Remora Fish, Those Suckers of the Sea, Are Inspiring New Adhesives

If you've ever watched documentaries on sharks or seen them out in the water, you've probably noticed their smaller companions—remora fish. These fish attach themselves to larger marine creatures, including sharks, turtles, manta rays, and the like, for a number of reasons that include an easy mode of transportation, to gain the protection provided by being one with a bigger animal, and for food in the form of scraps dropped by the host animal.

And yet, their hitching on to a shark causes no harm to the shark itself. As such, they are not considered to be a parasite, since their relationship is commensal; one animal benefits, one derives neither benefit nor harm. The remora fish also eats parasites off the shark's body that would otherwise bother the shark, hence the shark's willingness to let the remora fish remain.

The lack of harm to the shark's body is what intrigues scientists the most: How do the fish achieve such a solid attachment, particularly to a surface as rough as shark skin, without damaging their host? They're so tightly affixed to the host that they don't even come off when a shark leaps out of the ocean. Researchers from Georgia Tech are taking a closer look at the top of remoras' heads, at the structure and tissue properties of the area that adheres to the host, and hope to make a bio-inspired adhesive with the same qualities.

The Remora's Suction Plate

The remora’s suction plate is essentially a specialized dorsal fin which has become a disc covered by connective tissue which seals the fish to its host. "The intricate skeletal structure enables efficient attachment to surfaces including sharks, sea turtles, whales and even boats," reports Georgia Tech.

“While other creatures with unique adhesive properties—such as geckos, tree frogs and insects—have been the inspiration for laboratory-fabricated adhesives, the remora has been overlooked until now,” said GTRI senior research engineer Jason Nadler in the report. “The remora’s attachment mechanism is quite different from other suction cup-based systems, fasteners or adhesives that can only attach to smooth surfaces or cannot be detached without damaging the host.”

Researchers at Beihang University in China have found that the secret lies in highly elastic collagen fibers beneath the skin that allow the suction pad to bend to fit whatever uneven surface it's attaching to. This also reinforces it to create a tight seal.

Developing an Adhesive Based on Remoras

Along with detailed studies of remora species and their abilities, the researchers are using 3D printing to prototype versions of the remora's specialized dorsal fin. “We are not trying to replicate the exact remora adhesion structure that occurs in nature,” explained Nadler. “We would like to identify, characterize and harness its critical features to design and test attachment systems that enable those unique adhesive functions.”

According to the researchers, finding out the trick to this fish's reversible adhesion could be a benefit for many industries. It "could be used to create pain- and residue-free bandages, attach sensors to objects in aquatic or military reconnaissance environments, replace surgical clamps and help robots climb."

The team at Beihang says it has already managed to build a suction disc that "can stay stuck nearly 3.5 times longer than existing silicon suction discs," so it appears the remora's unique features are already driving interesting innovations.