Bone Morphogenetic Protein-9 (BMP-9), known as Growth differentiation factor 2 (GDF2), is an extracellular multifunctional cytokine that is also a member of the TGF-β family. BMP-8B can bind with the TGF-β receptor and trigger SMAD protein signal transduction. BMP-9 is the most effective for the differentiation of osteoblasts in vivo, and the general BMP blocker does not affect it.