1. Biomedical Polymers Laboratory; College of Chemistry; Chemical Engineering and Materials Science; Soochow University; Suzhou 215123 P.R. China
2. Department of Biomaterials Science and Technology; MIRA Institute for Biological Technology and Technical Medicine; University of Twente; PO Box 217 7500AE Enschede The Netherlands
3. Center for Molecular Imaging and Nuclear Medicine; School for Radiological and Interdisciplinary Sciences; Soochow University; Suzhou 215123 P.R. China