A new source of electrical energy

It sounds like something from the 1960s, but the “bionic mushroom” could be a tantalising glimpse of the future.

US researchers have generated electricity from a mushroom using energy-producing bacteria, an electrode network, and a 3D printer.

And while there wasn’t enough charge to actually power anything, they say it showcases the potential to engineer a mutually beneficial artificial symbiosis between “different species from the biological microworld to realise functional bionic architectures”.

In this case, a team led by Manu Mannoor and Sudeep Joshi from Stevens Institute of Technology in New Jersey, US, wanted to create such a relationship between button mushrooms (Agaricus bisporus) and cyanobacteria, a group of single-celled microbes that generate their own energy through photosynthesis.

To do that, they first 3D printed a branched pattern using electronic ink that contained graphene nanoribbons onto the cap of a living mushroom. Next, they printed a bio-ink containing cyanobacteria and added it onto the same cap, in a spiral pattern which intersected with the electronic ink at multiple points. 

At these sites, electrons could transfer through the outer membranes of the bacteria to the conductive network of graphene nanoribbons. Shining a light on the mushroom activated cyanobacterial photosynthesis, generating a current of about 65 nano-Amps.{%recommended 5758%}

That’s not a lot on its own, but the researchers say an array of bionic mushrooms could generate enough current to light up an LED, and they are working on ways to generate even more. 

The work, which is reported in a paper published in the journal Nano Letters, is very much focused on the bigger picture. They believe this 3D-printing approach could be used to organise other bacterial species in complex arrangements to perform useful functions, such as bioluminescence. 

“The biological microworld is classified into several kingdoms, wherein bacterial and fungal kingdoms reap mutual benefits by exhibiting significant mutualistic symbiosis,” Mannoor and colleagues write.

“Therein lies a greater engineering challenge in utilising inherent capabilities and functionalities by selectively and controllably teaming-up different species from the biological microworld to realise functional bionic architectures toward innovative applications. 

“Therefore, a compelling scientific interest is to pay attention for inquisitive resources and techniques for tapping into the biological microworld.”

The component parts for the experiment were not random choices. 

Cyanobacteria, the researchers say, has a unique ability for photosynthetic energy conversion, with an internal quantum efficiency of nearly 100%, while the mushroom is among the few organisms that have evolved over millions of years with a “compelling structure for biomimicking”.

The mushroom’s cap, or pileus, can be used to immobilise cyanobacterial colonies for efficient photosynthetic bioelectricity generation, and the water molecules required for photosynthesis can be delivered to the immobilised cyanobacteria via capillary action of hydrophilic fibrous stripes within the mushroom.

The mushroom’s porous structure transfers water molecules within the pileus and hence provides the necessary water channels.

“Engineering a multidimensional integration among different microbiological kingdoms can harness advantage by exploring the existence of rational bionic symbiosis,” the researchers write. 

“As the mushroom lacks the ability to perform photosynthesis due to the absence of chlorophyll pigments, these seamlessly intertwined cyanobacterial colonies can impart photosynthesis functionality to the mushroom.” 

Concurrently, the mushroom’s structure provides self-serving biophysiological conditions, such as humid shelter and stable source of nutrients for cyanobacterial colonies to survive longer. Hence, the proposed integration derives mutual benefits and is termed as “engineered bionic symbiosis”.

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