Failure of the Porcine Ascending Aorta: Multidirectional Experiments and a Unifying Microstructural Model

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The von Mises (VM) stress is a common stress measure for finite element models of tissue mechanics. The VM failure criterion, however, is inherently isotropic, and therefore may yield incorrect results for anisotropic tissues, and the relevance of the VM stress to anisotropic materials is not clear. We explored the application of a well-studied anisotropic failure criterion, the Tsai–Hill (TH) theory, to the mechanically anisotropic porcine aorta. Uniaxial dogbones were cut at different angles and stretched to failure. The tissue was anisotropic, with the circumferential failure stress nearly twice the axial (2.67 ± 0.67 MPa compared to 1.46 ± 0.59 MPa). The VM failure criterion did not capture the anisotropic tissue response, but the TH criterion fit the data well (R2 = 0.986). Shear lap samples were also tested to study the efficacy of each criterion in predicting tissue failure. Two-dimensional failure propagation simulations showed that the VM failure criterion did not capture the failure type, location, or propagation direction nearly as well as the TH criterion. Over the range of loading conditions and tissue geometries studied, we found that problematic results that arise when applying the VM failure criterion to an anisotropic tissue. In contrast, the TH failure criterion, though simplistic and clearly unable to capture all aspects of tissue failure, performed much better. Ultimately, isotropic failure criteria are not appropriate for anisotropic tissues, and the use of the VM stress as a metric of mechanical state should be reconsidered when dealing with anisotropic tissues.

Section: Resultssupporting

confidence: 81%

Section: Discussionmentioning

confidence: 66%

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Isotropic Failure Criteria Are Not Appropriate for Anisotropic Fibrous Biological Tissues

Korenczuk

Votava

Dhume

et al. 2017

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“…A primary goal of computational modeling of vascular mechano-adaptation is to develop patient-specific models to aide physicians making treatment decisions. Though current models are improving [75][76][77], the VSMCs' temporal dynamics are not yet well enough understood to capture their contribution to maladaptive growth and remodeling in disease. The methods and results presented here represent a first step toward development of more in-depth theory for use in models of artery mechanics.…”

Section: Discussionmentioning

confidence: 99%

Empirically Determined Vascular Smooth Muscle Cell Mechano-Adaptation Law

Steucke

Win

Stemler

et al. 2017

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Cardiovascular disease can alter the mechanical environment of the vascular system, leading to mechano-adaptive growth and remodeling. Predictive models of arterial mechano-adaptation could improve patient treatments and outcomes in cardiovascular disease. Vessel-scale mechano-adaptation includes remodeling of both the cells and extracellular matrix. Here, we aimed to experimentally measure and characterize a phenomenological mechano-adaptation law for vascular smooth muscle cells (VSMCs) within an artery. To do this, we developed a highly controlled and reproducible system for applying a chronic step-change in strain to individual VSMCs with in vivo like architecture and tracked the temporal cellular stress evolution. We found that a simple linear growth law was able to capture the dynamic stress evolution of VSMCs in response to this mechanical perturbation. These results provide an initial framework for development of clinically relevant models of vascular remodeling that include VSMC adaptation.

“…Early research by Roach and Burton suggested the contributions of compliant elastin fibers at lower levels of stress and stiff collagen fibers at higher levels of stress result in the nonlinear mechanics of the arterial wall [19]. Arterial structure-function has since been further explored from the macro-to nanoscale with the advancement of experimental approaches including mechanical characterization and optical imaging [20][21][22][23][24], and in computational modeling [25][26][27]. Alterations in structure and function to the arterial wall due to various pathological conditions are also being extensively studied, with the goal of early diagnosis, prevention, and the development of treatment options [28][29][30].…”

Section: Introductionmentioning

confidence: 99%

Structural and Functional Differences Between Porcine Aorta and Vena Cava

Mattson

Zhang

2017

Elastin and collagen fibers are the major load-bearing extracellular matrix (ECM) constituents of the vascular wall. Arteries function differently than veins in the circulatory system; however as a result from several treatment options, veins are subjected to sudden elevated arterial pressure. It is thus important to recognize the fundamental structure and function differences between a vein and an artery. Our research compared the relationship between biaxial mechanical function and ECM structure of porcine thoracic aorta and inferior vena cava. Our study suggests that aorta contains slightly more elastin than collagen due to the cyclical extensibility, but vena cava contains almost four times more collagen than elastin to maintain integrity. Furthermore, multiphoton imaging of vena cava showed longitudinally oriented elastin and circumferentially oriented collagen that is recruited at supraphysiologic stress, but low levels of strain. However in aorta, elastin is distributed uniformly, and the primarily circumferentially oriented collagen is recruited at higher levels of strain than vena cava. These structural observations support the functional finding that vena cava is highly anisotropic with the longitude being more compliant and the circumference stiffening substantially at low levels of strain. Overall, our research demonstrates that fiber distributions and recruitment should be considered in addition to relative collagen and elastin contents. Also, the importance of accounting for the structural and functional differences between arteries and veins should be taken into account when considering disease treatment options.