1. National Engineering Laboratory for Modern Silk; College of Textile and Clothing Engineering, Soochow University; Suzhou 215123 People's Republic of China
2. Jiangsu Province Key Laboratory of Stem Cell Research; Soochow University; Suzhou 215006 People's Republic of China
3. Department of Biomedical Engineering; Tufts University; Medford Massachusetts 02155
4. Research Center of Materials Science, Beijing Institute of Technology; Beijing 100081 People's Republic of China