Fig. 1. Effect of different combinations of substrates and growth factors (at suboptimal concentrations) on OP proliferation. OPs were plated on different ECM substrates (Vn and Ln-1) or PDL, after which they were exposed to growth factors (PDGF-AA, FGF-2, NRG and EGF). The effect of these substrate–growth factor combinations on OP proliferation was determined after 16 h by BrdU incorporation, as described in Materials and methods. Values shown are means ± SD of at least three independent experiments, each in duplicate. Statistical significance is shown (***P <0.001) for the indicated growth factor concentration and substrate as compared with the PDL control at the same growth factor concentration. Note that the proliferation was significantly increased on a Vn substrate in the presence of PDGF-AA.