It’s going to be a very, very long time before robots come anywhere close to matching the power-efficient mobility of animals, especially at small scales. Lots of folks are working on making tiny robots, but another option is to just hijack animals directly, by turning them into cyborgs. We’ve seen this sort of thing before with beetles, but there are many other animals out there that can be cyborgized. Researchers at Stanford and Caltech are giving sea jellies a try, and remarkably, it seems as though cyborg enhancements actually make the jellies more capable than they were before.
Usually, co-opting the mobility system of an animal with electronics doesn’t improve things for the animal, because we’re not nearly as good at controlling animals as they are at controlling themselves. But when you look at animals with very simple control systems, like sea jellies, it turns out that with some carefully targeted stimulation, they can move faster and more efficiently than they do naturally.
The researchers, Nicole W. Xu and John O. Dabiri, chose a friendly sort of sea jelly called Aurelia aurita, which is “an oblate species of jellyfish comprising a flexible mesogleal bell and monolayer of coronal and radial muscles that line the subumbrellar surface,” so there you go. To swim, jellies actuate the muscles in their bells, which squeeze water out and propel them forwards. These muscle contractions are controlled by a relatively simple stimulus of the jelly’s nervous system that can be replicated through external electrical impulses.
To turn the sea jellies into cyborgs, the researchers developed an implant consisting of a battery, microelectronics, and bits of cork and stainless steel to make things neutrally buoyant, plus a wooden pin, which was used to gently impale each jelly through the bell to hold everything in place. While non-cyborg jellies tended to swim with a bell contraction frequency of 0.25 Hz, the implant allowed the researchers to crank the cyborg jellies up to a swimming frequency of 1 Hz.
Peak speed was achieved at 0.62 Hz, resulting in the jellies traveling at nearly half a body diameter per second (4-6 centimeters per second), which is 2.8x their typical speed. More importantly, calculating the cost of transport for the jellies showed that the 2.8x increase in speed came with only a 2x increase in metabolic cost, meaning that the cyborg sea jelly is both faster and more efficient.
This is a little bit weird from an evolutionary standpoint—if a sea jelly has the ability to move faster, and moving faster is more efficient for it, then why doesn’t it just move faster all the time? The researchers think it may have something to do with feeding:
A possible explanation for the existence of more proficient and efficient swimming at nonnatural bell contraction frequencies stems from the multipurpose function of vortices shed during swimming. Vortex formation serves not only for locomotion but also to enable filter feeding and reproduction. There may therefore be no evolutionary pressure for A. aurita to use its full propulsive capabilities in nature, and there is apparently no significant cost associated with maintaining those capabilities in a dormant state, although higher speeds might limit the animals’ ability to feed as effectively.
Sea jelly with a swim controller implant consisting of a battery, microelectronics, electrodes, and bits of cork and stainless steel to make things neutrally buoyant. The implant includes a wooden pin that is gently inserted through the jelly’s bell to hold everything in place, with electrodes embedded into the muscle and mesogleal tissue near the bell margin.Image: Science Advances
The really nice thing about relying on cyborgs instead of robots is that many of the advantages of a living organism are preserved. A cyborg sea jelly is perfectly capable of refueling itself as well as making any necessary repairs to its structure and function. And with an energy efficiency that’s anywhere from 10 to 1000 times more efficient than existing swimming robots, adding a control system and a couple of sensors could potentially lead to a useful biohybrid monitoring system.
Lastly, in case you’re concerned about the welfare of the sea jellies, which I definitely was, the researchers did try to keep them mostly healthy and happy (or at least as happy as an invertebrate with no central nervous system can be), despite stabbing them through the bell with a wooden pin. They were all allowed to take naps (or the sea jelly equivalent) in between experiments, and the bell piercing would heal up after just a couple of days. All animals recovered post-experiments, the researchers say, although a few had “bell deformities” from being cooped up in a rectangular fish tank for too long rather than being returned to their jelliquarium. Also, jelliquariums are a thing and I want one.
You may have noticed that over the course of this article, I have been passive-aggressively using the term “sea jelly” rather than “jellyfish.” This is because jellyfish are not fish at all—you are more closely related to a fish than a jellyfish is, which is why “sea jelly” is the more accurate term that will make marine biologists happy. And just as jellyfish should properly be called sea jellies, starfish should be called sea stars, and cuttlefish should be called sea cuttles. The last one is totally legit, don’t even question it.
“Low-power microelectronics embedded in live jellyfish enhance propulsion,” by Nicole W. Xu and John O. Dabiri from Stanford University and Caltech, is published in Science Advances.
[ Science Advances ]
Evan Ackerman is a senior editor at IEEE Spectrum. Since 2007, he has written over 6,000 articles on robotics and technology. He has a degree in Martian geology and is excellent at playing bagpipes.