Bioeffects of Microgravity and Hypergravity on Animals

Gravity alterations in space cause significant adaptive effects on the human body,including changes to the muscular,skeletal,and vestibular systems.However,multiple factors besides gravity exist in space;therefore,it is difficult to distinguish gravity-related bioeffects from those of the other factors,including radiation.Although everything on the Earth surface is subject to gravity,gravity-induced effects are not explicitly clear.Here,different research methods that have been used in gravity alterations,including parabolic flight,diamagnetic levitation,and centrifuge,are reviewed and compared.The bioeffects that are reported to be associated with altered gravity in animals are summarized,and the potential risks of hypergravity and microgravity are discussed,with a focus on microgravity,which has been studied more extensively.It should be noted that although various microgravity and hypergravity research methods have their limitations,such as the inevitable magnetic field effects in diamagnetic levitation and short duration of parabolic flight,it is evident that ground-based clinical,animal,and cellular experiments that simulate gravity alterations have served as important and necessary complements to space research.These researches not only provide critical and fundamental biological information on the effects of gravity from biomechanics and the biophysical perspectives,but also help in developing future countermeasures for astronauts.

Hypergravity experiments on multiphase media evolution

The gravitational field affects the evolution of multiphase media, such as rocks, soil, and alloy melts. Hypergravity increases the body force of matter, enhancing the driving force of the relative motion between substances with different densities and accelerating the evolution of multiphase media. Hypergravity experiments provide a new approach to exploring the motion of multiphase media and solving engineering problems. Hypergravity experiments have been conducted in different disciplines,such as materials science, geological science, and geotechnical engineering. However, the knowledge barriers between various research fields have caused the development of centrifuges/inflight devices and theoretical research on the mechanisms of matter in motion in hypergravity to lag behind the application of hypergravity experiments, limiting the progress in these experiments.This article systematically summarizes and proposes the fundamentals of hypergravity experiments, while the scientific challenge of the nonlinear hypergravity effect induced by high hypergravity on multiphase media evolution is clarified. Evaluation criteria are proposed for the noninertial frame effects of the centrifugal hypergravity field. The development of the high-centrifugal acceleration, large-capacity, and long-beam centrifuges are determined as the future research direction. Representative cases are used to demonstrate the effectiveness and great potential of the hypergravity experiments for the solidification of alloy melts and physical modeling. Challenges in the experimental methodology are also clarified. This paper reviews the fundamentals and applications of hypergravity experiments in various disciplines, pointing out the research direction of hypergravity experiments on multiphase media evolution.

Biomedical response of femurs in male Wistar rat in chronic hypergravity environments

Bone is sensitive to mechanical stimulation and plays a loading-bearing role in the human body.However,regulation of bone biomechanical properties in chronic hypergravity environments is still unclear.In this study,male Wistar rats exposed to chronic hypergravity environments(4
g,8
g,10
g,and 20
g)for 4 weeks were set as the hypergravity groups,and rats exposed to the normal gravity as the control group.Morphology parameters and bone remodeling factors were obtained by means of micro-CT,Western blot,and q-PCR.Mechanical properties of femurs were measured utilizing three points bending test and creep test and were fitted into a viscoelastic-viscoplastic constitutive equation.The results indicate osteoporosis occurred in femurs of hypergravity groups.Accordingly,the protein and gene expressions of bone remodeling factors(OPG,RANKL,runx2)in hypergravity groups were significantly different from that in the control group,demonstrating that bone formation level increased and bone resorption level decreased.Meanwhile,mechanical properties of femurs in hypergravity groups showed that Young's modulus of femurs in the 20
g group was significantly higher than that in the control group.The viscoelastic-viscoplastic properties of bone tissue were changed in hypergravity environments.Among them,the 8
g group was closest to the control group in morphology and mechanical properties.To sum up,the biomechanical response regulation of rat femur under 4-20
g chronic hypergravity environments was presented.Hypergravity environments could lead to osteoporosis.The balance between bone formation and bone resorption would be disrupted in hypergravity groups due to bone adaptation.20
g environment has a significant effect on elastic modulus on femurs.Due to the difference in biomechanical response of femurs,the viscoelastic-viscoplastic characteristics of femurs have a nonlinear relationship with hypergravity values.Bone tissue was least affected by 8
g hypergravity in morphology and mechanical properties.

Gravireception in <i>Phycomyces</i>: Threshold Determination on the Sounding Rocket TEXUS 50

Under parabolic flight conditions microgravity is not lower than 3 to 5 times 10-2 g. In contrast to parabolic flights, sounding rocket flights are virtually vibrational-free allowing microgravity as low as 10-5 g. Thus, a rotating platform serving as centrifuge allows the precise generation of gravitational forces ranging from 5 to 100 mg (not possible during parabolic flights). On this basis we determined the threshold1 for optical reflection/absorption changes in Phycomyces to be lower than 25 × 10-3 g. This compares well with the threshold determination of gravitropism in Phycomyces on a clinostat centrifuge. Kinetics of gravity-induced absorption changes and gravity as generated by the on-board centrifuge do not coincide but show a distinctive hysteresis with a latency of 4 s (75 mg-ramp, pull-up).

Hyper Gravity-Induced Transients in <i>Phycomyces</i>as Measured by Single Beam Spectrophotometer on the Sounding Rocket TEXUS 50

In the first paper of two referring to the TEXUS 50 campaign using micro dual wavelength spectrometers (MDWS) we kinetically determined the threshold1 for GIACs (gravity-induced absorption changes) in Phycomyces to be lower than 25 × 10&minus;3 g (http://file.scirp.org/pdf/JMP_2015082810060783.pdf). In this second paper, we attended measurement of GIAC-spectra. Unexpectedly, during the upwards movement, i.e. the hypergravity phase up to top acceleration values reaching 11.6 g at 35.4 s after liftoff we observed transient GIAC-spectra ranging from 380 to 750 nm. In addition, during the whole acceleration phase of 68.2 s, another component near 700 nm develops which remains stable during the whole “free fall trajectory parabola” for 381.3 s. The subsequent reentry of the rocket leads to extraordinary deceleration values up 37.8 g, completely destroying Phycomyces sporangiophores excluding their spectral measurement. During the microgravity phase and by centrifuge operation we were unable to detect any GIAC-spectra (in contrast to kinetic MDWS-measurements, first paper).

Dependence of Gravity Induced Absorption Changes on the Earth’s Magnetic Field as Measured during Parabolic Flight Campaigns

Various spectroscopic experiments performed on the AIRBUS ZERO G—located in Bordeaux, France—in the years 2002 to 2012 exhibit minute optical reflection/absorption changes (GIACs) as a result of gravitational changes between 0 and 1.8 g in various biological species such as maize, oats, Arabidopsis and particularly Phycomyces sporangiophores. During a flight day, the AIRBUS ZERO G conducts 31 parabolas, each of which lasts about three minutes including a period of 22 s of weightlessness. So far, we participated in 11 parabolic flight campaigns including more than 1000 parabolas performing various kinds of experiments. During our campaigns, we observed an unexplainable variability of the measuring signals (GIACs). Using GPS-positioning systems and three dimensional magnetic field sensors, these finally were traced back to the changing earth’s magnetic field associated with the various flight directions. This is the first time that the interaction of gravity and the Earth’ magnetic field in the primary induction process in living system has been observed.

The effect of different gravity fields on mass transfer in the rat bone lacunar-canalicular system

The bone lacunar-canalicular system(LCS)is an important microscopic infrastructure for signaling and solute transport in bone tissue,which guarantees normal physiological processes of the tissue,but the mass transfer laws in the LCS under different gravity fields have not yet been clarified.SD rats were injected intraperitoneally with different concentrations of sodium fluorescein tracer and subjected to mass transfer experiments in the LCS under normal gravity and hypergravity.The fluorescence distribution in the osteon was observed using laser scanning confocal microscopy.The hypergravity environment was provided by a self-designed high-G loading centrifuge.The fluorescence intensity of the Haversian canal in the osteon was the highest.The fluorescence intensity of lacunae farther away from the Haversian canal was lower,and the fitted curve was parabolic.With the increasing distance from the Haversian canal,the curve first rapidly decreased,and then the decreasing trend gradually became slower.Hypergravity promoted mass transfer in the LCS,and the 10 G hypergravity showed varying degrees of fluorescence intensity in each layer of the osteon relative to normal gravity,with intensity enhancements in the range of 132.7–249.0%.The fluorescence intensity was also significantly increased when the tracer concentration was halved and the gravity field magnitude was increased to 10G.In conclusion,hypergravity promoted the transport of solute molecules,nutrients,and signaling molecules within the LCS.The effect of hypergravity on mass transfer in the LCS was greater than that of tracer concentration.This may help to understand bone diseases from a mass transfer perspective.