Biomedical Engineering Reference
In-Depth Information
that biological materials will have different mechanical properties at
different length scales due to their hierarchical structures, the
interpretation of the quantitative values measured by indentation does
appear daunting.
However, even though they are desirable, quantitative values that
translate to macroscale properties may not be essential for all
applications. Even as a qualitative tool, nanoindentation of biological
materials has the ability to answer many research questions that are
unachievable by traditional bulk mechanical testing techniques. For
example, when comparing the effects of different clinical treatments on
tissue properties,
18,19
investigating the effects of surface treatments on
wood mechanics,
8,34-37
mapping mechanical properties in small
samples,
9,20,45
or correlating changes in mechanical properties with
variations in chemical composition in heterogeneous samples,
24,25,41,44,47
qualitative analysis by nanoindentation is sufficient and provides
valuable insight into local structure-property relationships. Hence, it is
always important to consider the question to be answered when
determining the appropriate analysis to be used.
5.
Conclusions and Future Directions
Nanoindentation has been used to measure quasi-static and viscoelastic
mechanical properties in a broad range of biological materials, including
soft tissues, plants, and spider silk. Because nanoindentation was
developed for mechanical characterization of engineering materials such
as metals and ceramics, adapting nanoindentation to the study of
biological materials has posed many challenges to researchers. The study
of soft tissues has posed the most challenges because soft tissues differ
the most from traditional engineering materials: they are hydrated,
compliant, have time-dependent properties, and have a complex
hierarchical microstructure. Efforts to address these properties have
led to the development of new nanoindentation sample preparation
techniques and data acquisition and analysis methods. While these
methods have furthered the field of soft tissue characterization using
nanoindentation, there is still a need for continued developments and
improvements in many areas in order to ensure that accurate, repeatable,
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