PLATELET PROCOAGULANT SURFACE AS AN ESSENTIAL PARAMETER FOR THE IN-VITRO EVALUATION OF THE BLOOD COMPATIBILITY OF POLYMERS

Thrombus formation at an artificial surface in contact with blood is t he result of the interplay of two tightly linked biological systems, n amely blood platelets and blood coagulation. While initiation of the o verall process is thought to originate from proenzyme-enzyme conversio ns at the artificial surface, propagation of the process is only possi ble when a suitable phospholipid surface is available. The outer leafl et of the plasma membrane of activated platelets is such a surface; it contains negatively charged phospholipids which are normally present in the inner leaflet of the membrane. An examination of the thrombogen icity of materials, therefore, should include a quantitative assay for procoagulant sites at an artificial surface. In the present study we have evaluated polymers, exposed to platelet-rich plasma, for their pr ocoagulant properties by using two sets of assays. With the one set, m arkers of blood coagulation were assayed (recalcification time of plat elet rich plasma and kallikrein-C1-Inhibiter complex formation) and wi th the other set the surfaces were analysed for platelet adherence and procoagulant sites utilising annexin V, which has a high affinity for negatively charged phopholipids. For the polymers, the fastest rate o f contact activation, as determined from kallikrein-C1-inhibitor gener ation, was found with polyethylene. in spite of that, the conventional partial thromboplastin time (PTT) could not reveal differences betwee n the various materials. However, when clotting was performed with pla telet-rich plasma, it was found that the polymers differed significant ly in their clot promoting activities. The shortest clotting time (5 m in) was found with polyethylene (PE), and polyvinyl chloride (PVC) gav e the longest clotting time (10 min). These findings closely correlate d with the amount of procoagulant sites generated at the platelet-rich plasma-polymer interface.