How hagfish slime gets its incredible clogging ability

Hagfish produce copious amounts of slime when attacked, which chokes predators’ gills in a gooey net. Scientists now know that mucus plays a critical role in hagfish slime’s remarkable clogging ability, and fibrous threads keep the slime from washing away.

Within half a second of being provoked, eel-like hagfishes release bundles of fibrous protein threads and mucus from glands along their bodies. The threads spread into an intricate tangle and, in combination with mucus, transform seawater into a thick goo.

“It has these spider-silk-like fibres running throughout it, which give it this strength and toughness that is utterly shocking and surprising,” says Douglas Fudge at Chapman University in California. “The slime is amazing.”

To test the clogging power of Pacific hagfish (Eptatretus stoutii) slime, Fudge and his colleagues built a custom slime sieve. They dissolved the slime in water and recorded its weight over time as water drained through the holes below – the slower the flow, the greater the clogging power.

They then compared the drain rate of the hagfish slime with that of three other common thickening agents at various concentrations: psyllium husk, xanthan gum and polyethylene oxide (PEO). For its weight, hagfish slime was two to three orders of magnitude better at clogging than its competitors. Around 35 milligrams of slime per litre of water produced maximum clogging.

“The shocking result was that [other thickeners] are not even close to what hagfish slime is doing in terms of performance,” says Fudge. “You can have somewhere between 100 times to 1000 times less hagfish slime to get the same clogging performance as those other materials.”

When the team removed the threads from the slime in the lab, they were surprised to find its clogging abilities were preserved. “The mucus is really doing the heavy lifting when it comes to the clogging performance,” says Fudge. That made him wonder, why does hagfish slime have threads at all?

In a similar follow-up experiment, the team flushed the mucus-only hagfish slime with seawater. At first, the slime held up in the sieve, but further blasts of water quickly washed it away. When they tried again with slime containing both mucus and threads, the slime stuck around for more than a dozen flushes of seawater. “We think that the threads are there to hold the slime in place and to prevent the mucus from dissipating,” says Fudge.

“It’s surprising to see how well mucus can clog even in the absence of threads,” says Sarah Schorno at the University of Guelph in Canada who was not involved in the work. “It is fantastic, high-quality science.”

Fudge hopes these insights into hagfish slime could bring scientists closer to developing synthetic alternatives to the super-strong goo, which could be used in bandages, clothing and for military defence.