Composition and bioactivity of calcium phosphate coatings on anodic oxide nanotubes formed on pure Ti and Ti-6Al-4V alloy substrates.

Electronic structure and bioactivity of calcium phosphate (CaP) coatings on Ti-based anodic nanotubes are investigated. Nanotubes on pure Ti and Ti-6Al-4V alloy, respectively, are used as substrates for CaP deposition. The CaP coatings are formed by first growing a seeding CaP layer using alternative immersion (AIM) treatment followed by crystallization in Dulbecco's phosphate-buffered saline (DPBS). CaP coatings formed on both Ti and Ti-6Al-4V substrates are found containing a variety of bioactive CaP species, such as hydroxyapatite (HA), amorphous CaP (ACP), octacalcium phosphate (OCP), and dicalcium phosphate dihydrate (DCPD). The compositions of the coatings during the nucleation and crystallization processes are tracked and analyzed using X-ray absorption near-edge structure (XANES). The variation of CaP species in the resulted coatings are found strongly dependent on the choice of metal substrates, which leads to different bioactivities. By comparing the proliferation and differentiation of osteoblast cells (MC3T3-E1) on the CaP coatings, correlations between CaP species and their bioactivities are established.