Abstract: The separation device of the invention is directed to a container having an interior surface defining a channel. The container further has an inlet and an outlet. On the interior surface of the channel are pole tips which may be in a sawtooth configuration having sharp angles facing the interior of the channel that generate a high gradient magnetic field in the channel. Within the channel may be incorporated separating material. The separating material eliminates the direct contact of cells with the magnetic pole material. The separating material, as well as the sawtooth pole tips also serves the purpose of creating a field gradient across the entire container to avoid the problem of zero field gradient in the center of the container where the velocity is greatest, and where more cells flow. The separating material is designed to cause a substantially unobstructed flow of medium through the channel so that unlabeled substances are not trapped in the separating material.

Abstract: The present invention provides methods and bioreactors for expanding stem cells in a population of cells substantially enriched in hematopoietic stem cells and substantially free of stromal cells. The method comprising the steps of inoculating the population of cells in an expansion container in a volume of suitable medium such that the cell density is at least about 5,000 cells/1 mL and at an initial oxygen concentration of less than 8%; adding an effective amount of at least one cytokine to cause stem cell expansion; culturing the cells under suitable conditions such that the cells condition the medium; increasing the oxygen concentration to about 20%; exchanging the medium at a rate which allows expansion of the stem cells; and culturing the cells under conditions such that the stem cells are expanded. The present invention also provides a bioreactor constructed to accomodate the operational requirements for stroma-free stem cell expansion.