Northwestern University Researchers 3D Print Flexible Objects with Simulated Lunar and Martian Soil

Photographs of LRS (A,B) and MRS (C,D) inks being 3D-printed into a many-layered 2 cm-diameter cylinders and 12 cm long wrenches, respectively.

Just a few days ago, scientists from Fotec revealed that they had 3D printed small structures from simulated Martian soil. The structures, a small conical dwelling and a portion of a wall, are miniaturized replicas of what humans may one day create from the actual soil of Mars once we finally reach its surface. The Fotec group, which undertook the research for the European Space Agency, isn’t the only research team to be studying 3D printing with simulated extraterrestrial regolith, however – far from it.

As space scientists from around the world focus on the potential of travel to the moon and Mars in the next few decades, 3D printing is at the top of everyone’s list – particularly the use of native lunar and Martian soil to 3D print structures in which humans will be able to actually live and work. If humans are to stay on the moon and Mars and study their surroundings, they’re going to need somewhere to stay, and it’s become fairly certain that those who land on the lunar and Martian surfaces will be 3D printing their own habitats out of the soil around them. Before that can happen, though, we need to be sure that’s doable, and without access to actual soil from the moon or Mars, scientists have been practicing with simulated materials that replicate the composition of their faraway counterparts as closely as possible.

The Fotec team used soil taken from a volcano in Hawaii to simulate regolith from Mars, and a research paper recently published by a group of scientists from Northwestern University details their work with materials designed to simulate both lunar and Martian soils. The Northwestern team points out that the entirety of the work done with 3D printing simulated Martian and lunar regolith thus far has focused on hard materials, which are obviously necessary, but no one has yet tried using the soils to create and print soft, flexible materials, which will also be important in terms of meeting the needs of people in space.

To create a flexible 3D printing material, the Northwestern team used the same simulated Martian soil as Fotec: JSC MARS-1A, as well as JSC-1A, a simulated lunar regolith also taken from volcano soil. The two are somewhat similar in composition, being composed mainly of silicates, aluminates and iron oxides, but morphologically they’re quite different: lunar regolith simulant (LRS) is composed of irregular, jagged powder particles, according to the researchers, while the Martian regolith simulant (MRS) is made from particles that are rough but rounded. Both materials, however, have similar 3D printable and rheological (flow) characteristics once they’ve been mixed with other materials to turn them into 3D printing “ink.”

The team created the material using a process that they’ve previously used to make ceramic, graphene, metal and metal oxide, and mixed particle 3D printing inks. The soil, sifted to remove larger particles that could interfere with extrusion, was mixed with an elastomeric binder and a solvent.

“The elastomeric binder was commercially available polylactide-co-glycolide (PLGA: Evonik), a commonly utilized medical polymer that can be synthesized from biologically derived, renewable reagents…Regolith powder and PLGA are incorporated into the inks in (70–75% by volume regolith, 30–25% by volume PLGA), which corresponds to approximately 85 wt.% LRS and MRS powder (solids content only),” the researchers explain. “The solvent mixture…includes majority dichloromethane (DCM), a high volatility evaporant, and less quantities of 2-butoxyethanol (2-Bu), a non-specific surfactant, which mitigates electrostatic and steric interactions between suspended particles, and dibutyl phthalate (DBP), a plasticizer that improves the flow properties of the dissolved PLGA and further inhibits particle-particle interaction during flow.”

E) Photograph of MRS ink being 3D-printed into multiple stackable building blocks. (F) Photographs of 3D-printed LRS and MRS building blocks before and after manual assembly into an arbitrary structure.

As the excess DCM evaporated, the inks thickened to a printable consistency that resembled the ceramic and metal inks the team had created with the same method in the past. They’re also shelf-stable, and can be stored for several months prior to use. When extruded with an EnvisionTEC 3D-Bioplotter, the MRS and LRS inks demonstrated fast print speed – over 150 mm/s – and required no time to dry before they could be handled. The material was viscous enough that successive layers could span gaps in earlier layers – as long as the first layer adhered successfully, which is tricky enough on Earth with any 3D printing material, without the reduced gravity environments we’ll be facing on the moon and Mars. The Northwestern team was able to get the material to adhere well at the first layer by printing on sandpaper and silicon carbide paper, which allowed for both strong adhesion and easy removal upon completion.

“Importantly, the regolith inks are compatible with a range of nozzle diameters and extrusion pressures, imparting significant versatility and control to the user with respect to the types of structures that can created, achievable resolution, and fabrication rate,” the researchers add.

The resulting 3D printed structures showed impressive elasticity, able to withstand significant deformation before returning to their original shapes. You can read the full details of the study, entitled “Robust and Elastic Lunar and Martian Structures from 3D-Printed Regolith Inks,” here. Authors include Adam E. Jakus, Katie D. Koube, Nicholas R. Geisendorfer and Ramille N. Shah.

Dr. Shah will be presenting a keynote in May at RAPID + TCT, along with Dr. Sue Jordan, discussing medical/biomedical applications for 3D printing technologies. Dr. Shah’s team at Northwestern has been behind some incredible advances we have been following, from materials to fuel cells to 3D printed hyperelastic bone. Discuss in the Northwestern University forum at 3DPB.com.