| Description |
The elevated shear force caused by anastomotic stenosis is a common complication at the blood vessel-vascular implant interface. The majority of previous studies investigated the platelet function at the sites of stenosis while the priming effects of transient platelet exposure to elevated shear forces and subsequent downstream events occurring under lower shear forces were largely ignored. It is not known how long these priming effects persist downstream and how antiplatelet agents interact with platelets to minimize these effects. In this dissertation, microfluidic methods were developed to determine how effective upstream shear forces are in priming of platelets for downstream adhesion and activation. The flow system was designed to mimic a vascular implant with upstream stenotic anastomosis and downstream procoagulant surface or exposed subendothelium. Following transient exposure to an elevated upstream shear force, downstream platelet response was measured by a surface-capture assay, flow cytometry, and a lactate dehydrogenase assay. It was demonstrated that the flow system is capable of determining the downstream platelet response to a variable upstream shear force equivalent to moderate to severe stenosis. Platelet adhesion was characterized at varying periods of post-stenotic flow to investigate how long the priming response of platelets persists downstream. It was found that upstream stenosis increases the propensity for adhesion to platelet binding protein fibrinogen in a time-dependent manner. Several antiplatelet agents were evaluated iv for their efficacy in mitigating downstream platelet response after upstream priming. It was demonstrated that the microfluidic flow system can be used to screen antiplatelet agents in vitro for suppressing shear-induced platelet adhesion and activation. Here, the evidence was provided that upstream stenosed geometries result in altered fluid mechanical conditions that promote priming of platelets for enhanced downstream adhesion and activation. The findings are relevant to understanding the mechanisms of thrombus formation in the post-stenotic regions of vascular implants. The microfluidic flow system could be further utilized to explore platelet response to a variety of surface coatings and biomaterials under different flow conditions and antiplatelet therapy. |
