Growth of hydroxyapatite coatings on tantalum by plasma electrolytic oxidation in a single step

Aiming at the improvement of tantalum bioactivity, hydroxyapatite coatings have been grown on Ta samples by plasma electrolytic oxidation (PEO) without any pre- or post-treatment. It has been evaluated the influence of polarization voltage, which ranged from 350 to 500 V, and treatment time, ranging from 60 to 600 s, on the characteristics of the modified samples. Surface morphology, chemical and phase compositions of the coatings were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffractometry (XRD). The evaluation of the performance of the samples when in biological media has been carried out through colorimetric determination of metabolic oxidation of MTT and alkaline phosphatase activity. It has been observed that the characteristics of the surfaces are strongly influenced by the treatment parameters. FTR and EDS spectra revealed increasing incorporation of calcium and phosphorus as both the voltage and the treatment time were increased. Furthermore, XRD confirmed the formation of crystalline hydroxyapatite on samples treated for > 180 s at 500 V. The treatments, which resulted in coatings containing up to 80% of hydroxyapatite, lead to surfaces with improved bioactivity.