The nice thing about us humans is that we're so soft. Water makes up about 50 percent of our body mass, allowing our muscles to be firm enough to practice karate, but squishy enough to pick up a delicate orchid.

Researchers from North Carolina State University have figured out a new technique for creating devices out of flexible, water-based material, which could serve as the foundation for soft muscle tissue for robots. Devices made of this material could be used underwater, increasing the versatility of future machines.

"This work brings us one step closer to developing new soft robotics technologies that mimic biological systems and can work in aqueous environments," said co-author Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State.

The artificial tissue is a hydrogel — a jelly-like mixture of water and organic polymers — with a copper wire embedded in it. The researchers found that shooting positively charged copper ions into hydrogel caused it to bend and stiffen due to interactions with the negatively charged ions in the polymer. They named this technique "ionoprinting".

"The bonds between the biopolymer molecules and the copper ions also pull the molecular strands closer together, causing the hydrogel to bend or flex," said co-senior author Dr. Orlin Velev, the INVISTA Professor of Chemical and Biomolecular Engineering at NC State.

"And the more copper ions we inject into the hydrogel by flowing current through the electrodes, the further it bends."

Reversing the flow of the electrical charge had the opposite effect of relaxing the material.

In this study, the researchers were able to construct flexible fingers from this new hydrogel that could bend around an underwater object and pick it up. Future applications may also include building tissue scafflolds for growing cells and organs in three dimensions.

Researchers have created a hydrogel "grabber" that can grasp and release objects. Credit: Orlin Velev.

Soft robots are an exciting engineering challenge for researchers across the globe, as it could yield life-like cyborgs. One group in Greece has developed a robot that swims with whippy octopus-like arms.

Source: Palleau E, Morales D, Dickey MD, Orlin D. Velev OD. Reversible patterning and actuation of hydrogels by electrically assisted ionoprinting. Nature Communications. 2013.