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Chung TK, Kim J, Gueldner PH, Vorp DA, Raghavan ML. A Comparative Study of Machine Learning and Algorithmic Approaches to Automatically Identify the Yield Point in Normal and Aneurysmal Human Aortic Tissues. J Biomech Eng 2024; 146:044503. [PMID: 38323620 DOI: 10.1115/1.4064365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Accepted: 12/20/2023] [Indexed: 02/08/2024]
Abstract
The stress-strain curve of biological soft tissues helps characterize their mechanical behavior. The yield point on this curve is when a specimen breaches its elastic range due to irreversible microstructural damage. The yield point is easily found using the offset yield method in traditional engineering materials. However, correctly identifying the yield point in soft tissues can be subjective due to its nonlinear material behavior. The typical method for yield point identification is visual inspection, which is investigator-dependent and does not lend itself to automation of the analysis pipeline. An automated algorithm to identify the yield point objectively assesses soft tissues' biomechanical properties. This study aimed to analyze data from uniaxial extension testing on biological soft tissue specimens and create a machine learning (ML) model to determine a tissue sample's yield point. We present a trained machine learning model from 279 uniaxial extension curves from testing aneurysmal/nonaneurysmal and longitudinal/circumferential oriented tissue specimens that multiple experts labeled through an adjudication process. The ML model showed a median error of 5% in its estimated yield stress compared to the expert picks. The study found that an ML model could accurately identify the yield point (as defined) in various aortic tissues. Future studies will be performed to validate this approach by visually inspecting when damage occurs and adjusting the model using the ML-based approach.
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Affiliation(s)
- Timothy K Chung
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260
| | - Joseph Kim
- Roy J. Carver Department of Biomedical Engineering, University of Iowa, Iowa City, IA 52240
| | - Pete H Gueldner
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260
- University of Pittsburgh
| | - David A Vorp
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260; Department of Mechanical Engineering and Materials Science, University of Pittsburgh,Pittsburgh, PA 15261; Department of Surgery, University of Pittsburgh,Pittsburgh, PA 15213; McGowan Institute for Regenerative Medicine, University of Pittsburgh,Pittsburgh, PA 15219; Department of Chemical and Petroleum Engineering, University of Pittsburgh,Pittsburgh, PA 15261; Department of Mechanical Engineering and Materials Science, University of Pittsburgh,Pittsburgh, PA 15261; Department of Cardiothoracic Surgery, University of Pittsburgh,Pittsburgh, PA 15213; Clinical and Translational Sciences Institute, University of Pittsburgh, Pittsburgh, PA 15213
| | - M L Raghavan
- Roy J. Carver Department of Biomedical Engineering, University of Iowa, Iowa City, IA 52242
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Constantin BD, Simão da Silva E, Lessard S, Kauffman C, Soulez G. Morphology of Abdominal Aortic Aneurysms and Correlation with Biomechanical Tests of Aneurysmal Wall Fragments. Ann Vasc Surg 2024; 100:101-109. [PMID: 38110080 DOI: 10.1016/j.avsg.2023.10.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 09/30/2023] [Accepted: 10/17/2023] [Indexed: 12/20/2023]
Abstract
BACKGROUND Evaluate how specific morphologic aspects of abdominal aortic aneurysms (AAAs), including asymmetries, curvatures, tortuosities, and angulations, among others can influence the intrinsic biomechanical properties of the AAA's wall. This study analyzed the correlation of geometric measurements (1-dimensional, 2-dimensional, and 3-dimensional) of preoperative tomographic images of AAA with uniaxial biomechanical tests of the arterial wall fragments of these AAA obtained in open surgical repair of aneurysms. METHODS It was a multicenter, experimental, and observational study, and initially 54 individuals were selected who underwent open surgical of AAA, with valid biomechanical tests of the anterior wall of the AAA. Seven individuals were excluded because they had poor preoperative quality computed tomography scans and/or artifacts that impeded image segmentation and extraction of AAA geometric indices. The aortic fragments were subjected to uniaxial biomechanical destructive tests to obtain the following data: maximum load, failure stress, failure tension, failure strain energy, strain, and fragment thickness. In the same patients, preoperative computed tomography scans were performed with the extraction of 26 geometric indices, subdivided into 9 1-dimensional indices, 6 2-dimensional indices, and 11 3-dimensional indices. Data were subjected to statistical analysis using SPSS version 28. RESULTS Comparing ruptured and unruptured AAA, no statistical difference was observed between the biomechanical and geometric parameters. The fragment thickness of the ruptured AAA was lower than that of the unruptured AAA (P < 0.05). By comparing tomographic geometric indices and biomechanical parameters of the aortic fragments using Pearson's coefficient, positive and linear correlations (P < 0.05) were observed between the geometric variable maximum diameter (Dmax) of the AAA with maximum load (r = 0.408), failure tension (r = 0.372), and failure stress (r = 0.360). Positive and linear correlations were also observed between the variable diameter/height ratio (DHr) and the maximum load (r = 0.360), failure tension (r = 0.354), and failure stress (r = 0.289). The geometric variable DHr was dependent and correlated with Dmax. Simple regression analysis showed that R2 varied between 8.3% and 16.7%, and all models were significant (P < 0.05). CONCLUSIONS Dmax and DHr were linearly and positively correlated with the resistance parameters (maximum load, failure tension, and failure stress) of the AAA fragments. The DHr variable is dependent and correlated with Dmax. There was no correlation between the other geometric indices and the biomechanical parameters of the AAA wall. The asymmetries did not globally influence the biomechanics of AAA wall; however, they may influence regionally. Larger AAAs were stronger than smaller ones. Therefore, such findings may point toward Dmax is still the main geometric parameter, which influences the anterior wall, and possibly globally in the AAA.
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Affiliation(s)
- Bruno Donegá Constantin
- Department of Vascular and Endovascular Surgery, Medical School Hospital, University of Sao Paulo (HC-FMUSP), Sao Paulo, SP, Brazil.
| | - Erasmo Simão da Silva
- Department of Vascular and Endovascular Surgery, Medical School Hospital, University of Sao Paulo (HC-FMUSP), Sao Paulo, SP, Brazil
| | - Simon Lessard
- Université de Montréal, Centre de recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montreal, Quebec, Canada
| | - Claude Kauffman
- Université de Montréal, Centre de recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montreal, Quebec, Canada
| | - Gilles Soulez
- Université de Montréal, Centre de recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Montreal, Quebec, Canada
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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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Li Z, Pei M, Zhang J, Liu N, Wang J, Zou D. A study to characterize the mechanical properties and material constitution of adult descending thoracic aorta based on uniaxial tensile test and digital image correlation. Front Bioeng Biotechnol 2023; 11:1178199. [PMID: 37388776 PMCID: PMC10306407 DOI: 10.3389/fbioe.2023.1178199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 06/05/2023] [Indexed: 07/01/2023] Open
Abstract
The mechanical properties and material constitution of the aorta are important in forensic science and clinical medicine. Existing studies on the material constitution of the aorta do not satisfy the practical requirements of forensic and clinical medicine, as the reported failure stress and failure strain values for human aortic materials have a high dispersion. In this study, descending thoracic aortas were obtained from 50 cadavers (dead within 24 h) free of thoracic aortic disease, aged from 27 to 86 years old, which were divided into six age groups. The descending thoracic aorta was divided into proximal and distal segments. A customized 4-mm cutter was used to punch a circumferential and an axial dog-bone-shaped specimen from each segment; the aortic ostia and calcification were avoided. Instron 8,874 and digital image correlation were used to perform a uniaxial tensile test on each sample. Four samples from each descending thoracic aorta produced ideal stress-strain curves. All parameter-fitting regressions from the selected mathematical model converged, and the best-fit parameters of each sample were obtained. The elastic modulus of collagen fiber, failure stress, and the strain showed a decreasing trend with age, while the elastic modulus of elastic fiber showed an increasing trend with age. The elastic modulus of collagen fiber, failure stress, and strain of circumferential tensile were all greater than those for axial tensile. There was no statistical difference in model parameters and physiological moduli between the proximal and distal segments. The failure stress and strain in the proximal circumferential, distal circumferential, and distal axial tensile were all greater for the male group than for the female group. Finally, the Fung-type hyperelastic constitutive equations were fitted for the different segments in different age groups.
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Affiliation(s)
- Zhengdong Li
- Shanghai Key Laboratory of Forensic Medicine, Key Laboratory of Forensic Science, Ministry of Justice, Shanghai Forensic Service Platform, Academy of Forensic Science, Shanghai, China
| | - Ming Pei
- Institute of Forensic Science, Xuzhou Public Security Bureau, Xuzhou, Jiangsu, China
| | - Jianhua Zhang
- Shanghai Key Laboratory of Forensic Medicine, Key Laboratory of Forensic Science, Ministry of Justice, Shanghai Forensic Service Platform, Academy of Forensic Science, Shanghai, China
| | - Ningguo Liu
- Shanghai Key Laboratory of Forensic Medicine, Key Laboratory of Forensic Science, Ministry of Justice, Shanghai Forensic Service Platform, Academy of Forensic Science, Shanghai, China
| | - Jinming Wang
- Shanghai Key Laboratory of Forensic Medicine, Key Laboratory of Forensic Science, Ministry of Justice, Shanghai Forensic Service Platform, Academy of Forensic Science, Shanghai, China
| | - Donghua Zou
- Shanghai Key Laboratory of Forensic Medicine, Key Laboratory of Forensic Science, Ministry of Justice, Shanghai Forensic Service Platform, Academy of Forensic Science, Shanghai, China
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Gasser TC, Miller C, Polzer S, Roy J. A quarter of a century biomechanical rupture risk assessment of abdominal aortic aneurysms. Achievements, clinical relevance, and ongoing developments. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2023; 39:e3587. [PMID: 35347895 DOI: 10.1002/cnm.3587] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 01/28/2022] [Accepted: 03/03/2022] [Indexed: 05/12/2023]
Abstract
Abdominal aortic aneurysm (AAA) disease, the local enlargement of the infrarenal aorta, is a serious condition that causes many deaths, especially in men exceeding 65 years of age. Over the past quarter of a century, computational biomechanical models have been developed towards the assessment of AAA risk of rupture, technology that is now on the verge of being integrated within the clinical decision-making process. The modeling of AAA requires a holistic understanding of the clinical problem, in order to set appropriate modeling assumptions and to draw sound conclusions from the simulation results. In this article we summarize and critically discuss the proposed modeling approaches and report the outcome of clinical validation studies for a number of biomechanics-based rupture risk indices. Whilst most of the aspects concerning computational mechanics have already been settled, it is the exploration of the failure properties of the AAA wall and the acquisition of robust input data for simulations that has the greatest potential for the further improvement of this technology.
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Affiliation(s)
- T Christian Gasser
- Department of Engineering Mechanics, KTH Royal Institute of Technology, Stockholm, Sweden
- Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark
| | - Christopher Miller
- Department of Engineering Mechanics, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Stanislav Polzer
- Department of Applied Mechanics, VSB-Technical University of Ostrava, Ostrava-Poruba, Czech Republic
| | - Joy Roy
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden
- Department of Vascular Surgery, Karolinska University Hospital, Stockholm, Sweden
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Hossack M, Fisher R, Torella F, Madine J, Field M, Akhtar R. Micromechanical and Ultrastructural Properties of Abdominal Aortic Aneurysms. Artery Res 2022. [DOI: 10.1007/s44200-022-00011-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
AbstractAbdominal aortic aneurysms are a common condition of uncertain pathogenesis that can rupture if left untreated. Current recommended thresholds for planned repair are empirical and based entirely on diameter. It has been observed that some aneurysms rupture before reaching the threshold for repair whilst other larger aneurysms do not rupture. It is likely that geometry is not the only factor influencing rupture risk. Biomechanical indices aiming to improve and personalise rupture risk prediction require, amongst other things, knowledge of the material properties of the tissue and realistic constitutive models. These depend on the composition and organisation of the vessel wall which has been shown to undergo drastic changes with aneurysmal degeneration, with loss of elastin, smooth muscle cells, and an accumulation of isotropically arranged collagen. Most aneurysms are lined with intraluminal thrombus, which has an uncertain effect on the underlying vessel wall, with some authors demonstrating a reduction in wall stress and others a reduction in wall strength. The majority of studies investigating biomechanical properties of ex vivo abdominal aortic aneurysm tissues have used low-resolution techniques, such as tensile testing, able to measure the global material properties at the macroscale. High-resolution engineering techniques such as nanoindentation and atomic force microscopy have been modified for use in soft biological tissues and applied to vascular tissues with promising results. These techniques have the potential to advance the understanding and improve the management of abdominal aortic aneurysmal disease.
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Jun KW, Yoo JH, Ko KJ, Cho HJ, Kim MH, Han KD, Hwang JK. Chronic kidney disease as a risk factor for abdominal aortic aneurysm: a nationwide population-based study. Ann Surg Treat Res 2022; 103:297-305. [DOI: 10.4174/astr.2022.103.5.297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 09/14/2022] [Accepted: 09/15/2022] [Indexed: 11/12/2022] Open
Affiliation(s)
- Kang-woong Jun
- Division of Vascular and Transplant Surgery, Department of Surgery, Bucheon St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Ju-hwan Yoo
- Department of Biomedicine and Health Science, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Kyung-jai Ko
- Department of Surgery, Kangdong Sacred Heart Hospital, Seoul, Korea
| | - Hyung-jin Cho
- Division of Vascular and Transplant Surgery, Department of Surgery, Eunpyeong St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Mi-hyeong Kim
- Division of Vascular and Transplant Surgery, Department of Surgery, Eunpyeong St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Kyung-do Han
- Department of Statistics and Actuarial Science, Soongsil University, Seoul, Korea
| | - Jeong-kye Hwang
- Division of Vascular and Transplant Surgery, Department of Surgery, Eunpyeong St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea
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Li T, Liu X, Sun H, Ning H, Yang J, Ma C. Assessment of the Global and Regional Circumferential Strain of Abdominal Aortic Aneurysm with Different Size by Speckle-Tracking Echocardiography. JOURNAL OF ULTRASOUND IN MEDICINE : OFFICIAL JOURNAL OF THE AMERICAN INSTITUTE OF ULTRASOUND IN MEDICINE 2021; 40:2619-2627. [PMID: 33555036 DOI: 10.1002/jum.15651] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 01/05/2021] [Accepted: 01/20/2021] [Indexed: 06/12/2023]
Abstract
OBJECTIVES We aimed to use speckle-tracking echocardiography (STE) to quantify circumferential aortic strain of abdominal aortic aneurysms (AAA) with different size. METHODS A total of 87 AAA patients were included. The morphological variables, including aortic maximum diameter (MD), end systolic area (ESA), end diastolic area (EDA), and thickness and area of intraluminal thrombus (ILT), were measured by ultrasound. STE was applied to calculate circumferential strain (CS) at 6 equally divided segments of the aorta at MD. We evaluated the mean value of peak strain along the 6 segments as global circumferential strain (GCS). RESULTS Large AAA (≥5.5 cm) patients had higher MD, ESA, EDA, AAA length, ILT thickness, and area, but lower fractional area change, GCS, and segmental CSs than small AAA (<5.5 cm) subjects (all P < .05). Compared with AAA <4.5 cm group, AAA patients ≥4.5 cm possessed increased MD, ESA, EDA, AAA length, ILT thickness, and area, which results were also reflected in the comparison between AAA <6.5 and ≥6.5 cm group. In small AAA patients, GCS and regional strains in CS1, CS3, and CS5 segments were lower in AAA subjects ≥4.5 cm than those <4.5 cm (all P<.05). However, no significant differences in the GCS and regional CS between ≥6.5 and <6.5 cm group were found. Correlation analysis revealed a significant negative association of GCS with MD, ESA, and EDA, even after adjusting the potential confounding factors (all P < .05). CONCLUSIONS Our findings may yield insight into the structural strain characteristics of AAA wall with different size, which adds the benefit of using simple echocardiography-derived biomechanics to stratify AAA patients.
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Affiliation(s)
- Tan Li
- Department of Cardiovascular Ultrasound, The First Hospital of China Medical University, Shenyang, China
| | - Xiaozheng Liu
- Department of Cardiovascular Ultrasound, The First Hospital of China Medical University, Shenyang, China
| | - Haiyang Sun
- Department of Ultrasound, Shenyang Women's and Children's Hospital, Shenyang, China
| | - Hongxia Ning
- Department of Cardiovascular Ultrasound, The First Hospital of China Medical University, Shenyang, China
| | - Jun Yang
- Department of Cardiovascular Ultrasound, The First Hospital of China Medical University, Shenyang, China
| | - Chunyan Ma
- Department of Cardiovascular Ultrasound, The First Hospital of China Medical University, Shenyang, China
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Development of an FEA framework for analysis of subject-specific aortic compliance based on 4D flow MRI. Acta Biomater 2021; 125:154-171. [PMID: 33639309 DOI: 10.1016/j.actbio.2021.02.027] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 02/15/2021] [Accepted: 02/18/2021] [Indexed: 12/30/2022]
Abstract
This paper presents a subject-specific in-silico framework in which we uncover the relationship between the spatially varying constituents of the aorta and the non-linear compliance of the vessel during the cardiac cycle uncovered through our MRI investigations. A microstructurally motivated constitutive model is developed, and simulations reveal that internal vessel contractility, due to pre-stretched elastin and actively generated smooth muscle cell stress, must be incorporated, along with collagen strain stiffening, in order to accurately predict the non-linear pressure-area relationship observed in-vivo. Modelling of elastin and smooth muscle cell contractility allows for the identification of the reference vessel configuration at zero-lumen pressure, in addition to accurately predicting high- and low-compliance regimes under a physiological range of pressures. This modelling approach is also shown to capture the key features of elastin digestion and SMC activation experiments. The volume fractions of the constituent components of the aortic material model were computed so that the in-silico pressure-area curves accurately predict the corresponding MRI data at each location. Simulations reveal that collagen and smooth muscle volume fractions increase distally, while elastin volume fraction decreases distally, consistent with reported histological data. Furthermore, the strain at which collagen transitions from low to high stiffness is lower in the abdominal aorta, again supporting the histological finding that collagen waviness is lower distally. The analyses presented in this paper provide new insights into the heterogeneous structure-function relationship that underlies aortic biomechanics. Furthermore, this subject-specific MRI/FEA methodology provides a foundation for personalised in-silico clinical analysis and tailored aortic device development. STATEMENT OF SIGNIFICANCE: This study provides a significant advance in in-silico medicine by capturing the structure/function relationship of the subject-specific human aorta presented in our previous MRI analyses. A physiologically based aortic constitutive model is developed, and simulations reveal that internal vessel contractility must be incorporated, along with collagen strain stiffening, to accurately predict the in-vivo non-linear pressure-area relationship. Furthermore, this is the first subject-specific model to predict spatial variation in the volume fractions of aortic wall constituents. Previous studies perform phenomenological hyperelastic curve fits to medical imaging data and ignore the prestress contribution of elastin, collagen, and SMCs and the associated zero-pressure reference state of the vessel. This novel MRI/FEA framework can be used as an in-silico diagnostic tool for the early stage detection of aortic pathologies.
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Pei M, Zou D, Gao Y, Zhang J, Huang P, Wang J, Huang J, Li Z, Chen Y. The influence of sample geometry and size on porcine aortic material properties from uniaxial tensile tests using custom-designed tissue cutters, clamps and molds. PLoS One 2021; 16:e0244390. [PMID: 33556052 PMCID: PMC7869995 DOI: 10.1371/journal.pone.0244390] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 12/08/2020] [Indexed: 11/18/2022] Open
Abstract
The aim of this study was to identify the influence of specimen geometry and size on the results of aortic uniaxial tensile tests using custom-designed tissue cutters, clamps and molds. Six descending thoracic aortas from pigs were used for rectangular sample tests, in which the circumferential and axial specimens had widths of 6 mm, 8 mm and 10 mm. The other six aortas were used for the dog-bone-shaped sample tests and were punched into circumferential, axial and oblique specimens with widths of 2 mm, 4 mm and 6 mm. We performed uniaxial tensile tests on the specimens and compared the test results. The results showed that mid-sample failure occurred in 85.2% of the dog-bone-shaped specimens and in 11.1% of the rectangular samples, which could be caused by Saint-Venant’s principle. Therefore, rectangular specimens were not suitable for aortic uniaxial tensile testing performed until rupture. The results also showed that the size effect of the aorta conformed to Weibull theory, and dog-bone-shaped specimens with a width of 4 mm were the optimal choice for aortic uniaxial tensile testing performed until rupture.
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Affiliation(s)
- Ming Pei
- West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province, China
- Shanghai Key laboratory of Forensic Medicine, Academy of Forensic Science, Ministry of Justice, Shanghai, China
- Institute of Forensic Science, Xuzhou Public Security Bureau, Xuzhou, Jiangsu Province, China
| | - Donghua Zou
- Shanghai Key laboratory of Forensic Medicine, Academy of Forensic Science, Ministry of Justice, Shanghai, China
- School of Forensic Medicine, Guizhou Medical University, Guiyang, Guizhou Province, China
| | - Yong Gao
- School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai, China
| | - Jianhua Zhang
- Shanghai Key laboratory of Forensic Medicine, Academy of Forensic Science, Ministry of Justice, Shanghai, China
| | - Ping Huang
- Shanghai Key laboratory of Forensic Medicine, Academy of Forensic Science, Ministry of Justice, Shanghai, China
| | - Jiawen Wang
- School of Forensic Medicine, Guizhou Medical University, Guiyang, Guizhou Province, China
| | - Jiang Huang
- School of Forensic Medicine, Guizhou Medical University, Guiyang, Guizhou Province, China
| | - Zhengdong Li
- Shanghai Key laboratory of Forensic Medicine, Academy of Forensic Science, Ministry of Justice, Shanghai, China
- Department of Forensic Medicine, School of Basic Medical Sciences, Fudan University, Shanghai, China
- * E-mail: (ZL); (YC)
| | - Yijiu Chen
- West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Chengdu, Sichuan Province, China
- Shanghai Key laboratory of Forensic Medicine, Academy of Forensic Science, Ministry of Justice, Shanghai, China
- * E-mail: (ZL); (YC)
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Failure properties of abdominal aortic aneurysm tissue are orientation dependent. J Mech Behav Biomed Mater 2020; 114:104181. [PMID: 33153925 DOI: 10.1016/j.jmbbm.2020.104181] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Revised: 08/12/2020] [Accepted: 10/23/2020] [Indexed: 10/23/2022]
Abstract
INTRODUCTION Biomechanical rupture risk assessment of abdominal aortic aneurysm (AAA) requires information about failure properties of aneurysmal tissue. There are large differences between reported values. Among others, studies vary in using either axially or circumferentially oriented samples. This study investigates the effect of sample orientation on failure properties. METHODS Aneurysmal tissues from 45 patients (11 females) were harvested during open AAA repair, cut into uniaxial samples (90) and tested mechanically within 3 h. If possible, the samples were cut in both axial (49 samples) and circumferential (41 samples) directions. Wall thickness, First Piola-Kirchhoff strength Pult and ultimate tension Tult were recorded. Influence of sample orientation and other clinical parameters were investigated using non parametric tests. RESULTS Medians of Pult (values 1100 kPa for circumferential vs. 715 kPa for axial direction, p < 10-4) and Tult (17.4 N/cm in circumferential vs. 11.2 N/cm in axial direction, p < 10-4) were significantly higher in circumferential direction. For paired data, the median of difference was 411 kPa (p < 10-3) in Pult and 7.4 N/cm (p < 10-4) in Tult in favor of circumferential direction. CONCLUSIONS In this first study of anisotropy in AAA wall failure properties using paired comparisons, the strength in circumferential orientation was found to be higher than in axial orientation.
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de Lucio M, García MF, García JD, Rodríguez LER, Marcos FÁ. On the importance of tunica intima in the aging aorta: a three-layered in silico model for computing wall stresses in abdominal aortic aneurysms. Comput Methods Biomech Biomed Engin 2020; 24:467-484. [PMID: 33090043 DOI: 10.1080/10255842.2020.1836167] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Layer-specific experimental data for human aortic tissue suggest that, in aged arteries and arteries with non-atherosclerotic intimal thickening, the innermost layer of the aorta increases significantly its stiffness and thickness, becoming load-bearing. However, there are very few computational studies of abdominal aortic aneurysms (AAAs) that take into account the mechanical contribution of the three layers that comprise the aneurysmal tissue. In this paper, a three-layered finite element model is proposed from the simplest uniaxial stress state to geometrically parametrized models of AAAs with different asymmetry values. Comparisons are made between a three-layered artery wall and a mono-layered intact artery, which represents the complex behavior of the aggregate adventitia-media-intima in a single layer with averaged mechanical properties. Likewise, the response of our idealized geometries is compared with similar experimental and numerical models. Finally, the mechanical contributions of adventitia, media and intima are analyzed for the three-layered aneurysms through the evaluation of the mean stress absorption percentage. Results show the relevance and necessity of considering the inclusion of tunica intima in multi-layered models of AAAs for getting accurate results in terms of peak wall stresses and displacements.
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Affiliation(s)
- Mario de Lucio
- School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA
| | - Marcos Fernández García
- Structural Impact Laboratory (SIMLab) and Centre for Advanced Structural Analysis (CASA), Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Jacobo Díaz García
- Structural Mechanics Group, School of Civil Engineering, Universidade da Coruña, A Coruña, Spain
| | | | - Francisco Álvarez Marcos
- Angiology and Vascular Surgery Department, Asturias University Central Hospital (HUCA), Oviedo, Spain
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13
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ANTONOVA MARIYA, ANTONOVA SOFIA, SHIKOVA LYUDMILA, KANEVA MARIA, GOVEDARSKI VALENTIN, ZAHARIEV TODOR, STOYTCHEV STOYAN. A REVIEW OF THE MECHANICAL STRESSES PREDISPOSING ABDOMINAL AORTIC ANEURYSMAL RUPTURE: UNIAXIAL EXPERIMENTAL APPROACH. J MECH MED BIOL 2020. [DOI: 10.1142/s021951942030001x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In this paper, problems concerning the uniaxial experimental investigation of the human abdominal aortic aneurysm (AAA) biomechanical characteristics, concomitant values of the associated Cauchy stress, failure (ultimate) stress in AAA, and the constitutive modeling of AAA are considered. The aim of this paper is to review and compare the disposable experimental data, to reveal the reasons for the high dissipation of the results between studies, and to propound some unification criteria. We examined 22 literature sources published between 1994 and 2017 and compared their results, including our own results. The experiments in the reviewed literature have been designed to obtain the stress–strain characteristics and the failure (ultimate) stress and strain of the aneurysmal tissue. A variety of forms of the strain–energy function (SEF) have been applied in the considered studies to model the biomechanical behavior of the aneurysmal wall. The specimen condition and physical parameters, the experimental protocols, the failure stress and strain, and SEFs differ between studies, contributing to the differences between the final results. We propound some criteria and suggestions for the unification of the experiments leading to the comparable results.
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Affiliation(s)
- MARIYA ANTONOVA
- Department of Behavioral Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Acad. G. Bonchev St, Bl. 23, 1113 Sofia, Bulgaria
| | - SOFIA ANTONOVA
- Department of Vascular Surgery and Angiology, Medical Faculty, Medical University Sofia, P. Slaveykov Bl. 52, 1000 Sofia, Bulgaria
| | - LYUDMILA SHIKOVA
- Department of Behavioral Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Acad. G. Bonchev St, Bl. 23, 1113 Sofia, Bulgaria
| | - MARIA KANEVA
- Department of Behavioral Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Acad. G. Bonchev St, Bl. 23, 1113 Sofia, Bulgaria
| | - VALENTIN GOVEDARSKI
- Department of Vascular Surgery and Angiology, Medical Faculty, Medical University Sofia, P. Slaveykov Bl. 52, 1000 Sofia, Bulgaria
| | - TODOR ZAHARIEV
- Department of Vascular Surgery and Angiology, Medical Faculty, Medical University Sofia, P. Slaveykov Bl. 52, 1000 Sofia, Bulgaria
| | - STOYAN STOYTCHEV
- Department of Biomechanics, Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St, Bl. 4, 1113 Sofia, Bulgaria
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14
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Abrão SR, Campos CM, Cavalcante R, Eggermont J, Lemos P, Lederman A, da Silva ES, Aun R, Belczak SQ, Abizaid A, de Brito FS. Percutaneous endovascular delivery of calcium chloride to the intact porcine carotid artery: A novel animal model of arterial calcification. Catheter Cardiovasc Interv 2020; 96:E484-E492. [PMID: 32558228 DOI: 10.1002/ccd.29070] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 05/26/2020] [Indexed: 11/09/2022]
Abstract
OBJECTIVE The present study evaluated the effect of endovascular administration of calcium chloride to the carotid artery of swines, to create a model of arterial calcification. METHODS Fifteen Large White pigs were used for the study. Via endovascular treatment, carotid arteries were exposed during 9 min to either calcium chloride (experimental artery) or saline (control artery) with the use of the TAPAS catheter. Intravascular ultrasound (IVUS) imaging was obtained at baseline, postprocedure and at 30 days. Optical coherence tomography (OCT) imaging was obtained in vitro after carotids were harvested. Longitudinally cut parallel arterial segments were placed in a system of delicate clamps and underwent uniaxial strain test. All arteries underwent histopathological examination. RESULTS Calcium chloride treated segments showed extensive circumferential parietal calcification evident on both IVUS and OCT. Reduction in minimal lumen area on IVUS was evident in experimental arteries both at 24 hr and 30 days postprocedure. Histopathologic assessment (Von Kossa stain) confirmed medial calcification with mild intimal thickening. Biomechanical testing showed treated segments to have smaller breaking strength and less elastic deformation than controls. CONCLUSION We developed a nonexpensive, reproducible model of early carotid medial calcification in pigs. Our model has the potential to help the development of research to unravel mechanisms underlying arterial calcification, the use of current or new devices to treat calcified lesions as well as to serve as an option for training interventionalists on the use of such devices.
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Affiliation(s)
| | - Carlos M Campos
- Hospital Israelita Albert Einstein, Sao Paulo, Brazil.,Heart Institute (InCor), University of São Paulo Medical School, Sao Paulo, Brazil
| | | | | | - Pedro Lemos
- Hospital Israelita Albert Einstein, Sao Paulo, Brazil.,Heart Institute (InCor), University of São Paulo Medical School, Sao Paulo, Brazil
| | - Alex Lederman
- Hospital Israelita Albert Einstein, Sao Paulo, Brazil.,Department of Vascular Surgery, University of São Paulo Medical School, Sao Paulo, Brazil
| | - Erasmo S da Silva
- Department of Vascular Surgery, University of São Paulo Medical School, Sao Paulo, Brazil
| | - Ricardo Aun
- Hospital Israelita Albert Einstein, Sao Paulo, Brazil.,Department of Vascular Surgery, University of São Paulo Medical School, Sao Paulo, Brazil
| | - Sergio Q Belczak
- Hospital Israelita Albert Einstein, Sao Paulo, Brazil.,Hospital Sao Camilo, Sao Paulo, Brazil
| | - Alexandre Abizaid
- Heart Institute (InCor), University of São Paulo Medical School, Sao Paulo, Brazil
| | - Fabio Sandoli de Brito
- Heart Institute (InCor), University of São Paulo Medical School, Sao Paulo, Brazil.,Hospital Sao Camilo, Sao Paulo, Brazil
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15
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Fortunato RN, Robertson AM, Sang C, Maiti S. Computational modeling reveals the relationship between intrinsic failure properties and uniaxial biomechanical behavior of arterial tissue. Biomech Model Mechanobiol 2019; 18:1791-1807. [PMID: 31165377 PMCID: PMC6825527 DOI: 10.1007/s10237-019-01177-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 05/27/2019] [Indexed: 01/20/2023]
Abstract
Biomechanical failure of the artery wall can lead to rupture, a catastrophic event with a high rate of mortality. Thus, there is a pressing need to understand failure behavior of the arterial wall. Uniaxial testing remains the most common experimental technique to assess tissue failure properties. However, the relationship between intrinsic failure parameters of the tissue and measured uniaxial failure properties is not fully established. Furthermore, the effect of the experimental variables, such as specimen shape and boundary conditions, on the measured failure properties is not well understood. We developed a finite element model capable of recapitulating pre-failure and post-failure uniaxial biomechanical response of the arterial tissue specimen. Intrinsic stiffness, strength and fracture toughness of the vessel wall tissue were used as the input material parameters to the model. Two uniaxial testing protocols were considered: a conventional setup with a rectangular specimen held at the grips by cardboard inserts, and the other used a dogbone specimen with soft foam inserts at the grips. Our computational study indicated negligible differences in the peak stress and post-peak mechanical behavior between these two testing protocols. It was also found that the tissue experienced only modest localized failure until higher levels of applied stretch beyond the peak stress. A robust cohesive model was capable of modeling the post-peak biomechanical response, which was primarily governed by tissue fracture toughness. Our results suggest that the post-peak region, in conjunction with the peak stress, must be considered to evaluate the complete biomechanical failure behavior of the soft tissue.
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Affiliation(s)
- Ronald N Fortunato
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 636 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA
| | - Anne M Robertson
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 636 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA
- Department of Bioengineering, University of Pittsburgh, 302 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA
| | - Chao Sang
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 636 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA
| | - Spandan Maiti
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 636 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA.
- Department of Bioengineering, University of Pittsburgh, 302 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA.
- Department of Chemical and Petroleum Engineering, University of Pittsburgh, 940 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA, 15261, USA.
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16
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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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17
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Meekel JP, Mattei G, Costache VS, Balm R, Blankensteijn JD, Yeung KK. A multilayer micromechanical elastic modulus measuring method in ex vivo human aneurysmal abdominal aortas. Acta Biomater 2019; 96:345-353. [PMID: 31306785 DOI: 10.1016/j.actbio.2019.07.019] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2019] [Revised: 06/23/2019] [Accepted: 07/11/2019] [Indexed: 02/07/2023]
Abstract
Abdominal aortic aneurysms (AAA) are common and potentially life-threatening aortic dilatations, due to the effect of hemodynamic changes on the aortic wall. Previous research has shown a potential pathophysiological role for increased macroscopic aneurysmal wall stiffness; however, not investigating micromechanical stiffness. We aimed to compile a new protocol to examine micromechanical live aortic stiffness (elastic moduli), correlated to histological findings with quantitative immunofluorescence (QIF). Live AAA biopsies (n = 7) and non-dilated aortas (controls; n = 3) were sectioned. Local elastic moduli of aortic intima, media and adventitia were analysed in the direction towards the lumen and vice versa with nanoindentation. Smooth muscle cells (SMC), collagen and fibroblasts were examined using QIF. Nanoindentation of AAA vs. controls demonstrated a 4-fold decrease in elastic moduli (p = 0.022) for layers combined and a 26-fold decrease (p = 0.017) for media-to-intima direction. QIF of AAA vs. controls revealed a 4-, 3- and 6-fold decrease of SMC, collagen and fibroblasts, respectively (p = 0.036). Correlations were found between bidirectional intima and media measurements (ρ = 0.661, p = 0.038) and all QIF analyses (ρ = 0.857-0.905, p = 0.002-0.007). We present a novel protocol to analyse microscopic elastic moduli in live aortic tissues using nanoindentation. Hence, our preliminary findings of decreased elastic moduli and altered wall composition warrant further microscopic stiffness investigation to potentially clarify AAA pathophysiology and to explore potential treatment by wall strengthening. STATEMENT OF SIGNIFICANCE: Although extensive research on the pathophysiology of dilated abdominal aortas (aneurysms) has been performed, the exact underlying pathways are still largely unclear. Previously, the macroscopic stiffness of the pathologic and healthy aortic wall has been studied. This study however, for the first time, studied the microscopic stiffness changes in live tissue of dilated and non-dilated abdominal aortas. This new protocol provides a device to analyse the alterations on cellular level within their microenvironment, whereas previous studies studied the aorta as a whole. Outcomes of these measurements might help to better understand the underlying origin of the incidence and progression of aneurysms and other aortic diseases.
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Affiliation(s)
- Jorn P Meekel
- Department of Vascular Surgery, Amsterdam University Medical Centers, Location VU Medical Center, Amsterdam, The Netherlands; Department of Physiology, Amsterdam University Medical Centers, Location VU Medical Center, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands
| | - Giorgio Mattei
- Optics11 B.V., Amsterdam, The Netherlands; Biophotonics & Medical Imaging and LaserLaB, VU University Amsterdam, Amsterdam, The Netherlands; Department of Information Engineering, University of Pisa, Pisa, Italy
| | - Victor S Costache
- Department of Cardiovascular Surgery, Polisano Medlife Hospital, University "L. Blaga" Sibiu, Sibiu, Romania
| | - Ron Balm
- Department of Vascular Surgery, Amsterdam University Medical Centers, Location Amsterdam Medical Center, Amsterdam, the Netherlands
| | - Jan D Blankensteijn
- Department of Vascular Surgery, Amsterdam University Medical Centers, Location VU Medical Center, Amsterdam, The Netherlands
| | - Kak K Yeung
- Department of Vascular Surgery, Amsterdam University Medical Centers, Location VU Medical Center, Amsterdam, The Netherlands; Department of Physiology, Amsterdam University Medical Centers, Location VU Medical Center, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands.
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18
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Leach J, Kao E, Zhu C, Saloner D, Hope MD. On the relative impact of intraluminal thrombus heterogeneity on abdominal aortic aneurysm mechanics. J Biomech Eng 2019; 141:2737715. [PMID: 31253989 DOI: 10.1115/1.4044143] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Indexed: 01/31/2023]
Abstract
Intraluminal thrombus (ILT) is present in the majority of abdominal aortic aneurysms (AAA) of a size warranting consideration for surgical or endovascular intervention. The rupture risk of AAAs is thought to be related to the balance of vessel wall strength and the mechanical stress caused by systemic blood pressure. Previous finite element analyses of AAAs have shown that ILT can reduce and homogenize aneurysm wall stress. These works have largely considered ILT to be homogeneous in mechanical character or have idealized a stiffness distribution through the thrombus thickness. In this work, we use MRI to delineate the heterogeneous composition of ILT in 7 AAAs and perform patient-specific finite element analysis under multiple conditions of ILT layer stiffness disparity. We find that explicit incorporation of ILT heterogeneity in the finite element analysis is unlikely to substantially alter major stress analysis predictions regarding aneurysm rupture risk in comparison to models assuming a homogenous thrombus, provided that the maximal ILT stiffness is the same between models. Our results also show that under a homogeneous ILT assumption, the choice of ILT stiffness from values common in the literature can result in significantly larger variations in stress predictions compared to the effects of thrombus heterogeneity.
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Affiliation(s)
- Joseph Leach
- University of California, San Francisco, Department of Radiology and Biomedical Imaging, 513 Parnassus Ave, Suite S-261, Box 0628, San Francisco, CA 94143
| | - Evan Kao
- University of California, San Francisco, Department of Radiology and Biomedical Imaging, San Francisco, CA 94143
| | - Chengcheng Zhu
- University of California, San Francisco, Department of Radiology and Biomedical Imaging, San Francisco, CA 94143
| | - David Saloner
- University of California, San Francisco, Department of Radiology and Biomedical Imaging, San Francisco, CA 94143
| | - Michael D Hope
- University of California, San Francisco, Department of Radiology and Biomedical Imaging, San Francisco, CA 94143
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19
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Attarian S, Xiao S, Chung T, da Silva ES, Raghavan ML. Investigation of the observed rupture lines in abdominal aortic aneurysms using crack propagation simulations. J Biomech Eng 2019; 141:2735557. [PMID: 31150536 DOI: 10.1115/1.4043940] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Indexed: 11/08/2022]
Abstract
OBJECTIVE To use crack propagation simulation to study the rupture site characteristics in ruptured abdominal aortic aneurysms (AAA). METHODS Rupture lines were precisely documented in four ruptured AAA harvested whole from cadavers. Wall thickness and material parameters were experimentally determined. Using subject-specific 3D geometry and subject-specific finite elastic model parameters, crack propagation simulations were conducted based on basic fracture mechanics principles to investigate if and how localized weak spots may have led to the observed rupture lines. RESULTS AND CONCLUSION When an initial crack was imposed at the site of peak wall stress, the propagated path did not match the observed rupture line. This indicates that in this study population, the peak wall stress was unlikely to have caused the observed rupture. When cracks were initiated at random locations in the AAA along random orientations for random initial lengths, the orientation of the resulting propagated rupture line was consistently longitudinal. This suggests that the AAA morphology predisposes the AAA to rupture longitudinally, which is consistent with observations. It was found that, in this study population, rupture may have initiated at short segments of less than about 1 cm that then propagated to form the observed rupture lines. This suggests that ex vivo experimental and in vivo elastography studies should seek a spatial resolution (approx. 1 cm) to reliably identify weak spots in AAA. The small study population and lack of a reliable failure model for AAA tissue make these findings preliminary.
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Affiliation(s)
- Siamak Attarian
- Department of Mechanical Engineering, University of Iowa, Iowa City, IA, USA
| | - Shaoping Xiao
- Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA
| | - Timothy Chung
- Department of Surgery, University of São Paulo School of Medicine, São Paulo, SP, Brazil
| | | | - Madhavan L Raghavan
- Professor, Biomedical Engineering, University of Iowa, Iowa City, IA, USA 52242
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20
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LEACH JOSEPHR, ZHU CHENGCHENG, SALONER DAVID, HOPE MICHAELD. COMPARISON OF TWO METHODS FOR ESTIMATING THE UNLOADED STATE FOR ABDOMINAL AORTIC ANEURYSM STRESS CALCULATIONS. J MECH MED BIOL 2019. [DOI: 10.1142/s0219519419500155] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Biomechanical analyses can be used to better understand the rupture risk of abdominal aortic aneurysms (AAAs) on a patient-specific basis using vascular geometries obtained from medical imaging. Methodologies of varying complexity are used to estimate the unloaded state of the imaged vessel to provide a reference configuration for finite element simulations. In this work, we compare the implementation and results of two of these methods, one based on geometric scaling and the other using an iterative determination of unloaded vessel geometry. We find that the two methods result in significantly different stress predictions, and that the iterative method offers superior geometric accuracy. Our findings lend context to the variation in finite element results presented in the AAA stress analysis literature.
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Affiliation(s)
- JOSEPH R. LEACH
- Department of Radiology and Biomedical Imaging, University of California, 505 Parnassus Avenue, M-391 San Francisco, CA 94143-0628, USA
| | - CHENGCHENG ZHU
- Department of Radiology and Biomedical Imaging, University of California, 505 Parnassus Avenue, M-391 San Francisco, CA 94143-0628, USA
| | - DAVID SALONER
- Department of Radiology and Biomedical Imaging, University of California, 505 Parnassus Avenue, M-391 San Francisco, CA 94143-0628, USA
- Department of Radiology, Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA 94121, USA
| | - MICHAEL D. HOPE
- Department of Radiology and Biomedical Imaging, University of California, 505 Parnassus Avenue, M-391 San Francisco, CA 94143-0628, USA
- Department of Radiology, Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA 94121, USA
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21
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Niestrawska JA, Regitnig P, Viertler C, Cohnert TU, Babu AR, Holzapfel GA. The role of tissue remodeling in mechanics and pathogenesis of abdominal aortic aneurysms. Acta Biomater 2019; 88:149-161. [PMID: 30735809 DOI: 10.1016/j.actbio.2019.01.070] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2018] [Revised: 01/03/2019] [Accepted: 01/31/2019] [Indexed: 12/28/2022]
Abstract
Arterial walls can be regarded as composite materials consisting of collagen fibers embedded in an elastic matrix and smooth muscle cells. Remodeling of the structural proteins has been shown to play a significant role in the mechanical behavior of walls during pathogenesis of abdominal aortic aneurysms (AAA). In this study, we systematically studied the change in the microstructure, histology and mechanics to link them to AAA disease progression. We performed biaxial extension tests, second-harmonic generation imaging and histology on 15 samples from the anterior part of AAA walls harvested during open aneurysm surgery. Structural data were gained by fitting to a bivariate von Mises distribution and yielded the mean fiber direction and in- and out-of-plane fiber dispersions of collagen. Mechanical and structural data were fitted to a recently proposed material model. Additionally, the mechanical data were used to derive collagen recruitment points in the obtained stress-stretch curves. We derived 14 parameters from histology such as smooth muscle cell-, elastin-, and abluminal adipocyte content. In total, 22 parameters were obtained and statistically evaluated. Based on the collagen recruitment points we were able to define three different stages of disease progression. Significant differences in elastin content, collagen orientation and adipocyte contents were discovered. Nerves entrapped inside AAA walls pointed towards a significant deposition of newly formed collagen abluminally, which we propose as neo-adventitia formation. We were able to discriminate two types of remodeled walls with a high collagen content - potentially safe and possibly vulnerable walls with a high adipocyte content inside the wall and significant amounts of inflammation. The study yielded a hypothesis for disease progression, derived from the systematic comparison of mechanical, microstructural and histological changes in AAAs. STATEMENT OF SIGNIFICANCE: Remodeling of the structural proteins plays an important role in the mechanical behavior of walls during pathogenesis of abdominal aortic aneurysms (AAA). We analyzed changes in the microstructure, histology and biomechanics of 15 samples from the anterior part of AAA walls and, for the first time, linked the results to three different stages of disease progression. We identified significant differences in elastin content, collagen orientation, adipocyte contents, and also a deposition of newly formed collagen forming a neoadventitia. We could discriminate two types of remodeled walls: (i) potentially safe and (ii) possibly vulnerable associated with inflammation and a high amount of adipocytes.
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22
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Computational Evaluation for Age-Dependent Material Nonlinear Behavior of Aortic Wall Tissue on Abdominal Aortic Aneurysms. APPLIED SCIENCES-BASEL 2018. [DOI: 10.3390/app9010101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
An abdominal aortic aneurysm is a localized expansion of the abdominal aorta with a diameter >3 cm or >50% larger than the normal diameter. In this study, the stretch and strength of the materials in the abdominal aorta in patients with aneurysms were examined based on the results of tensile tests, and databases of failure stress and stretch were established according to age. Generally, the tensile test results of the axial and circumferential directions have become a priority in the tests of aortic materials. However, this study focused on the results of the axial direction. In addition, finite element analysis, where the Holzapfel model and the test results were applied, was performed. As a result, the behavior characteristics of the abdominal aortic materials were precisely simulated. The formula and material constants used in the Holzapfel model were studied and proposed in order to simulate the failure stress and stretch according to age as well as simulation.
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23
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Sang C, Maiti S, Fortunato RN, Kofler J, Robertson AM. A Uniaxial Testing Approach for Consistent Failure in Vascular Tissues. J Biomech Eng 2018; 140:2675125. [PMID: 29560496 PMCID: PMC5938069 DOI: 10.1115/1.4039577] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Although uniaxial tensile testing is commonly used to evaluate failure properties of vascular tissue, there is no established protocol for specimen shape or gripping method. Large percentages of specimens are reported to fail near the clamp and can potentially confound the studies, or, if discarded will result in sample waste. The objective of this study is to identify sample geometry and clamping conditions that can achieve consistent failure in the midregion of small arterial specimens, even for vessels from older individuals. Failure location was assessed in 17 dogbone specimens from human cerebral and sheep carotid arteries using soft inserts. For comparison with commonly used protocols, an additional 22 rectangular samples were tested using either sandpaper or foam tape inserts. Midsample failure was achieved in 94% of the dogbone specimens, while only 14% of the rectangular samples failed in the midregion, the other 86% failing close to the clamps. Additionally, we found midregion failure was more likely to be abrupt, caused by cracking or necking. In contrast, clamp failure was more likely to be gradual and included a delamination mode not seen in midregion failure. Hence, this work provides an approach that can be used to obtain consistent midspecimen failure, avoiding confounding clamp-related artifacts. Furthermore, with consistent midregion failure, studies can be designed to image the failure process in small vascular samples providing valuable quantitative information about changes to collagen and elastin structure during the failure process.
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Affiliation(s)
- Chao Sang
- Department of Mechanical Engineering and
Materials Science,
University of Pittsburgh,
636 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
| | - Spandan Maiti
- Department of Bioengineering,
University of Pittsburgh,
302 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
| | - Ronald N. Fortunato
- Department of Mechanical Engineering and
Materials Science,
University of Pittsburgh,
636 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
| | - Julia Kofler
- Department of Pathology,
University of Pittsburgh,
S701.3 Scaife Hall,
Pittsburgh, PA 15261
e-mail:
| | - Anne M. Robertson
- Department of Mechanical Engineering and
Materials Science,
University of Pittsburgh,
440 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
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24
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Hemmler A, Lutz B, Reeps C, Kalender G, Gee MW. A methodology for in silico endovascular repair of abdominal aortic aneurysms. Biomech Model Mechanobiol 2018; 17:1139-1164. [PMID: 29752606 DOI: 10.1007/s10237-018-1020-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 04/23/2018] [Indexed: 11/29/2022]
Abstract
Endovascular aneurysm repair (EVAR) can involve some unfavorable complications such as endoleaks or stent-graft (SG) migration. Such complications, resulting from the complex mechanical interaction of vascular tissue, SG and blood flow or incompatibility of SG design and vessel geometry, are difficult to predict. Computational vascular mechanics models can be a predictive tool for the selection, sizing and placement process of SGs depending on the patient-specific vessel geometry and hence reduce the risk of potential complications after EVAR. In this contribution, we present a new in silico EVAR methodology to predict the final state of the deployed SG after intervention and evaluate the mechanical state of vessel and SG, such as contact forces and wall stresses. A novel method to account for residual strains and stresses in SGs, resulting from the precompression of stents during the assembly process of SGs, is presented. We suggest a parameter continuation approach to model various different sizes of SGs within one in silico EVAR simulation which can be a valuable tool when investigating the issue of SG oversizing. The applicability and robustness of the proposed methods are demonstrated on the example of a synthetic abdominal aortic aneurysm geometry.
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Affiliation(s)
- André Hemmler
- Mechanics and High Performance Computing Group, Technische Universität München, Parkring 35, 85748, Garching b. München, Germany
| | - Brigitta Lutz
- Klinik für Viszeral-, Thorax- und Gefäßchirurgie, Universitätsklinikum Carl Gustav Carus Dresden, Fetscherstraße 74, 01307, Dresden, Germany
| | - Christian Reeps
- Klinik für Viszeral-, Thorax- und Gefäßchirurgie, Universitätsklinikum Carl Gustav Carus Dresden, Fetscherstraße 74, 01307, Dresden, Germany
| | - Günay Kalender
- Klinik für vaskuläre und endovaskuläre Chirurgie, DRK Kliniken Berlin, Salvador-Allende-Straße 2-8, 12559, Berlin, Germany
| | - Michael W Gee
- Mechanics and High Performance Computing Group, Technische Universität München, Parkring 35, 85748, Garching b. München, Germany.
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Schroeder F, Polzer S, Slažanský M, Man V, Skácel P. Predictive capabilities of various constitutive models for arterial tissue. J Mech Behav Biomed Mater 2018; 78:369-380. [DOI: 10.1016/j.jmbbm.2017.11.035] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 11/09/2017] [Accepted: 11/20/2017] [Indexed: 11/16/2022]
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Farotto D, Segers P, Meuris B, Vander Sloten J, Famaey N. The role of biomechanics in aortic aneurysm management: requirements, open problems and future prospects. J Mech Behav Biomed Mater 2018; 77:295-307. [DOI: 10.1016/j.jmbbm.2017.08.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 08/09/2017] [Accepted: 08/15/2017] [Indexed: 12/18/2022]
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Local distribution of collagen fibers determines crack initiation site and its propagation direction during aortic rupture. Biomech Model Mechanobiol 2017; 17:577-587. [DOI: 10.1007/s10237-017-0979-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Accepted: 10/31/2017] [Indexed: 12/29/2022]
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Chung TK, da Silva ES, Raghavan SM. Does elevated wall tension cause aortic aneurysm rupture? Investigation using a subject-specific heterogeneous model. J Biomech 2017; 64:164-171. [DOI: 10.1016/j.jbiomech.2017.09.041] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Revised: 07/30/2017] [Accepted: 09/25/2017] [Indexed: 11/24/2022]
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Niestrawska JA, Viertler C, Regitnig P, Cohnert TU, Sommer G, Holzapfel GA. Microstructure and mechanics of healthy and aneurysmatic abdominal aortas: experimental analysis and modelling. J R Soc Interface 2017; 13:rsif.2016.0620. [PMID: 27903785 DOI: 10.1098/rsif.2016.0620] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 11/07/2016] [Indexed: 11/12/2022] Open
Abstract
Soft biological tissues such as aortic walls can be viewed as fibrous composites assembled by a ground matrix and embedded families of collagen fibres. Changes in the structural components of aortic walls such as the ground matrix and the embedded families of collagen fibres have been shown to play a significant role in the pathogenesis of aortic degeneration. Hence, there is a need to develop a deeper understanding of the microstructure and the related mechanics of aortic walls. In this study, tissue samples from 17 human abdominal aortas (AA) and from 11 abdominal aortic aneurysms (AAA) are systematically analysed and compared with respect to their structural and mechanical differences. The collagen microstructure is examined by analysing data from second-harmonic generation imaging after optical clearing. Samples from the intact AA wall, their individual layers and the AAA wall are mechanically investigated using biaxial stretching tests. A bivariate von Mises distribution was used to represent the continuous fibre dispersion throughout the entire thickness, and to provide two independent dispersion parameters to be used in a recently proposed material model. Remarkable differences were found between healthy and diseased tissues. The out-of-plane dispersion was significantly higher in AAA when compared with AA tissues, and with the exception of one AAA sample, the characteristic wall structure, as visible in healthy AAs with three distinct layers, could not be identified in AAA samples. The collagen fibres in the abluminal layer of AAAs lost their waviness and exhibited rather straight and thick struts of collagen. A novel set of three structural and three material parameters is provided. With the structural parameters fixed, the material model was fitted to the mechanical experimental data, giving a very satisfying fit although there are only three material parameters involved. The results highlight the need to incorporate the structural differences into finite-element simulations as otherwise simulations of AAA tissues might not be good predictors for the actual in vivo stress state.
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Affiliation(s)
- Justyna A Niestrawska
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2, 8010 Graz, Austria
| | - Christian Viertler
- Institute of Pathology, Medical University of Graz, Auenbruggerplatz 25, 8036 Graz, Austria
| | - Peter Regitnig
- Institute of Pathology, Medical University of Graz, Auenbruggerplatz 25, 8036 Graz, Austria
| | - Tina U Cohnert
- Clinical Department of Vascular Surgery, Medical University of Graz, Graz, Austria
| | - Gerhard Sommer
- 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 .,Faculty of Engineering Science and Technology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
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de Gelidi S, Tozzi G, Bucchi A. The effect of thickness measurement on numerical arterial models. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2017; 76:1205-1215. [DOI: 10.1016/j.msec.2017.02.123] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Revised: 02/03/2017] [Accepted: 02/24/2017] [Indexed: 10/20/2022]
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Kontopodis N, Galanakis N, Tsetis D, Ioannou CV. Perfusion computed tomography imaging of abdominal aortic aneurysms may be of value for patient specific rupture risk estimation. Med Hypotheses 2017; 101:6-10. [DOI: 10.1016/j.mehy.2017.01.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 11/27/2016] [Accepted: 01/21/2017] [Indexed: 10/20/2022]
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Ruiz de Galarreta S, Cazón A, Antón R, Finol EA. A Methodology for Verifying Abdominal Aortic Aneurysm Wall Stress. J Biomech Eng 2017; 139:2554137. [PMID: 27636678 DOI: 10.1115/1.4034710] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Indexed: 11/08/2022]
Abstract
An abdominal aortic aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta of at least 1.5 times its normal diameter. Although the criterion of maximum diameter is still used in clinical practice to decide on a timely intervention, numerical studies have demonstrated the importance of other geometric factors. However, the major drawback of numerical studies is that they must be validated experimentally before clinical implementation. This work presents a new methodology to verify wall stress predicted from the numerical studies against the experimental testing. To this end, four AAA phantoms were manufactured using vacuum casting. The geometry of each phantom was subject to microcomputed tomography (μCT) scanning at zero and three other intraluminal pressures: 80, 100, and 120 mm Hg. A zero-pressure geometry algorithm was used to calculate the wall stress in the phantom, while the numerical wall stress was calculated with a finite-element analysis (FEA) solver based on the actual zero-pressure geometry subjected to 80, 100, and 120 mm Hg intraluminal pressure loading. Results demonstrate the moderate accuracy of this methodology with small relative differences in the average wall stress (1.14%). Additionally, the contribution of geometric factors to the wall stress distribution was statistically analyzed for the four phantoms. The results showed a significant correlation between wall thickness and mean curvature (MC) with wall stress.
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Affiliation(s)
- Sergio Ruiz de Galarreta
- Department of Mechanical Engineering, TECNUN, University of Navarra, Paseo Manuel de Lardizabal, 13, San Sebastián 20018, Spain e-mail:
| | - Aitor Cazón
- Department of Mechanical Engineering, TECNUN, University of Navarra, Paseo Manuel de Lardizabal, 13, San Sebastián 20018, Spain e-mail:
| | - Raúl Antón
- Department of Mechanical Engineering, TECNUN, University of Navarra, Paseo Manuel de Lardizabal, 13, San Sebastián 20018, Spain e-mail:
| | - Ender A Finol
- Department of Biomedical Engineering, The University of Texas at San Antonio, One UTSA Circle, AET 1.360, San Antonio, TX 78249-0669 e-mail:
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33
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Biomechanical Characterization of Ascending Aortic Aneurysms. Biomech Model Mechanobiol 2016; 16:705-720. [DOI: 10.1007/s10237-016-0848-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 10/17/2016] [Indexed: 12/26/2022]
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Schwarz C, Aldrich BT, Burckart KA, Schmidt GA, Zimmerman MB, Reed CR, Greiner MA, Sander EA. Descemet membrane adhesion strength is greater in diabetics with advanced disease compared to healthy donor corneas. Exp Eye Res 2016; 153:152-158. [PMID: 27777123 DOI: 10.1016/j.exer.2016.10.015] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Revised: 10/19/2016] [Accepted: 10/20/2016] [Indexed: 11/27/2022]
Abstract
Descemet membrane endothelial keratoplasty (DMEK) is an increasingly popular surgical procedure for treating ocular diseases that require a corneal transplant. Previous studies have found that tissue tearing during surgical preparation is more likely elevated in eyes from donors with a history of diabetes mellitus. To quantify these potential differences, we established an experimental technique for quantifying the force required to separate the endothelium-Descemet membrane complex (EDM) from stroma in human donor corneal tissue, and we assessed differences in adhesion strength between diabetic and non-diabetic donor corneas. Transplant suitable corneas were obtained from 23 donors 50-75 years old with an average preservation to assay time of 11.5 days. Corneas were classified from a medical records review as non-diabetic (ND, n = 9), diabetic without evidence of advanced disease (NAD, n = 8), or diabetic with evidence of advanced disease (AD, n = 10). Corneas were sectioned into 3 mm wide strips and the EDM peeled from the stroma. Using the force-extension data obtained from mechanical peel testing, EDM elastic peel tension (TE), elastic stiffness (SE), average delamination tension (TD), and maximum tension (TMAX) were calculated. Mean TE, SE, TD, and TMAX values for ND corneas were 0.78 ± 0.07 mN/mm, 0.37 ± 0.05 mN/mm/mm, 0.78 ± 0.08 mN/mm, and 0.94 ± 0.17 mN/mm, respectively. NAD values did not differ significantly. However, AD values for TE (1.01 ± 0.18 mN/mm), TD (1.09 ± 0.21 mN/mm), and TMAX (1.37 ± 0.24 mN/mm) were greater than ND and NAD corneas (P < 0.05). SE did not differ significantly between groups. These findings provide proof of the concept that chronic hyperglycemia from diabetes mellitus results in a phenotypically more adhesive interface between Descemet membrane and the posterior stroma in donor corneal tissue. Results of this study provide a foundation for further investigations into the impact of diabetes on the posterior cornea, eye banking, and keratoplasty.
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Affiliation(s)
- Chaid Schwarz
- Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA
| | - Benjamin T Aldrich
- Department of Ophthalmology and Visual Sciences, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Iowa Lions Eye Bank, Coralville, IA, USA
| | | | | | - M Bridget Zimmerman
- College of Public Health, Department of Biostatistics, University of Iowa, Iowa City, IA, USA
| | | | - Mark A Greiner
- Department of Ophthalmology and Visual Sciences, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Iowa Lions Eye Bank, Coralville, IA, USA; Cornea Research Center, Stephen A. Wynn Institute for Vision Research, Iowa City, IA, USA.
| | - Edward A Sander
- Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA.
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Noble C, Smulders N, Green NH, Lewis R, Carré MJ, Franklin SE, MacNeil S, Taylor ZA. Creating a model of diseased artery damage and failure from healthy porcine aorta. J Mech Behav Biomed Mater 2016; 60:378-393. [DOI: 10.1016/j.jmbbm.2016.02.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 02/05/2016] [Accepted: 02/10/2016] [Indexed: 01/24/2023]
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Probabilistic noninvasive prediction of wall properties of abdominal aortic aneurysms using Bayesian regression. Biomech Model Mechanobiol 2016; 16:45-61. [DOI: 10.1007/s10237-016-0801-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 05/20/2016] [Indexed: 10/21/2022]
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37
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Gasser TC. Biomechanical Rupture Risk Assessment: A Consistent and Objective Decision-Making Tool for Abdominal Aortic Aneurysm Patients. AORTA : OFFICIAL JOURNAL OF THE AORTIC INSTITUTE AT YALE-NEW HAVEN HOSPITAL 2016; 4:42-60. [PMID: 27757402 DOI: 10.12945/j.aorta.2015.15.030] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 02/04/2016] [Indexed: 12/20/2022]
Abstract
Abdominal aortic aneurysm (AAA) rupture is a local event in the aneurysm wall that naturally demands tools to assess the risk for local wall rupture. Consequently, global parameters like the maximum diameter and its expansion over time can only give very rough risk indications; therefore, they frequently fail to predict individual risk for AAA rupture. In contrast, the Biomechanical Rupture Risk Assessment (BRRA) method investigates the wall's risk for local rupture by quantitatively integrating many known AAA rupture risk factors like female sex, large relative expansion, intraluminal thrombus-related wall weakening, and high blood pressure. The BRRA method is almost 20 years old and has progressed considerably in recent years, it can now potentially enrich the diameter indication for AAA repair. The present paper reviews the current state of the BRRA method by summarizing its key underlying concepts (i.e., geometry modeling, biomechanical simulation, and result interpretation). Specifically, the validity of the underlying model assumptions is critically disused in relation to the intended simulation objective (i.e., a clinical AAA rupture risk assessment). Next, reported clinical BRRA validation studies are summarized, and their clinical relevance is reviewed. The BRRA method is a generic, biomechanics-based approach that provides several interfaces to incorporate information from different research disciplines. As an example, the final section of this review suggests integrating growth aspects to (potentially) further improve BRRA sensitivity and specificity. Despite the fact that no prospective validation studies are reported, a significant and still growing body of validation evidence suggests integrating the BRRA method into the clinical decision-making process (i.e., enriching diameter-based decision-making in AAA patient treatment).
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Affiliation(s)
- T Christian Gasser
- KTH Royal Institute of Technology, KTH Solid Mechanics, Stockholm, Sweden
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38
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Batagini NC, Ventura CAP, Raghavan ML, Chammas MC, Tachibana A, da Silva ES. Volumetry and biomechanical parameters detected by 3D and 2D ultrasound in patients with and without an abdominal aortic aneurysm. Vasc Med 2016; 21:209-16. [DOI: 10.1177/1358863x16629727] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The objective was to demonstrate the ability of ultrasound (US) with 3D properties to evaluate volumetry and biomechanical parameters of the aorta in patients with and without abdominal aortic aneurysm (AAA). Thirty-one patients with normal aortas (group 1), 46 patients with AAA measuring 3.0–5.5 cm (group 2) and 31 patients with AAA ⩾ 5.5 cm (group 3) underwent a 2D/3D-US examination of the infra-renal aorta, and the images were post-processed prior to being analyzed. In the maximum diameter, the global circumferential strain and the global maximum rotation assessed by 2D speckle-tracking algorithms were compared among the three groups. The volumetry data obtained using 3D-US from 40 AAA patients were compared with the volumetry data obtained by a contemporary computed tomography (CT) scan. The median global circumferential strain was 2.0% (interquartile range (IR): 1.0–3.0), 1.0% (IR: 1.0–2.0) and 1.0% (IR: 1.0–1.75) in groups 1, 2 and 3, respectively ( p < 0.001). The median global maximum rotation decreased progressively from group 1 to group 3 (1.38º (IR: 0.77–2.13), 0.80º (IR: 0.57–1.0) and 0.50º (IR: 0.31–0.75), p < 0.001). AAA volume estimations by 3D-US correlated well with CT ( R2 = 0.76). In conclusion, US with 3D properties is non-invasive and has the potential to evaluate volumetry and biomechanical characteristics of AAA.
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Affiliation(s)
| | | | - Madhavan L Raghavan
- Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA
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39
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Ninomiya OH, Tavares Monteiro JA, Higuchi MDL, Puech-Leão P, de Luccia N, Raghavan ML, da Silva ES. Biomechanical Properties and Microstructural Analysis of the Human Nonaneurysmal Aorta as a Function of Age, Gender and Location: An Autopsy Study. J Vasc Res 2016; 52:257-64. [PMID: 26799837 DOI: 10.1159/000442979] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 12/01/2015] [Indexed: 11/19/2022] Open
Abstract
INTRODUCTION The biomechanical failure properties and histological composition of the human nonaneurysmal aorta were studied. METHODS Twenty-six human aortas were harvested from fresh cadavers at autopsy. A total of 153 circumferentially oriented strips were obtained from the aortas for biomechanical and histological studies. RESULTS The failure load (6.18 ± 2.03 vs. 4.85 ± 2.04 N; p = 0.001), failure tension (19.88 ± 9.05 vs. 14.53 ± 7 N/cm; p = 0.001), failure strain (0.66 ± 0.31 vs. 0.49 ± 0.25; p = 0.003) and amount of elastic fibers (19.39 ± 15.57 vs. 14.06 ± 9.5%; p = 0.011) were all significantly higher for the thoracic than the abdominal aorta. There was a significant negative correlation between age and failure load (R = -0.35; p < 0.0001), failure stress (R = -0.63; p < 0.0001), failure tension (R = -0.52; p < 0.0001) and failure strain (R = -0.8; p < 0.0001). Male aortas had a higher failure load and failure tension than female aortas. CONCLUSION The thoracic aorta has a higher strength and elasticity than the abdominal aorta. The elderly have weaker and stiffer aortas than the young. Male aortas are stronger than female aortas.
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Affiliation(s)
- Otavio Henrique Ninomiya
- Division of Vascular and Endovascular Surgery, Department of Surgery, University of Sx00E3;o Paulo School of Medicine, Sx00E3;o Paulo, Brazil
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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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Tanios F, Gee M, Pelisek J, Kehl S, Biehler J, Grabher-Meier V, Wall W, Eckstein HH, Reeps C. Interaction of Biomechanics with Extracellular Matrix Components in Abdominal Aortic Aneurysm Wall. Eur J Vasc Endovasc Surg 2015; 50:167-74. [DOI: 10.1016/j.ejvs.2015.03.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 03/09/2015] [Indexed: 10/23/2022]
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Teng Z, Feng J, Zhang Y, Huang Y, Sutcliffe MPF, Brown AJ, Jing Z, Gillard JH, Lu Q. Layer- and Direction-Specific Material Properties, Extreme Extensibility and Ultimate Material Strength of Human Abdominal Aorta and Aneurysm: A Uniaxial Extension Study. Ann Biomed Eng 2015; 43:2745-59. [PMID: 25905688 PMCID: PMC4611020 DOI: 10.1007/s10439-015-1323-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Accepted: 04/12/2015] [Indexed: 11/26/2022]
Abstract
Mechanical analysis has the potential to provide complementary information to aneurysm morphology in assessing its vulnerability. Reliable calculations require accurate material properties of individual aneurysmal components. Quantification of extreme extensibility and ultimate material strength of the tissue are important if rupture is to be modelled. Tissue pieces from 11 abdomen aortic aneurysm (AAA) from patients scheduled for elective surgery and from 8 normal aortic artery (NAA) from patients who scheduled for kidney/liver transplant were collected at surgery and banked in liquid nitrogen with the use of Cryoprotectant solution to minimize frozen damage. Prior to testing, specimen were thawed and longitudinal and circumferential tissue strips were cut from each piece and adventitia, media and thrombus if presented were isolated for the material test. The incremental Young’s modulus of adventitia of NAA was direction-dependent at low stretch levels, but not the media. Both adventitia and media had a similar extreme extensibility in the circumferential direction, but the adventitia was much stronger. For aneurysmal tissues, no significant differences were found when the incremental moduli of adventitia, media or thrombus in both directions were compared. Adventitia and media from AAA had similar extreme extensibility and ultimate strength in both directions and thrombus was the weakest material. Adventitia and media from AAA were less extensible compared with those of NAA, but the ultimate strength remained similar. The material properties, including extreme extensibility and ultimate strength, of both healthy aortic and aneurysmal tissues were layer-dependent, but not direction-dependent.
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Affiliation(s)
- Zhongzhao Teng
- Department of Radiology, School of Clinical Medicine, University of Cambridge, Cambridge Biomedical Campus, Box 218, Cambridge, CB2 0QQ, UK.
- Department of Engineering, University of Cambridge, Cambridge, UK.
| | - Jiaxuan Feng
- Department of Vascular Surgery, Changhai Hospital, 168 Changhai Rd., Shanghai, 200433, China
| | - Yongxue Zhang
- Department of Radiology, School of Clinical Medicine, University of Cambridge, Cambridge Biomedical Campus, Box 218, Cambridge, CB2 0QQ, UK
- Department of Vascular Surgery, Changhai Hospital, 168 Changhai Rd., Shanghai, 200433, China
| | - Yuan Huang
- Department of Radiology, School of Clinical Medicine, University of Cambridge, Cambridge Biomedical Campus, Box 218, Cambridge, CB2 0QQ, UK
| | | | - Adam J Brown
- Division of Cardiovascular Medicine, University of Cambridge, Cambridge, UK
| | - Zaiping Jing
- Department of Vascular Surgery, Changhai Hospital, 168 Changhai Rd., Shanghai, 200433, China
| | - Jonathan H Gillard
- Department of Radiology, School of Clinical Medicine, University of Cambridge, Cambridge Biomedical Campus, Box 218, Cambridge, CB2 0QQ, UK
| | - Qingsheng Lu
- Department of Vascular Surgery, Changhai Hospital, 168 Changhai Rd., Shanghai, 200433, China.
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Determining the influence of calcification on the failure properties of abdominal aortic aneurysm (AAA) tissue. J Mech Behav Biomed Mater 2015; 42:154-67. [DOI: 10.1016/j.jmbbm.2014.11.005] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Revised: 10/21/2014] [Accepted: 11/03/2014] [Indexed: 11/20/2022]
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Simsek FG, Kwon YW. Investigation of material modeling in fluid-structure interaction analysis of an idealized three-layered abdominal aorta: aneurysm initiation and fully developed aneurysms. J Biol Phys 2015; 41:173-201. [PMID: 25624113 DOI: 10.1007/s10867-014-9372-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 11/06/2014] [Indexed: 01/26/2023] Open
Abstract
Different material models for an idealized three-layered abdominal aorta are compared using computational techniques to study aneurysm initiation and fully developed aneurysms. The computational model includes fluid-structure interaction (FSI) between the blood vessel and the blood. In order to model aneurysm initiation, the medial region was degenerated to mimic the medial loss occurring in the inception of an aneurysm. Various cases are considered in order to understand their effects on the initiation of an abdominal aortic aneurysm. The layers of the blood vessel were modeled using either linear elastic materials or Mooney-Rivlin (otherwise known as hyperelastic) type materials. The degenerated medial region was also modeled in either linear elastic or hyperelastic-type materials and assumed to be in the shape of an arc with a thin width or a circular ring with different widths. The blood viscosity effect was also considered in the initiation mechanism. In addition, dynamic analysis of the blood vessel was performed without interaction with the blood flow by applying time-dependent pressure inside the lumen in a three-layered abdominal aorta. The stresses, strains, and displacements were compared for a healthy aorta, an initiated aneurysm and a fully developed aneurysm. The study shows that the material modeling of the vessel has a sizable effect on aneurysm initiation and fully developed aneurysms. Different material modeling of degeneration regions also affects the stress-strain response of aneurysm initiation. Additionally, the structural analysis without considering FSI (called noFSI) overestimates the peak von Mises stress by 52% at the interfaces of the layers.
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Affiliation(s)
- Fatma Gulden Simsek
- Institute of Biomedical Engineering, Bogazici University, Kandilli Camp, Istanbul, Turkey,
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45
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Towards efficient uncertainty quantification in complex and large-scale biomechanical problems based on a Bayesian multi-fidelity scheme. Biomech Model Mechanobiol 2014; 14:489-513. [DOI: 10.1007/s10237-014-0618-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Accepted: 09/02/2014] [Indexed: 10/24/2022]
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46
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O’Leary SA, Healey DA, Kavanagh EG, Walsh MT, McGloughlin TM, Doyle BJ. The Biaxial Biomechanical Behavior of Abdominal Aortic Aneurysm Tissue. Ann Biomed Eng 2014; 42:2440-50. [DOI: 10.1007/s10439-014-1106-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 08/28/2014] [Indexed: 11/24/2022]
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Lederman A, Saliture Neto FT, Ferreira R, de Figueiredo LFP, Otoch JP, Aun R, da Silva ES. Endovascular model of abdominal aortic aneurysm induction in swine. Vasc Med 2014; 19:167-174. [DOI: 10.1177/1358863x14534006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Abdominal aortic aneurysms are among the main causes of death. The high morbidity and mortality associated with aneurysm rupture and repair represents a challenge for surgeons and high risk for patients. Although experimental models are useful to understand, train, and develop new treatment and diagnostic methods for this pathology, animal models developed to date are far from ideal. Animals are either too small and do not represent the pathology of humans, or the procedures employ laparotomy, or the aortic behavior does not resemble that of a true aneurysm. We developed a novel, less invasive and effective method to induce true aortic aneurysms in Large White pigs. Animals were submitted to an endovascular chemical induction using either calcium chloride (25%) or swine pancreatic elastase. Controls were exposed to saline solution. All animals were operated on using the same surgical technique under general anesthesia. They were followed weekly with ultrasound examinations and at 4 weeks the aorta was harvested. Although elastase induced only arterial dilation, imaging, histological, and biomechanical studies of the aorta revealed the formation of true aneurysms in animals exposed to calcium chloride. Aneurysms in the latter group had biomechanical failure properties similar to those of human aneurysms. These findings indicate that the endovascular approach is viable and does not cause retroperitoneal fibrosis.
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Affiliation(s)
- Alex Lederman
- Vascular Surgery, Hospital Universitário, Universidade de São Paulo (USP), São Paulo, Brazil
- Vascular Surgery, Hospital Israelita Albert Einstein, São Paulo, Brazil
| | | | - Rimarcs Ferreira
- Pathology, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | | | - Jose Pinhata Otoch
- Surgical Techniques, Faculdade de Medicina da Universidade de São Paulo (USP), São Paulo, Brazil
| | - Ricardo Aun
- Vascular Surgery, Hospital Israelita Albert Einstein, São Paulo, Brazil
- Vascular Surgery, Faculdade de Medicina da Universidade de São Paulo (USP), São Paulo, Brazil
| | - Erasmo Simão da Silva
- Vascular Surgery, Faculdade de Medicina da Universidade de São Paulo (USP), São Paulo, Brazil
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Histologic, histochemical, and biomechanical properties of fragments isolated from the anterior wall of abdominal aortic aneurysms. J Vasc Surg 2014; 59:1393-401.e1-2. [DOI: 10.1016/j.jvs.2013.04.064] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Revised: 04/23/2013] [Accepted: 04/29/2013] [Indexed: 11/20/2022]
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Silva ESD. Abdominal aortic aneurysm: while there is still no cure, the key question is which patients to select for intervention and which intervention to select! J Vasc Bras 2014. [DOI: 10.1590/jvb.2014.040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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A novel strategy to translate the biomechanical rupture risk of abdominal aortic aneurysms to their equivalent diameter risk: method and retrospective validation. Eur J Vasc Endovasc Surg 2014; 47:288-95. [PMID: 24456739 DOI: 10.1016/j.ejvs.2013.12.018] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Accepted: 12/11/2013] [Indexed: 11/21/2022]
Abstract
OBJECTIVE To translate the individual abdominal aortic aneurysm (AAA) patient's biomechanical rupture risk profile to risk-equivalent diameters, and to retrospectively test their predictability in ruptured and non-ruptured aneurysms. METHODS Biomechanical parameters of ruptured and non-ruptured AAAs were retrospectively evaluated in a multicenter study. General patient data and high resolution computer tomography angiography (CTA) images from 203 non-ruptured and 40 ruptured aneurysmal infrarenal aortas. Three-dimensional AAA geometries were semi-automatically derived from CTA images. Finite element (FE) models were used to predict peak wall stress (PWS) and peak wall rupture index (PWRI) according to the individual anatomy, gender, blood pressure, intra-luminal thrombus (ILT) morphology, and relative aneurysm expansion. Average PWS diameter and PWRI diameter responses were evaluated, which allowed for the PWS equivalent and PWRI equivalent diameters for any individual aneurysm to be defined. RESULTS PWS increased linearly and PWRI exponentially with respect to maximum AAA diameter. A size-adjusted analysis showed that PWS equivalent and PWRI equivalent diameters were increased by 7.5 mm (p = .013) and 14.0 mm (p < .001) in ruptured cases when compared to non-ruptured controls, respectively. In non-ruptured cases the PWRI equivalent diameters were increased by 13.2 mm (p < .001) in females when compared with males. CONCLUSIONS Biomechanical parameters like PWS and PWRI allow for a highly individualized analysis by integrating factors that influence the risk of AAA rupture like geometry (degree of asymmetry, ILT morphology, etc.) and patient characteristics (gender, family history, blood pressure, etc.). PWRI and the reported annual risk of rupture increase similarly with the diameter. PWRI equivalent diameter expresses the PWRI through the diameter of the average AAA that has the same PWRI, i.e. is at the same biomechanical risk of rupture. Consequently, PWRI equivalent diameter facilitates a straightforward interpretation of biomechanical analysis and connects to diameter-based guidelines for AAA repair indication. PWRI equivalent diameter reflects an additional diagnostic parameter that may provide more accurate clinical data for AAA repair indication.
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