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These Artificial Muscles Are Made of Onion Cells

Onion cells can expand and contract, which makes them good for muscles.

Scientists have found that artificial muscles built from onions, yes, onions, may be the most versatile structure of its kind ever made.

Research from scientists at National Taiwan University published Tuesday in the journal Applied Physics Letters has shown that artificial muscles created from onion cells can move in ways no other artificial muscle can. Although the research is in its early stages, artificial muscles could eventually be used in everything from robotics to artificial limbs.

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"This present artificial muscle is the first one made of vegetables," lead researcher Wen-Pen Shih told Motherboard in an email. "It can bend and contract simultaneously like human muscles, that other existing technology can not do."

A wide range of artificial muscle technology exists, including structures created from elastomers, shape memory alloys, and fishing lines. Shih said in this case, researchers hoped to engineer an artificial muscles with a better capacity for bending and stretching, so they chose the onion.

To create the structure, researchers used the onion's epidermis: the thin skin under the surface of the vegetable. The epidermis contains a layer of blocky cells arranged in a way that is especially conducive to versatile movement. Shih said they have not yet found any other plant materials that have the same effect and are as accessible as the onion.

"First of all, an onion is easy to obtain and easy to process," he said. "We can obtain a thin and single layer of onion cells by simply peeling the vegetable. The dimensions and latticed arrangement of the cells are just right to induce bending and contraction at the same time."

Image: Applied Physics Letters

Researchers removed the protein hemicellulose with acid to make the plant's cell walls more elastic, and coated the layer of skin with gold to make it more conductive to electricity. When they applied an electric field, researchers found high voltage caused the cells to contract and flex upwards while low voltage made them expand and flex downwards.

The technology could have applications in many realms, Shih said. He said the artificial onion could also induce acoustic waves to deliver sound, and could have robotic applications in the future. But for now, there's more research to be done, since they don't yet fully understand the mechatronic properties of onion cell walls. "We plan to dig into it so that we could probably develop a robust actuation," Shih said. To show off the fact that onions can actually behave like muscles, Shih and his team created a "gripper" that contracts to hold an object when electricity is run through it. "We demonstrated a gripper made of two pieces of onion muscles," he said. "This gripper can statically hold a small object when a voltage is applied."