From Stiff to Soft in a Snap

Could tiny magnetic objects, that rapidly clump together and instantly fall apart again, one day perform delicate procedures inside the human body? A new study from researchers at the Max Planck Institute for Intelligent Systems in Stuttgart and at ETH Zurich introduces a wireless method to stiffen and relax small structures using magnetic fields, without wires, pumps, or physical contact.

Stuttgart – In music, 'jamming' refers to the spontaneous gathering of musicians who often improvise without aiming for a predefined outcome. In physics, jamming describes the transition of a material from a fluid-like to a solid-like state – like a traffic jam, where the flow of cars suddenly stops. This transformation can also be triggered on demand, offering a powerful and versatile way to control stiffness for robotic systems.

In most robotic applications, jamming is achieved using vacuum systems that suck air out of flexible enclosures filled with materials such as particles, fibers, or grains. But these systems require pumps, valves, and tubing – making them difficult to miniaturize.

This is where the work of Buse Aktaş, head of the “Robotic Composites and Compositions (RoCoCo) Group” at MPI-IS, comes in. Together with colleagues from ETH Zürich, Aktaş developed a way to jam and unjam magnetic particles using only wireless magnetic fields – no tubes or pumps required.

“We combined magnetic and non-magnetic materials into composite particles that can attract and cling to one another on demand,” explains Aktaş. “When the magnetic field is switched off, they easily fall apart. This reversible and programmable clumping allows us to remotely tune the mechanical properties of materials.”

In the paper published in Nature Communications on September 30, the team presented millimeter-sized, dice-shaped magnetic composite particles which they placed on a platform surrounded by magnetic coils. Depending on the composite design and the configuration of the magnetic field, the particles attract each other to form aggregates – along lines, surfaces, or throughout a volume. The resulting system enables structures to assemble, stiffen, relax, or break apart, all via magnetic control.

While the current prototypes are a few millimeters in size, the researchers aim to scale the system down to the micrometer level – starting with a deeper understanding of the fundamental physics behind magnetic jamming.

“Vacuum-based or other tethered actuation methods, such as electrostatic systems, don’t scale easily,” Aktaş explains. “But with magnetism, we can reduce the size of the building blocks while maintaining control over their behavior. This introduces a new strategy for achieving wireless, reversible mechanical control at small scales – offering a foundation for future tools in microrobotics, smart materials, biomedical systems, and micro-manipulation.”

Reference: Aktaş, B., Kim, M., Bäckert, M. et al.  Jamming with magnetic composites. Nat Commun 16, 8711 (2025).  https://doi.org/10.1038/s41467-025-63729-z