Jello molds aren't just for dinner parties — when humans start building habitats on Mars, the structures could be made partly of gelatin and yeast.
A team of engineers devised a recipe for concrete that uses yeast and gelatin to bind together sand into a light, porous material. Theoretically, this should work with Mars material, or regolith, as well. In the lab, Hong Kong University of Science and Technology environmental engineer Ning Liu and colleagues already built tiny versions of future Martian habitats using the substance.
And in fact, the researchers say this biology-based concrete could be easier to use on Mars than some other options that have been proposed. Still, there's a long way to go and a lot of technological hurdles to overcome before we're ready to build a Mars base out of yeast.
Welcome to Mars; don't eat the habitat
Like regular concrete, Liu and colleagues' version uses sand or crushed rock as an aggregate: the solid stuff that's held together by material called binder (usually something like Portland cement, a powder of heated limestone and clay mixed with a little gypsum). Water turns the binder into a gel-like glue, and as it dries, the whole binder-and-aggregate mixture hardens into something solid and reasonably strong. But instead of good old Portland cement, Liu and colleagues use a mix of pork gelatin (the same stuff that makes jello) and genetically engineered yeast.
The researchers swapped a couple of key genes in their special strain of the yeast called Saccharomyces cerevisiae. One gene makes the cells bind more tightly to each other, and the other produces what are called "mussel foot proteins," or the adhesives that help mussels latch onto rocks.
In the lab, Liu and colleagues 3D-printed their concrete creation in cold, low-pressure conditions meant to mimic the surface of Mars; they also tried a version that involved casting the yeast-based material in a mold, the classic way to manipulate gelatin.
As the yeasty mixture cures — over about 48 hours at -67 degrees Fahrenheit, or -55 degrees Celsius, and 0.000 atmospheres of air pressure, if you're looking for the recipe — the water in it freezes and then sublimates. This leaves behind a light and porous, but remarkably strong, scaffolding of gelatin, crushed regolith and yeast proteins. Those proteins act as very strong anchors between the gelatin binder and the rocky aggregate, "creating a bond that is stronger than the bulk material," Liu and colleagues write in their recent paper.
How strong is the substance? Well, the 1.77-inch-tall and 1.18-inch-wide (4.5-centimeter-tall, 3-centimeter-wide) domes Liu and colleagues built have a compressive strength of about 12 megapascals, which is roughly on par with low-grade concrete. It can also withstand bending forces of up to about 6 megapascals.
"This is actually strong enough to build a one- or two-story building on Earth, whose gravity is three times that of Mars. So you can probably easily build a multistory building on Mars with the material," Hong Kong University engineer Jishen Qiu, the study's senior author, said in a statement. "We are confident in scaling it up."
Mars habitats are going to need more than just study walls, though; they also need to shield astronauts from radiation, keep breathable air inside and maintain air pressure against a near-vacuum outside. A concrete dome, no matter how strong, can't do all of that on its own.
The yeast-and-gelatin-based concrete is "best regarded as a printable and recyclable in situ structural component," as Liu and colleagues put it, "not as a complete airtight, pressure-retaining, or radiation-shielding habitat envelope by itself." A real Mars habitat dome would probably need a structure with several layers: inflatable or pre-fabricated pressure modules, airtight liners or coatings and seals, a water-filled radiation-shielding layer — and possibly a concrete structure bound together by genetically engineered yeast.
A long way to go
It's going to take more research before engineers can be sure that yeast will even survive well enough on Mars to help assemble anything with it at all.
Mars is bitterly cold, and its thin atmosphere and long-dead magnetic field leave the surface open to deadly radiation (both from the sun and from deep space). But just as Liu and colleagues modified parts of P. cerevisiae's genome to make it a better concrete binder, other researchers may be able to tweak the yeast to withstand higher doses of radiation and colder temperatures.
"In principle, this platform can be engineered for stress tolerance traits, including resistance to cold, vacuum, and even radiation," the researchers wrote in their paper.
Of course, a yeast that can survive on Mars is … well, a yeast that can survive on Mars, which could actually risk contaminating the planet with hardy and fast-multiplying Earth microbes. Liu and colleagues mentioned in their paper that planetary protection strategies would be an important part of future research, along with testing the material's long-term durability and how well it retains heat.
But the gelatin-and-yeast concrete could offer some advantages over some of the other leading ideas for making building materials on Mars, most of which rely on heating and melting regolith to form bricks and support beams. Those methods get around the challenges of shipping materials from home, but they still require tremendous amounts of energy to use, not to mention industrial equipment that is, in the researchers' words, "difficult to scale with rocket-transportable systems."
Liu and colleagues' approach uses an order of magnitude less energy than traditional regolith-melting methods, they estimate. But building anything substantial on would still require shipping tons of materials from Earth, Qiu estimates.
When it comes to building a home for humanity on Mars, there are never going to be any easy answers. On the other hand, the yeast could be a renewable and re-usable resource that only needs to be delivered once. When astronauts are finished with one building, they can recycle the concrete and put the yeast into a bioreactor to grow a fresh batch.
"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," said Qiu.
Liu and colleagues published their work in the journal Chem Circularity.
