Cardiovascular Biomechanics
Hadi Taghizadeh; Faezeh Amini
Volume 16, Issue 1 , May 2022, , Pages 11-21
Abstract
Atherosclerosis, a common cardiovascular disease, is among the leading causes of death. Many of the heart attacks results from ruptured atherosclerotic lesion and emboli formation. Then, the susceptibility of the lesion is a key factor in preventing negative outcomes of the rupture. Mechanisms of plaque ...
Read More
Atherosclerosis, a common cardiovascular disease, is among the leading causes of death. Many of the heart attacks results from ruptured atherosclerotic lesion and emboli formation. Then, the susceptibility of the lesion is a key factor in preventing negative outcomes of the rupture. Mechanisms of plaque rupture are under debate. However, a general agreement on the bold contribution of hemodynamic factors including the blood pressure is established. In the current study, biomechanical impacts of plaque calcification procedure and the changed thickness of fibrous cap were investigated. To do so, a cross-section of the constricted coronary artery is reconstructed from the histological images and extruded in the axial direction of the artery to produce the three dimensional configuration of the coronary model. Holzapfel strain energy density function is utilized for mechanical description of the arterial tissue and the fibrous cap which enables us to adopt collagen fiber orientation into the mechanical model. Furthermore, since the constricted vessel configuration is asymmetrical, instead of simplified cylindrical coordinates for collagen orientation, a discrete coordinate system is assigned to every element and respective circumferential, axial and radial directions were assigned. With calcification, plaque is more stable and produces monotonic stress patterns in its vicinity. Also, the fibrous cap thickness plays an important role as a barrier to inhibit stress concentration from soft lipid core and disturb the mechanical loads to the neighboring regions. These two parameters, provide useful insight on mechanical load distribution around an atherosclerotic lesion and the pathway of arterial tissue toward a new homeostasis.
Biomechanics / Biomechanical Engineering
Hadi Taghizadeh
Volume 14, Issue 1 , May 2020, , Pages 23-30
Abstract
Determining mechanical properties of very soft tissues have been considered as a popular and challenging topic in biomechanics only in the last decades. In addition, these tissues do not have any weight-bearing functions, however, their mechanical characterization is important for designing new safety ...
Read More
Determining mechanical properties of very soft tissues have been considered as a popular and challenging topic in biomechanics only in the last decades. In addition, these tissues do not have any weight-bearing functions, however, their mechanical characterization is important for designing new safety equipment, diagnosis and treatment of the diseases and tumors. Liver is one of the vital body organs that is highly porous and tearable and is highly susceptible to mechanical damage during accidents and minimally invasive surgeries. In this study, a set of uniaxial tension tests was performed on a bovine liver tissue. Linear elastic model in combination with the Bridgman correction method was utilized to determine the mechanical properties, i.e., Young’s modulus. An image processing software was also developed utilizing MS Visual Fortran language in order to obtain and track required geometric dimensions, i.e., radii of curvature, minimal sample radius in the necking zone, and probable detaching during the test session. Our experiments showed a tensile elastic modulus of 15.51±1.62 kPa for the samples (p < 0.05). Different amounts for elastic modulus of the liver have been reported in the literature. Hence, we conducted tension tests on samples with progressively increasing diameters. The changes in the sample diameter was in the range of 2.5 to 20 mm. In this way, the effect of sample diameter on elastic modulus was inquired. Our results indicate an inverse relation between elastic modulus and diameter in the tested zone. Such phenomena can be attributed to small sample size which is similar to the size of liver lobules (a few millimeters). Hence, samples with diameters in the range of lobule size cannot constitute a suitable representative element for the liver tissue. To obtain valid results the sample diameters should be more than three times that of the lobule.
