Video: Under the spell of magnetic force, this robot can liquify, flow out of its prison, and then regenerate its body shape in a mold. © Wang and Pan et al.
Clever play with the melting point: Researchers have developed a metallic material that can be used to form magnetically controllable robots that can switch reversibly between the liquid and solid state. They illustrate this, among other things, by allowing a doll made of the material to escape from a prison in a liquid way. They also show that their so-called "magnetoactive solid-liquid phase transition machines" could perform medical and electrical engineering tasks.
Robotics is booming: Numerous research teams are currently working on sophisticated systems with different characteristics and for different areas of application. There are two basic concepts: In addition to constructions made of hard materials, electronics and motors, soft robotics relies on flexible structures and alternative control systems. While the traditional robots are stiff and inflexible, the soft versions have the opposite problem: they are gentle and adaptable, but weak and difficult to control. A combination would be ideal. This idea forms the basis of the work of a Chinese-US research team. Their concept is not based on combinations of hard and soft materials, but on induced phase transitions of a newly developed material.
Magnetic microparticles make it possible
The basic substance is the metal gallium, which has a very low melting point: it changes from a solid to a liquid state at just 29.8 degrees Celsius. For the development of their robotic material "Magnetoactive Phase Transitional Matter" (MPTM), the scientists embedded neodymium-iron-boron microparticles in the gallium. "These magnetic particles serve two purposes," explains co-author Carmel Majid of Carnegie Mellon University in Pittsburgh. Under the influence of magnetic fields, structures made of the material can be moved precisely as if by magic and thus used as robots for tasks. "The other task of the particles is to make the material receptive to an alternating magnetic field so that you can heat it up by induction and bring about a phase change," says Majid.
According to the researchers, their development differs from existing phase-change materials that rely on heat guns, electric currents, or other external heat sources to effect a solid-to-liquid transition. The new material is also characterized by favorable flow properties, say the scientists: other phase-changing materials are much more viscous in their molten state.
Medical and electrotechnical potential
The researchers have now been able to impressively demonstrate the potential of their material through experiments: Controlled by magnetic fields, they allowed differently shaped MPTM structures to climb over walls and jump over ditches. In the liquefied state, the droplets can also be guided in a targeted manner. They can even be split in half to move other objects together. The scientists illustrate the potential of the concept particularly impressively with a small “gimmick”: they let a robot in the shape of a LEGO man seep through a grid. Freed from prison, the mass then flows into a mold from which the LEGO man rises again after it has cooled and moves under the spell of the magnetic field.
"But the material system could also be used to solve specific medical and technical problems," says co-author Chengfeng Pan of the Chinese University of Hong Kong. To illustrate this, the scientists used their concept to remove a foreign body from a model stomach. An MPTM structure flows around the object after it has liquefied and thereby captures it. The connection can then be transported out of the model stomach by magnetic force.
Video: An MPTM robot removes a foreign body from a model stomach. © Wang and Pan et al.
In another experiment, the researchers are also demonstrating the technical potential of the electrically conductive substance. First, two MPTM structures move an electronic component to a desired location with electrical contacts. The researchers then melt the robots so that they automatically solder the component into the electronics.
Video: Two MPTM robots transport and solder an electronic component. © Wang and Pan et al.
"What we are presenting here is for demonstration purposes as part of a proof of concept," says Majidi. "Future work should now further explore which possible applications are available for this robotic system," says the scientist.
Source: Cell Press, Article: Matter, doi: 10.1016/j.matt.2022.12.003