The incredible properties of hagfish slime have fascinated scientists for decades, but researchers are only just beginning to make sense of this mucilaginous secretion. In doing so, they hope to create superfibers that could one day be used in everything from bullet-proof vests to artificial tendons.
The hagfish is not a looker. The eel – to which the hagfish is not directly related but often compared, on account of its elongated body – is an attractive animal, by comparison. When I look at a hagfish, the phrase "naked zombie-skin tubesock" inevitably comes to mind. Look at this one – it's all but indistinguishable from a coil of fake dog poop:
Apart from being aggressively ugly, the hagfish is widely known for being an evolutionarily ancient fish that has changed very little over the last 300-million years (a fact that could explain why it's the only animal known to have a skull but no backbone), its repulsive feeding habits, and for its ability to exude a fibrous slime from its body when it is agitated or threatened.
Hagfish slime – in keeping with the hagfish's general state of being – is disgusting. But it's also fascinating. A teaspoon of the stuff can turn a beaker of water into a mass of viscid, gloppy gunk. A hassled hagfish can render a five-gallon bucket snotty with ooze, or, researchers confirmed in 2011, choke a would-be predator.
The slime contains tens of thousands of very thin, very strong protein threads. If you stretch these proteinaceous fibers out and let them dry they take on properties similar to the famously rugged dragline silks of spiders. Like spider silk, scientists think the proteins in hagfish slime could be used to create superfibers that could be used in everything from bulletproof vests to artificial tissues.
But hagfish slime, like spider silk, is difficult to harvest from the source (we know very little about the mating habits of hagfishes, which is probably why no-one has succeeded at breeding them in captivity), so scientists must engineer it from scratch. To do so, they need to understand how it's made, on the molecular level. According to Douglas Fudge, professor of Integrative Biology at the University of Guelph, it's a level of understanding that has eluded scientists for over a century.
But in a paper published in a recent issue of Nature Communications, researchers led by Fudge got their best look yet at the hagfish's mysterious slime, and how it's made. Using light and electron microscopy and 3D imagery, Fudge and his team peered inside the gland thread cells that produce the slime to examine the patterns into which the threads of protein are coiled and organized. The video above, via Fudge and his team, depicts the internal structure of a dveloping bland thread cell.
"For the first time, we had the technology to study the morphology and structure of the threads in the cells," said Fudge in a statement.
What they found was a series of incredibly long protein threads arranged in yarn-like "skeins" of 15–20 conical layers of loops. As the cells mature, their threads change in size, but remain stored in a way that allows them to be uncoiled without tangling, reaching up to 15 centimeters in length. "It's pretty amazing, considering that one of these threads is the equivalent of a rope that is one centimetre in diameter and 1.5 kilometres long," Fudge said.
"This study provided information about how the thread coils and fills the cells as it grows," he continued, "and these results led us to some very strong clues about how the threads are actually made, and figuring that out is the ultimate goal."
Read the full study in Nature Communications.
Images and animations adapted from this video by the Vancouver Aquarium