Micromachines driven by microorganisms

Like a plow pulled by oxen, researchers at the University of Tokyo have created microscopic machines that can be powered by tiny, lively single-celled green algae.

The algae are caught in baskets attached to the micromachines, which have been carefully designed to leave them enough room to continue swimming.

Two types of vehicles were created: the “rotator,” which spins like a wheel, and the “scooter,” which was meant to move forward but in testing moved more surprisingly. The team is planning to test different, more complex designs for their next vehicles. In the future, these mini algae rigs could be used to help with engineering and environmental research at the micro level.

“We were inspired by the idea of ​​trying to harness Chlamydomonas reinhardtii, a very common algae found around the world, after being impressed by its fast and unrestricted swimming ability,” Naoto Shimizu, a student at the University of Tokyo’s Graduate School of Information Science and Technology who initiated the project, said in a statement. “We have now shown that these algae can be trapped without impairing their mobility, offering a new option for propelling micromachines that could be used for engineering or research purposes.”

The micromachines were created using a 3D printing technology called two-photon stereolithography. This printer uses light to create microstructures from plastic. The team worked at a scale of 1 micrometer, equivalent to 0.001 millimeters. According to the researchers, the most challenging part was optimizing the design of the basket-shaped trap, so that it could effectively capture and hold algae when they swam toward it.

The traps were attached to two different micromachines. The first, called a scooter, has two traps containing one algae in each and looks a bit like a Star Wars podracer. The second, called a rotator, has four traps containing four algae in total and is similar to a Ferris wheel. The size and shape of the baskets allowed the algae’s two flagella (small whip-like appendages) to keep moving, powering the machines.

“As we expected, the rotator showed a smooth rotational motion. However, we were surprised by the scooter. We thought it would move in one direction, as the algae all face the same direction. Instead, we observed a series of erratic rocking and flipping movements,” explained lead author of the project, research associate Haruka Oda, also from the Graduate School of Information Science and Technology (IST). “This has prompted us to further investigate how the collective motion of multiple algae influences the motion of the micromachine.”

According to the researchers, the main advantage of these micromachines over those powered by different organisms is that neither the machine nor the algae require any chemical modification. The algae do not need external structures to guide them into the trap, which allows greater freedom of movement for the micromachine and simplifies the process.

We do not yet know how long these microcars and their tiny steeds can survive and continue to function. Individual Chlamydomonas reinhardtii can live for about two days and multiply to produce four new algae. The experiments were carried out over several hours, during which the micromachines maintained their shape.

Next, the team wants to improve the rotator to spin faster and create new, more complex machine designs. “The methods developed here are not only useful for visualizing individual algae movements, but also for developing a tool that can analyze their coordinated movements under limited conditions,” said IST Professor Shoji Takeuchi, who supervised the project. “These methods have the potential to evolve in the future into technology that can be used for environmental monitoring in aquatic environments and for the transport of substances by microorganisms, such as the movement of pollutants or nutrients in water.”

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