PREVIEW

Scientists have created the tiniest chariot in the world, powered by microscopic algae.

At the University of Tokyo, researchers devised minuscule vehicle-like structures where algae are captured in baskets connected to what they call micromachines. The design allows the algae enough freedom to swim and propel the structure.

Two distinct vehicle types were developed: the “rotator,” which spins like a wheel, and the “scooter,” likened to a Podracer from Star Wars, designed to move forward but demonstrated unexpected movements in tests.

The team aims to explore more intricate designs for their future vehicles.

These tiny algae-powered teams could eventually play a role in micro-level environmental engineering and research.

The University of Tokyo remarked: "You’ve likely heard of horsepower, but how about algae power? Like a sled drawn by dogs or a plough pulled by oxen, researchers have created microscopic machines powered by lively, single-celled green algae."

"Unhindered, these algae can zip along at over 100 micrometers per second. With four algae in the traps, the rotator achieved speeds between 20-40 micrometers per second."

Naoto Shimizu, a student at the University of Tokyo’s Graduate School of Information Science and Technology and the project's initiator, shared: "Inspired by Chlamydomonas reinhardtii’s swift swimming abilities, we harnessed this common algae for our project."

"We’ve shown that algae can be captured without hindering their movement, providing a novel method for propelling micromachines for engineering or research."

The micromachines were created using two-photon stereolithography, a 3D printing technique using light to form microstructures from plastic, working at a scale of 1 micrometer, equivalent to 0.001 millimeters.

The main challenge was optimizing the basket-shaped traps to effectively capture and hold the algae.

Two types of micromachines were developed: the scooter, resembling a Star Wars Podracer with two traps holding algae, and the rotator, with four traps holding four algae, akin to a Ferris wheel. The design enabled the algae’s flagella to keep moving, propelling the machines.

Lead author Haruka Oda from the Graduate School of Information Science and Technology noted: "The rotator moved smoothly as expected, but the scooter surprised us with its erratic rolling and flipping movements, despite algae facing the same direction."

This unexpected behaviour has led to further investigation into how the collective movement of algae influences micromachine motion.

The main advantage of these micromachines is that neither the machines nor the algae require chemical modification. The algae do not need external structures to guide them into the traps, allowing greater freedom of movement and simplifying the process.

The researchers are uncertain how long these micro-chariots and their tiny drivers can function. Individual Chlamydomonas reinhardtii can live for about two days, reproducing to create four new algae. The experiments lasted several hours, during which the micromachines maintained their form.

The team’s future goals include enhancing the rotator’s speed and creating more complex designs.

Dr. Shoji Takeuchi from IST, the project supervisor, stated: "Our methods not only help visualize individual algae movements but also develop tools to analyze their coordinated movements under constraints."

"These methods could evolve into technologies for environmental monitoring in aquatic settings and transporting substances like pollutants or nutrients in water."