Scientists built a fish-like soft robot that can survive in the Mariana Trench

Down in the abyssal depths of our oceans, there are a lot of wild terrors. Bizarre-but-beautiful nightmare fuel exists down there. Some of these magnificent and ghastly creatures have developed an incredible resistance to the bone-crushing pressures of the deep. And scientists have used these cues from nature to build a small soft robot, one that can reach the very deepest point of the ocean: the Mariana Trench. These types of robots might one day change how we monitor and clean up the oceans.

In a study, published in the journal Nature on Wednesday, a team of engineers in China reveal a lithium battery-powered soft robot that can explore at depths previously only reached by rigid, sturdy submersibles. The untethered robotic diver is a mere 22 centimeters long and kind of resembles a tiny manta ray, but its design is actually based on the hadal snailfish, a translucent slab of cartilage that lurks up to 26,000 feet below the surface.

To achieve the deep sea dive, the researchers took two of the snailfish's characteristics that help it flourish in the deep: its "distributed skull" and its side fins. 

We normally think of the skull as a hard, closed border between the brain and the world, a near-impenetrable part of the skeleton. The snailfish's skull is the opposite -- its filled with holes. It's a necessary adaptation for the fish, because the crushing pressures of the ocean's deepest point would crumble a closed skull. Better distribution of bone means less stress.

The researchers applied this idea to the electronics within their robot. They spaced the electronic components, like the microcontrol unit (a tiny computer), the battery and a voltage amplifier, apart from each other and put the design to the test. In the lab, the stress was dramatically reduced. 

A silicon body was built in the shape of the snailfish with small sidefins built to enable swimming. The fins are wired into a device known as a dielectric elastomer, a smart material that contracts or expands when a current is applied. Small voltages can inspire movement. In the video above you can see how the robot performs. Admittedly, it's not zipping through the water: the researchers state it was able to move at almost 4 centimeters per second in a test 70 meters below sea level.

To test the performance of the robot in the Mariana Trench, the team attached it to a "lander" that dropped to the seabed, about 35,000 feet beneath the surface. A recording device was also attached to monitor how successfully the robot could move, but it wasn't allowed to swim freely in the trench. It survived for about 45 minutes, and fortunately it wasn't left at the bottom of the ocean for good (the deep waters are already polluted enough, it seems). After a timer expired, ballast on the lander was released, returning the robot to the surface. 

The new research won't see soft robots flooding the depths anytime soon, according to an accompanying News and Views article in Nature written by Cecilia Laschi, a mechanical engineer at the National University of Singapore, and Marcello Calisti, a roboticist at the University of Lincoln in the UK. The new robot still has a few flaws. For one, the researchers say, it "cannot withstand sizeable disturbances" and thus "could easily be swept away by underwater currents."

However, the work does provide a new pathway for machines to explore and monitor the oceans. Laschi and Calisti point out that soft robots might be able to perform delicate procedures like collecting underwater specimens without damage or even while swimming among schools of fish without disturbance. 

At the very least, the robots aren't quite as frightening as some of the creatures that once roamed the deep.