Japanese Scientists Pull Tiniest Cart and Ferris Wheel With Microscopic Workhorses

You wouldn’t choose algae of all things as a beast of labor, but in the microscopic world, these microorganisms are veritable workhorses. Researchers in Japan harnessed the motion of green algae cells by attaching micromachines, including a “scooter” that moves forward and a “rotator” that might just be the smallest Ferris wheel in the world.

These micromachines, reminiscent of futuristic nanobots, showcase the potential for algae-driven technology. The results are spectacular.

Researchers at the University of Tokyo’s Shoji Takeuchi Research Group decided to embark on this study after being impressed with Chlamydomonas reinhardtii’s locomotion. These tiny algae measure only 10 microns (a hundredth of a millimeter), but they can move at 100 microns per second — that’s ten body lengths every second.

“We were inspired to try and harness Chlamydomonas reinhardtii, a very common algae found all over the world, after being impressed by its swift and unrestricted swimming capabilities,” said Naoto Shimizu, a student from the Graduate School of Information Science and Technology at the University of Tokyo.

“We’ve now shown that these algae can be trapped without impairing their mobility, offering a new option for propelling micromachines which could be used for engineering or research purposes.”

Shimizu and colleagues devised two types of micromachines: the “scooter” and the “rotator.” Both are propelled by the single-celled green algae. These algae are trapped in basket-like structures which act as a harness to attach the micromachines, allowing them to swim freely and move the devices. The algae use their two flagella at the front of the cell to propel the machines, similar to a swimmer’s breaststroke.

The micromachines were fabricated using a cutting-edge 3D printing technology known as two-photon stereolithography. This method allows for precise manufacturing of microstructures from plastic at a scale of 1 micrometer (0.001 millimeter).

The “scooter” — made of two traps each holding algae, which look a lot like a podracer from Star Wars — was designed to move in a straightforward direction but surprised researchers with its erratic rolling and flipping motions reminiscent of some extreme sports show. The “rotator,” on the other hand, is made of four traps spaced evenly on an imaginary circle; it displayed the expected smooth rotational movement.  

“This has prompted us to further investigate how the collective movement of multiple algae influences the motion of the micromachine,” said lead author Project Research Associate Haruka Oda.

The researchers believe that these algae-powered micromachines could prove useful in environmental engineering and research. The algae do not require chemical modifications or external guidance structures, which is a major plus for such applications. On the flipside, green algae cells only live for about two days but during this time they reproduce into new algae. These experiments were carried out over several hours during which the micromachines maintained their form and mode of operation.

The team plans to enhance the design of the rotator to achieve faster speeds and create more complex micromachine models.

“The methods developed here are not only useful for visualizing the individual movements of algae, but also for developing a tool that can analyze their coordinated movements under constrained conditions,” said Professor Shoji Takeuchi from IST, who supervised the project. “These methods have the potential to evolve in the future into a technology that can be used for environmental monitoring in aquatic environments, and for substance transport using microorganisms, such as moving pollutants or nutrients in water.”

The micromachines were described in the journal Small.