Viscoelastic Material Properties of Human Thoracic and Abdominal Aortic Aneurysmal Tissue

Objectives: Individualized patient rupture risk for abdominal (AAA) and thoracic (TAA) aortic aneurysms remains elusive partly due to the difficulties of obtaining in vivo aortic biomechanical tissue properties. While various... [ view full abstract ]

Objectives: Individualized patient rupture risk for abdominal (AAA) and thoracic (TAA) aortic aneurysms remains elusive partly due to the difficulties of obtaining in vivo aortic biomechanical tissue properties. While various modalities of elastography provide data about tissue stiffness, to date there has been paucity of biomechanics testing of aortic aneurysmal tissue at a physiologic preload and under pulsatile conditions, to guide these measurements. We hypothesize that aneurysmal aortic tissue will be stiffer (E*), store (E’) more, and dissipate (E”) more cyclic energy.

Methods: Human healthy and diseased aortic samples were obtained from cadaveric and surgical specimens. Uniaxial mechanical testing (ADMET BioTense) was performed in the circumferential orientation with the tissue pre-loaded to an equivalent 110 mmHg mean pressure. A sinusoidal ±5% strain was applied at 1 Hz for 40 cycles with simultaneous force measurements in order to calculate viscoelastic material properties.

Results: Only AAA tissue was significantly stiffer under dynamic conditions as compared to healthy thoracic tissue indicated by a greater (E*) 1838±365 vs. 1015±99 kPa (p<0.01). AAA tissue also stored more energy (E’) 1833±365 vs 1014±98 (p<0.01) and lost more energy (E”) 128±24 vs. 43±24 kPa (p<0.01), but only trended toward a greater loss ratio (tan(δ)) 0.070±0.01 vs. 0.041±0.02 (p=0.1) (Figure#1).

Conclusions: Our data demonstrates that AAA tissue, under pulsatile conditions is stiffer and has a greater energy storage and loss modulus, while maintaining a similar loss ratio. Further work is needed to determine the contribution of collagen and elastin to the viscoelastic material properties.