Review of Mechanical Testing and Modelling of Thrombus Material for Vascular Implant and Device Design

Abstract

A thrombus or blood clot is a solid mass, made up of a network of fibrin, platelets and other blood components. Blood clots can form through various pathways, for example as a result of exposed tissue factor from vascular injury, as a result of low flow/stasis, or in very high shear flow conditions. Embolization of cardiac or vascular originating blood clots, causing an occlusion of the neurovasculature, is the major cause of stroke and accounts for 85% of all stroke. With mechanical thrombectomy emerging as the new standard of care in the treatment of acute ischemic stroke (AIS), the need to generate a better understanding of the biomechanical properties and material behaviour of thrombus material has never been greater, as it could have many potential benefits for the analysis and performance of these treatment devices. Defining the material properties of a thrombus has obvious implications for the development of these treatment devices. However, to-date this definition has not been adequately established. While some experimentation has been performed, model development has been extremely limited. This paper reviews the previous literature on mechanical testing of thrombus material. It also explores the use of various constitutive and computational models to model thrombus formation and material behaviour.

A Whole Blood Thrombus Mimic: Constitutive Behavior Under Simple Shear

“…Additionally, thrombus testing methods have varied, employing uniaxial tensile and compressive testing, planar biaxial testing, nanoindendation, small and large angle shear rheometry, and now simple shear (this publication). For a comprehensive review of the thrombus mechanics literature please see Johnson et al and the works cited therein (Johnson et al, 2017). Interestingly, van Oosten et al have argued that it is the densely-packed cellular ele-ments in thrombus that may render it non-shear stiffening.…”

“…The latter outcome is the most catastrophic leading to approximately 100,000 deaths every year in the US alone according to the CDC (Beckman et al, 2010). The deformation, fracture, and eventual embolization of thrombus are inherently mechanical processes (Basmadjian, 1989;Johnson et al, 2017). Thus, the mechanics of thrombus, and venous thrombus in particular, has been of immense interest.…”

Bileaflet Prosthesis Design and Orientation Affect Fluid Shear, Residence Time, and Thrombus Formation

“…The absence of red blood cells gives rise to a white thrombus that is stiffer and possesses a higher coefficient of friction than red thrombi. 6,7 Shear Exposure Depends on Mitral MHV Design and Orientation Previous studies have found the mitral inflow jet is altered for MHV recipients and is highly dependent on the geometry of the prosthesis. 8,9 In the authors' laboratory, the velocity field of a dilated left ventricle (LV) model was measured in a mock cardiovascular loop for different mitral prostheses and used to characterize the blood residence time (TR) and platelet shear activation potential (SAP) based on the cumulative exposure to shear.…”

Quantifying Embolism: Label‐Free Volumetric Mapping of Thrombus Structure and Kinesis in a Microfluidic System with Optical Holography

“…The spontaneous embolism of a thrombus especially in acute coronary events may be a natural protective mechanism against infarction in organs [43] . Past studies have focused on individual platelet behaviour and more recently, there has been new interest in investigating factors related to thrombus stability that are able to be correlated with acute coronary events.…”