Phase-Field Simulation Dendritic Growth Under Forced Flow with Hypergravity
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AbstractWe studied the functional adaptation process in 40 hamsters subjected to either prolonged hypergravity or normal gravity. Subadult golden hamsters (n = 20) exposed to a hypergravity condition of 2.5 G for 6 months were tested to investigate the effect of hyper gravity on the perceptive motor skills and compared with control hamsters (n = 20). the motor coordination of the hypergravity hamsters hardly changed; locomotion was normal and swimming was possible. Equilibrium maintenance was disturbed during the first 3 months as was shown by the higher crossing time (p <0.001) and higher fall frequency (p <0.001) for the hypergravity group. Significant differences were also found in orientation during swimming (p = 0.007) and turning behaviour in the rotation task (p < 0.001) and in the no-rotation task (p = O.029). After 6 months, 10 hamsters of both groups were tested for another 4 months, also the hypergravity hamsters were living at 1 G. Differences in orientation in the two groups did not change during swimming and turning behaviour during the rotation task (p = 0.026). Based on our findings, we conclude that the hamsters functionally adapted to hypergravity, which led to an altered performance of several tasks. the condition continued after 4 months of normal gravityKey Words: sustained accelerationequilibrium maintenanceswimming behaviourlocomotor activityanimal experiments
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Gravity may influence multiple aspects of legged locomotion, from the periods of limbs moving as pendulums to the muscle forces required to support the body. We present a system for exposing mice to hypergravity using a centrifuge and studying their locomotion and activity during exposure. Centrifuge-induced hypergravity has the advantages that it both allows animals to move freely, and it affects both body and limbs. The centrifuge can impose two levels of hypergravity concurrently, using two sets of arms of different lengths, each carrying a mouse cage outfitted with a force and speed measuring exercise wheel and an infrared high-speed camera; both triggered automatically when a mouse begins running on the wheel. Welfare is monitored using infrared cameras. As well as detailing the design of the centrifuge and instrumentation, we present example data from mice exposed to multiple levels of hypergravity and details of how they acclimatized to hypergravity.
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Altered gravity is a strong physical cue able to elicit different cellular responses, representing a largely uninvestigated opportunity for tissue engineering/regenerative medicine applications. Our recent studies have shown that both proliferation and differentiation of C2C12 skeletal muscle cells can be enhanced by hypergravity treatment; given these results, PC12 neuron-like cells were chosen to test the hypothesis that hypergravity stimulation might also affect the behavior of neuronal cells, in particular promoting an enhanced differentiated phenotype. PC12 cells were thus cultured under differentiating conditions for either 12 h or 72 h before being stimulated with different values of hypergravity (50 g and 150 g). Effects of hypergravity were evaluated at transcriptional level 1 h and 48 h after the stimulation, and at protein level 48 h from hypergravity exposure, to assess its influence on neurite development over increasing differentiation times. PC12 differentiation resulted strongly affected by the hypergravity treatments; in particular, neurite length was significantly enhanced after exposure to high acceleration values. The achieved results suggest that hypergravity might induce a faster and higher neuronal differentiation and encourage further investigations on the potential of hypergravity in the preparation of cellular constructs for regenerative medicine and tissue engineering purposes.
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In ciliates with clear graviresponses it was studied how the physical signal of gravity is transformed into a physiological response. The orientation and kinetic responses of Paramecium and Loxodes were analyzed under varied gravitational stimulation - ranging from simulated and actual near-weightlessness, to 1 x g and to hypergravity. Both ciliates showed gravitaxis and gravikinesis at 1 x g, which increased under hypergravity (5 x g) and disappeared under gravity-free conditions. Centrifuge experiments in space revealed a lower sensitivity of Loxodes (0.15 x g) in comparison to Paramecium (0.3 x g), indicating that they have developed different mechanisms for gravity perception. Biochemical analyses revealed a significant, time-dependent decrease of the cAMP level in Paramecium under hypergravity conditions. Even after 12 h of 5 x g a decrease of 40 % was measured.
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Paramecium caudatum
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Gravitropism
Gravitational force
mechanobiology
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Previous reports of the behavior of aquatic organisms in the microgravity environment of space (~10(-6) g) or during the brief weightless period of parabolic flight indicate that most species display a dramatic "looping" or "circling" response (De Jong et al. 1996, Anken, Ibsch and Rahmann 1998). However, the behavior of aquatic species under hypergravity conditions is less clear. Our objectives in the present study were to examine the behavioral response of adult zebrafish (Danio rerio) to hypergravity conditions (2-g), quantify changes in adult swimbladder volume, and to determine if the larvae of zebrafish are capable of accessing the air-water interface for initial swimbladder inflation under hypergravity conditions.
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Danio
Escape response
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Hypergravity
Bone remodeling
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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.
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