1. a Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Bl. 108, Sofia 1113, Bulgaria
2. b Institute of Polymer Research, GKSS Research Centre, Kantstrasse 55, Teltow 14513, Germany
3. c Institute of Polymer Research, GKSS Research Centre, Kantstrasse 55, Teltow 14513, Germany
4. d Institute of Polymer Research, GKSS Research Centre, Kantstrasse 55, Teltow 14513, Germany
5. e Institute of Polymer Research, GKSS Research Centre, Kantstrasse 55, Teltow 14513, Germany
6. f Biomedical Materials Group, Department of Pharmaceutics and Biopharmaceutics, Institute of Pharmacy, Martin Luther University, Halle-Wittenberg, Kurt-Mothes-Strasse 1, 06120 Halle/Saale, Germany