An interdisciplinary team of researchers based in Colorado has developed a type of brick that, through a process of biomineralization, is able to replicate and grow multiple generations of itself. Taking a parent inoculum and combining it with additional base materials, researchers have been able to grow bricks in many shapes. The bricks reach their final strengths and sizes when they are fully dried.
“The built environment as we know it today is quite sterile and static,” said Wil Srubar, Ph.D., LEED AP, A.M.ASCE, in written comments to Civil Engineering. Srubar is an assistant professor of building systems engineering and materials science and engineering at the University of Colorado Boulder and the head of its Living Materials Laboratory, at which the research was conducted. “We wanted to blur the boundaries between nature and the built environment by bringing building materials to life.”
To create this “living” building material, the team placed a strain of Synechococcus, a photosynthetic cyanobacterium, into a mixture of sand, gelatin, and a calcium-containing nutritional medium. Calcium was converted into calcium carbonate through the cyanobacterium’s photosynthesis, which made the mixture more alkaline, prompting the mineralization, explains Chelsea M. Heveran, Ph.D., who was a postdoctoral researcher at the University of Colorado Boulder during the study. Heveran is now an assistant professor in the Mechanical and Industrial Engineering Department of Montana State University in Bozeman, where she specializes in biomineralized and biomimetic materials.
Exponential Expansion
As part of the research, various sizes, shapes, and humidity levels were assessed, according to Heveran. “We showed that we could grow a parent generation of the material, and under the right conditions, split it in half, and that half would grow into two. Two could then grow into four and four into eight—all with a single inoculum of the parent generation,” said Srubar. Parent samples had to be kept in a relatively cool, damp place to enable them to be used as starters for the next generation.
River sand in Boulder was used as the fine aggregate for the bricks. The team chose gelatin because of its melting point, which is compatible with bacterial viability, and because it gains strength as it dries, according to the paper “Biomineralization and Successive Regeneration of Engineered Living Building Materials,” which appeared in the February 5, 2020, issue of the journal Matter.
The compressive strength of the material was similar to the minimum compressive strength of cementitious mortar, according to the paper.
The study’s authors included biochemists, microbiologists, materials scientists, and structural and environmental engineers. The interdisciplinary collaboration “pushed all of us to think more creatively about science and to utilize the resources around us better. So it was just fabulous,” says Heveran, who was also the lead author of the paper.
Scholastic Skeleton
Heveran’s doctoral studies focused on bone biomechanics. She says that looking at the characteristics of self-repair that are found in bones could lead to extremely exciting developments for human-made materials. “When we can take lessons from these biological materials systems, in either how we make the materials or how we repair them over time, we might get closer to lower-energy, more sustainable, or maybe more multifunctional kinds of materials,” she says. “Bacteria are so diverse, and we are just at the beginning of understanding all the functionalities that bacteria and other microorganisms [have] that we can leverage through understanding their metabolisms.”
The application developed by the team is slightly different than self-healing concrete, according to Srubar. “Some researchers have leveraged biomineralization to seal cracks, stabilize soils, or densify recycled concrete aggregates,” he said. (Read “Self-Healing Concrete Uses Bacteria to Repair Cracks,” Civil Engineering, July/August 2015, pages 44–45.)
“We simply rethought the environment in which we place the bacteria. In doing so, we not only enabled the biominerals to be a primary cementing phase, but [we] also created an environment within the microstructure so that bacteria could remain alive more readily than they do in self-healing concrete applications.”
Multifunctional Material
Creating multifunctional, biology-infused building materials is an important idea that researchers should be exploring, according to Heveran. “If we can leverage the metabolic activities of bacteria, building materials might be able to do more for us and intersect in novel ways with the environment around them,” she says.
And creating a strong, tough building material that is not cement-based could prove to be a more sustainable choice for construction projects. “Cementitious materials have a very high carbon footprint in their manufacturing, and their options for use are very limited after their primary purpose has [been fullled],” Heveran says.
“We envision this material could be used as a building block for many applications, including carbon-sequestering mortar, lightweight concrete in buildings, biologically active surfaces, temporary disaster-relief shelters, or roadways,” Srubar said. “We believe this material is particularly suitable in resource-scarce environments such as deserts or the Arctic—even human settlements on other planets. The sky is the limit, really, for creative applications of the technology.”
Once the bricks’ service lives have ended, they can be ground down and reused as aggregate for future living bricks.
Once the bricks’ service lives have ended, they can be ground down and reused as aggregate for future living bricks.
Srubar hopes that the material will become commercially available in the next 10–15 years. But first, the researchers must optimize the formulations to maximize the mechanical properties and the long-term viability and durability of the materials. After that, regulatory approvals and certification can be sought, he noted.
The research was funded by the U.S. Department of Defense’s Defense Advanced Research Projects Agency (DARPA). The full paper can be read at https://doi.org/10.1016/j.matt.2019.11.016.
This news article first appeared in the July/August issue of Civil Engineering.
