| 1. |
- Ambrosi, D., et al.
(författare)
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Perspectives on biological growth and remodeling
- 2011
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Ingår i: Journal of the mechanics and physics of solids. - : Elsevier BV. - 0022-5096 .- 1873-4782. ; 59:4, s. 863-883
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Forskningsöversikt (refereegranskat)abstract
- The continuum mechanical treatment of biological growth and remodeling has attracted considerable attention over the past fifteen years. Many aspects of these problems are now well-understood, yet there remain areas in need of significant development from the standpoint of experiments, theory, and computation. In this perspective paper we review the state of the field and highlight open questions, challenges, and avenues for further development.
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| 2. |
- Eriksson, T. S. E., et al.
(författare)
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Influence of myocardial fiber/sheet orientations on left ventricular mechanical contraction
- 2013
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Ingår i: Mathematics and mechanics of solids. - : SAGE Publications. - 1081-2865 .- 1741-3028. ; 18:6, s. 592-606
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Tidskriftsartikel (refereegranskat)abstract
- At any point in space the material properties of the myocardium are characterized as orthotropic, that is, there are three mutually orthogonal axes along which both electrical and mechanical parameters differ. To investigate the role of spatial structural heterogeneity in an orthotropic material, electro-mechanically coupled models of the left ventricle (LV) were used. The implemented models differed in their arrangement of fibers and sheets in the myocardium, but were identical otherwise: (i) a generic homogeneous model, where a rule-based method was applied to assign fiber and sheet orientations, and (ii) a heterogeneous model, where the assignment of the orthotropic tissue structure was based on experimentally obtained fiber/sheet orientations. While both models resulted in pressure-volume loops and metrics of global mechanical function that were qualitatively and quantitatively similar and matched well with experimental data, the predicted deformations were strikingly different between these models, particularly with regard to torsion. Thus, the simulation results strongly suggest that heterogeneous structure properties play an important nonnegligible role in LV mechanics and, consequently, should be accounted for in computational models.
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| 3. |
- Eriksson, T. S. E., et al.
(författare)
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Modeling the dispersion in electromechanically coupled myocardium
- 2013
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939. ; 29:11, s. 1267-1284
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Tidskriftsartikel (refereegranskat)abstract
- We present an approach to model the dispersion of fiber and sheet orientations in the myocardium. By utilizing structure parameters, an existing orthotropic and invariant-based constitutive model developed to describe the passive behavior of the myocardium is augmented. Two dispersion parameters are fitted to experimentally observed angular dispersion data of the myocardial tissue. Computations are performed on a unit myocardium tissue cube and on a slice of the left ventricle indicating that the dispersion parameter has an effect on the myocardial deformation and stress development. The use of fiber dispersions relating to a pathological myocardium had a rather big effect. The final example represents an ellipsoidal model of the left ventricle indicating the influence of fiber and sheet dispersions upon contraction over a cardiac cycle. Although only a minor shift in the pressure-volume (PV) loops between the cases with no dispersions and with fiber and sheet dispersions for a healthy myocardium was observed, a remarkably different behavior is obtained with a fiber dispersion relating to a diseased myocardium. In future simulations, this dispersion model for myocardial tissue may advantageously be used together with models of, for example, growth and remodeling of various cardiac diseases.
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| 4. |
- Famaey, Nele, et al.
(författare)
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Arterial clamping : Finite element simulation and in vivo validation
- 2012
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Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161 .- 1878-0180. ; 12, s. 107-118
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Tidskriftsartikel (refereegranskat)abstract
- Commonly used techniques in cardiovascular interventions such as arterial clamping always entail a certain degree of unavoidable iatrogenic tissue damage. Therefore, studies have been directed towards the decrease of undesired intraoperative trauma, for example, through the design of less traumatic surgical instruments. Obviously, the effectiveness of new clamp designs and techniques depends on how well damage mechanisms are understood and how accurate thresholds for safe tissue loading can be set. This information can in part be derived from reliable finite element simulations. This study is the first to describe a finite element simulation of the clamping of a rat abdominal aorta with occlusion and in vivo validation. Material nonlinearity, large deformations, contact interactions and residual strains are hereby taken into account. The mechanical parameters of the model are derived from inflation experiments. The effect of the residual strains, different clamp geometries as well as the effect of variations in material properties are studied. In all simulations, stress concentrations in different regions of the tissue are noticed, especially for a corrugated clamp design. This shows the importance of finite element modeling in understanding the relation between mechanical loading and damage mechanisms. The inclusion of residual strains has its effect not only in the physiological loading regime, but also during clamping. Just as in the physiologic regime, it lowers the stress gradients through the wall thickness. Varying the material properties with the measured standard deviation between specimens leads to an average change of +/- 17% in the maximum and minimum principal stresses. Finally, the model is validated with an in vivo clamping experiment on a Wistar rat in which the clamping force was measured, showing good correspondence with the modeled clamping force.
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| 5. |
- Schmidt, T., et al.
(författare)
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Modeling and experimental investigations of the stress-softening behavior of soft collagenous tissues
- 2013
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Ingår i: Computational Plasticity XII. - Barcelona : International Center for Numerical Methods in Engineering (CIMNE). - 9788494153150 ; , s. 133-144
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the formulation of a micro-mechanically based damage model for soft collagenous tissues. The model is motivated by (i) a sliding filament model proposed in the literature [1] and (ii) by experimental observations from electron microscopy (EM) images of human abdominal aorta specimens, see [2]. Specifically, we derive a continuum damage model that takes into account statistically distributed proteoglycan (PG) bridges. The damage model is embedded into the constitutive framework proposed by Balzani et al. [3] and adjusted to cyclic uniaxial tension tests of a human carotid artery. Furthermore, the resulting damage distribution of the model after a circumferential overstretch of a simplified arterial section is analyzed in a finite element calculation.
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| 6. |
- Schriefl, A. J., et al.
(författare)
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Layer-specific distributed collagen fiber orientations in human arteries, from thoracic aorta to common iliac
- 2011
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Ingår i: ASME 2011 Summer Bioengineering Conference, SBC 2011. - 9780791854587 ; , s. 5-6
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Konferensbidrag (refereegranskat)abstract
- We use the well established method of polarized microscopy on picrosirius red stained tissue samples and a dispersion model to quantify over 37000 measured layer-specific 3D fiber orientations of 11 human thoracic and abdominal aortas and common iliac arteries. Our results yield mean fiber directions, quantitative dispersion data and the existence of two distinct and prominent fiber families for all layers of the aortic wall.
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| 7. |
- Schriefl, A. J., et al.
(författare)
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Remodeling of Intramural Thrombus and Collagen in an Ang-II Infusion ApoE-/- Model of Dissecting Aortic Aneurysms
- 2012
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Ingår i: Thrombosis Research. - : Elsevier BV. - 0049-3848 .- 1879-2472. ; 130:3, s. E139-E146
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Tidskriftsartikel (refereegranskat)abstract
- Fibrillar collagen endows the normal aortic wall with significant stiffness and strength and similarly plays important roles in many disease processes. For example, because of the marked loss of elastic fibers and functional smooth cells in aortic aneurysms, collagen plays a particularly important role in controlling the dilatation of these lesions and governing their rupture potential. Recent findings suggest further that collagen remodeling may also be fundamental to the intramural healing of arterial or aneurysmal dissections. To explore this possibility further, we identified and correlated regions of intramural thrombus and newly synthesized fibrillar collagen in a well-established mouse model of dissecting aortic aneurysms. Our findings suggest that intramural thrombus that is isolated from free-flowing blood creates a permissive environment for the synthesis of fibrillar collagen that, albeit initially less dense and organized, could protect that region of the dissected wall from subsequent expansion of the dissection or rupture. Moreover, alpha-smooth muscle actin positive cells appeared to be responsible for the newly produced collagen, which co-localized with significant production of glycosaminoglycans.
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| 8. |
- Selimovic, A., et al.
(författare)
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A computational framework to explore the role of pulsatile haemodynamics on cerebral aneurysm development for patient-specific arterial geometries
- 2010
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Ingår i: 6th World Congress of Biomechanics (WCB 2010). August 1-6, 2010 Singapore. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642145148 ; , s. 759-762
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Konferensbidrag (refereegranskat)abstract
- A patient-specific cerebral aneurysm case was identified from clinical imaging data, and then segmented to create a geometrical representation of the aneurysm and surrounding vasculature. Using ANSYS ICEM CFD, the geometry was manipulated to remove the aneurysm and replace it with a short (initially cylindrical) section, which reconnected to the upstream and downstream arterial sections so that the surface gradients were continuous. This section is modelled using a realistic constitutive model of the arterial wall and is the location where the computational model of the aneurysm evolves. The aneurysm evolution FEA model is combined with detailed 3D haemodynamic solutions using ANSYS CFX. A rigid-wall approach is adopted to solve the flow, to derive the haemodynamic stimuli that act on the endothelial cell layer of the tissue. Additionally, the geometry of the aneurysm is obtained at systolic and diastolic pressures (using a quasi-static approach) to obtain the cyclic stretch experienced by the cells within the arterial wall. This is the first patient-specific model of cerebral aneurysm evolution to explicitly link growth and remodelling of arterial tissue to the local mechanical environment. It will provide the basis for investigating the role and importance of various mechanical stimuli on the progression of the disease and will yield improved understanding of the aetiology of cerebral aneurysm formation.
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| 9. |
- Sommer, Gerhard, et al.
(författare)
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3D constitutive modeling of the biaxial mechanical response of intact and layer-dissected human carotid arteries
- 2012
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Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161 .- 1878-0180. ; 5:1, s. 116-128
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Tidskriftsartikel (refereegranskat)abstract
- Human arteries with non-atherosclerotic intimal thickening consist of three distinct layers: adventitia, media and intima. From a series of axial extension and inflation tests on intact and layer-dissected human carotid arteries (adventitia and media-intima composite), a 3D structurally-based strain-energy function (SEF) is calibrated, and a set of five material parameters is identified which is not yet available in the literature. The zero-stress states of the artery tubes investigated are considered in the calibration process, and the related kinematics for the finite deformation of the individual continuum are described in detail. The SEF employed is capable of describing the different mechanical properties of the intact and layer-dissected tissue tubes (arterial segments) investigated at different pressure domains and axial stretches. The correlation coefficients and error measures determined indicate good correlation between the model and the experimental data for all tested tubes. Mean values of each individual material parameter provide a kind of 'master model' that characterizes the mean response of all mechanical data obtained from the human carotid arteries. The material parameters and the 3D constitutive model serve as a foundation for finite element simulations, and hence the analysis of more complex patient-specific boundary-value problems in the human carotid physiology and pathology.
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| 10. |
- Sommer, G., et al.
(författare)
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Biomechanical Properties Of The Human Ventricular Myocardium
- 2013
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Ingår i: Biomedizinische Technik (Berlin. Zeitschrift). - : Walter de Gruyter. - 1862-278X .- 0013-5585. ; 58:(Suppl. 1)
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Tidskriftsartikel (refereegranskat)abstract
- In the multidisciplinary field of heart research it is of utmost importance, for the description of phenomena such as mechano-electric feedback or heart wall thickening, to accurately identify the biomechanical properties of the myocardium. Hence, this study aims at determining biaxial tensile and triaxial shear properties of the passive human myocardium. This novel combination of biaxial and shear testing, together with the investigation of the myocardial microstructure, yields new innovative and essential information of the material properties to fulfil the short term goals of constructing realistic myocardial models. Through such modeling efforts, capable to capture the biomechanical behaviour of the heart, it is possible to improve some methods of medical treatment, and hence the quality of life for people suffering from heart diseases - at least as a long-term goal.
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