(B-53) Investigating Shear Induced Coagulation via Thromboelastography

Introduction::
Thromboelastography (TEG) is a clinical assay used to evaluate blood coagulation. TEG mechanically agitates whole blood to mimic physiological shear stresses in veinous blood. This, along with the addition of kaolin to the sample, activates the intrinsic coagulation pathway. TEG calculates key parameters that are used to assess the sample: R (clot formation time), K (kinetics, or time for the clot to reach a certain strength indicative of fibrinogen activity), a angle (a proxy metric of fibrinogen activity), and maximum amplitude, MA, a metric of clot strength. TEG is used clinically for diagnosis and monitoring of cardiovascular disease, primarily in emergency care, surgery, and postoperative care. TEG provides detailed descriptions of whole blood activity that could also be valuable for basic and applied research. Here, we used TEG to investigate shear induced coagulation in a microfluidic device designed to generate high shear conditions. TEG data in this context could be used to better understand the relationship between fluid shear and whole blood clotting kinetics. which is necessary for design improvements to Mechanical Circulatory Support Devices (MCSD). Additionally, TEG has the potential to be used for bench-top evaluation of thrombogenicity which has the potential aid in device development and pre-clinical testing.




Materials and Methods::
A microfluidic device designed to apply a high shear rate to flowing blood was fabricated. The device consisted of a stainless-steel tube 0.43mm in diameter and 30mm in length. Both ends of the device were attached to 1/8” tygon tubing, and the two ends were attached to a syringe pump and a blood bag, respectively. The syringe pump was used to pass 50mL of citrated whole bovine blood through the device at 100mL/min, corresponding to a shear rate of 60,000 1/s, in a reciprocating fashion so that blood may is exposed to multiple passes. This is done to simulate the experience of blood repeatedly passing through the circulatory system, and because the effect from a single pass is normally below the detection limits of most systems




Blood samples were collected prior to shear exposure (referred to as 0 passes), after 60 passes through the device, and again after 100 passes. After collection, samples were tested with the citrated kaolin TEG assay using the TEG 5000 hemostasis analyzer system and following the Haemonetics protocol. After the TEG assay, data regarding the R (clot formation time), K (clot growth time and fibrinogen activity), angle (fibrinogen activity), and MA (clot strength) values were recorded for each sample and then analyzed using an ANOVA test.




Results, Conclusions, and Discussions::
Figure 1 shows the results from the TEG analysis. There was a decrease in MA with increased exposure to a high shear rate. Additionally, a significant increase in K was observed (p< 0.05). These results indicate that as exposure to shear rate increases, fibrinogen activity within the blood also increases, however resulting clots are weaker. The trend towards a decrease in R with increased exposure to a high shear rate was also observed, suggesting that prolonged exposure to a high shear rate increases the rate of platelets activation and clot formation. These results demonstrate the capability of TEG to effectively evaluate shear induced platelet activation. TEG characterizes the mechanics and kinetics of coagulation in detail and has powerful applicability for further basic and applied research in biofluid mechanics.




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