听CU Boulder researchers are developing new types of living building materials that incorporate bacteria and can absorb carbon dioxide from the air.
听Bricks made out of these materials are hardy and also show survival rates among bacteria that are much higher than in many other similar materials.
听Such materials could, one day, heal their own cracks, suck up toxins from the air and even glow on command.
CU Boulder researchers have developed a new approach to designing more sustainable buildings with help from some of the tiniest contractors out there.
In a study , engineer Wil Srubar and his colleagues describe their strategy for using bacteria to develop building materials that live and multiply鈥攁nd might deliver a lower carbon footprint, to boot.
鈥淲e already use biological materials in our buildings, like wood, but those materials are no longer alive,鈥� said Srubar, an assistant professor in the Department of Civil, Environmental and Architectural Engineering (CEAE). 鈥淲e鈥檙e asking: Why can鈥檛 we keep them alive and have that biology do something beneficial, too?鈥�
You can鈥檛 buy these microorganisms turned bricks at your local Home Depot just yet. But the researchers say that 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 up dangerous toxins from the air or even glow on command.
鈥淭hough this technology is at its beginning, looking forward, living building materials听could be used to improve the efficiency and sustainability of building material production and could allow materials to sense and interact with their environment," said study lead author Chelsea Heveran, a former postdoctoral research assistant at CU Boulder, now at Montana State University.听
Rice crispy treats
Today's more corpse-like buildings materials, in contrast, can be costly and polluting to produce, Srubar said: Making the cement and concrete alone needed for roads, bridges, skyscrapers and other structures generates nearly 6% of the world鈥檚 annual emissions of carbon dioxide.
Srubar鈥檚 solution: Hire some bacteria.听
In particular, he and his colleagues experimented with cyanobacteria belonging to the genus Synechococcus. Under the right conditions, these green microbes absorb carbon dioxide gas to help them grow and make calcium carbonate鈥攖he main ingredient in limestone and, it turns out, cement.
To begin the manufacturing process, the researchers inoculate colonies of cyanobacteria into a solution of sand and gelatin. With the right tweaks, the calcium carbonate churned out by the microbes mineralize the gelatin which binds together the sand鈥攁nd, presto, a brick.
鈥婽op: Wil Srubar and CU Boulder graduate student Sarah Williams in the lab. Bottom: A mold for shaping bricks made out of living materials. (Credit: CU Boulder College of Engineering and Applied Science)
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鈥淚t鈥檚 a lot like making rice crispy treats where you toughen the marshmallow by adding little bits of hard particles,鈥� Srubar said.
As an added bonus, such bricks would actually remove carbon dioxide from the air, not pump it back out.
They鈥檙e durable, too. In the new study, the team discovered that under a range of humidity conditions, they have about the same strength as the mortar used by contractors today.
鈥淵ou can step on it, and it won鈥檛 break,鈥� he said.
Buildings making buildings
The researchers also discovered that they could make their materials reproduce. Chop one of these bricks in half, and each of half is capable of growing into a new brick.听
Those new bricks are resilient: According to the group鈥檚 calculations, roughly 9-14% of the bacterial colonies in their materials were still alive after 30 days and three different generations in brick form. Bacteria added to concrete to develop self-healing materials, in contrast, tend to have survival rates of less than 1%.
鈥淲e know that bacteria grow at an exponential rate,鈥� Srubar said. 鈥淭hat鈥檚 different than how we, say, 3D-print a block or cast a brick. If we can grow our materials biologically, then we can manufacture at an exponential scale.鈥�
He notes that there鈥檚 a lot of work to do before that happens. The team鈥檚 cyanobacteria, for example, need humid conditions to survive鈥攕omething that鈥檚 not possible in more arid regions of the world. So he and his team are working to engineer microbes that are more resistant to drying out so they remain alive and functional.
But the possibilities are big. Srubar imagines a future in which suppliers could mail out sacks filled with the desiccated ingredients for making living building materials. Just add water, and people on site could begin to grow and shape their own microbial homes.听
鈥淣ature has figured out how to do a lot of things in a clever and efficient way,鈥� Srubar said. 鈥淲e just need to pay more attention.鈥�
Other coauthors of the new study include CU Boulder鈥檚 Jeffrey Cameron, assistant professor in Biochemistry; Sherri Cook and Mija Hubler, both assistant professors in CEAE; postdoctoral researchers Juliana Artier and Jishen Qui; and graduate student Sarah Williams.
