Scientists have discovered a surprisingly simple way to make tiny objects spin without using electricity, magnets, chemicals or even direct contact.
Instead, the new technique relies only on the movement of water at its surface.
The breakthrough could lead to new ways of making delicate materials used in electronics, medicine and soft robotics.
The research was carried out by scientists from the Karlsruhe Institute of Technology (KIT) in Germany and the Suzhou Institute of Nano-tech and Nano-bionics (SINANO) of the Chinese Academy of Sciences.
Their findings were published in Science Advances.
Creating controlled movement on a microscopic scale has always been difficult. Many existing systems depend on chemical reactions, electric fields or magnetic forces to produce motion. These methods can be complicated, expensive or wear out over time.
The new approach avoids all of these problems by using the natural forces that exist on the surface of water.
The researchers designed a tiny 3D-printed device with a spiral-shaped channel that floats on water while holding a microscopic object just above the surface.
When the device is gently moved up and down at a slow speed, the object simply rocks back and forth without turning. However, when the movement becomes faster, something unexpected happens.
Small swirling currents, known as vortices, appear on the water’s surface. These tiny whirlpools break the balance of the back-and-forth motion, causing the object to rotate a little with each movement.
Over time, these small rotations add up, making the object spin continuously in one direction. The process works much like a ratchet, where repeated small movements create steady forward motion.
Computer simulations helped the team understand exactly how this happens. They showed that once the water begins forming vortices, the flow becomes uneven, allowing the repeated up-and-down motion to generate a consistent rotation instead of canceling itself out.
Although the tiny water-powered rotor produces only about 10⁻⁸ newton-meters of torque, it is much stronger than the forces generated by many biological molecular motors. This is enough to perform useful tasks at microscopic scales.
To demonstrate its practical value, the researchers used the rotating system to twist extremely fine silk fibers measuring only 10 to 20 micrometers across into strong, multilayered bundles. Similar twisted structures are found in products such as Litz wires, which reduce energy losses in electrical systems, and surgical sutures used to close wounds.
Producing these kinds of structures at such a small scale has been a major challenge because conventional braiding machines can easily snap the fragile fibers. Since the new method relies entirely on water flow rather than mechanical contact, it avoids damaging the materials while still creating precisely controlled helical shapes.
The researchers believe this simple technique could eventually help manufacture advanced materials for low-loss electrical cables in data centers, stronger and more versatile surgical sutures, and even artificial muscles for future soft robotic devices.
By showing that water alone can drive tiny motors, the study opens an unexpected new path for building microscopic structures with remarkable precision.
