1. Department of Spinal and Neural Function Reconstruction China Rehabilitation Research Center Beijing 100068 P. R. China
2. School of Rehabilitation Medicine Capital Medical University Beijing 100068 P. R. China
3. Beijing Key Laboratory of Neural Injury and Rehabilitation China Rehabilitation Research Center China Rehabilitation Science Institute Beijing 100068 P. R. China
4. CAS Key Laboratory of Bio‐inspired Materials and Interfacial Science CAS Center for Excellence in Nanoscience Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing 100190 P. R. China
5. State Key Laboratory of Chemical Engineering College of Chemical and Biological Engineering Zhejiang University Hangzhou 310027 P. R. China
6. University of Chinese Academy of Sciences Beijing 100049 P. R. China
7. Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA