Elastic and Rupture Properties of Porcine Aortic Tissue Measured Using Inflation Testing

Abstract

A new inflation test device was developed to study the mechanical properties of aortic tissue. The device was used to measure failure (rupture) strength and to determine the nonlinear, anisotropic elastic properties of porcine thoracic aorta. The tester was designed to stretch initially flat, circular tissue specimens to rupture under uniform biaxial loading. Water was chosen as the pressurizing fluid. Mechanical stretch and radius of curvature during inflation were measured optically in two orthogonal directions, and the Cauchy stress components were calculated from the deformation and the applied pressure. All porcine samples that ruptured successfully did so via a tear in the circumferential direction. Thus, the failure strength was taken to be the stress in the axial direction immediately prior to rupture. The mean failure strength was 1.75 MPa and mean axial stretch at failure was 1.52. These values agree well with published data for other arterial tissues. The nonlinearly elastic deformation behavior was modeled using a hyperelastic constitutive law of the type proposed by Holzapfel et al. [Holzapfel GA, Gasser TC, Ogden RW. J Elasticity 2000;61:1-48]. The results showed that the dominant directions of anisotropy in the porcine aortas were approximately 45 degrees to the axial and circumferential directions, and that the isotropic contribution to the constitutive model was insignificant.

Experimental characterization of rupture in human aortic aneurysms using a full-field measurement technique

“…In order to identify anisotropic hyperelastic material parameters and to quantify the rupture stress of aneurismal aortic tissues, a bulge inflation test (Mohan and Melvin 1983;Hsu et al 1995;Seshaiyer 2001;Marra et al 2006;Brunon et al 2011) is chosen in this study. The bulge inflation test has several advantages compared to a uniaxial tensile test, a simple biaxial tensile test and a pressurized cylinder test.…”

Nondestructive mechanical characterization of developing biological tissues using inflation testing

“…When characterizing true membranes, without any residual stretches, this method has been shown to be capable of providing a rapid and accurate estimate of the material parameters of soft tissues, even for nonlinear and anisotropic materials [20,37]. However, this method's accuracy decreases when the tissue thickness and prestretch increase, as shown by the virtual simulations performed in this study (Figure 3).…”

“…These equations were initially derived for thin axisymmetric geometries [10,11], however it has been demonstrated that they can closely approximate the stress resultants in geometries that do not necessarily deform axisymmetrically due to material anisotropy [35,36] including anisotropic tissues subjected to inflation testing [19,20,37].…”

“…This reduction was most evident in the fiberreinforced materials, where more parameters were to be estimated. Without such an initial estimate, an inverse FE analysis with 3D elements is computationally costly, therefore previous studies typically resorted to faster methods such as shell meshes [18,21,22,23,39,36] or analytical solutions as used in the initial estimate [20,37]. These methods can provide excellent estimates for thin membranes, but possibly lead to inaccurate material parameter estimates when the tissues become too thick or feature residual stretches.…”

“…US imaging is key to this setup, as it allows for measurements of the tissue deformation during bulge testing, a test that can now be performed inside the bioreactor. Previous studies have typically measured the tissue deformation during bulging using stereo camera setups [19,21,22,23,37,39] or advanced optical rigs [18,40], which are incompatible with the limited view of samples insides a bioreactor. In contrast, US is able to measure throughout the tissue cross-section, and can therefore be easily mounted on top of a bioreactor.…”