Study of hMSC proliferation and differentiation on Mg and Mg-Sr containing biphasic β-tricalcium phosphate and amorphous calcium phosphate ceramics.

Biphasic mixtures of either Mg(2+) or combined Mg(2+) and Sr(2+) cation substituted β-tricalcium phosphate (β-TCP) and amorphous calcium phosphate (ACP) were prepared using a low temperature chemical phosphatizing and hydrolysis reaction approach. Scaffolds prepared using the cation substituted calcium phosphates were capable of supporting similar levels of human mesenchymal stem cell proliferation in comparison to commercially available β-TCP. The concentrations of Mg(2+), Sr(2+), and PO4(3-) released from these scaffolds were also within the ranges desired from previous reports to support both hMSC proliferation and osteogenic differentiation. Interestingly, hMSCs cultured directly on scaffolds prepared with only Mg(2+) substituted β-TCP were capable of supporting statistically significantly increased alkaline phosphatase activity, osteopontin, and osteoprotegerin expression in comparison to all compositions containing both Mg(2+) and Sr(2+), and commercially available β-TCP. hMSCs cultured in the presence of scaffold extracts also exhibited similar trends in the expression of osteogenic markers as was observed during direct culture. Therefore, it was concluded that the enhanced differentiation observed was due to the release of bioactive ions rather than the surface microstructure. The role of these ions on transforming growth factor-β and bone morphogenic protein signaling was also evaluated using a PCR array. It was concluded that the release of these ions may support enhanced differentiation through SMAD dependent TGF-β and BMP signaling.