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Foam/Wax Material Adapted for Shape-Changing Robotics

Anette Hosoi

Anette Hosoi (Arthur Petron, MIT)

14 July 2014. Engineers at Massachusetts Institute of Technology developed a process for combining foam and wax materials into components that allow robot devices to become pliable for changing their shape, yet return to a rigid state when needed to do their tasks. The team from the lab of mechanical engineering professor Anette Hosoi, with colleagues from Max Planck Institute for Dynamics and Self-Organisation in Germany and Stony Brook University in New York, published its findings online on 30 June in the journal Macromolecular Materials and Engineering (paid subscription required).

The researchers were seeking a technology to would allow creation of robotic devices that can squeeze through small spaces, even inside the body. Yet the devices would also need to retain their strength and rigidity to apply pressure to objects in their environment to perform their tasks. In addition, a rigid state is also more desirable for predicting and controlling movements of the robot.

To meet these seemingly contradictory properties, the team started with open-cell polyurethane foam that could be squeezed down to a fraction of its original size. To provide the stiffness and rigidity, the researchers coated the foam with wax. In order to switch the pieces from rigid to soft and pliable, the pieces were wired to allow an electric current to flow through the supporting matrix, with the heat from the current melting the wax.

Melting the wax also provides a repair function. “This material is self-healing,” says Hosoi in an MIT statement, “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.” Cutting off the current then allows the wax to cool and revert back to its original rigid state.

By using commonplace materials, like polyurethane foam and wax, Hosoi and colleagues kept the cost of their process to a minimum, but it restricted their ability to precisely define the properties of the new material. The team found it could gain more control over the materials’ qualities by 3-D printing the foam structure to determine the position of struts and pores.

Hosoi’s lab plans to test more robust coatings, such as solder, and investigate unconventional materials, such as liquids with suspended particles that respond to electric current or magnetic fields.

In the following video, Hosoi and first author Nadia Cheng tell more about and demonstrate the materials.

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