Self-amputation in nature has been an effective survival strategy for certain animals. The ability to shed parts of their body has allowed creatures like lizards and crabs to escape danger and continue moving forward.
Inspired by this, Yale roboticists have developed a technology that enables robots to selectively disconnect their limbs to free themselves from potential hazards, such as getting stuck under debris during search-and-rescue missions. This innovation also allows separate robots to join together and collaborate on tasks beyond their individual capabilities.
Central to this technology is a material called a bicontinuous thermoplastic elastomer, developed by the roboticists in the lab. This unique thermoplastic is initially a rubbery solid at room temperature but transforms into a liquid at approximately 284 °F. It is embedded within a foam-like silicone structure, which acts as a sponge, holding the thermoplastic in place when it turns into a liquid.
The process works as follows: Two silicone bodies are each coated with a layer of bicontinuous thermoplastic elastomer on their exposed surfaces. The foams are heated, causing the thermoplastic to melt into a liquid state, which is held in place by the silicone matrix.
When the two parts come into contact, the molten material combines to form a continuous liquid mass. As it cools and solidifies, it securely connects the two parts. When it’s time to disconnect, the joint is heated, causing the material to melt and weaken, allowing the two parts to separate easily.
“So if the robot is doing its normal operations and walking around the wild, but then something happens to one of its legs – a big rock falls on it, for example – normally the whole robot would be stuck if it were cast in whole,” said Bilige Yang, a Ph.D. student and the lead author of the work. “But because we have the ability to melt away and weaken this joint where the material is, the rest of the robot will be able to walk away without its amputated leg.”
Like lizards releasing their tail when attacked and crabs shedding injured limbs, the Kramer-Bottiglio lab draws inspiration from nature’s survival tactics. Ants, for example, can link up to form a bridge across gaps in the forest or come together to float on water. This adaptation from the natural world serves as the basis for innovative robotics.
In the lab, robotic devices are shown to be unable to cross a wide gap alone, prompting the exploration of collaborative strategies inspired by nature.
“If each individual robot tried to cross the gap, it would just fall through,” he said. “But if you have a few of them together, they can make it across. You can imagine this in different types of search-and-rescue missions where the robot will be able to navigate these types of scenarios much better.”
Next, the research team will utilize this technology in various other soft robots that they have created in the lab.
“Our material not only aids in robot survival – it enables dynamic shape-change,” Kramer-Bottiglio said. “Robotic modules can self-reconfigure into different morphologies to perform tasks that demand specific shapes and behaviors.”
Journal reference:
- Bilige Yang, Amir Mohammadi Nasab, Stephanie J. Woodman, Eugene Thomas, Liana G. Tilton, Michael Levin, Rebecca Kramer-Bottiglio. Self-Amputating and Interfusing Machines. Advanced Materials, 2024; DOI: 10.1002/adma.202400241
