World’s smallest chariot pulled along by single-celled algae


From dog sleds to horse-drawn carts, animals have been pulling vehicles for thousands of years. Now, scientists at the University of Tokyo have made what might be the smallest version ever, designing microscopic vehicles that can be pulled by single-celled algae.

On their own, single cells of algae can zip around at speeds of over 100 micrometers per second – about 10 body-lengths. The research team wondered whether they could (literally) harness that speed, and design micromachines that the algae can pull.

“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, an author of the study. “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.”

Left: An illustration of an alga caught in a trap. Right: A microscope image of the trap in action

The Shoji Takeuchi Research Group at the University of Tokyo

The first thing they needed to design was a trap that could hold algae that swim into it, but still let them move freely. After some trial and error, they settled on a design shaped like a basket, made of three rings measuring 7, 10 and 13 micrometers. The algae are too big to fit through the smallest ring, but they can still stretch out their flagella – whip-like appendages that they use to drag themselves through water.

Then, these traps were attached to two different vehicle designs. The first, which the team calls the “scooter,” is made up of two traps for algae pulling a box behind them, like a classic horse-drawn cart. The second, known as the “rotator,” looks kind of like a ferris wheel with four traps that propel the vehicle around in a circle.

The "Scooter" micromachine moved around in unexpected ways
The “Scooter” micromachine moved around in unexpected ways

The Shoji Takeuchi Research Group at the University of Tokyo

In practice, the rotator seems to work as described, spinning at an average speed of about 20 to 40 micrometers per second. But while the team assumed the scooter would simply move in one direction, experiments showed that it kind of rolled and flipped around instead.

While it looks like little more than the world’s smallest flea circus, the team has loftier goals. They plan to create more complex micromachines that can move in a variety of ways, which can help the study of algae and maybe put them to work.

The "Rotator" micromachine spins under the power of four algae
The “Rotator” micromachine spins under the power of four algae

The Shoji Takeuchi Research Group at the University of Tokyo

“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,” said Professor Shoji Takeuchi, supervisor of the project.

The research was published in the journal Small.

Source: University of Tokyo





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