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Design and use of novel compression device for microtomography under applied load
Fíla, Tomáš ; Zlámal, Petr ; Koudelka_ml., Petr ; Jiroušek, Ondřej ; Doktor, Tomáš ; Kytýř, Daniel
This paper deals with modification and usage of custom-designed compression device, that allows real time X-ray tomography scanning of specimen under applied pressure. In this case microtomography is used to obtain data required to determine specimens morphology and to develop 3D material model (especially for cellular materials such as bones, metal foams and quasi-brittle materials or particle composites such as concrete or cementitious composites). Important design changes were made in the existing device frame to increase its load capabilities, stiffness and to accomodate a larger specimen. Finally device displacement measurements were conducted and calibration experiment was carried out.
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On the reliability of microstructural models of trabecular bone with tissue properties from nanoindentation for bone quality assessment
Jiroušek, Ondřej ; Zlámal, Petr
Material properties of trabecular bone can be inversely determined by microstructural finite element (FE) models. The geometry of these models is developed using three-dimensional image data from microfocus Computed Tomography (micro-CT). The reliability of these models to predict the overall elastic properties is influenced by several factor, namely the tissue material properties, resolution of the input images, quality of the segmentation and quality of the FE mesh. This article describes all the aspects of proper and reliable inverse estimation of bone quality using the microstructural models with tissue properties assessed by nanoindentation.
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Indirect determination of material model parameters for single trabecula based on nanoindentation and three-point bending test
Zlámal, P. ; Jiroušek, Ondřej ; Kytýř, Daniel ; Doktor, Tomáš
The aim of the paper is to develop a procedure for determination of elasto-visco-plastic constitutive model with damage for human single trabecula. The procedure is suited for indirect establishing of material model based on nanoindentation and three-point bending test. Constants of the material model are identified by Finite Element (FE) simulations and curve fitting using an algorithm based on least squares fitting of the experimental curves. In the case of nanoindentation, the penetration depth of tip during the FE analyses (FEA) is fitted to experimental nanoindentation curves. In the case of three-point bending, displacements of nodes are compared with displacements of markers observed during the experiment using digital image correlation.
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Assessment of micromechanical properties of trabecular bone using quantitative backscattered electron microscopy
Kytýř, Daniel ; Petráňová, Veronika ; Jiroušek, Ondřej
The biomechanical behaviour of trabecular bone depends not only on its microarchitecture but also on mineral density distribution. Bone mineral density distribution is coupled with mechanical properties of the tissue. In this preliminary study intratrabecular composition of individual trabeculae was investigated. The quantitative backscattered electron microscopy (qBSE) a method based on detection of electrons backscattered from surface layer of the specimen was employed to obtain high resolution images of the transverse sections of a trabecula. From acquired data the element map was created, organic (collagen fibres) to anorganic (hydroxyapatite) material ratio computed and collagen fibres orientation assessed. To conclude qBSE allows to obtain detail information about intratrabecular composition and material properties at the level of individual trabeculae.
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Early Defect Detection of Acetabular Implants
Kytýř, Daniel ; Jiroušek, Ondřej ; Zlámal, Petr ; Doktor, Tomáš ; Jandejsek, I.
The paper is focused on possibilities of modern X-ray detectors and micro-focus X-ray source for investigation of early degradation processes of acetabular implants. To simulate the most adverse activity (downstairs walking) a hip joint simulator was developed. The experimental setup was designed for cyclic loading of polyethylene acetabular cup implanted into the human pelvic bone and fixed by commercial polymethyl methacrylate bone cement. To predict the bone degradation numerical analysis of detailed three-dimensional model of the acetabular cup and the cement mantle implanted in a bone block was performed. Using large area flat panel detector and microfocus X-ray source it is possible to investigate micro-damage propagation and detect early defect in the bone-implant interface.
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Large-scale micro-finite element simulation of compressive behavior of trabecular bone microstructure
Jiroušek, Ondřej ; Zlámal, Petr
Microstructural finite element analysis has become a standard technique for evaluation of mechanical properties of trabecular bone. Due to the high complexity of the trabecular bone microstructure, the FE models have a very large number of elements (about 1 million elements per cubic cm in 50 μm3 resolution). To perform FE analysis of the microstructural FE models based on micro-CT scanning of whole bone samples (e.g. vertebral bodies) it is needed to solve 107 -- 108 equations. This article deals with comparison of approaches using voxel-based microstructural FE models to calculate the overall mechanical properties of trabecular bone.
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Microstructural models of trabecular bone - comparison of CT-based FE models
Jiroušek, Ondřej ; Zlámal, Petr
In the article a detailed comparison of techniques used to developed detailed FE models of trabeculra bone microstructure is presented. The FE models are built using a stack of microtomographic images of trabecular bone. Compression test of a cylindrical sample taken from human proximal femur is virtually performed using FE models developed using different procedures. Effect of improper segmentation, mesh smoothing, mesh density, use of hexahedral/ tetrahedral elements, linear/ quadratic shape function is evaluated in parametric study. Material model is based on nanoindentation and numerical elastic properties of sample are compared to experimental results.
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Pore Size Distribution of Human Trabecular Bone - Comparison of Intrusion Measurements with Image Analysis
Doktor, Tomáš ; Valach, Jaroslav ; Kytýř, Daniel ; Jiroušek, Ondřej
This paper deals with pore size distribution assessment of trabecular structure of human proximal femur. Two distinct methods for estimation of the pore size distribution histograms are tested, mercury intrusion porosimetry and image analysis. For the image analysis two-dimensional images of crosssections of the specimens were used and the pore size distribution was estimated using a stereological calculation method based on the geometrical properties of an idealized pore. Comparison of the results of both methods is presented. Suitability of both methods for biological materials is discussed regarding to mechanical properties of these materials, characteristics of pores and range of pore sizes present in the structure.
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