Influence of strain rate on the mechanical behavior of cortical bone interstitial lamellae at the micrometer scale
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e-Emmanuel Mazeran Laboratoire Roberval Unité de Recherche en Mécanique, CNRS FRE 2833 (Centre National de la Recherche Scientifique Formation de Recherche en Evolution 2833), Université de Technologie de Compiègne, 60205 Compiègne Cedex, France
Marie-Christine Ho Ba Thoa) Laboratoire de Biomécanique et Génie Biomédical, CNRS UMR 6600 (Centre National de la Recherche Scientifique Unité Mixte de Recherche), Université de Technologie de Compiègne, 60205 Compiègne Cedex, France (Received 21 December 2005; accepted 3 May 2005)
Investigations of bone mechanical properties are of major importance for bone pathology research, biomaterials, and development of in vivo bone characterization devices. Because of its complex multiscale structure, assessment of bone microstructure is an important step for understanding its mechanical behavior. In this study, we have investigated the strain rate influence on the mechanical properties of interstitial lamellae on two human femur bone samples. Nanoindentation tests were performed with the continuous stiffness measurement technique. Young’s modulus and hardness were calculated using the Oliver and Pharr method. A statistical significant influence of strain rate on hardness was found (p < 0.05) showing a viscoplastic behavior of interstitial bone at the micrometer scale. This phenomenon may reflect the role of the organic component in the bone matrix mechanical behavior. I. INTRODUCTION
Mechanical properties of bone are of importance in understanding bone pathologies, to develop biomimetic materials and in vivo bone characterization devices. Cortical bone is described as a very complex material with a multiscale hierarchical architecture: molecular level (matrix of collagen fibrils and apatite crystals), tissue level (haversian system), and organ level (trabecular and cortical bones).1 Bone mechanical behavior resulting from this complex structure has been widely investigated at the macroscale level over the last forty years, using classical mechanical tests (tensile, compressive, torsion and bending)2–6 or ultrasonic tests (transmission, reflection).7–9 Heterogeneity, anisotropy, and elastoviscoplastic behavior of bone tissue have been demonstrated. However, few investigations have been performed at the microstructural level.10–13 The recent development of the nanoindentation technique14–16 has allowed the investigation of bone mechanical behavior at the lamella level. At this micrometer scale, a difference of mechanical properties between cortical and trabecular bones has been observed.17–19
II. MATERIALS AND METHODS
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0255 J. Mater. Res., Vol. 21, No. 8, Aug 2006
http://journals.cambridge.org
Moreover, differences of mechanical properties have been observed between osteon and interstitial lamellae and also within osteon lamellae.20–23 The investigation of bone anisotropy at the lamella scale has also been conducted on human and bovine specimens.24,25 The study of bone viscoelasticity of t
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