Organic Machines Mix Animal, Robot Parts

A new device uses muscle and skin tissue from the California sea slug to build swimming bot.

Bio-engineers have used muscle tissue from rats, mice, as well as some birds to construct part-living, part-mechanical "organic machines," but now they've turned to the lowly sea slug as a model for an ocean-exploring robot.

In a new research paper, the scientists extracted a muscle from the animal's feeding apparatus (an organ that grabs food), and combined with robot arms to make a small swimming device.

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"When we stimulate the muscle, the robot moves forward," said Vickie Webster, a doctoral student at Case Western Reserve University in the department of mechanical and aerospace engineering. "We are taking tissue as well as collagen from the skin of the sea slug to make living machines. In this paper we focused on the material aspects of the sea slug and what we can make with it."

Webster and colleagues will present their findings next month at the "Living Machines" conference in Edinburgh. She chose the California sea slug (Aplysia californica) because it can withstand cold ocean temperatures as well as more moderate water found in coastal tide pools.

"They experience large changes in temperature and that makes their cells very robust," Webster said.

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The team removed collagen cells from the animal's skin and used it to fabricate gels and scaffolds for the device. Muscle from the mouth was used as an organic actuator to move the 3D-printed polymer arms back and forth.

"Collagen is the mortar of a body, while cells are the bricks," Webster said. "We took material from the skin and fabricated it to make a scaffold. These are structures that we can use to grow cells inside."

The team built a robot body that has two arms and a tail. Twelve muscles connected between body and arms allow the biohybrid robot to scoot backwards and push the body forward.

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In the future, such biohybrid "organic machines" could be used to explore the oceans for lost objects -- like a black box recorder for example -- because they need little power and can withstand the tough environmental conditions that often corrode regular steel-and-silicon robots.

Because the sea slug has big cells and big neurons, it's easy to work with, according to Hillel Chiel, a biology professor at Case Western who worked on the project. He foresees controlling a squad of biohybrid robots with a brain-computer interface.

"Because the neurons are large and generate large electrical signals, interfacing isn't as hard as with a brain that has hundreds of million of small neurons," Chiel said. "The idea of creating arrays of [biohybrid devices] that could interact is quite reasonable. It's still a challenge, but not insurmountable."

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Adam Feinberg, associate professor of materials science and biomedical engineering at Carnegie Mellon University, likes the idea of a sea slug-based machine.

"In an actual animal, you have a circulation system, an immune system and skin," he said. "These are things that are still not simple to replicate."

Mellon said it may still be a ways off before these simple laboratory-based devices are ready to march across the tundra or explore deep oceans.

"There are lots of advantages of these devices," he said. "Their energy stored in sugar in muscles. It's a lightweight source and you don't need lots of power. The challenge is how do you make it robust and function outside of an organism."

For his part, Feinberg is going forward with his own research. He's designing artificial human tissue that can be one day used to replace prosthetic limbs or damaged body parts.