Engineers from Chongqing University in Beijing have designed puck-shaped robots that simulate foraging for food in a similar fashion to bacteria and other organisms. The robots were released onto an LED screen where emitted light was adjusted to mimic the amount of consumable food. Once the resource was eaten, the robotic swarm then vacated the depleted area in search of more food. According to the team, the programmed behavior led to collective patterns that resembled several phases of matter, including liquid, crystal, and glass.
In nature, the term active matter denotes systems comprised of many elements that move on their own. Biological examples include bacterial colonies and birds' flocks, which researchers try to mimic with artificial active elements. Past experiments have utilized robots or self-propelled particles that move in response to some physical input, such as light or chemical concentrations. In the real world, however, the environment isn't an artificial test platform and constantly changes in response to organisms' activity within that environment.
The engineers have come close to replicating organisms' natural behavior in nature using tiny 8cm-wide hockey puck-looking robots equipped with wheels and light sensors attached underneath. The robots were programmed to move in response to light emitted from LEDs, always heading toward brighter light, in the direction in which the brightness increased the fastest. The researchers placed 50 of these robots on a 4x4m LED light platform outfitted with individually controlled pixels. The light underneath each robot was dimmed over a specific spatial region and for a chosen time duration, replicating how local resources are consumed and replenished. The robots responded to the dimming light by rolling by moving in the direction with the brightest light.
The team showed that the robots repel one another, as they are attracted to bot-free regions, where food (in this case, light) is more plentiful. They then researched these interactions' effects by designing a circular light environment, with its outer edges surrounded by darkness. In the beginning, the circular platform was large, and the robots responded by moving around randomly, like atoms in a gas. But as the researchers reduced the circle's diameter, the robots packed together into a hexagonal crystalline pattern like snowflakes, each surrounded by six neighbors. The depleted regions began to overlap with further shrinking, forming a uniform light landscape with no area brighter than the other. This smoothing of the landscape caused the crystal to "melt" into a liquid-like phase, followed by a disordered, glass-like phase, where the robots became locked in place as they contacted each other.
They then went even further by incorporating color sensitivity, where some robots preferring to feed on the red light, while others developed a taste for blue. Those color preferences could then be passed from one to another during robot-like reproduction. The engineers state these insights could be utilized to look at how cancerous tumor cells develop and how to mitigate their growth.