Life is at the heart of much of our material world. We make two-by-four beams from wood, ethanol from corn, and textiles from cotton. But bricks? Researchers have now created a form of concrete that not only comes from living creatures but—given the right inputs—can turn one brick into two, two into four, and four into eight. Although the new material won’t build self-assembling houses anytime soon, it could soon lead to building components that can heal themselves when damaged. The living concrete could even offer Mars-bound astronauts a way to build structures from local materials plus a few adventurous microbes.
The new concrete is the latest addition to the burgeoning field of engineered living materials (ELMs), in which organisms—typically bacteria—are added to inanimate materials to enable them to sense, communicate, and even respond to their environments. In recent years, researchers have created ELMs that sense pressure, kill dangerous bacteria, and sense light. But those materials are usually thin films grown atop structural supports.
For this project, Wil Srubar, a materials scientist at the University of Colorado, Boulder, and his colleagues wanted to engineer life into a bulk structural material. To do so, they turned to a hearty photosynthetic cyanobacterial species in the genus Synechococcus. They mixed the cyanobacterium with sand and a hydrogel that helped retain water and nutrients. The mix provided structural support to the bacteria, which—as they grew—lay down calcium carbonate, similar to the way some ocean creatures create shells. When dried, the resulting material was as strong as cement-based mortar. “It looks like a Frankenstein-type material,” Srubar says. “That’s exactly what we’re trying to create, something that stays alive.”
Under the right conditions, which included relatively high humidity, Srubar’s living material not only survived but reproduced. After the researchers split the original brick in half and added extra sand, hydrogel, and nutrients, the cyanobacteria grew in 6 hours into two full-size bricks; after three generations (in which the researchers again split the bricks), they had eight bricks, they report today in Matter.
This harnessing of a natural process to create building materials is “interesting,” and the potential applications mesmerizing, says Sarah Glaven, a microbiologist and ELM expert at the U.S. Naval Research Laboratory. “Could you grow a temporary runway somewhere by seeding bacteria in sand and gelatin?”
Srubar hopes structural ELMs could also help astronauts venture to Mars. Even though spacecraft couldn’t easily carry all the building materials, astronauts could bring cultures of bacteria that could help them convert local ingredients into hardened structures. That’s likely to be a lot easier than bringing saplings and attempting to grow trees on a frigid planet without liquid water and little atmosphere.