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Relating Local Bone Stiffness and Calcium Content by Combined Nanoindentation and Backscattered Electron Imaging

Published online by Cambridge University Press:  01 February 2011

M. Weber
Affiliation:
Erich Schmid Institute of Material Science, Austrian Academy of Sciences, and University of Leoben, A-8700 Leoben, Austria.
T. Schoeberl
Affiliation:
Erich Schmid Institute of Material Science, Austrian Academy of Sciences, and University of Leoben, A-8700 Leoben, Austria.
P. Roschger
Affiliation:
Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Centre Meidling, 4th Medical Department, Hanusch Hospital, A-1140 Vienna, Austria.
K. Klaushofer
Affiliation:
Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Centre Meidling, 4th Medical Department, Hanusch Hospital, A-1140 Vienna, Austria.
P. Fratzl
Affiliation:
Department of Biomaterials, Max-Planck-Institute of Colloids and Interfaces, D-14424 Potsdam, Germany.
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Abstract

Bone is a hierarchically structured mineral-organic composite material that has to bear static and dynamic mechanical loads applied by body weight and locomotion. Bone mechanical properties are influenced by a number of factors, depending on the particular hierarchical levels. The high stiffness of bone material is mainly achieved by reinforcement with calcium phosphate mineral platelets. A model for this elementary structure level consists of an arrangement of staggered mineral bricks, embedded in collagen matrix, which provides both stiffness and toughness. The mechanical properties depend on the amount, shape and arrangement of the mineral particles but also on the properties of the collagen-rich matrix.

One of the difficulties in assessing the properties of hierarchical structures is the inherent inhomogeneity of the tissue: Parameters such as stiffness or calcium content vary throughout a bone section. Such type of investigations becomes more meaningful by a combination of two complementary methods e.g. quantitative backscattered electron imaging (qBEI) and nanoindentation. The local Ca-content, representing the degree of the mineralization, is extracted from the qBEI measurements, whereas the local mechanical properties, elastic modulus and hardness, are measured by nanoindentation, a miniaturized hardness testing using a small diamond tip. The measured correlations between local Ca-content and mechanical strength help, for example, to verify biomechanical models based on the nanocomposite structure of bone. They may also shed new light on bone diseases such as osteoporosis or osteogenesis imperfecta.

Type
Research Article
Copyright
Copyright © Materials Research Society 2005

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