Biaxial Tensile Properties of Thoracic Aortic Aneurysm Tissues

Abstract

Mechanical properties of human aortic aneurysm tissues were measured with a biaxial tensile tester. Fifteen-mm-square specimens were obtained from thoracic aortic aneurysms of various origins and from undilated aortas adjacent to the aneurysms during aneurysmectomy, and were stored frozen until the measurement. Each specimen was stretched biaxially in physiological saline at room temperature at the rate of ~0.2 mm/sec. Although the ordered displacement was set equal for both directions, real strain applied to the specimens was not equibiaxial. The stress-strain curves under equibiaxial stretch were obtained by fitting measured curves with a strain energy function considering material anisotropy. Effects of freezing and ambient temperature on the mechanical properties were evaluated with porcine thoracic aortas. The mechanical properties of the frozen-stored specimens at 23°C were almost similar to those of the fresh specimens at 37 °C. Elastic modulus at zero load averaged for both directions H m i = (H x i +H y i)/2 was higher (P < 0.01) in the aneurysm tissues (1450 ± 250 kPa, mean ± SEM, n = 26) than in the undilated tissues (650 ± 140 kPa, n = 10). Anisotropy index K = |H x i-H y i |/H m i was not significantly different between the aneurysm (20 ± 3%) and the undilated tissues (12 ± 3%) for all specimens. For the specimens whose elastic modulus H m i was smaller than 1 MPa, however, the index K was significantly higher (P < 0.05) in the aneurysm specimens (23.1 ± 5.3%, n = 14) than the undilated tissues (9.5 ± 2.5%, n = 8). These results indicate aneurysm tissues are not only stiffer but also more anisotropic than the nonaneurysmal tissues.

Three-Dimensional Full-Field Strain Measurements across a Whole Porcine Aorta Subjected to Tensile Loading Using Optical Coherence Tomography–Digital Volume Correlation

“…About the freezing effects in porcine thoracic aorta samples, Matsumoto et al (2009) showed that the mechanical properties were similar for samples stored at −23°C in comparison to fresh specimens at 37°C. Before the OCT acquisition, the tissue was placed into an osmotically active solution of 85% (v/v) PG in PBS, at 37°C for 2 h (Lomas et al, 2003).…”

Leaflet stress and strain distributions following incomplete transcatheter aortic valve expansion

“…The stress-strain curves converted to the equibiaxial stretch condition, and the anisotropic index, the difference in stiffness between circumferential and longitudinal directions divided by the average stiffness, was calculated for each sample (Matsumoto et al, 2009). …”

Human dilated ascending aorta: Mechanical characterization via uniaxial tensile tests

“…In particular, some studies move from the presentation of new tools in imaging analysis to evidence possible alterations in the morphology and in the micro-structure of the diseased aortic tissues [26,27]. Other studies focus on the use of mechanical tests (uniaxial and biaxial tensile tests) to evaluate and compare mechanical properties of both healthy and diseased tissues [28][29][30][31][32][33] and, at the same time, to investigate factors which can influence tissue properties like location and orientation [23,[34][35][36][37], patient age [30,38,39], patient sex [39,40], and presence of concomitant pathologies [25,33,36,[41][42][43][44].…”