Robust and Elastic Lunar and Martian Structures from 3D-Printed Regolith Inks

Influence of Polymeric Microparticle Size and Loading Concentration on 3D Printing Accuracy and Degradation Behavior of Composite Scaffolds

Successful employment of 3D printing for delivery of therapeutic biomolecules requires protection of their bioactivity on exposure to potentially inactivating conditions. Although intermediary encapsulation of the biomolecules in polymeric particulate delivery vehicles is a promising strategy for this objective, the inclusion of such particles in 3D printing formulations may critically impact the accuracy or precision of 3D printed scaffolds relative to their intended designed architectures, as well as the degradation behavior of both the scaffolds and the included particles. The present work aimed to elucidate the effect of poly(d,l-lactic-co-glycolic acid) particle size and loading concentration on material accuracy, machine precision, and degradation of 3D printed poly(ɛ-caprolactone)-based scaffolds. Using a main effects analysis, the sizes and loading concentrations of particle delivery vehicles investigated were found to have neither a beneficial nor disadvantageous influence on the metrics of printing quality such as material accuracy and machine precision. Meanwhile, particle loading concentration was determined to influence degradation rate, whereas printing temperature affected the trends in composite weight-average molecular weight. Neither of the two particle-related parameters (concentration nor diameter) was found to exhibit a significant effect on intra-fiber nor inter-fiber porosity. These findings evidence the capacity for controlled loading of particulate delivery vehicles in 3D printed scaffolds while preserving construct accuracy and precision, and with predictable dictation of composite degradation behavior for potential controlled release of encapsulated biomolecules.

Towards sustainable horizons: A comprehensive blueprint for Mars colonization

This paper thoroughly explores the feasibility, challenges, and proposed solutions for establishing a sustainable human colony on Mars. We quantitatively and qualitatively analyze the Martian environment, highlighting key challenges such as radiation exposure, which astronauts could experience at minimum levels of 0.66 sieverts during a round trip, and the complications arising from Mars' thin atmosphere and extreme temperature variations. Technological advancements are examined, including developing Martian concrete, which utilizes sulfur as a binding agent, and innovative life support strategies like aeroponics and algae bioreactors. The human aspect of colonization is addressed, focusing on long-term space habitation's psychological and physiological impacts. We also present a cost-benefit analysis of in-situ resource utilization versus Earth-based supply missions, emphasizing economic viability with the potential reduction in launch costs through reusable rocket technology. A timeline for the colonization process is suggested, spanning preliminary unmanned missions for resource assessment, followed by short-term manned missions leading to sustainable settlements over several decades. The paper concludes with recommendations for future research, particularly in refining resource utilization techniques and advancing health and life support systems, to solidify the foundation for Mars colonization. This comprehensive assessment aims to guide researchers, policymakers, and stakeholders in planning and executing a strategic and informed approach to making Mars colonization a reality.

Microbial biomanufacturing for space-exploration-what to take and when to make

As renewed interest in human space-exploration intensifies, a coherent and modernized strategy for mission design and planning has become increasingly crucial. Biotechnology has emerged as a promising approach to increase resilience, flexibility, and efficiency of missions, by virtue of its ability to effectively utilize in situ resources and reclaim resources from waste streams. Here we outline four primary mission-classes on Moon and Mars that drive a staged and accretive biomanufacturing strategy. Each class requires a unique approach to integrate biomanufacturing into the existing mission-architecture and so faces unique challenges in technology development. These challenges stem directly from the resources available in a given mission-class-the degree to which feedstocks are derived from cargo and in situ resources-and the degree to which loop-closure is necessary. As mission duration and distance from Earth increase, the benefits of specialized, sustainable biomanufacturing processes also increase. Consequentially, we define specific design-scenarios and quantify the usefulness of in-space biomanufacturing, to guide techno-economics of space-missions. Especially materials emerged as a potentially pivotal target for biomanufacturing with large impact on up-mass cost. Subsequently, we outline the processes needed for development, testing, and deployment of requisite technologies. As space-related technology development often does, these advancements are likely to have profound implications for the creation of a resilient circular bioeconomy on Earth.

Toward the utilisation of resources in space: knowledge gaps, open questions, and priorities

There are many open science questions in space resource utilisation due to the novelty and relative immaturity of the field. While many potential technologies have been proposed to produce usable resources in space, high confidence, large-scale design is limited by gaps in the knowledge of the local environmental conditions, geology, mineralogy, and regolith characteristics, as well as specific science questions intrinsic to each process. Further, the engineering constraints (e.g. energy, throughput, efficiency etc.) must be incorporated into the design. This work aims to summarise briefly recent activities in the field of space resource utilisation, as well as to identify key knowledge gaps, and to present open science questions. Finally, future exploration priorities to enable the use of space resources are highlighted.

Terrestrial Laser Scanning of Lunar Soil Simulants

In the near future, permanent human settlements on the Moon will become increasingly realistic. It is very likely that the Moon will serve as a transit point for deep space exploration (e.g., to Mars). The key to human presence on the Moon is the ability to erect the necessary structures and habitats using locally available materials, such as lunar soil. This study explores the feasibility of using terrestrial laser scanning technology as a measurement method for civil engineering applications on the Moon. Three lunar soil simulants representing highland regions (LHS-1, AGK-2010, CHENOBI) and three lunar soil simulants representing mare regions (LMS-1, JSC-1A, OPRL2N) were used in this study. Measurements were performed using three terrestrial laser scanners (Z+F IMAGER 5016, FARO Focus^3D, and Leica ScanStation C10). The research programme focused on the radiometric analysis of datasets from the measurement of lunar soil simulants. The advantages and limitations of terrestrial laser scanning technology for possible lunar applications are discussed. Modifications of terrestrial laser scanners that are necessary to enable their use on the Moon are suggested.

Material extrusion additive manufacturing of dense pastes consisting of macroscopic particles

Additive manufacturing of dense pastes, those with greater than 50 vol% particles, via material extrusion direct ink write is a promising method to produce customized structures for high-performance materials, such as energetic materials and pharmaceuticals, as well as to enable the use of waste or other locally available particles. However, the high volume fraction and the large sizes of the particles for these applications lead to significant challenges in developing inks and processing methods to prepare quality parts. In this prospective, we analyze challenges in managing particle characteristics, stabilizing the suspensions, mixing the particles and binder, and 3D printing the pastes.

3D direct printing of mechanical and biocompatible hydrogel meta-structures

Direct Ink Writing (DIW) has demonstrated great potential as a versatile method to 3D print multifunctional structures. In this work, we report the implementation of hydrogel meta-structures using DIW at room temperature, which seamlessly integrate large specific surface areas, interconnected porous characteristics, mechanical toughness, biocompatibility, and water absorption and retention capabilities. Robust but hydrophobic polymers and weakly crosslinked nature-origin hydrogels form a balance in the self-supporting ink, allowing us to directly print complex meta-structures without sacrificial materials and heating extrusion. Mechanically, the mixed bending or stretching of symmetrical re-entrant cellular lattices and the unique curvature patterns are combined to provide little lateral expansion and large compressive energy absorbance when external forces are applied on the printed meta-structures. In addition, we have successfully demonstrated ear, aortic valve conduits and hierarchical architectures. We anticipate that the reported 3D meta-structured hydrogel would offer a new strategy to develop functional biomaterials for tissue engineering applications in the future.

Blood, sweat, and tears: extraterrestrial regolith biocomposites with in vivo binders

The proverbial phrase 'you can't get blood from a stone' is used to describe a task that is practically impossible regardless of how much force or effort is exerted. This phrase is well-suited to humanity's first crewed mission to Mars, which will likely be the most difficult and technologically challenging human endeavor ever undertaken. The high cost and significant time delay associated with delivering payloads to the Martian surface means that exploitation of resources in situ - including inorganic rock and dust (regolith), water deposits, and atmospheric gases - will be an important part of any crewed mission to the Red Planet. Yet there is one significant, but chronically overlooked, source of natural resources that will - by definition - also be available on any crewed mission to Mars: the crew themselves. In this work, we explore the use of human serum albumin (HSA) - a common protein obtained from blood plasma - as a binder for simulated Lunar and Martian regolith to produce so-called 'extraterrestrial regolith biocomposites (ERBs).' In essence, HSA produced by astronauts in vivo could be extracted on a semi-continuous basis and combined with Lunar or Martian regolith to 'get stone from blood', to rephrase the proverb. Employing a simple fabrication strategy, HSA-based ERBs were produced and displayed compressive strengths as high as 25.0 MPa. For comparison, standard concrete typically has a compressive strength ranging between 20 and 32 MPa. The incorporation of urea - which could be extracted from the urine, sweat, or tears of astronauts - could further increase the compressive strength by over 300% in some instances, with the best-performing formulation having an average compressive strength of 39.7 MPa. Furthermore, we demonstrate that HSA-ERBs have the potential to be 3D-printed, opening up an interesting potential avenue for extraterrestrial construction using human-derived feedstocks. The mechanism of adhesion was investigated and attributed to the dehydration-induced reorganization of the protein secondary structure into a densely hydrogen-bonded, supramolecular β-sheet network - analogous to the cohesion mechanism of spider silk. For comparison, synthetic spider silk and bovine serum albumin (BSA) were also investigated as regolith binders - which could also feasibly be produced on a Martian colony with future advancements in biomanufacturing technology.

Utilisation of Moon Regolith for Radiation Protection and Thermal Insulation in Permanent Lunar Habitats

In the context of a sustainable long-term human presence on the Moon, solutions for habitat radiation and thermal protection with regolith are investigated. Regolith compression is studied to choose the optimal density-thickness combination in terms of radiation shielding and thermal insulation. The applied strategy is to protect the whole habitat from the hazards of galactic cosmic rays and design a dedicated shelter area for protection during solar particle events, which eventually may be a lava tube. Simulations using NASA’s OLTARIS tool show that the effective dose equivalent decreases significantly when a multilayer structure mainly constituted of regolith and other available materials is used instead of pure regolith. The computerised anatomical female model is considered here because future missions will be mixed crews, and, generally, more sex-specific data are required in the field of radiation protection and human spaceflight. This study shows that if reasonably achievable radioprotection conditions are met, mixed crews can stay safely on the lunar surface. Compressed regolith demonstrates a significant efficiency in thermal insulation, requiring little energy management to keep a comfortable temperature inside the habitat. For a more complete picture of the outpost, the radiation protection of lunar rovers and extravehicular mobility units is considered.

Ceramic Material Processing Towards Future Space Habitat: Electric Current-Assisted Sintering of Lunar Regolith Simulant

In situ utilization of available resources in space is necessary for future space habitation. However, direct sintering of the lunar regolith on the Moon as structural and functional components is considered to be challenging due to the sintering conditions. To address this issue, we demonstrate the use of electric current-assisted sintering (ECAS) as a single-step method of compacting and densifying lunar regolith simulant JSC-1A. The sintering temperature and pressure required to achieve a relative density of 97% and microhardness of 6 GPa are 700 °C and 50 MPa, which are significantly lower than for the conventional sintering technique. The sintered samples also demonstrated ferroelectric and ferromagnetic behavior at room temperature. This study presents the feasibility of using ECAS to sinter lunar regolith for future space resource utilization and habitation.

Martian biolith: A bioinspired regolith composite for closed-loop extraterrestrial manufacturing

Given plans to revisit the lunar surface by the late 2020s and to take a crewed mission to Mars by the late 2030s, critical technologies must mature. In missions of extended duration, in situ resource utilization is necessary to both maximize scientific returns and minimize costs. While this present a significantly more complex challenge in the resource-starved environment of Mars, it is similar to the increasing need to develop resource-efficient and zero-waste ecosystems on Earth. Here, we make use of recent advances in the field of bioinspired chitinous manufacturing to develop a manufacturing technology to be used within the context of a minimal, artificial ecosystem that supports humans in a Martian environment.

3D Printing and Solvent Dissolution Recycling of Polylactide-Lunar Regolith Composites by Material Extrusion Approach

The in situ resource utilization of lunar regolith is of great significance for the development of planetary materials science and space manufacturing. The material extrusion deposition approach provides an advanced method for fabricating polylactide/lunar regolith simulant (PLA/CLRS-1) components. This work aims to fabricate 3D printed PLA-lunar regolith simulant (5 and 10 wt.%) components using the material extrusion 3D printing approach, and realize their solvent dissolution recycling process. The influence of the lunar regolith simulant on the mechanical and thermal properties of the 3D printed PLA/CLRS-1 composites is systematically studied. The microstructure of 3D printed PLA/CLRS-1 parts was investigated by scanning electron microscopy (SEM) and X-ray computed tomography (XCT) analysis. The results showed that the lunar regolith simulant can be fabricated and combined with a PLA matrix utilizing a 3D printing process, only slightly influencing the mechanical performance of printed specimens. Moreover, the crystallization process of PLA is obviously accelerated by the addition of CLRS-1 because of heterogeneous nucleation. Additionally, by using gel permeation chromatography (GPC) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) characterization, it is found that the 3D printing and recycling processes have a negligible influence on the chemical structure and molecular weight of the PLA/CLRS-1 composites. As a breakthrough, we successfully utilize the lunar regolith simulant to print components with satisfactory mechanical properties and confirm the feasibility of recycling and reusing 3D printed PLA/CLRS-1 components via the solvent dissolution recycling approach.

Multi-material additive manufacturing technologies for Ti-, Mg-, and Fe-based biomaterials for bone substitution

The growing interest in multi-functional metallic biomaterials for bone substitutes challenges the current additive manufacturing (AM, =3D printing) technologies. It is foreseeable that advances in multi-material AM for metallic biomaterials will not only allow for complex geometrical designs, but also improve their multi-functionalities by tuning the types or compositions of the underlying base materials, thereby presenting unprecedented opportunities for advanced orthopedic treatments. AM technologies are yet to be extensively explored for the fabrication of multi-functional metallic biomaterials, especially for bone substitutes. The aim of this review is to present the viable options of the state-of-the-art multi-material AM for Ti-, Mg-, and Fe-based biomaterials to be used as bone substitutes. The review starts with a brief review of bone tissue engineering, the design requirements, and fabrication technologies for metallic biomaterials to highlight the advantages of using AM over conventional fabrication methods. Five AM technologies suitable for metal 3D printing are compared against the requirements for multi-material AM. Of these AM technologies, extrusion-based multi-material AM is shown to have the greatest potential to meet the requirements for the fabrication of multi-functional metallic biomaterials. Finally, recent progress in the fabrication of Ti-, Mg-, and Fe-based biomaterials including the utilization of multi-material AM technologies is reviewed so as to identify the knowledge gaps and propose the directions of further research for the development of multi-material AM technologies that are applicable for the fabrication of multi-functional metallic biomaterials. STATEMENT OF SIGNIFICANCE: Addressing a critical bone defect requires the assistance of multi-functional porous metallic bone substitutes. As one of the most advanced fabrication technology in bone tissue engineering, additive manufacturing is challenged for its viability in multi-material fabrication of metallic biomaterials. This article reviews how the current metal additive manufacturing technologies have been and can be used for multi-material fabrication of Ti-, Mg-, and Fe-based bone substitutes. Progress on the Ti-, Mg-, and Fe-based biomaterials, including the utilization of multi-material additive manufacturing, are discussed to direct future research for advancing the multi-functional additively manufactured metallic bone biomaterials.

Effect of Polymer Binder on the Synthesis and Properties of 3D-Printable Particle-Based Liquid Materials and Resulting Structures

Recent advances have demonstrated the ability to 3D-print, via extrusion, solvent-based liquid materials (previously named 3D-Paints) which solidify nearly instantaneously upon deposition and contain a majority by volume of solid particulate material. In prior work, the dissolved polymer binder which enables this process is a high molecular weight biocompatible elastomer, poly(lactic-co-glycolic) acid (PLGA). We demonstrate in this study an expansion of this solvent-based 3D-Paint system to two additional, less-expensive, and less-specialized polymers, polystyrene (PS) and polyethylene oxide (PEO). The polymer binder used within the 3D-Paint was shown to significantly affect the as-printed and thermal postprocessing behavior of printed structures. This development enables users to select one of several polymers to impart the most desirable properties for a given application. Additionally, 3D-Paints based on these new binders are not adversely affected by classes of particles that can chemically degrade PLGA, notably particles containing large quantities of alkali ions. This study demonstrates the ability to successfully use PS and PEO as binders in the 3D-Paint system and compares the rheological, mechanical, microstructural, and thermal properties of the modified 3D-Paints and resulting as-printed and thermally post-processed objects. These objects include, for the first time, structures resulting from 3D-Painting which mostly contain soda-lime glass and 45S5 bioactive glass.

Towards the colonization of Mars by in-situ resource utilization: Slip cast ceramics from Martian soil simulant

Here we demonstrate that by applying exclusively Martian resources a processing route involving suspensions of mineral particles called slurries or slips can be established for manufacturing ceramics on Mars. We developed water-based slurries without the use of additives that had a 51 wt. % solid load resembling commercial porcelain slurries in respect to the particle size distribution and rheological properties. These slurries were used to slip cast discs, rings and vases that were sintered at temperatures between 1000 and 1130 °C using different sintering schedules, the latter were set-up according the results of hot-stage microscopic characterization. The microstructure, porosity and the mechanical properties were characterized by SEM, X-ray computer tomography and Weibull analysis. Our wet processing of minerals yields ceramics with complex shapes that show similar mechanical properties to porcelain and could serve as a technology for future Mars colonization. The best quality parts with completely vitrificated matrix supporting a few idiomorphic crystals are obtained at 1130 °C with 10 h dwell time with volume and linear shrinkage as much as ~62% and ~17% and a characteristic compressive strength of 51 MPa.

Three-Dimensional Printing of Cytocompatible, Thermally Conductive Hexagonal Boron Nitride Nanocomposites

Hexagonal boron nitride (hBN) is a thermally conductive yet electrically insulating two-dimensional layered nanomaterial that has attracted significant attention as a dielectric for high-performance electronics in addition to playing a central role in thermal management applications. Here, we report a high-content hBN-polymer nanocomposite ink, which can be 3D printed to form mechanically robust, self-supporting constructs. In particular, hBN is dispersed in poly(lactic- co-glycolic acid) and 3D printed at room temperature through an extrusion process to form complex architectures. These constructs can be 3D printed with a composition of up to 60% vol hBN (solids content) while maintaining high mechanical flexibility and stretchability. The presence of hBN within the matrix results in enhanced thermal conductivity (up to 2.1 W K^-1 m^-1) directly after 3D printing with minimal postprocessing steps, suggesting utility in thermal management applications. Furthermore, the constructs show high levels of cytocompatibility, making them suitable for use in the field of printed bioelectronics.

3D-printing porosity: A new approach to creating elevated porosity materials and structures

We introduce a new process that enables the ability to 3D-print high porosity materials and structures by combining the newly introduced 3D-Painting process with traditional salt-leaching. The synthesis and resulting properties of three 3D-printable inks comprised of varying volume ratios (25:75, 50:50, 70:30) of CuSO₄ salt and polylactide-co-glycolide (PLGA), as well as their as-printed and salt-leached counterparts, are discussed. The resulting materials are comprised entirely of PLGA (F-PLGA), but exhibit porosities proportional to the original CuSO₄ content. The three distinct F-PLGA materials exhibit average porosities of 66.6-94.4%, elastic moduli of 112.6-2.7 MPa, and absorbency of 195.7-742.2%. Studies with adult human mesenchymal stem cells (hMSCs) demonstrated that elevated porosity substantially promotes cell adhesion, viability, and proliferation. F-PLGA can also act as carriers for weak, naturally or synthetically-derived hydrogels. Finally, we show that this process can be extended to other materials including graphene, metals, and ceramics.

STATEMENT OF SIGNIFICANCE

Porosity plays an essential role in the performance and function of biomaterials, tissue engineering, and clinical medicine. For the same material chemistry, the level of porosity can dictate if it is cell, tissue, or organ friendly; with low porosity materials being far less favorable than high porosity materials. Despite its importance, it has been difficult to create three-dimensionally printed structures that are comprised of materials that have extremely high levels of internal porosity yet are surgically friendly (able to handle and utilize during surgical operations). In this work, we extend a new materials-centric approach to 3D-printing, 3D-Painting, to 3D-printing structures made almost entirely out of water-soluble salt. The structures are then washed in a specific way that not only extracts the salt but causes the structures to increase in size. With the salt removed, the resulting medical polymer structures are almost entirely porous and contain very little solid material, but the maintain their 3D-printed form and are highly compatible with adult human stem cells, are mechanically robust enough to use in surgical manipulations, and can be filled with and act as carriers for biologically active liquids and gels. We can also extend this process to three-dimensionally printing other porous materials, such as graphene, metals, and even ceramics.

3D printed hyperelastic "bone" scaffolds and regional gene therapy: A novel approach to bone healing

The purpose of this study was to evaluate the viability of human adipose-derived stem cells (ADSCs) transduced with a lentiviral (LV) vector to overexpress bone morphogenetic protein-2 (BMP-2) loaded onto a novel 3D printed scaffold. Human ADSCs were transduced with a LV vector carrying the cDNA for BMP-2. The transduced cells were loaded onto a 3D printed Hyperelastic "Bone" (HB) scaffold. In vitro BMP-2 production was assessed using enzyme-linked immunosorbent assay analysis. The ability of ADSCs loaded on the HB scaffold to induce in vivo bone formation in a hind limb muscle pouch model was assessed in the following groups: ADSCs transduced with LV-BMP-2, LV-green fluorescent protein, ADSCs alone, and empty HB scaffolds. Bone formation was assessed using radiographs, histology and histomorphometry. Transduced ADSCs BMP-2 production on the HB scaffold at 24 hours was similar on 3D printed HB scaffolds versus control wells with transduced cells alone, and continued to increase after 1 and 2 weeks of culture. Bone formation was noted in LV-BMP-2 animals on plain radiographs at 2 and 4 weeks after implantation; no bone formation was noted in the other groups. Histology demonstrated that the LV-BMP-2 group was the only group that formed woven bone and the mean bone area/tissue area was significantly greater when compared with the other groups. 3D printed HB scaffolds are effective carriers for transduced ADSCs to promote bone repair. The combination of gene therapy and tissue engineered scaffolds is a promising multidisciplinary approach to bone repair with significant clinical potential. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1104-1110, 2018.

"Tissue Papers" from Organ-Specific Decellularized Extracellular Matrices

Using an innovative, tissue-independent approach to decellularized tissue processing and biomaterial fabrication, the development of a series of "tissue papers" derived from native porcine tissues/organs (heart, kidney, liver, muscle), native bovine tissue/organ (ovary and uterus), and purified bovine Achilles tendon collagen as a control from decellularized extracellular matrix particle ink suspensions cast into molds is described. Each tissue paper type has distinct microstructural characteristics as well as physical and mechanical properties, is capable of absorbing up to 300% of its own weight in liquid, and remains mechanically robust (E = 1-18 MPa) when hydrated; permitting it to be cut, rolled, folded, and sutured, as needed. In vitro characterization with human mesenchymal stem cells reveals that all tissue paper types support cell adhesion, viability, and proliferation over four weeks. Ovarian tissue papers support mouse ovarian follicle adhesion, viability, and health in vitro, as well as support, and maintain the viability and hormonal function of nonhuman primate and human follicle-containing, live ovarian cortical tissues ex vivo for eight weeks postmortem. "Tissue papers" can be further augmented with additional synthetic and natural biomaterials, as well as integrated with recently developed, advanced 3D-printable biomaterials, providing a versatile platform for future multi-biomaterial construct manufacturing.