What’s the better source of inspiration for military innovation other than nature, right? We have the 2019 Airbus with wings and tail structure that mimics the eagles. Insect-sized nano UAVs for reconnaissance and surveillance missions were also a result of observing the aerodynamic characteristic of a bumblebee. When the US Navy found out about the hagfish and how it uses its slime to disable its potential attacker, they knew that they had to use the same concept to their advantage.

The Goo Eel

Entering from stage right, an interesting eel-shaped, slime-producing fish first. Also called slime eels, the hagfish is a unique and interesting creature, being the only known living animal with a skull but no vertebral column. It is also jawless and did not evolve much from the hagfish of 300 million years ago.

Hagfish exhibiting self-knotting behavior. (JustinCC BY 2.0, via Wikimedia Commons)

To survive for such a very long time without the need to evolve meant an effective way of keeping yourself alive. The hagfish have an interesting way of avoiding falling victim to predators. Whenever threatened, hagfish will fill the gills and mouth of its attacker with goo. What’s more interesting is that the slime they exude increases to 10,000 times its original volume once it comes into contact with seawater. For instance, 90 mg of their slime could turn into a liter once it gets mixed with seawater, making it a truly unique and interesting biomaterial.

As per Ryan Kincer, Materials Engineer and co-creator of the slime,

From a tactical standpoint, it would be interesting to have a material that can change the properties of the water at dilute concentrations in a matter of seconds.

Slime Under the Microscope

For it to be recreated, the scientists had to look at what makes the hagfish slime the way it is. Looking closer at the hagfish goo reveals a lot of things about it.

The slime they produce is made up of two protein-based parts: a thread and mucin. The coiled thread acts like a spring that unravels every time it comes in contact with the seawater. How it works is that whenever the fish releases this gooey goo, the mucin binds with water that would then constrain the flow between the channels made by the dispersion of the thread. Kincer further explained,

The interaction between the thread, mucin, and seawater creates a three-dimensional, viscoelastic network. Over time, the thread begins to collapse on itself, causing the slime to slowly dissipate.

Hagfish Slime. (DVIDS/U.S. Navy photo by Ron Newsome, NSWC PCD)

Researchers have also found out that the slime they produced can act both as a Non-Newtonian and Newtonian fluid, thus the reason why it could clog its predators’ gills and incapacitate them without accidentally suffocating itself. Non-Newtonian fluids, like a mixture of water and corn starch, become stiffer and more resistant whenever force is applied.

The more the predators try to suck in water to capture their prey, the more the hagfish would produce slime to block their gills until they are suffocated.

“The Possibilities Are Endless”

The US Naval Surface Warfare Center, Panama City Division (NSWC PCD) scientists and engineers successfully recreated the same defensive biomaterial that the hagfish use. They did the artificial one by using the E. coli bacteria to produce the alpha and gamma proteins that they then combined together and quickly assembled in a crosslinking solution.

Kincer and biochemist Josh Kogot developed the human-made version, which they think could be used to stop enemy boats by having the slime clog their propellers, the same way the hagfish clogs the enemy’s gills.

At the moment, the Navy uses plastic rope with a pneumatic launcher that would tangle in the target boat’s propeller. As per Kogot, “the synthetic hagfish slime may be used for ballistics protection, firefighting, anti-fouling, diver protection, or anti-shark spray. The possibilities are endless.”

Kincer added, “From a tactical standpoint, it would be interesting to have a material that can change the properties of the water at dilute concentrations in a matter of seconds.”