science tech in_theory robots biologically_inspired_engineering bio_bots medicine cyborg
Robots Powered by Rat Heart Cells to Deliver Drugs, Environmental Decontaminants

by Charles Q. Choi

A new biological robot or “bio-bot” made with cells from rat hearts can inch across surfaces like a caterpillar.

Future bio-bots could incorporate neurons to intelligently react to their surroundings.

"You can imagine a bio-bot that can look for toxins in water and then annihilate them," says researcher Rashid Bashir, a University of Illinois at Urbana-Champaign bioengineer. "They could sense where those toxins are, move toward them and release chemicals that neutralize them, helping in environmental cleanup."

The investigators developed bio-bots. Each less than a centimeter long, using 3-D printers that laid down layers of living cells and other materials on top of each other, much like ordinary printers would lay down layers of ink on paper. Scientists are increasingly using 3-D printers to manufacture a dazzling variety of robotic devices.

The researchers first used 3-D printers to create scaffolds for the living cells. These platforms were made of a hydrogel similar to the material used to produce soft contact lenses.

The 3-D printers extrude the scaffolds layer by layer, solidifying each with ultraviolet lasers before depositing the next. In the end, the scaffolds each resemble a stick of gum with a rectangular block sticking out from it.

Living cells from rat hearts are then printed onto the scaffold on either side of this rectangular block and immersed in a nutrient bath that keeps them alive for three to five days. These heart cells simultaneously contract, making the scaffold flex under them.

The rectangular block on the bio-bot’s scaffold does not sit directly in the device’s middle. Rather, it lies slightly closer to one of its ends. This ensures that one end or “leg” of the scaffold has more rat cells on it, meaning that it bends more than the other side when the cells contract. This asymmetry gives bio-bots directed movement. If the rectangular block were in the middle, both of the robot’s ends would bend equally, resulting in it essentially going nowhere.

The side of the bio-bot with more rat cells on it serves as its propelling leg, providing that it has enough friction to grip the surface it is moving on. The bio-bots can propel themselves forward at speeds up to roughly 236 microns per second. (The average human hair is about 100 microns wide.) This movement amounts to a little more than a half-inch per minute.

"The resulting actuation and movement is very promising, and we will work to improve the designs further," Bashir says. He and his colleagues detailed their findings online Nov. 15 in the journal Scientific Reports.

(Courtesy Vincent Chan)

The next step could involve tinkering with the bio-bot scaffolds to grant them novel capabilities. For instance, scientists could tailor the hydrogel that comprises the scaffolds to release certain molecules in response to any of a wide range of stimuli, such as acidity or temperature. These molecules might include vital nutrients or growth factors to keep the cells alive, or drugs that increase or decrease cell movements to alter bio-bot speed.

A more advanced form of control over the units could involve giving them neurons, Bashir says. For instance, researchers could engineer clusters of sensory neurons that can both monitor the environment and trigger bio-bot movements.

"What I find most interesting and exciting about this work is the potential to construct systems that are steerable and can be combined with other cell types to sense their environment and move in response to it," says bioengineer Roger Kamm at MIT, who did not take part in this research.

Bio-bots also could have a wide range of applications in the body or in the lab, Bashir says. For instance, bio-bots might help deliver life-saving medicines within a person, or be used to mimic organs like hearts to help test potential pharmaceuticals.

"The goal is to build biological machines using cells as building blocks," Bashir says.

He stressed that his team is still working on the technology. “What we have now are just building blocks for more complex systems that can eventually be used for the benefit of humankind,” he says.

Top Image: Courtesy Elise A. Corbin.

Charles Q. Choi
 has written for Scientific American, The New York Times, Wired, Science and Nature, among others. In his spare time, he has traveled to all seven continents, including scaling the side of an iceberg in Antarctica, investigating mummies from Siberia, snorkeling in the Galapagos, climbing Mt. Kilimanjaro, camping in the Outback, avoiding thieves near Shaolin Temple and hunting for mammoth DNA in Yukon.

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