1. a Humboldt University, School of Medicine, Biomaterial Research Unit, O-1040 Berlin, Tucholskystrasse 2, Germany
2. b University of Sofia, Faculty of Chemistry, Sofia 1126, Bulgaria
3. c Humboldt University, School of Medicine, Biomaterial Research Unit, O-1040 Berlin, Tucholskystrasse 2, Germany
4. d Humboldt University, School of Medicine, Biomaterial Research Unit, O-1040 Berlin, Tucholskystrasse 2, Germany
5. e Humboldt University, School of Medicine, Biomaterial Research Unit, O-1040 Berlin, Tucholskystrasse 2, Germany