Nonlinear Stiffness and Viscoelasticity of Inhibitor-Treated Blood Clots by Tensile Testing

Abstract

NONLINEAR STIFFNESS AND VISCOELASTICITY OF INHIBITOR-TREATED BLOOD CLOTS BY TENSILE TESTING by Wilson S. Eng Although blood clots are vital to wound healing, little is known about what factors influence clot stiffness and dynamic response. This work investigates the mechanics of inhibitor-treated clots by direct tensile testing using a custom designed system for forces below 1 N. Inhibitors that affect clot formation include blebbistatin, which affects myosin II movement on actin, and cytochalasin D, which affects actin polymerization. The hypothesis of this investigation is that blebbistatin will have a greater effect on mechanical behavior than cytochalasin D, because the inhibition of myosin II will weaken the overall clot more than actin. This hypothesis was investigated using clots that were treated with blebbistatin and cytochalasin, using untreated whole blood as a reference. Clots were tested from five different donors with at least two replicates from each donor. Each clot was subjected to an initial stretch ratio of 1.5 to measure nonlinear stiffness, followed by a series of 1 mm increments to record stress relaxation. At a stretch ratio of 1.5, blebbistatin-treated clots exhibited 4.3% lower tensile stress than cytochalasin-treated clots. The relaxation time constant for blebbistatin-treated clots was 10% faster than for cytochalasin-treated clots. This evidence supports the hypothesis about the role of myosin II in blood and introduces experimental methodology that can be extended to studies on mechanics of other soft biological tissues. v ACKNOWLEDGMENTS This work was supported in part by the Kordestani Endowment to the Charles W. Davidson College of Engineering at San José State University (SJSU) and in part by the AHA Institutional Research Enhancement Award (AIREA) program of the American Heart Association (Award Number 18AIREA33960524). I would like to thank Dr. Anand Ramasubramanian for providing background on the project and direction needed in testing blood clots. I would like to thank Dr. Amit Saha for his support with the specimen testing development. I would like to thank Dr. Sang-Joon (John) Lee for tirelessly providing guidance throughout the entire project and reviewing. I would like to thank members of the MEMS Lab at SJSU for help with fabrication and testing. Finally, I would like to thank my friends and family for their support. vi TABLE OF CONTENTS List of Tables .