Biomedical Engineering Reference
In-Depth Information
outer and inner aortic walls of the artificially created 'false lumen' for evaluating the
propensity of either intimal flap propagation or frank disruption. SEM investigations
was also performed to examine the failure modality of AoD.
11.2 Material and Methods
11.2.1 Human Aortic Tissue Specimens
All human ascending thoracic aorta tissue specimens were obtained after informed
consent following guidelines of our Institutional Review Board and Center for Or-
gan Recovery and Education. Segments of non-aneurysmal aorta (control) were col-
lected from organ donor subjects whereas non-dissected ATAAs were collected from
patients undergoing elective ascending aortic replacement at the University of Pitts-
burgh Medical Center. A total of 31 aortic segments (7 controls and 24 ATAAs)
with age range of 41-79 yr, aortic diameter of 40-68 mm and gender comprised of
24 males and 7 females were analyzed. The aneurysmal groups were composed of
16 BAV and 8 TAV segments, respectively. All non-aneurysmal segments were col-
lected from individuals with TAV. The aortic samples were tested within 48 hours of
harvest after storing at 4 °C in a calcium-free and glucose-free 0
.
9 % physiological
saline solution (Raghavan et al.,
1996
).
11.2.2 Biomechanical Testing
The harvested aortic segments were cut into long, thin, rectangular (approximately
30
6 mm) strips with their long axis in either longitudinal (LONG) or circum-
ferential (CIRC) orientation with respect to that of the aorta. Generally, the same
aortic segment was used to obtain strips of both orientations for direct comparison.
To create an initial delamination plane, a delaminating incision was made with the
aid of a surgical scalpel between elastic lamellae of each specimen, parallel with the
plane of the aortic wall and 8-12 mm in length (Fig.
11.1
).
Since the initial incision was made manually, there naturally was a moderate vari-
ation in terms of the exact location of the incision plane with respect to the center of
the media or to the external or internal elastic lamina. However, the artificial delam-
ination plane was reproducible. The dimension of each specimen (i.e., the width,
thickness and length) were measured at three different locations using a dial caliper
and then averaged and recorded before testing. The two free flaps of each delam-
inated half of the ATAA specimen were mounted between the grips of an Instron
tensile system (model 5542) with a 5 N load cell. To avoid slipping of the speci-
men in the pneumatic grips, surfalloy jaw faces with gritty, sandpaper-like surfaces
were used. During testing, the mounted specimens were submerged in 0
.
9 % phys-
iological saline solution in a BioPuls bath under controlled temperature of 37 °C.
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