Adsorption of Plasminogen to Glass and Polyurethane Surfaces K. A. WOODHOUSE, P. W. WOJCIECHOWSKI, J. P. SANTERRE, AND J. L. BRASH ~ Departments of Chemical Engineering and Pathology, McMaster University, Hamilton, Ontario, Canada Received August 14, 1991; accepted December 4, 1991 The adsorption of plasminogen,the principal protein of the fibrinolyticpathway 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 fibfinolyticsurface for blood-contactingapplications. Our approach is to create a material that will selectivelyadsorb plasminogen from blood by incorporating lysine residues (known to bind plasminogen)into the surface. Lysine-containing polyurethaneswere 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-derivatizedpolyurethanes 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 polyurethaneswere fit to an "irreversible" Langmuir model. The two polyurethanesdiffered 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, Pm,~, 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 Pmax 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 Academic Press, Inc. INTRODUCTION The major complication limiting the use- fulness of biomaterials in blood-contacting implants is the activation of coagulation and platelets resulting in thrombus formation at the surface (1-4). While blood-material in- teractions result in other serious problems, in- cluding complement activation, thrombocy- topenia, and calcification, coagulation and thrombotic events remain the major concern (1-4). The mechanism of thrombosis on sur- faces has been extensively studied and adsorp- tion of proteins is implicated as an important early event (3). 1To whom correspondence should be addressed. 0021-9797/92 $5.00 Copyright © 1992 by Academic Press, Inc. All rights of reproduction in any form reserved. The work described in this paper is con- cerned with plasminogen, a plasma protein not previously studied in detail relative to blood interactions with artificial surfaces. Plasmin- ogen is the primary proenzyme of the fibri- nolytic system, the function of which is to dis- solve clots when they are no longer required. Plasminogen is composed of a single polypep- tide chain containing 791 amino acids. It also contains approximately 2% carbohydrate, which contributes to the heterogeneity of the molecule (5-9). Plasminogen binds to fibrin, to the extracellular matrix, and to cell surfaces via sites within the molecule which interact specifically with the amino acid lysine (10, 1 1 ). It is converted to its enzymatic form, plasmin, by cleavage of the Arg-Val peptide 60 .hmrnal of Colloid and Interface Science, Vol. 152, No. 1, August 1992