* Corresponding authors

^a Laboratory of Bone Tissue Engineering of Beijing Research Institute of Traumatology and Orthopaedics, Beijing 100035, China

^b Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing 100029, China
E-mail: zhanglq@mail.buct.edu.cn
Fax: +86 10 64433964
Tel: +86 10 64421186

^c Department of Neurosurgery of Beijing JiShuiTan Hospital, The Fourth Clinical Medical College of Peking University, Beijing 100035, China

^d Department of Spine Surgery of Beijing JiShuiTan Hospital, The Fourth Clinical Medical College of Peking University, Beijing 100035, China
E-mail: tianweijst@vip.163.com
Fax: +86 10 58516538
Tel: +86 10 58516538