University of PittsburghVascular Bioengineering Laboratory

Departments of Surgery and Bioengineering and the McGowan Institute for Regenerative Medicine

Pittsburgh, PA

Ascending aortic aneurysm biomechanical properties are variable depending on aortic

valve morphology

Joseph Muthu, ME,MS, Julie Philippi, PhD, Thomas Gleason, MD, David A. Vorp, PhD

Introduction• Biomechanical models of wall strength are being

developed to better predict Ascending Aortic Aneurysm (TAA) dissection or disruption as compared to diameter criterion

• TAA dissection/disruption represents a mechanical failure of the diseased aortic wall, and has been associated with diminished tensile strength.

• BAV patients are predisposed to TAA formation

• The correlation of variable TAA wall strength with aortic valve morphology is unknown

Purpose of This Study • Determine whether differences in wall

tensile strength exist between BAV and TAV TAAs

• Determine whether tensile strength depends on location and orientation of the tissue

• Evaluate biomechanical model differences in BAV and TAV

Methods• Rectangular tissue specimens from TAA

patients with BAV and TAV were harvested in circumferential and longitudinal orientations, and tested in uniaxial tensile test machine within 48 hrs.

• The specimens were preconditioned for 10 cycles of loading and unloading

• After preconditioning, the tissues were stretched at the rate of 8.5% of its initial gauge length until its failure

• The Cauchy stress and strain were derived from force displacement data and initial tissue dimensions

Uniaxial Tensile Testing (LONG)

Ultimate Tensile Strength

Uniaxial Tensile Testing (CIRC)

Ultimate Tensile Strength

THORACIC ANEURYSM TENSILE TESTING

0

50

100

150

200

250

300

Ult

imate

Ten

sil

e S

tren

gth

(UT

S)

N/c

m^

2

Longitudinal Circumferential

Comparison of Strength of TAA

0

20

40

60

80

100

120

140

160

180

200

Bicuspid-Avg (n=9) Tricuspid-Avg (n=5) Control- Avg (n=3)

Ult

ima

te T

en

sile

Str

en

th (

UT

S)

N/c

m^

2

Longitudinal Circumferential

P=0.0001

P=0.009

P= 0.29

P= 0.004

Histology: Collagen (Trichrome staining)

Non-Aneurysmal Aneurysmal w/ TAV Aneurysmal w/ BAV

40X BrightfieldTrichrome stain5 µm paraffin sections

Blue=collagenRed= cytoplasm

Diameter

Conclusion• The average strength of aneurysmal wall in

the circumferential direction was significantly higher than that of the longitudinal direction within the groups exhibiting anisotropic nature of the wall.

• Wall strength of BAV may be stronger than TAV in both the orientations