1. Institute of Biomaterials University of Erlangen-Nuremberg Cauerstr. 6 Erlangen 91058 Germany
2. National Engineering Research Center for Nanomedicine College of Life Science and Technology Huazhong University of Science and Technology Wuhan 430074 P. R. China
3. Institute of Particle Technology Department of Chemical and Biological Engineering University of Erlangen-Nuremberg Cauerstr. 4 Erlangen 91058 Germany