Composite calcium phosphate coatings with sustained Zn release

Zinc-substituted tricalcium phosphate/fluoridated hydroxyapatite (ZnTCP/FHA) biphasic composite coatings and Zinc containing fluoridated hydroxyapatite (ZnFHA) coating were prepared on Ti6Al4V substrates through a modified sol–gel method. The release of zinc ions from these coatings was characterized through a designed cycled immersion test: the coatings were soaked in the TRIS solution with pH of 7.25 at 37 °C for 96 h (one cycle). This process was repeated twice with the solution refreshed at the end of the each cycle. The Zn concentrations were measured at a 24-hour interval during the first cycle and at the end of each cycle. The results indicated that ZnTCP/FHA coatings released Zn at a rather slow and sustained rate while ZnFHA coatings released Zn at a rapid and therefore unsustained rate. This Zn release behavior difference is attributed to the different chemical states of Zn in the coatings. The current results demonstrated that the designed biphasic composite approach could potentially be a good way to tailor the release of Zn through combinations of different Zn chemical states, with the durability of the coatings not impaired.