The finger-sized Northern clingfish employs one of the best suction cups in the world. A small disk on its belly can attach to wet, slimy, even rough surfaces and hold up to 230 times its own body weight.

A ÌìÃÀÓ°ÊÓ´«Ã½ team inspired by the clingfish’s suction power set out to develop an artificial suction cup that borrows from nature’s design. Their prototype, described in a published Sept. 9 in the journal Philosophical Transactions of the Royal Society B, actually performed better than the clingfish.

“I like to say, nature is always best,” said lead author , who started this work as a postdoctoral researcher at UW on San Juan Island. “In this case, when considering their attachment force, our suction cups are better.”

The suction cups could be useful across a number of industries that require a strong but reversible sticking force on rough or textured surfaces. These could include tagging whales and other marine animals, attaching sensors to fouled aquatic surfaces or operating underwater vehicles to clean ship hulls. Applications in shower caddy design or industrial processing are other interesting fields of application for the bioinspired suction cups, the researchers said.

Key to their suction cup breakthrough was understanding how the clingfish’s natural suction works so effectively — especially on rough surfaces that normally cause a manufactured suction cup to fail.

Clingfish have a disc on their bellies that allows them to hold on with great tenacity. The rim of the disc is covered with layers of micro-sized, hairlike structures, in many different sizes. This layered effect creates more friction along the rim and helps the fish stick to rough surfaces. The entire disk is flexible and elastic, allowing it to adapt and hold on to coarse, uneven surfaces.

“These fish are so evocative in what they can do. They can stick to irregular rocks covered in algae, and you cannot buy something that will reversibly stick to those rocks,” said co-author , a professor of biology and of aquatic and fishery sciences based at Friday Harbor Labs. “An awful lot of experimentation and skepticism finally led us to understanding how it worked.”

There are about 110 known species in the clingfish family found all over the world. The population around the San Juan Islands is robust and healthy. They often cling to rocks near the shore, and at low tide they can be seen in tide pools and under rocks.

Many marine animals can stick strongly to underwater surfaces — sea stars, mussels and anemones, to name a few — but few can release as fast as the clingfish, particularly after generating so much sticking power.

After more than five years spent deciphering how the clingfish suction cups work, the researchers began building their own prototype, borrowing from the innovations of nature.

The team discovered after years of lab tests that combining different materials helped give the artificial suction cups a rigid structure that was strong enough to hold tension, while also soft and flexible enough to conform and stick to rough surfaces. They also found a way to increase the friction on the rim of the cup.

“This combination of all these different aspects finally gave us good results and enabled us really to build a suction cup that is able to attach strongly to rough surfaces,” Ditsche said.

The researchers tested several iterations of their suction cup design by sticking them to a spectrum of rough and smooth surfaces, then pulling until each cup failed using a testing machine. They did the same tests using the natural clingfish suction disk. Each time, the most advanced artificial cup outperformed the clingfish suction across all surfaces.

The prototype is ready to be taken to the next step, ideally in collaboration with engineers who could develop the concept further with specific products and applications in mind, Ditsche said. Depending on how the cups are used, factors like temperature and sun exposure might require fine-tuning of the design.

“There’s understanding of how something works. And then there’s understanding how it works so well that you can actually make one. Biology doesn’t always give you that opportunity,” Summers said. “This is a really unusual situation, where when we looked closely over time, we realized we could mimic what we saw.”

This research was funded by the National Science Foundation and the Seaver Institute.

For more information, contact Ditsche at petraditsche999@gmail.com and Summers at fishguy@uw.edu. Note: Ditsche currently is based in Germany (Central European Time).

It’s called the Northern clingfish, and its small, finger-sized body uses suction forces to hold up to 150 times its own body weight. These fish actually hold on better to rough surfaces than to smooth ones, putting to shame industrial suction devices that give way with the slightest uneven surface.

Researchers at the ÌìÃÀÓ°ÊÓ´«Ã½’s on San Juan Island are studying this quirky little fish to understand how it can summon such massive suction power in wet, slimy environments. They are beginning to look at how the biomechanics of clingfish could be helpful in designing devices and instruments to be used in surgery and even to tag and track whales in the ocean.

“Northern clingfish’s attachment abilities are very desirable for technical applications, and this fish can provide an excellent model for strongly and reversibly attaching to rough, fouled surfaces in wet environments,” said , a postdoctoral researcher with ‘ team at Friday Harbor Labs.

Ditsche presented her research on the sticky benefits of clingfish last month in Nashville at the Adhesive and Sealant Council’s in a talk, “Bio-inspired suction attachment from the sea.”

Clingfish have a disc on their bellies that is key to how they can hold on with such tenacity. The rim of the disc is covered with layers of micro-sized, hairlike structures. This layered effect allows the fish to stick to surfaces with different amounts of roughness.

“Moreover, the whole disc is elastic and that enables it to adapt to a certain degree on the coarser sites,” Ditsche added.

Many marine animals can stick strongly to underwater surfaces – sea stars, mussels and anemones, to name a few – but few can release as fast as the clingfish, particularly after generating so much sticking power.

On land, lizards, beetles, spiders and ants also employ attachment forces to be able to move up walls and along the ceiling, despite the force of gravity. But unlike animals that live in the water, they don’t have to deal with changing currents and other flow dynamics that make it harder to grab on and maintain a tight grip. (Read a by Ditsche and Summers on the differences between adhesion in water and on land.)

Clingfish’s unique ability to hold with great force on wet, often slimy surfaces makes them particularly intriguing to study for biomedical applications. Imagine a bio-inspired device that could stick to organs or tissues without harming the patient.

“The ability to retract delicate tissues without clamping them is desirable in the field of laparoscopic surgery,” Summers said. “A clingfish-based suction cup could lead to a new way to manipulate organs in the gut cavity without risking puncture.”

Researchers are also interested in developing a tagging tool for whales that would allow a tag to noninvasively stick to the animal’s body instead of puncturing the skin with a dart, which is often used for longer-term tagging.

Ditsche, Summers and the UW graduate and undergraduate students who are studying the Northern clingfish have no shortage of specimens to choose from. This species is found in the coastal waters near Mexico all the way up to Southern Alaska. They often cling to the rocks near the shore, and at low tide the researchers can poke around in tide pools and turn over rocks to collect the fish. If they can unstick them, that is.

There are about 110 known species in the clingfish family found all over the world. The population around the San Juan Islands is robust and healthy.

Now that they have measured the strength of the suction on different surfaces, the researchers plan to look next at how long clingfish can stick to a surface. They also want to understand why bigger clingfish can stick better than smaller ones, and what implications that could have on developing materials based on their properties.

This research is funded by the National Science Foundation and the Seaver Foundation.

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For more information, contact Ditsche at pditsche@uw.edu or 360-610-0860.