T0201-3-6 Observation of microscopic deformation in the porcine thoracic aortic wall during circumferential stretch

Uno, Yohei; Nagayama, Kazuaki; Matsumotο, Takeo

doi:10.1299/jsmemecjo.2010.8.0_165

Cited by 3 publications

(5 citation statements)

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“…As for the circumferential EL waviness obtained at the selected cases (n = 19), the average value, W = 1.082 ± 0.038 (mean ± SD), agreed with the measured values reported in a previous study (Uno et al, 2010), indicating that the range of initial prestresses assigned for EL in this study was comparably reasonable. Notably, the residual stresses of EL and SML obtained at the unloaded state were compressive and tensile, respectively, and quantitatively equivalent to the values estimated by the prior works, i.e., ±10 kPa (Breslavsky and Amabili, 2018;Liu et al, 2019;Matsumoto et al, 2004a and2004b).…”

Section: Discussionsupporting

confidence: 89%

“…As we aimed to identify the specific mechanical parameters to computationally reconstruct both the circumferential EL waviness and the waviness of EL ridge, we excluded the cases in which the longitudinal EL undulation was not clearly observed (n = 45), and a further investigation was conducted for the remaining cases (n = 19) with W = 1.082 ± 0.038 (mean ± SD) on average. Notably, most of the selected circumferential EL waviness (n = 19) fell within the range of reasonable values, 1.05-1.15, which was experimentally observed in vitro for the medial strips from the porcine aortas (Uno et al, 2010). Figure 6 demonstrates the normal X-stress distribution in the unit structure obtained at the initial and unloaded states.…”

Section: Circumferential El Wavinesssupporting

confidence: 59%

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Modeling elastic lamina buckling in the unloaded aortic media

Tamura

Kato

Matsumoto

2021

Mechanical Engineering Journal

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Mathematical modeling of the thoracic aorta is important for detecting extraordinary and unusual stress or strain distributions of the hypertensive aortic wall, even in early stages, and for understanding the development and progression of various cardiovascular diseases. In a freshly isolated aortic media, which mainly comprises elastic laminas (ELs) and smooth muscle layers (SMLs), circumferential EL waviness and longitudinal EL undulation are often observed because of the buckling of ELs, which is closely associated with residual stresses of ELs and SMLs in the aortic wall. However, the mechanism underlying EL buckling or specific mechanical interactions between EL and SML remains unclear. We hypothesized that the longitudinal EL undulation is likely formed by the superposition of the circumferential EL waviness along the aortic axis. Hence, a series of numerical simulations were conducted based on a design of experiments approach by implementing residual stresses. We identified that the prestress initially administered to ELs in the circumferential and axial directions, and the predefined internodal gap, which couples the EL and SML, are essential mechanical parameters to computationally reconstruct the circumferential EL waviness and the longitudinal EL undulation at an unloaded state. In addition, a mechanical balance between the assigned prestresses along the circumferential and axial directions is crucial for successful representation of structural buckling of EL in the unloaded aortic media. Although further study is required, we have verified that our hypothesis is reasonable in the current work. Moreover, the information we obtained here will greatly help improve understanding the roles of EL and SML in the aortic medial wall at the in vitro and in vivo states, while simultaneously providing a basis for more sophisticated computational modeling of the aorta.

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Section: Discussionsupporting

confidence: 89%

Section: Circumferential El Wavinesssupporting

confidence: 59%

Modeling elastic lamina buckling in the unloaded aortic media

Tamura

Kato

Matsumoto

2021

Mechanical Engineering Journal

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“…This was also predicted by Yamada et al (1999) who conducted a layer-structured FE analysis of arteries by modeling active (SML) and passive (EL and collagen fibers) elements separately. Compared to experimental results obtained with micro-and macroscopic observations on an aortic medial strip subjected to uniaxial stretch (Uno et al, 2010), WEL = 1.11 we obtained (Fig. 10a) is reasonable in the in vitro unloaded state.…”

Section: Discussionsupporting

confidence: 85%

“…10a) is reasonable in the in vitro unloaded state. The aim of our additional series of simulations was to identify a specific contribution of collagen fibers that would make it possible for the computationally model-predicted WEL- relationship to match the one experimentally obtained by Uno et al (2010), most of which was within the range of WEL = 1.05-1.15 in vitro ( = 0%). They reported that EL waviness vanished at ~20% strain, which is equivalent to our simulation results.…”

Section: Discussionmentioning

confidence: 99%

Modeling of elastic lamina buckling coupled with smooth muscle layer deformation in the aortic media: technique for readily implementing residual stresses

Tamura

Kato

Matsumoto

2020

JBSE

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In vivo aortic wall thickening is a mechanical adaptation to the prolonged increase in intravascular pressure resulting from hypertension, which is mainly regulated by primary components of the aortic media, the elastic lamina (EL) and the smooth muscle-rich layer (SML). This study built a simplified finite element (FE) model of the aortic medial wall comprising the EL and SML, and simulated EL undulation or buckling at a no-load condition, i.e., (in the in vitro) unloaded state, by releasing a set of compressive prestresses initially given to the EL. Using the design of experiments approach (Graeco-Latin square method), we identified specific mechanical boundary conditions to computationally reconstruct EL buckling in the circumferential direction of the aorta. Additionally, it was shown that EL waviness almost vanished when ~20% strain (mimicking a circumferential stretch due to intravascular pressure) was applied to the buckled FE model obtained in the in vitro unloaded state. This feature is beneficial for numerical modeling of the detailed aortic wall structure, because the entire process is computationally efficient and can be readily implemented in a commercially available FE solver. Although further study is required, our findings will help clarify the roles of the EL and SML in the aortic wall and promote the understanding of the mechanisms of the medial tissue stress response. In addition, we expect this modeling technique to serve as a useful tool in the future for interpreting stress distribution relevant to vascular physiology at normal and pathological states.

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“…The specimen was stretched with a uniaxial tensile tester which was originally made in our laboratory. (9) Briefly, two ends of a specimen were glued on two separate lever arms, which were mounted on a linear guide with an oppositely threaded screw driven by a stepping motor. The lever arms moved to opposite direction to each other with this guide to keep the center part of the specimen inside the field of view.…”

Section: Uniaxial Tensile Testermentioning

confidence: 99%

Yielding Phenomena of Aortic Wall and Intramural Collagen Fiber Alignment: Possible Link to Rupture Mechanism of Aortic Aneurysms

Sugita

Matsumotο

2013

JBSE

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Estimation of wall strength of the aortic aneurysms is necessary for the prediction of their rupture risk. We previously found a significant correlation between their tensile strength σ MAX and a yielding parameter τ σ , which is the stress when tangent elastic modulus reaches at 63% of the plateau level. This may indicate that the wall strength is estimated from their pressure-diameter relationship. Here we show a possible mechanism of the correlation between τ σ and σ MAX by focusing on alignment of collagen fibers. Thin (150-µm) slices of porcine thoracic aortas were uniaxially stretched in circumferential direction until failure under a microscope, and a retardance, a phase shift when polarized light passes through a birefringent material, was measured as the degree of collagen fiber alignment. Strength σ MAX correlated significantly with τ σ as obtained previously. The retardance increased with the increase in the stress and reached a plateau at the stress σ Ret-plateau , indicating that σ Ret-plateau is the stress at which most of the intramural collagen fibers have aligned. The stress σ Ret-plateau correlated significantly with τ σ and both parameters has similar values. This may indicate that the aortic wall yields when all of collagen fibers become straight. Smaller σ Ret-plateau means that most collagen fibers are stretched and loaded at smaller stress, resulting in failure at smaller stress. This seems to be a reason for the significant correlation between τ σ and σ MAX .

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T0201-3-6 Observation of microscopic deformation in the porcine thoracic aortic wall during circumferential stretch

Cited by 3 publications

References 0 publications

Modeling elastic lamina buckling in the unloaded aortic media

Modeling elastic lamina buckling in the unloaded aortic media

Modeling of elastic lamina buckling coupled with smooth muscle layer deformation in the aortic media: technique for readily implementing residual stresses

Yielding Phenomena of Aortic Wall and Intramural Collagen Fiber Alignment: Possible Link to Rupture Mechanism of Aortic Aneurysms

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