Date of Graduation

12-2015

Document Type

Thesis

Degree Name

Master of Science in Biomedical Engineering (MSBME)

Degree Level

Graduate

Department

Biomedical Engineering

Advisor

Ashok Saxena

Committee Member

Hanna Jensen

Second Committee Member

Kartik Balchandran

Third Committee Member

Woodrow Shew

Fourth Committee Member

Morten Jensen

Abstract

Quantification of abdominal aortic aneurysm development, its growth kinetics, and rupture criteria are important to decrease the risk of this life-threatening event. Uniaxial testing of healthy and collagen degraded aortic specimens from pigs was performed. A mathematical model, from the literature, for the stress-strain relationship that is suitable for describing the behavior of abdominal aortic tissue was used to derive specific tissue properties/parameters as a function of strain rate and as a function of specimen orientation. Analyses consisting of Finite Element Modeling of healthy and collagen degraded abdominal aortas were performed using ABAQUS finite element code and the measured properties. The focus was on finding the values of ultimate tensile strength (σmax), maximum strain at rupture (εmax), elastic modulus (E), and the critical strain (εc), identified as the point beyond which high rupture risk is present. These properties vary significantly between healthy tissue and collagen-degraded (aneurysmal) tissue. No significant differences were found in the mechanical properties between longitudinal and circumferential orientation both in healthy and collagen degraded specimens. However, σmax, εmax, and εc values were significantly higher for healthy tissue group than for collagen degraded tissue group. For example, εc= 0.44 ± 0.08 versus εc= 0.0077 ± 0.0002 (Mean ± SEM), σmax=0.93 ± 0.07 MPa versus σmax= 0.047 ± 0.002 MPa, and εmax= 0.87 ± 0.12 versus εmax= 0.49 ± 0.10. In conclusion, the data indicate that collagen is important in maintaining a high critical strain value in healthy abdominal aortic tissue and the risk of AAA rupture increases significantly in the collagen degraded tissue.

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