining method at least 100-fold more sensitive than these other techniques has been used. 

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 Canine Model. While ex vivo models often are considered to be an improvement over in vitro biocompatibility test systems, the problem of describing extremely complex blood—polymer interactions still remains. In this study, we used radioisotope-labeled proteins and platelets and scanning electron microscopy. In other studies, we applied immunolabeling techniques and transmission electron microscopy. The application of these tools to an in vivo or ex vivo system provides more pertinent data than that often obtained in an in vitro system. Through this approach we hope to gain some insights into the complicated interactions of blood with biomaterials. 

Of course, the primary requirement for use of these polymers as part or all of a medical device is that the protein-based polymer must be sufficiently nontoxic, that is, it must exhibit adequate biocompatibility. As representative polymers for each of the interesting physical states, each of the above three compositions has been thoroughly examined by the standard set of 11 tests recommended by the American Society for the Testing of Materials (ASTM) for materials in contact with tissue, tissue fluids, and blood. 

Table 6 shows that the surface of polycarbonate with adsorbed serum albumin is the most suitable one to be used in implant devices. The behavior of all lipids toward blood-polymer interaction is not similar and may change depending on the nature of lipid, net charge of the lipid-adsorbed surface and the lipid-protein/ lipid-platelet interaction at the interface. Under conditions of high cholesterol concentrations addition of vitamin C leads to suitable surface characteristics of polycarbonate. The question is how to garantee the preferential the albumin adsorption on an implant surface In works of Malmsten and Lassen [123] competitive adsorption at hydrophobic surfaces from binary protein solutions was... 

ELRs are a promising model of biocompatible protein-based polymers. The basic structure of ELRs involves a repeating sequence based on the recurring sequences found in the mammalian elastic protein elastin [4]. As far as their properties are concerned, some of their main characteristics are derived from those of the natural protein. Elastin is an extracellular matrix protein that is present in aU vertebrate connective tissue. Its functions include the provision of elasticity and resilience to tissues, such as large elastic blood vessels (aorta), elastic ligaments, lung and skin, which are subjected to repetitive and reversible deformation [5, 6]. 

Proteins, natural polymers, polysaccharides, and surgars from foodstuffs and animal or plant secretions (albumin, starch, blood, sugars, resins, etc.). The polymeric, cross-linkable nature of these soils and their possible reactivity (with cellulose, for instance) makes them difficult to eliminate, for they can adhere strongly to porous textile surfaces and polymerize there. They can be removed by depolymerization with specific enzymes, together with the action of the other ingredients of the formulations (alkaline substances, surface-active agents). 

The direct demonstration of a surfactant film in the airways is relatively recent (2-4), although a surface-active film had been inferred from physiological (5) and electron microscopic studies (6) many years before. The surface tension in large airways has been measured directly with a bronchoscope from the spreading behavior of oil droplets placed onto the tracheal walls or bronchi of anesthetized sheep and horses (7,8). A surface tension of approximately 32 mN/m has been recorded at the mucus-air interface in these animals. This relatively low surface tension suggests the presence of a surface film in large airways, because proteins, surface polymers of blood cells, polysaccharides, and other biopolymers, all have... 

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