December 16, 2012 | 1
Is there anything less conventionally appealing, on a purely aesthetic level, than the lowly hagfish? Perhaps — Mother Nature likes to experiment — but the hagfish is definitely near the top of the list. It’s an ugly eel-like creature — gray, with big whiskers, no eyes, clammy, and a bit stinky to boot — that excretes copious amounts of slime from pores all along its body when it feels threatened in any way. That slime mixes with saltwater to transform into a sticky goo.
And it’s that slime that makes the hagfish so very interesting from the perspective of materials science. Last week we were chuffed to hear that the latest research from hagfish specialist Douglas Fudge’s lab at the University of Guelph in Canada could result in a new kind of mucus-based thread, which may then be woven into a fabric, like a protein-based silk. Per Discovery News, Fudge’s team recently “managed to harvest the slime from the fish, dissolve it in liquid and then reassemble its structure by spinning it like silk.”
Eventually this could lead to super-strong fabrics and petroleum-free plastics. We could be seeing haute couture made of hagfish slime on Fashion Week runways any time now.
A paper to that effect just appeared in the journal, Biomacromolecules, along with an accompanying video of the new technique for harvesting the hagfish mucus in action (above). This inspired me to dig up portions of a prior post on the hagfish and the wonderful materials properties of mucus, including a handy recipe for slime-based scones at the very end. Enjoy!
The hagfish puts the human mucus production system to shame: it can churn out 1 liter of mucus in less than a second, according to Fudge. Hence the creature’s Latin name, Myxine glutinosa, from the Greek myxa (“mucus”) and the Latin gluten (“glue”). The resulting slime bonds to the gills of an attacking fish and blocks respiratory flow: the victim perishes by choking on snot. Should the victim attempt to chew its way through the slime to escape, the stuff will just expand further, and the victim will suffocate that much faster. The hagfish gets out of its own mess by tying itself into a knot, then pushing the knot down the length of its body to scrape off the slime.
Mucus is what’s known as a “phase-change” material because it moves from liquid to solid. The change is usually triggered by temperature (hot to cold, or vice versa) or environmental factors (wet to dry, dry to wet). Mucus is made up of protein-and-sugar molecules (mucin), as well as lots of water, which gives the material its slippery texture. As the substance loses moisture, it becomes more rigid, undergoing a sort of phase transition, although scientists who study these strange materials prefer to describe the process in more vague terms: the substance goes from a “fluid-like” to a “solid-like” state. Once ejected, the substance rapidly cools down and begins losing moisture. As it dries out, it forms a hard shell.
Unlike other forms of mucus, hagfish slime doesn’t harden. It stays slimy even in very chilly water, in part because both the hagfish and its victim are immersed in salty seawater, so it never has a chance to dry out. But hagfish slime has a secret ingredient: the usual protein-and-sugar concoction also contains long threadlike fibers.
The technical term is “intermediate filaments,” and these fibers are finer than spider’s silk, and as strong. The fibers form protein strands that expand rapidly once the mucins comes into contact with seawater, causing the substance to “blow up” into a sticky gel. The consistency is a bit like half-solidified Jell-O, or watered-down hair gel.
The fibers are so stretchy, they can elongate like taffy to three times their length before finally snapping. Fudge designed his own apparatus to stretch the filaments: something akin to a ping pong paddle, except with a filament where the paddle part should be. (Diagnostic electronics are embedded in the handle.)
Intermediate filaments can be found in most animal cells, creating a kind of scaffolding so that the cells are rigid enough to maintain their shape, yet still flexible enough to have a bit of give and take. That’s an interesting finding, because until quite recently, most biologists had assumed cell structure was rigidly inflexible. So they were initially skeptical of Fudge’s model, until French researchers traced a 3D contour of the fibers using an atomic force microscope, and also found them to be stretchy rather than inflexible.
There’s still a lot to learn about hagfish slime. For instance, the goo is ejected as a mix of disc-shaped vesciles and wound-up protein fibers (just like balls of yarn), and the vesicles burst when they come into contact with sea water, and the fibers unwind. The resulting mixture traps sea water, and that’s what causes it to swell. But what keeps those vesicles from bursting prematurely? There has to be a stabilizaing compound among the ingredients.
In 2003, Fudge thought he’d found the answer when an analysis revealed very high concentrations of methylamines, notably trimethylamine oxide. That’s a compound often found in shark tissue, for instance, to keep salt water from leaching bodily fluids out of the shark through osmosis. But it turned out to be something of a red herring.
His team actually “milked” the glands of drugged-up hagfish, releasing the substance into air instead of salt water — and still there was an explosion of slime. Fudge surmises that the gland might be pressurized — kind of like how Reddi-Wip doesn’t foam up until it’s released from the can.
All promising materials have potential applications and hagfish slime is no exception. Its unique properties could help save human lives by curtailing bleeding in an accident victim during surgery, for example. The mucus would expand upon contact with the blood (which is mostly water and salt), staunching blood flow.
That stretchy property is another bonus for potential applications. Fudge compares them to the plastic rings that hold together a six-pack of beer: pull them apart and they start to loosen and deform; in the case of the fibers, they actually rearrange into new molecular formations, eerily similar to spider silk. So in addition to ultra-light yet super-strong textiles (“bio-steel”), it could be used in biomedical devices, tissue engineering and biosensors.
And as any hagfish could attest, mucus is a terrific defense mechanism, which is one reason why the U.S. military is investigating its properties for military applications.
More frivolously, hagfish slime makes a dandy egg substitute in scones; An interpid blogger at the Museum of Awful Food adapted a recipe for just that purpose, which we reproduce here (duly credited) for those in need of some fresh-baked hagfish slime scones for the holidays.
Hagfish-Slime Cheddar-Gruyere Scones
4 cups all-purpose flour
2 tablespoons baking powder
4 teaspoons sugar
1/2 teaspoon salt
1 cup (two sticks) chilled unsalted butter, cut into 1/2-inch cubes
2 cups (packed) coarsely grated extra-sharp yellow cheddar cheese (about 9 ounces), or a mix of 6 ounces cheddar and 3 ounces gruyere.
1-1/2 cups chilled heavy whipping cream
6 tablespoons hagfish slime
Preheat oven to 375F
In a food processor, blend flour, baking powder, sugar, and salt. Cut in the butter using quick pulses until the mixture resembles coarse meal. Add cheese and cut in using quick pulses. In a small bowl, whisk together the cream and hagfish slime. With the food processor running, add cream mixture through feed tube. Process until dough just holds together Â– donÂ’t overmix!
Turn dough out onto a lightly floured work surface. Gather the dough together and divide into quarters. Pat each quarter into a round just short of 1 inch high (it should be about 6-7 inches in diameter). Using a clean, sharp knife, cut each round into six wedges. Transfer half the wedges to ungreased baking sheets lined with parchment paper, spacing them about 2 inches apart.
Bake the first batch of scones until the edges just start to brown and a toothpick comes out clean, about 20 minutes. Transfer them, still on their parchment paper, to a wire rack to cool at least 10 minutes, during which time put in the second batch of scones.
Serve warm or at room temperature. The scones will stand for about 8 hours. Do not refrigerate. If you want to reheat them, warm them in a 350F oven for about 5 minutes.
Fudge, D.S. et al. (2010) “Hagfish slime threads as a biomimetic model for high performance protein fibres,” Bioinsp. Biomim. 5: 035002.
Herr, J.E. et al. (2010) “Stabilization and swelling of hagfish slime mucin vesicles,” Journal of Experimental Biology, 213: 1092-1099.
Kreplak, L. and Fudge, D.S. (2007) “Biomechanical properties of intermediate filaments: from tissues to single filaments and back,” Bioessays 29: 26-35.
Negishi, Atsuko et al. (2012) “The production of fibers and films from solubilized hagfish slime thread proteins,” Biomacromolecules 13: 3475-82.