Covalent functionalization of TiO2 nanotube arrays with EGF and BMP-2 for modified behavior towards mesenchymal stem cells

In the present work we show the covalent immobilization of two bioactive molecules, epidermal growth factor (EGF) and bone morphogenetic protein-2 (BMP-2), on TiO2 nanotube surfaces and the resulting influence on the behavior of mesenchymal stem cells. Covalent immobilization of these growth factors onto the oxide surfaces was achieved by N, N-carbonyldiimidazole (CDI) coupling via binding to amine groups of the proteins either directly or via a spacer, namely 11-hydroxy-undecylphosphonic acid (PhoA). The behavior of mesenchymal stem cells can be significantly altered by such an activation procedure. The effect is depending on the diameters of the nanotubes. Most importantly, on 100 nm diameter tubes the cell activity and cell number were drastically increased by grafting such nanotube surfaces with EGF. This demonstrates that the strong diameter dependence on cell activity in the range between 15 and 100 nm observed in prior work can be compensated by coating of the nanotube surfaces with EGF.