'Robot blood' powers machines for lengthy tasks

The researchers have created a synthetic vascular system capable of pumping an energy-dense hydraulic liquid that stores energy, transmits force, operates appendages and provides structure, all in an integrated design.

"In nature we see how long organisms can operate while doing sophisticated tasks. Robots can't perform similar feats for very long," said Rob Shepherd, associate professor of mechanical and aerospace engineering at Cornell. "Our bio-inspired approach can dramatically increase the system's energy density while allowing soft robots to remain mobile for far longer."

Shepherd, director of the Organic Robotics Lab, is senior author of "Electrolytic Vascular Systems for Energy Dense Robots," which published June 19 in Nature. Doctoral student Cameron Aubin is lead author.

The researchers tested the concept by creating an aquatic soft robot inspired by a lionfish, designed by co-author James Pikul, a former postdoctoral researcher, now an assistant professor at the University of Pennsylvania. Lionfish use undulating fanlike fins to glide through coral-reef environments.

Silicone skin on the outside with flexible electrodes and an ion separator membrane within allows the robot to bend and flex. Interconnected zinc-iodide flow cell batteries power onboard pumps and electronics through electrochemical reactions. The researchers achieved energy density equal to about half that of a Tesla Model S lithium-ion battery.

The robot swims using power transmitted to the fins from the pumping of the flow cell battery. The initial design provided enough power to swim upstream for more than 36 hours.

Underwater soft robots offer tantalizing possibilities for research and exploration. Since aquatic soft robots are supported by buoyancy, they don't require an exoskeleton or endoskeleton to maintain structure. By designing power sources that give robots the ability to function for longer stretches of time, Shepherd thinks autonomous robots could soon be roaming Earth's oceans on vital scientific missions and for delicate environmental tasks like sampling coral reefs. These devices could also be sent to extraterrestrial worlds for underwater reconnaissance missions.

The work was supported by the Office of Naval Research. Co-authors include Lynden Archer, the James A. Friend Family Distinguished Professor of Engineering in the Smith School of Chemical and Biomolecular Engineering; Snehashis Choudhury, currently a postdoctoral researcher at Stanford; and doctoral candidate Rhiannon Jerch.