Watch a Hydrogel Robotic Hand Gently Catch and Release a Fish

The soft, transparent material is both gentle and firm, a quality that could make it ideal for manipulating tissues and organs during surgeries.

Xuanhe Zhao and Hyunwoo Yuk didn't start out with the intention of making invisible robots. Zhao, an associate professor of mechanical engineering and civil and environmental engineering at MIT, and Yuk, a graduate student there, had merely been experimenting with materials made from polymers and water.

But over time, after varying the mixtures, they developed a highly durable and flexible hydrogel. It didn't take long for Zhao and Yuk to realize that the hydrogel they created could be used to make soft, transparent robots.

This week in the journal Nature Communications, Zhao and Yuk present their transparent, gel-based robot, which is capable of performing a variety of vigorous actions, such as kicking a ball underwater, but which can also operate more gently than the human hand.

"We didn't think of this kind of [soft robotics] project initially, but realized maybe our expertise can be crucial to translating these jellies as robust actuators and robotic structures," Yuk said in an interview with MIT News.

This particular design also has the potential to transform the way surgeons perform their handiwork.

"Hydrogels are soft, wet, biocompatible and can form more friendly interfaces with human organs," Zhao said. "We are actively collaborating with medical groups to translate this system into soft manipulators such as hydrogel 'hands,' which could potentially apply more gentle manipulations to tissues and organs in surgical operations."

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Zhao and Yuk used 3-D printing and laser cutting to construct their hydrogel robots. The hydrogel was inserted into robotic structures and bonded to flexible tubes connected to external pumps.

Pumping water through the tubes causes the hydrogel to bend an flex.

Their group designed several models, including one with a fin, another with an appendage that makes a kicking motion and a version that is soft and hand-shaped that makes a gentle grasping motion. In the video below, the nearly invisible robotic hand loosely closes around the fish and then releases it.

WATCH: Hydrogel Robotic Hand Catches and Releases a Fish

The material's transparency is due, in part, to its optical and acoustic properties, which are equal to those of water.

"[The robot] is almost transparent, very hard to see," Zhao told MIT News. "When you release the fish, it's quite happy because [the robot] is soft and doesn't damage the fish. I imagine a hard robotic hand would probably squash the fish."

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