A shape-shifting robot has been invented by MIT scientists. It can switch between soft and hard states, and was developed to fit in tight spaces and heal itself.  

The phase-changing material that gives the robot its ability to go from soft to hard and back again was developed by MIT mechanical engineering and applied mathematics professor Anette Hosoi and her former graduate student Nadia Cheng, alongside researchers from Stony Brook University and the Max Planck Institute for Dynamics and Self-Organization.

As the material would allow robots to squeeze through tight spaces, it has been envisioned for use in surgeries where the robots can move inside the body without damaging organs along the way to reach a certain point or in search-and-rescue missions where robots can squeeze through openings in rubble to look for survivors.

The squishy material takes inspiration from octopuses that can squeeze their bodies into tight spaces and then expand again once there is more room. The challenge, however, was to design the robot in such a way that it would still be able to exert force, allowing meaningful tasks to be performed.

To address this problem, researchers picked a material that is capable of switching between soft and hard states, choosing to coat a foam structure with wax. Foam was used because of its ability to retain its shape after being squeezed, while wax was chosen because it can go from hard to soft with some level of heating.

Aside from offering control over the state of the material, heating also makes it possible for the material to heal itself. Any damage it sustains can be repaired with a round of heating and cooling that allows the material to return back to its original state.

There were two forms of the material created for the research: one was polyurethane foam soaked in wax and the other was a 3D-printed version of the material. Researchers preferred the printed version because it allowed for greater control over each area and it made it possible for the wax coating to be replaced with something stronger, like solder.

Soft robotics like this isn't new, but the way to make a robot switch between two different states, most especially at a low cost, is. "A lot of materials innovation can be very expensive, but in this case you could just buy really low-cost polyurethane foam and some wax from a craft store," explained Cheng.

Harvard's Whitesides Research Group is developing fabric infused with wax that could also be potentially used to build self-healing robots.

The paper was published in the journal Macromolecular Materials and Engineering.

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