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Taken out of context, it must have been an odd scene. Late on a cold October night in Montreal in 2006, a room of engineering students and their professor, Sylvain Martel, were watching the limp, anesthetized body of a pig in an MRI machine when the still air was punctuated with gasps and applause.
A hospital technician had just injected a steel bead roughly the size of the tip of a ballpoint pen through a catheter into the pig’s carotid artery, and after a few excruciating minutes of, well, nothing, they watched the bead on a computer screen suddenly hop into motion, ticking off every point the team had plotted for it to go.
It was the first time an object was steered wirelessly through a living creature’s blood vessel, and to the world of microrobotics, it was the dawn of a new era – an accomplishment akin to the moon landing, albeit on a dramatically smaller scale.
Legions of research teams around the world are now working on proof-of-concept studies that take this tiny step further, engineering microscopic robots that may some day be able to cruise through both the large arteries and small veins of living bodies to perform a wide range of medical feats that would otherwise require invasive surgery.
Dr. Roboto will see you now
Writing in the sci/tech journal IEEE Spectrum, Dr. Martel said the first feat will be treating cancer, where bots will be deployed to release drugs directly at tumor sites, thereby killing only the compromised cells instead of also compromising healthy ones.
The challenges of this and other medical applications are numerous and complex – one that Martel wrote will “require input from many disciplines.” There’s the physics problem of getting bots this size to move inside the viscous fluid that fills the complex circuitry of large arteries and tiny vessels alike. There’s the engineering challenge of both powering and imaging something this small. And there’s the biology problem of using materials that aren’t toxic to living things, and that might even be able to biodegrade to override the need to eventually leave the body.
Mechanical engineering professor Eric Diller at the University of Toronto told me these bots need to be so small that it simply doesn’t physically work to scale down existing technologies. The parts don’t exist, and even if they did, they couldn’t sufficiently power and instruct such tiny machinery. Instead, researchers get their inspiration from nature – bio-inspired designs that resemble, say, bacteria.
“The environment that tiny things experience is different than what you’re intuitively used to at a larger scale,” Dr. Diller said. “If something small is swimming through water, the liquid will seem very thick, so the method you would use to swim at the tiny scale needs to be much different. With bacteria, many types swim with flagella, which is different from what you’d see with a fish on a larger scale.”
Earlier this year Diller’s team unveiled its latest endeavor: building 1 millimeter bots that have two gripping arms and are propelled and controlled via magnetic field. (Check out the video here.) In this case, the bots were able to construct a bridge. Diller said microrobots won’t just be useful in drug delivery, but perhaps even to build or repair structures in our vasculature or organs.
At the University of Illinois at Urbana-Champaign, grad student Caroline Cvetkovic is working on a similar project – walking bots that are powered by muscles. In this case, her team harnessed the electrical impulse of skeletal muscle cells to propel the small bot, whose backbone is made of hydrogel, forward.
“?Our system is modeled off a muscle-tendon-bone system found in many mammals,” Cvetkovic told me by email. “Not only is this physiologically relevant, but [it] allows us to mimic the way natural systems use energy to produce force and motion.? In a human, for example, when a muscle contracts, the force is transmitted to the bone through a connecting tendon. In our bio-bots, when the muscle cells contract (upon applied electrical stimulation), this produces an inward force on the pillars, which are connected by a beam. Since the beam is made of a flexible hydrogel, it can bend with sufficient force. If one pillar (or ‘leg’) is moving more than the other, which happens when one pillar is longer than the other, we observe directional motion (i.e., walking) from the bio-bot.”
Cvetkovic envisions “a generation of biological machines that could aid in drug delivery, surgical robotics, ‘smart’ implants, or mobile environmental analyzers, among countless other applications.”
Robert Woods, an electrical engineer who founded Harvard University’s Microrobotics Lab and is one of National Geographic’s 2014 emerging explorers, thinks that the future of robotics isn’t just small, it’s soft, taking its cue from nature.
Dr. Woods is working on an inexpensive, disposable swarm of RoboBees that could pollinate crops, perform search and rescue, or detect hazardous materials. “If you want to make something … that can fly,” he said, “several hundred thousand solutions already exist in nature. We don’t just copy nature. We try to understand the what, how, and why behind an organism’s anatomy, movement, and behavior, and then translate that into engineering terms.”
And just last week a team of scientists in Europe and Israel said they’re a step closer to solving the physics problem of self-propulsion at the micro scale by mimicking scallops. Writing in the journal Nature Communications, they say their bioengineered scallop is so small – just a fraction of a millimeter – that it could swim through one’s eyeball. The real feat here is that the bots are truly swimmers; like many current models, they’re powered by an external magnetic field, but unlike existing microbots today, the power only provides energy input, it’s not dragging the scallops along.
Back in 1959, Physics Nobel laureate Richard Feynman delivered a famous speech in which he described a friend’s “wild” fantasy that “it would be very interesting in surgery if you could swallow the surgeon.” The interesting question, Feynman told the American Physical Society at the California Institute of Technology, is: “How do we make such a tiny mechanism? I leave that to you.”
Decades later researchers from many disciplines are still working on just that, but the notion no longer seems so wild. The surgeon may be injected instead of swallowed, but it will be tinier than even Feynman himself described, and perhaps more cunning than we can yet imagine.
This post was updated at 11:25am PT to correct that the robots in the University of Illinois at Urbana-Champaign are powered by skeletal muscle cells, and later updated to correct the spelling of that school’s name.
Featured photo courtesy Shutterstock user Vinne.