Effects of ultrasonic treatment and current density on the properties of hydroxyapatite coating via electrodeposition and its in vitro biomineralization behavior

In this study, ultrasonic-assisted electrodeposition is used to prepare uniform and smooth hydroxyapatite (HA) coating on the surface of the braids, which can be potentially applied as biodegradable bone scaffolds. During the electro-deposition process, the ultrasonic power (0 W and 20 W) and current density (2.5, 5.0, and 7.5 mA/cm(2)) are altered in order to evaluate their influences on the properties of HA coating over the braid surface. The field emission scanning electron microscope (FE-SEM) images show that the crystals growth stages of HA include spherical particles, plate-like and needle-like crystals when electro-deposited for 15, 30, 45, and 60 min. In particular, when electro-deposited for 60 min, the needle-like structure of HA coatings shows a significant increase in density as a result of increasing the current density or the employment of ultrasonic treatment. Transmission electron microscope (TEM) results show that when the current density increases from 2.5 mA/cm(2) to 7.5 mA/cm(2), the grain size decreases from 413.65 +/- 63.12 nm to 264.56 +/- 65.33 nm. With the aid of ultrasonic treatment, the HA coating demonstrates a calcium-phosphorus (Ca/P) ratio that resembles that of the human skeleton being 1.67. The X-ray Diffraction (XRD) results show the highest crystallinity reaches 73.52% at 7.5 mA/cm(2)-20 W. The cavitation effect of ultrasonic can improve the roughness of HA coating distinctively. Finally, the 7-day immersion into simulated body fluid (SBF) demonstrated a denser and finer apatite precipitation on the HA coating fabricated by ultrasonic-assisted electrodeposition. Therefore, this study provides a feasible ultrasonic-assisted electrodeposition method that yields a good morphology of bioactive substances coating over braid or other rugged deposition substrate for potential degradable bone scaffolds.