Biomedical evaluation of vacuum plasma sprayed tantalum coatings processed by alkali treatment and alkali-heat treatment with different NaOH concentrations

Alkali-heat treatment (AHT) is an effective surface treatment technology for improving the bioactivity of medical metal biomaterials. However, the effects of AHT on the biocompatibility of the original material are not yet fully clear. Accordingly, in the present study, tantalum (Ta) coatings are deposited on Ti6Al4V substrates using a vacuum plasma spraying (VPS) technique and the coatings are then processed using either alkali treatment (AT) or AHT using 0.5 M and 1.0 M NaOH aqueous solution. In vitro bioactivity tests are performed in simulated body fluid for 3 similar to 14 days. It is shown that the surface of the AHT sample treated with 0.5 M NaOH (0.5 M AHT) has excellent bioactivity, irrespective of whether or not ultrasonic cleaning (UC) is performed following the heat treatment process. The surface of the AHT sample processed with 1.0 M NaOH (1.0 M AHT) contains a large number of irregular block-shaped compounds, which hinder the bioactivity of the coating. However, following UC treatment, the block-shaped compounds are removed, and the bioactivity of the AHT-UC sample is similar to that of the 0.5 M AHT sample. In in vitro biocompatibility tests for 1-7 days, the Ta coating and 0.5 M AHT-UC coating exhibited significantly better cellular attachment, growth, spreading, and viability of osteoblast-like osteosarcoma MG-63 cells than the 1.0 M AHT-UC coating. It is speculated that this is due to the presence of excess amorphous sodium tantalate on the surface of the 1.0 M AHT-UC coating. Overall, the present results show that AHT treatment performed with an appropriate NaOH concentration yields a significant improvement in both the bioactivity and the biocompatibility of VPS Ta coatings.