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Analysis of residual stresses in arterial wall
Novák, Kamil ; Fuis, Vladimír (referee) ; Burša, Jiří (advisor)
This thesis deals with computational modeling of the influence of residual stresses in idealized geometry of blood vessels and subsequent application of acquired knowledge to abdominal aortic aneurysm. In the terms of quality of the computational model, we reduced the uncertainties that are included in the computational model without considering the influence of residual stresses. The basic assumption of homogenization significant peaks of the stress between inner and outer vessel wall was met for each level of the computational model Methods that have been used are: deformation method (opening angle method), inverse mechanics of large deformations, fictitious temperature – for linear elastic material and hyperelastic material defined by the constitutive model. Numerical verification was carried out using program ANSYS.
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Exploitation of Experiments for Improvement of Level Constitutive Models of Aortic Aneurysm Tissues
Man, Vojtěch ; Horný,, Lukáš (referee) ; Rosenberg, Josef (referee) ; Burša, Jiří (advisor)
This paper deals with the problem of abdominal aortic aneurysms (AAA), taking into account the possibility of using mechanical tests of aortic tissues for improvement of level of their constitutive models. First part of thesis deals with the introduction into the problem, description of the structure of the wall of the healthy aorta, its main components and the degenerative changes which lead to formation of AAA. This is followed by a brief excursion into constitutive modeling, which focuses closely on the description of the models used to describe the mechanical behavior of soft tissues. The theoretical part is then supplemented by a narrower selection of constitutive models used for modeling aortic wall and intraluminal thrombus, together with published results, which are reviewed and discussed at the end of this section. The main part of this thesis is devoted to tests of mechanical properties of arterial tissues. First, the methodology is presented together with the description of the customizations of the laboratory equipments together with the test rig. In addition, attention is focused on the results of mechanical tests of intraluminal thrombus, where the results of both uniaxial tensile tests and equbiaxial testing are presented. Also the influence of distance ILT from the lumen on the mechanical properties of the thrombus is examined. Another area of interest is the investigation of the effect of elastase on the chnage of mechanical properties of pig aorta. In this case, porcine aortas are experimentally tested only by biaxial testing, and the time of elastase action to alter the mechanical properties is analyzed so that the resulting tissue has a similar stress-strain response as aneurysmal tissue. Finally, the results of experimental measurements, limitations and other possible ways of research are summarized.
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Design of cylindrical apparatus for determination of directions of reinforcing fibres in aorta in its deformed state
Král, Martin ; Vaverka, Jiří (referee) ; Burša, Jiří (advisor)
This bachelor thesis deals with the design of cylindrical apparatus, which allows the cont- rolled biaxial deformation of a cylindrical sample of the aorta. This apparatus is designed to determine the direction of collagen fibers in the deformed aorta. The theoretical part of the thesis is focused mainly on description of the structure and mechanical properties of the wall of the aorta. In the design part, attention is paid to the design of the cylindrical apparatus. In the conclusion, the deformation of the cylindrical sample of the abdominal aorta from the pig is carried out on the apparatus and its strain is measured.
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Stress-strain analysis of anastomosis between artery and artificial vascular graft
Hrubanová, Anna ; Švancara, Pavel (referee) ; Burša, Jiří (advisor)
This bachelor’s thesis deals with anatomy and pathology of arteries and possibilities of their replacement with vascular grafts. The first part of the thesis describes structure and mechanical properties of arterial wall. Furthemore, the biological and mechanical properties of vascular grafts and their influence of healing process are described. The second part of this thesis starts with non-linear calculation of deformation of arterial wall using generalized Hooke’s law. The analytical calculation of connection of artery and vascular graft using cylindrical momentum shell theory was made at the end of this thesis. Description of limitations of this method is also included.
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Design of apparatus for determination of directions of reinforcing fibres in soft biological tissues in their deformed state
Sodomka, Tomáš ; Vaverka, Jiří (referee) ; Burša, Jiří (advisor)
The Bachelor´s thesis is focused on the determination of directions of collagen fibres in elastic arteries. The first aim of this thesis is a general introduction into soft tissue mechanics with turning attention to connective tissue where collagen fibres are their inseparable part. Also the thesis introduces arrangement of collagen fibres, their waviness and how the waviness thwarts determination of direction of fibres. The second aim is a design and test of the mechanical apparatus, which is able to stretch a squared aortic sample in two perpendicular directions (independently on each other) up to the relative deformation of 30 %. Design of the apparatus allows the sample to be dipped into the formaldehyde solution, which fixes the deformation. Consequent histologic sections of the sample will be used for the determination of global directions of collagen fibres in the aorta. The apparatus is designed to simulate conditions in a human or animal body where aorta is axially pre-stretched and at the same time expanded in the radial direction by blood pressure.
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Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries
Novák, Kamil ; Daniel, Matej (referee) ; Vimmr, Jan (referee) ; Burša, Jiří (advisor)
This dissertation thesis concerns with Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries and it is divided into three main parts. Motivation for this dissertation thesis was in a study reviewing effect of material model upon resulting stresses in AAA. The effect was calculated in 70 patient-specific geometries of AAA, which exceeds the number of geometries in other scientific papers by one order. Within this study, two material models were used, i.e. real one and 100× stiffer, and obtained stresses were mutually compared. It was quantified that peak stress difference can be higher than 20 % in 10% of patients and therefore the real material model should be preferred over the artificial one although operation with this model is more demanding. The second part of this thesis deals with an identification of structural parameters (orientation and dispersion of collagen fibres) of porcine aortic tissue by using adjusted Fast Fourier Transform based algorithm. The extracted structural parameters were inserted into two-layer structure-motivated constitutive model Martufi-Gasser. This model was validated and its predictive capabilities were also tested with fine results. The most important information obtained from the digital image processing of ~9000 micrographs is existence of only one family of dispersed collagen fibres which breaks the current dogma present in many scientific papers about two families of collagen fibres. The third part concerns with a proposal of an automated phase-correlation based algorithm for obtaining collagen fibre direction from polarized light microscopy images. The proposed algorithm was verified and validated and it yields histograms of collagen fibre directions with overall number of measured points larger than it would be possible to get from any manual measurement. The limitation of the original proposed algorithm is in 90° period of polarized light intensity, thus the method results in angles in the range of 0°–90. Therefore the end of the thesis is dedicated resolving this problem and obtaining real angles in a span of 0°–180°. To this end, the microscope set-up was changed and the algorithm was adjusted accordingly. The original and the adjusted algorithms are collagen-specific, fast and an operator independent. Despite all the author´s effort put into collagen fibre waviness quantification directly from the histograms, the waviness has not been quantified yet in this way and it remains at the stage of research.
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Intra-Aortic Balloon Counterpulsation
Žbánková, Alena ; Tannenberg,, Milan (referee) ; Sekora, Jiří (advisor)
The thesis is concerned with intraaortic balloon counterpulsation, which serves as a supporting method for the operation of failing heart. In the teoretical part is described principle of this method, its effects and the basic indications and contraindications of using. In the practical part of this work is proposed method for detecting triggering points realized in graphical program LabVIEW. The program outputs are detected ends of T wave for balloon inflation and R wave for its deflation.
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Analysis of direction dispersion of collagen fibers in soft tissues
Sádovská, Terézia ; Lisický, Ondřej (referee) ; Turčanová, Michaela (advisor)
The bachelor thesis deals with the directional distribution of collagen fibres in soft tissues especially in arteries and tendons. The first part gives basic information about anatomy of human vascular system, particulary structure of the arteries. There are explained polarization microscopy principle of materials exhibiting birefringence. Further is described relation between direction of density and mechanical properties expresses as modulus in tensile. In the next section, we will be defined stress in arterial wall using linear stregth and stiffness. In the last part of thesis will be observed dispertion of collagen fibres in tendon. This dispertion is described by circular distribution Von Mises. At the end is evaluated how dispertion of collagen fibres effects mechanical properties of arteries.
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Analysis of possibilities of analytical approaches suitable for evaluating of stress-strain states of idealized aortic shapes
Turčanová, Michaela ; Burša, Jiří (referee) ; Novák, Kamil (advisor)
The bachelor's thesis deals with possibilities of analytical solution of stress-strain states of arteries. The first part of the thesis gives an information about cardiovascular system and continuum mechanics. The calculation was performed analytically and also numerically using ANSYS program. The analytical calculation was carried out considering non-linear theory of thin and thick-walled vessels involving the residual stress and fictitious temperature approach. Furthermore, the analysis of solutions of abdominal aortic aneurysms was done based on linear theory. Description of other methods of linear theory and techniques of calculating with residual stress are briefly summarized.
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Influence of strain rate on stress-strain dependencies of aortic tissues
Slažanský, Martin ; Fuis, Vladimír (referee) ; Burša, Jiří (advisor)
The thesis deals with the influence of strain rate on stress-strain dependencies of aortic tissues to estimate the error of hyperelastic models, which are neglecting the viscoelastic effects that are typical for soft biological tissues. It was found by the experiment and the subsequent evaluation that in the range of the strain rate from 0,167 to 5,000 mm/s the influence of strain rate on stress-strain dependencies is negligible. The deviation by transition from experimental data to a constitutive model was significantly larger than the deviation between the data sets varying at different strain rates, which means that the use of stress-strain curves varying at different strain rates in given range of the strain rate has no effect on the resulting model. The best of analysis models that were examined in this thesis appears to be the Yeoh hyperelastic model using the FEM.
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