Bacteria help robot to get a grip

A robot with a handful of E.coli can do things other robots can’t. Mark Bruer reports.

Fluorescent proteins expressed by bacteria on the bacteria-operated robotic gripper.

Justus et al., Sci. Robot. 4, eaax0765 (2019)

Scientists have equipped a robot with sensors powered by genetically engineered bacteria, enabling it to make decisions appropriate to its environment.

The project shows how living cells can equip robots with added functions without adding great design complexity.

It is a step forward in so-called soft robotics, which uses soft materials to create compliant, lightweight systems matching the flexibility and versatility of natural biological tissues and organisms.

To date the building blocks of soft robots have largely been polymers, fluids, metal alloys, and other inorganic materials.

But Kyle Justus and colleagues at Carnegie Mellon University, Pittsburgh, US, added an organic layer containing trapped Escherichia coli bacteria into their 3D-printed soft robotic gripper.

That’s right: e.coli, more commonly associated with bad food and faeces, but here a technical marvel.

But then, this was no ordinary e.coli. This bacterial strain was genetically engineered to respond to the presence of particular chemicals by quickly releasing a fluorescent protein.

The light from these proteins was in turn detected by a flexible LED circuit embedded in the gripper, which sent information to a central processing unit (CPU) controlling the robot, letting it know that the target chemicals were present.

This approach addressed one of the fundamental challenges of integrating biological cells with the internal electronics of robots: how can they be made to talk to each other? The answer is light.

Another challenge was finding a method to allow biological cells to react with the environment, but not escape into it. This was achieved by containing the e.coli behind a super-thin flexible membrane that chemicals could pass through, but not cells.

In a pick-and-place task, the bacteria helped the robot make decisions. The scientists attached the gripper to a robot arm programmed to lower the gripper into a bath.

If the bath contained a widely used chemical named IPTG, which the e.coli had been engineered to respond to, the robot was programmed to do nothing. But if the bath contained no IPTG, then the gripper would pick up a target object and place it in the bath.

Justus writes that robots using this method could someday be used in agriculture or medicine, where many procedures depend on the detection of chemical cues in the environment.

“This integrated approach allows for truly autonomous robotic functionality in which grasping tasks are performed following decisions based on external stimuli that are detected and photonically transmitted by embedded synthetic cells.

“The next generation of soft robotic systems will be tremendously enhanced by integrating synthetic biology and soft materials.”

The researchers now want to engineer the bacteria for faster responses and a longer lifespan.

The research report is published in Science Robotics.

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Mark Bruer is a freelance journalist based in Adelaide, Australia. He is a former Features Editor of The Age newspaper in Melbourne, and Online Editor of The Australian and in Sydney.
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