The Effect of the Delivery Carrier on the Quality of Bone Formed via Bone Morphogenetic Protein-2

Bone morphogenetic protein-2 (BMP-2) can induce bone generation in vivo. Although many studies have demonstrated an increased quantity of regenerated bone after the delivery of BMP-2 using various carriers, little is known about the effect of the carrier type on the quality of the regenerated bone. In this study, we compared the quality of regenerated bone when BMP-2 was delivered with either beta-tricalcium phosphate (beta-TCP) or heparin-conjugated fibrin (HCF), both of which are shown to be excellent carriers for BMP-2. The profile of the release of BMP-2 was not significantly different between the delivery carriers. However, the alkaline phosphate activity of cultured osteoblasts was significantly higher when BMP-2 was delivered using HCF than when BMP-2 was delivered using beta-TCP. To evaluate the quality of the regenerated bone, both types of BMP-2 carriers were implanted into critical-sized calvarial defects in mice. Eight weeks after implantation, the regenerated bone was examined by histomorphometry. Importantly, the treatment using HCF + BMP-2 and beta-TCP + BMP-2 resulted in similar bone formation areas. However, the treatment using HCF + BMP-2 resulted in significantly higher bone density than the treatment using beta-TCP + BMP-2. This study shows that a BMP-2 delivery carrier can modulate the quality of bone regenerated via BMP-2 delivery.