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  • 1. Cui, Zhao Ying
    et al.
    Famaey, Nele
    Depreitere, Bart
    Ivens, Jan
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Vander Sloten, Jos
    On the assessment of bridging vein rupture associated acute subdural hematoma through finite element analysis2017In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 20, no 5, p. 530-539Article in journal (Refereed)
    Abstract [en]

    Acute subdural hematoma (ASDH) is a type of intracranial haemorrhage following head impact, with high mortality rates. Bridging vein (BV) rupture is a major cause of ASDH, which is why a biofidelic representation of BVs in finite element (FE) head models is essential for the successful prediction of ASDH. We investigated the mechanical behavior of BVs in the KTH FE head model. First, a sensitivity study quantified the effect of loading conditions and mechanical properties on BV strain. It was found that the peak rotational velocity and acceleration and pulse duration have a pronounced effect on the BV strains. Both Young's modulus and diameter are also negatively correlated with the BV strains. A normalized multiple linear regression model using Young's modulus, outer diameter and peak rotational velocity to predict the BV strain yields an adjusted -value of 0.81. Secondly, cadaver head impact experiments were simulated with varying sets of mechanical properties, upon which the amount of successful BV rupture predictions was evaluated. The success rate fluctuated between 67 and 75%. To further increase the predictive capability of FE head models w.r.t. BV rupture, future work should be directed towards improvement of the BV representation, both geometrically and mechanically.

  • 2.
    Hedenstierna, Sofia
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Halldin, Peter
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Brolin, Karin
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Evaluation of a combination of continuum and truss finite elements in a model of passive and active muscle tissue2008In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 11, no 6, p. 627-639Article in journal (Refereed)
    Abstract [en]

    The numerical method of finite elements (FE) is a powerful tool for analysing stresses and strains in the human body. One area of increasing interest is the skeletal musculature. This study evaluated modelling of skeletal muscle tissue using a combination of passive non-linear, viscoelastic solid elements and active Hill-type truss elements, the super-positioned muscle finite element (SMFE). The performance of the combined materials and elements was evaluated for eccentric motions by simulating a tensile experiment from a published study on a stimulated rabbit muscle including three different strain rates. It was also evaluated for isometric and concentric contractions. The resulting stress-strain curves had the same overall pattern as the experiments, with the main limitation being sensitivity to the active force-length relation. It was concluded that the SMFE could model active and passive muscle tissue at constant rate elongations for strains below failure, as well as isometric and concentric contractions.

  • 3.
    Heintz, Sofia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Evaluation of load-sharing and load capacity in force-limited muscle systems2006In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259Article in journal (Other academic)
    Abstract [en]

    This study had the objective to develop an algorithm for accurate force decomposition in a redundant musculoskeletal system. The hypothesis was that the calculated load-sharing is dependent on the optimality criterion adopted, but also on the magnitude of carried load. The developed algorithm emphasizes that several established optimization techniques can be unified, by identifying and separating the underlying optimization functions and the numerical methods to solve the resulting system. A numerically efficient and easily adaptable solution method is thereby created. In addition, individual capacity values are introduced for the muscles, allowing the evaluation of a magnitude-dependent load-sharing, and a load carrying capacity of the whole system. By modularizing the optimization method, the algorithm can be used as part of larger simulation systems. To illustrate the possibilities of the algorithm, a model of the upper limb is used in a set of demonstrative examples. The results from the examples show how the interactions between synergistic muscles is predicted in different configurations, and at different load levels.

  • 4.
    Kroon, Martin
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Optimal length of smooth muscle assessed by a microstructurally and statistically based constitutive model2011In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 14, no 1, p. 43-52Article in journal (Refereed)
    Abstract [en]

    Smooth muscle exhibits an optimal length at which it is able to generate a maximum amount of force. In this study, the optimal length is assessed by use of a microstructurally and statistically based constitutive model for smooth muscle. The model is based on the sliding filament theory, and a modified version of Hill's mechanical model was adopted. It was conjectured, that a variation in the overlap in the actomyosin contractile units together with a statistical dispersion in the size of the dense bodies are responsible for the optimal length characteristics. The influence of contractile unit length, dense body size and dense body compliance was investigated, and the model was fully able to predict experimental data. The results indicate that the compliance of the dense bodies does not contribute significantly to the total compliance of the contractile apparatus.

  • 5.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701). Karolinska institutet.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Influences of brain tissue poroelastic constants on intracranial pressure (ICP) during constant-rate infusion2013In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 16, no 12, p. 1330-1343Article in journal (Refereed)
    Abstract [en]

    A 3D finite element (FE) model has been developed to study the mean intracranial pressure (ICP) response during constant-rate infusion using linear poroelasticity. Due to the uncertainties in the poroelastic constants for brain tissue, the influence of each of the main parameters on the transient ICP infusion curve was studied. As a prerequisite for transient analysis, steady-state simulations were performed first. The simulated steady-state pressure distribution in the brain tissue for a normal cerebrospinal fluid (CSF) circulation system showed good correlation with experiments from the literature. Furthermore, steady-state ICP closely followed the infusion experiments at different infusion rates. The verified steady-state models then served as a baseline for the subsequent transient models. For transient analysis, the simulated ICP shows a similar tendency to that found in the experiments, however, different values of the poroelastic constants have a significant effect on the infusion curve. The influence of the main poroelastic parameters including the Biot coefficient alpha, Skempton coefficient B, drained Young's modulus E, Poisson's ratio nu, permeability kappa, CSF absorption conductance C-b and external venous pressure p(b) was studied to investigate the influence on the pressure response. It was found that the value of the specific storage term S-epsilon is the dominant factor that influences the infusion curve, and the drained Young's modulus E was identified as the dominant parameter second to S-epsilon. Based on the simulated infusion curves from the FE model, artificial neural network (ANN) was used to find an optimised parameter set that best fit the experimental curve. The infusion curves from both the FE simulation and using ANN confirmed the limitation of linear poroelasticity in modelling the transient constant-rate infusion.

  • 6. Pierce, David M.
    et al.
    Ricken, Tim
    Holzapfel, Gerhard A.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). Institute of Biomechanics, Center of Biomedical Engineering, Graz University of Technology.
    A hyperelastic biphasic fibre-reinforced model of articular cartilage considering distributed collagen fibre orientations: continuum basis, computational aspects and applications2013In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 16, no 12, p. 1344-1361Article in journal (Refereed)
    Abstract [en]

    Cartilage is a multi-phase material composed of fluid and electrolytes (68-85% by wet weight), proteoglycans (5-10% by wet weight), chondrocytes, collagen fibres and other glycoproteins. The solid phase constitutes an isotropic proteoglycan gel and a fibre network of predominantly type II collagen, which provides tensile strength and mechanical stiffness. The same two components control diffusion of the fluid phase, e.g. as visualised by diffusion tensor MRI: (i) the proteoglycan gel (giving a baseline isotropic diffusivity) and (ii) the highly anisotropic collagenous fibre network. We propose a new constitutive model and finite element implementation that focus on the essential load-bearing morphology: an incompressible, poroelastic solid matrix reinforced by an inhomogeneous, dispersed fibre fabric, which is saturated with an incompressible fluid residing in strain-dependent pores of the collagen-proteoglycan solid matrix. The inhomogeneous, dispersed fibre fabric of the solid further influences the fluid permeability, as well as an intrafibrillar portion that cannot be squeezed out' from the tissue. Using representative numerical examples on the mechanical response of cartilage, we reproduce several features that have been demonstrated experimentally in the cartilage mechanics literature.

  • 7. Schmid, Holger
    et al.
    Grytsan, Andrii
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
    Poshtan, Emad
    Watton, Paul N.
    Itskov, Mikhail
    Influence of differing material properties in media and adventitia on arterial adaptation: application to aneurysm formation and rupture2013In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 16, no 1, p. 33-53Article in journal (Refereed)
    Abstract [en]

    Experimental and computational studies suggest a substantial variation in the mechanical responses and collagen fibre orientations of the two structurally important layers of the arterial wall. Some observe the adventitia to be an order of magnitude stiffer than the media whilst others claim the opposite. Furthermore, studies show that molecular metabolisms may differ substantially in each layer. Following a literature review that juxtaposes the differing layer-specific results we create a range of different hypothetical arteries: (1) with different elastic responses, (2) different fibre orientations, and (3) different metabolic activities during adaptation. We use a finite element model to investigate the effects of those on: (1) the stress response in homeostasis; (2) the time course of arterial adaptation; and (3) an acute increase in luminal pressure due to a stressful event and its influence on the likelihood of aneurysm rupture. Interestingly, for all hypothetical cases considered, we observe that the adventitia acts to protect the wall against rupture by keeping stresses in the media and adventitia below experimentally observed ultimate strength values. Significantly, this conclusion holds true in pathological conditions.

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