Fluid Dynamics Appearing during Simulated Microgravity Using Random Positioning Machines

Abstract

Random Positioning Machines (RPMs) are widely used as tools to simulate microgravity on ground. They consist of two gimbal mounted frames, which constantly rotate biological samples around two perpendicular axes and thus distribute the Earth’s gravity vector in all directions over time. In recent years, the RPM is increasingly becoming appreciated as a laboratory instrument also in non-space-related research. For instance, it can be applied for the formation of scaffold-free spheroid cell clusters. The kinematic rotation of the RPM, however, does not only distribute the gravity vector in such a way that it averages to zero, but it also introduces local forces to the cell culture. These forces can be described by rigid body analysis. Although RPMs are commonly used in laboratories, the fluid motion in the cell culture flasks on the RPM and the possible effects of such on cells have not been examined until today; thus, such aspects have been widely neglected. In this study, we used a numerical approach to describe the fluid dynamic characteristic occurring inside a cell culture flask turning on an operating RPM. The simulations showed that the fluid motion within the cell culture flask never reached a steady state or neared a steady state condition. The fluid velocity depends on the rotational velocity of the RPM and is in the order of a few centimeters per second. The highest shear stresses are found along the flask walls; depending of the rotational velocity, they can reach up to a few 100 mPa. The shear stresses in the “bulk volume,” however, are always smaller, and their magnitude is in the order of 10 mPa. In conclusion, RPMs are highly appreciated as reliable tools in microgravity research. They have even started to become useful instruments in new research fields of mechanobiology. Depending on the experiment, the fluid dynamic on the RPM cannot be neglected and needs to be taken into consideration. The results presented in this study elucidate the fluid motion and provide insight into the convection and shear stresses that occur inside a cell culture flask during RPM experiments.

TRPC6 in simulated microgravity of intervertebral disc cells

“…shear stresses) that may create artefacts. These forces present in the culture flasks on the RPM and their effects on the cultured cells were recently thoroughly studied by numerical analysis [40]. Parameters such as rotational velocity of the RPM play a role in the appearance of shear stress [40].…”

“…These forces present in the culture flasks on the RPM and their effects on the cultured cells were recently thoroughly studied by numerical analysis [40]. Parameters such as rotational velocity of the RPM play a role in the appearance of shear stress [40]. Therefore, additional stressors and artefacts can be prevented by taking the necessary measures for an accurate operation of the RPM [40].…”

“…Parameters such as rotational velocity of the RPM play a role in the appearance of shear stress [40]. Therefore, additional stressors and artefacts can be prevented by taking the necessary measures for an accurate operation of the RPM [40]. IVD cell culture in flasks on the RPM does not recapitulate the complex three-dimensional disc matrix environment.…”

Validation of Random Positioning Versus Clinorotation Using a Macrophage Model System

“…Therefore, there is a huge demand for comparative studies. Even more, since recent studies point out that random positioning results in the induction of fluid shear forces, which may affect the exposed cells and mask gravity-related effects (Wüest et al 2015(Wüest et al , 2017. Using the dinoflagellate Pyrocystis noctiluca and its capacity to act as bioassay for mechanical stress, Hauslage and coworkers visualized the shear forces induced by random positioning in contrast to clinorotation (Hauslage et al 2017).…”

Guanylyl Cyclase-cGMP Signaling Pathway in Melanocytes: Differential Effects of Altered Gravity in Non-Metastatic and Metastatic Cells

“…Comparative studies between the different simulation approaches are necessary to understand what is really achieved for the exposed systems [68,69]. For example, exposure of a fast biosensor of mechanical stress-the dinoflagellate Pyrocystis noctiluca-visualized the shear forces induced by random positioning in contrast to clinorotation [70,71]. It is therefore recommended to perform comparative studies due to the different working principles of the RPM and the clinostat.…”