A simple 3D-printed device can pave the way for much more powerful cell phones and Wi-Fi

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This simple machine that uses the surface tension of water to grasp and manipulate microscopic objects. Credit: Manoharan Lab/Harvard SEAS

A 3D-printed device in a water reservoir braids nanowires and moves microparticles.

New antennas to access higher and higher frequency ranges will be needed for the next generation of cordless phones and devices. One way to make antennas that operate at tens of gigahertz — the frequencies needed for 5G devices and above — is to braid filaments about 1 micrometer in diameter. However, today’s industrial manufacturing techniques will not work on such small fibers.

“It was a joyful moment when – on our first try – we crossed two fibers using only a piece of plastic, a water tank and a stage that goes up and down.” — Maya Faaborg

Today, a team of engineers and scientists from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a simple machine that uses the surface tension of water to grasp and manipulate objects. microscopic. This remarkable innovation offers a potentially powerful tool for nanoscale fabrication.

The research was published in the journal Nature October 26.

“Our work offers a potentially inexpensive way to fabricate microstructured and possibly nanostructured materials,” said Vinothan Manoharan, Wagner Family Professor of Chemical Engineering and Professor of Physics at SEAS and lead author of the paper. “Unlike other micromanipulation methods, like laser tweezers, our machines can be fabricated easily. We use a water tank and a 3D printer, like those found in many public libraries.”

The machine is a 3D-printed plastic rectangle that’s about the size of an old Nintendo cartridge. The interior of the device is carved with intersecting channels. Each channel has wide and narrow sections, similar to a river that expands in some parts and narrows in others. The channel walls are hydrophilic, meaning they attract water.

Through a series of simulations and experiments, scientists discovered that when they submerged the device in water and placed a millimeter-sized plastic float in the channel, the surface tension of the water caused the wall pushed back the float. If the float was in a narrow section of the channel, it moved to a wide section, where it could float as far away from the walls as possible.

Once in a wide section of the channel, the float would be trapped in the center, held in place by the repulsive forces between the walls and the float. When the device is taken out of the water, the repulsive forces change as the shape of the channel changes. If the float was in a wide channel to begin with, it may end up in a narrow channel when the water level drops and must move left or right to find a wider spot.

“The eureka moment came when we discovered that we could move objects by changing the cross-section of our trapping channels,” said Maya Faaborg, partner at SEAS and co-first author of the paper.

“The amazing thing about surface tension is that it produces forces that are gentle enough to grip tiny objects, even with a machine big enough to fit in your hand.” — Ahmed Cherif

Next, the researchers attached microscopic fibers to the floats. As the water level changed and the floats moved left or right in the channels, the fibers twisted around each other.

“It was a joyful moment when – on our first try – we crossed two fibers using only a piece of plastic, a water tank and a stage that goes up and down,” Faaborg said.

The team then added a third float with fiber and designed a series of channels to move the floats around in a braiding pattern. They succeeded in braiding fibers on a micrometric scale of the synthetic material Kevlar. The braid looked like a traditional three-strand hair braid, except each fiber was 10 times smaller than a single human hair.

Then the investigators demonstrated that the floats themselves could be microscopic. They built machines capable of trapping and moving colloidal particles as small as 10 micrometers in size – even though the machines were a thousand times bigger.

“We weren’t sure it would work, but our calculations showed it was possible,” said Ahmed Sherif, PhD student at SEAS and co-author of the paper. “So we tried and it worked. The amazing thing about surface tension is that it produces forces gentle enough to grip tiny objects, even with a machine big enough to hold in your hand.

Next, the team aims to design devices capable of manipulating many fibers simultaneously, with the aim of making high-frequency conductors. They also plan to design other machines for microfabrication applications, such as building materials for optical devices from microspheres.

Reference: “3D printed machines that manipulate microscopic objects using capillary forces” by Cheng Zeng, Maya Winters Faaborg, Ahmed Sherif, Martin J. Falk, Rozhin Hajian, Ming Xiao, Kara Hartig, Yohai Bar-Sinai, Michael P. Brenner and Vinothan N. Manoharan, October 26, 2022, Nature.
DOI: 10.1038/s41586-022-05234-7

The research was co-authored by Cheng Zeng, Ahmed Sherif, Martin J. Falk, Rozhin Hajian, Ming Xiao, Kara Hartig, Yohai Bar-Sinai and Michael Brenner, Michael F. Cronin Professor of Applied Mathematics and Applied Physics and Professor of Physics at SEAS. It was supported in part by the Defense Advanced Research Projects Agency (DARPA), under grant FA8650-15-C-7543; the National Science Foundation through the Harvard University Materials Research Science and Engineering Center, under grants DMR-2011754 and ECCS-1541959; and the Office of Naval Research under grant N00014-17-1-3029.

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