Enhancement of bone formation with a synthetic matrix containing bone morphogenetic protein-2 by the addition of calcium citrate.

Purpose: The aim of the study was to test whether calcium citrate combined with rhBMP-2 was able to enhance bone regeneration compared with a matrix containing only rhBMP-2.

Methods: In each of experimental mice, one cylinder of calcium citrate-rhBMP-2 or rhBMP-2 alone was implanted into the thigh muscle pouches of the mouse. The following two treatment modalities were randomly allocated: (1) empty control with rhBMP-2 alone in a gelatin matrix and (2) a gelatin matrix including both calcium citrate and BMP-2. After several weeks, bone granules were obtained by histological analysis.

Results: Histomorphometric analysis showed the greatest amount of newly formed bone was observed in the group that contained 10.0 mg calcium citrate with 2.0 mg rhBMP-2 (p < 0.05). Quantitative histomorphometry revealed in the calcium citrate-rhBMP-2 group an obvious increase in the fractional area and the average new bone mineral density of newly formed bone at 2, 4 and 6 weeks than in the rhBMP-2 group (p < 0.05). At 2 weeks time-point, the mature cancellous bone had formed in the calcium citrate-rhBMP-2 group.

Conclusions: From this study, it can be concluded that calcium citrate combined with rhBMP-2 significantly enhances bone regeneration in muscle. This synthetic gelatin matrix containing calcium citrate/gelatin granules fulfils a number of criteria required for an ideal carrier system for rhBMP-2. The calcium ions that calcium citrate releases into the surrounding environment can activate bone formation when used as part of a combination of calcium citrate and BMP-2.