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Tag: engineering

Origami Robots: How Technology Moves at the Micro Level

Imagine a robot small enough to fit on a U.S. penny. Or even small enough to rest on Lincoln’s chest. It sounds preposterous enough. Now, imagine a robot small enough to rest on the chest of Lincoln – not the Lincoln whose head decorates the front side of the penny, but the even tinier version of him on the back. 

Before it was changed to a Union Shield, the tail side of pennies contained the Lincoln Memorial, including a miniscule representation of the seated Lincoln statue that rests inside. Barely visible to the naked eye, this miniature Lincoln is on the order of a few hundred micrometers wide. As incredible as it sounds, this is the scale of robots being built by Professor Itai Cohen and his lab at Cornell University. On February 22, Cohen shared several of his lab’s cutting-edge technologies with an audience in Duke’s Schiciano Auditorium. 

Dr. Itai Cohen from Cornell University begins his presentation by demonstrating the scale of the microrobots being developed by his lab.

To begin, Cohen describes the challenge of building robots as consisting of two distinct parts: the brain of the robot, and the brawn. The brain refers to the microchip, and the brawn refers to the “legs,” or actuating limbs of the robot. Between these two, the brain – believe it or not – is the easy part. As Cohen explains, “fifty years of Moore’s Law has solved this problem.” (In 1965, Gordon Moore theorized that roughly every two years, the number of transistors able to fit on microchips will double, suggesting that computational progress will become exponentially more efficient over time.) We now possess the ability to create ridiculously small microcircuits that fit on the footprint of a few micrometers. The brawn, on the other hand, is a major challenge. 

This is where Cohen and his lab come in. Their idea was to use standard fabrication tools used by the semiconductor industry to build the chips, and then build the robot around the chip by folding the robot into the 3D shape they desired. Think origami, but at the microscopic scale. 

Like any good origami artist, the researchers at the Cohen lab recognized that it all starts with the paper. Using the unique tools at the Cornell Nanoscale Facility, the Cohen team created the world’s thinnest paper, including one made out of a single sheet of graphene. To clarify, that’s a single atom thickness.

Next, it came to the folding.  As Cohen describes, there’s really two main options. The first is to shrink down the origami artist to the microscopic level. He concedes that science doesn’t know how to do that quite yet. Alas, the second strategy is to have the paper fold itself. (I will admit that as an uneducated listener, option number two sounds about as absurd as the first one.) Regardless, this turns out to be the more reasonable option.

Countless different iterations of microrobots can be fabricated using the origami folding technique.

The basic process works like this: a seven nanometer thick platinum layer is coated on one side with an inert material. When put in a solution and voltage applied, ions that are dissociated in the solvent will absorb onto the platinum surface. When this happens, a stress is created that bends the device. Reversing the voltage drives away the ions and unbends the device. Applying stiff elements to certain regions restricts the bending to occur only in desired locations. Devices about the thickness of a hair diameter can be created (folded and unfolded) using this method. 

This microscopic origami duck developed by the Cohen Lab graced the covered of Science Robotics in March 2021.

As incredible as this is, there is still one defect: it requires a wire to an external power source that attaches onto the device. To solve this problem, the Cohen lab uses photovoltaics (mini solar panels) that attach directly onto the device itself. When light is shined on the photovoltaic (via sunlight or lasers), it moves the limb. With this advance and some continuous tweaking, the Cohen lab was able to develop the world’s smallest walking robot. 

At just 40 microns by 70 microns by 2 microns thick, the smallest walking microrobot in the world is able to fold itself up and walk off the page.

The Cohen Lab also achieved “BroBot” – a microrobot that “flexes his muscles” when light is shined on the front photovoltaics and truly “looks like he belongs on a beach somewhere.”

The “BroBot,” complete with “chest hair,” was one of the earlier versions of the robot that eventually was refined into the world record-winning microrobot.

The Cohen Lab successfully eliminated the need for any external wire, but there was still more left to be desired. These robots, including “BroBot” and the Guinness World Record-winning microrobot, still required lasers to activate the limbs. In this sense, as Cohen explains, the robots were “still just marionettes” being controlled by “strings” in the form of laser pulses.

To go beyond this, the Cohen Lab began working with a commercial foundry, X-Fab, to create microchips that would act as a brain that could coordinate the limb movements. In this way, the robots would be able to move on their own, without using lasers pointed at specific photovoltaics. Cohen describes this moment as “cutting the strings on the marionette, and bringing Pinocchio to life.”

This is the final key step in the development of Ant Bot: a microrobot that moves all on its own. It uses a hexapod gate, meaning a tripod on each side. All that has to be done is placing the robot in sunlight, and the brain does the rest of the coordination.

“Ant Bot,” one of the most advanced of all microrobots to come out of the Cohen Lab, is able to move autonomously, without the aid of lasers.

The potential for these kinds of microrobots is nearly limitless. As Cohen emphasizes, the application for robots at the microscale is “basically anything you can imagine doing at the macroscale.” Cleaning surfaces, transporting cargo, building components. Perhaps conducting microsurgeries, or exploring new worlds that appear inaccessible. One particularly promising application is a robot that mimics that movement of cilia – the microscopic cellular hair responsible for countless locomotion and sensory functions in the body. A cilia-covered chip could become the basis of new portable diagnostic devices, enabling field testing that would be much easier, cheaper, and more efficient.

The researchers at the Cohen Lab envision a possible future where microscopic robots are used in swarms to restructure blood vessels, or probe large swathes of the human brain in a new form of healthcare based on quantum materials. 

Until now, few would have imagined that the ancient art of origami would predict and enable technology that could transform the future of medicine and accelerate the exploration of the universe.

Post by Kyla Hunter, Class of ’23

Origami-inspired robots that could fit in a cell?

Imagine robots that can move, sense and respond to stimuli, but that are smaller than a hair’s width. This is the project that Cornell professor and biophysicist Itai Cohen, who gave a talk on Wednesday, January 29 as a part of Duke’s Physics Colloquium, has been working on with and his team. His project is inspired by the microscopic robots in Paul McEuen’s book Spiral. Building robots at such a small scale involves a lot more innovation than simply shrinking all of the parts of a normal robot. At low Reynolds number, fluids are viscous instead of inertial, Van der Waals forces come into play, as well as other factors that affect how the robot can move and function. 

Cohen’s team designs robots that fold similar to origami creatures. Image from Origami.me

To resolve this issue, Cohen and his team decided to build and pattern their micro robots in 2D. Then, inspired by origami, a computer would print the 2D pattern of a robot that can fold itself into a 3D structure. Because paper origami is scale invariant, mechanisms built at one scale will work at another, so the idea is to build robot patterns than can be printed and then walk off of the page or out of a petri dish. However, as Cohen said in his talk last Wednesday, “an origami artist is only as good as their origami paper.” And to build robots at a microscopic scale, one would need some pretty thin paper. Cohen’s team uses graphene, a single sheet of which is only one atom thick. Atomic layer deposition films also behave very similarly to paper, and can be cut up, stretch locally and adopt a 3D shape. Some key steps to making sure the robot self-folds include making elements that bend, and putting additional stiff pads that localize bends in the pattern of the robot. This is what allows them to produce what they call “graphene bimorphs.” 

Cilia on the surface of a cell. Image from MedicalXpress.

Cohen and his team are looking to use microscopic robots in making artificial cilia, which are small leg-like protrusions in cells. Cilia can be sensory or used for locomotion. In the brain, there are cavities where neurotransmitters are redirected based on cilial beatings, so if one can control the individual beating of cilia, they can control where neurotransmitters are directed. This could potentially have biomedical implications for detecting and resolving neurological disorders. 

Right now, Cohen and his lab have microscopic robots made of graphene, which have photovoltaics attached to their legs. When a light shines on the photovoltaic receptor, it activates the robot’s arm movement, and it can wave hello. The advantage of using photovoltaics is that to control the robot, scientists can shine light instead of supplying voltage through a probe—the robot doesn’t need any tethers. During his presentation, Cohen showed the audience a video of his “Brobot,” a robot that flexes its arms when a light shines on it. His team has also successfully made microscopic robots with front and back legs that can walk off a petri dish. Their dimensions are 70 microns long, 40 microns wide and two microns thick. 

Cohen wants to think critically about what problems are important to use technology to solve; he wants make projects that can predict the behavior of people in crowds, predict the direction people will go in response to political issues, and help resolve water crises. Cohen’s research has the potential to find solutions for a wide variety of current issues. Using science fiction and origami as the inspiration for his projects reminds us that the ideas we dream of can become tangible realities. 

By Victoria Priester

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