Injectable tissue‐engineered bone repair of a rat calvarial defect

Abstract

OBJECTIVES/HYPOTHESIS: Advances in bone repair have focused on the minimally-invasive delivery of tissue-engineered bone (TEB). A promising injectable biopolymer of chitosan and inorganic phosphates was seeded with mesenchymal stem cells (MSCs) and a bone growth factor (BMP-2), and evaluated in a rat calvarial critical size defect (CSD). Green fluorescent protein (GFP)-labeled MSCs are used to evaluate patterns of cell viability and proliferation. STUDY DESIGN: Prospective, controlled trial in an animal model. METHODS: In 30 male rats, 8-mm calvarial CSDs were created, and divided into five groups of six animals each. In the experimental groups, the defects were injected with either chitosan gel, gel loaded with MSCs (0.3 x 10(6) cells/defect), gel loaded with BMP-2 (2 microg/defect), or gel loaded with both MSC and BMP-2. In the control group, the defect was left untreated. At 4 weeks, in vivo microcomputed tomography (micro-CT) analysis was performed. At 8 weeks, calvarial specimens were examined by micro-CT, histology, and immunohistochemistry. RESULTS: New areas of bone growth were seen in the defects of all treated animals. Micro-CT analysis revealed a significant (P < .001) time-dependent increase in the regeneration of bone volume and bone area in defects treated with gel/MSC/BMP-2 as compared to all other groups. Histological analysis confirmed this difference. GFP-labeled TEB was detected within the areas of new bone, indicating cell viability and contribution to new bone growth by the injected MSC. CONCLUSIONS: This study demonstrates that an injectable form of TEB using a chitosan gel, MSC, and BMP-2 can enhance bone formation in a rat calvarial CSD.