Miniature robots can act collectively to perform tasks like supporting weight. Brian Long/UCSB
Smart materials can change their shape or form in response to external stimuli, making them indispensable for many applications, including health equipment and automobiles, among others.
Now, a research team led by scientists from UC Santa Barbara and TU Dresden has developed a material-like robot collective that behaves like a smart material, capable of changing shape and transitioning between fluid and solid states.
The collective of robots can perform these functions while maintaining cohesion, supporting substantial weight, and even self-healing.
The researchers were inspired by biological processes in embryonic development.
During embryonic development, a collection of seemingly simple cells transforms into tissues and organs through coordinated movements and changes in mechanical properties.
In a press release, one of the study’s co-authors, Prof. Otger Campàs, explained, “Living embryonic tissues are the ultimate smart materials. To sculpt themselves, cells in embryos can make the tissues switch between fluid and solid states.”
Replicating biological processes
To replicate the fluidity and movement of the embryonic cells, the researchers identified three biological processes occurring during embryonic development—fluidization, polarization, and adhesion.
Embryonic tissues are capable of switching between a fluid-like and solid state due to the internal forces in the cells. This allows them to move past each other, as a fluid does, and reorganize and stabilize like a solid.
The polarization process allows embryonic cells to orient in a certain direction, allowing directional forces to be applied accordingly. In other words, the cells can arrange themselves such that forces can be applied in an organized, directional manner rather than randomly.
Finally, embryonic cells maintain connections or adhesion with their neighbors even while rearranging, eventually providing structural strength once the organs are formed.
These three processes were key to developing a robot collective capable of rearranging and forming complex shapes.
Implementing a robot collective
Each robot in the system is a circular disc, like a hockey puck, five centimeters wide. The robots are powered by an internal lithium-ion battery, providing 30 minutes of continuous operation.
Eight gears run along the perimeter of the robots to facilitate movements against each other by pushing against each other. Additionally, rotatable magnets embedded around the perimeter maintain adhesion with the neighbors.
Each robot is equipped with a light sensor with polarized filters on top that can detect the direction of the polarized light, which tells each robot which way to rotate its gears. Polarized light is light waves that vibrate in a particular direction and not all directions.
Each robot is programmed on two parameters—the direction of the polarized light, which tells them which direction to move in, and the intensity of the polarized light, which controls how forcefully to move and how much to fluctuate those forces.
The programming creates the “if-then” ruleset (if light comes from this direction with this intensity, then move this way). This creates a flexible control system where the researchers can guide the collective behavior without needing to program new instructions for each desired movement or shape.
Think of it like a school of fish, where the movement of each fish determines the school’s behavior.
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The 20-robot collective impressively transitioned between solid and fluid states through controlled light intensity fluctuations. Surprisingly, these fluctuating signals improved efficiency over steady signals.
In demonstrations, two groups of robots could stretch toward each other and connect in the middle to form a bridge capable of bearing five kilograms, while other arrangements could bear an adult human weighing up to 70 kilograms.
The collective could flow around objects, form shapes like wrenches, and repair defects.
While reminiscent of the shape-shifting T-1000 robot from Terminator 2, researchers emphasize this is only a first step toward adaptive materials previously seen only in science fiction.
The study is published in the journal Science.
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Tejasri Gururaj Tejasri is a versatile science writer dedicated to making complex research accessible and engaging for all. She earned her Master’s in Physics from NIT Karnataka, giving her a strong foundation for translating intricate scientific concepts into clear insights.
