Giving robots a “nose”

You might have heard of the analogy of the canary in the coal mine. Back in the old days, the miners took caged canaries to work. The canaries would die if there were dangerous chemicals such as carbon monoxide in the mine, and everyone would take that as a warning sign and leave.

What if they had machines that could sense the chemicals? No sacrifices would be needed. Everyone could stay safe.

This is what researchers at Carnegie Mellon University have been working on for years: developing soft robots that can sense and respond to chemical signals.

“A lot of the inspiration actually comes from looking at different kinds of species around us that can interact and respond to their surrounding environment in exciting ways,” said Kyle Justus, an alumnus of the mechanical engineering doctoral program. “The ones that always stuck out to me were the octopus and cuttlefish and how they can interact with their environment and camouflage themselves to hide from predators. The fact that these organisms have cells that can sense and respond to their surrounding environment and basically act as soft machines was really exciting to us.”

Inspired by the fascinating organisms in nature, Justus and his team decided to collaborate across biology, mechanical engineering, and robotics to build their ideal machine. The work was supervised by Carmel Majidi, an associate professor of mechanical engineering, and Philip LeDuc, a professor of mechanical engineering.

To gain further expertise in synthetic biology, the Carnegie Mellon researchers teamed up with Cheemeng Tan, an associate professor of biomedical engineering at the University of California, Davis. They became one of the first groups in the world to combine synthetic biology and soft robotics. Their findings were recently published in Science Robotics.

Together, the researchers have implemented engineered bacteria cells in a flexible gripper on the robot’s arm. These cells can respond to IPTG, a chemical that can unlock an engineered genetic circuit. Once that circuit is unlocked, the cells produce a fluorescent protein that functions as a signal.

But the tricky part was to help the robot understand that signal. “That was one of the hardest things we had to accomplish: how do you turn a biological signal into a signal that a robot can process?” said LeDuc.

Since robots usually pick up electronic signals, the researchers have built a flexible light-emitting diode (LED) circuit to convert biological to electronic signals. This LED circuit can detect and excite the fluorescent protein produced by the cells, thereby sending an electronic signal to the gripper’s central processing unit. In this way, the robot can make decisions about picking up or releasing items.

“The main goal we wanted to achieve with this is integrating a cellular system as a functional component within the larger soft system,” said Justus. “What we have in most living systems are largely soft organism-level architectures that rely on the smaller subcomponents—cellular systems—to sense and respond to different cues and maintain life. Obviously, we’re doing it in non-living systems, but we’re using living subcomponents and trying to increase device capabilities by relying on that existing biological hardware.”

So far, the researchers have run experiments with sensing chemicals in liquid media and hydrogels (polymer networks that can retain large volumes of water). For example, the gripper checked a laboratory water bath for IPTG and deployed an object in the bath after deciding that it was IPTG absent.

We are closer to future breakthroughs like soft biohybrid robots that can sense, feel, and move in response to their environment.

Carmel Majidi, Associate Professor, Mechanical Engineering

Of course, sensing IPTG in these media is just the first step. The researchers are planning to use the biohybrid system on swimming and crawling soft robots to monitor water quality by sensing different chemicals and collecting samples. They will explore these through a recent project funded by the National Oceanographic Partnership Program.

“By combining our work in flexible electronics and robotic skin with synthetic biology, we are closer to future breakthroughs like soft biohybrid robots that can adapt their ability to sense, feel, and move in response to changes in their environmental conditions,” said Majidi.

Aside from detecting chemical signals, synthetic bacteria could also be engineered for other functions, such as helping with repair or generating energy. Whether it’s isolating dangerous chemicals, sending out warnings, or making polymers for repairs, these biohybrid robots can improve efficiency and protect us from danger.