Fabrication of Mesoporous Hydroxycarbonate Apatite/Polyaniline Composite Coatings on Ti6Al4V Substrates

Hydroxycarbonate apatite/polyaniline composite coatings (HCp/PANI coatings) with mesoporous structure were fabricated by the electrophoretic deposition of calcium carbonate particles and polyaniline (PANI) nanofibers on Ti6Al4V substrates followed by treatment with phosphate buffer solutions (PBS) at 37 °C. After soaking in PBS, the perfect crack-free CaCO3/PANI coatings are converted to HCp/PANI coatings with platelet-like structure via a dissolution-precipitation reaction. The mesopores and the macropores (or apertures) are formed within and among the platelets, respectively. Simulated body fluid (SBF) immersion tests reveal that the porous structure can improve the in vitro apatite forming ability of coatings. In SBF, the bone-like apatite nanocrystals are firstly deposited around the mesopores, and then fill the macropores with the increase of immersion time. Moreover, the superior in vitro apatite forming ability of HCp/PANI coatings is related to the PANI nanofibers. The functional groups (H2PO4) in PANI not only increase the local supersaturation, but also induce the heterogeneous nucleation and the growth of bone-like apatites.