Elasticity and Viscoelasticity of Human Tibial Cortical Bone Measured by Nanoindentation
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Elasticity and Viscoelasticity of Human Tibial Cortical Bone Measured by Nanoindentation Leandro de Macedo Soares Silva*, Vincent Ebacher*, Danmei Liu†, Heather McKay†, Thomas R. Oxland† and Rizhi Wang* * Department of Materials Engineering, University of British Columbia, # 309-6350 Stores Road, Vancouver, BC, Canada V6T 1Z4 † Division of Orthopaedic Engineering Research, Departments of Orthopaedics, University of British Columbia, 3114-910 West 10th Avenue, Vancouver BC, Canada V5Z 4E3
ABSTRACT Bone is a composite material composed of collagen, carbonated apatite mineral, water, and other non-collagenous proteins. The bone structure inside human body is under constant remodelling. The mechanical properties of bone and their dynamic changes during remodelling are crucial to the health and quality of life. In this study, the elastic and viscoelastic properties of a 73 year-old female cortical bone were investigated at the lamellar level. This was realized by a nanoindentation technique equipped with dynamic loading function. 325 indentations were made in individual Haversian systems and interstitial bone at both dry and wet condition, and under two different loading frequencies. The results showed no statistically significant differences in elastic modulus between Haversian systems and interstitial bone. There were no systematic differences in modulus across the cortex except for a slight drop at the periosteal site. The lamellar structure of both Haversian system and interstitial bone is viscoelastic with water playing a significant role to the properties. When dry bone is re-hydrated, elastic modulus decreases and loss tangent increases. INTRODUCTION Bone is a composite material combining a fibrous collagen matrix with carbonated apatite nanocrystals and a small amount of non-collagenous proteins at its primary level of organization. The degree of mineralization varies from bone to bone and also at different locations within an individual bone. The mechanical properties of bone strongly depend on its multi-level hierarchical structure, its degree of mineralization as well as water content [1]. Bone is viscoelastic due to the presence of water and proteins. The viscous portion enables energy dissipation during deformation and may significantly contribute to bone fracture. The viscoelastic property of bone is far less understood than its elastic property both at structural and material levels. Nanoindentation is a popular technique in determining the mechanical properties of bone. Due to its capability of making indentations in the submicron dimension, nanoindentation enables us to study the mechanical properties down to individual Haversian system and even individual bone lamellae within an osteon [2]. However, most of the nanoindentation studies so far were only able to measure one elastic modulus value at one sample location from the loading-unloading curve due to limitations of the instrument [3-9]. A multiple partial
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unloading technique would need to be employed to measure the modulus as a fu
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