Highlights
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Space experiments in microgravity conditions advance the development of biofabrication technologies.
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Human organoids are useful novel in vitro human organ models, which can advance space life science research to study the effect of space microgravity.
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Human organoids could be used as biological ‘sentinels’ to study the effect and biomonitor space radiation.
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Histo-typical and organo-typical functional and vascularized human tissues and organs could be biofabricated in space from human organoids, ultimately using space environmental conditions (i.e., microgravity and cosmic radiation) as accelerators of human aging on Earth.
Biofabrication in space is one of the novel promising and prospective research directions in the rapidly emerging field of space STEM. There are several advantages of biofabrication in space. Under microgravity, it is possible to engineer constructs using more fluidic channels and thus more biocompatible bioinks. Microgravity enables biofabrication of tissue and organ constructs of more complex geometries, thus facilitating novel scaffold-, label-, and nozzle-free technologies based on multi-levitation principles. However, when exposed to microgravity and cosmic radiation, biofabricated tissues could be used to study pathophysiological phenomena that will be useful on Earth and for deep space manned missions. Here, we provide leading concepts about the potential mutual benefits of the application of biofabrication technologies in space.
Keywords
Setting the stage: biofabrication, organoids, and space
]. These models can be used to study the physiology of tissues and organs exposed to a variety of environmental conditions, such as microgravity (μg) and radiation, as encountered in space. Knowledge acquired from these models is crucial to understand the biological effects of the space environment for long-term manned missions, such as outlined in the ‘Moon village’ and ‘Mission to Mars’ programs (http://www.esa.int/About_Us/Ministerial_Council_2016/Moon_Village; http://exploration.esa.int/mars/; http://www.esa.int/Our_Activities/Human_Spaceflight/A_new_European_vision_for_space_exploration). Practical examples are not only well-known effects, such as osteoporosis for bone [
], but also muscle loss [
,
], cardiovascular [
,
] and lung capacity deficiencies due to microgravity [
], and the effect of radiation on sensitive organs such as thyroid, gonads, and intestine [
,
,
,
]. In addition to the more immediate effects, like acute radiation sickness, exposure to radiation also increases astronauts’ and cosmonauts’ risk to develop several cancers, genetic mutations, nervous system damage, and even cataracts [
,].
]. Despite these attempts, further steps need to be taken to move from proof-of-concept studies to real functional tissues and organs; in particular, for bioprinted soft tissues, such as blood vessels, which have proven to be more difficult to engineer [
,
]. However, these studies show that the potential of the bioprinting technology is close to reach. Bioprinting in microgravity has been so far mostly proven in parabolic flights, showing feasibility to deposit cell-laden hydrogel constructs with softer gels, which is otherwise difficult on Earth due to the lack of self-standing capacity of such gel formulations. More recently, Techshot Inc., a US commercial developer and operator of spaceflight equipment, and nScrypt, a manufacturer of industrial 3D bioprinters and electronics printers, developed the 3D BioFabrication Facility, which uses adult human cells (such as stem or pluripotent cells) and adult tissue-derived proteins as its bioink to create viable tissues on board the International Space Station (ISS). In addition, magnetic levitation bioprinting has been tested and validated on the ISS when, at the end of 2019, Russian scientists from 3D Bioprinting Solutions were able to bioprint bone tissue by growing fragments of bone structure in zero gravity conditions [
]. So far, these systems are the only ones that have been successfully tested in space. Besides the developments of NASA and ROSKOSMOS, the European Space Agency (ESA) is also planning for the implementation of a 3D bioprinting and cell culture module on the ISS.
]. Recently, the advent of instructive hydrogels has also allowed the successful bioprinting of pluripotent stem cells, opening to broader applications where multiple tissues or organ patches could be conceived [
,
,
]. It is only very recently, however, that bioprinting of organoids has been reported [
,
,
]. This advancement opens up new horizons, as bioprinted organ models may become closer and closer to reality, initially to provide 3D in vitro models for personalized medicine and with possible implications in the near future for translational regenerative medicine.
]. Organoids created from human stem cells open up new unique possibilities for creating in vitro models of human diseases, studying new drugs and their possible toxicity, and finally for regenerative medicine and tissue engineering purposes [
,
,
]. The study of organoids is becoming an extremely promising and rapidly developing area in biomedicine. The use of organoids in space research will solve many important issues of space biology and medicine, such as the effect of weightlessness on the functional and morphological characteristics of human tissues; the effect of cosmic radiation on human cells, tissues and organs; and the study of the regenerative potential of human tissues, encompassing the reproductive and cognitive ability in space. Utilizing the effects of microgravity, the study of organoids under space conditions is also very relevant for drug R&D, cancer research, and stem cell research, with benefit for Earth. Planned experiments and technological challenges associated with the implementation of research using organoids in space are discussed later. Finally, the integration of organoids with biofabrication technologies (Table 1) is further discussed in the context of space biology research and its implication back on Earth. Particular attention is paid to the technological support of experiments with human organoids to study the effect of a prolonged stay in space, long-distance interplanetary travel, and constant work on future extraterrestrial planetary settlements.
Definition of organoids and a brief history of the study of organoids
]. This definition does not embrace the achievements of recent years. More recently, pioneering works from the Clevers, Knoblich, and Lancaster labs primarily emphasized in their definitions the origin of organoids from stem cells and their self-development and self-differentiation [
,
].
].
Fundamental differences between organoids and tissue spheroids
Unfortunately, tissue spheroids are often mistakenly identified with organoids. In fact, significant and fundamental differences exist between these two types of microtissues. Tissue spheroids and organoids are often globular microtissues, composed of densely packed cells. However, this is where the apparent similarity between them essentially ends. Organoids are often irregular in shape, with jagged contours. Organoids are essentially a systematically cultivated teratoma, which often has an ugly shape and a chaotic structure. Organoids rarely consist of one type of cell, since they have an authentic histotype and an organ-specific structure and organization on histological sections. Organoids, unlike tissue spheroids, often have a lumen, which they cannot form without a natural ECM, such as Matrigel or its synthetic analogs. However, we would like to specifically draw attention to three fundamental differences between organoids and tissue spheroids: first, organoids are formed from stem cells and not from differentiated cells and tissues; second, organoids develop and are formed by self-organization and differentiation and not by assembling a cell suspension, as in the case of tissue spheroids; and third, in the case of organoids, as a rule, we are talking mainly about human cells.
Classification of organoids
,
].
Vascularization of organoids
]. Despite the current technological advancements [
], achieving in vivo-like organ complexity and maturation in vitro remains a challenge [
]. Novel concepts and ideas are therefore awaited. Some of these ideas are the use of mesodermal progenitor cells [
], engineered human embryonic stem cells ectopically expressing human ETS variant 2 [
], modified lab-on-chip systems [
], or even using photosynthetic strategies [
]. Figure I depicts the overall process of mature organ generation from the building blocks (cell source, biomaterials, and scaffolds), through 3D bioprinting, vascularization, continuous monitoring, and, finally, organ maturation.
Figure IOverview of a process to generate organs using 3D bioprinting and organoid technology.
Table 1Recent studies performing 3D bioprinting of organoids
Effect of spaceflight on the human body
Spaceflight affects the human body in several ways, but we will focus here on the main health issues that astronauts will have to face in the context of a long-term space mission, namely, some effects of microgravity and radiation.
The effects of microgravity on humans
,
,
]. Furthermore, astronauts will be subjected to different gravity levels and going from 1 g to weightlessness to Moon gravity (0.17 g) or Mars gravity (0.376 g) (Figure 2).
Figure 1Possible health impairment of astronauts and space travelers.
,
,
].
Figure 2Hazards of human spaceflights.
Different microgravity and radiation levels are developed. Individual as well as a combination of these hazards can cause different dysfunction, as seen previously. Created with BioRender. Abbreviations: ISS, International Space Station.
]. But the most serious effects of weightlessness are muscle atrophy and, more importantly, bone loss. During a spaceflight, humans in space lose an average of 0.5% to 2% of bone mass per month, or from 6% to 24% per year [
]. By comparison, postmenopausal osteoporosis causes a bone loss of 3% to 4% per year and senile osteoporosis causes a bone loss of approximately 1% per year.
].
].
Radiation
]. Consequently, astronauts will be exposed to a range of effective doses [
] (Figure 2).
]. In extreme cases, it could cause an acute radiation sickness in the short-term [
].
]. As cosmic radiation is also different in nature, shields should be several meters thick (and composed of materials with different atomic mass) to completely shield astronauts, which is technically impossible today [
]. Hence, radiation is mitigated by partial protective shielding (with lower atomic mass materials such as hydrogen content materials), by shielding responses to dosimeters, alerts, and radiation sensors.
Isolation constraints and difficulty in returning to Earth in a short time during a long Mars mission
]. The ISS is also continually resupplied with resources and medical equipment. In addition, the ISS is equipped with an advanced life support pack, providing advanced cardiac life support and advanced trauma life support [
,
,
].
In contrast, in the case of a long-term expedition, it is months before a return to Earth is possible and there is no resupply. Therefore, it is vital that the spacecraft should be as self-sufficient as possible in terms of resources and even more in respect to medical capability. Facing a communication delay and the possibility of equipment failures or a medical emergency, humans in space must be capable of confronting several situations without support from Earth. Examples are emergency surgery, acute trauma, burns, and wounds. At the moment, critical aspects in surviving a trauma or a surgery are wound/suture behavior and healing in space. For these reasons, the spacecraft should host cutting-edge medical technology, like 3D bioprinting equipment, regenerative medicine capacities, surgical instruments, as well as (amongst other medical devices), microscopes and freezers for blood samples and tissues to be medically self-sufficient and to be able to face any kind of health issues.
Long-term travel, for instance, an extended stay on the Moon and, even more, a mission to Mars, imposes various technical constraints. Indeed, during such travel there are no possibilities to return in case of technical or medical issues. From a medical point of view, all eventualities should be considered and countermeasures have to be taken to avoid medical complications. In addition, the spacecraft and the crew members should have the ability to be medically self-sufficient, at least as far as possible, to face any kind of unexpected events. From this point of view, translational regenerative medicine seems to offer promising prospects considering engineering of tissues like cartilage, bone, thyroid, liver, muscle, and heart, among others.
A combination of 3D bioprinters and an operational medical/surgical block containing samples of blood, bone marrow, and various types of tissues will help the mission to approach self-sufficiency and to be able to face critical situations requiring a medical intervention.
Why use organoids in space research?
Why is it so important to use organoids in space research? First, human organoids are essentially small ‘avatars’ of a person, since they provide a unique opportunity to study authentic (histologically in structure and functionally similar in function to mature tissues and organs) human tissue. Secondly, this can be done without causing any inconvenience or damage to a person, since microtissues of a person are used, which have grown in vitro through self-organization. Thirdly, the genetic modification of the used stem cells provides unique possibilities for the creation of organoids that include self-reporting genes that are turned on when activated and expression of which can be easily visualized using fluorescent proteins and registered with built-in automatic biosensors.
Organoids for studying deep space exploration
]. In the last century, radiobiologists discovered that the most radiosensitive tissues are tissues and organs with a high level of proliferation. Thus, it would be logical to focus on research in space not only on the traditional study, as, for example, on the mechanisms of osteoporosis, but above all on the study of human organoids that recapitulate in vitro the development of organs with a high level of proliferation. These are mainly the intestines, bone marrow, and also reproductive organs such as ovary and testes. The effect of cosmic radiation on reproductive tissues can be studied initially on frozen samples of human organoids and then on living organoids using self-reproducing genes for apoptosis (programmed cell death) via fluorescent proteins [
]. Studying the possible effect of cosmic radiation on the differentiation of bone marrow cells into vascular endothelium in vascular organoids, as well as on angiogenesis and vasculogenesis, would be very important. Specially designed microfluidic perfusion chambers could assist in biomonitoring and visualize, in real time, angiogenesis as well as vasculogenesis from endothelial progenitor cells. Also, in vascular organoids, genetically modified stem cells could directly visualize in vivo the expression of tissue-specific cell markers, such as platelet endothelial cell adhesion molecule-1 (PECAM-1; CD31) or vascular endothelial growth factor (VEGF). The functionality of excitable and contractile tissues of organoids of the human brain and heart could be observed and visualized in real time using elegant and modern methods of optogenetics [
,
,
].
Technical support for experiments with organoids in space
Adequate technical support for the study of human organoids in space will require an additional solution to some still unresolved technological problems or challenges. First of all, the need for maximum automation of research is becoming increasingly obvious, especially in the case of using unmanned spacecraft and satellites for research. Minimizing and compacting devices is undoubtedly the second important technological imperative, especially in the case of space (satellite) research. The use of biosensors, built-in cameras, and other devices allows for noninvasive and nondestructive biomonitoring, in real time, of changes occurring in organoids in space. In the case of effective biomonitoring of experiments in space in real time from the Earth, the urgent need to return the organoids to Earth automatically disappears. Alternatively, technologies for delivering organoids both to space and to Earth also require optimization, either by cryopreservation or by using specially designed or carefully selected stimulus-sensitive hydrogels. The study of the effect of space radiation can be carried out as simply as possible on frozen objects, provided that the appropriate cryo-equipment is available. Finally, the development of special bioassemblers and microfluidic perfusion devices is required for placement on board space stations or satellites. For ideal space experiments, it is also necessary to provide an adequate ground control, which means parallel experiments are conducted with similar human organoids on Earth under conditions of Earth’s gravity and normal Earth radiation levels, but applying the same time-line, temperature, and CO2 profile as well as pH conditions.
Ethics and feasibility
]. A next-decade goal is to create entire organs and nervous systems, which is essential to transplant muscles (Box 2).
]. Furthermore, the progress in componentation of the human body, as well as the ‘enhancement’ of such ‘human body parts’, is one of the most prominent ethical dilemmas in regenerative medicine.
Indeed, the componentation of the human body is a first step toward what is called ‘commodification’ (the organ is regarded as a simple commodity) of the human body. The componentation and the commodification of the human body, regardless of the degree of regenerative medicine’s contribution, are seen as an ethical challenge to the traditional image of human bodies and the abstract concept of ‘human dignity’. However, in the future, a new ethical view of human bodies may arise, which is defined as ‘a perspective in which human bodies, organs, tissues, and even the bodies themselves are regarded as disposable tools like disposable cameras, syringes, or contact lenses’; therefore a new ethical view would be appropriate for a new reality.
].
].
,
].
Ethically, biofabrication in space brings new questions, such as whether new tissue or even entire organs could be simply printed off to replace injured/aged or dysfunctional body parts in space? In particular, the possibility to transplant tissues made from the astronaut’s own cells or replacing aged organs in astronauts during a mission with younger and healthier ones would be extremely beneficial. However, the prospect of being able to print or biofabricate human organs in space, like on Earth, is likely to have a profound ethical impact on long-term missions as it would have on society on Earth. Amongst others, it could potentially boost the average longevity and viability of astronauts. It can bring criticisms, however, that the ability to print organs and so extend life in space is not right, given the scarcity and shortage of organ transplants and potential biofabrication on Earth, which is already a great concern.
Another aspect is the fact that, on Earth, tissues require some scaffold to hold all the structure in place, especially for cavities like the chambers of the heart. However, in a microgravity environment, much better biofabricated organs could potentially be produced. Faced with the exorbitant expense of printing organs, offering improved hearts or lungs created in space could be a method to attract people and a new market of rich people ready to pay for these improved space-grown organs and techniques.
At the moment, the focus is on using/biofabricating organs for life-saving surgery, also in space. However, there is a risk for enhanced organs to be used as a possibility for performance-improving in sport or other potential activities, since the technologies would be commercialized and thus available on the market for those able to afford them.
Finally, another ethical issue is: if many organs were changed in a person or an astronaut, arguably, what is then left would not be the human who was born, but some other creature. An important consideration when living in extreme and isolated space environments, lies on how to survive in a self-sustaining manner with a lack of immediate Earth-based medical assistance, equipment, and resources. Space travelers will need to cope with and to develop medical emergencies involving regenerative medicine within their own space habitats. On Earth, ethical issues of regenerative medicine are tied to medical decisions that might cause disagreement and conflict. In the same way, space regenerative medicine will be intimately related to bioethical standards that impinge on strictly medical decisions. However, a tunnel-vision-like perspective on medical diagnosis and treatment in space, certainly from an ethical point of view, might prove very difficult and might force us to rethink in terms of developing further complementary perspectives on biomedical and ethical issues related to regenerative medicine. Furthermore, with the development of space tourism in the near future, that will pave the way for rather less-trained civilian space farers, additional medical but also ethical pressures on the future development of regenerative medicine for this particular population might be indirectly affected by a combination of higher risk of potential biomedical and heath interventions and complications in space among the space tourists and a lowering of safety standards with regard to health requirements of space tourists prior to spaceflight.
Concluding remarks and future trends
Compared with the classical 2D cultures that allow cell organization only in monolayers, organoids are complex (3D) human tissues that are being developed with a closer recapitulation of the ‘authentic’ histological structure and organ function. When combined with biofabrication technologies, human organoids could hold the potential to further capture the complexity of different biological systems communicating with each other. If proven functional, such more complex 3D in vitro models could also hold the potential to advance over current animal models, which approximate only what could occur at the organism level in humans, are expensive both in space and on Earth, and are associated with ethical concerns on the well-being and sacrifice of animals. We expect, therefore, that human organoids will have stronger and stronger implications for space research as they are already providing on Earth, thus possibly replacing 2D cultures and reducing, if not replacing, research in animal models.
]. At a cellular level, ageing entails decreased replicative capacity and dysregulation of cellular processes. Consequently, a number of physiological functions are impaired, leading to arrhythmias, the reduction of aerobic capacity, and cardiac atrophy, ultimately resulting in two major age-associated cardiac pathologies: heart failure and atrial fibrillation [
]. The same technologies, in a more distanced future, could also be used to fabricate regenerative medicine solutions to promptly treat patients on Earth as well as space travelers that develop relevant conditions during long-term space missions.
,
]. Using off-the-shelf microelectromechanical print heads, this technology has been applied to the printing of (human) tissues. Several investigators are using this approach to print single cells [
] and cell aggregates [
], demonstrating that printing of complex tissues [
] and eventually of whole organs [
,
] is technologically within our reach. Despite several commercially available additive manufacturing technologies capable of fabricating biological constructs [
,
], these systems still move in Cartesian coordinates, which limits the capacity to mimic the complexity of tissue organization. More recently, volumetric bioprinting with photosensible hydrogels has been introduced, achieving more complex tissues and geometries [
,
]. However, this technology is still limited by the availability of a broad gamma of biocompatible photosensible hydrogels.
,
]. These special conditions would result in an easier control of the floating building elements in microgravity during bioprinting. At the same time, microgravity conditions would provide a biophysical environment where more dynamic hydrogels could be developed without the limitations of the force of gravity. A microgravity environment would also allow us to answer to an everlasting question in the field: do we need hydrogels at all or could we bioprint tissues, and in the future organs, with organoids only? This is not an easy question to answer, because hydrogels have been initially used as bioinks with the purpose to provide a physical support to cells to move from 2D to 3D bioprinting. However, in recent years bioinks have advanced more and more, to include instructive biological cues able to better recapitulate the cell–extracellular matrix (ECM) microenvironment [
], thus moving from shaping to biological function support. In this respect, the use of molecularly designed hydrogels by using self-assembly and supramolecular principles have been proposed as bioinks and shown to better recapitulate the multiscale hierarchical organization and dynamicity of the ECM [
,
]. Yet, these hydrogels are often more fluid than conventional bioinks and more difficult to process in gravity conditions on Earth. In space, microgravity conditions could facilitate the integration of such dynamic and molecularly designed bioinks within bioprinting approaches, thus resulting in biofabrication with higher precision and molecular diversity. In addition, the volumetric deposition in space microgravity allows control of how different organoids can come together in space, thus providing more fundamental tools to better understand organoid–organoid fusion and tissue morphogenesis. Ultimately, the space environment allows biofabrication of 3D in vitro models in a biophysical environment where ageing is accelerated, therefore providing also a functional research environment for ageing back on Earth or for drug development and testing with relevance for us earthlings.
]. It is possible to fabricate ad hoc nutrients and currently efforts to engineer meat have gained a lot of momentum [
,
]. Beyond food, the use of vegetal forms of life with specific properties, such as production of energy and oxygen, has also been shown to be feasible [
,
]. Ultimately, we could also foresee the use of biofabrication technologies to make 3D in vitro models to study bacteria and virus infections in space, on one side to understand the risks of bringing Earth species on other planets and, on the other, serving as a possible testbed to be better prepared in the distant future for testing new viruses found on new planets (Figure 3).
Figure 3A vision for biofabrication in space.
These technologies give great hope in the context of a long-term space exploration mission as it would be a serious and flexible response to some hazards astronauts will face in deep space. Several diseases caused by space stresses might be treated by the potential ability to replace damaged tissues or organs. Weakened bones and muscles should also be treated and, if necessary, replaced using 3D bioprinted grafts.
Can space constraints and limits provide new, ‘out-of-the-box’ solutions to further advance biofabrication technologies?
Is it possible to develop a magneto-acoustic bioassembler for rapid biofabrication of human tissue and organs from organoids in space with minimal nontoxic concentration of paramagnetic solutions?
Is it possible to fabricate human organoids working as radiation-sensitive ‘centinels’ from genetically modified cells with self-reporting radio-sensitive apoptotic genes?
Is it possible to develop automated microdevices for noninvasive and nondestructive biomonitoring of viability and functionality of human organoids?
Is it possible to design and develop human vascularized and perfused tissue- and organo-specific microtissues (organ-on-a-chip) connected with organoids mimicking bone marrow to study the relative role of angiogenesis and vasculogenesis in pathogenesis of radiation-induced apoptosis associated with tissue and organ atrophy in space?
Is it possible to develop laser magneto-acoustic bioassemblers thanks to the use of space for rapid biofabrication on Earth of functional, vascularized, and perfusable complex human tissues and organs with low, nontoxic concentration of paramagnetic media?
Can the combination of human organoids and biofabrication technologies reach that level of organism complexity that is not possible with single organoids and not completed represented by animal models?
Do we need hydrogels at all or could we bioprint tissues, and in the future organs, with organoids only?
How can biofabricated constructs be preserved for months or years in a spacecraft?
Acknowledgments
Declaration of interests
No interests are declared.
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Glossary
Angiogenesis
new blood vessel formation by the growth and sprouting of existing blood vessels.
Arteriogenesis
process of structural enlargement and remodeling of pre-existing small arterioles into larger vessels.
Bioassembly
fabrication of hierarchical constructs with a prescribed 2D or 3D organization through automated assembly of preformed cell-containing fabrication units generated via cell-driven self-organization or through preparation of hybrid cell–material building blocks, typically by applying enabling technologies, including microfabricated molds or microfluidics.
Biofabrication
automated generation of biologically functional products with structural organization from living cells, bioactive molecules, biomaterials, cell aggregates such as microtissues, or hybrid cell-material constructs, through bioprinting or bioassembly and subsequent tissue maturation processes.
Bioink
formulation of material(s) and biological molecules or cells processed using bioprinting technologies.
Biomaterial
material that is used as (part of) a medical device or an advanced therapy medicinal product to replace, restore, or regenerate a tissue or organ and its function.
Bioprinting
computer-aided transfer processes for patterning and assembly of living and nonliving materials with a prescribed 2D or 3D organization to produce bioengineered structures relevant for regenerative medicine, pharmacokinetics, and basic cell biology studies. In this context, additive manufacturing of 3D scaffolds able to instruct or induce the cells to develop into a tissue mimetic or tissue analog structure.
Centinels
organoids with built-in capacity to report about chemical cytotoxicity or radiation exposure by special easy detectable, usually fluorescent, signal.
Componentation
organ is regarded as a simple component of the human body.
Induced pluripotent stem (iPS) cells
pluripotent cells derived from any differentiated cell type through ectopic expression of transcription factors. Originally, through retroviral expression of Oct4, Sox2, Klf4, and C-Myc, as reported by Shinya Yamanaka. Other combinations and ways of generating iPS cells have been developed since then.
Magneto-acoustic bioassembly
a rapid formative biofabrication of 3D tissues and organs with using physical fields as ‘scaffields’ instead of more traditional solid scaffolds or scaffold-like hydrogels and bionics.
Microgravity
condition in which living materials or objects are in weightlessness.
Noninvasive and nondestructive biomonitoring
a method of estimation of viability and functionality of organoids without destruction and invasion.
Organoids
3D microtissues self-developing from stem cells and having the histological and functional characteristics of mature organs/from stem cells and their self-development and self-differentiation.
Pluripotent cells
cells capable of differentiating all germ layers (endoderm, mesoderm, and ectoderm) and the germline, but not extra embryonic tissues (e.g., inner cell mass, embryonic stem cells, embryonic germ cells, epiblast stem cells, iPS cells).
Radiosensitive tissues
usually highly proliferative tissues and organs, which die after exposure to radiation.
Regenerative medicine
interface between engineering and life sciences, exploits the properties of living cells in combination with biomaterials, drugs, or genes to repair or replace tissues and organs.
Scaffolds
temporal and removable (usually biodegradable) supports in tissue engineering.
Self-reporting genes
usually labelled with GFP protein genes, which enable manifestation of cell viability and functionality using noninvasive and nondestructive fluorescent microscopy.
Space radiation
the space radiation environment includes energetic solar particles emitted during solar flares and coronal mass ejections, as well as galactic cosmic rays, which are composed of electrons (2%), protons (85%), helium nuclei (12%), and heavier ions referred to as high-energy and high-charge particles (HZE; 1%).
Spheroid
a cluster of cells with a spherical shape, typically formed by allowing a cell suspension to settle into a droplet of media.
Vascularization
formation of new blood vessels, which involves vasculogenesis, angiogenesis, and arteriogenesis.
Vasculogenesis
de novo formation of blood vessels by endothelial progenitor cells.
Article Info
Publication History
Published online: September 17, 2021
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