Interaction blood-foreign material

Horbett, T. A., Frinciples underlying the role of adsorbed plasma proteins in blood interactions with foreign materials. Cardiovasc. Pathol. 2,137S-148S (1993). 

Table II. Blood-Foreign Material Interactions Some Conventional Wisdom and Some Unresolved Hypotheses...

Protein adsorption comprises the initial interaction of a foreign material with blood. 

During blood contact with any foreign material, several components in the blood are activated through a variety of enzymatic and cellular processes. In the setting of chronic hemodialysis with up to 15 h of weekly blood—material interactions, the immune system, in particular, appears to be in a constantly activated, inflammatory state. Some have su ested the high incidence of infection and septicemia in these patients is due, in part, to the activated immune system s inability to adequately respond to microbial pathogens. Therefore, the search for more biocompatible materials for hemodialysis and hemoperfusion is of great importance. 

Bioinert materials are materials tliat do not release any substances that are, for example, toxic or inflammatory and do not trigger a material-tissue interaction. In the case of a blood-contacting foreign material this means that the blood components do not recognize the artificial surface as artificial and thus do not initiate a foreign body reaction [41,57]. 

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. 

It is a widely accepted fact that protein adsorption is the first event that occurs upon foreign surface-blood contact. Human albumin (Alb) is the most abundant protein in the body with a concentration of 35-53 mg/mL in blood plasma. Due to its high concentration and low molecular weight, it is the first protein that adsorbs on the surface of implanted materials. Unlike fibrinogen, albumin is not known to have a peptide sequence that can facilitate binding of the platelet receptors and hence has been used as a coating to block non-specific platelet-surface interactions. 

As we will show, biocompatibility of a device can be approached from two perspectives. This is most clearly established in a discussion of how blood or plasma interacts with a foreign body. We can approach a project with the goal of allowing the body to react to the device and encapsulate it by a natural process, or alternatively, adopt a strategy to make the material as transparent as possible. Both techniques have been used with some degree of success. It is testimony to the versatility of polyurethanes that either approach can be accomplished with a simple change in the polyol. 

A wide number and great variety of clinically important cardiovascular implants and devises exist. Some (e.g., catheters) may only contact the blood once, and for a relatively short time others (e.g., kidney dialyzers and blood oxygenators) may be exposed to blood for hours, while tissue implants (e.g., heart valves and vascular grafts) will hopefully last for years, or the lifetime of the patient. All of these implants nd devices contain materials that are recognized by blood as foreign the result is a process of thrombosis often followed by formation of thromboemboli. This process generally involves a sequence of protein adsorption steps followed by blood cell interactions (especially involving platelets). 

The foreign body reaction occurring around soft tissue implants and thrombosis on surfaces in contact with blood are the major reactions encountered with implants. Both reactions involve the interaction of cells with the implant, especially in the later stages, and much previous study has therefore emphasized cellular events in the biocompatibility process. However, cells encounter foreign polymer implants under conditions that ensure the prior adsorption of a layer of protein to the polymer interface. The properties of the adsorbed layer are therefore important in mediating cellular response to the material. 

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