Abstract: A bioreactor for cell culture medium is provided including a flask for holding the culture medium, a screen at or just below the surface of the culture medium, a mover for the screen to cause it to move generally parallel to the surface of the culture medium, and an integral or separate impeller to cause circulation of the culture medium to the surface of the liquid culture medium. The screen is preferably on a float, and is connected to be driven at different levels of the liquid in the flask.

Abstract: A stirrer apparatus for stirring culture medium has a flask with a lid, a floating magnetic stirrer responsive to a moving magnetic field, and a moving field generator including poles and coils. A guide system is provided for the stirrer including a rod which extend upwardly from the stirrer and a tube which extends through the lid, the rod extending into and being rotatable in the tube; the tube has a closed upper end. A stirrer apparatus having a floating magnetic stirrer with a central, downwardly extending, closed end guide tube, and lid with a guide rod extending into the guide tube. The stirrer included one or more continuous impellers extending across the rotational axis of the stirrer; in one embodiment, the impeller is provided by a bar magnet or magnets beneath a float and in another embodiment a bar magnet is within the float, and the impeller is a continuous blade.