| 1. |
- Schriefl, Andreas J., et al.
(författare)
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Quantitative assessment of collagen fibre orientations from two-dimensional images of soft biological tissues
- 2012
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Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 9:76, s. 3081-3093
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we outline an automated method for the extraction and quantification of material parameters characterizing collagen fibre orientations from two-dimensional images. Morphological collagen data among different length scales were obtained by combining the established methods of Fourier power spectrum analysis, wedge filtering and progressive regions of interest splitting. Our proposed method yields data from which we can determine parameters for computational modelling of soft biological tissues using fibre-reinforced constitutive models and gauge the length scales most appropriate for obtaining a physically meaningful measure of fibre orientations, which is representative of the true tissue morphology of the two-dimensional image. Specifically, we focus on three parameters quantifying different aspects of the collagen morphology: first, using maximum-likelihood estimation, we extract location parameters that accurately determine the angle of the principal directions of the fibre reinforcement (i.e. the preferred fibre directions); second, using a dispersion model, we obtain dispersion parameters quantifying the collagen fibre dispersion about these principal directions; third, we calculate the weighted error entropy as a measure of changes in the entire fibre distributions at different length scales, as opposed to their average behaviour. With fully automated imaging techniques (such as multiphoton microscopy) becoming increasingly popular (which often yield large numbers of images to analyse), our method provides an ideal tool for quickly extracting mechanically relevant tissue parameters which have implications for computational modelling (e.g. on the mesh density) and can also be used for the inhomogeneous modelling of tissues.
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| 2. |
- Schmidt, Thomas, et al.
(författare)
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Material Modeling Of The Damage Behavior Of Arterial Tissues
- 2013
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Ingår i: Biomedizinische Technik (Berlin. Zeitschrift). - : Walter de Gruyter GmbH. - 1862-278X .- 0013-5585. ; 58:(Suppl. 1)
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution we present a damage model for collagenous soft tissues such as arterial walls, which takes into account the statistical distributions of microscopic parameters. This approach extends the constitutive framework proposed in [1] by specific damage functions arising from microscopical considerations. In detail, statistical distributions of proteoglycan (PG) orientations, fibril length parameters and ultimate proteoglycan stretch can be considered, cf. [2]. The influence of each distributed quantity on the damage behavior is investigated by adjusting the model to uniaxial experimental data of a human carotid artery. Furthermore, the proposed model is implemented into a finite element framework and used within a numerical example in order to show its applicability to inhomogeneous boundary-value problems.
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| 3. |
- Schriefl, Andreas J., et al.
(författare)
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An automated approach for three-dimensional quantification of fibrillar structures in optically cleared soft biological tissues
- 2013
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Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 10:80, s. 20120760-
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel approach allowing for a simple, fast and automated morphological analysis of three-dimensional image stacks (z-stacks) featuring fibrillar structures from optically cleared soft biological tissues. Five non-atherosclerotic tissue samples from human abdominal aortas were used to outline the multi-purpose methodology, applicable to various tissue types. It yields a three-dimensional orientational distribution of relative amplitudes, representing the original collagen fibre morphology, identifies regions of isotropy where no preferred fibre orientations are observed and determines structural parameters throughout anisotropic regions for the analysis and numerical modelling of biomechanical quantities such as stress and strain. Our method combines optical tissue clearing with second-harmonic generation imaging, Fourier-based image analysis and maximum-likelihood estimation for distribution fitting. With a new sample preparation method for arteries, we present, for the first time to our knowledge, a continuous three-dimensional distribution of collagen fibres throughout the entire thickness of the aortic wall, revealing novel structural and organizational insights into the three arterial layers.
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| 4. |
- Schriefl, Andreas J., et al.
(författare)
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Determination Of Mechanical And Microstructural Tissue Quantities For Modeling Damage In Arterial Tissues
- 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
- The overstretching of arterial walls as it occurs, e.g., during balloon angioplasty, results in a stress-softening of the collagenous wall which is believed to arise from microscopic tissue damage. To model such damage we use a macroscopic, fiber-reinforced constitutive framework including a characterization of the individual tissue components. We employed traditional and novel experimental investigations to determine and quantify the required mechanical and microstructural tissue parameters for the constitutive model. Herein we present some of our experimental approaches and the resulting preliminary findings.
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| 5. |
- Schriefl, Andreas J., et al.
(författare)
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Determination of the layer-specific distributed collagen fibre orientations in human thoracic and abdominal aortas and common iliac arteries
- 2012
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Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 9:71, s. 1275-1286
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Tidskriftsartikel (refereegranskat)abstract
- The established method of polarized microscopy in combination with a universal stage is used to determine the layer-specific distributed collagen fibre orientations in 11 human non-atherosclerotic thoracic and abdominal aortas and common iliac arteries (63 +/- 15.3 years, mean +/- s.d.). A dispersion model is used to quantify over 37 000 recorded fibre angles from tissue samples. The study resulted in distinct fibre families, fibre directions, dispersion and thickness data for each layer and all vessels investigated. Two fibre families were present for the intima, media and adventitia in the aortas, with often a third and sometimes a fourth family in the intima in the respective axial and circumferential directions. In all aortas, the two families were almost symmetrically arranged with respect to the cylinder axis, closer to the axial direction in the adventitia, closer to the circumferential direction in the media and in between in the intima. The same trend was found for the intima and adventitia of the common iliac arteries; however, there was only one preferred fibre alignment present in the media. In all locations and layers, the observed fibre orientations were always in the tangential plane of the walls, with no radial components and very small dispersion through the wall thickness. A wider range of in-plane fibre orientations was present in the intima than in the media and adventitia. The mean total wall thickness for the aortas and the common iliac artery was 1.39 and 1.05 mm, respectively. For the aortas, a slight thickening of the intima and a thinning of the media in increasingly distal regions were observed. A clear intimal thickening was present distal to the branching of the celiac arteries. All data, except for the media of the common iliac arteries, showed two prominent collagen fibre families for all layers so that two-fibre family models seem most appropriate.
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