Scientists in Japan are reporting an advance toward giving artificial cells another hallmark of life: the ability to tap an energy source and use it to undergo sustained movement.

They developed self-propelled oil droplets equipped with chemical “engines” (highly reactive catalysts) that provide self-propelled motion in the presence of a chemical “fuel”: special substances that react in the presence of the catalyst.

When the researchers placed droplets in water containing the fuel, the droplets moved in a controlled fashion toward areas with the highest concentration of fuel.