1. Department of Neurosurgery, West China Hospital, Sichuan University, 37# Guoxue Lane, Chengdu, Sichuan 610041, P.R. China
2. National Engineering Research Center for Biomaterials, Sichuan University, 29# Wangjiang Road, Chengdu, Sichuan 610064, P.R. China
3. College of Biomedical Engineering, Sichuan University, 29# Wangjiang Road, Chengdu, Sichuan 610064, P.R. China
4. National Research Council, Institute of Polymers, Composites and Biomaterials, Naples 80125, Italy