ADSORPTION OF PLASMINOGEN TO GLASS AND POLYURETHANE SURFACES

The adsorption of plasminogen, the principal protein of the fibrinolytic pathway in blood, to a number of solid surfaces has been investigated. This study forms part of a larger project, the objective of which is to develop a fibrinolytic surface for blood-contacting applications. Our approach is to create a material that will selectively adsorb plasminogen from blood by incorporating lysine residues (known to bind plasminogen) into the surface. Lysine-containing polyurethanes were used for this purpose. In the present work the adsorption of plasminogen to these surfaces as well as to glass, "conventional" polyurethanes, and precursor sulfonated polyurethanes was investigated. Adsorption from isotonic Tris buffer, pH 7.4, was measured under static conditions at room temperature using radioiodinated plasminogen. Most of the surfaces except glass reached isotherm plateaux at about 0.1 mg/ml solution concentration. The sulfonated and lysine-derivatized polyurethanes showed higher adsorption capacities than any of the other surfaces but there appeared to be little difference in either capacity or apparent binding affinity between corresponding "lysinated" and sulfonated materials. The adsorption data for glass and the two conventional polyurethanes were fit to an "irreversible" Langmuir model. The two polyurethanes differed by chain extender, one being based on methylene dianiline (MDA), the other on ethylene diamine (ED). A computer simulation was used to account for mass transfer effects in the cylindrical geometry of the experiment. Two parameters, Γmax, the maximum adsorption, and k, the rate constant for adsorption, were estimated for the three surfaces. Monolayer adsorption on glass appears to be about half that on MDA, while on ED it is intermediate between glass and MDA and the residual error is much larger. The Γmax values suggest that plasminogen attains a more spread conformation on glass than on MDA, assuming that both surfaces are equally smooth. The rate constant is also highest for the MDA surface, intermediate for the ED-based polyurethane, and lowest for glass. © 1992.