||For few decades, Ti-based, Fe-based and Co-based alloys have been widely investigated and applied in biomedical aspect. Yet, such alloys contain elements which will harm human body in high level; also, the Young’s moduli of these alloys are much higher than that of human bone, which will induce stress-shielding effect, causing negative effect to surrounding tissues. Moreover, secondary surgery may be necessary to remove the implant while the tissue is fully healed. To solve these problems, a new embryonic field, biodegradable materials, was under investigated. Among this field, Mg alloys received most attention, which was mainly because Mg exists abundantly in human body; furthermore, Mg alloys possess closer Young’s modulus to that of human bone. However, the obstacle for Mg alloys in biomedical application was its rapid degradation rate, which would lead to complete dissolution earlier than the tissue was sufficiently healed. Hence, the degradation rate control for Mg alloys became a critical issue. Scientists used surface modification methods to fabricate a coating on the material surface, achieving the goal for controlling the degradation rate. Hydroxyapatite (HA) was a suitable composition for biomaterial coating owing to its excellent biocompatibility and osteointegrity. Electrodeposition was a well-developed method featuring simple process, low deposition temperature and controllable for coating thickness and composition. In addition, Komarov et al. announced a new way that can fabricate coating through the mechanical method, the technique was called ultrasonic mechanical coating and armoring (UMCA). However, for this technique, its application on biomaterials was not observed yet; moreover, the corrosion study for the coating made by this technique was barely found. In this study, both electrodeposition and ultrasonic mechanical coating and armoring techniques were applied to form hydroxyapatite coating on AZ31B Mg alloy, respectively. Their corrosion resistance was also investigated and their extent of enhancement was under evaluation.|
In this study, through X-ray diffraction (XRD), electron dispersive spectroscopy (EDS) and Fourier-transformed infrared spectroscopy (FT-IR) analyses, it can be confirmed that both electrodeposition and ultrasonic mechanical coating and armoring (UMCA) can successfully fabricate hydroxyapatite coating on AZ31B surface. As for the most concerned corrosion resistance, according to electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (Tafel) results, coated AZ31B showed larger polarization resistance and decreased corrosion current density. Hence, it can be demonstrated the degradation rate of hydroxyapatite coating can be effectively inhibited, which makes Mg biodegradable materials step forward to practical application.