This new type of delivery system can be used to release drugs into specific locations within the body.
In stomach acid, the zinc reacts to produce bubbles of hydrogen, which propel the machines into the lining of the stomach, where they attach.
As the machines dissolve, they deliver their cargoes into the stomach tissue.
The researchers say the method may offer an efficient way to deliver drugs into the stomach, to treat peptic ulcers and other illnesses.
In their paper, they suggest that further work is needed to "further evaluate the performance and functionalities of various man-made micro-motors in living organisms. This study represents the very first step toward such a goal".