A stem cell niche for expanding stem cells in culture is described. The stem cell niche includes a scaffold, a plurality of stromal mesenchymal stem cells, and a plurality of umbilical cord blood stem cells grown in a rotating culture chamber. One embodiment of the rotating culture chamber has a fluid-filled compartment in which the umbilical cord blood stem cells are grown in the presence of the mesenchymal stem cells seeded on the scaffold. The culture chamber has a dual flow valving member at each end, wherein a first flow path passes under a molecular cut-off membrane covering a central core that transverses the culture chamber and a second flow path flows through the culture chamber and allows cells to be harvested while in suspension.