1. Department of Biomaterials, Max Planck Institute of Colloids and Interfaces; Potsdam 14476 Germany
2. Max Planck Institute of Microstructure Physics; 06120 Halle Germany
3. Fraunhofer Institute for Mechanics of Materials; 06120 Halle Germany
4. Micropaléontologie, UFR TEB; Université P. & M. Curie; 75252 Paris Cedex 05 France
5. Department of Materials Science and Engineering; Technion - Israel Institute of Technology; Haifa 32000 Israel
6. Department of Biomaterials; Max Planck Institute of Colloids and Interfaces; Potsdam 14476 Germany