Mechanical anisotropy of inflated elastic tissue from the pig aorta |
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| Authors: | MA Lillie RE Shadwick JM Gosline |
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| Institution: | 1. Department of Surgery, University of California at San Francisco Medical Center, and San Francisco Veterans Affairs Medical Center, San Francisco, California;2. Department of Cardio-thoracic Surgery, Erasmus University Medical Center, Rotterdam, The Netherlands;1. Department of Biomedical Engineering, Yale University, New Haven, CT 06520-8260, USA;2. Department of Bioengineering, King''s College London, England, SE1 8WA, UK;3. Department of Surgery, Yale School of Medicine, New Haven, CT 06510, USA;4. Vascular Biology and Therapeutics Program, Yale School of Medicine, New Haven, CT 06510, USA;1. Department of Biomedical Engineering, Yale University, New Haven, CT, USA;2. Departments of Cell Biology and Medicine, New York University, New York, NY, USA;3. Department of Pharmacology and Systems Therapeutics, Icahn School of Medicine at Mount Sinai, New York, NY, USA;4. Vascular Biology and Therapeutics Program, Yale School of Medicine, New Haven, CT, USA;1. Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel;2. Lahav CRO, Kibbutz Lahav 85335, Israel;1. Centre LOEX de l?Université Laval, Centre de recherche FRQS du CHU de Québec, Québec, QC, Canada;2. Department of Mechanical Engineering, Faculty of Science and Engineering, Université Laval, Québec, QC, Canada;3. Department of Surgery, Faculty of Medicine, Université Laval, Québec, QC, Canada |
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| Abstract: | Uniaxial and biaxial mechanical properties of purified elastic tissue from the proximal thoracic aorta were studied to understand physiological load distributions within the arterial wall. Stress–strain behaviour was non-linear in uniaxial and inflation tests. Elastic tissue was 40% stiffer in the circumferential direction compared to axial in uniaxial tests and～100% stiffer in vessels at an axial stretch ratio of 1.2 or 1.3 and inflated to physiological pressure. Poisson’s ratio vθz averaged 0.2 and vzθ increased with circumferential stretch from ～0.2 to ～0.4. Axial stretch had little impact on circumferential behaviour. In intact (unpurified) vessels at constant length, axial forces decreased with pressure at low axial stretches but remained constant at higher stretches. Such a constant axial force is characteristic of incrementally isotropic arteries at their in vivo dimensions. In purified elastic tissue, force decreased with pressure at all axial strains, showing no trend towards isotropy. Analysis of the force–length–pressure data indicated a vessel with vθz≈0.2 would stretch axially 2–4% with the cardiac pulse yet maintain constant axial force. We compared the ability of 4 mathematical models to predict the pressure-circumferential stretch behaviour of tethered, purified elastic tissue. Models that assumed isotropy could not predict the stretch at zero pressure. The neo-Hookean model overestimated the non-linearity of the response and two non-linear models underestimated it. A model incorporating contributions from orthogonal fibres captured the non-linearity but not the zero-pressure response. Models incorporating anisotropy and non-linearity should better predict the mechanical behaviour of elastic tissue of the proximal thoracic aorta. |
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