1Polymer Chemistry and Biomaterials, Institute for Biomedical Technology, Department of Science and Technology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
2Biophysical Engineering, MESAþ Institute for Nanotechnology, Departmet of Science and Technology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands