Researchers at the Max Planck Institute for Intelligent Systems, working with the University of Michigan and Cornell University, have developed a microrobotic system capable of manipulating millimeter-scale objects without physical contact by generating torque through fluid motion.
The study, published in Science Advances, describes how swarms of magnetic microrobots can create controllable fluid flows that exert rotational forces on nearby objects. By adjusting parameters including spin rate, the number of microrobots, and their spatial configuration, the researchers demonstrated the ability to rotate, transport, assemble, and reorganize objects substantially larger than the robots themselves.
Each microrobot measures approximately 300 micrometers in diameter and rotates under the influence of an externally applied magnetic field. This rotation generates circular flow fields in the surrounding fluid, producing torque that can be transferred to passive objects. Experimental results showed that torque levels could be tuned and increased by modifying operational parameters, reaching values up to 3.6 × 10⁻⁹ newton-meters.
According to Gaurav Gardi, a postdoctoral researcher in the Physical Intelligence Department at the Max Planck Institute for Intelligent Systems and one of the study’s lead authors, “Fluidic torque provides a fundamentally new way to manipulate delicate objects that are only a few millimeters small.”
Rather than relying on direct mechanical contact, the microrobot collectives use fluid motion to induce rotational movement in adjacent structures. The team demonstrated this capability by rotating gear wheels in both matching and opposing directions, depending on the positioning of the microrobots relative to the gears. The system also actuated gear trains and rotated three-dimensional objects weighing more than 45,000 times the mass of a single microrobot.
Steven Ceron, a lead author of the study and now an assistant professor in the Robotics Department at the University of Michigan, said that while hydrodynamic drag has previously enabled various collective microrobot behaviors, the current work extends those interactions to remote object control. “Hydrodynamic drag has been an important mechanism in enabling diverse behaviors in microrobot collectives, but here, we use those same fluid-mediated interactions to control objects at a distance,” he said. “This is incredibly exciting because it opens an avenue of remote manipulation at small scales where we can use the microrobots’ surrounding environment to our advantage.”
The researchers also observed collective behaviors that emerged under specific operating conditions. At certain spin rates and configurations, microrobot swarms transitioned from dispersed rotational patterns to a “crawling” motion along object surfaces. These adaptive dynamics allowed the collectives to reorganize themselves while manipulating target objects, depending on environmental and task-related conditions.
The findings suggest potential applications in microscale manufacturing, assembly, and biomedical engineering. Because the system operates without direct contact, it may reduce the risk of mechanical damage when handling delicate structures and allow multiple objects to be manipulated simultaneously within fluid environments.
Metin Sitti, former head of the Physical Intelligence Department at the Max Planck Institute for Intelligent Systems and now president of Koç University, said that improved understanding and control of fluidic torque could support the development of programmable microrobot systems capable of coordinated tasks. “By understanding and controlling fluidic torque, we are moving toward programmable microrobot systems capable of complex, coordinated tasks,” he said.
Photo credit: MPI-IS
