1. Applied Stem Cell Technologies, Technical Medical Centre, University of Twente, PO Box 217, Enschede 7500 AE, The Netherlands
2. BIOS Lab on a Chip Group, MESA+ Institute for Nanotechnology, Technical Medical Centre, Max Planck Institute for Complex Fluid Dynamics, University of Twente, Enschede, 7500 AE, The Netherlands
3. Department of Anatomy and Embryology, Leiden University Medical Center, Leiden 2300 RC, The Netherlands