The lack of knowledge of the mechanisms underlying the reactions of blood with polymeric biomaterials continues to be an obstacle to the design of better materials for use in contact with blood. Our hypothesis about these mechanisms can be stated generally as follows: a specific materials variable causes changes in the adsorbed protein layer that are responsible for changes in platelet adhesion and/or activation. For certain polyurethanes (PEUs), important specific materials variables are thought to be the alkyl chain length and density and the degree of surface enrichment of the fluorocarbon (FC) groups in FC PEUs. A systematic study of the effect of these materials variables on protein and platelet interactions will contribute to better understanding of blood reactivity with polymers.
The specific aims are as follows: 1. The role of the adsorbed adhesion proteins fibrinogen, von Willebrand factor, fibronectin, and vitronectin in causing platelet activation will be determined using plasmas selectively deficient in the protein and a series of PEUs interacting with platelets under flow. Platelet activation will be characterized by measuring the ability of the adherent platelets to participate in platelet-platelet aggregate formation, the conversion of the platelets to the procoagulant state, and in situ measurement of intracellular calcium mobilization in platelets adhering under flow conditions. Dose-response studies of the effect of restoration of the deficient factors will also be done. 2. To test the hypothesis that the platelet activation by biomaterials is a function of both the amount and the state of adsorbed fibrinogen on each type of substrate, the activation of platelets deposited from flowing suspensions will be compared to the total amount and platelet recognizable fraction of fibrinogen on a series of polyurethanes. The platelet recognizability of the adsorbed fibrinogen will be characterized using monoclonal antibodies that bind to each of the putative platelet binding domains of fibrinogen. 3. A series of specially made polyurethanes (PEUs) with variations in chemical composition that should affect the adsorption and the biologic activity of the adhesion proteins and albumin will be used to test our mechanistic material hypotheses. PEUs with differences in side chain length, chain density, and chain type (CH2 or CF2) will be used. PEUs exhibiting low platelet adhesion despite the presence of relatively high amounts of adsorbed fibrinogen will be studied in greater depth, since we believe understanding of the mechanisms by which fibrinogen's biological activity is altered by these materials can contribute to the intelligent design of improved biomaterials. Reference materials will be Biospan and NIH PE and PDMS.
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