Biomedical Engineering Reference
In-Depth Information
Fig. 8.13 ( a ) Cross-sectional SEM image of a scale of the beetle T. isabellae in the dry state.
( b )and( c ) Cross-sectional TEM images of a scale in the dry state. ( d )-( g )ESEMimagesofa
scale. ( d ) Top view of the dorsal side in the dry state. ( e ) Top view of the dorsal side in the fully
wet state. ( f )and( g ) Transverse cross-sections in the dry and fully wet states, respectively. Scale
bars: ( a )1 m; ( b )2 m; ( c )0.5 m; ( d )and( e )5 m; and ( f )and( g )1 m (Reproduced
from [ 53 ])
The microstructures of the scales in the dry state were characterized by SEM and
TEM, as shown in Fig. 8.13 a-c. Cross-sectional SEM images revealed a multilayer
structure in the interior of the scales. The thickness of the scales is about 3 m.
As seen from both SEM and TEM images, the multilayer is composed of two
alternating layers. The first one is a homogeneous layer (dark layers in TEM images)
and the second one is an inhomogeneous layer. The inhomogeneous layer consists
of nanoparticles (gray areas in TEM images) and air voids (bright areas in TEM
images). The number of periods of the multilayer in different regions is different. In
the central region of a scale, it is about 10. The thickness of the homogeneous layers
is about 105 nm while it is about 70 nm for the inhomogeneous layers.
In order to get insight into the color change of the scales, environmental SEM
(ESEM) was used to measure the change in the microstructure of the scales in the
wet state, shown in Fig. 8.13 d-g. Scales swell noticeably after water absorption.
Close-up images show that both the cortex and the multilayer swell in the wet state.
The swelling of both the cortex and multilayer is due to the water absorption. The
period of the multilayer swells from about 175 nm in the dry state to about 190 nm
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