PSI - Issue 45

89

2 2

Xiaochen Wang/ Structural Integrity Procedia 00 (2023) 000 – 000 Xiaochen Wang/ Structural Integrity Procedia 00 (2023) 000 – 000

of the artery wall has great effect on the wall deformation. This analysis confirms that considering ILT anatomy and anisotropy of aortic wall in computational modelling is important in studying the severity of an abdominal aortic aneurysm. © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Prof. Andrei Kotousov Keywords: abdominal aortic aneurysm; biomechanics; finite element analysis; fluid-structure interaction; intraluminal thrombus; sensitivity study; rupture risks; failure investigation. 1. Introduction Abdominal aortic aneurysm (AAA) is a common condition affecting 4-14% of males over the age of 60 (Cornuz et al., 2004). It is characterised by a continuous dilation of the main aorta in the abdominal cavity, which can lead to serious consequences if left untreated. AAA is often asymptomatic, but if ruptured, it can result in internal bleeding and death. In fact, the mortality rate of AAA is as high as 80%, with 50% of those affected dying before receiving medical treatment (Acosta et al., 2006). The rising prevalence of death rate in many countries has brought rising needs for assessment to assist the treatment of AAA. Advanced simulation techniques have provided valuable insights into the computational investigation of AAA rupture risk algorithms. This has enabled researchers to better understand the role of different parameters in the risk of AAA rupture, and which factors should be prioritised in future studies. In AAA research, both isotropic and anisotropic material property models are used to simulate the properties of the aortic wall. Experimental evidence has shown that the aortic wall is anisotropic, and its structure is not homogeneous (Amabili et al., 2020, Avril et al., 2010, Basciano and Kleinstreuer, 2009, Di Achille et al., 2011, Murphy, 2013, Ruiz de Galarreta et al., 2017). Anisotropic models can provide a more accurate representation of the distribution of mechanical stresses and strains, and thus, better predicting the risk of AAA rupture. However, some researchers still use isotropic material models, as a lack of detailed data on the mechanical properties of the aortic wall in different directions may make isotropic models sufficient for simulating its mechanical behaviour (Avril et al., 2010). Fracture mechanics and failure investigation in the context of AAA can be used to understand how stress distribution related to material properties and contribute to the risk of AAA rupture. This information can then be used to develop predictive models and provide better understanding of the mechanical properties of the aortic wall and their influence on AAA rupture risks. Intraluminal thrombus (ILT) can be found in most AAAs with various sizes and is believed to play a critical role in AAA growth rate and rupture risks (Sladojevic et al., 2022, Throop et al., 2022). As blood clot that forms inside the vessel lumen, ILT can cause blood flow restriction within the aorta, leading to changes in aortic wall stress and pressure, which can contribute to the growth of the aneurysm. The role of ILT in AAA rupture risk is a topic of ongoing debate and is not fully understood. Yet, some numerical studies showed that lower wall shear stress can be found in AAA with ILT, which potentially prevents AAA rupture (Wang et al., 2002, Haller et al., 2018). However, some debate that the presence of ILT increases the risks of aneurysm rupture by causing inflammation and reducing oxygen flux in the wall tissue (Boyd, 2021, Coutard et al., 2010). The AAA-ILT relationship and behaviour have been explored in computational studies via finite element method (FEM) in terms of wall stress, while there are very few studies considered the haemodynamic of the blood flow as well as the interaction between the fluid and solid domain. The relationship and behaviour between AAA and ILT have been explored in computational studies using the finite element method to examine wall stress (Zambrano et al., 2016, Wang et al., 2002, Haller et al., 2018); however, limited research has considered both the haemodynamics of blood flow and the interaction between fluid and solid domains. There is a pressing requirement to investigate the impact of ILT through the use of fluid-structure interaction (FSI) model. The aim of this study is to explore the interplay between the mechanical stress, flow abnormality, and deformation in AAAs with diverse nonlinear material properties, both with and without the presence of ILT. The current study makes a novel contribution to the field by examining the failure stresses AAAs using FSI simulation. This study is unique as it incorporates different material properties of both the ILT and the AAA wall, providing a more comprehensive understanding of the mechanical behaviour of AAAs. Furthermore, the study also determines the importance of including anisotropy of the aortic wall in failure prediction, which has not been fully explored in previous research. These findings contribute to advancing the knowledge in the area of AAA biomechanics. Numerical of the artery wall has great effect on the wall deformation. This analysis confirms that considering ILT anatomy and anisotropy of aortic wall in computational modelling is important in studying the severity of an abdominal aortic aneurysm. © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Prof. Andrei Kotousov Keywords: abdominal aortic aneurysm; biomechanics; finite element analysis; fluid-structure interaction; intraluminal thrombus; sensitivity study; rupture risks; failure investigation. 1. Introduction Abdominal aortic aneurysm (AAA) is a common condition affecting 4-14% of males over the age of 60 (Cornuz et al., 2004). It is characterised by a continuous dilation of the main aorta in the abdominal cavity, which can lead to serious consequences if left untreated. AAA is often asymptomatic, but if ruptured, it can result in internal bleeding and death. In fact, the mortality rate of AAA is as high as 80%, with 50% of those affected dying before receiving medical treatment (Acosta et al., 2006). The rising prevalence of death rate in many countries has brought rising needs for assessment to assist the treatment of AAA. Advanced simulation techniques have provided valuable insights into the computational investigation of AAA rupture risk algorithms. This has enabled researchers to better understand the role of different parameters in the risk of AAA rupture, and which factors should be prioritised in future studies. In AAA research, both isotropic and anisotropic material property models are used to simulate the properties of the aortic wall. Experimental evidence has shown that the aortic wall is anisotropic, and its structure is not homogeneous (Amabili et al., 2020, Avril et al., 2010, Basciano and Kleinstreuer, 2009, Di Achille et al., 2011, Murphy, 2013, Ruiz de Galarreta et al., 2017). Anisotropic models can provide a more accurate representation of the distribution of mechanical stresses and strains, and thus, better predicting the risk of AAA rupture. However, some researchers still use isotropic material models, as a lack of detailed data on the mechanical properties of the aortic wall in different directions may make isotropic models sufficient for simulating its mechanical behaviour (Avril et al., 2010). Fracture mechanics and failure investigation in the context of AAA can be used to understand how stress distribution related to material properties and contribute to the risk of AAA rupture. This information can then be used to develop predictive models and provide better understanding of the mechanical properties of the aortic wall and their influence on AAA rupture risks. Intraluminal thrombus (ILT) can be found in most AAAs with various sizes and is believed to play a critical role in AAA growth rate and rupture risks (Sladojevic et al., 2022, Throop et al., 2022). As blood clot that forms inside the vessel lumen, ILT can cause blood flow restriction within the aorta, leading to changes in aortic wall stress and pressure, which can contribute to the growth of the aneurysm. The role of ILT in AAA rupture risk is a topic of ongoing debate and is not fully understood. Yet, some numerical studies showed that lower wall shear stress can be found in AAA with ILT, which potentially prevents AAA rupture (Wang et al., 2002, Haller et al., 2018). However, some debate that the presence of ILT increases the risks of aneurysm rupture by causing inflammation and reducing oxygen flux in the wall tissue (Boyd, 2021, Coutard et al., 2010). The AAA-ILT relationship and behaviour have been explored in computational studies via finite element method (FEM) in terms of wall stress, while there are very few studies considered the haemodynamic of the blood flow as well as the interaction between the fluid and solid domain. The relationship and behaviour between AAA and ILT have been explored in computational studies using the finite element method to examine wall stress (Zambrano et al., 2016, Wang et al., 2002, Haller et al., 2018); however, limited research has considered both the haemodynamics of blood flow and the interaction between fluid and solid domains. There is a pressing requirement to investigate the impact of ILT through the use of fluid-structure interaction (FSI) model. The aim of this study is to explore the interplay between the mechanical stress, flow abnormality, and deformation in AAAs with diverse nonlinear material properties, both with and without the presence of ILT. The current study makes a novel contribution to the field by examining the failure stresses AAAs using FSI simulation. This study is unique as it incorporates different material properties of both the ILT and the AAA wall, providing a more comprehensive understanding of the mechanical behaviour of AAAs. Furthermore, the study also determines the importance of including anisotropy of the aortic wall in failure prediction, which has not been fully explored in previous research. These findings contribute to advancing the knowledge in the area of AAA biomechanics. Numerical © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Prof. Andrei Kotousov