Figure 5. Observed at the interface separating the top of the cell bed from the PBS above is the presence of Rayleigh-Taylor (RT) instabilities.

RT instabilities result from the nonuniform acceleration of a more dense fluid into a less dense fluid, when the two fluids are separated by a sharp interface. Previous results have shown the addition of BPB to a dilute salt solution decreases solution density. Therefore, the observed RT instabilities are an artifact of the dye injection procedure used to visualize the flow profile and would not be present during cell culture with a homogeneous culture medium.