3D Bioprinting in Microgravity: Opportunities, Challenges, and Possible Applications in Space

Taking the 3Rs to a higher level: replacement and reduction of animal testing in life sciences in space research

Human settlements on the Moon, crewed missions to Mars and space tourism will become a reality in the next few decades. Human presence in space, especially for extended periods of time, will therefore steeply increase. However, despite more than 60 years of spaceflight, the mechanisms underlying the effects of the space environment on human physiology are still not fully understood. Animals, ranging in complexity from flies to monkeys, have played a pioneering role in understanding the (patho)physiological outcome of critical environmental factors in space, in particular altered gravity and cosmic radiation. The use of animals in biomedical research is increasingly being criticized because of ethical reasons and limited human relevance. Driven by the 3Rs concept, calling for replacement, reduction and refinement of animal experimentation, major efforts have been focused in the past decades on the development of alternative methods that fully bypass animal testing or so-called new approach methodologies. These new approach methodologies range from simple monolayer cultures of individual primary or stem cells all up to bioprinted 3D organoids and microfluidic chips that recapitulate the complex cellular architecture of organs. Other approaches applied in life sciences in space research contribute to the reduction of animal experimentation. These include methods to mimic space conditions on Earth, such as microgravity and radiation simulators, as well as tools to support the processing, analysis or application of testing results obtained in life sciences in space research, including systems biology, live-cell, high-content and real-time analysis, high-throughput analysis, artificial intelligence and digital twins. The present paper provides an in-depth overview of such methods to replace or reduce animal testing in life sciences in space research.

Pharmacological countermeasures for long-duration space missions: addressing cardiovascular challenges and advancing space-adapted healthcare

Future long-duration crewed space missions beyond Low Earth Orbit (LEO) will bring new healthcare challenges for astronauts for which pharmacological countermeasures (pharmacological countermeasures) are crucial. This paper highlights current pharmacological countermeasures challenges described in the ESA SciSpacE Roadmap, with a focus on the cardiovascular system as a model to demonstrate the potential implication of the challenges and recommendations. New pharmacological approaches and procedures need to be adapted to spaceflight (spaceflight) conditions, including ethical and reglementary considerations. Potential strategies include combining pharmacological biomarkers such as pharmacogenomics with therapeutic drug monitoring, advancing microsampling techniques, and implementing a pharmacovigilance system to gain deep insights into pharmacokinetics/pharmacodynamics (PK/PD) spaceflight alteration on drug exposure. Emerging therapeutic approaches (such as long-term regimens) or manufacturing drugs in the space environment, can address specific issues related to drug storage and stability. The integration of biobanks and innovative technologies like organoids and organ-on-a-chip, artificial intelligence (AI), including machine learning will further enhance PK modelling leading to personalized treatments. These innovative pharmaceutical tools will also enable reciprocal game-changing healthcare developments to be made on Earth as well as in space and are essential to ensure space explorers receive safe effective pharmaceutical care.

Hydrogels in Simulated Microgravity: Thermodynamics at Play

Hydrogels have become indispensable in biomedical research and regenerative therapies due to their high water content, tissue-like mechanics, and tunable biochemical properties. However, their behavior under altered gravitational conditions-particularly simulated microgravity (SMG)-presents a frontier of challenges and opportunities that remain underexplored. This comprehensive review provides a detailed comparative analysis of hydrogel performance in normal gravity versus SMG environments, focusing on the structural, physicochemical, and thermodynamic parameters that govern their functionality. We critically examine how microgravity influences polymer network formation, fluid dynamics, swelling behavior, mechanical stability, and degradation kinetics. SMG disrupts convection, sedimentation, and phase separation, often leading to inhomogeneous crosslinking and altered diffusion profiles. These changes can compromise hydrogel uniformity, anisotropy, and responsiveness, which are essential for biomedical applications such as drug delivery, tissue regeneration, and biosensing. To address these limitations, we propose a thermodynamic framework that integrates osmotic pressure regulation, entropy-driven swelling, and pressure-temperature control to enhance hydrogel stability and functionality in low-gravity environments. The integration of predictive modeling approaches-including finite element simulations, phase-field models, and swelling kinetics-provides a robust pathway to design space-adapted hydrogel systems. The review also outlines future directions for optimizing hydrogel platforms in extraterrestrial settings, advocating for synergistic advances in material science, biophysics, and space health. These insights offer a strategic foundation for the rational development of next-generation hydrogel technologies tailored for long-duration space missions and planetary biomedical infrastructure.

Risk of Permanent Corneal Injury in Microgravity: Spaceflight-Associated Hazards, Challenges to Vision Restoration, and Role of Biotechnology in Long-Term Planetary Missions

Human space exploration presents an unparalleled opportunity to study life in extreme environments-but it also exposes astronauts to physiological stressors that jeopardize key systems like vision. Corneal health, essential for maintaining precise visual acuity, is threatened by microgravity-induced fluid shifts, cosmic radiation, and the confined nature of spacecraft living environments. These conditions elevate the risk of corneal abrasions, infections, and structural damage. In addition, Spaceflight-Associated Neuro-Ocular Syndrome (SANS)-while primarily affecting the posterior segment-has also been potentially linked to anterior segment alterations such as corneal edema and tear film instability. This review examines these ocular challenges and assesses current mitigation strategies. Traditional approaches, such as terrestrial eye banking and corneal transplantation, are impractical for spaceflight due to the limited viability of preserved tissues, surgical complexities, anesthetic risks, infection potential, and logistical constraints. The paper explores emerging technologies like 3D bioprinting and stem cell-based tissue engineering, which offer promising solutions by enabling the on-demand production of personalized corneal constructs. Complementary advancements, including adaptive protective eyewear, bioengineered tear substitutes, telemedicine, and AI-driven diagnostic tools, also show potential in autonomously managing ocular health during long-duration missions. By addressing the complex interplay of environmental stressors and biological vulnerabilities, these innovations not only safeguard astronaut vision and mission performance but also catalyze new pathways for regenerative medicine on Earth. The evolution of space-based ophthalmic care underscores the dual impact of space medicine investments across planetary exploration and terrestrial health systems.

Advanced Toolboxes for Cryobioprinting Human Tissue Analogs

The increasing demand for biofabricating human tissue analogs for therapeutic applications has encouraged the pursuit of innovative techniques that shift from conventional bioprint-to-use approaches toward instantaneous bioprint-cryopreserve strategies. Such enabling concepts and next-generation technologies open new possibilities for fabricating shelf-ready living constructs for applications in regenerative medicine, preclinical disease modeling, and beyond. The generation of living constructs either for short- or long-term cryostorage requires, however, a careful design of cryoprotective bioinks to maximize biofunctionality and limit cell damage during processing. Gathering on this, herein the most recent updates in cryo(bio)printing technologies are showcased and discussed, along with demonstrative applications of these approaches. The technical toolboxes for designing cryoprotective inks and optimizing freezing/thawing processes are also critically addressed, considering their underlying bioengineering challenges. Realizing the full potential of cryobioprinting is envisioned to unlock the fabrication of increasingly biomimetic tissue constructs and personalized medicine solutions that are readily available, precisely when needed.

Xolography for 3D Printing in Microgravity

Xolography is a volumetric 3D printing technique utilizing intersecting light beams within a volume of photopolymer for a spatially controlled photopolymerization. Unlike layer-based methods, Xolography creates structures continuously within a closed photopolymer vat, eliminating the prevalent need for support structures and allowing full geometrical freedom at high printing speeds. The volumetric working principle does not rely on gravity, making Xolography an outstanding technology for additive manufacturing under microgravity conditions as illustrated in a set of experiments during a parabolic flight campaign. The microgravity environment obviates the need for rheology control of resins, enabling the use of low-viscosity formulations (e.g., 11 mPa s) while maintaining the fast and precise 3D printing of acrylic polymer resins and hydrogels. Xolography's speed and reliability facilitate rapid iterations of a print task between Earth's gravity and microgravity conditions. This capability positions Xolography as an ideal tool for material research and manufacturing in space, offering significant cost and efficiency advantages over traditional methods.

Light-based 3D bioprinting techniques for illuminating the advances of vascular tissue engineering

Vascular tissue engineering faces significant challenges in creating in vitro vascular disease models, implantable vascular grafts, and vascularized tissue/organ constructs due to limitations in manufacturing precision, structural complexity, replicating the composited architecture, and mimicking the mechanical properties of natural vessels. Light-based 3D bioprinting, leveraging the unique advantages of light including high resolution, rapid curing, multi-material adaptability, and tunable photochemistry, offers transformative solutions to these obstacles. With the emergence of diverse light-based 3D bioprinting techniques and innovative strategies, the advances in vascular tissue engineering have been significantly accelerated. This review provides an overview of the human vascular system and its physiological functions, followed by an in-depth discussion of advancements in light-based 3D bioprinting, including light-dominated and light-assisted techniques. We explore the application of these technologies in vascular tissue engineering for creating in vitro vascular disease models recapitulating key pathological features, implantable blood vessel grafts, and tissue analogs with the integration of capillary-like vasculatures. Finally, we provide readers with insights into the future perspectives of light-based 3D bioprinting to revolutionize vascular tissue engineering.

Bioengineered human arterial equivalent and its applications from vascular graft to in vitro disease modeling

Arterial disorders such as atherosclerosis, thrombosis, and aneurysm pose significant health risks, necessitating advanced interventions. Despite progress in artificial blood vessels and animal models aimed at understanding pathogenesis and developing therapies, limitations in graft functionality and species discrepancies restrict their clinical and research utility. Addressing these issues, bioengineered arterial equivalents (AEs) with enhanced vascular functions have been developed, incorporating innovative technologies that improve clinical outcomes and enhance disease progression modeling. This review offers a comprehensive overview of recent advancements in bioengineered AEs, systematically summarizing the bioengineered technologies used to construct these AEs, and discussing their implications for clinical application and pathogenesis understanding. Highlighting current breakthroughs and future perspectives, this review aims to inform and inspire ongoing research in the field, potentially transforming vascular medicine and offering new avenues for preclinical and clinical advances.

Cellular response in three-dimensional spheroids and tissues exposed to real and simulated microgravity: a narrative review

The rising aging population underscores the need for advances in tissue engineering and regenerative medicine. Alterations in cellular response in microgravity might be pivotal in unraveling the intricate cellular mechanisms governing tissue and organ regeneration. Microgravity could improve multicellular spheroid, tissue, and organ formation. This review summarizes microgravity-induced cellular alterations and highlights the potential of tissue engineering in microgravity for future breakthroughs in space travel, transplantation, drug testing, and personalized medicine.

3D bioprinting meniscus tissue onboard the International Space Station

We bioprinted meniscus tissue on the International Space Station (ISS) using the onboard BioFabrication Facility (BFF). The three dimensional (3D) printing bioink, cells, culture media and fixative were delivered to the ISS on NG-18 and SpX-27 vehicles and stored prior to the printing operation. The meniscus tissue was fabricated from ink composed of collagens type I and II, chondroitin sulfate and mesenchymal stem cells. Following printing, the meniscus tissue was cultured for 2 weeks in growth media, then stored at 4 °C and returned to earth for analysis. The print showed good overall shape fidelity, and dimensions were comparable to control meniscus tissue printed on Earth. Young's modulus of the ISS printed meniscus was approximately 4-fold lower than the control. Histologic evaluation showed good cell distribution within the print. Though logistical challenges were encountered during payload delivery to the ISS and operational challenges limited the cell culture portion of this study, this investigation demonstrated the feasibility for 3D printed musculoskeletal tissue in microgravity. The completed meniscus tissue print is the largest tissue engineered model 3D printed on the ISS to date, the first to be 3D bioprinted using an ink similar in composition to native tissue, and the first to be fabricated on the ISS in an anatomically relevant shape. These experiments help advance the field of tissue engineering in low or microgravity where 3D bioprinting may have a role in future long term space flight or extraterrestrial habitation.

Electrohydrodynamic Direct-Writing Micro/Nanofibrous Architectures: Principle, Materials, and Biomedical Applications

Electrohydrodynamic (EHD) direct-writing has recently gained attention as a highly promising additive manufacturing strategy for fabricating intricate micro/nanoscale architectures. This technique is particularly well-suited for mimicking the extracellular matrix (ECM) present in biological tissue, which serves a vital function in facilitating cell colonization, migration, and growth. The integration of EHD direct-writing with other techniques has been employed to enhance the biological performance of scaffolds, and significant advancements have been made in the development of tailored scaffold architectures and constituents to meet the specific requirements of various biomedical applications. Here, a comprehensive overview of EHD direct-writing is provided, including its underlying principles, demonstrated materials systems, and biomedical applications. A brief chronology of EHD direct-writing is provided, along with an examination of the observed phenomena that occur during the printing process. The impact of biomaterial selection and architectural topographic cues on biological performance is also highlighted. Finally, the major limitations associated with EHD direct-writing are discussed.

Omics Studies of Specialized Cells and Stem Cells under Microgravity Conditions

The primary objective of omics in space with focus on the human organism is to characterize and quantify biological factors that alter structure, morphology, function, and dynamics of human cells exposed to microgravity. This review discusses exciting data regarding genomics, transcriptomics, epigenomics, metabolomics, and proteomics of human cells and individuals in space, as well as cells cultured under simulated microgravity. The NASA Twins Study significantly heightened interest in applying omics technologies and bioinformatics in space and terrestrial environments. Here, we present the available publications in this field with a focus on specialized cells and stem cells exposed to real and simulated microgravity conditions. We summarize current knowledge of the following topics: (i) omics studies on stem cells, (ii) omics studies on benign specialized different cell types of the human organism, (iii) discussing the advantages of this knowledge for space commercialization and exploration, and (iv) summarizing the emerging opportunities for translational regenerative medicine for space travelers and human patients on Earth.

Exploring New Horizons: Advancements in Cartilage Tissue Engineering Under Space Microgravity

Novel investigations of how microgravity affects cellular and tissue development have recently been made possible by the multidisciplinary fusion of tissue engineering and space science. This review examines the intersection of cartilage tissue engineering (CTE) and space science, focusing on how microgravity affects cartilage development. Space microgravity induces distinct physiological changes in chondrocytes, including a 20-30% increase in cell diameter, a 1.5- to 2-fold increase in proliferation rates, and up to 3-fold increases in chondrogenic markers such as SOX9 and collagen type II. These cellular alterations impact extracellular matrix composition and tissue structure. Space-optimized bioreactors using dynamic culture methods replicate physiological conditions and enhance tissue growth, but the absence of gravity raises concerns about the mechanical properties of engineered cartilage. Key research areas include the role of growth factors in cartilage development under microgravity, biocompatibility and degradation of scaffold materials in space, and in situ experiments on space stations. This review highlights the opportunities and challenges in leveraging microgravity for CTE advancements, emphasizing the need for continued research to harness space environments for therapeutic applications in cartilage regeneration. The multidisciplinary fusion of tissue engineering and space science opens novel avenues for understanding and improving cartilage tissue engineering, with significant implications for the future of biomedical applications in space and on Earth.

Satellite-Based On-Orbit Printing of 3D Tumor Models

Space three dimension (3D） bioprinting provides a precise and bionic tumor model for evaluating the compound effect of the space environment on tumors, thereby providing insight into the progress of the disease and potential treatments. However, space 3D bioprinting faces several challenges, including prelaunch uncertainty, possible liquid leakage, long-term culture in space, automatic equipment control, data acquisition, and transmission. Here, a novel satellite-based 3D bioprinting device with high structural strength, small volume, and low weight (<6 kg) is developed. A microgel-based biphasic thermosensitive bioink and suspension medium that supports the on-orbit printing and in situ culture of complex tumor models is developed. An intelligent control algorithm that enables the automatic control of 3D printing, autofocusing, fluorescence imaging, and data transfer back to the ground is developed. To the authors' knowledge, this is the first time that on-orbit printing of tumor models is achieved in space with stable morphology and moderate viability via a satellite. It is found that 3D tumor models are more sensitive to antitumor drugs in space than on Earth. This study opens up a new avenue for 3D bioprinting in space and offers new possibilities for future research in space life science and medicine.

Light from Afield: Fast, High-Resolution, and Layer-Free Deep Vat 3D Printing

Harnessing light for cross-linking of photoresponsive materials has revolutionized the field of 3D printing. A wide variety of techniques leveraging broad-spectrum light shaping have been introduced as a way to achieve fast and high-resolution printing, with applications ranging from simple prototypes to biomimetic engineered tissues for regenerative medicine. Conventional light-based printing techniques use cross-linking of material in a layer-by-layer fashion to produce complex parts. Only recently, new techniques have emerged which deploy multidirection, tomographic, light-sheet or filamented light-based image projections deep into the volume of resin-filled vat for photoinitiation and cross-linking. These Deep Vat printing (DVP) approaches alleviate the need for layer-wise printing and enable unprecedented fabrication speeds (within a few seconds) with high resolution (>10 μm). Here, we elucidate the physics and chemistry of these processes, their commonalities and differences, as well as their emerging applications in biomedical and non-biomedical fields. Importantly, we highlight their limitations, and future scope of research that will improve the scalability and applicability of these DVP techniques in a wide variety of engineering and regenerative medicine applications.

Effects of high gravity on properties of parts fabricated using material extrusion system by additive manufacturing

Additive manufacturing (AM) has gained significant attention in recent years owing to its ability to fabricate intricate shapes and structures that are often challenging or unattainable using conventional manufacturing techniques. This high-quality development trend entails higher requirements for the structural design of 3D printers. In this study, polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) filaments were fed through a heated extrusion nozzle, which melted the material and deposited it onto a build platform. This study's objectives are high-gravitational material extrusion (HG-MEX) systems development, analyzing the high gravity influences on the flow behavior of materials during extrusion, and understanding the effects of gravitational on material flow and overall extrusion performance. HG-MEX systems have great potential for addressing various challenges in additive manufacturing, such as precise manufacturing. The highlight of the progress is that we developed an HG-MEX system and applied surface science to material extrusion in different gravity. We established a system and obtained results on different gravity, we analyzed the analogy between different gravity phenomena. We analyzed the interplay between the behavior of the fabricated parts and gravity. We analyzed high gravity effects on extrusion processes. The results confirmed the characteristics and feasibility of the developed system. The results suggest that a material extrusion line operating under 15 G conditions resulted in better printing quality compared to one operating under 1 G conditions. This observation implies that high gravity had a positive effect on the extrusion process, leading to improved material extrusion performance.

On-demand fabrication of piezoelectric sensors for in-space structural health monitoring

Inflatable structures, promising for future deep space exploration missions, are vulnerable to damage from micrometeoroid and orbital debris impacts. Polyvinylidene fluoride-trifluoroethylene (PVDF-trFE) is a flexible, biocompatible, and chemical-resistant material capable of detecting impact forces due to its piezoelectric properties. This study used a state-of-the-art material extrusion system that has been validated for in-space manufacturing, to facilitate fast-prototyping of consistent and uniform PVDF-trFE films. By systematically investigating ink synthesis, printer settings, and post-processing conditions, this research established a comprehensive understanding of the process-structure-property relationship of printed PVDF-trFE. Consequently, this study consistently achieved the printing of PVDF-trFE films with a thickness of around 40 μm, accompanied by an impressive piezoelectric coefficient of up to 25 pC N-1. Additionally, an all-printed dynamic force sensor, featuring a sensitivity of 1.18 V N-1, was produced by mix printing commercial electrically-conductive silver inks with the customized PVDF-trFE inks. This pioneering on-demand fabrication technique for PVDF-trFE films empowers future astronauts to design and manufacture piezoelectric sensors while in space, thereby significantly enhancing the affordability and sustainability of deep space exploration missions.

Enhancing cell-scale performance via sustained release of the varicella-zoster virus antigen from a microneedle patch under simulated microgravity

The immune system of astronauts might become weakened in the microgravity environment in space, and the dormant varicella-zoster virus (VZV) in the body might be reactivated, seriously affecting their work and safety. For working in orbit for the long term, there is currently no efficient and durable delivery system of general vaccines in a microgravity environment. Accordingly, based on the previous foundation, we designed, modified, and synthesized a biodegradable and biocompatible copolymer, polyethylene glycol-polysulfamethazine carbonate urethane (PEG-PSCU) that could be mainly adopted to fabricate a novel sustained-release microneedle (S-R MN) patch. Compared with conventional biodegradable microneedles, this S-R MN patch could not only efficiently encapsulate protein vaccines (varicella-zoster virus glycoprotein E, VZV gE) but also further prolong the release time of VZV gE in a simulated microgravity (SMG) environment. Eventually, we verified the activation of dendritic cells by VZV gE released from the S-R MN patch in an SMG environment and the positive bioeffect of activated dendritic cells on lymphocytes using an in vitro lymph node model. This study is of great significance for the exploration of long-term specific immune responses to the VZV in an SMG environment.