Mars is a terrible place to build a house. It's bitterly cold, blasted by radiation, and a near vacuum. Not to mention that the building materials, even for a modest shelter, could spend months hurtling through space before construction begins.
But they don't have to. In a study publishing September 10 in the journal Chem Circularity, researchers developed a recipe that could one day be used to 3D print houses on Mars. The recipe combines Martian rocks with Earthly ingredients: gelatin and yeast. Once dried and hardened, this living building material is as strong as low-grade concrete and can be broken down, recycled, and brewed again for new construction.
"My inspiration came from freeze-dried fruits that become harder," says civil engineer and senior author Jishen Qiu of The Hong Kong University of Science and Technology. Mars's extremely low temperature and pressure create conditions similar to freeze-drying. "So I asked myself if we can take advantage of that and make some materials."
To conjure the printable material, Qiu needed the right mixture of sand and glue, the latter, which is made from gelatin and a specialized yeast. The team engineered yeast coated with highly adhesive proteins, including those that mussels use to cling to rocks. The gelatin knits the ingredients together and provides a place for the cells to grow, while the sand gives mass and structure.
The team then tested the material in simulated Martian conditions. Once the mixture pushes through the nozzle, the extreme cold and low pressure freeze-dry it. Water freezes and turns directly from ice into vapor, leaving behind microscopic pores. The result resembles a foam, light and porous.
For now, the printed structures are about wine-cork-sized small domes, standing at 45 mm tall and 30 mm wide. But the material itself is strong—with a compressive strength of 10 to 12 megapascals, comparable to low-grade concrete.
"So this is actually strong enough to build a one- or two-story building on Earth whose gravity is three times that of Mars," says Qiu. "So, you can probably easily build a multistory building on Mars with the material."
Many proposals for building extraterrestrial cities involve heating and melting Martian rocks or moon dust into bricks and beams. But that requires substantial energy. The biology-based material not only does it save energy on heat by taking an entirely different manufacturing approach, but it could also support a circular economy on Mars. Settlers could recover the yeast from dismantled structures and regrow it in bioreactors.
"As long as there's one yeast that's still alive, you can grow them again," Qiu says.
So far, the biology-based material has only been tested on Earth. The team doesn't know whether the yeasts can survive actual Martian conditions. The living building material still relies on, albeit less, Earthly ingredients, and its success will depend on advances in rocket technology. Qiu estimates a meaningful on-site engineering could require hundreds of tons of cargo from Earth.
"I always ask myself: Is there any physical law or fundamental mechanism that prevents us from doing this?" says Qiu. "I can't see any at this point in time. We are confident in scaling it up. It would surprise me if materials for future Martian engineering will not be as diverse as those used in Earth engineering—and biology will certainly contribute."
