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Robotic Micro-Scallops Can Swim Through Your Eyeballs

Tiny robots modeled on scallops are able to swim through all the fluids in your body

3 min read
Robotic Micro-Scallops Can Swim Through Your Eyeballs
An engineered scallop that is only a fraction of a millimeter in size and that is capable of swimming in biomedically relevant fluids has been developed by researchers at the Max Planck Institute for Intelligent Systems in Stuttgart.
Image: Alejandro Posada/MPI-IS

Designing robots on the micro or nano scale (like, small enough to fit inside your body) is all about simplicity. There just isn’t room for complex motors or actuation systems. There’s barely room for any electronics whatsoever, not to mention batteries, which is why robots that can swim inside your bloodstream or zip around your eyeballs are often driven by magnetic fields. However, magnetic fields drag around anything and everything that happens to be magnetic, so in general, they’re best for controlling just one single microrobot robot at a time. Ideally, you’d want robots that can swim all by themselves, and a robotic micro-scallop, announced today in Nature Communications, could be the answer.

When we’re thinking about robotic microswimmers motion, the place to start is with understanding how fluids (specifically, biological fluids) work at very small scales. Blood doesn’t behave like water does, in that blood is what’s called a non-Newtonian fluid. All that this means is that blood behaves differently (it changes viscosity, becoming thicker or thinner) depending on how much force you’re exerting on it. The classic example of a non-Newtonian fluid is oobleck, which you can make yourself by mixing one part water with two parts corn starch. Oobleck acts like a liquid until you exert a bunch of force on it (say, by rapidly trying to push your hand into it), at which point its viscosity increases to the point where it’s nearly solid.

These non-Newtonian fluids represent most of the liquid stuff that you have going on in your body (blood, joint fluid, eyeball goo, etc), which, while it sounds like it would be more complicated to swim through, is actually an opportunity for robots. Here’s why:

At very small scales, robotic actuators tend to be simplistic and reciprocal. That is, they move back and forth, as opposed to around and around, like you’d see with a traditional motor. In water (or another Newtonian fluid), it’s hard to make a simple swimming robot out of reciprocal motions, because the back and forth motion exerts the same amount of force in both directions, and the robot just moves forward a little, and backward a little, over and over. Biological microorganisms generally do not use reciprocal motions to get around in fluids for this exact reason, instead relying on nonreciprocal motions of flagella and cilia.

However, if we’re dealing with a non-Newtonian fluid, this rule (it’s actually a theorem called the Scallop theorem) doesn’t apply anymore, meaning that it should be possible to use reciprocal movements to get around. A team of researchers led by Prof. Peer Fischer at the Max Planck Institute for Intelligent Systems, in Germany, have figured out how, and appropriately enough, it’s a microscopic robot that’s based on the scallop:

As we discussed above, these robots are true swimmers. This particular version is powered by an external magnetic field, but it’s just providing energy input, not dragging the robot around directly as other microbots do. And there are plenty of kinds of micro-scale reciprocal actuators that could be used, like piezoelectrics, bimetal strips, shape memory alloys,  or heat or light-actuated polymers. There’s lots of design optimizations that can be made as well, like making the micro-scallop more streamlined or “optimizing its surface morphology,” whatever that means.

The researchers say that the micro-scallop is more of a “general scheme” for micro-robots rather than a specific micro-robot that’s intended to do anything in particular. It’ll be interesting to see how this design evolves, hopefully to something that you can inject into yourself to fix everything that could ever be wrong with you. Ever.

[ Nature Communications ]

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The Bionic-Hand Arms Race

The prosthetics industry is too focused on high-tech limbs that are complicated, costly, and often impractical

12 min read
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A photograph of a young woman with brown eyes and neck length hair dyed rose gold sits at a white table. In one hand she holds a carbon fiber robotic arm and hand. Her other arm ends near her elbow. Her short sleeve shirt has a pattern on it of illustrated hands.

The author, Britt Young, holding her Ottobock bebionic bionic arm.

Gabriela Hasbun. Makeup: Maria Nguyen for MAC cosmetics; Hair: Joan Laqui for Living Proof
DarkGray

In Jules Verne’s 1865 novel From the Earth to the Moon, members of the fictitious Baltimore Gun Club, all disabled Civil War veterans, restlessly search for a new enemy to conquer. They had spent the war innovating new, deadlier weaponry. By the war’s end, with “not quite one arm between four persons, and exactly two legs between six,” these self-taught amputee-weaponsmiths decide to repurpose their skills toward a new projectile: a rocket ship.

The story of the Baltimore Gun Club propelling themselves to the moon is about the extraordinary masculine power of the veteran, who doesn’t simply “overcome” his disability; he derives power and ambition from it. Their “crutches, wooden legs, artificial arms, steel hooks, caoutchouc [rubber] jaws, silver craniums [and] platinum noses” don’t play leading roles in their personalities—they are merely tools on their bodies. These piecemeal men are unlikely crusaders of invention with an even more unlikely mission. And yet who better to design the next great leap in technology than men remade by technology themselves?

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