1. Institute of Hard Tissue Development and Regeneration; the Second Affiliated Hospital of Harbin Medical University and Heilongjiang Academy of Medical Sciences; Harbin 150001 Heilongjiang China
2. Department of Spine Surgery; the Second Affiliated Hospital of Harbin Medical University; Harbin 150086 China
3. National Engineering Laboratory for Modern Silk; Soochow University; Suzhou 215123 China
4. Department of Biomedical Engineering; Tufts University; Medford MA 02155 USA