Stranger Than Fiction #6: Night of the Living Concrete 

Cement, a widely used construction material due to its cost-effectiveness and durability, is also a major contributor to global CO2 emissions, with an annual production rate of 2.8 gigatons. As the world grapples with the need to reduce carbon emissions, researchers are actively exploring alternative production methods and substitute materials to mitigate the environmental impact of cement.

Recently, a team of scientists at the University of Colorado Boulder made a significant breakthrough. They devised a novel approach by combining sand, a hydrogel, and bacteria to create a living material that exhibits strength similar to cement-based mortar while possessing the unique capability to perform biological functions.

How Does Concrete Live?

Microorganisms play a crucial role in designing "living building materials" by expediting manufacturing processes, enhancing mechanical properties, and maintaining biological functions. The researchers at the University of Colorado Boulder harnessed this potential to develop an innovative material platform.

Their method involved utilising a 3D sand-hydrogel scaffold, which they infused with Synechococcus sp. PCC 7002, a photosynthetic cyanobacterium known for its ability to convert CO2 into sugars during photosynthesis. These cyanobacteria are renowned for their resilience in extreme environmental conditions, making them ideal candidates for creating living materials.

The project's lead author, Wil Srubar, who heads the Living Materials Laboratory at the University of Colorado Boulder, describes their work as venturing into uncharted territory. He explains that they used photosynthetic cyanobacteria to biomineralised the scaffold, creating a visually distinctive material that emphasises its eco-friendliness and resilience.

Beyond its unique composition, this innovative material can also be regenerated from a single parent "brick" by carefully controlling temperature and humidity. Through a controlled process of incubation at 37 °C followed by low-temperature storage, the gelatin matrix solidifies and encapsulates the bacteria. 

While this innovative development holds significant potential, it comes with a trade-off between biological viability and mechanical performance. The gelatin matrix reaches its maximum strength when dehydrated, while the bacteria rely on humidity to function. Balancing these two factors is challenging, but researchers believe that optimisation can be achieved by exploring the use of additives to enhance bacteria tolerance to dry conditions.

Funding and Future Prospects

The research behind these living bricks was funded by the Defense Advanced Research Projects Agency (DARPA), a branch of the U.S. Department of Defense. DARPA's interest in rapidly solidifying concrete played a pivotal role in the development of these living materials. To achieve their current objectives, the research team incorporated supermarket gelatin into the mixture. This strategic move aimed to address the issue of dehydration sensitivity, which the team aims to improve in future iterations.

Potential Use

Transporting conventional construction materials to desert areas can be both expensive and logistically challenging. However, with the living bricks, as long as a single brick contains living bacteria, it can effectively bind together various materials. This unique feature means they are not restricted to a specific type of sand. These living bricks have the potential to utilise unconventional resources such as ground glass or recycled concrete.

This innovative approach has the potential to revolutionise construction in arid regions, making it more sustainable and cost-effective, as highlighted by Wil Srubar's insights.

Beyond Earth's Horizons

While the living bricks have the potential to address pressing construction challenges on Earth, Wil Srubar envisions an even broader horizon for this technology. He envisions a future where these living materials could be instrumental in extraterrestrial construction projects. Srubar's vision extends to Mars, where he suggests that transporting traditional cement may not be a feasible solution. Instead, he sees the possibility of bringing biology with us when we embark on interplanetary missions.

In a statement with the Smithsonian, Srubar succinctly captures this pioneering perspective, saying, "We're not going to be trucking bags of cement all the way to Mars. I really do think that we'll be bringing biology with us once we go."

It is crucial to understand that this technology is still in its nascent stages and is not intended to entirely replace cement. Nevertheless, it represents a promising avenue in material manufacturing, introducing a new category of responsive materials where structural functionality is complemented by biological capabilities. Their potential role in future space exploration ventures demonstrates that this innovation is not just limited to Earth but can extend to the far reaches of our universe.