Quasistatic and dynamic nanomechanical properties of cancellous bone tissue relate to collagen content and organization
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Rebecca M. Williams Department of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853
Seth A. Downs and Michelle E. Dickinson Hysitron, Inc., Eden Prairie, Minnesota 55344
Shefford P. Baker Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853
Marjolein C.H. van der Meulen Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York 14853; and Musculoskeletal Integrity Program, Hospital for Special Surgery, New York, New York 14853 (Received 21 December 2005; accepted 16 May 2006)
Cancellous bone plays a crucial structural role in the skeleton, yet little is known about the microstructure-mechanical property relationships of the tissue at the microscale. Cancellous tissue is characterized by a microstructure consisting of layers interspaced with transition zones with different proportions of collagen and mineral. In this study, the quasistatic and dynamic mechanical properties of lamellar and interlamellar tissue in human vertebrae were assessed with nanoindentation, and the collagen content and organization were characterized with second harmonic generation microscopy. Lamellar tissue was 35% stiffer, 25% harder, and had a 13% lower loss tangent relative to interlamellar tissue. The stiff, hard lamellae corresponded to areas of highly ordered, collagen-rich material, with a relatively low loss tangent, whereas the compliant, soft interlamellar regions corresponded to areas of disordered or collagen-poor material. These data suggest an important role for collagen in the tissue-level mechanical properties of bone.
I. INTRODUCTION
Bone structural integrity is essential to skeletal function. A whole bone contains two macroscopic tissue structures: cortical bone, the dense tissue of the long bone shaft, and cancellous bone, the lattice-like tissue composed of struts known as trabeculae at the ends of long bones and in the centers of the vertebrae.1 Clinically, diseases such as osteoporosis preferentially affect cancellous bone and disrupt its ability to bear loads, producing fracture and related complications, including mortality.2,3 The structural behavior of cancellous bone is governed by the amount of tissue present and the tissue architecture
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0259 2106 J. Mater. Res., Vol. 21, No. 8, Aug 2006 http://journals.cambridge.org Downloaded: 09 Apr 2015
and material properties. The relationship between mechanical behavior and tissue mass is well studied,4–6 and, more recently, microcomputed tomography imaging has enabled examination of the effects of cancellous architecture on structural performance.7 However, relatively little is known about the local variation of material properties within bone tissue or their effect on whole-bone structural performance. In addition, because in vivo skeletal loads are time-varying, and dynamic mechanical stimuli regulate postnatal bone formation and growth, assessment of the dynamic material pro
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