Biohybrid robotic jellyfish to gather data from deep sea

Developed at Caltech (California Institute of Technology), the jellyfish - which have the most efficient method for traveling through water of any living creature - are being augmented with electronics that enhance their swimming and a prosthetic ‘hat’ that carries a small payload and makes the jellyfish swim in a more streamlined manner.

The work, published in Bioinspiration & Biomimetics, was conducted in the lab of John Dabiri, the Centennial Professor of Aeronautics and Mechanical Engineering.

"It's well known that the ocean is critical for determining our present and future climate on land, and yet, we still know surprisingly little about the ocean, especially away from the surface," Dabiri said in a statement. "Our goal is to finally move that needle by taking an unconventional approach inspired by one of the few animals that already successfully explores the entire ocean."

Dabiri added that jellyfish are the original ocean explorers, reaching its deepest corners and thriving just as well in tropical or polar waters.

Previously, Dabiri's lab implanted jellyfish with a kind of electronic pacemaker that controls the speed at which they swim. In doing so, they found that if they made jellyfish swim faster than the pace they normally keep, the animals became even more efficient. Furthermore, a jellyfish swimming three times faster than it normally would use only twice as much energy.

The research team has now taken a step forward with the addition of a forebody to the jellyfish that is placed on the creature’s bell, which is its mushroom-shaped bodily part. The devices were designed by graduate student and lead author Simon Anuszczyk, who aimed to make the jellyfish more streamlined while also providing a place where sensors and other electronics can be carried.

"Much like the pointed end of an arrow, we designed 3D-printed forebodies to streamline the bell of the jellyfish robot, reduce drag, and increase swimming performance," said Anuszczyk. "At the same time, we experimented with 3D printing until we were able to carefully balance the buoyancy and keep the jellyfish swimming vertically."

To test the augmented jellies' swimming abilities, Dabiri's lab built a three-story vertical aquarium inside Caltech's Guggenheim Laboratory. Dabiri said the tank is tall, rather than wide, because researchers want to gather data on oceanic conditions far below the surface.

"In the ocean, the round trip from the surface down to several thousand meters will take a few days for the jellyfish, so we wanted to develop a facility to study that process in the lab," said Dabiri. "Our vertical tank lets the animals swim against a flowing vertical current, like a treadmill for swimmers. We expect the unique scale of the facility - probably the first vertical water treadmill of its kind - to be useful for a variety of other basic and applied research questions."

Swim tests conducted in the tank show that a jellyfish equipped with a combination of the swimming pacemaker and forebody can swim up to 4.5 times faster than an all-natural jelly while carrying a payload. The total cost is about $20 per jellyfish, making biohybrid jellies an alternative to renting a research vessel that can cost over $50,000 a day to run.

"By using the jellyfish's natural capacity to withstand extreme pressures in the deep ocean and their ability to power themselves by feeding, our engineering challenge is a lot more manageable," said Dabiri. "We still need to design the sensor package to withstand the same crushing pressures, but that device is smaller than a softball, making it much easier to design than a full submarine vehicle operating at those depths.

Funding for the research was provided by the US National Science Foundation and the Charles Lee Powell Foundation.