Researchers have been trying for decades to create smaller gears in order to construct micro-engines, but progress stopped at 0.1mm as it was not possible to build the drive trains needed to make them move any smaller.
Now, the team in Sweden, along with their colleagues, has overcome this hurdle by abandoning traditional mechanical drive trains and instead using laser light to set the gears in motion. Their work is detailed in Nature Communications.
Light-powered Gears
In their study, the researchers show that microscopic machines can be driven by optical metamaterials, which are small, patterned structures that can capture and control light on the nanoscale.
Using traditional lithography, gears with an optical metamaterial are manufactured with silicon directly on a microchip, with the gear having a diameter of a few tens of micrometres.
By shining a laser on the metamaterial, the researchers can make the gear wheel spin. The intensity of the laser light controls the speed, and it is also possible to change the direction of the gear wheel by changing the polarisation of the light.
Shift in Thinking
“We have built a gear train in which a light-driven gear sets the entire chain in motion,” said the study’s first author, Gan Wang, a researcher in soft matter physics at the University of Gothenburg. “The gears can also convert rotation into linear motion, perform periodic movements and control microscopic mirrors to deflect light.”
The team believes that the ability to integrate such machines directly onto a chip and drive them with light creates entirely new possibilities. Furthermore, since laser light does not require any fixed contact with the machine and is easy to control, the micromotor can be scaled up to complex microsystems.
“This is a fundamentally new way of thinking about mechanics on a microscale. By replacing bulky couplings with light, we can finally overcome the size barrier,” said Gan Wang.
With these advances, researchers are beginning to imagine micro- and nanomachines that can control light, manipulate small particles or be integrated into future lab-on-a-chip systems.
A gear wheel can be as small as 16–20 micrometres and medicine is a field that is within reach, said Gan Wang.
“We can use the new micromotors as pumps inside the human body, for example to regulate various flows. I am also looking at how they function as valves that open and close.”