Date of Award

5-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Bioengineering

Advisor

Nagatomi, Jiro

Committee Member

Simionescu , Dan

Committee Member

Vyavahare , Naren

Abstract

Abdominal aortic aneurysms (AAA) are localized, progressive dilations of the aortic wall and are the 13th most common cause of death in the United States (~15,000 per year) and surgery is usually recommended when the aneurysm is 5 cm or larger in diameter. Because of this clinical parameter, previous studies of AAA biomechanics have utilized a one-dimensional analysis that focuses solely on changes in wall diameter and have attempted to model geometric changes with mathematical formulas, generally based on the LaPlace equation. This is not sufficient however, as the mechanical behavior of the tissue at sites of aneurysm have been documented as being nonlinear, anisotropic, and non-homogeneous in addition to having a complex geometry. Further, since aneurysms have been found to vary in their progression, the success of such models in predicting geometric changes leading to rupture has been minimal. Therefore, an approach to quantify the 3D changes in the wall geometry of AAA is necessary for adequate estimations of the abnormal wall stresses that occur at the site of aneurysm. The overall aim of this project was to develop an ex vivo tissue testing system that will allow for 3D biomechanical analysis of aorta specimens from small animals. More specifically, we have designed, assembled, and calibrated a computer-controlled experimental setup that allows tissue samples to be pressure loaded and imaged from multiple angles at prescribed pressure increments. We have also developed custom LabVIEW scripts to control the hardware and MATLAB scripts to produce 3D images and geometry data of the specimen at these prescribed pressure levels. Our calibration study with image phantoms revealed that percent error for curvature and diameter calculations ranged between 2-10%. Additionally, aortic wall stresses under varying pressures were calculated and compared in normal tissue samples and an aorta with an artificially induced bulge. The stress levels ranged between 96-219 kPa and 15-76kPa (under 30-150 mmHg pressure) for the artificially bulging sample and normal tissues, respectively. These results demonstrated that the novel ex vivo tissue testing system developed in the present study was capable of quantifying both surface curvature and diameter of small animal aorta specimens under a wide range of pressures, allowing for wall stress estimations and opening up the possibility of more thorough testing of experimental AAA treatments.

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