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Non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus.

van Dam EA, Dams SD, Peters GW, Rutten MC, Schurink GW, Buth J, van de Vosse FN - Biomech Model Mechanobiol (2007)

Bottom Line: To describe the phenomena observed experimentally, a non-linear multimode model is presented.The parameters for this model are obtained by fitting this model successfully to the experiments.To determine the influence on the wall stress of the behavior observed the model proposed needs to implemented in the finite element wall stress analysis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Technische Universiteit Eindhoven, PO box 513, WH4.120, 5600 MB, Eindhoven, The Netherlands.

ABSTRACT
The objective of this work was to determine the linear and non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus and to study the changes in mechanical properties throughout the thickness of the thrombus. Samples are gathered from thrombi of seven patients. Linear viscoelastic data from oscillatory shear experiments show that the change of properties throughout the thrombus is different for each thrombus. Furthermore the variations found within one thrombus are of the same order of magnitude as the variation between patients. To study the non-linear regime, stress relaxation experiments are performed. To describe the phenomena observed experimentally, a non-linear multimode model is presented. The parameters for this model are obtained by fitting this model successfully to the experiments. The model cannot only describe the average stress response for all thrombus samples but also the highest and lowest stress responses. To determine the influence on the wall stress of the behavior observed the model proposed needs to implemented in the finite element wall stress analysis.

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ForceGap Test: The gap distance versus the normal force. When the gap distance is decreased, capillary forces will lead to a negative force. When the gap is decreased even further the force will rise through zero and the sample will be compressed. The sample thickness is taken equal to the smallest gap distance at which the normal force equals zero, in this case 0.5 mm
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Fig5: ForceGap Test: The gap distance versus the normal force. When the gap distance is decreased, capillary forces will lead to a negative force. When the gap is decreased even further the force will rise through zero and the sample will be compressed. The sample thickness is taken equal to the smallest gap distance at which the normal force equals zero, in this case 0.5 mm

Mentions: To avoid compression to be applied during the shear experiments, the exact thickness of each sample was determined. The gap between the plates needs to be equal to this thickness. To this end, the upper plate is positioned above the sample and is then lowered with a constant velocity, while measuring the normal force. A typical representation of this procedure, called the force gap test, is given in Fig. 5, where the normal force is plotted as a function of the gap width during the force gap test. Samples are saturated with PBS, which will form a layer of liquid on top of the sample. When the upper plate nearly contacts the fluid, capillary effects will cause a negative normal force. When the plate is lowered further and reaches the sample top, the normal force will have increased again to zero. Evidently, the normal force will increase rapidly when the upper plate is lowered even further and compresses the sample.


Non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus.

van Dam EA, Dams SD, Peters GW, Rutten MC, Schurink GW, Buth J, van de Vosse FN - Biomech Model Mechanobiol (2007)

ForceGap Test: The gap distance versus the normal force. When the gap distance is decreased, capillary forces will lead to a negative force. When the gap is decreased even further the force will rise through zero and the sample will be compressed. The sample thickness is taken equal to the smallest gap distance at which the normal force equals zero, in this case 0.5 mm
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2813187&req=5

Fig5: ForceGap Test: The gap distance versus the normal force. When the gap distance is decreased, capillary forces will lead to a negative force. When the gap is decreased even further the force will rise through zero and the sample will be compressed. The sample thickness is taken equal to the smallest gap distance at which the normal force equals zero, in this case 0.5 mm
Mentions: To avoid compression to be applied during the shear experiments, the exact thickness of each sample was determined. The gap between the plates needs to be equal to this thickness. To this end, the upper plate is positioned above the sample and is then lowered with a constant velocity, while measuring the normal force. A typical representation of this procedure, called the force gap test, is given in Fig. 5, where the normal force is plotted as a function of the gap width during the force gap test. Samples are saturated with PBS, which will form a layer of liquid on top of the sample. When the upper plate nearly contacts the fluid, capillary effects will cause a negative normal force. When the plate is lowered further and reaches the sample top, the normal force will have increased again to zero. Evidently, the normal force will increase rapidly when the upper plate is lowered even further and compresses the sample.

Bottom Line: To describe the phenomena observed experimentally, a non-linear multimode model is presented.The parameters for this model are obtained by fitting this model successfully to the experiments.To determine the influence on the wall stress of the behavior observed the model proposed needs to implemented in the finite element wall stress analysis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Technische Universiteit Eindhoven, PO box 513, WH4.120, 5600 MB, Eindhoven, The Netherlands.

ABSTRACT
The objective of this work was to determine the linear and non-linear viscoelastic behavior of abdominal aortic aneurysm thrombus and to study the changes in mechanical properties throughout the thickness of the thrombus. Samples are gathered from thrombi of seven patients. Linear viscoelastic data from oscillatory shear experiments show that the change of properties throughout the thrombus is different for each thrombus. Furthermore the variations found within one thrombus are of the same order of magnitude as the variation between patients. To study the non-linear regime, stress relaxation experiments are performed. To describe the phenomena observed experimentally, a non-linear multimode model is presented. The parameters for this model are obtained by fitting this model successfully to the experiments. The model cannot only describe the average stress response for all thrombus samples but also the highest and lowest stress responses. To determine the influence on the wall stress of the behavior observed the model proposed needs to implemented in the finite element wall stress analysis.

Show MeSH
Related in: MedlinePlus