Biomedical Engineering Reference
In-Depth Information
200 µm
Fig. 2 Unique structural motifs exist at each scale level. At the nanoscale, 67 nm d-banding is
observed (left), at the microscale fiber crimp is present (middle) and at the macroscale fascicles
align in a parallel fashion (right). Note that crimp is generally in register within fascicles
(reproduced with permission from [
50
,
67
,
224
])
The mechanical role of small PGs (decorin, biglycan) is debated [
175
,
259
], but
our own research demonstrated that their GAG side chains have a negligible
contribution to tissue level mechanics in ligament [
102
,
104
,
144
,
145
]. Elastin and
fibrillin are thought to contribute to the toe region of the stress-strain curve in
ligament and tendon [
32
,
136
,
166
,
220
].
Structurally, ligaments and tendons share the same hierarchical organization
and structural motifs. However, there are significant differences in fibril diameter
distributions, fiber diameter and crimp morphologies, metabolic activity and the
relative percentage of certain components such as water, proteoglycans and types I
and III collagen [
7
,
121
,
125
,
194
].
3 Multiscale Material Characterization
The normal mechanical function of ligament and tendon is an emergent property
of complex interactions between physical scale levels (Fig.
3
). In order to model
these complex interactions, a firm experimental basis must first be obtained. This
section reviews and summarizes the experimentally observed material behavior of
ligament and tendon at the macroscale, mesoscale, microscale and nanoscale.
3.1 Elastic and Viscoelastic Behavior
When studying the material behavior of ligament and tendon, it is convenient to
isolate the equilibrium elastic response from the dynamic, or time dependent
response. The elastic response is experimentally measured using slow strain rates
or stress relaxation and creep testing, whereby step displacements or loading are
applied and equilibrium values are obtained [
144
]. The elastic response arises
primarily
from
stretching
and
interactions
of
the
solid
phase
components.
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