The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Heiko Stark - One of the best experts on this subject based on the ideXlab platform.
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tracking tendon fibers to their insertion a 3D Analysis of the achilles tendon enthesis in mice
Acta Biomaterialia, 2020Co-Authors: Julian Sartori, Heiko StarkAbstract:Abstract Tendon insertions to bone are heavily loaded transitions between soft and hard tissues. The fiber courses in the tendon have profound effects on the distribution of stress along and across the insertion. We tracked fibers of the Achilles tendon in mice in micro-computed tomographies and extracted virtual transversal sections. The fiber tracks and shapes were analyzed from a position in the free tendon to the insertion. Mechanically relevant parameters were extracted. The fiber number was found to stay about constant along the tendon. But the fiber cross-sectional areas decrease towards the insertion. The fibers mainly interact due to tendon twist, while branching only creates small branching clusters with low levels of divergence along the tendon. The highest fiber curvatures were found within the unmineralized entheseal fibrocartilage. The fibers inserting at a protrusion of the insertion area form a distinct portion within the tendon. Tendon twist is expected to contribute to a homogeneous distribution of stress among the fibers. According to the low cross-sectional areas and the high fiber curvatures, tensile and compressive stress are expected to peak at the insertion. These findings raise the question whether the insertion is reinforced in terms of fiber strength or by other load-bearing components besides the fibers. Statement of significance The presented study is the first Analysis of the 3D fiber tracks in macroscopic tendon samples as determined by a combination of cell-maceration, phase-contrast µCT and template-based tracking. The structural findings change the understanding of the tendon-bone insertion and its biomechanics: (1) The insertion is not reinforced in terms of fiber numbers or sizes. Its robustness remains unexplained. (2) The orientation of fibers in the tendon center is higher than in the margins. This arrangement could inspire material development. (3) Fibers inserting at a protrusion of the insertion area stem from a distinct portion within the tendon. The results show that fibrous structure Analysis can link macro- to micromechanics and that it is ready for the application to complete muscle-tendon units.
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tracking tendon fibers to their insertion a 3D Analysis of the achilles tendon enthesis in mice
bioRxiv, 2020Co-Authors: Julian Sartori, Heiko StarkAbstract:Tendon insertions to bone are heavily loaded transitions between soft and hard tissues. The fiber courses in the tendon have profound effects on the distribution of stress along and across the insertion. We tracked fibers of the Achilles tendon in mice in micro-computed tomographies and extracted virtual transversal sections. The fiber tracks and shapes were analyzed from a position in the free tendon to the insertion with regard to their mechanical consequences. The fiber number was found to stay about constant along the tendon. But the fiber cross-sectional areas decrease towards the insertion. The fibers mainly interact due to tendon twist, while branching only creates small branching clusters with low levels of divergence along the tendon. The highest fiber curvatures were found within the unmineralized entheseal fibrocartilage. The fibers inserting at a protrusion of the insertion area form a distinct portion within the tendon. Tendon twist is expected to contribute to a homogeneous distribution of stress among the fibers. According to the low cross-sectional areas and the high fiber curvatures, tensile and compressive stress are expected to peak at the insertion. These findings raise the question whether the insertion is reinforced in terms of fiber strength or by other load-bearing components besides the fibers.
Julian Sartori - One of the best experts on this subject based on the ideXlab platform.
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tracking tendon fibers to their insertion a 3D Analysis of the achilles tendon enthesis in mice
Acta Biomaterialia, 2020Co-Authors: Julian Sartori, Heiko StarkAbstract:Abstract Tendon insertions to bone are heavily loaded transitions between soft and hard tissues. The fiber courses in the tendon have profound effects on the distribution of stress along and across the insertion. We tracked fibers of the Achilles tendon in mice in micro-computed tomographies and extracted virtual transversal sections. The fiber tracks and shapes were analyzed from a position in the free tendon to the insertion. Mechanically relevant parameters were extracted. The fiber number was found to stay about constant along the tendon. But the fiber cross-sectional areas decrease towards the insertion. The fibers mainly interact due to tendon twist, while branching only creates small branching clusters with low levels of divergence along the tendon. The highest fiber curvatures were found within the unmineralized entheseal fibrocartilage. The fibers inserting at a protrusion of the insertion area form a distinct portion within the tendon. Tendon twist is expected to contribute to a homogeneous distribution of stress among the fibers. According to the low cross-sectional areas and the high fiber curvatures, tensile and compressive stress are expected to peak at the insertion. These findings raise the question whether the insertion is reinforced in terms of fiber strength or by other load-bearing components besides the fibers. Statement of significance The presented study is the first Analysis of the 3D fiber tracks in macroscopic tendon samples as determined by a combination of cell-maceration, phase-contrast µCT and template-based tracking. The structural findings change the understanding of the tendon-bone insertion and its biomechanics: (1) The insertion is not reinforced in terms of fiber numbers or sizes. Its robustness remains unexplained. (2) The orientation of fibers in the tendon center is higher than in the margins. This arrangement could inspire material development. (3) Fibers inserting at a protrusion of the insertion area stem from a distinct portion within the tendon. The results show that fibrous structure Analysis can link macro- to micromechanics and that it is ready for the application to complete muscle-tendon units.
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tracking tendon fibers to their insertion a 3D Analysis of the achilles tendon enthesis in mice
bioRxiv, 2020Co-Authors: Julian Sartori, Heiko StarkAbstract:Tendon insertions to bone are heavily loaded transitions between soft and hard tissues. The fiber courses in the tendon have profound effects on the distribution of stress along and across the insertion. We tracked fibers of the Achilles tendon in mice in micro-computed tomographies and extracted virtual transversal sections. The fiber tracks and shapes were analyzed from a position in the free tendon to the insertion with regard to their mechanical consequences. The fiber number was found to stay about constant along the tendon. But the fiber cross-sectional areas decrease towards the insertion. The fibers mainly interact due to tendon twist, while branching only creates small branching clusters with low levels of divergence along the tendon. The highest fiber curvatures were found within the unmineralized entheseal fibrocartilage. The fibers inserting at a protrusion of the insertion area form a distinct portion within the tendon. Tendon twist is expected to contribute to a homogeneous distribution of stress among the fibers. According to the low cross-sectional areas and the high fiber curvatures, tensile and compressive stress are expected to peak at the insertion. These findings raise the question whether the insertion is reinforced in terms of fiber strength or by other load-bearing components besides the fibers.
Philipp Morgenstern - One of the best experts on this subject based on the ideXlab platform.
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3D Analysis suitable t splines definition linear independence and m graded local refinement
arXiv: Numerical Analysis, 2015Co-Authors: Philipp MorgensternAbstract:This paper addresses the linear independence of T-splines in three space dimensions. We give an abstract definition of Analysis-suitability, and prove that it is equivalent to dual-compatibility, wich guarantees linear independence of the T-spline blending functions. In addition, we present a local refinement algorithm that generates Analysis-suitable meshes and has linear computational complexity in terms of the number of marked and generated mesh elements.
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globally structured 3D Analysis suitable t splines definition linear independence and m graded local refinement
arXiv: Numerical Analysis, 2015Co-Authors: Philipp MorgensternAbstract:This paper addresses the linear independence of T-splines that correspond to refinements of three-dimensional tensor-product meshes. We give an abstract definition of Analysis-suitability, and prove that it is equivalent to dual-compatibility, wich guarantees linear independence of the T-spline blending functions. In addition, we present a local refinement algorithm that generates Analysis-suitable meshes and has linear computational complexity in terms of the number of marked and generated mesh elements.
Viggo Tvergaard - One of the best experts on this subject based on the ideXlab platform.
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3D Analysis of failure modes in the charpy impact test
Modelling and Simulation in Materials Science and Engineering, 1994Co-Authors: K K Mathur, Alan Needleman, Viggo TvergaardAbstract:A three-dimensional Analysis of the Charpy V-notch specimen subject to impact loading is carried out, using a data parallel implementation in a transient three-dimensional finite element programme. An elastic-viscoplastic constitutive relation for a porous plastic solid is used to model ductile fracture by the nucleation and subsequent growth of voids to coalescence. Cleavage is modelled in terms of attaining a critical value of the maximum principal normal stress over a specified material volume. A convected coordinate Lagrangian formulation is employed and the discretization is based on twenty-node brick elements with 2*2*2 Gauss points. The equations of motion are integrated numerically by an explicit integration procedure using a lumped mass matrix. The predictions of the full three-dimensional calculations are compared with those of corresponding plane-strain analyses.
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dynamic 3D Analysis of the charpy v notch test
Modelling and Simulation in Materials Science and Engineering, 1993Co-Authors: K K Mathur, Alan Needleman, Viggo TvergaardAbstract:A full three-dimensional Analysis of the Charpy V-notch specimen subject to impact loading is carried out, in order to study deviations from predictions of the plane strain analyses that have been used to estimate the energy absorption and the competition between brittle and ductile failure mechanisms. An elastic-viscoplastic version of the simplest plasticity flow theory is used to describe the material behavior, and the 3D transient Analysis is based on twenty-node brick elements, using a data parallel numerical implementation. It is found that the stress and strain fields show strong surface effects, but near the specimen center the stress and strain quantities governing the failure mechanisms are in rather good agreement with plane strain predictions.
W. Skalli - One of the best experts on this subject based on the ideXlab platform.
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Sequential 3D Analysis of patellofemoral kinematics from biplanar x-rays: In vitro validation protocol
Orthopaedics and Traumatology - Surgery and Research, 2015Co-Authors: L. Dagneaux, P. Thoreux, B. Eustache, F. Canovas, W. SkalliAbstract:BACKGROUND: Developing criteria for assessing patellofemoral kinematics is crucial to understand, evaluate, and monitor patellofemoral function. The objective of this study was to assess a sequential 3D Analysis method based on biplanar radiographs, using an in vitro protocol. HYPOTHESIS: Biplanar radiography combined with novel 3D reconstruction methods provides a reliable evaluation of patellofemoral function, without previous imaging. MATERIAL AND METHODS: Eight cadaver specimens were studied during knee flexion cycles from 0° to 60° induced by an in vitro simulator. The protocol was validated by investigating sequential and continuous motion using an optoelectronic system, evaluating measurement accuracy and reproducibility using metallic beads embedded in the patella, and comparing the 3D patellar geometry to computed tomography (CT) images. RESULTS: The differences in position between the sequential and continuous kinematic analyses were less than 1mm and 1°. The protocol proved reliable for tracking several components of knee movements, including patellar translations, flexion, and tilt. In this Analysis, uncertainty was less than 2 mm for translations and less than 3° for rotations, except rotation in the coronal plane. For patellar tilt, uncertainty was 5°. Mean difference in geometry was 0.49 mm. DISCUSSION: Sequential Analysis results are consistent with continuous kinematics. This Analysis method provides patellar position parameters without requiring previous CT or magnetic resonance imaging. A clinical study may deserve consideration to identify patellofemoral kinematic profiles and position criteria in vivo. LEVEL OF EVIDENCE: IV, experimental study.
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volumetric quantitative computed tomography of the proximal femur relationships linking geometric and densitometric variables to bone strength role for compact bone
Osteoporosis International, 2006Co-Authors: Valerie Bousson, W. Skalli, Le A Bras, F Roqueplan, Yan Kang, David Mitton, S Kolta, C Bergot, Eric Vicaut, Willi A KalenderAbstract:Introduction In assessing cervical fractures of the proximal femur, this in vitro quantitative computed tomography (QCT) study had three objectives: to compare QCT to dual-energy X-ray absorptiometry (DXA) for predicting the failure load of the proximal femur, to compare the contributions of density and geometry to bone failure load, and to compare the contributions of cortical and trabecular bone to bone failure load. A novel three-dimensional (3D) Analysis tool [medical image Analysis framework (MIAF-Femur)] was used to analyze QCT scans.
