Development of Calvarial-Derived Osteogenic Cells on GDF-5 Coated Nanoporous Titanium Surfaces

This study evaluated the impact of a single variation in the etching time of H2SO4/H2O2-treated titanium (Ti) surfaces on the adsorption of growth and differentiation factor-5 (GDF-5) and their effects on the acquisition of the osteogenic phenotype in vitro. Rat primary calvarial osteogenic cells were grown for up to 14 days on the following Ti surfaces: (1) 30 min: nanotopography obtained with a 1:1 mixture of H2SO4/H2O2 for 30 min (control); (2) 30 min + GDF-5: a 30 min-etched Ti sample adsorbed with recombinant human (rh) GDF-5; (3) 4 h: nanotopography obtained with a 1:1 mixture of H2SO4/H2O2 for 4 h (control); (4) 4 h + GDF-5: a 4 h-etched Ti sample adsorbed with rhGDF-5. The GDF-5 adsorption procedure was carried out on the day before cell plating using 200 ng/mL rhGDF-5 overnight at 4 °C. The 30 min- and 4 h-etched Ti samples exhibited a high hydrophilic network of nanopits with a tendency towards larger nanopits for the 4 h group, which corresponded to an enhanced GDF-5 adsorption. For both etching times, coating with GDF-5 resulted in less hydrophilic surfaces that supported (1) a reduction in the proportion of spread cells and an enhanced extracellular osteopontin labeling at early time points of culture, and (2) increased alkaline phosphatase activity preceding an enhanced mineralized matrix formation compared with controls, with a tendency towards higher osteogenic activity for the 4 h + GDF-5 group. In conclusion, the osteogenic potential induced by the GDF-5 coating can be tailored by subtle changes in the nanotopographic characteristics of Ti surfaces.