NEWS
Micromachines on the Horizon
Researchers at Sweden’s University of Gothenburg take the first step in creating micro-engines by developing light-powered micro-gears.
Written by Kayt Sukel
The gear has a structure that reacts to light and makes it move. Photo: Gan Wang
IN THE 1996 SCIENCE FICTION CLASSIC, Fantastic Voyage, scientists miniaturize a submarine to roughly the size of a microbe to journey through the human body. While today’s researchers may not be relying on a miniaturized Raquel Welch to save the life of a defecting physicist, many are interested in being able to create micro-sized mechanical machines to support applications ranging from advanced manufacturing techniques to novel drug delivery devices. Yet, to date, there’s been one problem: How to design, build, and control the gears to power machines of such a diminutive size.
We’ve long relied on gears to power automobile engines, as well as other types of large machines, to efficiently transfer power, increase and decrease speed, and manage torque, explained Gan Wang, a scientist at the University of Gothenburg in Sweden. With growing interest in applications for smaller spaces, many physicists and engineers have looked at new ways to create controllable gears on the microscale.
An optical metamaterial that reacts to laserlight makes the gear move. All gears are made in silica directly on a chip. Each gear is about 0.016 millimeters in diameter. Photo: Gan Wang
We’ve long relied on gears to power automobile engines, as well as other types of large machines, to efficiently transfer power, increase and decrease speed, and manage torque, explained Gan Wang, a scientist at the University of Gothenburg in Sweden. With growing interest in applications for smaller spaces, many physicists and engineers have looked at new ways to create controllable gears on the microscale.
“There are so many ways to use gears on the macroscale. They are everywhere,” he said. “As we’ve thought about developing new, smaller applications, we’ve looked for ways to reduce the size of gears and create a machine to help us do powerful things. As scientists, it also provides an opportunity to break the boundaries of science and do something new.”
Historically, efforts to design smaller gears and micromotors have been stymied once they get to 0.1 millimeters. Not only is this the smallest size the human eye can detect unaided, it’s also the point where finding ways to construct drive and coupling systems becomes next to impossible.
By changing the polarization of light, researchers can change the gears’ rotational direction. Photo: Gan Wang
“The first challenge to working even smaller is how to fabricate those kinds of machines,” Wang said. “How do you bound different gears—put one gear here, another gear here, and then bundle them together. You could use a tweezer, but it’s very small and hard to put them together. Then you have to find a way to make them move together.”
Wang and colleagues decided to take a completely different approach. They leveraged optical metasurfaces so that the tiny machines can be literally kicked into gear using laser light. These gear systems can be fabricated using existing lithography techniques, at the size of tens of millimeters. More importantly, the light allows precise movement of the gear trains thanks to the driving gear with the light-sensitive metasurface.
“We knew we had to do something really different to achieve this. We used measures that we use to fabricate the integrated chips we use in our phones to fabricate the gear drives on chips,” he said.
“Photons have no mass, but do have momentum. So, we can use light to move a driving gear, it rotates, and it pushes on the other gears to move the train.”
— Gan Wang, a researcher in soft matter physics at the University of Gothenburg
The second challenge, however, was how to power the gears that were now lithographed directly onto chips. Wang said the team looked to basic principles of physics to overcome it.
“Photons have no mass, but do have momentum,” Wang said. “So, we can use light to move a driving gear, it rotates, and it pushes on the other gears to move the train.”
The group developed a small pinion and rack micromachine, which fits inside a single strand of hair (16–20 micrometers), to demonstrate how this concept might work. They were able to use light to start the driving gear and power the micromachine with precision control. With this proof of principle in place, Wang and his colleagues are thinking about ways such machines could be used in the future.
“There are many interesting ideas on ways they could be used. First, because the size of the gear is approximately the size of some biological cells, we could use these gears for different biological applications, perhaps to measure the stiffness or strength of cells. But there are also applications for aerospace and other places. We just must use our imagination,” he said.
But in the meantime, he hopes that other engineers will be inspired to think outside the box when approaching old problems.
“Maybe this work will create a whole new field and encourage more scientists to think about how we can use these tiny gears,” he said.
Perhaps, one day, even to allow a team of scientists to travel, at least virtually, through the body’s circulatory system.
Kayt Sukel is a technology writer and author in Kansas City.
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