Despite being in liquid form, the LRS and MRS inks can be rapidly 3D-printed into user defined architectures (Fig. 2A,E; Supplementary Videos 1 and 2), at linear 3D-printing speeds demonstrated upwards of 150 mm/s, resulting in objects that do not require time to dry and can be handled immediately (Supplementary Video 3). LRS and MRS 3D-printing parameters and behavior do not significantly differ. Figure 2F illustrates this similarity through the production and assembly of LRS and MRS building blocks, which were 3D-printed from the same digital file using near identical 3D-printing parameters. The LRS and MRS structures maintain their as-printed fidelity (Fig. 2G–J), and successive layers of 3D-printed material can even span gaps (Fig. 2H,J), which is enabled by the rapid solidification of the material via DCM evaporation upon extrusion. It is important to note that adhesion of the first deposited layer of material to the platform substrate is important not only for ensuring a successful print-job on Earth (gravity = 1), but for ensuring success in reduced-gravity environments such as the Moon (gravity = 0.17) and Mars (gravity = 0.38). In this work, standard sand papers and silicon carbide papers (320grit) resulted in substantial adhesion of the first layer, and resulting printed object, to the platform while still permitting the object to be easily removed without sustaining damage or altering the underlying substrate (allowing the sandpapers and silicon carbide papers to be used repeatedly).

Figure 2 (A–D) 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. (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. (G,J) SEM micrographs of 3D-printed LRS (G,H) and MRS (I,J) structures. Top-down (G,I) and cross-sectional (H,J) are shown. Insets show macroscopic photographs of structures. (K) Linear deposition (extrusion) rate of LRS Ink as a function of applied pressure and nozzle diameter. Low pressures and small tip diameters result in increased fidelity, but decreased fabrication times, while high pressures and larger tip diameters result in reduced fidelity, but faster fabrication times. (L) Experimentally measured and corresponding extrapolated volumetric deposition rates of LRS inks as a function of applied pressure and nozzle diameter. Colored lines correspond to extrusion pressures indicated in (K). Full size image

Importantly, the regolith inks are compatible with a range of nozzle diameters and extrusion pressures (Fig. 2K), imparting significant versatility and control to the user with respect to the types of structures that can created, achievable resolution (Supplementary Figure 2), and fabrication rate. On the finer end of the spectrum, LRS inks were able to be continuously be extruded from 330 μm nozzles without clogging at linear deposition rates as low as 2.1 mm/s (200 KPa) and as high as 19.2 mm/s (500 KPa). Similarly, 2.9 mm-diameter nozzles were utilized under the same low and elevated extrusion pressures to achieve linear deposition rates of 46 and 633 mm/s, respectively. MRS inks exhibit a similar rate v. pressure relationship, but were unable to be extruded from 330 μm nozzles without frequent clogging events, which was likely due to the presence of large particles (Fig. 1A). In terms of volume, this corresponds to 6.5 × 10−7 – 1.5 × 10−2 m3/h. This versatility provides a large, parametric space with which to create both small, high resolution objects, and large, low-resolution objects, without altering the ink. If the ink is further thickened, to a consistency similar to soft modeling clay, large extrusion diameters, such as 1.4 cm, can be achieved (Supplementary Figure 3), potentially resulting in single-nozzle volumetric deposition rates approaching 1 m3/h. Multi/parallel nozzle extrusion-based 3D-printing platforms22 could potentially be employed to substantially increase material deposition and fabrication rates, allowing for high-throughput production of small and moderate sized parts. Additionally, similar to the metal, metal oxide, ceramic, and graphene 3D systems described by Jakus et al.8,10,11,12. 3D-printed LRS and MRS objects can be recycled into new inks, by dissolving them in DCM, or joined to previously 3D-printed objects via application of ink at points of contact9,10,11. It is unclear at this time, however, what modifications would need to be made to the 3D-printing process to permit it to be successfully applied in external environments characterized by low atmospheric pressures and extreme temperatures. Regardless, the process in its current form can be readily employed in a pressurized moderate temperature environment.