This 3D-printed ‘living waffle’ could help solve water pollution

The 'waffle' is covered in genetically engineered bacteria that could clean pollution from water. ( David Baillot/UC San Diego Jacobs School of Engineering)
The 'waffle' is covered in genetically engineered bacteria that could clean pollution from water. (UC San Diego Jacobs School of Engineering)

It looks like a bizarre, green waffle, but the 3D printed structure could offer a sustainable way to clean pollutants from water, say University of California San Diego researchers.

The researchers describe the structure as an "engineered living material”.

The ‘waffle’ is a 3D-printed structure made of a seaweed-based substance combined with genetically engineered bacteria.

The bacteria are engineered to produce an enzyme that transforms various organic pollutants into safe molecules.

The bacteria were also engineered to self-destruct in the presence of a molecule called theophylline, which is often found in tea and chocolate. This offers a way to eliminate them after they have done their job.

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Jon Pokorski, a professor of nanoengineering at UC San Diego who co-led the research, said, "What's innovative is the pairing of a polymer material with a biological system to create a living material that can function and respond to stimuli in ways that regular synthetic materials cannot.”

Susan Golden, a faculty member in the School of Biological Sciences, said, "This collaboration allowed us to apply our knowledge of the genetics and physiology of cyanobacteria to create a living material.

“Now we can think creatively about engineering novel functions into cyanobacteria to make more useful products."

To create the living material in this study, the researchers used alginate, a natural polymer derived from seaweed.

The researchers hydrated it to make a gel and mixed it with a type of water-dwelling, photosynthetic bacteria known as cyanobacteria.

The mixture was fed into a 3D printer.

After testing various 3D-printed geometries for their material, the researchers found that a grid-like structure was optimal for keeping the bacteria alive.

The chosen shape has a high surface area to volume ratio, which places most of the cyanobacteria near the material's surface to access nutrients, gases and light.

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The increased surface area also makes the material more effective at decontamination.

In this study, the researchers demonstrated that their material can be used to decontaminate the dye-based pollutant indigo carmine, which is a blue dye that is widely used in the textile industry to color denim.

In tests, the material decolourised a water solution containing the dye.

The researchers also developed a way to eliminate the cyanobacteria after the pollutants have been cleared. They genetically engineered the bacteria to respond to a molecule called theophylline. The molecule triggers the bacteria to produce a protein that destroys their cells.

Pokorski said, "The living material can act on the pollutant of interest, then a small molecule can be added afterwards to kill the bacteria. This way, we can alleviate any concerns about having genetically modified bacteria lingering in the environment."

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