Research using Earth-based techniques to simulate the microgravity in space

Here we summarize research articles in npj Microgravity that used ground-based spaceflight analogues to study the effects of microgravity

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Effects of angular frequency during clinorotation on mesenchymal stem cell morphology and migration

New findings and novel technology provide a closer look at how stem cells respond to microgravity. Adam Hsieh at the University of Maryland and co-workers studied the morphology and migration behavior of mesenchymal stem cells (MSCs) under simulated zero-gravity conditions using a device specially designed to resolve the contradictory results of past studies involving clinostats-rotating systems used to study the cellular effects of microgravity. They observed a clear relationship between the rotational frequency and the extent to which MSCs spread out in culture. MSCs can form a variety of tissue types, and the biophysical features observed by Hsieh’s group suggest that rapidly rotated MSCs might preferentially form cartilage or fat, whereas slower rotation may tend to yield bone. These results could help resolve previous contradicatory reports and guide future tissue-engineering efforts.


The influence of simulated microgravity on the proteome of Daphnia magna

Low-gravity conditions could trigger physiological changes in tiny crustaceans, reports a German team. The planktonic crustacean Daphnia consumes algae and acts as food for fish, and could thus contribute to sustainable mini-ecosystems that provide oxygen and food for astronauts. In order to learn how microgravity might affect Daphnia, Christian Laforsch at Bayreuth University and colleagues subjected the crustaceans to simulated microgravity with a device known as a clinostat and examined the resulting changes in protein production. They identified striking differences in specific biological pathways—for example, simulated microgravity interfered with proteins that form the cellular infrastructure and facilitate movement, and appeared to increase overall energy consumption. These findings offer a peek into the stresses that cultured Daphnia are likely to experience in low-gravity environments, representing an important starting point for further research into space life-support systems.


Microlayered flow structure around an acoustically levitated droplet under a phase-change process

High-speed visualizations of acoustically levitated droplets reveal differences in flow field interactions depending on droplet composition. Koji Hasegawa and colleagues from Kogakuin University and the University of Tsukuba in Japan have used a high-speed camera system to observe the evolution of internal and external flow fields in droplets levitated using acoustic standing waves. They found that droplets of pure water develop simple toroidal vortices at the base, while hexane and binary mixtures of water and ethanol develop microlayered vortices near the droplet interface. The results show that the flow fields of an acoustically levitated droplet affect the evaporation process, and that the concentration of volatile fluid affects the configuration of the flow fields. This experimental insight is expected to help in the development of improved contactless sample manipulation at the micro- and nanoscale.


Effects of microgravity simulation on zebrafish transcriptomes and bone physiology—exposure starting at 5 days post fertilization

Zebrafish larvae show decreased bone formation and altered gene expression after exposure to simulated microgravity, says a European team. To better understand how the human body responds to the near weightlessness of space, Marc Muller at the University of Liège in Belgium and colleagues in Norway, Italy and the Netherlands used zebrafish larvae as a model organism. Zebrafish larvae are tiny and can be grown in tubes and subjected to simulated microgravity using a benchtop device, called a clinostat, that spins the tubes rapidly. After one day, the larvae showed altered expression of genes involved in bone, muscle and cardiovascular development; after five days, they showed decreased bone formation. The findings pave the way for future studies using zebrafish larvae as a model system to study the effects of microgravity on humans. 


Long-term effects of simulated microgravity and/or chronic exposure to low-dose gamma radiation on behavior and blood–brain barrier integrity

The combined effects of low-gravity conditions and exposure to radiation in space may have subtle neurological and behavioral effects. Both of these environmental factors have the potential to induce physiological changes in astronauts, but few studies have directly examined the interplay between them. Xiao Wen Mao and colleagues at Loma Linda University in the USA assessed the impact of experimental simulations of microgravity conditions and chronic exposure to low-dose gamma radiation on mice. After three weeks of simulated microgravity and low-dose radiation exposure, animals subjected to microgravity-like conditions exhibited increased exploratory and risk-taking behavior relative to controls up to 8 months, with no other apparent changes in cognitive function. The combination of microgravity and radiation was also tentatively linked with increased leakiness of the blood vessels within the brain, an effect that could adversely influence both behavior and neurological health.


Treadmill exercise within lower-body negative pressure attenuates simulated spaceflight-induced reductions of balance abilities in men but not women

Men and women may respond differently to measures to counteract balancing difficulties caused by long-duration spaceflight. The suggestion comes from a microgravity simulation study by US researchers led by Timothy Macaulay at the University of California, San Diego. Eight pairs of male and seven pairs of female identical twins undertook 30 days of bed-rest with their heads tilted downward–a standard method to simulate the microgravity conditions of spaceflight. One member of each pair exercised regularly with a treadmill while still lying supine in negative pressure conditions on their lower body. At the end of the study, the males who had exercised performed significantly better than their twins in a single-leg balancing test. However, the females who exercised showed no statistically significant benefit relative to their twins. 


Evaluation of techniques for performing cellular isolation and preservation during microgravity conditions

Successful pipetting trials under microgravity conditions have opened up new avenues for research in space. Andrew Feinberg at John Hopkins University School of Medicine in Baltimore and Brian Crucian at Johnson Space Center in Houston, together with scientists in the United States and Germany, aimed to clarify whether common sampling techniques that allow scientists to purify and separate out different cell types can be successfully conducted under microgravity conditions. The team tested the viability of different pipetting techniques under microgravity conditions during parabolic atmospheric flights. They found that all procedures needed to fully isolate different cell types were possible in microgravity, and determined that syringe-type pipettors (or ‘positive displacement’ pipettors) with small tips worked best. The results represent a new step towards expanding the types of research that can be done in microgravity conditions, such as on board the International Space Station.


The effect of reduced gravity on cryogenic nitrogen boiling and pipe chilldown

It takes longer and more liquid nitrogen to cool down a pipe of cryogenic propellant in reduced gravity conditions. The finding, from a team led by Jacob Chung at the University of Florida, USA, should help in the design of future space explorations that rely on cryogenic propulsion systems like liquid hydrogen or liquid oxygen. Chung and colleagues studied cryogenic chilldown aboard a C9 aircraft flying parabolic trajectories to simulate reduced gravity. They delivered liquid nitrogen through a short, narrow, stainless steel pipe at various flow rates and pressures. The researchers found that heat transfer efficiency was reduced by around 25% in reduced gravity, but could be enhanced by increasing the flow rate. This can be explained by the absence of buoyancy force in reduced gravity, leaving forced convection to propagate the heat transfer process. 


Exposure of Mycobacterium marinum to low-shear modeled microgravity: effect on growth, the transcriptome and survival under stress

Microgravity alters gene expression in a pathogenic waterborne microbe — changes that could pose a health risk to astronauts in space. Lynn Harrison from the Louisiana State University Health Sciences Center in Shreveport, USA, and colleagues grew an infectious bacterium called Mycobacterium marinum, a close relative to the microbe responsible for tuberculosis, in a rotary cell culture system that causes the low fluid shear dynamics associated with microgravity. Bacteria in this state grew slower with different expression levels of several hundred genes compared to those cultured under normal gravity conditions. Some of these molecular differences are similar to those elicited when mycobacteria infect human cells, suggesting that space might make the microbes more pathogenic. However, microgravity also made the bacteria more sensitive to certain stressors like hydrogen peroxide, so the overall impact on virulence is still unclear. 


Contactless processing of SiGe-melts in EML under reduced gravity

Low-gravity environments help to produce a semiconducting alloy with great promise for electronics, shows researchers from Germany. Yuansu Luo from the Georg-August-Universität and co-workers measure the thermal properties of molten silicon–germanium during parabolic flights. Silicon is the dominant material in the electronic industry. Adding germanium, however, creates a semiconductor with even more useful properties. Producing high-quality crystals of this alloy is challenging because gravity separates the two elements when in liquid form. A low-gravity environment could help, but more must be known about the properties of silicon–germanium under such conditions. Luo et al. processed a silicon–germanium melt in an electromagnetic levitation facility in microgravity conditions, analyzed video images to determine its thermal expansion, viscosity, and surface tension and observed an alloying effect and a crossover phenomenon. The results pave the way for more detailed investigations on the International Space Station.


Investigation of simulated microgravity effects on Streptococcus mutans physiology and global gene expression

The gene expression patterns, metabolism and physiology of tooth cavities-causing microbes change in a space-like gravity environment. These findings could help explain why astronauts are at a greater risk for dental diseases when in space. Kelly Rice and colleagues from the University of Florida, Gainesville, USA, cultured Streptococcus mutans bacteria under simulated microgravity and normal gravity conditions. The bacteria grown in microgravity were more susceptible to killing with hydrogen peroxide, tended to aggregate in more compact cellular structures, showed changes in their metabolite profile and expressed around 250 genes at levels that were either much higher or lower than normal gravity control cultures. These genes included many involved in carbohydrate metabolism, protein production and stress responses. The observed changes collectively suggest that space flight and microgravity could alter the cavities-causing potential of S. mutans.


RhoGTPase stimulation is associated with strontium chloride treatment to counter simulated microgravity-induced changes in multipotent cell commitment

A chemical element naturally found for instance in seafood or grains, could counter bone loss from long-term spaceflight. Alain Guignandon and colleagues from the Université de Lyon à St-Etienne in France exposed multipotent embryonic fibroblasts to microgravity conditions similar to those found in space. They found the balance shifted in these stem cells from differentiating to bone-forming cells (osteoblasts) to differentiating to fatty-tissue forming cells (adipocytes). When the cells were treated with strontium, the shift toward osteoblastogenesis was regained. Strontium achieves this by sustaining the activity of two proteins that play a role in bone development but are suppressed in space. Strontium’s effect on the proteins could happen via release of vascular endothelial growth factor, which, under normal gravity conditions, plays a role in committing the cell to differentiation into osteoblasts rather than adipoyctes. 




Three-dimensional organotypic co-culture model of intestinal epithelial cells and macrophages to study Salmonella enterica colonization patterns

Using spaceflight analog bioreactor technology, Cheryl Nickerson at Arizona State University and collaborators developed and validated a new three-dimensional (3-D) intestinal co-culture model containing multiple differentiated epithelial cell types and phagocytic macrophages with antibacterial function to study infection by multiple pathovars of Salmonella. This study is the first to show that these pathovars (known to possess different host adaptations, antibiotic resistance profiles and disease phenotypes), display markedly different colonization and intracellular co-localization patterns using this physiologically relevant new 3-D intestinal co-culture model. This advanced model, that integrates a key immune cell type important for Salmonella infection, offers a powerful new tool in understanding enteric pathogenesis and may lead to unexpected pathogenesis mechanisms and therapeutic targets that have been previously unobserved or unappreciated using other intestinal cell culture models.


Pyrocystis noctiluca represents an excellent bioassay for shear forces induced in ground-based microgravity simulators (clinostat and random positioning machine)

Earth-based laboratories can now assess the accuracy of tools used to simulate living organism growth and behaviour in space with bioluminescent assays. Researchers often use rotating machines to minimize gravity effects during the design of extra-terrestrial experiments with plants, cells, and small animals. Jens Hauslage from the DLR German Aerospace Center and colleagues report that device-specific shear forces produced during mechanical movements may cause misinterpretations of initial test data. They developed a biosensor based on marine plankton, known as dinoflagellates, which have cell membranes that naturally emit light when touched by predators. Calibrating this bioluminescence against mechanical stress helped determine the top-like, 2D rotations of ‘‘clinostat’’ devices provided microgravity-like conditions. However, the unexpected 3D movements of Random Positioning Machines generated enough shear force to impact studies of cell signaling pathways or metabolic reactions.


The adaptation of Escherichia coli cells grown in simulated microgravity for an extended period is both phenotypic and genomic

Bacteria grown for an extended period of time under simulated microgravity adopt growth advantages. George Fox and colleagues from the University of Houston, Texas, USA, cultured Escherichia coli bacteria for 1000 generations in a high aspect rotating vessel to simulate the low fluid shear microgravity environment encountered during spaceflight. They then performed growth competition assays and found that the 1000-generation adapted bacteria outcompeted control bacteria grown without simulated microgravity. Genomic sequencing of the adapted bacteria revealed 16 mutations, five of which altered protein sequences. These DNA changes likely explain the growth advantage of the bacteria grown for multiple generations in simulated microgravity. Similar adaptations during prolonged space missions could result in nastier pathogens that might threaten the health of astronauts. Fortunately, the microbes did not appear to acquire antibiotic resistance over the 1000 generation in the modeled microgravity culture.


MRI-derived diffusion parameters in the human optic nerve and its surrounding sheath during head-down tilt

Bacteria grown for an extended period of time under simulated microgravity adopt growth advantages. George Fox and colleagues from the University of Houston, Texas, USA, cultured Escherichia coli bacteria for 1000 generations in a high aspect rotating vessel to simulate the low fluid shear microgravity environment encountered during spaceflight. They then performed growth competition assays and found that the 1000-generation adapted bacteria outcompeted control bacteria grown without simulated microgravity. Genomic sequencing of the adapted bacteria revealed 16 mutations, five of which altered protein sequences. These DNA changes likely explain the growth advantage of the bacteria grown for multiple generations in simulated microgravity. Similar adaptations during prolonged space missions could result in nastier pathogens that might threaten the health of astronauts. Fortunately, the microbes did not appear to acquire antibiotic resistance over the 1000 generation in the modeled microgravity culture.


Go to the profile of Marie-Elizabeth Barabas

Marie-Elizabeth Barabas

Managing Editor, Springer Nature

I'm an interdisciplinary neuroscientist with a research background in peripheral sensory/pain research, retinal development, and stem cell research. As the Managing Editor of npj Microgravity, my role is to assist the editorial process, implement editorial policies, and promote the journal, its articles, and the community. I also attend conferences and meetings to develop a relationship with our readers, authors, and editors. If you see me at a conference, feel free to introduce yourself.

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