# Bio-Corrosion Behavior of Ceramic Coatings Containing Hydroxyapatite on Mg-Zn-Ca Magnesium Alloy
## 2 Experimental
### Characterization of the Coatings  
The morphologies of the coatings were characterized by scanning electron microscopy (SEM, Hitachi S-3000N) coupled with an energy dispersion spectroscopy (EDS). The phase composition was characterized by X-ray diffraction (XRD, D8 Advance) with Cu \(K\alpha\) in scanning angles of 20\({}^{\circ}\)-70\({}^{\circ}\).  
The thickness and microhardness of the coatings were examined using an eddy-current coating thickness gauge (Minitest 600B) and micro Vickers equipment (HXD-1000 TMC), respectively. Measurements were carried out for 10 times, and the average values were determined.  
Electrochemical measurements were performed in [PERSON]'s solution at 37 \({}^{\circ}\)C by using an electrochemical workstation (CHI 660D). [PERSON]'s solution was synthesized in the laboratory and composed of 8 g/L NaCl, 0.40 g/L KCl, 0.10 g/L MgCl\({}_{2}\)-6H\({}_{2}\)O, 0.10 g/L MgSO\({}_{4}\)-7H\({}_{2}\)O, 0.14 g/L CaCl\({}_{2}\), 0.06 g/L Na\({}_{2}\)HPO\({}_{4}\) 2H\({}_{2}\)O, 0.06 g/L KH\({}_{2}\)PO\({}_{4}\) and 1 g/L glucose. The experimental set-up comprised a conventional three-electrode cell containing a working electrode, a platinum sheet as the counter electrode, and an Ag-AgCl electrode as reference. The area of the working electrode that was exposed in the solution was 1.54 cm\({}^{2}\). The potentiodynamic polarization curves of the samples were measured at a scan rate of 1 mV/s. Prior to each test, the specimen was immersed in the solution for 10 min to stabilize the open circuit potential (OCP).  
The immersion corrosion tests were performed in Hank's solution for 20 d at a constant temperature of 37 \({}^{\circ}\)C. Every day, the samples were removed from the solution, rinsed ultrasonically with deionized water, and then dried. An electronic balance (FA 1004) was used to weigh the mass before and after the immersion, and mass loss curves were obtained by calculating the relative mass loss rate.  
The static water contact angles of the coatings were measured by a video optical contact angle measuring instrument (DSA 25) to study the wetting properties.  
In vitro blood platelet adhesion test was investigated to identify the blood compatibility of the coatings. Platelet-rich plasma (PRP) was prepared by centrifuging the whole blood for 15 min at a rate of 1000 rpm. The samples with and without HA coatings were ultrasonically rinsed with ethanol and deionized water for 10 min, respectively. The samples were then dried and placed into culture plates. The PRP was dropped on the surface of the samples and incubated in an electro-heating standing-temperature cultivator (Thermo 3110) at 37 \({}^{\circ}\)C for 2 h. After incubation, the samples were rinsed thrice with normal saline to remove non-adherent platelets. The platelets that adhered on the samples were fixed in 2.5% glutaraldehyde solutions for 1.5 h at room temperature, and the samples were dehydrated in a gradient ethanol/distilled water mixture (50%, 60%, 70%, 80%, 90%, and 100%) for 10 min each and then dried in air for more than 48 h. The morphology and distribution of the platelets were observed by SEM. The platelet shape change was evaluated from high-magnification micrographs. At least 50 platelets were analyzed for each sample.