Surface Characteristics of Nano-ZrO₂ Coated Pure Titanium and Titanium Alloy

Objective:  to evaluate the surface characteristics of pure titanium and titanium alloy coated with nano-zirconia by using an atomic layer deposition (ALD) technique. Method:  CP-Ti and Ti6Al4V discs, 14 mm in diameter and 2 mm in thickness, were prepared. Two different thicknesses of nano-zirconia layers (20 nm and 100 nm) were coated, with ALD technique, on the CP-Ti discs (Ti20 and Ti100, respectively) and Ti6Al4V discs (V20 and V100, respectively). The shade, contact angles and SEM were observed or measured to assess the surface characteristics. The MTT assay, LDH assay and F-actin fluorescence stain were used to evaluate the in vitro cytotoxicity and biocompatibility of nano-zirconia coated discs with MG63, the human osteosarcoma cell line. Result: The SEM of V20, V100, Ti20 and Ti100 demonstrated the ZrO₂nano particles on the disc surfaces. The L*a*b system was used to evaluate the change of shade. The original shade of CP-Ti was silver grey which was converted into brown (Ti20) and reddish brown (Ti100). The original shade of Ti6Al4V was silver grey which was converted into dark grey (V20) and gold (V100). The contact angle of untreated CP-Ti was higher than Ti20 and Ti100; however, the contact angle of V100 was higher than untreated Ti6Al4V and V20. The results of MTT assay suggested that there was no significant difference among these nano-zirconia coated groups and untreated control groups. However, the LDH levels of Ti20, Ti100, V20 and V100 were significant decreased. The F-actin fluorescence showed that the growth of MG63 was elevated in Ti20, V20, and Ti100 groups. Conclusion:  By using ALD technique, the nano-zirconia layer can be coated on CP-Ti and Ti6Al4V surfaces. While CP-Ti becomes hydrophilic after coating, Ti6Al4V becomes hydrophobic. The nano-zirconia coating could enhance the growth of MG63. However, further investigations are needed to clarify the detail mechanism.