A team at Northwestern University developed a comprehensive approach for creating robust, elastic, designer Lunar and Martian regolith simulant (LRS and MRS, respectively) architectures using ambient condition, extrusion-based 3D printing of regolith simulant inks. The LRS and MRS powders were characterized by distinct, highly inhomogeneous morphologies and sizes, where LRS powder particles are highly irregular and jagged and MRS powder particles are rough, but primarily rounded. The inks are synthesized via simple mixing of evaporant, surfactant, and plasticizer solvents, polylactic-co-glycolic acid (30% by solids volume), and regolith simulant powders (70% by solids volume). The Study was published in Nature Journal.

Both LRS and MRS inks exhibited similar rheological and 3D printing characteristics, and were 3D-printed at linear deposition rates of 1–150 mm/s using 300 μm to 1.4 cm-diameter nozzles. The resulting LRS and MRS 3D printed materials exhibit similar, but distinct internal and external microstructures and material porosity. These microstructures contribute to the rubber-like quasi-static and cyclic mechanical properties of both materials. Finally, the researchers discussed the potential for LRS and MRS ink components to be reclaimed and recycled, as well as be synthesized in resource-limited, extraterrestrial environments.

3D Terraforming

Establishing autonomous or inhabited extraterrestrial sites has been part of science fiction culture for many years. This past decade has witnessed not only tremendous advances in technology that can make such endeavors technically feasible, but also substantial growth in commercial and government interest. Developing the capacity to establish and maintain extraterrestrial sites on the Moon, Mars, and additional planetary and large, non-planetary bodies would be an achievement for humanity and would lay the foundation for further, extraterrestrial scientific and engineering advances as well as private commercialization. To this end, additive manufacturing (AM) and 3D printing (3DP) approaches have recently been considered as promising means to enable prolonged off-world activities through utilization of native planetary regoliths for manufacturing.

Although promising, current AM and 3DP approaches, such as those that utilize powder beds, high-energy beams, or both to selectively sinter or melt regolith materials suffer from numerous process- and material-related restrictions that make them ill-suited for utilization in such environmentally extreme, resource-starved, reduced-gravity environments. On the other hand, while traditional material-deposition 3D-printing approaches, such as fused deposition modeling (FDM), are currently being successfully and safely utilized in the micro-gravity environment of the International Space Station (Zero-G Printer, Made In Space) to create objects on demand, traditional deposition approaches have only been compatible with a select set of simple thermoplastics and low-particle-content thermoplastic composites, but not regolith materials. Additionally, although valuable for a variety of applications, previous work with planetary regoliths has focused entirely on the fabrication of hard materials, primarily via thermal or microwave sintering, melting of regolith powder compacts, or cementation reactions of extruded materials, and has not addressed the need for soft-material manufacturing.

3D Bioplotting a Course for the Stars

Northwestern University is also known for Dr Shah’s TEAM lab work on materials and biomaterials using EnvisionTEC’s pneumatic extrusion based 3D Bioplotter to 3D print with metals and alloys as well as regenerative ceramic and graphene biomaterials (from relatively, compositionally and morphologically pristine powders). In this new work, which also sees Dr. Shah among the authors, the researchers extended the 3D printable particle based liquid ink platform to Lunar and Martian regolith simulants (LRS and MRS; JSC-1A and JSC MARS-1A, respectively); which are unrefined, highly compositionally and morphologically inhomogeneous natural, volcanic materials that emulate the surface environments of specific regions on the Moon and Mars, respectively. The results are rapidly 3 -printed, highly versatile and mechanically elastic composites comprised of approximately 90 wt. % LRS or MRS and 10 wt.% bio-derived polymer (polylactic-co-glycolic acid, PLGA) that have the potential to address the need for soft materials off-world.

All LRS and MRS samples were 3D-printed via direct extrusion, under ambient conditions using the 3D Bioplotter by EnvisionTEC. Linear deposition speeds and extrusion pressures ranged from 5–120 mm/s and 100–550 KPa, respectively, depending on the samples produced. LRS and MRS samples intended for quasi-static and cyclic tensile testing were 3D-printed into a standard dog-bone geometry defined as being 20 mm long, 3 mm wide, and 1.5 mm thick using a 510 μm nozzle. The LRS ink was deposited in the direction of gauge-length (loading direction), with 450 μm spacing between parallel struts (resulting in a non-porous architecture), for a total of 5-layers (~1.5 mm thick samples). 12 × 12 cm LRS and MRS sheets were produced using a 600 μm diameter nozzle and deposition speeds of 60–80 mm/s. Each sheet was comprised of three-layers, each layer oriented 120° with respect to the previous layer.

To Space and Beyond

The researchers concluded that this new approach for additively manufacturing planetary materials represents a new, powder-bed-free and energy-beam-free, resource utilization scheme for fabricating user-defined, soft-material structures from unrefined, highly inhomogeneous regoliths. Processes for regolith ink synthesis appear to be primarily independent of regolith composition and particle morphology. Due to the purely physical nature of ink synthesis (simple mixing of components, with no chemical reactions/transformations involved this process is potentially scalable. Additionally, the simple, rapid extrusion nature of the regolith ink 3D-printing process is also likely amenable to application with parallel nozzle extruders, larger diameter extruders, large build-area platforms, mobile extruders, or any combinations thereof. Although not investigated in this work, the resulting printed structures (due to the high LRS and MRS particle packing densities) can also be processed to create hard regolith structures via post-3D-printing sintering, as described previously for 3D-printed metal, alloy, and metal oxide ink systems8,9. Collectively, this work represents an extension of a newly established, materials-centric 3D-printing platform to unrefined, physically and compositionally inhomogeneous powders, and also illustrates that soft-materials, can be fabricated from hard, inhomogeneous, native resources and components that can potentially be recycled and reused.

An EPIC Find

This work made use of the EPIC facility of the NUANCE Center at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. The authors acknowledge support from the Simpson Querrey Institute for BioNanotechnology at Northwestern University developed by support from The U.S. Army Research Office, the U.S. Army Medical Research and Material Command, and Northwestern University. This research was partially supported by a gift from Google. AEJ was supported by a postdoctoral fellowship from The Hartwell Foundation.