Basis for the biological responses due to instationary fluid motion during Random Positioning

In order to understand the role of gravity in biological systems one may either increase the g force using centrifuges or decrease it going into free-fall conditions such as available on various platforms (sounding rockets, manned or unmanned spacecraft). Performing space experiments is cumbersome, expensive, and can only be done infrequently. Hence, alternative techniques are highly desirable and several have been developed. Instruments like 2D clinostats or Random Positioning Machines (RPM) are now widely used within the biological arena. The conditions that these offer to samples ? such as suspended or attached cell cultures - are assumed similar to free-fall conditions. Justification of this assumption is based on plausibility arguments and on comparison of results with those of actual flight experiments. The comparison is not always without ambiguity, which increases the argument for a study of the actual physical conditions that can be provided in these terrestrial instruments. With this knowledge one can link earth-based to free-fall experimental conditions and investigate in more detail how a specific biological process is affected by specific parameters. Within the proposed study we want to address this issue via Computational Fluid Dynamics (CFD), and experimentally via Particle Image Velocimetry (PIV). Using the knowledge acquired from this part of the study, we will develop a user-protocol for the RPM. Based on this, we will perform two biological verification test series, in which we will expose cells to various RPM regimes: first, the production of nitric oxide by bone cells will be used as a marker for response to fluid shear stress; secondly, single-cell experiments with non-motile bacterial cultures will be carried out. Comparison of the outcome with previous results both in spaceflight and under simulated microgravity conditions can be used to validate the developed user-protocol.