TEM analysis and in vitro and in vivo biological performance of the hydroxyapatite crystals rapidly formed on the modified microarc oxidation coating using microwave hydrothermal technique

A bioactive coating with the outwards growth of the uniform and abundant hydroxyapatite (HA) crystals was quickly fabricated on titanium (Ti) by microarc oxidation (MAO) and microwave hydrothermal (MH) treatment. The MAO coating consisted of a few of TiO2 nanocrystals and lots of amorphous phase containing Ca, P, Si, Ti and O. The MH treating time has significant influence on the surface morphology, elemental concentration and phase composition of the MAO coating. After MH treatment for 10 min, large numbers of HA columnar crystals were rapidly formed on the outermost surface of the MAO coating. However, long MH treating time (60 min) could give rise to the dissolution of the HA columnar crystals and lead to the formation of lots of Na0.23TiO2 nanoflakes on the outer surface. As compared with the Ti and MAO coating, the MH treated MAO coatings showed better cell adhesion and proliferation as well as higher expression levels of various genes such as the bone morphogenetic protein 2, bone sialoprotein, osteopontin and alkaline phosphates genes. This improvement was probably attributed to the formation of large numbers of HA columnar crystals on the surface. After implantation for 16 weeks, the MH treated MAO coating for 10 min possessed the best osseointegration ability due to the high bioactivity of the HA columnar crystals, including the good bone-implant contact interface, less soft tissue at the interface, more new bone formation and higher interface bonding strength with the bones. Thus, the hybrid technology of the MAO and MH treatment could be considered as the rapid and effective surface modification technology, showing a promising application in the biochemical filed.