INTERACTIONS BETWEEN ADSORBED BLOOD-CLOTTING FACTORS PROBED AT THE NANOMETER-SCALE USING THE SURFACE FORCE APPARATUS

Understanding the interfacial interactions involved in the blood-clotting cascade is fundamental to the design of non-thrombogenic materials. In this study, blood plasma components have been deposited on to molecularly smooth mica surfaces by physisorption from solution and their interactions directly measured using the surface force apparatus. This technique allows the distance dependence of the intermolecular forces operating between macroscopic surfaces to be ascertained at nanometre resolution. The interactions between surfaces bearing the blood protein thrombin have been investigated and the effect of the glycosaminoglycan heparin on these surfaces has been quantified. Thrombin is shown to adsorb on the mica surface from solution giving rise to uncharged, compressible layers which exceed the dimensions expected for monolayer coverage. These layers partially desorb following a secondary incubation with heparin, giving rise to considerably thinner layers which exhibit an electrostatically repulsive nature. These results provide insights into the importance of non-specific interfacial interactions in the prevention of blood clotting.