Slime, baby, slime!


Paper: Chaudhary, G., Ewoldt, R. H., Thiffeault, J., & Ewoldt, R. H. (2019). Unravelling hagfish slime. Journal of Royal Society Interface, 16.

Article was originally posted in Jan 24, 2019

The weird and wonderful world of slime eels

Hagfish are extremely flexible and capable of tying themselves into knots (image from flickr )

Hagfish tend to get a bad rap. Sure, these eel-like fish may look like a parasitic alien out of a horror film, but they are actually incredibly cool and important animals.

Hagfish, also called “slime eels”, are not eels at all, but rather belong to a group of primitive, jawless fishes (order Myxiniformes) that originated well before the bony fishes we are more accustomed to seeing. There are currently 82 different species of hagfishes found worldwide ranging from shallow to extremely deep waters habitats.

Given their distant relationship to the fishes you are used to, hagfishes have a slew of features that do make them seem a bit like aliens. For one, these are the only living animals with a skull (made of cartilage – no bones here, folks) but completely lacking vertebrae! This makes hagfishes incredibly flexible and able to tie themselves into knots to avoid predators or tear hunks of meat off of a carcass. Hagfish have slow metabolisms and can go for months without eating. When they do eat, they scavenge for dead or dying organisms and can either tear at their meal with rasping teeth (they have no jaws and should not be confused with the parasitic lampreys known for their whirls of external teeth) or they can skip the hassle and just absorb nutrients directly through their skin. Hagfish also have multiple hearts. That’s right, in addition to their main heart, these fishes have an additional 3 accessory hearts that help pump blood around their bodies. Even crazier, these hearts can continue to pump for long periods of time without any oxygen (i.e. under anoxic conditions).

Hagfish use slime to repel predators but scientists could use it to form revolutionary fabrics

Without a doubt the hagfish’s most notorious – and some may say repulsive- characteristic is their ability to produce slime. Lots and lots of slime. When hagfish are attacked by predators, they shoot slime out of pores in their sides to clog the gills or mouth of their assailant. This slime production has even made hagfish stars in the media – like in 2017 when an Oregon highway was coated in hagfish slime after a truck carrying 7,500 hagfish crashed and released its cargo.

Hagfish appear to use slime to avoid predators like sharks (top) and large fish (bottom). The images above are from videos showing fish eating a hagfish, which then produces slime and is able to escape. Images from wikimediacommons.  You can also watch the video of this sequence

But scientists are interested in these mucous-making machines for a much different reason: hagfish slime could inspire eco-friendly fabrics.  Hagfish slime is composed of two parts: mucous cells and thread cells. When released from the body, the slime combines with saltwater, quickly expanding up to 10,000 times in volume! The end product is a viscous and flexible, fibrous slime that is 10 times stronger than nylon. Because of its unique composition and ability to increase so drastically in volume, scientists have been very curious to describe just how hagfish slime works.

The thread cells are several inches long, but are held in densely packed bundles, called skeins (not unlike balls of yarn by the same name), no thicker than a single human hair. Once ejected from the slime pores, these skeins quickly unravel and form a network of mucous-covered threads. This process is incredibly fast and it takes a mere 100 – 400 milliseconds (that is 0.1 – 0.4 seconds) for the thread cells to expand and form slime.  To see just how this slime is created, watch this video.

A fisherman gathers a fist full of slime from a hagfish tank. Image from flickr.

To test how hagfish slime is able to develop so rapidly, a group of scientists at the University of Illinois at Urbana-Champaign and at the University of Wisconsin recently conducted experiments, putting hagfish thread cells to the test. By pulling on thread cell skeins, the team was able to calculate just how much force was required to unravel the thread cell under different scenarios (such as if the thread cells were attached to the inside of a predators mouth or floating freely in water). You can watch the scientists unraveling a thread cell skein under a microscope here.  The scientists found that water motion alone could create a force large enough to rapidly unravel the skeins and that unraveling speeds would be increased by the thread cell being stuck to a surface (like the inside of a predator’s mouth).

The scientists note that there is still a lot to learn about the mechanics of hagfish slime, but by understanding how the slime is able to rapidly expand, we may be able to construct biomaterials and even invent rapid, self-deploying fabrics. Who needs Spiderman’s webs when you could deploy your own hagfish slime?!

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