Dynamics of a microcarrier particle in the simulated microgravity environment of a rotating-wall vessel.

Rotating-wall vessel (RWV), a low-shear, low turbulence microcarrier culture system provides a simulated microgravity environment suitable for 3-dimensional tissue culture. In this paper, the motion of a microcarrier particle in the rotating fluid has been analytically/numerically studied. If the microcarrier is less dense than the surrounding liquid medium, it eventually migrates towards an equilibrium state in the fluid. This state corresponds to a stationary location in the inertial frame of reference or equivalently, a circular orbit about the rotational axis in a rotating frame. If the particle is denser, it may move away indefinitely to reach or collide with the outer wall of the rotating vessel (outer boundary of the rotating fluid). Such a collision may damage the cells and could be undesirable for tissue culture. We have calculated migration times for a denser microcarrier to reach the outer wall of the vessel. Several factors--rotational speed, fluid viscosity, density difference between that of the microcarrier and the fluid, microcarrier radius, and the initial position of the microcarrier--were found to affect this migration time. We have also evaluated the variation of the fluid shear stress on the microcarrier surface. Decreasing the density difference between the microcarrier and the fluid, and decreasing the size of the microcarrier, can both decrease the maximum shear stress. The results for a solid, a hollow, and a hollow-porous microcarrier show that with a denser microcarrier material, the hollow or hollow-porous spherical microcarriers are preferable in order to increase the suspension time and decrease the maximum shear stress. The results of this study are thought to be useful for the development of optimal conditions for cell growth and metabolism in RWVs.