Stanford University mechanical engineers have developed a vine-like robot that is able to grow over long distances without moving its whole body, giving it the potential to be used in intelligence gathering, surveillance, search and rescue, and medical applications.

Researchers Allison Okamura, Stanford professor of mechanical engineering, and Elliot Hawkes, a visiting professor from the University of California-Santa Barbara, say vines, fungi, and nerve cells that are able to cover distances by growing inspired the robots development.

Hawkes says he watched an ivy plant on his bookshelf grow around a corner and seek sunlight at the same time he was working on pneumatic artificial muscles in the lab. "I was able to modify the standard stretching behavior to get tip-based extension," he says, "and when I attempted to grow an early prototype through the complete mess that is my desk, it easily passed through the clutter."

Hawkes notes the mechanism of the robot's extension is based on unfurling an inverted, thin-walled tube. When pressurized, the tube everts at the tip, much like a sock being turned inside out, he says.

"To this simple concept, we add the ability to steer by controlling the relative lengths of the two sides," he points out. "This can be done autonomously by the robot using feedback from the camera at the tip or can be done by a person driving the robot by looking at the camera feed."

Okamura points out the kind of growing robot she and Hawkes developed represents a new paradigm for mobility in robotics.

"While many bio-inspired and plant-like robots have been developed before, the extent and speed of growth achieved by our approach is new," Okamura says. "Our approach is part of the burgeoning field of soft robotics, which takes advantage of flexible materials in order to change shape and access locations not reachable by traditional robots."

Hawkes says the robot has been tested in challenging environments, such as moving across extremely sticky flypaper, through wet glue, over ice and water, through fire, and through a forest of nails.

"The base of the robot, with all the fragile components, like computation and control, stays put and safe," he says, "while only the much simpler, more robust tip 'grows' into the challenging environments. You could hold the body of the robot tightly or step on it, and it could keep growing."

The device can be small and portable but able to grow hundreds of times its initial length, Hawkes notes, which bodes well for the focus of their work on search and rescue.

"We imagine the robots could grow through rubble and debris, potentially searching for survivors," he says. "Unlike small animal-inspired search-and-rescue robots, the body of the growing robot could act as a conduit to pass oxygen or water to a trapped survivor. We also showed the robot bodies could apply significant forces to the environment, in one case lifting a 70-kilogram [about 154 pounds] crate, which could enable the robots to help free trapped victims."

Hawkes says the research team is exploring new, more robust materials for the body, such as rip-stop nylon and Kevlar. 

"We also are looking to develop surgical applications," he adds, "hopefully moving to in vivo testing in the near future."

Photo courtesy of Stanford University