1. AO Research Institute Davos; AO Foundation; Clavadelerstrasse 8 CH7270 Davos Switzerland
2. Department of Biomaterials Science and Technology; University of Twente; P.O. Box 217 7500 Enschede the Netherlands
3. Department of Biomedical Engineering, W.J. Kolff Institute, UMC Groningen; University of Groningen; Hanzeplein 1 9713 GZ Groningen the Netherlands