<p>Studying the mechanical properties of aortic tissue is important for determining future medical intervention for both healthy and diseased conditions. While previous uniaxial, biaxial, and inflation experiments have provided valuable insights, the effects of shear and combined loading modes remain less explored. In this study, we examine the response of porcine descending thoracic aorta under large-amplitude oscillatory shear and normal compression. Circular samples (0.5 in diameter) were tested using an Anton Paar MCR302 rheometer in a parallel plate configuration. The top plate applied a compressive strain of 5%, 10%, 15%, 20%, or 25% over 10 s, followed by 50 cycles of oscillatory shear between ±50% strain at a rate of 2%/s. Ten samples were tested at each compressive strain level. A continuum mechanics framework describing the coupled compression-torsion response of an incompressible, viscoelastic, fiber-reinforced solid was derived. Closed-form expressions for the normal force and torque in terms of the strain-energy function and fiber orientation angles were obtained. Three invariant-based constitutive models were fit to the experimental data within this unified framework: the Holzapfel–Gasser–Ogden (HGO) model, the Arvind–Kannan (vanGOH) model, and a Fung-type exponential model adapted to the invariant framework. All three models achieved comparably low residuals (RMSE < 0.02 N for normal force; RMSE < 1.5 <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\times $</EquationSource> <EquationSource Format="MATHML"><math> <mo>×</mo> </math></EquationSource> </InlineEquation> 10<InlineEquation ID="IEq2"> <EquationSource Format="TEX">$^{\varvec{-4}}$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mo mathvariant="bold">-</mo> <mn mathvariant="bold">4</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation> N<InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\varvec{\cdot }$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo mathvariant="bold">·</mo> </mrow> </math></EquationSource> </InlineEquation>m for torque), demonstrating that goodness of fit alone is insufficient for model selection. Across all three models, increasing compressive strain produced a consistent monotonic increase in the isotropic matrix stiffness parameter, indicating progressive recruitment of the collagen fiber network under through-thickness compression. The HGO and vanGOH models recovered stable fiber orientation angles near 45<InlineEquation ID="IEq4"> <EquationSource Format="TEX">$^\circ $</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mo>∘</mo> </mmultiscripts> </math></EquationSource> </InlineEquation> across all compression levels. The Fung-type model exhibited parameter identifiability problems and produced degenerate fiber orientations, suggesting that its single-exponential coupling structure is poorly suited to this loading regime. These results highlight how pre-compression modulates the mechanical response of arterial tissue under shear, providing new insight into the multiaxial mechanics of the aortic wall.</p>

Mechanical characterization of porcine descending thoracic aorta under combined compression and large-amplitude oscillatory shear

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发表日期：

2026年4月29日

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Luc Nguyen,
Chandler Benjamin

摘要

Studying the mechanical properties of aortic tissue is important for determining future medical intervention for both healthy and diseased conditions. While previous uniaxial, biaxial, and inflation experiments have provided valuable insights, the effects of shear and combined loading modes remain less explored. In this study, we examine the response of porcine descending thoracic aorta under large-amplitude oscillatory shear and normal compression. Circular samples (0.5 in diameter) were tested using an Anton Paar MCR302 rheometer in a parallel plate configuration. The top plate applied a compressive strain of 5%, 10%, 15%, 20%, or 25% over 10 s, followed by 50 cycles of oscillatory shear between ±50% strain at a rate of 2%/s. Ten samples were tested at each compressive strain level. A continuum mechanics framework describing the coupled compression-torsion response of an incompressible, viscoelastic, fiber-reinforced solid was derived. Closed-form expressions for the normal force and torque in terms of the strain-energy function and fiber orientation angles were obtained. Three invariant-based constitutive models were fit to the experimental data within this unified framework: the Holzapfel–Gasser–Ogden (HGO) model, the Arvind–Kannan (vanGOH) model, and a Fung-type exponential model adapted to the invariant framework. All three models achieved comparably low residuals (RMSE < 0.02 N for normal force; RMSE < 1.5 $\times $ $\times$ 10 $^{\varvec{-4}}$ $^{- 4}$ N $\varvec{\cdot }$ $\cdot$ m for torque), demonstrating that goodness of fit alone is insufficient for model selection. Across all three models, increasing compressive strain produced a consistent monotonic increase in the isotropic matrix stiffness parameter, indicating progressive recruitment of the collagen fiber network under through-thickness compression. The HGO and vanGOH models recovered stable fiber orientation angles near 45 $^\circ $ $^{\circ}$ across all compression levels. The Fung-type model exhibited parameter identifiability problems and produced degenerate fiber orientations, suggesting that its single-exponential coupling structure is poorly suited to this loading regime. These results highlight how pre-compression modulates the mechanical response of arterial tissue under shear, providing new insight into the multiaxial mechanics of the aortic wall.