Researchers have long been intrigued by the potential of microrobots, particularly for applications in healthcare like targeted drug delivery and microsurgery. A central challenge in this field is achieving mobility without the use of onboard batteries or traditional propulsion methods. While magnets are often considered for movement, a team at ETH Zurich has turned to ultrasound as an innovative solution.
These microrobots, which are even smaller than the width of a human hair, are fabricated using photolithography and feature synthetic cilia similar to those found on starfish larvae. In nature, these delicate, hair-like structures beat in specific patterns to generate tiny vortices in the surrounding water, enabling the larvae to move. Essentially, the cilia either push water away or pull it in, providing propulsion.
The researchers have successfully replicated this propulsion mechanism by applying ultrasound waves to the robots, allowing them to swim in a straight line. In demonstration videos, plastic microbeads added to the water illustrate how the surrounding fluid circulates in circular patterns due to the robot’s movement.
One of the most promising applications of this technology is targeted drug delivery—such as administering medication directly to a stomach tumor—which could enhance treatment efficiency while minimizing side effects. However, a significant hurdle remains: imaging. Accurately steering these tiny machines requires clear, real-time imaging. To address this, the researchers plan to incorporate contrast agents, similar to those used in medical ultrasound imaging, to make the microrobots more visible during operation.
