A complex web of biochemical and physical reactions of between platelets and coagulation factors at the site of vascular injury are required to achieve hemostasis. Under flow conditions, platelet activation and the coagulation processes are dynamically intertwined with one another affected by platelets, coagulation factors, and their various inhibitors and activators.
The AR chip has an 80 µm thick flow chamber coated with both collagen and thromboplastin (tissue factor). Blood flow is maintained at 600/s mimicking in vivo blood flow through large arteries.
Anticoagulated whole blood is perfused at physiologic temperatures at a constant rate through the flow chamber coated with tissue factor and collagen. As coagulation and platelet activation progresses and begins forming a thrombus, the pressure required to move the blood at the given shear rate increases. These pressure changes are monitored by a pressure sensor upstream of the chamber.
A distinct advantage of using a flow chamber system for the measurement of thrombus formation is the correlation with the in vivo thrombus formation process. Scanning electron micrographs (SEM) of thrombi inside the AR chip show that thrombi formed within the microchip capillary under flow conditions were tightly packed and contained numerous activated platelets. In contrast, thrombi formed under static conditions were mainly composed of erythrocytes and fibrin fibers.
Platelets adhere and aggregate on the surface of the tissue-factor and collagen coated capillary of the AR chip as the blood is moved through the analytical path of the T-TAS®01. The aggregate gradually increases in size as the activated platelets bind additional platelets and fibrin strands in the region occluding the path. This will result in an increase in flow pressure needed to maintain a steady flow-rate, which is measured by the T-TAS®01. The changes in the flow pressure pattern reflect the formation processes of the platelet plug.
The Occlusion Start Time (OST) is the lag time for the flow pressure to reach 10 kPa due to partial occlusion of the capillary.
The Occlusion Time (OT) is the time needed to increase pressure to 60 kPa above baseline owing to near or complete occlusion of the capillary.
The Area Under the Curve (AUC) is the number derived from the area under the flow-vs-time and is related to the overall thrombus formation. A low value could indicate low thrombus formation potential of the sample.
Dabigatran (direct thrombin inhibitor) or Rivaroxaban (Factor Xa inhibitor) was spiked to healthy blood in the presence or absence of aspirin and a P2Y12 inhibitor (AR-C66096). AUC and OT varied in a dose-dependent matter.
The AR chip is stable for ~18 months from manufacturer and until the day listed on the label when stored at 4oC. Once removed from the sealed pouch, the AR chip should be used as soon as possible.