Researchers at Carnegie Mellon University are one step closer to creating biological-mechanical hybrid machines as they work to develop 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, who graduated with a Ph.D. from Mechanical Engineering earlier this year. “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 collaborated across biology, mechanical engineering and robotics. Carmel Majidi, an associate professor of mechanical engineering, and Philip LeDuc, a professor of mechanical engineering, supervised the work. Cheemeng Tan, a former fellow of CMU’s Lane Center for Computational Biology, and now an associate professor of biomedical engineering at the University of California, Davis, 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. The tricky part was to help the robot understand that information.

“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?” LeDuc said.

Since robots usually pick up electronic signals, the researchers built a flexible light-emitting diode (LED) circuit to convert biological data 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,” Justus said. “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.

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,” Majidi said.

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