Three-dimensional (3D) in vitro culture is now a recognized technique to improve the performance and physiological relevance of immortalized and primary cells. 3D culture also increases proliferation rates in some cell types (e.g. mesenchymal stem cells[1], osteosarcoma cells[2], HUVECs[3], which puts extra demands on nutrient supply and waste removal. This issue can be addressed by the use of bioreactors, which circulate a large quantity of medium over or around the 3D culture and further improve cell proliferation and specific protein expression beyond that seen for static 3D cultures (e.g. dermal fibroblasts[4], cardiac cells[5], marrow stromal cells[6], osteogenic cells[7].