An anisotropic pseudo-elastic model for the mullins effect in arterial tissue

This paper is focused on developing the theory which describes the Mullins effect in human arterial tissue. Cyclic uni-axial tensile tests were performed to obtain data characterizing the Mullins effect in arterial tissue. In order to account anisotropy of arterial tissue, longitudinally as well as circumferentially resected samples of human aorta were tested. Each sample underwent repeated (four times) loading and unloading to a certain value of maximum stretch. This limiting stretch increased in several consecutive steps. The arterial wall is considered as hyperelastic, locally orthotropic, incompressible material. A strain energy function is adopted in the limiting fiber extensibility form. Description of primary material response, followed by material stress softening in the repeated cycles, is based on pseudo-elastic constitutive model proposed by Dorfmann and Ogden. This theory is developed using anisotropic form of the softening variable. The primary loading curve and the fourth unloading curve of each set of cycles are chosen for regression analysis. The model with thus estimated parameters successfully fits experimental data and is suitable for application in biomedicin

Collagen orientation and waviness within the vein wall

This paper presents the analysis of the internal structure and organization of components within the vein wall. Dominant directions and statistical distribution of collagen fibers undulation were investigated in digitalized histological sections from media and adventitia layer of human vena cava inferior. Orientations of collagen fibers were analyzed by the in-house developed software Binary Directions. Digital images were converted to binary pixel maps with collagen fibers enhanced. The software employs an algorithm of the Rotation Line Segment to determine significant directions in digital images. It was found that collagen fibers are aligned in circumferential direction in media layer. Contrary to that in adventitia fibers are arranged in longitudinal direction. In contrast to elastic artery, no evidence of helically reinforced composite structure was found. Second goal was to find out which statistical distribution, usually using in structural models (Gamma, Beta or Weibull), fits to the undulation distribution of collagen fibers. Collagen waviness was characterized by a probability density function for the strain necessary to straighten a crimped fiber. Computer analysis of the end-to-end and contour length was performed using Nis-Elements software. The statistical analysis suggests that the waviness of collagen fibers is identical in media and adventitia It was found that the average strain necessary for straightening collagen fibers is 0.24±0.11 (±SD) and that all three probability distributions fit straightening strains very well and can be used in structural model

Opening angle of human saphenous vein

In this study, the residual strain was evaluated for human saphenous vein. Rings of the vein from four donors (two male and two female; age 62±5 years) were radially cut to obtain the opening angle (α) of the tissue. It was found that the average opening angle (α) 45°±18° (mean±SD). Then, the intraluminal distribution of circumferential stress was computed for one donor in order to verify the uniform stress hypothesis (opening angle is homogenizing the stress distribution across the wall thickness). The results suggests that α obtained from experiments is close to the value of opening angle which homogenizes the stress distribution across the wall thickness determined from simulations

Constitutive modelling of human perivascular adipose tissue

The mechanical properties of adipose tissue are studied rarely despite the fact that surrounding tissue plays an important role in arterial physiology and mechanobiology. This study deals with the determination of material parameters of human perivascular adipose tissue surrounding the abdominal aorta. The selected representative experimental curve from uniaxial tensile test was used to be fitted by Ogden, Gent, and Fung hyperelastic models assuming isotropic and incompressible material of perivascular tissue. The estimated material parameters are μ = 0.001 MPa and α = 28, μ = 0.026 MPa and Jm =0.067, μ = 0.018 MPa and b = 31.834, respectively. It was concluded that all applied mathematical models predicted nonlinear stress-strain relation ship satisfactorily with coefficient of determination 0.995, 0.981, 0.994, respectively

An anisotropic pseudo-elastic model for the mullins effect in arterial tissue

This paper is focused on developing the theory which describes the Mullins effect in human arterial tissue. Cyclic uni-axial tensile tests were performed to obtain data characterizing the Mullins effect in arterial tissue. In order to account anisotropy of arterial tissue, longitudinally as well as circumferentially resected samples of human aorta were tested. Each sample underwent repeated (four times) loading and unloading to a certain value of maximum stretch. This limiting stretch increased in several consecutive steps. The arterial wall is considered as hyperelastic, locally orthotropic, incompressible material. A strain energy function is adopted in the limiting fiber extensibility form. Description of primary material response, followed by material stress softening in the repeated cycles, is based on pseudo-elastic constitutive model proposed by Dorfmann and Ogden. This theory is developed using anisotropic form of the softening variable. The primary loading curve and the fourth unloading curve of each set of cycles are chosen for regression analysis. The model with thus estimated parameters successfully fits experimental data and is suitable for application in biomedicin

Constitutive modelling of human perivascular adipose tissue

The mechanical properties of adipose tissue are studied rarely despite the fact that surrounding tissue plays an important role in arterial physiology and mechanobiology. This study deals with the determination of material parameters of human perivascular adipose tissue surrounding the abdominal aorta. The selected representative experimental curve from uniaxial tensile test was used to be fitted by Ogden, Gent, and Fung hyperelastic models assuming isotropic and incompressible material of perivascular tissue. The estimated material parameters are μ = 0.001 MPa and α = 28, μ = 0.026 MPa and Jm =0.067, μ = 0.018 MPa and b = 31.834, respectively. It was concluded that all applied mathematical models predicted nonlinear stress-strain relation ship satisfactorily with coefficient of determination 0.995, 0.981, 0.994, respectively

Mechanical Properties of Polyvinyl Alcohol/Collagen Hydrogel

Abstract. The effects of the polyvinyl alcohol (PVA) concentration on mechanical properties of hydrogels based on blends of native or denatured collagen / PVA were examined. Blends of PVA with collagen were obtained by mixing the solutions in different ratios, using glycerol as a plasticizer. The solutions were cast on polystyrene plates and the solvent was allowed to evaporate at room temperature. Uniaxial tensile tests were performed in order to obtain the initial stiffness (up to deformation 0.1), the ultimate tensile stress and the deformation at failure of the material in the water-saturated hydrogel form. It was found that the material was elastic and the addition of PVA helped to enhance both the ultimate tensile stress and stiffness of the films. Samples prepared form denaturated collagen showed the higher ultimate tensile stress and the deformation at failure in comparison with those prepared from native collagen. The results suggest that we could expect successful application of the collagen-PVA biomaterial for tissue engineering

Inovace vyuky "Experimentalni analyza zbytkovych napeti"Zbytkova napeti v cevach a myokardu.

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