Hagfish ‘slime clouds’ have scientists stumped

"As a chemist and material scientist, I couldn't help but wonder what this slime consists of and what factors allow to immobilize such enormous amounts of water," says Simon Kuster. (Credit: ETH Zurich/Simon Kuster et al.)

The hagfish has a bizarre way of fending off predators: It secretes a slime mass that can immobilize vast amounts of water. Any fish that attempts to attack the hagfish will likely suffocate on the slime.

This creature and its slime caught the attention of Simon Kuster, a researcher at ETH Zurich, after he saw a BBC documentary about the Atlantic hagfish (Myxine glutinosa).


“As a chemist and material scientist, I couldn’t help but wonder what this slime consists of and what factors allow to immobilize such enormous amounts of water,” says Kuster.

Kuster is supervising an effort to figure out how hagfish form the slime, its structure, and how to recreate it.

The natural hydrogel produced by the hagfish has two main components: 15- to 30-centimeter-long protein threads and mucin.

hagfish secretions
The milky-white secretions gel immediately in cold water (Credit: ETH Zurich/Simon Kuster)

Mucin sits between the threads and makes the slime slimy. The protein threads have properties similar to spider silk. According to Kuster, the threads are extremely tear-resistant and elastic, though only when moist.

The components are produced in special ventral glands. Two types of cells are embedded within the gland, producing either the filamentous protein or mucin. When in danger, the hagfish secretes these cells intermittently through its pores.

The cell envelopes rupture, releasing the two components (threads and mucins). They immediately interact with the seawater and form a matrix that “absorbs” and immobilizes the water.

protein filaments in hagfish slime
Under the microscope the protein filament is intricately coiled within the cocoon-like cells. (Credit: ETH Zurich/Simon Kuster)

The slime consists of almost 100 percent water and contains just 0.004 percent gelling agent. In other words, the weight ratio of gelling agent to water is 26,000-fold, which is 200 times more than conventional animal gelatin.

The researchers were especially fascinated by the fact that the protein filaments have the form of a sphere measuring 150 micrometers in diameter while still in the glands, but, once they are part of the slime, they extend to threads of several centimeters in length.

How the threads unwind from the sphere is not yet understood in depth.

“The way the threads coil within the cells is highly specialised and very unusual,” says doctoral student Lukas Böni.

How to study hagfish

The researchers collaborated with a project partner in Ålesund, Norway, that is authorized to catch Atlantic hagfish in the wild and keep them in an aquarium.

“Before we partnered with the aquarium, we carried out initial pre-trials on the slime in a garage equipped with basic laboratory infrastructure we brought to Norway,” says Professor Peter Fischer.

Why not transport the animals to Zurich?

“The transport would stress the hagfish too much. They would secrete slime throughout the journey and eventually suffocate in their own slime,” says graduate student Lukas Böcker.

[‘Suction cup’ fish can grab 150X its weight]

The team is investigating a way to stabilize the glandular secretion so that they can be transported.

Ultimately the researchers hope to mimic the hagfish gel to create new super hydrogels. However Böni suspects an exact functional imitation of the glandular secretion is unrealistic:

“We cannot copy the slime formation mechanism of the hagfish in the laboratory. This natural system is far too complex,” says Böni.

However, developing a gel that follows the principle of the natural slime seems possible, he adds.

The team describes their work in the journal ACS Biomaterials Science and Engineering.

Source: ETH Zurich