Published papers

Two-dimensional quantitative analysis of microbeam X-ray diffraction (XRD) was performed using a transmission optical system to examine biological apatite (BAp) orientation in an isolated trabecula of a human fourth lumber vertebral body. The incident X-ray beam is 20 μm in diameter, which is small enough for the isolated trabecula despite a slight beam divergence of 0.2°. Integrated intensities of (002) and (310) are obtained separately by different incident angles and detector positions. Distribution of the preferential orientation of the BAp c-axis is finally calculated quantitatively as an integrated intensity ratio of (002)/(310) in a plane containing the trabecular direction. Preferential alignment of the BAp c-axis was finally determined to be perfectly parallel to the fiber direction in a rod-shaped trabecula, since accurate one-dimensional alignment is different from the alignment in the femoral cortical bone as a long bone that shows the local maximum of preferential alignment perpendicular to the longitudinal bone axis. For example, the integrated intensity ratio of (002)/(310) has a maximum value of 16 along the trabecular fiber and a minimum value of 0.09 in the perpendicular direction. Using this method, the anisotropy of BAp orientation in the trabecular bone can be quantitatively evaluated in the plane including the trabecular fiber. Thus, we successfully obtained a methodology that two-dimensionally analyzes the distribution of the BAp c-axis along all axes within a plane in a bone specimen. © 2007 The Japan Institute of Metals.

The aim of this study was to identify the load transfer paths in cortical bone and trabecular structure of cancellous bone in the jawbones for loads from endosseous implants. Maxillae were resected from beagle dogs 6 months after implant surgery and imaged using micro-computed tomography (micro-CT). A three-dimensional structure was produced based on the CT data and peri-implant trabecular structure was observed. Load transfer paths were analyzed from the results of three-dimensional finite element analysis. Furthermore, buffer actions in bone trabeculae when strain increased during stress analysis and when loads were applied were observed. Peri-implant bone trabeculae were seen extending into the upper and lower cortical bone from the fixture. The direction of bone trabecular alignment corresponded with the load transfer paths. In addition, analysis with increased strain confirmed that trabecular structures could serve as load buffers. These results suggest that bone trabeculae supporting load transfer from implants undergo remodeling. © 2009 Springer-Verlag.

Copyright © 2016 John Wiley & Sons, Ltd. This contribution presents a numerical strategy to evaluate the effective properties of image-based microstructures in the case of random material properties. The method relies on three points: (1) a high-order fictitious domain method; (2) an accurate spectral stochastic model; and (3) an efficient model-reduction method based on the proper generalized decomposition in order to decrease the computational cost introduced by the stochastic model. A feedback procedure is proposed for an automatic estimation of the random effective properties with a given confidence. Numerical verifications highlight the convergence properties of the method for both deterministic and stochastic models. The method is finally applied to a real 3D bone microstructure where the empirical probability density function of the effective behaviour could be obtained. Copyright © 2016 John Wiley & Sons, Ltd.

© 2017 Informa UK Limited, trading as Taylor & Francis Group. Although the biomechanical behavior of the acetabular cup (AC) implant is determinant for the surgical success, it remains difficult to be assessed due to the multiscale and anisotropic nature of bone tissue. The aim of the present study was to investigate the influence of the anisotropic properties of peri-implant trabecular bone tissue on the biomechanical behavior of the AC implant at the macroscopic scale. Thirteen bovine trabecular bone samples were imaged using micro-computed tomography (μCT) with a resolution of 18 μm. The anisotropic biomechanical properties of each sample were determined at the scale of the centimeter based on a dedicated method using asymptotic homogenization. The material properties obtained with this multiscale approach were used as input data in a 3D finite element model to simulate the macroscopic mechanical behavior of the AC implant under different loading conditions. The largest stress and strain magnitudes were found around the equatorial rim and in the polar area of the AC implant. All macroscopic stiffness quantities were significantly correlated (R2 > 0.85, p < 6.5 e-6) with BV/TV (bone volume/total volume). Moreover, the maximum value of the von Mises stress field was significantly correlated with BV/TV (R2 > 0.61, p < 1.6 e-3) and was always found at the bone-implant interface. However, the mean value of the microscopic stress (at the scale of the trabeculae) decrease as a function of BV/TV for vertical and torsional loading and do not depend on BV/TV for horizontal loading. These results highlight the importance of the anisotropic properties of bone tissue.

For the design of porous titanium component, differently from its use as functional materials, structural strength prediction algorithm is proposed based on the micro-stress concentration analyzed by the multiscale simulation. The modeling of real microstructure is carried out by the image-based technique with X-ray micro-CT. The multiscale computational method consists of asymptotic homogenization and finite element mesh superposition (FEMS) techniques. A criterion is proposed to predict the nonlinearity initiation point in the load and displacement curve by means of micro-stress distribution expressed by histogram. Only the constituent's yield strength is referred regardless of the microscopic morphology. The originality of this paper lies in the validation of the homogenization process, the modeling guideline of micro-mesh superposition onto macro-mesh in FEMS, and the strength prediction algorithm. L-shaped components with different pore diameter were discussed in both experiment and simulation. © 2009 Elsevier Ltd. All rights reserved.