Validation of Microgravity Simulators (Random Positioning Machine and Clinostat) Using Cellular Bioassays

In the ESA ground-based facility program, clinostatsand Random Positioning Machines(RPM) are readily available for external scientists to apply simulated microgravity, and results from experiments in cell biology have been recently published. The results clearly demonstrate that device-specific operational modes have to be carefully considered and comprehensively discussed with respect to the induction of shear forces by the various simulators, which have a considerable impact on the quality of (simulated) microgravity. In order to directly visualize potential non-gravitational cellular responses during simulator operation, we exposed the dinoflagellatePyrocystis noctiluca as a highly sensitive reporter organism, which responds to shear stress with detectable bioluminescenceemission, to clinorotation and random positioning. Rotation around two axes with random velocities and directions (RPM mode) revealed significantly greater mechanical stress responses compared with constant and fast rotation around one axis ( clinostat). Another bioluminescenceassay using a well-studied immune cell (macrophage) system also showed that the oxidative burst response during RPM-exposure differs significantly from that observed during clinorotation. We conclude that fast one axis clinorotation should be the preferred method for simulation of microgravity in experiments using cells.