Fibronectin Adsorption on Hydroxyapatite Nanosensors and the Effect of Fibronectin Preadsorption on Biological Apatite Growth

In this study, hydroxyapatite (HA) nanoparticles were prepared at 30 °C by the chemical precipitation method. The adsorption behavior of fibronectin (Fn) on Au and HA surfaces at different Fn concentrations (50, 100, and 200 μg mL^–1 and the effect of fibronectin preadsorption on the apatite growth process were investigated by the quartz crystal microbalance technique. The surface properties of Au and HA were characterized by atomic force microscopy and field emission scanning electron microscopy. Fn adsorption experiments show that the adsorption capacity of Fn on Au and HA surfaces is in the order Au–Fn200> Au–Fn100≈ HA–Fn100≈ HA–Fn200> HA–Fn50> Au–Fn50, where the number after Fn corresponds to the concentration of the Fn solution. The order of the viscoelasticity of the adsorbed layer is HA–Fn200> HA–Fn100> Au–Fn200> HA–Fn50> Au–Fn50> Au–Fn100. These results suggest that the Fn concentration and the chemical composition and topography of the substrate surface affect Fn adsorption and the viscoelasticity of the adsorbed Fn layer. A high Fn concentration is not conducive to Fn adsorption on the HA surface and formation of a viscoelastic Fn layer. Based on the experimental results, the states and orientations of Fn adsorbed on Au and HA are rationally discussed. Mineralization experiments show that the order of the mass of the apatite layer is HA > HA–Fn50 > Au–Fn50» Au. The apatite growth rate on the Au surface is essentially zero, whereas the apatite growth rate on the Au–Fn50 surface linearly increases. For the HA and HA–Fn50 surfaces, the apatite growth rate can be divided into several stages. An adsorbed Fn layer affects apatite nucleation on both the Au and HA surfaces and decreases the apatite growth rate on the HA surface.