How Squishy Materials Could Build Better Shape-Shifting Robots

MIT researchers developed a phase-changing material that can make robots both soft and rigid when you need them to be.

The 3D-printed scaffold material. Image courtesy MIT

If someone asked me to imagine a robot, the first thing to spring to mind would likely be a metallic humanoid. It would almost definitely be something solid, probably shiny, and filled with artificial intelligence circuitry.

But the term “robot” is of course much broader than Hollywood would have us believe, and there are great advantages to robots that are a bit more flexible than your stereotypical tin man. Researchers at MIT have been developing a material for robots that goes squishy when heated, or as their paper published in the journal Macromolecular Materials and Engineering puts it, is “thermally tuneable.”

The point is that squishy things can squeeze into tight spaces. Navigating uneven terrains is something our current robots are notoriously bad at, but is a necessary skill for some of the most hyped applications for robotics like navigating rubble in disaster zones or, on a smaller scale, wiggling through the body for surgical manoeuvres. 

But unlike other soft robotics, such as MIT’s creepy “Glaucus” roboslug, it can also go rigid, making it something of a shapeshifter. “The idea is that the robot should be soft in situations where we want to conform to the environment or squeeze through tight spaces, but we also would need it to be rigid when we need to apply loads on the environment so we can adequately push against objects and that sort of thing,” explained lead author Nadja Cheng in a video.

Like many of the most dexterous robots we’ve seen, both soft and hard, the material takes inspiration from the world of nature; the researchers compared it to a mouse in their video and to an octopus in the MIT release, because of the way it can contract and expand in accordance to its environment. There’s also the inevitable Terminator reference, comparing their creation to the morphing, liquifying T-1000 robot in the second movie.

The material they came up with to emulate this action is a phase-changing material, meaning it can change state in response to some sort of external stimulation. They developed the material as part of a DARPA program and worked on it with Google-owned robotics company Boston Dynamics, but despite the high-end backing it’s pretty low-tech, essentially consisting of some foam coated in wax. 3D-print that into a lattice structure and it’s probably not too difficult to make your own low-cost squashable toy. 

The idea is that the wax can act as a hard shell but, when heated, goes soft—so you can squish the foamy structure. They suggest you could do this by connecting a wire to the material and applying a current to heat up. To cool it down again, you’d just flick the switch off. 

A further plus-point for the material is that it’s self-healing to some degree. “Preliminary studies indicate that the composites exhibit self-healing properties, in which heating between loading cycles can mend wax that has been plastically deformed,” the authors wrote. So push it too far, and you might just be able to melt it back into shape. 

As soft robotics continue gaining steam and our understanding of what a robot is expands beyond solid metal men, the future may in fact be somewhere in between.