Effect of Sulfuric Acid Treatment on Bioactivity of TiO₂ Coatings

In recent years, some ceramics, such as HA, wollastonite and bioglass (BG), were deposited onto titanium substrate using plasma spraying technology and exhibited an excellent application foreground as orthopedic and dental implant materials. However, these coatings often lead to a dissolution from the implants and result in failure or have a poor adhesion to substrate. Plasma sprayed TiO₂ coatings on titanium alloy substrates as bond coatings and composite coatings have recently demonstrated promising corrosion behavior in vivo, acting as chemical barrier against the release of metal ions from the implant. TiO₂ powders and films can exhibit bioactivity in many applications, but plasma-sprayed TiO₂ coating is always bioinert. In this work, TiO₂ coatlngs on titanium alloy substrates were prepared by atmospheric plasma spraying using commercial nano-powders. A chemical treatment method was employed to induce bioactivity on the TiO₂ surface. As-sprayed coatings were treated using sulfuric acid (H₂SO₄) of different concentration at room temperature for 24 hours. The bioactivity of these H2SO4 -treated TiO, coatings were evaluated by investigating the formation of apatite on their surface after they were soaked in simulated body fluid for a period of time. The results obtained indicated that H₂SO₄-treated TiO₂ coating can induce bone-like apatite formation on its surface but apatite cannot form on the surface of the as-sprayed TiO₂ coating. The concentration of H₂SO₄ play an important role in bioactivity and the bioactivity was lost when the concentration of H₂SO₄ decrease to 0.01M. The formation of a hydrogenated surface which gives rise to negatively charged functional groups was thought to be the primary reason to induce bioactivity of TiO₂ coating.