Building materials come alive with bacteria | CU Boulder today

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CU Boulder researchers are developing new types of living building materials that incorporate bacteria and can absorb carbon dioxide from the air.

Bricks made from these materials are tough and also have much higher survival rates among bacteria than many other similar materials.

Such materials could one day heal their own cracks, suck toxins from the air, and even glow on command.

CU Boulder researchers have developed a new approach to designing more sustainable buildings with the help of some of the smallest contractors.

In a study published today in the journal Questionengineer Wil Srubar and his colleagues describe their strategy of using bacteria to develop building materials that live and multiply, and which could, in addition, have a lower carbon footprint.

“We already use biological materials in our buildings, such as wood, but these materials are no longer living,” said Srubar, an assistant professor in the Department of Civil, Environmental and Architectural Engineering (CEAE). “We ask: why can’t we keep them alive and make this biology do something beneficial too?”

You cannot yet buy these microorganisms made into bricks at your local Home Depot. But the researchers say their ability to keep their bacteria alive with a high success rate shows that living buildings might not be too far off in the future.

Such structures could one day heal their own cracks, suck dangerous toxins into the air, or even glow on command.

“Although this technology is still in its infancy, looking to the future, living building materials could be used to improve the efficiency and sustainability of building materials production and could allow materials to sense and interact with their environment,” said the study’s lead author, Chelsea Heveran, a former postdoctoral research assistant at CU Boulder, now at Montana State University.

Crispy Rice Treats

By contrast, today’s more cadaverous building materials can be expensive and polluting to produce, Srubar said: Making the cement and concrete needed on their own for roads, bridges, skyscrapers and other structures generate nearly 6% of the world’s annual carbon dioxide emissions. .

Srubar’s solution: Engage bacteria.

In particular, he and his colleagues experimented with cyanobacteria belonging to the genus Synechococcus. Under the right conditions, these green microbes absorb carbon dioxide to help them grow and make calcium carbonate, the main ingredient of limestone and, in fact, cement.

To begin the manufacturing process, researchers inoculate colonies of cyanobacteria into a solution of sand and gelatin. With the right adjustments, the calcium carbonate produced by the microbes mineralizes the gelatin that binds the sand and, presto, a brick.

A mold for forming bricks from living materials.

Top: Wil Srubar and CU Boulder graduate student Sarah Williams in the lab. Bottom: A mold for shaping bricks into living materials. (Credit: CU Boulder College of Engineering and Applied Science)

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“It’s kind of like making crispy rice treats where you harden the marshmallow by adding little bits of hard particles,” Srubar said.

As a bonus, such bricks would actually remove carbon dioxide from the air, not pump it out.

They are also durable. In the new study, the team found that over a range of humidity conditions, they have about the same strength as the mortar used by contractors today.

“You can walk on it and it won’t break,” he said.

Buildings making buildings

The researchers also found that they could replicate their materials. Cut one of these bricks in half, and each of the halves is capable of becoming a new brick.

These new bricks are resistant: according to the group’s calculations, around 9 to 14% of the bacterial colonies in their materials were still alive after 30 days and three different generations in the form of bricks. Bacteria added to concrete to develop self-healing materials, on the other hand, tend to have survival rates of less than 1%.

“We know that bacteria grow at an exponential rate,” Srubar said. “It’s different from how we, say, 3D print a block or cast a brick. If we can grow our materials biologically, we can manufacture on an exponential scale. »

He notes that there is a lot of work to do before that happens. The team’s cyanobacteria, for example, need humid conditions to survive, which is not possible in more arid parts of the world. He and his team are therefore working to design microbes that are more resistant to drying out so that they remain alive and functional.

But the possibilities are great. Srubar imagines a future in which suppliers could mail bags full of desiccated ingredients to make living building materials. Just add water and the people there could start growing and forming their own microbial hotbeds.

“Nature has figured out how to do a lot of things smartly and efficiently,” Srubar said. “We just have to be more careful.”

Other co-authors of the new study include Jeffrey Cameron of CU Boulder, assistant professor of biochemistry; Sherri Cook and Mija Hubler, both assistant professors at the CEAE; postdoctoral researchers Juliana Artier and Jishen Qui; and graduate student Sarah Williams.

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