Researchers develop self-forming robotic material

The work, which takes inspiration from embryonic development, represents a step towards creating adaptable, self-assembling robotic structures.

Matthew Devlin, lead author of a paper published in Science and a former doctoral researcher in UCSB’s mechanical engineering department, explained: “We’ve figured out a way for robots to behave more like a material.”

The robotic system is composed of individual, disk-shaped autonomous robots resembling small hockey pucks. These units can assemble into various formations, displaying different material properties. The key challenge the researchers aimed to overcome was designing a system that could be both strong and stiff yet capable of flowing into new configurations when needed.

Unlike traditional robotic systems that respond to external forces, this robotic material reacts to internal signals to reshape itself. UCSB professor Elliot Hawkes, who supervised the project, described the objective: “The material should be able to take a shape and hold it, but also be able to selectively flow itself into a new shape.”

Learning from nature: embryonic development as a blueprint

The researchers turned to biology for inspiration, particularly the work of Otger Campàs, a former UCSB professor now leading the Physics of Life Excellence Cluster at TU Dresden. His research on embryonic tissue revealed that developing organisms exhibit unique material behaviours.

“Living embryonic tissues are the ultimate smart materials,” Campàs said. “They have the ability to self-shape, self-heal and even control their material strength in space and time.”

The disk-shaped robots with gears along their exterior to enable them to push against and move around each other (Photo Credit: Devlin, et al/Science)

His laboratory at UCSB previously discovered that embryos can transition between fluid and solid states – a process known as rigidity transitions. This enables cells to reorganise themselves and form distinct structures such as limbs and organs. The researchers identified three key biological mechanisms behind this transformation:

• Active forces – cells applying movement forces on one another
• Biochemical signalling – coordinating movement in space and time
• Cell adhesion – binding together to maintain structural integrity

By translating these principles into robotics, the team created a system that could change shape dynamically.

Engineering robotic materials

In the robotic material, the equivalent of intracellular forces comes from eight motorised gears along each unit’s circular exterior. These gears allow robots to push off one another and navigate tightly packed spaces. Meanwhile, the robots’ equivalent of biochemical signalling is a global coordination system using light sensors and polarised filters.

“Each cell ‘knows’ its head and tail, so then it knows which way to squeeze and apply forces,” Hawkes explained.

By shining light on the robots, researchers controlled their movements, directing them to change shape as needed. Devlin added: “You can just tell them all at once under a constant light field which direction you want them to go, and they can all line up and do whatever they need to do.”

For adhesion, the researchers incorporated magnets into each robot’s perimeter. These magnets could be switched on or off, allowing the collective to bind together or separate as necessary.

The researchers sought to duplicate certain mechanical functions of cells with their disk-shaped robots (Photo Credit: Devlin, et al/Science)

The role of signal fluctuations

One key discovery was the role of signal fluctuations in shaping the robotic material’s behaviour. Campàs noted: “We had previously shown that in living embryos, the fluctuations in the forces that cells generate are key to turning a solid-like tissue into a fluid one. So, we encoded force fluctuations in the robots.”

By adjusting both inter-unit forces and signal fluctuations, the team found they could control whether the collective remained rigid or fluid. Devlin explained: “Basically, as you increase both of those, especially fluctuations, you get a more flowing material. This allows the collective to change shape. Once in formation, switching off the force fluctuations rigidifies the collective again.”

This approach also proved energy-efficient. Rather than keeping the system active at all times, fluctuations allowed the robots to adjust their shape using less power. Hawkes highlighted the significance of this finding: “It’s an interesting result that we did not set out looking for, but discovered once we started gathering data on the robot behaviours.”

The ability to shift between solid and fluid states efficiently could have applications in fields ranging from robotics and materials science to medical technology.