Catalytic efficiency of a thrombomodulin-functionalized membrane-mimetic film in a flow model

The protein C anticoagulant pathway generates an on demand physiologic anticoagulant response, which is initiated when thrombin binds to thrombomodulin (TM), a transmembrane protein constitutively expressed by endothelial cells. A stable, protein C activating membrane-mimetic film was produced on a polyelectrolyte multilayer (PEM) by in situ photopolymerization of a phospholipid assembly containing TM. The monoacrylated phospholipid monomer was initially synthesized and prepared as unilamellar vesicles with varying molar concentrations of TM. Membrane-mimetic films were constructed on planar substrates with defined surface concentrations of catalytically active TM. I-125-labeled radiolabeling demonstrated little change in TM surface concentration over periods of up to 4 weeks. We utilized a parallel plate flow system to investigate the effects of simulated arterial (500 s(-1)) and venous (50 s(-1)) shear rates and TM surface concentration (0-1400 fmol cm(-2)) on the rate and extent of activation of protein C. The rate of production of activated protein C increased with shear rate and TM surface content. However, in agreement with an analysis of reaction kinetics and mass transfer, 2 experimental results demonstrate that reaction rates become saturated at TM surface densities greater than or equal to 800 fmol cm(-2). We believe that the design of membrane-mimetic films that have the capacity to activate the protein C pathway will provide a useful strategy for generating actively antithrombogenic surfaces. (c) 2005 Elsevier Ltd. All rights reserved.