Hagfish: Slimy Materials Scientists

To most, October 19th of this year may appear to be a typical Wednesday. But what they are unaware of is that scientists across the world celebrate Hagfish Day, an exciting holiday dedicated to the organism that plays an important and underrated role in modern science and biotechnology. But what is a hagfish, and why does it get a whole day to itself?

Hagfish are scavengers that live near the very bottom of the world’s oceans. There are over 40 different species of hagfish that vary in size and geographic location, but they all share a number of key features. They look like eels, but their closest relative is actually the lamprey. Among their many interesting features, such as their propensity for tying themselves in overhand knots, the most unique characteristic of hagfish is their primary defense mechanism. When stressed or attacked, a hagfish produces large quantities of viscous slime that clouds the water and allows the hagfish to make a clean getaway (click here for a video). Some scientists hypothesize that the thick slime acts to clogs attackers’ gills, causing the predator to suffocate.

Ninety-nine percent of the composition of this disgusting but remarkable slime is simply water, trapped in a relatively small amount of exudate, the actual substance produced by the hagfish. The exudate has two primary components. The first is mucin, which is also found in human mucus. These proteins absorb and constrain water, allowing hagfish slime to entrain a large volume of water in a small volume of exudate.  The second component is known as slime threads. They’re exactly what they sound like – long, thin threads that run through the slime and hold it together in a thick, cohesive mass. The slime threads are very similar to spider silk, both in appearance and in composition. Their structure differs from those of most well-characterized proteins but is most similar to keratin, the tough material that makes up our hair and fingernails. The threads have incredibly high tensile strength, withstanding more stress per unit than steel or nylon. Both the mucins and slime threads are packaged into vesicles of specialized glands that line the sides of the hagfish.

But why do we care? It turns out hagfish slime may help scientists toward a better understanding of how materials like hydrogels and protein fibers work. It may also prove to be a source of tough, flexible materials or serve as a model for artificially produced textiles of the future. Scientists like Dr. Douglas Fudge maintain that hagfish slime threads or synthetic mimics may someday replace petroleum-derived materials like Kevlar. Fudge, who until recently headed the Comparative Biomaterials Lab at the University of Guelph, has been a leading expert in hagfish for over a decade. He has been involved in many important experiments devoted to characterizing and understanding hagfish slime.

Photo Courtesy of Google Images
Photo Courtesy of Google Images

In recent years, Fudge’s research has gained attention among materials scientists and even in main-stream media, when experimental results revealed that hagfish slime threads are an even more promising model for modern synthetics than spider silk, though the latter was far more well-known. This is because, unlike spider silk, hagfish slime threads do not undergo supercontractions in high humidity, meaning they are tougher and more flexible under a larger variety of conditions. In addition, spider silk and similar materials usually require treatment with harsh chemicals that can be harmful to the environment, whereas hagfish slime threads are water-soluble and can therefore be processed in an environmentally friendly manner. The Fudge lab have successfully spun their own threads from hagfish slime, bringing us one step closer to being able to mass-produce slime materials for commercial and industrial use.

As researchers like those in the Fudge lab characterized the slime threads and increased recognition of their broad potential applications as a strong, versatile material, the scope of hagfish slime studies gradually broadened. Recent experiments have pursued goals such as using E. coli bacteria to synthetically produce hagfish slime proteins in the laboratory, performing experiments to find different types of materials that can be produced from hagfish exudate, and also determining the exact permeability of the whole slime to better understand naturally occurring hydrogels.

In 2013 and 2014, I spent an academic year running diagnostic prototype trials to determine the viability of hagfish slime as a biomaterial for use in bandages. From previous studies, I knew I could isolate the mucins and threads and use them to produce films, gels, and thread-based materials. Much like human mucus, hagfish slime contains various antibiotic agents that serve as part of the fish’s immune system. One of the most common antibiotic agents is lysozymes, which are enzymes that break down bacterial cell walls. Because of this antibiotic property and the slime’s exceptional absorbency, I hypothesized that it could serve as an ideal biomaterial for the creation of bandages. With ten hagfish of my own, I produced results that suggest that slime materials maintain their integrity and their absorbent and antibiotic properties even after the processing that would be necessary to produce bandage materials. These results serve as a sneak peek at the biotechnologies and materials that could eventually develop from hagfish slime.

However, if we are to make these dreams a reality we have to make sure hagfish are here to stay. Like many ocean creatures, hagfish currently face environmental challenges. Deep-sea trawling can destroy their habitats and remove their food sources. State Departments of Fish and Wildlife have only recently begun regulating the hagfish fishing industry. Hagfish are easy to catch and slow to reproduce, so their surprising popularity as a source of meat and “eelskin” leather has led to rapid population decline. Join me in wishing your friends and family a Happy Hagfish Day on the third Wednesday of every October to raise awareness for this strange little animal’s importance.

Grace Niewijk is a junior in Calhoun College. Contact her at grace.niewijk@yale.edu.

Featured Image courtesy of the author.