Biomedical Engineering Reference
In-Depth Information
This data suggests that less glycated bone is able to dissipate more energy through
diffuse damage formation while more glycated bone is less efficient in energy
dissipation due to increased linear microcrack formation. Thus, modifications of
bone matrix components can alter microdamage based toughening mechanisms
and lead to increased bone fragility.
6 Summary
This chapter provided a review of literature on microdamage and its effect on
bone's fracture behavior. Applied loading and its interaction with the hierarchy in
bone's extracellular matrix produces microdamage at various length scales where
microdamage can take two distinct forms (linear microcracks or diffuse damage).
Linear microcracks can coalesce and contribute to a large scale fracture. On the
other hand, the submicroscopic cracks of diffuse damage are self-limiting, and
consequently, this form of microdamage is beneficial to bone's energy absorption
capability, (i.e. toughness). Microdamage is conventionally detected via
two-dimensional histology methods using basic fuchsin for in vivo microdamage
detection or chelating agents for multi-labeling of in vitro induced microdamage.
However, a new technique incorporating heavy metal staining in conjunction
with microcomputed tomography has been developed for the three-dimensional
detection of microdamage. By means of imaging detection and fracture mechanics
based methods for quantification of bone's fracture properties, it has been deter-
mined that microdamage formation is an energy dissipation mechanism in bone.
The application of loading during regular/strenuous activities leads to formation of
microdamage in vivo. This microdamage helps to prevent fracture and is removed
by bone remodeling. However, deficiency in remodeling or age-related changes in
bone matrix cause increased bone fragility through inefficient repair and changes
in the magnitude and morphology of microdamage formation.
Acknowledgments
NIH grants AR49635, AG20618, and T32GM067545.
Appendix: Measurement of Bone's Fracture Resistance
As mentioned previously, the fracture properties of bone can be altered drastically
due to microdamage accumulation. These fracture properties include measures for
strength (resistance to permanent deformation) and toughness (resistance to frac-
ture) [
7
,
81
]. In order to measure these properties, early studies on bone fracture
utilized the strength-of-materials approach. The traditional method to measure
strength in bone involves mechanical testing on un-notched specimens. This
technique results in the initiation and propagation of fracture from random
distribution of natural flaws. Evaluation of strength with this method is based
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