Corrosion Behavior of Micro-Arc Oxidized Magnesium with Calcium Phosphate Coating in Flowing Simulated Body Fluids

Abstract

A micro-arc oxide (MAO) layer and calcium phosphate (Ca-P) coating were prepared on magnesium using a micro-oxidation technique and chemical deposition. The corrosion behavior of the MAO magnesium with and without a Ca-P coating in static and flowing simulated body fluids (SBF) was studied by electrochemical polarization and impedance spectroscopy. The microstructure of the coating was examined by scanning electron microscopy, X-ray diffraction and infrared spectroscopy. The results indicated that the micro-arc oxide layer was easily broken by the SBF, which breached the oxide layer and corroded the underlying magnesium. Solution flow promoted the failure of the oxide layer and the process of MAO magnesium corrosion. The prepared Ca-P coating consisted of hydroxyapatite (HA) and dicalcium phosphate dihydrate (DCPD). Although the Ca-P coating itself exhibited low resistance to corrosion, it effectively protected the oxide layer against failure, which then inhibited the corrosion of the Ca-P coated MAO in SBF. The presence of the Ca-P coating weakened the effect of flow on the corrosion of the coated MAO. Moreover, the Ca-P coating transformed into a thick apatite layer even in flowing SBF, which further improved the protection of the MAO magnesium.Magnesium and its alloys have received an ever-increasing amount of attention as biodegradable orthopedic implants. 1-8 Mg 2+ is one of the most abundant cations in the human body, playing an important role in human metabolism. 9 The biodegradable magnesium plates can be used to support injured bones and promote bone healing. [10][11][12] It is interesting that the use of magnesium implants could relieve the patient from secondary operations and diminish cost. 13,14 Moreover, magnesium alloy cardiovascular stents are also expected to be a desirable choice for long-term implants. 15,16 However, the rapid corrosion of magnesium in physiological media, causing too much hydrogen gas and OH − , inhibits its clinical application. 17,18 Alloying and surface treatments are commonly adopted to decrease the corrosion rate of magnesium. [19][20][21][22][23] Calcium phosphate (Ca-P) coatings have been widely studied as a barrier to the corrosion of magnesium alloys in vitro. 24-26 Various techniques of preparing Ca-P coating on the surface of magnesium alloys have been proposed, and previous studies have demonstrated that the corrosion rates of the coated magnesium alloys were strongly reduced. 27-29 Ca-P coatings have been found to increase in thickness and density during in vitro immersion, which further improved the corrosion performance of magnesium alloys. 30 Moreover, Ca-P coatings have been reported to enhance cellular adhesion, proliferation and differentiation to promote bone regeneration. 31 Xu et al. found that a Ca-P coating promoted the surface bioactivity of Mg-Mn-Zn alloy. 32 The presence of hydroxyapatite (HA) on a Mg-Zn alloy was reported to improve the bioactivity and mineralization ability of the magnesium alloy. 33 Cell culture results have also indicated that ca...

Fabrication of hydroxyapatite coatings on AZ31 Mg alloy by micro-arc oxidation coupled with sol–gel treatment

“… 17 Therefore, researchers are making efforts to fabricate biological layers improve the corrosion resistance and the biocompatibility of the MAO coating. 18,19 Hydroxyapatite (HA) is the main inorganic component of the bone tissue and has similar chemical and biological characteristics to human bone tissue as well as its ability to directly bond to the surrounding tissues. 20 A number of techniques, such as electrophoretic deposition, 21 chemical deposition, 22 and hydrothermal treatment 23 have been developed to form an HA layer on the surface of the MAO coating.…”

Corrosion Properties of Calcium Stearate-Based Hydrophobic Coatings on Anodized Magnesium Alloy

“…Electrochemical corrosion behavior was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) tests in a standard three-electrode cell configuration. A saturated calomel electrode (SCE) was used as the reference electrode, a graphite electrode as the counter electrode, and the as-prepared specimen as the working electrode with an exposed surface area of 1 cm 2 . The open-circuit potential (OCP) was fixed to 30 min to stabilize the specimen prior to potentiodynamic polarization tests, and the scanning rate was set to 0.5 mV/s.…”

“…Recently, there has been much attention paid to magnesium alloys in the biomedical field due to their low density, high specific strength, good biocompatibility, and similar mechanical properties to natural bone [1][2][3]. Magnesium is an essential element in the human body, and magnesium alloys can induce the formation of new bone when they are used as bio-absorbable implants [4,5].…”

Improved corrosion protection of titanium implant material by crystallographic texturing of Sr doped calcium phosphate electrodeposits

“…Nanocrystalline calcium phosphate (CaP) coatings have great potential for dental and orthopedic applications as these coatings on medical material provide better biocompatibility and corrosion resistance [1][2][3][4][5]. However, the long term stability of these coatings in biological environment is still challenging matter of concern.…”