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Multidisciplinary Approach to Modeling the Biomechanical Response and Failure of Diseased Cerebral Arterial Tissue

Fortunato, Ronald (2023) Multidisciplinary Approach to Modeling the Biomechanical Response and Failure of Diseased Cerebral Arterial Tissue. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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A cerebral aneurysm is an enlargement of the cerebral artery wall commonly seen in the adult population. Aneurysm rupture is a rare event associated with high morbidity and mortality highlighting the need to understand the disease progression and rupture mechanisms. Clinically useful metrics for assessment of rupture risk can thus be identified based on these mechanisms. In this work, we study failure mechanisms at the microscale as well as try to understand the stress environment at the macroscale that drives microscale mechanics.
High fidelity structural models of cerebral aneurysm tissue that incorporate multi-modality imaging to elicit important structural characteristics are essential for rupture risk assessment. Collagen is the major passive load bearing component in cerebral artery and aneurysmal walls. While passive, the network of collagen fibers can be remodeled by cells in response to changes in intramural loads and to avoid rupture. Other structural components of the wall include calcification and lipid pools which have been found to be prevalent in cerebral aneurysm samples. In this work, we demonstrated that stress is an important factor for failure initiation, however propagation of tears is influenced by the biomechanical state of the tissue. We used two primary methods of modeling failure, cohesive elements and embedded fiber elements. Each model has its advantages and disadvantages as we will discuss. Both reveal biomechanical understanding of how failure initiates and propagates through tissue.
At the macroscale, we observed a large variation in the wall thickness of cerebral aneurysms, in agreement with published results. To understand the role of heterogeneous wall thickness on the stress environment within cerebral aneurysms, we combined multiple imaging modalities to map patient specific high resolution thickness measurements obtained ex-vivo, onto in-vivo lumen aneurysm surfaces. Thus, we created a patient specific finite element model of the aneurysm, which we used to compare intramural stress fields and areas of stress concentration in models with patient specific and constant wall thickness models. As patient specific wall thickness measurements are not possible using standard clinical imaging, these results provide important guidance on the appropriate use of solid mechanics studies when assessing rupture risk in patients.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Fortunato, Ronaldrnf6@pitt.edurnf60000-0001-7914-5648
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMaiti, Spandanspm54@pitt.eduspm54
Committee CoChairRobertson, Anne
Committee MemberAbramowitch, Stevensdast9@pitt.edusdast9
Committee MemberPhillippi, Julie A.phillippija@upmc.edujap103
Committee MemberSchmidt, Daviddes53@pitt.edudes53
Date: 19 January 2023
Date Type: Publication
Defense Date: 31 October 2022
Approval Date: 19 January 2023
Submission Date: 13 October 2022
Access Restriction: 2 year -- Restrict access to University of Pittsburgh for a period of 2 years.
Number of Pages: 137
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Mechanical Engineering and Materials Science
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Cerebral aneurysm, finite element analysis, biomechanics, artery, failure, collagen fiber network, statistics
Date Deposited: 19 Jan 2023 19:08
Last Modified: 19 Jan 2023 19:08


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