Mechanical and in vitro biological performances of hydroxyapatite–carbon nanotube composite coatings deposited on Ti by aerosol deposition

Hydroxyapatite (HA)–carbon nanotube (CNT) composite coatings on Ti plate, produced by aerosol deposition using HA–CNT powders, were developed for biomedical applications. For the deposition process HA–CNT powder mixtures with CNT contents of 1 and 3 wt.% were used. Dense coatings with a thickness of 5 μm were fabricated, irrespective of the content of CNTs. No pores or microcracks were observed in the coatings. The coatings had good adhesion to the substrate, exhibiting a high adhesion strength, ranging from 27.3 to 29.0 MPa. Microstructural observation using field-emission gun scanning electron microscopy and transmission electron microscopy showed that CNTs with a typical tubular structure were found in the HA–CNT composite coatings. Nanoindentation tests revealed that the mechanical properties, such as the hardness and elastic modulus, were significantly improved by the addition of the CNTs to the HA coating. In addition, the proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 pre-osteoblast cells grown on the HA–CNT composite coatings were higher than those on the bare Ti and pure HA coating. The ALP activity of the composite coatings considerably improved as the CNT content increased. These results suggest that CNTs would be an effective reinforcing agent to enhance both the mechanical and biological performances of HA coatings.