Biomedical Engineering Reference
In-Depth Information
Fig. 5 Schematic
representation of glue like
bonds between mineralized
collagen fibrils presented by
Fantner et al. [
49
]
to reinforcing rings coated on each individual fibril. In this model, no more than
30% of the total mineral content is extrafibrillar and the fraction of extrafibrillar
minerals grows linearly with the overall degree of mineralization. The model
predictions for the elastic moduli and constants are found to be in a good agree-
ment with the experimental data reported in the literature [
48
].
Recently, a so-called glue-like bond model is proposed to describe the inter-
action between the mineralized collagen fibrils [
49
]. In this model, the mineralized
collagen fibrils are held together by a non-fibrillar organic matrix (Fig.
5
), which
acts as a glue. Such glue resists both separation and slippage between the min-
eralized collagen fibrils, thereby helping transmit force between fibrils. In addition,
so-called sacrificial bonds are formed in the organic matrix of the glue. When the
matrix is stretched, energy is dissipated through rupturing of sacrificial bonds and
by stretching of molecules in the glue to release so-called hidden length. Since the
sacrificial bonds are reformable, the break and reform of such bonds further
increase the total energy dissipation of the tissue during the deformation of bone.
3 Mechanical Behavior of Human Cortical Bone
3.1 Mechanical Testing of Cortical Bone
Tension, compression, and torsion tests are mechanical tests commonly used to
evaluate mechanical properties of human cortical bone. In general, these tests are
performed in a monotonic manner. However, cyclic diagnostic tests are also
performed
in
order
to
obtain
more
information
about
the
changes
in
bone
mechanical properties during the loading process [
50
-
52
].
3.1.1 Monotonic Tests
From monotonic tests, the uniaxial and torsional elastic modulus, yield stress/
strain, ultimate stress, failure strain, and toughness can be measured (Fig.
6
).
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