1. Center
for Craniofacial Stem Cell Research and Regeneration, Department of
Orthodontics, Peking University School and Hospital of Stomatology, Beijing 100081, P. R. China
2. School
of Materials Science and Engineering, Tsinghua University, Beijing 100084, P. R. China
3. Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics & Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
4. University of Chinese Academy of Sciences, Beijing 100049, P. R. China
5. Division
of Engineering in Medicine, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Cambridge, Massachusetts 02139, United States