'Smart' biomaterials and osteoinductivity

In their recent paper in Nature Reviews Rheumatology, Boyan and Schwartz discussed the use of synthetic biomaterials in repair strategies of large bone defects (Are calcium phosphate ceramics 'smart' biomaterials?Nat. Rev. Rheumatol. 7, 8–9; 2011).1 This News & Views commentary, which is largely based on our publication in the Proceedings of the National Academy of Sciences,2 justly emphasizes the importance of the search for alternatives to autologous bone grafts, which are limited in availability, for treatment of large bone defects. Boyan and Schwartz question if calcium phosphate ceramics are indeed 'smart' biomaterials, in the sense of being truly osteoinductive. Referring to our work they state: “...unfortunately, however, it is not clear whether the intramuscular implants used in the dog and sheep models were only the porous ceramics or if they were the composite grafts with human mesenchymal stem cells (hMSCs) that had been pre-differentiated in osteogenic medium”.1 We would like to explicitly emphasize and clarify that the referred data were obtained by using ceramics alone, without the addition of any cells and/or growth factors.