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Technical Briefs

Nanostructural Alteration in Bone Quantified in Terms of Orientation Distribution of Mineral Crystals: A Possible Tool for Fracture Risk Assessment

[+] Author and Article Information
Bijay Giri1

Division of Human Mechanical Systems and Design,  Faculty of Engineering, Hokkaido University, Kita ku, Kita 13 Nishi 8, Sapporo 060 8628, Japanbijay.giri@utsa.edu

Shigeru Tadano

Division of Human Mechanical Systems and Design,  Faculty of Engineering, Hokkaido University, Kita ku, Kita 13 Nishi 8, Sapporo 060 8628, Japantadano@eng.hokudai.ac.jp

1

Corresponding author. Present address: Department of Mechanical Engineering, College of Engineering, University of Texas at San Antonio, San Antonio, TX 78249.

J Biomech Eng 133(12), 124503 (Dec 21, 2011) (6 pages) doi:10.1115/1.4005482 History: Received May 27, 2011; Revised November 28, 2011; Published December 21, 2011; Online December 21, 2011

There may be different causes of failures in bone; however, their origin generally lies at the lowest level of structural hierarchy, i.e., at the mineral-collagen composite. Any change in the nanostructure affects the affinity or bonding effectiveness between and within the phases at this level, and hence determines the overall strength and quality of bone. In this study, we propose a novel concept to assess change in the nanostructure and thereby change in the bonding status at this level by revealing change in the orientation distribution characteristics of mineral crystals. Using X-ray diffraction method, a parameter called Degree of Orientation (DO) has been quantified. The DO accounts for the azimuthal distribution of mineral crystals and represents their effective amount along any direction. Changes in the DOs in cortical bone samples from bovine femur with different preferential orientations of mineral crystals were estimated under external loads. Depending on the applied loads, change in the azimuthal distribution of the DOs and the degree of reversibility of the crystals was observed to vary. The characteristics of nanostructural change and thereby possible affect on the strength of bone was then predicted from the reversible or irreversible characteristics of distributed mineral crystals. Significant changes in the organization of mineral crystals were observed; however, variations in the applied stresses and elastic moduli were not evinced at the macroscale level. A novel concept to assess the alteration in nanostructure on the basis of mineral crystals orientation distribution has been proposed. The importance of nanoscale level information obtained noninvasively has been emphasized, which acts as a precise tool to estimate the strength and predict the possible fracture risks in bone.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

(right) Representative diffracted intensity pattern from a longitudinal specimen, and (left) profile of azimuthally integrated intensity enveloping 002-region as indicated by the dotted lines and corresponding azimuthal DO.

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Figure 2

Azimuthal distribution of percentage change in the DO under three-stage repeated loads L1, L2, and L3 for longitudinal and transverse specimens. The changes are corresponding to the original state (before any load); the unloaded state indicated by “unload” is the change of the unloaded state (i.e., initial state of next loading stage) to the original state. Loading direction is nearly at 0 deg.

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Figure 3

Azimuthal distribution of percentage change in the DO for specimens aligned at 0 deg, 30 deg, 45 deg, 75 deg and 90 deg to the longitudinal axis under continuous step-loads. The changes are corresponding to the original state (before any load); the unloaded state indicated by “unload” is the change of the unloaded state (i.e., state after load is released) corresponding to the initial state. Loading direction is nearly at 0 deg.

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Figure 4

Stresses calculated from the load cell reading during diffraction experiments of repeated load case at three loading stages L1, L2, and L3 grouped in different applied strains for longitudinal and transverse specimens (top), and for differently aligned specimens under continuous loads (bottom).

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