Bone morphogenetic protein‐2 enhances bone formation when delivered by a synthetic matrix containing hydroxyapatite/tricalciumphosphate

Purpose: The aim of the present study was to test whether or not a synthetic matrix consisting of a polyethylene glycol (PEG) hydrogel containing recombinant human bone morphogenetic protein‐2 (rhBMP‐2) combined with grafting materials enhances bone regeneration compared with grafting alone or empty control sites. Material and methods: In each of 10 rabbits, four titanium cylinders were screwed in perforated slits made in the external cortical bones of the calvaria. The following four treatment modalities were randomly allocated: (1) empty control, (2) a combination of a PEG matrix and hydroxyapatite/tricalciumphosphate (HA/TCP) granules and a combination of a PEG matrix containing either 10 μg/ml (3) or 30 μg/ml (4) of BMP‐2 and HA/TCP granules. After 8 weeks, the animals were sacrificed and ground sections were obtained for histological analysis. For statistical analysis repeated measures ANOVA and subsequent pairwise Student's t ‐test were applied ( P <0.01). Results: Histomorphometric analysis showed an average area fraction of newly formed bone of 13.96±5.98% for the empty control, 15.16±7.95% for the PEG and HA/TCP group, 26.32±8.56% for the group containing 10 μg rhBMP‐2/ml, and 30.15±7.63% for the group containing 30 μg rhBMP‐2/ml. Statistical analysis revealed significantly more newly formed bone in the two rhBMP‐2 groups compared with the PEG and HA/TCP group and with the empty control. Regarding the surface fraction of the HA/TCP graft particles covered with newly formed bone the addition of rhBMP‐2 revealed a more than two‐fold increase compared with cylinders containing HA/TCP granules without rhBMP‐2. This difference reached statistical significance. Conclusions: It is concluded that rhBMP‐2 significantly enhances bone regeneration in rabbits when delivered by a synthetic matrix containing HA/TCP. This synthetic PEG matrix containing HA/TCP granules apparently fulfills a number of criteria required for an ideal carrier system for rhBMP‐2.