Double-layer TC4/Sr substituted hydroxyapatite bioactive coating for carbon/carbon composites

Double-layer TC4/Sr substituted hydroxyapatite bioactive coatings were applied on carbon/carbon composites using a combination method of magnetron sputtering and ultrasound-Assisted electrochemical deposition (UED). Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were adopted to investigate the morphology, microstructure and composition of the coating. The in vitro bioactivity of the coating was investigated using simulated body fluid (SBF) and cell culture tests. The results showed that the double-layer TC4/Sr substituted hydroxyapatite bioactive coatings were successfully applied on carbon/carbon composites. The deposition of TC4 inner layer was induced by the arrangement of the carbon fiber in carbon/carbon composites. The Sr substituted hydroxyapatite out layer formed a porous three-dimensional network structure with a pore size ranging from 15 nm to 400 nm after UED for 1 min and then exhibited a dense structure after UED for 2 h. The SBF immersion tests showed that the double-layer TC4/Sr substituted hydroxyapatite coating could induce the formation of a uniform apatite layer in SBF. The cell culture experiment showed that the cells were favorably elongated and flattened with plenty of filopods and microvilli on the double-layer coating, exhibiting excellent cell activity and cell proliferation behavior.