Living concrete photosynthesizes, reproduces itself – thanks to gelatin..

The New York Times covers a building material that could be a boon to the planet, a bacteria-enriched concrete that cleans the air and grows more of itself:

Now, an interdisciplinary team of researchers at the University of Colorado, Boulder, has created a rather different 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.

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 Department of Defense’s speculative research arm and the project’s funder, wanted the construction to go very quickly. Necessity, happily, birthed invention.

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,” Dr. 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 two-inch cubes, shoe box-size blocks and truss pieces with struts and cutouts. Individual two-inch cubes were strong enough for a person to stand on, although the material is weak compared to most conventional concretes. Blocks about the size of a shoe box showed potential for doing real construction.

Stored in relatively dry air at room temperature, the blocks reach their maximum strength over the course of days, and the bacteria gradually begin to die out. But even after a few weeks, the blocks are still alive; when again exposed to high temperature and humidity, many of the bacterial cells perk back up.

The group can take one block, cut it with a diamond-tipped saw, place half back in a warm beaker with more raw materials, pour it in a mold, and begin concrete formation anew. Each block could thus spawn three new generations, yielding eight descendant blocks.

The Department of Defense is interested in using the reproductive ability of these “L.B.M.s” — living building materials — to aid construction in remote or austere environments. “Out in the desert, you don’t want to have to truck in lots of materials,” Dr. Srubar said.

Read more of the team’s research published in the journal Matter.