Compressive mechanical properties of the intraluminal thrombus in abdominal aortic aneurysms and fibrin-based thrombus mimics

Abstract

An intraluminal thrombus (ILT) forms in the majority of abdominal aortic aneurysms (AAAs). While the ILT has traditionally been perceived as a byproduct of aneurysmal disease, the mechanical environment within the ILT may contribute to the degeneration of the aortic wall by affecting biological events of cells embedded within the ILT. In this study, the drained secant modulus (E 5 ∼ modulus at 5% strain) of ILT specimens (luminal, medial, and abluminal) procured from elective open repair was measured and compared using unconfined compression. Five groups of fibrin-based thrombus mimics were also synthesized by mixing various combinations of fibrinogen, thrombin, and calcium. Drained secant moduli were compared to determine the effect of the components' concentrations on mimic stiffness. The stiffness of the mimics was also compared to the native ILT. Preliminary data on the water content of the ILT layers and mimics was measured. It was found that the abluminal layer (E 5 = 19.3 kPa) is stiffer than the medial (2.49 kPa) and luminal (1.54 kPa) layers, both of which are statistically similar. E 5 of the mimics (0.63, 0.22, 0.23, 0.87, and 2.54 kPa) is dependent on the concentration of all three components: E 5 decreases with a decrease in fibrinogen (60 to 20 and 20 to 15 mg/ml) and a decrease in thrombin (3 to 0.3 units/ml), and E 5 increases with a decrease in calcium (0.1 to 0.01 M). E 5 from two of the mimics were not statistically different than the medial and luminal layers of ILT. A thrombus mimic with similar biochemical components, structure, and mechanical properties as native ILT would provide an appropriate test medium for AAA mechanobiology studies.

Biochemomechanics of Intraluminal Thrombus in Abdominal Aortic Aneurysms

“…Interestingly, they noted significant differences in the predicted mechanical behavior when comparing results from the biaxial and prior uniaxial results, highlighting the importance of appropriate protocols when formulating constitutive relations. Indeed, although tests are usually designed to explore tensile behavior, Ashton et al [46] used unconfined compression tests to calculate a drained secant modulus at 5% strain for all three layers. Interestingly, they reported significantly higher compressive stiffness for abluminal than for medial and luminal layers, a gradient opposite that observed in most tensile tests.…”

“…It is generally devoid of intact erythrocytes and only rarely has infiltrating leukocytes despite a dense fibrin network. The abluminal layer is distinguished by its location adjacent to the aortic wall in thick ILTs, a brown discoloration, lack of cells, degraded fibrin network, and weak gelatinous material with high compressive stiffness [46,53]. Its interface with the aneurysmal wall may exist as a liquid interphase with high levels of soluble proteins [37].…”

Endovascular Repair of Abdominal Aortic Aneurysm: Follow-up with Noninvasive Vascular Elastography in a Canine Model

“…Fresh thrombi, regions of immature structuring, displayed lower strain values than solid thrombi and higher strain values than endoleaks. Reported strain results may be used to identify specific aneurysm regions and possibly follow aneurysm healing with time (27)(28)(29). Indeed, characterization of thrombus organization has been presented as a new concept of follow-up with MR imaging (30,31).…”

Impact of calcifications on patient-specific wall stress analysis of abdominal aortic aneurysms

“…According to experimental data in Wang et al (2001) and Van de Geest et al (2006b), c 1 is set to 18.0 k Pa. β = 4.5 is used to simulate a nearly incompressible material behavior. As distinct ILT layers (luminal, medial and abluminal layers; Ashton et al 2009) cannot be captured from CT images, homogeneous ILT material is assumed.…”