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Under the sea hundreds of meters deep, a shark is quietly approaching its prey. What it fancy is a blind eel. This eccentric creature covered with gray-pink loose skin does not look very tasty, but in short, the shark bite it.
It turns out that this was a wrong decision. After almost a second or two, the shark quickly gave up the idea of eating blind eels. It loosened its mouth and swam away, and there was a big blurry and translucent thing hanging at the corner of the mouth.
(Original video source: Massey University)
What happened in the middle?
It is the mucus of the blind eel that defeats the shark. A large amount of thick mucus quickly filled the shark’s mouth, and also blocked their gills, so the shark had to give up the attack. This slime may be the most disgusting thing on blind eel, but for scientists, it is also a fascinating material.
When stimulated, the blind eel will first secrete some “raw materials” to produce mucus. These milky secretions themselves are very small, and together they may not fill a small tea spoon, but when they encounter seawater, they will quickly become nearly a liter of super large Tuo transparent mucus within a few hundred milliseconds.
This is the power of blind eel mucus: from the composition, it is actually incredibly rare. 99.996% of this big Tuo mucus is seawater, and the remaining little bit is the protein secreted by the blind eel. Compared with other biological mucus (such as the mucus in our mouth), the protein content of blind eel mucus is three orders of magnitude lower.
But at the same time, the texture of the blind eel slime is incredibly “thick”. It’s so thick that it can be picked up from the water, and it’s so thick that it seems to keep pulling…
(Feel…picture source: NOVA)
How can such a small amount of protein support such a constant thick texture? The answer lies in a special protein fiber in blind eel mucus. I like to call it the “yarn ball” of blind eel.
(Source: Douglas Fudge)
These fibers are really very similar to yarn balls. When they were first secreted, they were tightly wound small coils (as shown above), and gradually expanded in the sea water, they would become fibers of amazing length. The diameter of the fiber is only 1-3 microns, and the length is-10-17 cm! These ultra-long fibers and mucin form a network together, and enclose a very large amount of seawater in it, forming a jelly-like mucus.
(Some “wool ball” fibers intertwined. This picture is a typical deception. The color is the result of using a polarized light microscope. The fiber does not actually have a color.)
The slender fibers endow the blind eel mucus with “stretching thickening”, which means that if this group of mucus is pulled in one direction, it will appear particularly thick. This property also helps it stick to the shark’s gills well.
It is actually very easy to make it thinner: just rub it. This mucus also has the property of “shear thinning”. The friction inside the fluid will destroy the structure of the fiber network and make the mucus suddenly thin. Blind eels will use this feature to get rid of their own mucus. They make a circle with their bodies and pass through the middle, so that they can rub the mucus fully and avoid the mucus from sticking to themselves.
(A blind eel that is breaking away from mucus. Source: Lukas Böni et al)
If you just soak the “yarn balls” in the stationary salt water, they can eventually unfold, but the whole process will be very slow. In the actual ocean, these “yarn balls” mainly rely on the viscous drag of the water flow to achieve rapid stretching. If the end of the “yarn” is attached to a surface (such as the mouth of a shark), the entire process will be faster. The researchers actually observed the development process of “yarn balls”, and established a mathematical model to calculate the conditions required for their rapid deployment. Studying the mucus of blind eel not only improves our understanding of this strange creature, but also brings new inspiration to materials science.
Of course, the reason I would write “Blind Eel Yarn Ball” is simple-it’s really cute! !
(Routine blind eel expression)
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