Surface functionalization of dual growth factor on hydroxyapatite-coated nanofibers for bone tissue engineering

To improve bone growth and to imitate the function of natural extracellular matrix for sustained release of multiple growth factors, a scaffold of porous gelatin nanofibers were electrospun, coated with hydroxyapatite using a simulated body fluid solution, and surface-functionalized with avidin to facilitate binding with biotinylated growth factors, namely bone morphogenetic protein-2 (BMP-2) and fibroblast growth factor-2 (FGF-2) at different ratios. Scanning electron microscopy was used for structure characterization and Fourier-transform infrared spectroscopy and calcium assay were performed to evaluate the calcium composition. Immunostaining techniques confirmed the conjugation of multiple growth factors. The effects of the two growth factors and hydroxyapatite on osteogenic cell differentiation were studied using quantitative polymerase chain reaction analysis. Multiple growth factors were successfully conjugated onto the functionalized surface by controlling the FGF-2/BMP-2 ratio. Comparisons of the factor release profiles with those of the physical adsorption showed that avidin-biotin conjugation was more effective for sustained release. Bone regeneration was enhanced via synergism between multiple growth factor delivery and the hydroxyapatite nanofiber coating, as confirmed by the increased expression of osteogenic gene markers. The nanofibers thus provide a promising osteoconductive scaffold with controlled multiple growth factor delivery for bone tissue engineering.