Research Papers

Experimental Study of Anisotropic Stress/Strain Relationships of Aortic and Pulmonary Artery Homografts and Synthetic Vascular Grafts

[+] Author and Article Information
Yueqian Jia, Yangyang Qiao, Aung Maung, Jack Norfleet, Alain J. Kassab

Department of Mechanical and Aerospace Engineering,
College of Engineering and Computer Science,
University of Central Florida,
4000 Central Florida Boulevard,
Orlando, FL 32816

I. Ricardo Argueta-Morales

Cardiothoracic Surgery,
The Heart Center at Arnold Palmer Hospital for Children,
92 West Miller Street,
Orlando, FL 32806

Yuanli Bai

Department of Mechanical and Aerospace Engineering,
College of Engineering and Computer Science,
University of Central Florida,
4000 Central Florida Boulevard,
Orlando, FL 32816
e-mail: bai@ucf.edu

Eduardo Divo

Department of Mechanical Engineering,
College of Engineering,
Embry-Riddle Aeronautical University,
600 South Clyde Morris Boulevard,
Daytona Beach, FL 32114

William M. DeCampli

Cardiothoracic Surgery,
The Heart Center at Arnold Palmer Hospital for Children,
92 West Miller Street,
Orlando, FL 32806;
Medical Education,
College of Medicine,
University of Central Florida,
6850 Lake Nona Boulevard,
Orlando, FL 32827
e-mail: william.decampli@orlandohealth.com

1Corresponding authors.

Manuscript received October 14, 2016; final manuscript received July 11, 2017; published online August 16, 2017. Assoc. Editor: Jonathan Vande Geest.

J Biomech Eng 139(10), 101003 (Aug 16, 2017) (10 pages) Paper No: BIO-16-1405; doi: 10.1115/1.4037400 History: Received October 14, 2016; Revised July 11, 2017

Homografts and synthetic grafts are used in surgery for congenital heart disease (CHD). Determining these materials' mechanical properties will aid in understanding tissue behavior when subjected to abnormal CHD hemodynamics. Homograft tissue samples from anterior/posterior aspects, of ascending/descending aorta (AA, DA), innominate artery (IA), left subclavian artery (LScA), left common carotid artery (LCCA), main/left/right pulmonary artery (MPA, LPA, RPA), and synthetic vascular grafts, were obtained in three orientations: circumferential, diagonal (45 deg relative to circumferential direction), and longitudinal. Samples were subjected to uniaxial tensile testing (UTT). True strain-Cauchy stress curves were individually fitted for each orientation to calibrate Fung model. Then, they were used to calibrate anisotropic Holzapfel–Gasser model (R2 > 0.95). Most samples demonstrated a nonlinear hyperelastic strain–stress response to UTT. Stiffness (measured by tangent modulus at different strains) in all orientations were compared and shown as contour plots. For each vessel segment at all strain levels, stiffness was not significantly different among aspects and orientations. For synthetic grafts, stiffness was significantly different among orientations (p < 0.042). Aorta is significantly stiffer than pulmonary artery at 10% strain, comparing all orientations, aspects, and regions (p = 0.0001). Synthetic grafts are significantly stiffer than aortic and pulmonary homografts at all strain levels (p < 0.046). Aortic, pulmonary artery, and synthetic grafts exhibit hyperelastic biomechanical behavior with anisotropic effect. Differences in mechanical properties among vascular grafts may affect native tissue behavior and ventricular/arterial mechanical coupling, and increase the risk of deformation due to abnormal CHD hemodynamics.

Copyright © 2017 by ASME
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Grahic Jump Location
Fig. 2

Cauchy stress versus true strain curves in different orientations (C, D, and L) and aspects (anterior and posterior) of homografts. (a)–(c) AA, (d)–(f) DA, (g)–(i) Arch, (j)–(l) MPA, (m)–(o) LPA, (p)–(r) RPA, (s) IA, (t) LCCA, and (u) LsCA. Experimental raw data sets (dots) and fitted curves (solid lines) with fitting equations are presented.

Grahic Jump Location
Fig. 3

Cauchy stress versus true strain curves in different orientations of synthetic grafts samples: (a)–(c) SVG-GORE-TEX and (d)–(f) EVG-IMPRA

Grahic Jump Location
Fig. 1

(a) Anterior aspects of aortic and pulmonary artery homografts with a schematic of sampling locations and orientations (sample orientations shown in xy coordinate system). (b) Sample width and (c) sample thickness (same scales for all subfigures). (d) Schematic of sampling orientations for synthetic vascular grafts (sample orientations shown in xy coordinate system). The dotted line denotes midline of the graft where it was extended. (e) SVG-GORE-TEX with reinforcement layer (same scales for all subfigures).

Grahic Jump Location
Fig. 4

Comparison of Cauchy stress versus true strain curves between Holzapfel–Gasser model (dots) and experimentally fitted data (solid lines) in (a) AA, (b) DA, (c) Arch, (d) MPA, (e) LPA, and (f) RPA. The GRG calibrated Holzapfel–Gasser model parameters are provided. The difference of strain–stress response among orientations is also exhibited. All R2 values ≥0.97.

Grahic Jump Location
Fig. 5

Comparison of stiffnesses (E0=(dσ/dε)|ε=10%,20%,30%) among different samples, orientations, and aspects at the strain level of (a) 10%, (b) 20%, and (c) 30%

Grahic Jump Location
Fig. 6

Stiffness contours superimposed on entire aortic homograft, for different orientations, aspects, and strain levels

Grahic Jump Location
Fig. 7

Stiffness contours superimposed on entire pulmonary artery homograft, for different orientations, aspects, and strain level



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