Blood interactions with foreign surfaces

An important factor in the interaction of foreign surfaces with blood is the rapid adsorption of plasma proteins onto such surfaces when they are exposed to blood (4). For this reason the adsorption of radioactively tagged blood components on heparinized and unheparinized surfaces was measured. Proteins were dissolved in approximate physiological concentrations in a buffered (pH 7.35) physiological saline solution and the solutions were exposed to the test surfaces for 2 hours at 37 °C. in a static system. After the exposure, the surfaces were rinsed with physiological saline and distilled water and then dried. The amount of protein on the surfaces was determined in a 27r-gas flow proportional counter (7). As shown in Table III, although both heparinized surfaces were nonthrombogenic, there is no consistent pattern of either increased or decreased adsorption of the proteins caused by the heparinization. In-... 

Polytetrafluoroethylene, polyurethanes, polyethylene, silicones and acrylates have been proposed for replacement of both hard and soft tissues. These biomaterials must satisfy two in5)ortant criteria to provide an useful function in a biological environment they should possess the proper physical characteristics as replacement materials and should exhibit compatible interfacial properties with surroimding tissues and fluids. The interaction of blood with foreign surfaces resulting in thrombogenesis has received considerable attention, but still represents a problem. 

As shown above, detailed knowledge of the interactions of blood with foreign surfaces and the significance of these reactions to overall blood compatibility is, as yet, incomplete. As a result, research directed toward improved materials has been hindered. 

Adsorption of proteins is the primary event upon contact between blood and foreign surfaces (I), and subsequent cellular interactions leading to thrombus formation are determined by these adsorbed proteins (2). Much of the early work on the study of adsorption was done in buffered solutions of single proteins or relatively simple mixtures (3-7). More recently, studies have been conducted using more realistic media, particularly plasma (8,9). These studies have shown that the plasma interacts subsequently with the initially adsorbed proteins, causing some unexpected effects. For example, initially adsorbed fibrinogen is desorbed rapidly from several surfaces in the presence of plasma (3). 

The adsorption of proteins is the first interaction which occurs when a foreign surface comes in contact with blood. The processes which then lead to hemostasis are attachment of cellular elements to the surface, platelet adhesion and release, and triggering of the blood coagulation cascade. Investigations of interactions of proteins at the interface, which are the primary steps in blood clotting and determine whether it will occur, are hence of fundamental importance. 

The polyurethanes are the potentially hemocompatible polymers towards which we spent most of our efforts, as in several other laboratories in the world . The synthesis of these polymers aims to produce an elastomer with a surface that could react as little as possible with the proteins of the blood. These polymers are characterized by the insertion of a lot of different functional groups in their main chains in such a way to create a surface able to interact with the proteins mostly by Van der Waals forces in this way, probably, the main component of the resultant force field is of the dispersion type and its intensity fluctuates as a function of locus. Under these conditions, it can be expected that plasma proteins placed in such a force field will be in an energetically unstable state and so, probably, they are not inclined to interact with the foreign surface through an irreversible attachement. ... 

The adsorption of proteins on solid surfaces is an important phenomenon taking place as soon as a foreign material is brought into contact with a biological system. It is thus involved in situations of bio- and blood compatibility and in fouling in the process industry. Furthermore, there are several surface orientated diagnostic methods based on protein adsorption and interaction on solid surfaces. Proteins are large and complicated molecules and the adsorption process is therefore far from simple to model. 

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