Objectives: This study was performed to investigate the effect of electrolyte composition on the surface properties and in vitro biocompatibility of anodized and hydrothermally-treated Ti-6Al-7Nb alloy. Methods: Discs of Ti-6Al-7Nb alloy of 20 mm in diameter and 2 mm in thickness were polished sequentially from #300 to #1000 SiC paper, ultrasonically washed with acetone and distilled water for 5 min, and dried in an oven at 50 degrees C for 24 hours. Four different electrolytic solutions containing DL-a-glycerophosphate disodium salt hydrate(DL-a-GP), b-glycerophosphate disodium salt hydrate(b-GP), glycerophosphate disodium salt hydrate(GP), and glycerophosphate calcium salt hydrate (GP-CA) were used. Anodizing was performed at current density of 30 mA/cm^2 up to 300 V using a regulated DC power supply. Hydrothermal treatment was conducted by high pressure steam at 300 degrees C for 2 hours using a autoclave. Samples were soaked in the Hanks' solution with pH 7.4 at 36.5 degrees C for 30 days. Results: Needle-like hydroxyapatite (HA) crystals were observed on anodic oxide films after the hydrothermal treatment at 300 degrees C for 2 hours. When containing DL-a-GP and b-GP in electrolyte composition, the precipitated HA crystals showed the shape of thick and short rod. However, when containing GP and GP-Ca, the more fine needle shape HA crystals were appeared. In Hanks' solution, groups containing DL-a-GP and b-GP showed higher bioactivity than groups containing GP and GP-Ca in electrolyte composition. The bioactivity of the group containing DL-a-GP was higher than that containing GP and GP-Ca in electrolyte composition. The precipitated Ca and P in groups containing DL-a-GP and b-GP in electrolyte composition was increased in Hanks' solution. Conclusions: It was found that the anodized and hydrothermally-treated Ti-6Al-7Nb alloy using an electrolyte containing DL-a-GP showed the excellent in vitro biocompatibility and bone conduction as implant material.

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