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TECHNICAL PAPERS: Bone/Orthopedics

# An Application of Nanoindentation Technique to Measure Bone Tissue Lamellae Properties

[+] Author and Article Information
C. Edward Hoffler

Orthopaedic Research Laboratories, Orthopaedic Surgery,  The University of Michigan, Ann Arbor, MI 48109-0486

X. Edward Guo1

Orthopaedic Research Laboratories, Orthopaedic Surgery,  The University of Michigan, Ann Arbor, MI 48109-0486

Philippe K. Zysset2

Orthopaedic Research Laboratories, Orthopaedic Surgery,  The University of Michigan, Ann Arbor, MI 48109-0486

Steven A. Goldstein3

Orthopaedic Research Laboratories, Orthopaedic Surgery,  The University of Michigan, Ann Arbor, MI 48109-0486

1

Current address: Bone Bioengineering Laboratory, Department of Mechanical Engineering and Center for Biomedical Engineering, Columbia University, New York, NY 10027-6623.

2

Current address: Institut für Leichtbau und Struktur-Biomechanik (ILSB), Technische Universität Wein, A-1040 Vienna, Austria.

3

Corresponding author. Tel: (734) 763-9674; fax: (734) 647-0003; e-mail: stevegld@umich.edu

J Biomech Eng 127(7), 1046-1053 (Aug 01, 2005) (8 pages) doi:10.1115/1.2073671 History: Received June 08, 2004; Revised July 07, 2005; Accepted August 01, 2005

## Abstract

Measuring the microscopic mechanical properties of bone tissue is important in support of understanding the etiology and pathogenesis of many bone diseases. Knowledge about these properties provides a context for estimating the local mechanical environment of bone related cells that coordinate the adaptation to loads experienced at the whole organ level. The objective of this study was to determine the effects of experimental testing parameters on nanoindentation measures of lamellar-level bone mechanical properties. Specifically, we examined the effect of specimen preparation condition, indentation depth, repetitive loading, time delay, and displacement rate. The nanoindentation experiments produced measures of lamellar elastic moduli for human cortical bone (average value of $17.7±4.0GPa$ for osteons and $19.3±4.7GPa$ for interstitial bone tissue). In addition, the hardness measurements produced results consistent with data in the literature (average $0.52±0.15GPa$ for osteons and $0.59±0.20GPa$ for interstitial bone tissue). Consistent modulus values can be obtained from a 500-nm-deep indent. The results also indicated that the moduli and hardnesses of the dry specimens are significantly greater (22.6% and 56.9%, respectively) than those of the wet and wet and embedded specimens. The latter two groups were not different. The moduli obtained at a $5‐nm∕s$ loading rate were significantly lower than the values at the 10- and $20‐nm∕s$ loading rates while the 10- and $20‐nm∕s$ rates were not significantly different. The hardness measurements showed similar rate-dependent results. The preliminary results indicated that interstitial bone tissue has significantly higher modulus and hardness than osteonal bone tissue. In addition, a significant correlation between hardness and elastic modulus was observed.

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## Figures

Figure 1

Microscopic images show the microstructure of osteonal and interstitial bone tissue with the corresponding 30‐μm‐square array of indents in the square boxes. The inset demonstrates the shape of a typical pyramidal indentation impression.

Figure 2

Figure 3

A schematic of the custom irrigation system including the Nanoindenter II system (the schematic drawing of the nanoindenter was modified after Nanoindenter II User Manual)

Figure 4

The indentation experimental procedure. The experiment is under displacement control and involves five unloading segments from which indentation modulus and hardness can be calculated (labeled 1–5 in the figure).

Figure 5

A typical load and displacement curve of a nanoindentation experiment. The numbers in the figure indicate the unloading segments where mechanical properties are calculated.

Figure 6

Corrected modulus (a) and hardness (b) results for different indentation depth, repetition, and time delay. The error bars show the standard deviations of each group.

Figure 7

Corrected modulus (a) and hardness (b) results for different specimen preparation and testing conditions. The labels a, b, and c indicate the initial, immediate repeat, and delayed repeat indentation at 500 nm. The error bars show the standard deviations. The moduli and hardnesses of dry specimens are significantly greater than the wet and wet and embedded specimens (n=279–287 for each treatment).

Figure 8

Modulus (a) and (b) hardness measured for different displacement rates. The error bars indicate the standard deviations. The moduli and hardness at the 5‐nm∕s rate are significantly different from those measured from 10 and 20nm∕s. The measurements at 10 and 20nm∕s are not significantly different.

Figure 9

The modulus (a) and hardness (b) measured for osteons and interstitial bone tissue. The error bars indicate the standard deviations. The osteonal tissue has significantly lower modulus and hardness than the interstitial tissue.

Figure 10

The measured elastic modulus was correlated to the hardness measurements. There is a significant positive correlation between these two mechanical parameters (r2=0.71).

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