It’s alive!
Scientists create new type of concrete that grows to create structures using bacteria.
For centuries, builders have been making concrete roughly the same way: by mixing hard materials like sand with various binders, and hoping it stays fixed and rigid for a long time to come.
Now, an interdisciplinary team of researchers at the University of Colorado, Boulder, has created a rather di≠erent kind of concrete — one that is alive and can even reproduce.
Minerals in the new material are deposited not by chemistry but by cyanobacteria, a common class of microbes that capture energy through photosynthesis. The photosynthetic process absorbs carbon dioxide, in stark contrast to the production of regular concrete, which spews huge amounts of that greenhouse gas.
Photosynthetic bacteria also give the concrete another unusual feature: a green color. “It really does look like a Frankenstein material,” said Wil Srubar, a structural engineer and the head of the research project. The green color fades as the material dries.
Other researchers have worked on incorporating biology into concrete, especially concrete that can heal its own cracks. A major advantage of the new material, its creators say, is that instead of adding bacteria to regular concrete — an inhospitable environment — their process
is oriented around bacteria, enlisting them to build the concrete, and keeping them alive so they make more later on.
The new concrete, described in the journal Matter, “represents a new and exciting class of low-carbon, designer construction materials,” said Andrea Hamilton, a concrete expert at the University of Strathclyde in Scotland.
To build the living concrete, the researchers first tried putting cyanobacteria in a mixture of warm water, sand and nutrients. The microbes eagerly absorbed light and began producing calcium carbonate, gradually cementing the sand particles together. But the process was slow — and DARPA, the U.S. Defense Advanced Research
Projects Agency and the project’s funder, wanted the construction to go quickly. Necessity, happily, birthed invention.
Srubar had previously worked with gelatin, a food ingredient that, when dissolved in water and cooled, forms special bonds between its molecules. Importantly, it can be used at moderate temperatures that are gentle on bacteria. He suggested adding gelatin to strengthen the matrix being built by the cyanobacteria, and the team was intrigued.
The researchers bought Knox brand gelatin at a local supermarket and dissolved it in the solution with the bacteria. When they poured the mixture into molds and cooled it in a refrigerator, the gelatin formed its bonds — “just like when you make Jell-O,” Srubar said. The gelatin provided more structure, and worked with the bacteria to help the living concrete grow stronger and faster.
After about a day, the mixture formed concrete blocks in the shape of whatever molds the group used, including 2-inch cubes, shoe box-size blocks, and truss pieces with struts and cutouts.