Schematic illustration shows generation of tubules by renal stem/progenitor cells. a) After isolation renal stem/progenitor cells (s/pC) are placed between layers of polyester fleece (PF) to create an artificial interstitium. The fleece layers are mounted in a Minusheet® tissue carrier. b) For culture the carrier is transferred to a perfusion container with horizontal flow characteristics. c) Perfusion culture is performed for 13 days under atmospheric air. During this period always fresh culture medium is transported by a peristaltic pump (1.25 ml/h) from a storage bottle to the container and then to a waste bottle.