Yellow oil blobs in water

(Almost) home-made microswimmers

Microswimmers – micrometre-sized drops that can move through liquids – are used to study the way tiny organisms move. They can be naturally occurring or artificially made. Now, an international team of researchers have figured out a very simple artificial recipe for their creation using just oil, water, and something to mix the two.

“In biology, research shows that to create even the simplest artificial cells we need over 470 genes,” says Dr Stoyan Smoukov, reader in Chemical Engineering at Queen Mary University of London, UK.

“We show that just by using a few simple and inexpensive components we can create a new type of active matter that can change shape and move just like a living thing.”

The team – which also included Bulgarian, Polish and Chinese researchers – combined tiny amounts of pure water with tiny amounts of alkane oils, along with an even smaller amount of surfactant to combine them. They found that the mixtures formed droplets with diameters of around 0.5-2µm: roughly a thousandth of a millimetre, or the thickness of a red blood cell.

The droplets responded to small changes in temperature, releasing small threads that they used as tails to “swim” when cooled. When heated, the tails are retracted and the droplets “recharge”, gathering enough chemical energy to move again on cooling.

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“As the only equipment needed is a simple optical microscope, people could create these microswimmers with the most basic laboratory set-ups, or even at home,” says Smoukov.

“With thousands of swimmers per drop of water, it’s a world-in-a-drop situation. And when it costs 7p (13c) per teaspoon, there’s plenty for everyone.”

Back in the lab, Smoukov is hoping that the microswimmers can be used as a cheap, safe method of studying bacteria and other microorganisms.

“In nature we often see large numbers of organisms, such as bacteria, grouping together, but our understanding of how these organisms interact with each other is incomplete.

“By mixing our simple artificial swimmers with groups of living organisms we could develop a clearer picture of how biological microswimmers communicate with each other. For example, do they only communicate due to the physical act of ‘bumping’ into each other, or are there other chemicals or signals released into the environment essential for their interaction?”

If you’d like to try making the microswimmers yourself, the researchers have published their methods in the journal Nature Physics.