Biomedical Engineering Reference
In-Depth Information
Fig. 10 Schematic of viscosity measurement using a regular or carbon whisker AFM tip. The
right picture shows electron microscope image of a whisker tip. Bottom graphs show cantilever
torsion while scanning in the lateral force mode. For details, see Mechler et al. ( 2004 )
AFM has been able at a small scan size to show the features of a cross-sectioned
wool fi ber with similar amount of detail as transmission electron microscopy (TEM)
( Fig. 11 , left panels). To study the mechanical properties of the different constituents
of the fi bers, AFM force mapping has been used. The force curves gives information
about the stiffness and elastic modulus of the sample regions. For instance, it was
shown that the exocuticle part of wool fi bers has the highest elastic modulus
(19.8 GPa) while the endocuticle and cortical regions of the fi ber cross section have
signifi cant lower modulus (3.8 and 4.0 GPa, respectively). The indentations made by
a diamond tipped cantilever, all made with the same indentation force, look indeed
distinctly different for the different regions (Fig. 11 , right panel). Furthermore, the
AFM can give conclusive evidence of the role of disulfi de bonds in the fi ber stiffness.
Reduction of such bonds, abundant in the exocuticle, using dithiothreitol resulted in
a reduction of modulus to 0.3 GPa (Parbhu et al. 1999 ). This has shed new light on
the role of the exocuticle (small in mass proportion) in the rigidity of wool fi bers.
Using the unique feature of defi ned nanoindentation, one can create specifi c
patterned structures, like nanocavity, nanopores, nanowells, and nanochannels.
Signifi cantly, such nanopatterned features would also provide clues about the build-
ing materials and would be helpful in advancing the fi eld of biomimetics.
5.2
Nanomechanics of Human Bone
The mechanical properties of bone and more specifi cally the failure mechanisms of
healthy and diseased bone are receiving large scientifi c as well as medical interest.
The organic moiety in bone has a great infl uence on the mechanical properties of the
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