Computational Fluid Dynamics Simulation of Blood Clot Mechanical Deformation

Blood coagulation is the regulatory mechanism for preventing excessive blood loss at the site of an injury. However, coagulated blood cells and fibrous proteins can form blood clots that build up in the blood vessels. Blood clots that develop inside the blood vessels can cause heart attacks and strokes and are one of the leading causes of cardiovascular diseases. Existing clinical procedures for thrombolysis (breaking of blood clots) are limited due to ineffectiveness in breaking clots after the acute period immediately following formation of a clot and the safety concerns caused by significant risks of excessive bleeding with rigorous treatments. High-intensity focused ultrasound (HIFU) is being investigated experimentally as a non-invasive treatment option for thrombolysis¹. Our experimental collaborators have shown promising ability to lyse clots of various sizes and ages by incorporating lipid nanobubbles, which cavitate upon exposure to focused ultrasound waves, into the HIFU treatment modality². The contents of the nanobubbles vaporize at lower temperatures and lower ultrasound power ratings than are normally required for thrombolysis with HIFU alone. To better understand the effects of process parameters on the extent of clot lysis, we seek to develop a computational model. We anticipate that the model will be a tool for design of experiments and an in silico platform for accelerating the determination of the optimal treatment dose of the nanobubbles to maximize therapeutic clot lysis. In any thrombolysis technique, mechanical properties of blood clots play a crucial role in the effectiveness of the treatment. Thus, the objective of the research to be presented is to develop a computational fluid dynamics simulation for the mechanical deformation of a blood clot in a blood vessel using the three-dimensional modeling software COMSOL Multiphysics. We aim to accomplish this objective by incorporating laminar flow characteristic of physiological conditions and fluid-structure interactions between the fluid and the deformable surface of the blood clot. Solid structure is applied to the blood clot, the fluid domain represents the blood flow, and a set of equations generates a smooth extension of the mesh deformation from the clot into the blood domain. This interface assists in solving for the flow patterns in a continuously deforming geometry using the arbitrary Lagrangian-Eulerian technique³. The ALE method is the framework for the clot deformation analysis and the moving boundaries within the grid.  In future work, we aim to incorporate acoustics and nanobubble cavitation effects into the simulation and compare to the experimental data for the nanobubble-HIFU blood clot breakage system.

References:

1.  Maxwell AD, Cain CA, Durya AP, Yuan LQ, Gurm HS, Xu Z. Noninvasive thrombolysis using pulsed ultrasound cavitation therapy - histotripsy, Ultrasound in Med Biol, 2009; 35:12, 1982-1994, 2009. 
2.  Maples D, Newhardt R, Ranjan A. Novel ultrasound imageable low temperature sensitive liposomes for use with ultrasound-guided high intensity focused ultrasound. Soc Thermal Med Annu Meeting. 2014.
3.  COMSOL Application Gallery. Fluid-Structure Interaction. http://www.comsol.com/model/fluid-structure-interaction-361