Surface Grafts Involving Proteins

Two additional application areas of surface graft copolymers include (1) the use of heparinized surfaces to reduce thrombosis in surgical implants, and (2) the use of immobilized enzymes as catalysts. 

Heparin, a natural protein, is an important constituent of blood and contributes to blood clotting. When circulatory assist devices were first proposed, it was found that the artificial surfaces promoted unnatural thrombosis. An important proposed solution to the problem involved grafting heparin to the surfaces of the materials involved, including such polymers as poly(vinyl chloride) and poly(dimethyl siloxane) (Artificial Heart Program, 1968 Lyman, 1966 Sears, 1965). 

The grafting of several enzymes to surfaces has also found application in the form of biologically based catalysts (Carbonell and Kostin, 1972  

1968 Messing and Weetall, 1970 Silman and Katchalski, 1966). In this application the enzymes are immobilized on polymeric or inorganic solid support surfaces. The substrate to be reacted then is made to flow over the catalytic surface. The principal advantages include (1) The enzymes do not remain in the product as a difficultly separable impurity, (2) the enzymes may be reused, reducing cost, and (3) under certain conditions the useful life of the enzyme is prolonged. (Hasselberger et al, 1974.) 

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These infants with severe combined immunodeficiency are exquisitely susceptible to graft-versus-host disease which has been observed in them following administration of peripheral blood, fetal liver cells, or histoincom-patible bone marrow " The course of the reaction much resembles the disease of mice and is rapidly fatal in 10-14 days. It is characterized by fever, a maculopapular rash involving the volar surfaces, diarrhoea with protein-losing enteropathy and edema, haemolytic anaemia and thrombocytopenia. Haemorrhage into the gut or lung is usually the terminal event. Donor cells are most abundantly evident in the spleen and liver and less so in skin and kidney. Splenic enlargement resembles also the observation in mice and correlates with the severity of the reaction. 

Class 1 MHC molecules are integral membrane proteins found on the surface of all nucleated cells and platelets. They are the classical antigens involved in graft rejection. 

Plasma deposition has also been utilized to deposit PEO-like materials from volatile precursors onto a variety of subjects. This technique involves generating a reactive plasma containing PEO-like monomers, which polymerize and deposit, often with chemical grafting, onto any surface within the plasma. The availability of large-scale vacuum apparatus makes this technique feasible on an industrial scale. The materials deposited by this technique were often shown to contain only short PEO segments yet greatly reduced protein deposition was observed and the small amounts (ng/cm) that did deposit were easily eluted. ... 

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