The researchers’ “bionic mushroom” combines a white button mushroom with 3D-printed clusters of cyanobacteria, which generate electricity, and graphene nanoribbons, which are used to collect the electrical current. Their bio-hybrid system, say the researchers, is part of a broader effort to better understand cells’ biological “machinery” and how to use it to fabricate new technologies and useful systems for defense, healthcare, and the environment.
“In this case, our system – this bionic mushroom – produces electricity,” says Manu Mannoor, an assistant professor of mechanical engineering at Stevens. “By integrating cyanobacteria that can produce electricity with nanoscale materials capable of collecting the current, we were able to better access the unique properties of both, augment them, and create an entirely new functional bionic system.”
Previously, the use of cyanobacteria to produce electricity in bioengineered systems has been limited due to the microbes inability to survive long on artificial bio-compatible surfaces. The researchers wondered if a surface already rich in microbiota, such as that of a mushroom, could provide the right environment – i.e., nutrients, moisture, pH, and temperature – for the cyanobacteria to produce electricity for a longer period.
In experiments, they showed that cyanobacterial cells lasted several days longer when placed on the cap of a white button mushroom versus a silicone and dead mushroom as suitable controls.
“The mushrooms essentially serve as a suitable environmental substrate with advanced functionality of nourishing the energy producing cyanobacteria,” says Sudeep Joshi, a postdoctoral fellow in Mannoor’s lab. “We showed for the first time that a hybrid system can incorporate an artificial collaboration – or engineered symbiosis – between two different microbiological kingdoms.”
To create their “bionic mushroom,” the researchers first used a robotic arm-based 3D printer to print an electronic “ink” containing the graphene nanoribbons. This printed branched network, say the researchers, serves as an electricity-collecting network on top of the mushroom’s cap by acting like a nanoprobe to access bio-electrons generated inside the cyanobacterial cells.
They then printed a “bio-ink” containing cyanobacteria onto the mushroom’s cap in a spiral pattern, intersecting with the electronic ink at multiple contact points where electrons can transfer through the outer membranes of the cyanobacteria to the conductive network of graphene nanoribbons. Shining a light on the mushrooms activates cyanobacterial photosynthesis, generating a photocurrent.
The researchers showed that the amount of electricity the bacteria produce can vary depending on the density and alignment with which they are packed – the more densely packed together they are, the more electricity they produce. With 3D printing, it was possible to assemble them so as to boost their electricity-producing activity eight times more than the casted cyanobacteria using a laboratory pipette.
The researchers say they are the first to not only geometrically pattern 3D printed bacterial cells to augment electricity-generating behavior, but also to integrate it to develop a functional bionic architecture.
“With this work, we can imagine enormous opportunities for next-generation bio-hybrid applications,” says Mannoor. “For example, some bacteria can glow, while others sense toxins or produce fuel. By seamlessly integrating these microbes with nanomaterials, we could potentially realize many other amazing designer bio-hybrids for the environment, defense, healthcare, and many other fields.”
For more, see “Bacterial Nanobionics via 3D Printing.”
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