Surface modification with PEG and hirudin for protein resistance and thrombin neutralization in blood contact

In this work, we hypothesize that a surface modified with both polyethylene glycol (PEG) and hirudin may provide a non-fouling, thrombin-neutralizing surface suitable for blood contacting applications. With gold as a model substrate we used two different approaches to the preparation of such a surface: (1) a "direct" method in which PEG was conjugated to hirudin and the conjugate was then immobilized on the gold; (2) a "sequential" method in which PEG was immobilized on the gold and hirudin then attached to the immobilized PEG. The surfaces were characterized by water contact angle, ellipsometry and XPS. The biological properties were investigated by measuring protein adsorption (fibrinogen and thrombin) from buffer and plasma; thrombin inhibition was measured using a chromogenic substrate assay. Hirudin immobilization was found to be more efficient on surfaces prepared by the "direct" method. "Sequential" surfaces, however, despite having a lower density of hirudin, showed greater biological activity (thrombin binding and inhibition).