Effect of supplementing culture media with BMP2Pe or BMP2Pr grafted NPs on mRNA expression level (as fold difference) of osteogenic markers OP and OC, and vasculogenic marker PECAM-1. The expression level of S16 control gene was used as the reference and the fold difference in expression was normalized to that at time zero. Groups include BMS cells cultured in OM, OM supplemented with blank NPs, OM supplemented with BMP2 protein, OM supplemented with BMP2Pe, OM supplemented with BMP2Pe grafted NPs, and OM supplemented with BMP2Pr grafted NPs. One star indicates statistically significant difference (s.d.; p<0.05) between the test group and OM, two stars between the test group and free BMP2Pe, and three stars between the test group and BMP2Pr. Error bars correspond to means ± 1 SD for n = 3.