1. Department of Neurosurgery, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, P. R. China
2. Department of Neurovascular Surgery, General Hospital of Armed Police Forces, Beijing, P. R. China
3. Center of Excellence in Tissue Engineering, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, P. R. China