Tethering of rhBMP-2 upon calcium phosphate cement via alendronate/heparin for localized, sustained and enhanced osteoactivity

Abstract

Localized, continuous and effective osteogenic stimulation to defected sites is still a great challenge for recombinant human bone morphogenetic protein-2 (rhBMP-2) in clinical bone regeneration. In this study, a novel delivery system was engineered to tether rhBMP-2 onto the surface of calcium phosphate cement (CPC) based on the high affinity between alendronate and CPC, as well as the strong binding of heparin and rhBMP-2. Alendronate was first grated to heparin via the EDC/NHS reaction and then the resultant alendronate-heparin (AH) was adsorbed onto the CPC surface. RhBMP-2 was further anchored onto the CPC-AH surface. The results from in vitro release and in vivo fluorescence-labeled traces all indicated that the AH-tethered rhBMP-2 exhibited a more stable and stronger adherence to the CPC surface than the CPC-adsorbed and heparin-anchored ones. Moreover, based on the results of the alkaline phosphatase (ALP) activity in skeletal myoblasts (C2C12) in vitro and osteogenic efficacy in vivo, it could be seen that rhBMP-2-induced osteogenic bioactivity was also significantly enhanced on the CPC-AH surface. These results demonstrated that the tethering of rhBMP-2 onto calcium phosphate surface via AH presented an effective method to achieve a localized and sustained exposure to targeted cells, and consequently to promote bone regeneration.