Biomedical Engineering Reference
In-Depth Information
FIGURE 10.7
Drawing of Eptatretus polytrema (hagfish). Source: Wikimedia Commons.
through recombinant DNA approaches have not
met this promise.
The hagfish, which resembles an eel in
appearance ( Figure 10.7 ), has a skeleton entirely
made of cartilage and no scales. Its body cover-
ing is a soft skin containing many glands, which
can be seen in Figure 10.7 , that produce very
large amounts of slime as a defense mechanism.
This slime contains long microfibers, thought to
entrain water, which accounts for the gel-like
property [38] .
Some work on the mechanics of protein fibers
from the slime of hagfish suggests that these fibers
might provide an additional biomimetic model.
The proteins within these slime threads adopt
conformations that are similar to those in spider
silks when they are stretched. Draw processing of
slime threads were found to yield fibers compara-
ble to spider dragline silk in strength and tough-
ness. From a biomimetic textile vantage point, the
slime itself is a soft, fiber-reinforced composite
with very interesting properties [39] .
conditions to a unique fiber system that provides
robust attachment to any surface, including
rocks, piers, and bridges [12] . This attachment
system, the mussel byssus , is deployed as an
array of threads composed essentially of col-
lagen. Distinct from the extrusion process of
silk, the byssus is assembled in the foot of the
mussel [40] ; consequently, and what makes the
byssus threads unique, the threads have the
unusual mechanical property of being stiff at
one end and 160% extensible at the other end.
The extensive literature on the distinct structure
and molecular composition of the two regions of
the byssus has been reviewed by Waite et al . [41] .
The proximal region contains loosely packed
coiled fibrils, providing the extensibility; the dis-
tal region contains dense bundles of filaments
that account for the stiffness. In addition, thread
stiffness and damping increase with increasing
strain rate [42] .
The mussel employs the strategy, relatively
novel among most natural fiber producers but
not unlike the scales present on wool, of coating
the threads with a thin (2-4 mm) cuticle to
protect the core. To match the compliance of the
byssus, the cuticle is infused with nanoscale
MUSSELS
Mussels, which survive in ocean wave-swept
tidal zones, owe their success in these extreme
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