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Research Papers

Comparative Analysis of the Biaxial Mechanical Behavior of Carotid Wall Tissue and Biological and Synthetic Materials Used for Carotid Patch Angioplasty

[+] Author and Article Information
Alexey V. Kamenskiy

Department of Mechanical & Materials Engineering,  University of Nebraska-Lincoln, Lincoln, NE 68588

Iraklis I. Pipinos, Jason N. MacTaggart

Department of Surgery,  University of Nebraska-Medical Center, Omaha, NE 68198

Syed A. Jaffar Kazmi

Department of Pathology and Microbiology,  University of Nebraska-Medical Center, Omaha, NE 68198

Yuris A. Dzenis1

Department of Mechanical & Materials Engineering, W317 Nebraska Hall,  University of Nebraska-Lincoln, Lincoln, NE 68588ydzenis@unl.edu

1

Correspondence and reprint requests to: Yuris A. Dzenis, Ph.D., Department of Mechanical and Materials Engineering, W317 Nebraska Hall, University of Nebraska-Lincoln, Lincoln, NE 68588-0526, e-mail: ydzenis@unl.edu

J Biomech Eng 133(11), 111008 (Dec 08, 2011) (10 pages) doi:10.1115/1.4005434 History: Received May 06, 2011; Revised November 03, 2011; Posted November 08, 2011; Published December 08, 2011; Online December 08, 2011

Patch angioplasty is the most common technique used for the performance of carotid endarterectomy. A large number of patching materials are available for use while new materials are being continuously developed. Surprisingly little is known about the mechanical properties of these materials and how these properties compare with those of the carotid artery wall. Mismatch of the mechanical properties can produce mechanical and hemodynamic effects that may compromise the long-term patency of the endarterectomized arterial segment. The aim of this paper was to systematically evaluate and compare the biaxial mechanical behavior of the most commonly used patching materials. We compared PTFE (n = 1), Dacron (n = 2), bovine pericardium (n = 10), autogenous greater saphenous vein (n = 10), and autogenous external jugular vein (n = 9) with the wall of the common carotid artery (n = 18). All patching materials were found to be significantly stiffer than the carotid wall in both the longitudinal and circumferential directions. Synthetic patches demonstrated the most mismatch in stiffness values and vein patches the least mismatch in stiffness values compared to those of the native carotid artery. All biological materials, including the carotid artery, demonstrated substantial nonlinearity, anisotropy, and variability; however, the behavior of biological and biologically-derived patches was both qualitatively and quantitatively different from the behavior of the carotid wall. The majority of carotid arteries tested were stiffer in the circumferential direction, while the opposite anisotropy was observed for all types of vein patches and bovine pericardium. The rates of increase in the nonlinear stiffness over the physiological stress range were also different for the carotid and patching materials. Several carotid wall samples exhibited reverse anisotropy compared to the average behavior of the carotid tissue. A similar characteristic was observed for two of 19 vein patches. The obtained results quantify, for the first time, significant mechanical dissimilarity of the currently available patching materials and the carotid artery. The results can be used as guidance for designing more efficient patches with mechanical properties resembling those of the carotid wall. The presented systematic comparative mechanical analysis of the existing patching materials provides valuable information for patch selection in the daily practice of carotid surgery and can be used in future clinical studies comparing the efficacy of different patches in the performance of carotid endarterectomy.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 4

Values and range of tangent elastic moduli in longitudinal and circumferential directions calculated for 40 kPa, 80 kPa and 110 kPa levels of stress for common carotid arteries (CCA), external jugular veins (EJV), greater saphenous veins (GSV) and two types of bovine pericardium (BP) patches (Synovis VG and Neovasc PP)

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Figure 2

CCA specimen attached to the soft-tissue biaxial device. Arrows represent directions of stretch.

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Figure 5

Anisotropy indexes A40,A80,A110 and their variations calculated for 40 kPa, 80 kPa and 110 kPa levels of stress respectively for common carotid arteries (CCA), external jugular veins (EJV), greater saphenous veins (GSV) and two types of bovine pericardium (BP) patches (Synovis VG and Neovasc PP)

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Figure 3

Equibiaxial stress-stretch response of CCA specimens in longitudinal and circumferential directions. Graphs were separated into two plots for better visualization.

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Figure 6

Anisotropy index Aint and its variability calculated for common carotid arteries (CCA), external jugular veins (EJV), greater saphenous veins (GSV) and two types of bovine pericardium (BP) patches (Synovis VG and Neovasc PP)

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Figure 1

Human CCA specimen prepared for biaxial testing

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Figure 7

Equibiaxial stress-stretch response of EJV specimens in longitudinal and circumferential directions

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Figure 8

Equibiaxial stress-stretch response of GSV specimens in longitudinal and circumferential directions

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Figure 9

Equibiaxial stress-stretch response of commercially available BP in longitudinal and circumferential directions

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Figure 10

Equibiaxial stress-stretch response of commercially available synthetic patches: Acuseal polytetrafluoroethylene (PTFE), knitted Hemacarotid (HC) and knitted Hemashield (HS) patches

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Figure 11

Mean stress-stretch curves calculated for all types of materials tested

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Figure 12

Standard deviations (plotted as mean and one standard deviation in each direction) of mechanical properties of the human CCAs and materials used as patches during carotid endarterectomy. Data are presented for two directions of stretch – longitudinal and circumferential.

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