Time-dependent mechanical properties of rat femoral cortical bone by nanoindentation: An age-related study
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re-Emmanuel Mazeran Department of Mechanical Systems, Laboratoire Roberval Unité de Recherche en Mécanique, UMR CRNS-UTC 7337, Université de Technologie de Compiègne, Compiègne Cedex 60205, France
Karim El Kirat and Marie-Christine Ho Ba Thoa) Department of Biological Engineering, Laboratoire de Biomécanique et Bioingénierie, UMR CNRS-UTC 7338, Université de Technologie de Compiègne, Compiègne Cedex 60205, France (Received 4 December 2013; accepted 8 April 2014)
The aim of this study is to assess the time-dependent mechanical properties of rat femoral cortical bone in a lifespan model from growth to senescence. New nanoindentation protocol was performed to assess the time-dependent mechanical behavior. The experimental data were fitted with an elastic–viscoelastic–plastic–viscoplastic mechanical model allowing the calculus of the mechanical properties. Variation of mechanical response of bone as a function of the strain rate and age were highlighted. The most representative variations of the mechanical properties with age were found to be statistically significant (P , 0.001) from 1 to 4 months for elastic properties, from 1 to 9 months for viscoelastic properties and during all lifespan for plastic and viscoplastic properties, highlighting different maturation ages for elastic, viscoelastic, plastic and viscoplastic behaviors. These results suggest that different physical–chemical and structural processes occur at different ages reflecting bone modeling and remodeling activities in the rat’s whole lifespan.
I. INTRODUCTION
Cortical bone is a hierarchical biological material subject to dynamic changes, which has been widely studied from the organ level to the molecular level to assess their mechanical properties, chemical composition and physiological function.1–4 However, studies of the mechanical response of cortical bone related to aging are not common for humans.5 This is especially due to the difficulties in building up adequate lifespan models. The studies related to the evolution of the mechanical properties with age are important because bone undergoes changes in its structural composition over the whole lifespan. These variations are related to the changes of the ratio between organic and mineral components of the bone matrix.5–12 Previous studies have assessed the evolution of the mechanical properties of cortical bone with age. They used animal lifespan models, ultrasound,13 and the nanoindentation technique.14–17 Nanoindentation technique is commonly used to determine the mechanical response on the microscale for the case of elastoplastic materials18,19 and some biological materials.15–17,20–22 Oliver and Pharr’s method18 has been a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.104 J. Mater. Res., Vol. 29, No. 10, May 28, 2014
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developed to assess the materials elastic modulus and hardness. However, the determination of the mechanical properties of viscous materials is still challenging. Nev
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