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Wang X, Carpenter HJ, Ghayesh MH, Kotousov A, Zander AC, Amabili M, Psaltis PJ. A review on the biomechanical behaviour of the aorta. J Mech Behav Biomed Mater 2023; 144:105922. [PMID: 37320894 DOI: 10.1016/j.jmbbm.2023.105922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 05/14/2023] [Accepted: 05/20/2023] [Indexed: 06/17/2023]
Abstract
Large aortic aneurysm and acute and chronic aortic dissection are pathologies of the aorta requiring surgery. Recent advances in medical intervention have improved patient outcomes; however, a clear understanding of the mechanisms leading to aortic failure and, hence, a better understanding of failure risk, is still missing. Biomechanical analysis of the aorta could provide insights into the development and progression of aortic abnormalities, giving clinicians a powerful tool in risk stratification. The complexity of the aortic system presents significant challenges for a biomechanical study and requires various approaches to analyse the aorta. To address this, here we present a holistic review of the biomechanical studies of the aorta by categorising articles into four broad approaches, namely theoretical, in vivo, experimental and combined investigations. Experimental studies that focus on identifying mechanical properties of the aortic tissue are also included. By reviewing the literature and discussing drawbacks, limitations and future challenges in each area, we hope to present a more complete picture of the state-of-the-art of aortic biomechanics to stimulate research on critical topics. Combining experimental modalities and computational approaches could lead to more comprehensive results in risk prediction for the aortic system.
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Affiliation(s)
- Xiaochen Wang
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Harry J Carpenter
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Mergen H Ghayesh
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Andrei Kotousov
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Anthony C Zander
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Marco Amabili
- Department of Mechanical Engineering, McGill University, Montreal H3A 0C3, Canada
| | - Peter J Psaltis
- Adelaide Medical School, The University of Adelaide, Adelaide, South Australia 5005, Australia; Department of Cardiology, Central Adelaide Local Health Network, Adelaide, South Australia 5000, Australia; Vascular Research Centre, Heart Health Theme, South Australian Health & Medical Research Institute (SAHMRI), Adelaide, South Australia 5000, Australia
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2
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Is location a significant parameter in the layer dependent dissection properties of the aorta? Biomech Model Mechanobiol 2022; 21:1887-1901. [PMID: 36057051 DOI: 10.1007/s10237-022-01627-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Accepted: 08/07/2022] [Indexed: 11/02/2022]
Abstract
Proper characterisation of biological tissue is key to understanding the effect of the biomechanical environment in the physiology and pathology of the cardiovascular system. Aortic dissection in particular is a prevalent and sometimes fatal disease that still lacks a complete comprehension of its progression. Its development and outcome, however, depend on the location in the vessel. Dissection properties of arteries are frequently studied via delamination tests, such as the T-peel test and the mixed-mode peel test. So far, a study that performs both tests throughout different locations of the aorta, as well as dissecting several interfaces, is missing. This makes it difficult to extract conclusions in terms of vessel heterogeneity, as a standardised experimental procedure cannot be assured for different studies in literature. Therefore, both dissection tests have been here performed on healthy porcine aortas, dissecting three interfaces of the vessels, i.e., the intima-media, the media-adventitia and the media within itself, considering different locations of the aorta, the ascending thoracic aorta (ATA), the descending thoracic aorta and the infrarenal abdominal aorta (IAA). Significant differences were found for both, layers and location. In particular, dissection forces in the ATA were the highest and the separation of the intima-media interface required significantly the lowest force. Moreover, dissection in the longitudinal direction of the vessel generally required more force than in the circumferential one. These results emphasise the need to characterise aortic tissue considering the specific location and dissected layer of the vessel.
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Horný L, Roubalová L, Kronek J, Chlup H, Adámek T, Blanková A, Petřivý Z, Suchý T, Tichý P. Correlation between age, location, orientation, loading velocity and delamination strength in the human aorta. J Mech Behav Biomed Mater 2022; 133:105340. [PMID: 35785636 DOI: 10.1016/j.jmbbm.2022.105340] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 06/10/2022] [Accepted: 06/25/2022] [Indexed: 11/15/2022]
Abstract
Aortic dissection is a biomechanical phenomenon associated with a failure of internal cohesion, which manifests itself through the delamination of the aortic wall. The goal of this study is to deepen our knowledge of the delamination strength of the aorta. To achieve this, 661 peeling experiments were carried out with strips of the human aorta collected from 46 cadavers. The samples were ordered into groups with respect to (1) anatomical location, (2) orientation of the sample, and (3) extension rate used within the experiment. The obtained results are in accordance with the hypothesis that delamination resistance is not sensitive to the extension rates 0.1, 1, 10, and 50 mms-1. We arrived at this conclusion for all positions along the aorta investigated in our study. These were the thoracic ascending (AAs), thoracic descending (ADs), and the abdominal aorta (AAb), simultaneously considering both the longitudinal (L) as well as the circumferential (C) orientations of the samples. On the other hand, our results showed that the delamination strength differs significantly with respect to the anatomical position and orientation of the sample. The medians of the delamination strength were as follows, 4.1 in AAs-L, 3.2 in AAs-C, 3.1 in ADs-L, 2.4 in ADs-C, AAb-L in 3.6, and 2.7 in AAb-C case (all values are in 0.01·Nmm-1). This suggests that resistance to crack propagation should be an anisotropic property and that the aorta is inhomogeneous along its length from the point of view of delamination resistance. Finally, correlation analysis proved that the delamination strength of the human aorta significantly decreases with age.
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Affiliation(s)
- Lukáš Horný
- Czech Technical University in Prague, Faculty of Mechanical Engineering, Technická 4, 160 00, Prague, Czech Republic.
| | - Lucie Roubalová
- Czech Technical University in Prague, Faculty of Mechanical Engineering, Technická 4, 160 00, Prague, Czech Republic
| | - Jakub Kronek
- Czech Technical University in Prague, Faculty of Mechanical Engineering, Technická 4, 160 00, Prague, Czech Republic
| | - Hynek Chlup
- Czech Technical University in Prague, Faculty of Mechanical Engineering, Technická 4, 160 00, Prague, Czech Republic
| | - Tomáš Adámek
- Regional Hospital Liberec, Department of Forensic Medicine and Toxicology, Husova 357/10, 460 63, Liberec, Czech Republic
| | - Alžběta Blanková
- Regional Hospital Liberec, Department of Forensic Medicine and Toxicology, Husova 357/10, 460 63, Liberec, Czech Republic
| | - Zdeněk Petřivý
- Czech Technical University in Prague, Faculty of Mechanical Engineering, Technická 4, 160 00, Prague, Czech Republic
| | - Tomáš Suchý
- Czech Technical University in Prague, Faculty of Mechanical Engineering, Technická 4, 160 00, Prague, Czech Republic; Institute of Rock Structure and Mechanics of The Czech Academy of Sciences, V Holešovičkách 94/41, 182 09, Prague, Czech Republic
| | - Petr Tichý
- Czech Technical University in Prague, Faculty of Mechanical Engineering, Technická 4, 160 00, Prague, Czech Republic
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Živić J, Virag L, Horvat N, Smoljkić M, Karšaj I. The risk of rupture and abdominal aortic aneurysm morphology: A computational study. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2022; 38:e3566. [PMID: 34919341 DOI: 10.1002/cnm.3566] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 11/18/2021] [Accepted: 12/15/2021] [Indexed: 06/14/2023]
Abstract
Prediction of rupture and optimal timing for abdominal aortic aneurysm (AAA) surgical intervention remain wanting even after decades of clinical, histological, and numerical research. Although studies estimating rupture from AAA geometrical features from CT imaging showed some promising results, they are still not being used in practice. Patient-specific numerical stress analysis introduced too many assumptions about wall structure for the related rupture potential index (RPI) to be considered reliable. Growth and remodeling (G&R) numerical models eliminate some of these assumptions and thus might have the most potential to calculate mural stresses and RPI and increase our understanding of rupture. To recognize numerical models as trustworthy, it is necessary to validate the computed results with results derived from imaging. Elastin degradation function is one of the main factors that determine idealized aneurysm sac shape. Using a hundred different combinations of variables defining AAA geometry or influences AAA stability (elastin degradation function parameters, collagen mechanics, and initial healthy aortic diameters), we investigated the relationship between AAA morphology and RPI and compared numerical results with clinical findings. Good agreement of numerical results with clinical expectations from the literature gives us confidence in the validity of the numerical model. We show that aneurysm morphology significantly influences the stability of aneurysms. Additionally, we propose new parameters, geometrical rupture potential index (GRPI) and normalized aneurysm length (NAL), that might predict rupture of aneurysms without thrombus better than currently used criteria (i.e., maximum diameter and growth rate). These parameters can be computed quickly, without the tedious processing of CT images.
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Affiliation(s)
- Josip Živić
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Zagreb, Croatia
| | - Lana Virag
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Zagreb, Croatia
| | - Nino Horvat
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Zagreb, Croatia
| | | | - Igor Karšaj
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Zagreb, Croatia
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Tong J, Abudupataer M, Xu X, Zhang Z, Li J, Lai H, Wang C, Zhu K. OUP accepted manuscript. Interact Cardiovasc Thorac Surg 2022; 35:6548224. [PMID: 35285896 PMCID: PMC9297518 DOI: 10.1093/icvts/ivac068] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 03/09/2022] [Indexed: 11/12/2022] Open
Affiliation(s)
- Jianhua Tong
- Institute for Biomedical Engineering and Nano Science, Shanghai East Hospital, Tongji University School of Medicine, Shanghai, China
- Corresponding authors. Tongji University School of Medicine, Chifeng Road 67, Shanghai 200092, China. Tel: +86-21-65988029; e-mail: (J. Tong); Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Tel: +86-21-64041990; e-mail: (C. Wang); Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Tel: +86-21-64041990; e-mail: (K. Zhu)
| | - Mieradilijiang Abudupataer
- Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, and Shanghai Institute of Cardiovascular Diseases, Shanghai, China
| | - Xiaojuan Xu
- Department of Pathology and Pathophysiology, Tongji University School of Medicine, Shanghai, China
| | - Zhi Zhang
- Institute for Biomedical Engineering and Nano Science, Shanghai East Hospital, Tongji University School of Medicine, Shanghai, China
| | - Jun Li
- Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, and Shanghai Institute of Cardiovascular Diseases, Shanghai, China
| | - Hao Lai
- Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, and Shanghai Institute of Cardiovascular Diseases, Shanghai, China
| | - Chunsheng Wang
- Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, and Shanghai Institute of Cardiovascular Diseases, Shanghai, China
- Corresponding authors. Tongji University School of Medicine, Chifeng Road 67, Shanghai 200092, China. Tel: +86-21-65988029; e-mail: (J. Tong); Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Tel: +86-21-64041990; e-mail: (C. Wang); Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Tel: +86-21-64041990; e-mail: (K. Zhu)
| | - Kai Zhu
- Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, and Shanghai Institute of Cardiovascular Diseases, Shanghai, China
- Corresponding authors. Tongji University School of Medicine, Chifeng Road 67, Shanghai 200092, China. Tel: +86-21-65988029; e-mail: (J. Tong); Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Tel: +86-21-64041990; e-mail: (C. Wang); Department of Cardiac Surgery, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Tel: +86-21-64041990; e-mail: (K. Zhu)
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6
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Horvat N, Virag L, Karšaj I. Mechanical role of intraluminal thrombus in aneurysm growth: A computational study. Biomech Model Mechanobiol 2021; 20:1819-1832. [PMID: 34148166 DOI: 10.1007/s10237-021-01478-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 06/07/2021] [Indexed: 12/25/2022]
Abstract
Models that seek to improve our current understanding of biochemical processes and predict disease progression have been increasingly in use over the last decades. Recently, we proposed a finite element implementation of arterial wall growth and remodeling with application to abdominal aortic aneurysms (AAAs). The study focused on changes within the aortic wall and did not include the complex role of intraluminal thrombus (ILT) during the AAA evolution. Thus, in this work, we extend the model with a gradual deposition of ILT and its mechanical influence on AAA growth. Despite neglecting the increased biochemical activity due to the presence of a proteolytically active luminal layer of ILT, and thus underestimating rupture risk potential, we show that ILT helps to slow down the growth of the aneurysm in the axial direction by redirecting blood pressure loading from the axial-radial plane to predominately radial direction. This very likely lowers rupture potential. We also show that the ratio of ILT volume to volume sac is an important factor in AAA stabilization and that fully thrombosed aneurysms could stabilize quicker and at smaller maximum diameters compared to partially thrombosed ones. Furthermore, we show that ILT formation and the associated mural stress decrease negatively impact the wall constituent production and thickness. Although further studies that include increased biochemical degradation of the wall after the formation of ILT and ILT deposition based on hemodynamics are needed, the present findings highlight the dual role an ILT plays during AAA progression.
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Affiliation(s)
- Nino Horvat
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000, Zagreb, Croatia
| | - Lana Virag
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000, Zagreb, Croatia
| | - Igor Karšaj
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000, Zagreb, Croatia.
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Boyd AJ. Intraluminal thrombus: Innocent bystander or factor in abdominal aortic aneurysm pathogenesis? JVS Vasc Sci 2021; 2:159-169. [PMID: 34617066 PMCID: PMC8489244 DOI: 10.1016/j.jvssci.2021.02.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Accepted: 02/20/2021] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND Abdominal aortic aneurysms (AAAs) represent a complex multifactorial hemodynamic, thrombotic, and inflammatory process that can ultimately result in aortic rupture and death. Despite improved screening and surgical management of AAAs, the mortality rates have remained high after rupture, and little progress has occurred in the development of nonoperative treatments. Intraluminal thrombus (ILT) is present in most AAAs and might be involved in AAA pathogenesis. The present review examined the latest clinical and experimental evidence for possible involvement of the ILT in AAA growth and rupture. METHODS A literature review was performed after a search of the PubMed database from 2012 to June 2020 using the terms "abdominal aortic aneurysm" and "intraluminal thrombus." RESULTS The structure, composition, and hemodynamics of ILT formation and propagation were reviewed in relation to the hemostatic and proteolytic factors favoring ILT deposition. The potential effects of the ILT on AAA wall degeneration and rupture, including a review of the current controversies regarding the position, thickness, and composition of ILT, are presented. Although initially potentially protective against increased wall stress, increasing evidence has shown that an increased volume and greater age of the ILT have direct detrimental effects on aortic wall integrity, which might predispose to an increased rupture risk. CONCLUSIONS ILT does not appear to be an innocent bystander in AAA pathophysiology. However, its exact role remains elusive and controversial. Despite computational evidence of a possible protective role of the ILT in reducing wall stress, increasing evidence has shown that the ILT promotes AAA wall degeneration in humans and in animal models. Further research, with large animal models and with more chronic ILT is crucial for a better understanding of the role of the ILT in AAAs and for the potential development of targeted therapies to slow or halt AAA progression.
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Affiliation(s)
- April J. Boyd
- Department of Vascular Surgery, University of Manitoba, Winnipeg, Manitoba, Canada
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8
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Wang R, Yu X, Gkousioudi A, Zhang Y. Effect of Glycation on Interlamellar Bonding of Arterial Elastin. EXPERIMENTAL MECHANICS 2021; 61:81-94. [PMID: 33583947 PMCID: PMC7880226 DOI: 10.1007/s11340-020-00644-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 07/21/2020] [Indexed: 06/12/2023]
Abstract
BACKGROUND Interlamellar bonding in the arterial wall is often compromised by cardiovascular diseases. However, several recent nationwide and hospital-based studies have uniformly reported reduced risk of thoracic aortic dissection in patients with diabetes. As one of the primary structural constituents in the arterial wall, elastin plays an important role in providing its interlamellar structural integrity. OBJECTIVE The purpose of this study is to examine the effects of glycation on the interlamellar bonding properties of arterial elastin. METHODS Purified elastin network was isolated from porcine descending thoracic aorta and incubated in 2 M glucose solution for 7, 14 or 21 days at 37 °C. Peeling and direct tension tests were performed to provide complimentary information on understanding the interlamellar layer separation properties of elastin network with glycation effect. Peeling tests were simulated using a cohesive zone model (CZM). Multiphoton imaging was used to visualize the interlamellar elastin fibers in samples subjected to peeling and direct tension. RESULTS Peeling and direct tension tests show that interlamellar energy release rate and strength both increases with the duration of glucose treatment. The traction at damage initiation estimated for the CZM agrees well with the interlamellar strength measurements from direct tension tests. Glycation was also found to increase the interlamellar failure strain of arterial elastin. Multiphoton imaging confirmed the contribution of radially running elastin fibers to resisting dissection. CONCLUSIONS Nonenzymatic glycation reduces the propensity of arterial elastin to dissection. This study also suggests that the CZM effectively describes the interlamellar bonding properties of arterial elastin.
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Affiliation(s)
- R Wang
- Department of Mechanical Engineering, Boston University, Boston, MA 02215
| | - X Yu
- Department of Mechanical Engineering, Boston University, Boston, MA 02215
| | - A Gkousioudi
- Department of Mechanical Engineering, Boston University, Boston, MA 02215
| | - Y Zhang
- Department of Mechanical Engineering, Boston University, Boston, MA 02215
- Department of Biomedical Engineering, Boston University, Boston, MA 02215
- Divison of Materials Science & Engineering, Boston University, Boston, MA 02215
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Teixeira FS, Neufeld E, Kuster N, Watton PN. Modeling intracranial aneurysm stability and growth: an integrative mechanobiological framework for clinical cases. Biomech Model Mechanobiol 2020; 19:2413-2431. [PMID: 32533497 PMCID: PMC7603456 DOI: 10.1007/s10237-020-01351-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Accepted: 05/12/2020] [Indexed: 11/03/2022]
Abstract
We present a novel patient-specific fluid-solid-growth framework to model the mechanobiological state of clinically detected intracranial aneurysms (IAs) and their evolution. The artery and IA sac are modeled as thick-walled, non-linear elastic fiber-reinforced composites. We represent the undulation distribution of collagen fibers: the adventitia of the healthy artery is modeled as a protective sheath whereas the aneurysm sac is modeled to bear load within physiological range of pressures. Initially, we assume the detected IA is stable and then consider two flow-related mechanisms to drive enlargement: (1) low wall shear stress; (2) dysfunctional endothelium which is associated with regions of high oscillatory flow. Localized collagen degradation and remodelling gives rise to formation of secondary blebs on the aneurysm dome. Restabilization of blebs is achieved by remodelling of the homeostatic collagen fiber stretch distribution. This integrative mechanobiological modelling workflow provides a step towards a personalized risk-assessment and treatment of clinically detected IAs.
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Affiliation(s)
| | - Esra Neufeld
- IT’IS Foundation & ETH Zürich, Zürich, Switzerland
| | - Niels Kuster
- IT’IS Foundation & ETH Zürich, Zürich, Switzerland
| | - Paul N. Watton
- Department of Computer Science, Insigneo Institute for in silico Medicine, University of Sheffield, Sheffield, UK
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, USA
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Wang R, Yu X, Zhang Y. Mechanical and structural contributions of elastin and collagen fibers to interlamellar bonding in the arterial wall. Biomech Model Mechanobiol 2020; 20:93-106. [PMID: 32705413 DOI: 10.1007/s10237-020-01370-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Accepted: 07/15/2020] [Indexed: 12/25/2022]
Abstract
The artery relies on interlamellar structural components, mainly elastin and collagen fibers, for maintaining its integrity and resisting dissection propagation. In this study, the contribution of arterial elastin and collagen fibers to interlamellar bonding was studied through mechanical testing, multiphoton imaging and finite element modeling. Steady-state peeling experiments were performed on porcine aortic media and the purified elastin network in the circumferential (Circ) and longitudinal (Long) directions. The peeling force and energy release rate associated with mode-I failure are much higher for aortic media than for the elastin network. Also, longitudinal peeling exhibits a higher energy release rate and strength than circumferential peeling for both the aortic media and elastin. Multiphoton imaging shows the recruitment of both elastin and collagen fibers within the interlamellar space and points to in-plane anisotropy of fiber distributions as a potential mechanism for the direction-dependent phenomena of peeling tests. Three-dimensional finite element models based on cohesive zone model (CZM) of fracture were created to simulate the peeling tests with the interlamellar energy release rate and separation distance at damage initiation obtained directly from peeling test. Our experimental results show that the separation distance at damage initiation is 80 μm for aortic media and 40 μm for elastin. The damage initiation stress was estimated from the model for aortic media (Circ: 60 kPa; Long: 95 kPa) and elastin (Circ: 9 kPa; Long: 14 kPa). The interlamellar separation distance at complete failure was estimated to be 3 - 4 mm for both media and elastin. Furthermore, elastin and collagen fibers both play an important role in bonding of the arterial wall, while collagen has a higher contribution than elastin to interlamellar stiffness, strength and toughness. These results on microstructural interlamellar failure shed light on the pathological development and progression of aortic dissection.
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Affiliation(s)
- Ruizhi Wang
- Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA
| | - Xunjie Yu
- Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA
| | - Yanhang Zhang
- Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA. .,Department of Biomedical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA. .,Divison of Materials Science & Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA.
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11
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Myneni M, Rao A, Jiang M, Moreno MR, Rajagopal KR, Benjamin CC. Segmental Variations in the Peel Characteristics of the Porcine Thoracic Aorta. Ann Biomed Eng 2020; 48:1751-1767. [PMID: 32152801 DOI: 10.1007/s10439-020-02489-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 03/03/2020] [Indexed: 10/24/2022]
Abstract
Aortic dissection occurs predominantly in the thoracic aorta and the mechanisms for the initiation and propagation of the tear in aortic dissection are not well understood. We study the tearing characteristics of the porcine thoracic aorta using a peeling test and we estimate the peeling energy per unit area in the ascending and the descending segments. The stretch and the peel force per unit width undergone by the peeled halves of a rectangular specimen are measured. We find that there can be significant variation in the stretch within the specimen and the stretch between the markers in the specimen varies with the dynamics of peeling. We found that in our experiment the stretch achieved in the peeled halves was such that it was in the range of the stretch at which the stress-stretch curve for the uniaxial experiment starts deviating from linearity. Higher peeling energy per unit area is required in the ascending aorta compared to the descending aorta. Longitudinal specimens required higher peeling energy per unit area when compared to the circumferential specimens.
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Affiliation(s)
- Manoj Myneni
- Department of Mechanical Engineering, Texas A&M University, 100 Mechanical Engineering Office Building, College Station, TX, 77843-3123, USA
| | - Akshay Rao
- Department of Mechanical Engineering, Texas A&M University, 100 Mechanical Engineering Office Building, College Station, TX, 77843-3123, USA
| | - Mingliang Jiang
- Department of Mechanical Engineering, Texas A&M University, 100 Mechanical Engineering Office Building, College Station, TX, 77843-3123, USA
| | - Michael R Moreno
- Department of Mechanical Engineering, Texas A&M University, 100 Mechanical Engineering Office Building, College Station, TX, 77843-3123, USA
| | - K R Rajagopal
- Department of Mechanical Engineering, Texas A&M University, 100 Mechanical Engineering Office Building, College Station, TX, 77843-3123, USA
| | - Chandler C Benjamin
- Department of Mechanical Engineering, Texas A&M University, 100 Mechanical Engineering Office Building, College Station, TX, 77843-3123, USA.
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Sherifova S, Holzapfel GA. Biomechanics of aortic wall failure with a focus on dissection and aneurysm: A review. Acta Biomater 2019; 99:1-17. [PMID: 31419563 PMCID: PMC6851434 DOI: 10.1016/j.actbio.2019.08.017] [Citation(s) in RCA: 73] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Revised: 08/05/2019] [Accepted: 08/08/2019] [Indexed: 12/12/2022]
Abstract
Aortic dissections and aortic aneurysms are fatal events characterized by structural changes to the aortic wall. The maximum diameter criterion, typically used for aneurysm rupture risk estimations, has been challenged by more sophisticated biomechanically motivated models in the past. Although these models are very helpful for the clinicians in decision-making, they do not attempt to capture material failure. Following a short overview of the microstructure of the aorta, we analyze the failure mechanisms involved in the dissection and rupture by considering also traumatic rupture. We continue with a literature review of experimental studies relevant to quantify tissue strength. More specifically, we summarize more extensively uniaxial tensile, bulge inflation and peeling tests, and we also specify trouser, direct tension and in-plane shear tests. Finally we analyze biomechanically motivated models to predict rupture risk. Based on the findings of the reviewed studies and the rather large variations in tissue strength, we propose that an appropriate material failure criterion for aortic tissues should also reflect the microstructure in order to be effective. STATEMENT OF SIGNIFICANCE: Aortic dissections and aortic aneurysms are fatal events characterized by structural changes to the aortic wall. Despite the advances in medical, biomedical and biomechanical research, the mortality rates of aneurysms and dissections remain high. The present review article summarizes experimental studies that quantify the aortic wall strength and it discusses biomechanically motivated models to predict rupture risk. We identified contradictory observations and a large variation within and between data sets, which may be due to biological variations, different sample sizes, differences in experimental protocols, etc. Based on the findings of the reviewed literature and the rather large variations in tissue strength, it is proposed that an appropriate criterion for aortic failure should also reflect the microstructure.
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Affiliation(s)
- Selda Sherifova
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2, 8010 Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2, 8010 Graz, Austria; Department of Structural Engineering, Norwegian Institute of Science and Technology (NTNU), 7491 Trondheim, Norway.
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Angouras DC, Kritharis EP, Sokolis DP. Regional distribution of delamination strength in ascending thoracic aortic aneurysms. J Mech Behav Biomed Mater 2019; 98:58-70. [DOI: 10.1016/j.jmbbm.2019.06.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 05/24/2019] [Accepted: 06/01/2019] [Indexed: 12/22/2022]
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14
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Gültekin O, Hager SP, Dal H, Holzapfel GA. Computational modeling of progressive damage and rupture in fibrous biological tissues: application to aortic dissection. Biomech Model Mechanobiol 2019; 18:1607-1628. [PMID: 31093869 PMCID: PMC6825033 DOI: 10.1007/s10237-019-01164-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 04/29/2019] [Indexed: 12/21/2022]
Abstract
This study analyzes the lethal clinical condition of aortic dissections from a numerical point of view. On the basis of previous contributions by Gültekin et al. (Comput Methods Appl Mech Eng 312:542-566, 2016 and 331:23-52, 2018), we apply a holistic geometrical approach to fracture, namely the crack phase-field, which inherits the intrinsic features of gradient damage and variational fracture mechanics. The continuum framework captures anisotropy, is thermodynamically consistent and is based on finite strains. The balance of linear momentum and the crack evolution equation govern the coupled mechanical and phase-field problem. The solution scheme features the robust one-pass operator-splitting algorithm upon temporal and spatial discretizations. Based on experimental data of diseased human thoracic aortic samples, the elastic material parameters are identified followed by a sensitivity analysis of the anisotropic phase-field model. Finally, we simulate an incipient propagation of an aortic dissection within a multi-layered segment of a thoracic aorta that involves a prescribed initial tear. The finite element results demonstrate a severe damage zone around the initial tear and exhibit a rather helical crack pattern, which aligns with the fiber orientation. It is hoped that the current contribution can provide some directions for further investigations of this disease.
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Affiliation(s)
- Osman Gültekin
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/II, 8010, Graz, Austria.,Department of Mechanical Engineering, Middle East Technical University, Dumlupınar Bulvarı No. 1, Çankaya, 06800, Ankara, Turkey
| | - Sandra Priska Hager
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/II, 8010, Graz, Austria
| | - Hüsnü Dal
- Department of Mechanical Engineering, Middle East Technical University, Dumlupınar Bulvarı No. 1, Çankaya, 06800, Ankara, Turkey
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/II, 8010, Graz, Austria. .,Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway.
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15
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Simulation of arterial dissection by a penetrating external body using cohesive zone modelling. J Mech Behav Biomed Mater 2017; 71:95-105. [DOI: 10.1016/j.jmbbm.2017.03.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Revised: 02/23/2017] [Accepted: 03/05/2017] [Indexed: 11/19/2022]
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16
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Controlled peel testing of a model tissue for diseased aorta. J Biomech 2016; 49:3667-3675. [DOI: 10.1016/j.jbiomech.2016.09.040] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Revised: 09/19/2016] [Accepted: 09/30/2016] [Indexed: 11/22/2022]
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17
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Litvinov RI, Weisel JW. Fibrin mechanical properties and their structural origins. Matrix Biol 2016; 60-61:110-123. [PMID: 27553509 DOI: 10.1016/j.matbio.2016.08.003] [Citation(s) in RCA: 119] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 08/11/2016] [Indexed: 02/07/2023]
Abstract
Fibrin is a protein polymer that is essential for hemostasis and thrombosis, wound healing, and several other biological functions and pathological conditions that involve extracellular matrix. In addition to molecular and cellular interactions, fibrin mechanics has been recently shown to underlie clot behavior in the highly dynamic intra- and extravascular environments. Fibrin has both elastic and viscous properties. Perhaps the most remarkable rheological feature of the fibrin network is an extremely high elasticity and stability despite very low protein content. Another important mechanical property that is common to many filamentous protein polymers but not other polymers is stiffening occurring in response to shear, tension, or compression. New data has begun to provide a structural basis for the unique mechanical behavior of fibrin that originates from its complex multi-scale hierarchical structure. The mechanical behavior of the whole fibrin gel is governed largely by the properties of single fibers and their ensembles, including changes in fiber orientation, stretching, bending, and buckling. The properties of individual fibrin fibers are determined by the number and packing arrangements of double-stranded half-staggered protofibrils, which still remain poorly understood. It has also been proposed that forced unfolding of sub-molecular structures, including elongation of flexible and relatively unstructured portions of fibrin molecules, can contribute to fibrin deformations. In spite of a great increase in our knowledge of the structural mechanics of fibrin, much about the mechanisms of fibrin's biological functions remains unknown. Fibrin deformability is not only an essential part of the biomechanics of hemostasis and thrombosis, but also a rapidly developing field of bioengineering that uses fibrin as a versatile biomaterial with exceptional and tunable biochemical and mechanical properties.
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Affiliation(s)
- Rustem I Litvinov
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, United States
| | - John W Weisel
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, United States.
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18
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Tong J, Cheng Y, Holzapfel GA. Mechanical assessment of arterial dissection in health and disease: Advancements and challenges. J Biomech 2016; 49:2366-73. [PMID: 26948576 DOI: 10.1016/j.jbiomech.2016.02.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Accepted: 02/03/2016] [Indexed: 11/17/2022]
Abstract
Arterial dissection involves a complex series of coupled biomechanical events. The past two decades have witnessed great advances in the understanding of the intrinsic mechanism for dissection initiation, and hence in the development of novel therapeutic strategies for surgical repair. This is due in part to the profound advancements in characterizing emerging behaviors of dissection using state-of-the-art tools in experimental and computational biomechanics. In addition, researchers have identified the important role of the microstructure in determining the tissue׳s fracture modality during dissection propagation. In this review article, we highlight a variety of approaches in terms of biomechanical measurements, computational modeling and histological/microstructural analysis used to characterize a dissection that propagates in healthy and diseased arteries. Notable findings with quantitative mechanical data are reviewed. We conclude by discussing some unsolved problems that are of interest for future research.
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Affiliation(s)
- Jianhua Tong
- Shanghai East Hospital, Institute for Biomedical Engineering & Nano Science, Tongji University School of Medicine, Shanghai, PR China
| | - Yu Cheng
- Shanghai East Hospital, Institute for Biomedical Engineering & Nano Science, Tongji University School of Medicine, Shanghai, PR China
| | - Gerhard A Holzapfel
- Graz University of Technology, Institute of Biomechanics, Stremayrgasse 16-II, 8010 Graz, Austria.
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19
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Georg Y, Delay C, Schwein A, Lejay A, Thaveau F, Gaertner S, Stephan D, Heim F, Chakfe N. [Contribution of mathematical models and biomechanical properties in predicting the risk of abdominal aortic aneurysm rupture]. ACTA ACUST UNITED AC 2015; 41:63-8. [PMID: 26318549 DOI: 10.1016/j.jmv.2015.07.107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2015] [Accepted: 07/17/2015] [Indexed: 11/25/2022]
Abstract
INTRODUCTION Rupture is the worst outcome of abdominal aortic aneurysm (AAA). The decision to operate should include counterbalancing the risk of aneurysm rupture against the risk of aneurysm repair, within the context of a patient's overall life expectancy. Current surgical guidelines are based on population studies, and important variables are missed in predicting individual risk of rupture. METHODS In this literature review, we focused on the contribution of biomechanical and mathematical models in predicting risk of AAA rupture. RESULTS Anatomical features as diameter asymmetry and lack of tortuosity are shown to be anatomical risk factors of rupture. Wall stiffness (due to modifications of elastin and collagen composition) and increased inflammatory response are also factors that affect the structural integrity of the AAA wall. Biomechanical studies showed that wall strength is lower in ruptured than non-ruptured AAA. Intra-luminal thrombus also has a big role to play in the occurrence of rupture. Current mathematical models allow more variables to be included in predicting individual risk of rupture. CONCLUSION Moving away from using maximal transverse diameter of the AAA as a unique predictive factor and instead including biological, structural and biomechanical variables in predicting individual risk of rupture will be essential in the future and will help gain precision and accuracy in surgical indications.
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Affiliation(s)
- Y Georg
- Groupe européen de recherche sur les prothèses appliquées à la chirurgie vasculaire (Geprovas), faculté de médecine, institut d'anatomie pathologique, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Service de chirurgie vasculaire et transplantation rénale, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP n(o) 426, 67091 Strasbourg cedex, France
| | - C Delay
- Groupe européen de recherche sur les prothèses appliquées à la chirurgie vasculaire (Geprovas), faculté de médecine, institut d'anatomie pathologique, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Service de chirurgie vasculaire et transplantation rénale, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP n(o) 426, 67091 Strasbourg cedex, France
| | - A Schwein
- Groupe européen de recherche sur les prothèses appliquées à la chirurgie vasculaire (Geprovas), faculté de médecine, institut d'anatomie pathologique, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Service de chirurgie vasculaire et transplantation rénale, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP n(o) 426, 67091 Strasbourg cedex, France
| | - A Lejay
- Groupe européen de recherche sur les prothèses appliquées à la chirurgie vasculaire (Geprovas), faculté de médecine, institut d'anatomie pathologique, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Service de chirurgie vasculaire et transplantation rénale, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP n(o) 426, 67091 Strasbourg cedex, France
| | - F Thaveau
- Groupe européen de recherche sur les prothèses appliquées à la chirurgie vasculaire (Geprovas), faculté de médecine, institut d'anatomie pathologique, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Service de chirurgie vasculaire et transplantation rénale, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP n(o) 426, 67091 Strasbourg cedex, France
| | - S Gaertner
- Service des maladies vasculaires, hypertension artérielle et pharmacologie clinique, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, 67091 Strasbourg cedex, France
| | - D Stephan
- Service des maladies vasculaires, hypertension artérielle et pharmacologie clinique, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, 67091 Strasbourg cedex, France
| | - F Heim
- Groupe européen de recherche sur les prothèses appliquées à la chirurgie vasculaire (Geprovas), faculté de médecine, institut d'anatomie pathologique, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Laboratoire de physique et mécanique textile, ENSISA, 11, rue Alfred-Werner, 68093 Mulhouse cedex, France
| | - N Chakfe
- Groupe européen de recherche sur les prothèses appliquées à la chirurgie vasculaire (Geprovas), faculté de médecine, institut d'anatomie pathologique, 4, rue Kirschleger, 67085 Strasbourg cedex, France; Service de chirurgie vasculaire et transplantation rénale, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP n(o) 426, 67091 Strasbourg cedex, France.
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20
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Sassani SG, Kakisis J, Tsangaris S, Sokolis DP. Layer-dependent wall properties of abdominal aortic aneurysms: Experimental study and material characterization. J Mech Behav Biomed Mater 2015; 49:141-61. [DOI: 10.1016/j.jmbbm.2015.04.027] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Revised: 04/21/2015] [Accepted: 04/27/2015] [Indexed: 12/11/2022]
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21
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Tong J, Holzapfel GA. Structure, Mechanics, and Histology of Intraluminal Thrombi in Abdominal Aortic Aneurysms. Ann Biomed Eng 2015; 43:1488-501. [DOI: 10.1007/s10439-015-1332-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 05/06/2015] [Indexed: 01/08/2023]
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22
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Dietary Supplementation with Omega-3 Polyunsaturated Fatty Acids Modulate Matrix Metalloproteinase Immunoreactivity in a Mouse Model of Pre-abdominal Aortic Aneurysm. Heart Lung Circ 2015; 24:377-85. [DOI: 10.1016/j.hlc.2014.11.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 10/16/2014] [Accepted: 11/08/2014] [Indexed: 12/27/2022]
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23
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Grytsan A, Watton PN, Holzapfel GA. A Thick-Walled Fluid–Solid-Growth Model of Abdominal Aortic Aneurysm Evolution: Application to a Patient-Specific Geometry. J Biomech Eng 2015; 137:2020812. [DOI: 10.1115/1.4029279] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Indexed: 11/08/2022]
Abstract
We propose a novel thick-walled fluid–solid-growth (FSG) computational framework for modeling vascular disease evolution. The arterial wall is modeled as a thick-walled nonlinearly elastic cylindrical tube consisting of two layers corresponding to the media-intima and adventitia, where each layer is treated as a fiber-reinforced material with the fibers corresponding to the collagenous component. Blood is modeled as a Newtonian fluid with constant density and viscosity; no slip and no-flux conditions are applied at the arterial wall. Disease progression is simulated by growth and remodeling (G&R) of the load bearing constituents of the wall. Adaptions of the natural reference configurations and mass densities of constituents are driven by deviations of mechanical stimuli from homeostatic levels. We apply the novel framework to model abdominal aortic aneurysm (AAA) evolution. Elastin degradation is initially prescribed to create a perturbation to the geometry which results in a local decrease in wall shear stress (WSS). Subsequent degradation of elastin is driven by low WSS and an aneurysm evolves as the elastin degrades and the collagen adapts. The influence of transmural G&R of constituents on the aneurysm development is analyzed. We observe that elastin and collagen strains evolve to be transmurally heterogeneous and this may facilitate the development of tortuosity. This multiphysics framework provides the basis for exploring the influence of transmural metabolic activity on the progression of vascular disease.
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Affiliation(s)
- Andrii Grytsan
- Department of Solid Mechanics, Royal Institute of Technology (KTH), Teknikringen 8d, Stockholm 10044, Sweden
| | - Paul N. Watton
- Department of Computer Science, University of Sheffield, Sheffield, UK
- INSIGNEO Institute of In Silico Medicine, University of Sheffield, Sheffield, UK
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Kronesgasse 5-I, Graz 8010, Austria e-mail:
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24
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Pierce DM, Maier F, Weisbecker H, Viertler C, Verbrugghe P, Famaey N, Fourneau I, Herijgers P, Holzapfel GA. Human thoracic and abdominal aortic aneurysmal tissues: Damage experiments, statistical analysis and constitutive modeling. J Mech Behav Biomed Mater 2014; 41:92-107. [PMID: 25460406 DOI: 10.1016/j.jmbbm.2014.10.003] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Revised: 09/26/2014] [Accepted: 10/06/2014] [Indexed: 12/31/2022]
Abstract
Development of aortic aneurysms includes significant morphological changes within the tissue: collagen content increases, elastin content reduces and smooth muscle cells degenerate. We seek to quantify the impact of these changes on the passive mechanical response of aneurysms in the supra-physiological loading range via mechanical testing and constitutive modeling. We perform uniaxial extension tests on circumferentially and axially oriented strips from five thoracic (65.6 years ± 13.4, mean ± SD) and eight abdominal (63.9 years ± 11.4) aortic fusiform aneurysms to investigate both continuous and discontinuous softening during supra-physiological loading. We determine the significance of the differences between the fitted model parameters: diseased thoracic versus abdominal tissues, and healthy (Weisbecker et al., J. Mech. Behav. Biomed. Mater. 12, 93-106, 2012) versus diseased tissues. We also test correlations among these parameters and age, Body Mass Index (BMI) and preoperative aneurysm diameter, and investigate histological cuts. Tissue response is anisotropic for all tests and the anisotropic pseudo-elastic damage model fits the data well for both primary loading and discontinuous softening which we interpret as damage. We found statistically relevant differences between model parameters fitted to diseased thoracic versus abdominal tissues, as well as between those fitted to healthy versus diseased tissues. Only BMI correlated with fitted model parameters in abdominal aortic aneurysmal tissues.
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Affiliation(s)
- David M Pierce
- Departments of Mechanical Engineering, Biomedical Engineering and Mathematics, University of Connecticut, CT, USA
| | - Franz Maier
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Hannah Weisbecker
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | | | - Peter Verbrugghe
- Experimental Cardiac Surgery, Faculty of Medicine, UZ Leuven, Leuven, Belgium
| | - Nele Famaey
- Department of Mechanical Engineering, KU Leuven, Leuven, Belgium
| | - Inge Fourneau
- Vascular Surgery, Faculty of Medicine, UZ Leuven, Leuven, Belgium
| | - Paul Herijgers
- Experimental Cardiac Surgery, Faculty of Medicine, UZ Leuven, Leuven, Belgium
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25
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Arzani A, Suh GY, Dalman RL, Shadden SC. A longitudinal comparison of hemodynamics and intraluminal thrombus deposition in abdominal aortic aneurysms. Am J Physiol Heart Circ Physiol 2014; 307:H1786-95. [PMID: 25326533 DOI: 10.1152/ajpheart.00461.2014] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Abdominal aortic aneurysm (AAA) is often accompanied by in traluminal thrombus (ILT), which complicates AAA progression and risk of rupture. Patient-specific computational fluid dynamics modeling of 10 small human AAA was performed to investigate relations between hemodynamics and ILT progression. The patients were imaged using magnetic resonance twice in a 2- to 3-yr interval. Wall content data were obtained by a planar T1-weighted fast spin echo black-blood scan, which enabled quantification of thrombus thickness at midaneurysm location during baseline and followup. Computational simulations with patient-specific geometry and boundary conditions were performed to quantify the hemodynamic parameters of time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and mean exposure time at baseline. Spatially resolved quantifications of the change in ILT thickness were compared with the different hemodynamic parameters. Regions of low OSI had the strongest correlation with ILT growth and demonstrated a statistically significant correlation coefficient. Prominent regions of high OSI (>0.4) and low TAWSS (<1 dyn/cm(2)) did not appear to coincide with locations of thrombus deposition.
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Affiliation(s)
- Amirhossein Arzani
- Mechanical Engineering, University of California, Berkeley, California; and
| | - Ga-Young Suh
- Division of Vascular Surgery, Stanford University, Stanford, California
| | - Ronald L Dalman
- Division of Vascular Surgery, Stanford University, Stanford, California
| | - Shawn C Shadden
- Mechanical Engineering, University of California, Berkeley, California; and
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