Light-activated tissue inspires dream of squirming robots

By Meghan Rosen

Web edition: September 18, 2012
Print edition: October 20, 2012; Vol.182 #8 (p. 10)

Artificial muscle tissue that recoils when hit with a burst of light could one day be used to build soft-bodied robots that can be guided by light.

The light-sensitive tissue could also be used to test new drugs that target muscle-wasting diseases, says Mahmut Selman Sakar of ETH Zurich. The findings are slated to appear in an upcoming issue of the journal Lab on a Chip. Sakar and colleagues first reported their work August 21 on the publication's website.

The work is “a neat step forward,” says bioengineer Hang Lu of the Georgia Institute of Technology, although Lu notes that making a light-controllable robot might still be a long way off.

Sakar and colleagues at MIT teamed up with scientists at the University of Pennsylvania to genetically engineer mouse muscle cells that twinge in response to light. The researchers loaded the cells with a light-activated protein, let the cells fuse into fibers, and mixed them with a special gel to form 3-D strips smaller than the width of a grain of rice. Then, they hit the strips with narrow beams of blue light.

Only the light-zapped fibers jumped; those in the dark stayed still. “I was hoping it would work, but the first time I saw it, it was amazing,” Sakar says. “I was very, very excited.”

Sakar and colleagues even got the muscle fibers to show off a bit of brawn. Tissue strips stretched between two tiny elastic posts pulled the structures together when scientists switched on the light.

Burly tissues with controllable fibers could help researchers make muscle-bound robots that crawl along the ground like worms, Sakar says. These wormbots could wiggle over dirt, scouting out toxic chemicals in the environment with built-in sensors.

The itty-bitty biological machines would have to carry a light source to turn on their muscles. But other research groups are working to merge LED lights onto elastic sheets that could ride atop a wormbot’s muscles like skin, Sakar says.

The real challenge would be making the bots bigger: If the muscles strips got much thicker than the ones Sakar and his colleagues have created, oxygen and nutrients wouldn’t be able to pass into the tissue to power its contractions. That means a beefed-up robot would need something like a blood vessel system to carry fuel through its body. Another problem, Sakar says, would be getting light to penetrate opaque chunks of tissue.

Though building a big, strapping muscle bot may not be possible for decades, mini robotic glow worms may be able to wriggle outside much sooner. “Maybe 10 years,” Sakar says. “I’m actually very optimistic.”