Generally if osteoblasts are to mineralise, they will need a phosphate donor such as beta glycerophosphate (BGP) or potassium phosphate... are you sure one of these are not in or meant to be in the media?

Hi Nathan,

Thanks for the reply. No. We dint add both to the medium. But we did observe mineralization. Do you think the phosphate could be from PBS as PBS contains NaH2PO4?

Dear Guddu Sam,

Of course NaH2PO4 can dissociate into its constitute ions, and could serve as phosphate source.. try reconstituting BMP directly  in culture media and check. 

Thanks Arun.