Mouthy sea urchin inspires engineers to take a bite out of other planets

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Researchers tested the claw-like device on a Mars soil simulant(Credit: UC San Diego)

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The sea urchin may be a restaurant delicacy, but it's also well equipped to satisfy its own appetite. The spiny invertebrate has a rock-crushing mouth so powerful that a herd of them can destroy a kelp forest or devastate a coral reef. Now its dinner manglers have inspired a team of engineers and marine biologists at the University of California, San Diego, to create a claw-like manipulator for robotic rovers tasked with collecting soil samples on other planets.

The past few decades have seen some of the most advanced machines ever built landing on the inner planets of the Solar System. Many of these are equipped with marvelously designed robotic arms, but the scoops they use for collecting soil samples are so simple that they wouldn't be out of place in a window-box garden.

According to the UC San Diego team, one answer to the space explorer's problem may be found in the mouth of the sea urchin. Located at the bottom of the its bulbous body, the mouth of the urchin (also called "Aristotle's lantern" after the Greek philosopher who first described it) is made up of five curved teeth held in a star pattern by an intricate muscle framework. This dome-like formation opens outwards and closes inwards like an arcade-game lucky dip claw, or the grabbers used in auto scrap yards. It's an arrangement that is not only elegant, but allows the urchin to cut, scrape, chew, and bore holes in solid rock.

The UC San Diego claw mimics the architecture of Aristotle's lantern and according to the team, it has the potential to collect samples with greater precision and efficiency than conventional "shovel" methods, without disturbing the surrounding area.

The UC research focussed on the pink sea urchin (Strongylocentrotus fragilis), a native of the waters off the west coast of North American that is found at depths of 100 to 1,000 m (330 to 3,300 ft). After removing the mouth parts, the team scanned then using micro–computed tomography to form 3D microscope images, while individual teeth were scanned under an electron microscope to determine their microstructure.

From this the researchers were able to build an accurate digital model of the mouthpiece. They then used finite element analysis, which is a computer method for predicting how a structure will react to physical effects, to determine the structure of the teeth and how they stand up under stress.

They discovered, for example, that a T-shaped structure called the keel that runs down the middle of each tooth like a ridge was an important feature. Computer simulations showed that the keel lowered stress on the teeth by 16 percent under a 10 lb (4.5 kg) load, yet only increased the mass by four percent.

The team reverse engineered this formation to create digital files and build a series of prototypes using 3D printing. These went through three iterations. The first closely mimicked the urchin's natural mouth structure, but this wasn't very good at picking up sand. A second was made with flatter points, but this didn't close right, so a third was created with a different tooth connection.

Once the final design was assembled, the team installed it on the arm of a miniature, remote-controlled rover, which was used to pick up beach stand. It worked, so the team moved on to simulated Martian soil with a similar humidity and density, which the claw also handled effectively.

The team says that the claw could be used on a fleet of tiny rovers that fan out to collect samples, then return to the main rover for analysis.

The research was published in the Journal of Visualized Experiments.

The video below shows the sea urchin-inspired claw in action.

Source: UC San Diego

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