New material for shape-shifting robots

In what may revolutionise surgical robotics technology, researchers have now developed a phase-changing material built from wax and foam that is capable of switching between hard and soft states.

The material - developed by Anette Hosoi, a professor of mechanical engineering and applied mathematics at Massachusetts Institute of Technology (MIT) in the US, and her colleagues - could be used to build deformable surgical robots.

"This material is self-healing," said Hosoi.

"So 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," she added.

Working with US-based robotics company Boston Dynamics, the researchers began developing the material as part of the Chemical Robots programme of the Defense Advanced Research Projects Agency (DARPA).

To build a material capable of shifting between squishy and rigid states, the researchers coated a foam structure in wax.

The wax coating, meanwhile, can change from a hard outer shell to a soft, pliable surface with moderate heating.

This could be done by running a wire along each of the coated foam struts and then applying a current to heat up and melt the surrounding wax. Turning off the current again would allow the material to cool down and return to its rigid state.

In addition to switching the material to its soft state, heating the wax in this way would also repair any damage sustained, Hosoi noted.

To build the material, the researchers simply placed the polyurethane foam in a bath of melted wax.

They then squeezed the foam to encourage it to soak up the wax.

The study appeared in the journal Macromolecular Materials and Engineering.