New phase changing material paves way for ‘squishy robots’

Engineers at the Massachusetts Institute of Technology (MIT) and Google owned Boston Dynamics have developed a new material capable of switching between soft and hard states.

Drawing parallels with the T-1000 in Terminator 2, the team behind the material say it could be used to give even low-cost robots the ability to switch states. A deformable surgical robot could travel through the body without harming organs or vessels. A search and rescue robot could use a soft state to squeeze through rubble and search for survivors.

But the challenge wasn't just to create a soft robot. In order to perform any meaningful task – opening a door, using a hammer - once at its destination, the robot has to become rigid. As Anette Hosoi, the MIT professor who led the project, says: “You can't just create a bowl of Jell-O, because if the Jell-O has to manipulate an object, it would simply deform without applying significant pressure to the thing it was trying to move.”

The solution was a combination of foam and wax. Foam because it can be compressed to a fraction of its original size and bounce back to its original shape once released. The wax is used to create a hard coating that can be heated to become pliable, and cooled again to harden. This could be achieved by running a wire along the wax and sending a current through to heat.

The approach yields another advantage: the material is self-healing. “If you push it too far and fracture the coating, you can heat it and then cool it, and the structure returns to its original configuration,” says Hosoi.

If it sounds surprisingly simple, it's because it is. The prototype was built by putting polyurethane foam into a bath of melted wax, before squeezing to encourage the foam to soak up the wax. Hosoi's former graduate student Nadia Cheng says: “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.”

The team then created a new version of their foam lattice prototype using a 3D printer. This afforded greater control over the positioning of struts and pores within the structure. It's more expensive to produce, but the researchers insist the initial version could still have applications in low-cost robotics.

Since developing the foam and wax material, Hosoi has moved on to more complex phase-changing materials for robotics, investigating the use of magnetorheological and electrorheological fluids. These are liquids containing suspended particles that can be made to switch between soft and hard states by using magnetic or electric fields respectively.

The project was commissioned by the Defense Advanced Research Projects Agency (DARPA) as part of its Chemical Robots programme and was a collaboration between MIT, Stony Brook University, the Max Planck Insitute for Dynamics and Self-Organization and robotics firm Boston Dynamics.

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