Diversified Material Designs in Biological Underwater Adhesives - Structural Interfaces and Attachments in Biology - page 175

Fig. 9.4 Cross-section of a unique crustacean, the barnacle. The animal firmly fixes its base shell
to a foreign material surface in water via an underwater adhesive called “cement,” whose adhesive
layer has a thickness of a few microns
might have complex properties beyond those of the original proteins. A gradient of
ratio among the amount of the three proteins was found to exist along the longitu-
dinal line of the byssal thread, which may contribute to formation of the gradient in
the mechanical property of the whole byssal thread.
9.5 Overview of the Barnacle Cement
The barnacle is a unique sessile crustacean and attaches two materials together in
water using a thin adhesive layer (Fig. 9.1 ). Its soft body is covered by a full armor
of calcareous shell plates, which are generally composed of four to six peripheral
plates, four opercular valves, and a base plate (Fig. 9.4 ). The animal firmly fixes its
calcareous base shell to a foreign material in water via an underwater adhesive
called “cement” [ 33 ] that has an adhesive layer a few microns in thickness [ 34 ].
When the barnacle grows, its base reaches a few centimeters in diameter, thus the
barnacle cement fixes the calcareous base with an area of several cm 2 by an
adhesive layer with a few microns in thickness. In other words, barnacle cement
could support a much larger area of distinctly different materials with a thinner
adhesive layer than tubeworm cement, described in the next section.
9.5.1 Unique Barnacle Adhesive
In this section, the adhesive cement formed on general hard materials is discussed
with a focus on how the barnacle successfully attaches to materials in water.