Bone formation of Escherichia coli expressed rhBMP-2 on absorbable collagen block in rat calvarial defects

Objectives: The aim of this study was to evaluate the osteogenic and space-providing effect of rhBMP-2 produced in an Escherichia coli expression system (ErhBMP-2) with absorbable collagen block (ACB) as the carrier system in the rat calvarial defect model. Study design: Eight-millimeter diameter calvarial defects were created in 60 male Sprague-Dawley rats. The animals were divided into 6 groups containing 10 animals each that received sham-surgery control (no material applied), ACB control (ACB alone), or ErhBMP-2/ACB (ACB loaded with 0.025 mg/mL ErhBMP-2). Histological and histometric analysis was performed after 2- and 8-week healing intervals. Results: On histological observation, the level of bone formation in the defects was generally higher at 8 weeks than at 2 weeks. Surgical implantation of ErhBMP-2/ACB resulted in the enhanced bone regeneration compared with controls. Moreover, the collagen remnants of ACB appeared to be completely resorbed in ACB control and ErhBMP-2/ACB group after 8 weeks. Histometic analysis revealed that the ErhBMP-2/ACB group had a significantly greater augmented area, new bone area, and new bone ratio after 2 and 8 weeks than both control groups. However, there was no difference between 2 and 8 weeks in the ErhBMP-2/ACB group in all aspects of the augmented area, new bone area, and new bone ratio (P < .05). Conclusion: ErhBMP-2 loaded on ACB can induce favorable bone formation in the rat calvarial defect model, but this collagen carrier in block type did not fulfill the space-maintaining expectations for bone formation by ErhBMP-2.