Fibrinogen adsorption and platelet interactions on polymer membranes

The hemocompatibility of four different wettable polymer membranes, namely Cuprophan (CE), polyether-polycarbonate (PC-PE), polysulfone (PSU), and polyetherimide (PEI), was investigated with respect to fibrinogen (Fng) adsorption and platelet adhesion/activation. In order to estimate the polar and dispersion components of the surface free energy, contact angles using water/vapor and water/n-hexadecane systems were measured. Adsorption of fibrinogen was studied using fluorescence-labeled protein. The adsorption isotherms showed that the amount and the affinity of adsorbed Fng increased with decreasing surface wettability of the membranes, which correlates with the dispersion and polar components of the surface free energy. The conformational changes of adsorbed Fng were detected by measuring the difference between monoclonal antibody binding to the conformation-sensitive epitope in the D-domain and the binding of polyclonal anti-Fng antibody. The anticipated conformational/orientational changes were greater for PEI and PSU membranes (the least wettable membranes) and negligible for the more wettable PC-PE and CE membranes. In addition, a possible relationship with the degree of platelet activation was found, showing negligible platelet adhesion on PC-PE and CE, but high platelet adhesion on PEI and PSU. Furthermore, platelets were spread to a large extent on PEI, while the formation of aggregates was observed on PSU. This may correspond to the anticipated differences in the conformational state of Fng on both membranes.