Nanoindentation and Finite Element Analysis of Resin-Embedded Bone Samples as a Three-Phase Composite Material
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Nanoindentation and Finite Element Analysis of Resin-Embedded Bone Samples as a Three-Phase Composite Material Michelle L. Oyen1, Ching-Chang Ko1, Amanpreet K.Bembey2, Andrew J. Bushby2 and Alan Boyde3. 1
University of Minnesota, Minneapolis, MN 55455 Department of Materials, Queen Mary, University of London, London, E1 4NS, UK 3 Dental Institute, Queen Mary, University of London, London, E1 1BB, UK 2
ABSTRACT The effective elastic modulus of composite materials results from a combination of elastic moduli of the component phases. Recent efforts to understand the mechanical behavior of calcified tissues in bones and teeth require estimates of the component phase properties, which are difficult to establish independently. A three-phase system, based on naturally occurring bone, is therefore examined by a combined nanoindentation and finite element modelling approach to better understand the proportions and properties of the component phases. Bone samples were prepared in four two- or three-phase composite configurations as follows: (1) as a dehydrated mineral-protein composite (with some void space); (2) similarly dehydrated mineralprotein composite but with polymethylmethacrylate (PMMA) resin filling the voids resulting in three solid phases; (3) as a PMMA-mineral composite following protein removal and replacement with PMMA, and (4) as a PMMA-protein composite following mineral removal and replacement with PMMA. Effective component volume fractions and elastic moduli for each phase in each system were computed based on the composite nanoindentation results. Finite element models of the two- and three-phase systems were constructed to explore the structural anisotropy of the composite systems, as demonstrated in the nanoindentation tests, and to examine the sensitivity of the composite results to changes in the assumed component properties. INTRODUCTION Cortical bone is an anisotropic material, and its mechanical properties are determined by its composition as well as its microstructure. Mechanical properties of bone are a consequence of the proportions of, and the interactions between, mineral, collagen and water. Mid-shaft dorsal cortical tissue from the equine third metacarpal bone is relatively dense and uniform with low porosity. The mainly primary osteons are aligned to within a few degrees of the long axis of the bone. In recent years nanoindentation has been applied to study mineralized tissues to determine mechanical properties at the scale of individual microstructural elements such as lamellae in bone [1]. Nanoindentation may also be able to elucidate further information at the ultrastructural level and can be conducted in different tissue orientations to investigate anisotropy of individual microstructural components [2]. At the ultrastructural level, bone can be thought of as a 3 phase co-continuous composite consisting of collagen and other proteins, bone mineral and water. The relationships between collagen orientation and mineral content and how these influence mechanical properties of bone
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