The 1991 film Terminator 2: Judgment Day depicted an incredibly advanced robot, the T-1000, made of virtually indestructible smart, reconfigurable material exhibiting remarkable features including rapid morphing, stiffness change, self-healing, infiltration through small structures. Through the lens of modern materials science, these characteristics collectively defined a “dream material” whose fundamental building blocks must possess unique capabilities, including distributed information processing and exchanging, active energy conversion, as well as adaptive interactions, etc. Engineering such building blocks is clearly beyond the 1990’s technology, but how far are we from that dream today?

Reconfigurability and multifunctionality is a growing trend in advanced materials, which play an important role in reducing the costs of manufacturing, transportation and degradation, as well as promoting scientific and technological progress. Although significant efforts have been made in developing novel building blocks such as DNA coated nanoparticles, Janus particles, key-lock colloids, etc., enabling distributed information processing (i.e., making the building blocks “intelligent”), which is key to the aforementioned “dream material” system, seems extremely challenging to achieve along the traditional path. 

From a completely different angle, the recent rapid development of the micro-electronics and machine techniques enables scalable manufacturing of “microrobots”--- those similar to the “Microbots” in the film Big Hero 6 --- individually simple structured, with some build-in broken symmetry and reversible binding, yet capable of distributed information processing to achieve highly complex and sophisticated collective tasks.  

In our paper, we demonstrated a proof-of-concept of such building block, which we referred to as “Magbots” --- a coin-sized micro-robot that spins and reversibly connects to each other via tunable magnets, and capable of sensing and responding to external light field for information processing and exchanging. The simple design of Magbots allows us to make thousands of such building blocks, a scale that is necessary to collectively exhibit behaviors of a “matter”. This heretofore largest micro-robot swarm, which is called “Robo-Matter” demonstrates a remarkable novel property of Robot-Matter duality --- the system can “melt” and “freeze” like H₂O, and in the meantime, it can transform, generate active forces, self-heal, infiltrate complex manifolds, carry cargos, and even play Ping Pong --- which are characteristics of complex robotic systems.

The rich spectrum of unique properties of the Robo-Matter enables a wide range of promising potential applications. For example, the liquid-like Robo-Matter can easily go over an obstacle, get through narrow channels, or dynamically adjust the internal structure, enabling the system to overcome complex terrains to reach the destinations and switch or retain its own shapes and functions. The controllable transition between liquid-like and active crystal states via external cues would enable the Robo-Matter system to perform a variety of tasks in complex environments. For example, carefully designed macro-scale Robo-Matter (each unit ~0.1m) could infiltrate into the ruins to rescue the victims and aid with post-disaster reconstruction, or explore underground caves to collect samples. Microscopic Robo-Matter (each unit ~1 μm) could help deliver targeted drugs, clear clogged blood vessels, or hunt down and kill targeted malignant cells or tissues in vivo.