The designs found in biological systems never cease to amaze me. Even something as gross and seemingly insignificant as hagfish slime displays remarkable properties, befitting the handiwork of a Creator. In fact, the design of hagfish slime is so ingenious, it is serving as the source of inspiration for researchers from the US Navy in their quest to develop new types of military technology.
What Are Hagfish?
Hagfish are ancient creatures that first appeared on Earth around 520 million years ago, with representative specimens recovered in the Cambrian fossil assemblages. These eel-like creatures are about 20 inches in length with loose fitting skin that varies in color from pink to blue-gray, depending on the species.
The hagfish are jawless but have a mineralized encasement around their skull (cranium). With eyespots instead of true eyes, these creatures have no vision. Hagfish are bottom-dwellers. To explore their environment, they make use of whisker-like structures. As scavengers, hagfish consume dead and dying creatures by burrowing into their bodies and ingesting the remains from the inside out. Remarkably, hagfish absorb nutrients through their skin and gills, in addition to feeding with their mouths. In fact, researchers estimate that close to half their nutrient intake comes through absorption.
When disturbed or attacked by predators, hagfish secrete a slime from about 100 glands that line the flanks of their bodies. (This behavior explains why hagfish are sometimes called slime eels.) Produced by epithelial and gland thread cells, the slime rapidly expands to 10,000 times its original volume. A single hagfish can generate around 5.5 gallons of slime each time it’s disturbed. Once secreted, the slime coats the gills of attacking fish, suffocating the predator. With the predator distracted, the hagfish performs this defensive maneuver that allows it to escape, while scrapping the slime off its body to prevent self-suffocation.
Two different types of proteins comprise hagfish slime. One of the components, mucin, is a large protein found widely throughout nature, serving as the primary component of mucus. Secreted by epithelial cells, mucin interacts with water molecules, restricting their movement, contributing to the slime’s viscosity.1
Additionally, hagfish slime consists of long, thread-like proteins. These protein threads are 12 nanometers in diameter and 15 centimeters long! (That is one big molecule.) These dimensions equate to a rope that is 1 centimeter in diameter and 1.5 kilometers in length. These protein fibers are incredibly strong, equivalent to a string that is 100 times thinner than a strand of human hair, but 10 times stronger than a piece of nylon.
Inside the gland thread cells, these protein fibers are carefully packaged like a skein of yarn, held together by other proteins that serve as a type of molecular glue.2 When the secreted hagfish slime contacts seawater, the glue proteins dissolve, leading to an explosive unraveling of the protein skeins, without any of the fibers becoming tangled. The protein threads contribute to the slime’s viscoelastic properties and provide the mechanism for the rapid swelling of the slime.
Hagfish Slime Inspires Military Technologies
The unusual and ingenious properties of the slime and the slime’s thread proteins have inspired researchers from the US Navy to explore their use in military technology. For example, the remarkable durability of the protein fibers (reminiscent of Kevlar) suggests an application for them in bulletproof vests. The properties of the hagfish slime could also be used as a flame retardant and a shark repellent for Navy divers.
Other commercial labs are exploring applications that include food packaging, bungee cords, and bandages. In fact, some have gone as far as to dub the thread proteins as the ultimate biodegradable biofiber.
Biomimetics and the Case for a Creator
In recent years, engineers have routinely and systematically benefited by insights from biology to address engineering problems and to inspire new technologies by either directly copying (or mimicking) designs from biology, or using insights from biological designs to guide the engineering enterprise.
From my perspective, the use of biological designs to guide engineering efforts fits awkwardly within the evolutionary paradigm. Why? Because evolutionary biologists view biological systems as the products of an unguided, historically contingent process that co-opts preexisting systems to cobble together new ones. Evolutionary mechanisms can optimize these systems, but they are still kludges.
Given the unguided nature of evolutionary mechanisms, does it make sense for engineers to rely on biological systems to solve problems and inspire new technologies? Conversely, biomimetics and bioinspiration find a natural home in a creation model approach to biology. Using designs in nature to inspire engineering makes sense only if these designs arose from an intelligent Mind—even if they are as disgusting as the slime secreted by a bottom-dwelling scavenger.