Biomedical Engineering Reference
In-Depth Information
structure with relevant length scales at the submicrometer level. Hence,
nanoindentation has become a valuable tool for understanding structure-
property relationships in wood, particularly at the cell and sub-cell level.
8
The primary goals of nanoindentation studies of wood have been to
understand how wood maintains such a high strength-to-weight ratio and
to develop methods to treat wood to improve its surface properties
without sacrificing those unique mechanical properties.
Many papers have investigated the effects of the wood cell
microstructure and composition, including fiber orientation within the
cell wall and the degree of lignification, on the wood cell's mechanical
properties.
8,30,31
Other studies have studied mechanical properties as a
function of wood maturity,
32
tree ring,
31
or degree of pyrolization.
33
Another focus of wood research is product development,
8
such as
investigating the penetration of coatings and adhesives into the wood
cells to determine whether the mechanical properties of the wood will be
influenced by the treatments.
8,34-37
Investigations into the anisotropic
properties of wood
30,38,39
and bamboo
40
have also been performed,
including a study specifically highlighting the concerns of using
nanoindentation to characterize highly anisotropic wood cells.
38
The waxy layers on pitcher plants play a key role in trapping insects
in the plant by interfering with their adhesion mechanisms. Because
individual setae on insect feet end in spatulae on the order of 1
micrometer in diameter,
1
the nanoindenter provides a valuable method
for investigating the behavior of the waxy coatings on the same scale as
insect feet are interacting with those coatings. Several studies have
investigated the mechanisms by which these waxy layers prevent insect
attachment using nanoindentation in conjunction with high resolution
imaging and chemical analysis tools.
1,41
Both the wood review by Moon
et al.
8
and the pitcher plant studies
1,41
identify numerous limitations of the nanoindentation technique for
characterization of plant materials. These limitations and areas for
improvement will be summarized in Section 4. These studies of wood
and pitcher plants also represent examples of biomimetic applications of
nanoindentation. Biomimetics is the field of learning design concepts
from nature to solve engineering problems. Studies of wood shed insight
into how to achieve high strength and low density, while pitcher plants
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