SURFACE COATING FOR DEGRADABLE MAGNESIUM AND MAGNESIUM ALLOYS AND METHOD FOR PREPARING THE SAME

Abstract

A surface coating for degradable magnesium and magnesium alloys, including: an inner layer and an outer layer. The inner layer is a magnesium phosphate conversion layer, and the outer layer is a hydroxyapatite layer. A method for fabricating the surface coating is also provided herein, which includes: soaking the magnesium or magnesium alloy in an acidic solution containing magnesium salt and phosphate under heating to form the magnesium phosphate conversion layer on a surface of the magnesium or magnesium alloy; and transferring the magnesium or magnesium alloy to an alkaline solution containing calcium salt and phosphate followed by soaking under heating to form a hydroxyapatite layer on a surface of the magnesium phosphate conversion layer.

Claims

1. A surface coating for degradable magnesium and magnesium alloy, comprising: an inner layer; and an outer layer; wherein the inner layer is a magnesium phosphate conversion layer, and the outer layer is a hydroxyapatite layer.

2. The surface coating of claim 1, wherein the magnesium phosphate conversion layer has a thickness of 50 nm-10 μm; and the hydroxyapatite layer has a thickness of 0.1 μm-500 μm.

3. The surface coating of claim 1, wherein a bonding strength between the surface coating and a magnesium substrate or a magnesium alloy substrate is equal to or larger than 50 MPa; and an atomic ratio of calcium to phosphorus in the hydroxyapatite layer is (1.5-1.67):1.

4. A method for preparing the surface coating of claim 1, comprising: (S1) soaking a magnesium or magnesium alloy substrate in an acidic solution containing a magnesium salt and a first phosphate under heating to form a magnesium phosphate conversion layer on a surface of the magnesium or magnesium alloy substrate; and (S2) transferring the magnesium or magnesium alloy substrate with the magnesium phosphate conversion layer to an alkaline solution containing a calcium salt and a second phosphate followed by soaking under heating to form a hydroxyapatite layer on a surface of the magnesium phosphate conversion layer.

5. The method of claim 4, wherein in step (S1), the magnesium salt is selected from the group consisting of magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium phosphate, magnesium perchlorate, magnesium acetate, magnesium hydroxide and a combination thereof; a concentration of the magnesium salt in the acidic solution is 0.001˜10 mol/L; the first phosphate is selected from the group consisting of sodium phosphate, potassium phosphate, magnesium phosphate, ammonium phosphate, calcium phosphate, and a combination thereof; and a concentration of the first phosphate in the acidic solution is 0.001˜10 mol/L.

6. The method of claim 5, wherein a molar ratio of magnesium ions to phosphate ions in the acidic solution in step (S1) is (0.2˜5):1.

7. The method of claim 4, wherein in step (S1), the acidic solution is adjusted to pH 2˜7 with nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid or a combination thereof; and the soaking is performed at 5˜99° C. for 5 min˜12 h.

8. The method of claim 4, wherein in step (S2), the second phosphate is selected from the group consisting of sodium phosphate, potassium phosphate, magnesium phosphate, ammonium phosphate, calcium phosphate, and a combination thereof; and a concentration of the second phosphate in the alkaline solution is 0.001˜10 mol/L; the calcium salt is selected from the group consisting of calcium phosphate, ethylenediaminetetraacetic acid calcium disodium salt (EDTA-Ca), calcium citrate, calcium acetate, calcium chloride, calcium nitrate, calcium maleate, calcium polyacrylate, calcium polymethacrylate and a combination thereof; a concentration of the calcium salt in the alkaline solution is 0.001˜10 mol/L; and a molar ratio of the second phosphate to the calcium salt is (0.2˜5):1.

9. The method of claim 4, wherein in step (S2), the alkaline solution is adjusted to pH 7˜13 with sodium hydroxide, potassium hydroxide, aqueous ammonia or a combination thereof; and the soaking is performed at 5˜99° C. for 5 min˜48 h.

10. The method of claim 4, wherein the magnesium alloy substrate is Mg—Zn alloy, Mg—Ca alloy, Mg—Li alloy, Mg—Mn alloy or Mg—Re alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a curve diagram showing weight loss of coated AZ31 magnesium alloys fabricated in Examples 1-2 and weight loss of an uncoated AZ31 magnesium alloy over time; and

[0031] FIG. 2 is a computerized tomography (CT) scanning image showing degradation of the uncoated Mg alloy screw and the Mg alloy screw coated with the coating fabricated in Example 1 after implantation.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] This application will be described in detail below with reference to the accompanying drawings and the embodiments. The following embodiments are merely illustrative, and are not intended to limit the disclosure. It should be noted that these embodiments and the features therein may be combined with each other in the case of no contradiction.

EXAMPLE 1

[0033] A coating, which was capable of controlling the degradation of magnesium alloys, was prepared on a surface of an AZ31 magnesium alloy bar through the following steps.

[0034] (1) The AZ31 magnesium alloy was processed into a sample with a size of 13×10 mm, which was sanded sequentially with 800#, 1200#, 2000# sandpapers, and subjected to ultrasonic cleaning in anhydrous acetone for 5 min to remove surface oil and blow drying.

[0035] (2) A solution containing magnesium nitrate (0.25 mol/L) and sodium dihydrogen phosphate (0.25 mol/L) was prepared, adjusted to pH 3.5 with dilute nitric acid, and heated to 75° C. in water bath.

[0036] (3) The AZ31 magnesium alloy sample obtained in step (1) was soaked into the solution prepared in step (2) for reaction for 60 min, rinsed with deionized water, and dried to obtain a magnesium phosphate conversion layer-coated AZ31 magnesium alloy sample.

[0037] (4) A solution containing calcium citrate (0.25 mol/L) and sodium dihydrogen phosphate (0.25 mol/L) was prepared and adjusted to pH to 9.5 with sodium hydroxide.

[0038] (5) The magnesium phosphate conversion layer-coated AZ31 magnesium alloy sample obtained in step (3) was soaked into the solution prepared in step (4) and heated to 95° C. in a water bath for reaction for 6 h. After the reaction, the sample was taken out, cooled, rinsed with deionized water and dried to obtain a sample with a uniform and complete surface coating.

[0039] (6) The bonding strength between the coating and the alloy substrate was measured to be 63 MPa by a universal mechanical testing machine.

EXAMPLE 2

[0040] A coating, which was capable of controlling the degradation of magnesium alloys, was prepared on a surface of an AZ31 magnesium alloy bar through the following steps.

[0041] (1) The AZ31 magnesium alloy was processed into a sample with a size of Φ3×10 mm, which was sanded sequentially with 800#, 1200#, 2000# sandpapers, and subjected to ultrasonic cleaning in anhydrous acetone for 5 min to remove surface oil and blow drying.

[0042] (2) A solution containing magnesium sulfate (0.5 mol/L) and potassium dihydrogen phosphate (0.5 mol/L) was prepared and adjusted to pH 2.5 with dilute sulfuric acid, and heated to 60° C. in water bath.

[0043] (3) The AZ31 magnesium alloy sample obtained in step (1) was soaked into the solution prepared in step (2) for reaction for 120 min, rinsed with deionized water, and dried to obtain a magnesium phosphate conversion layer-coated AZ31 magnesium alloy sample.

[0044] (4) A solution containing ethylenediaminetetraacetic acid calcium disodium salt (EDTA-Ca) (0.15 mol/L) and potassium dihydrogen phosphate (0.15 mol/L) was prepared and adjusted to pH to 9.0 with potassium hydroxide.

[0045] (5) The magnesium phosphate conversion layer-coated AZ31 magnesium alloy sample obtained in step (3) was soaked into the solution prepared in step (4) and heated to 80° C. in a water bath for reaction for 12 h. After the reaction, the sample was taken, cooled, and rinsed with deionized water and dried to obtain a AZ31 magnesium alloy sample with a surface evenly covered by a coating of white particles.

[0046] (6) The bonding strength between the coating and the substrate was measured to be 58 MPa by a universal mechanical testing machine.

EXAMPLE 3

[0047] A coating, which was capable of controlling the degradation of magnesium alloys, was prepared on a surface of a ZK60 magnesium alloy bar through the following steps.

[0048] (1) The ZK60 magnesium alloy was processed into a sample with a size of Φ3×10 mm, which was sanded sequentially with 800#, 1200#, 2000# sandpapers and subjected to ultrasonic cleaning in anhydrous acetone for 5 min to remove surface oil and blow drying.

[0049] (2) A solution containing magnesium dihydrogen phosphate (0.25 mol/L) was prepared, and adjusted to pH 3.0 with phosphoric acid, and heated to 70° C. in water bath.

[0050] (3) The ZK60 magnesium alloy sample obtained in step (1) was soaked into the solution prepared in step (2) for reaction for 45 min, rinsed with deionized water, and dried to obtain a magnesium phosphate conversion layer-coated ZK60 magnesium alloy sample.

[0051] (4) A solution containing calcium citrate (0.10 mol/L) and sodium dihydrogen phosphate (0.10 mol/L) was prepared and adjusted to pH to 9.0 with sodium hydroxide.

[0052] (5) The magnesium phosphate conversion layer-coated ZK60 magnesium alloy sample obtained in step (3) was soaked into the solution prepared in step (4) and heated to 80° C. in a water bath for reaction for 6 h. After the reaction, the sample was taken out, cooled, rinsed with deionized water and dried to obtain a ZK60 magnesium alloy sample with a uniform and complete surface coating.

[0053] (6) The bonding strength between the coating and the alloy substrate was measured to be 70 MPa by a universal mechanical testing machine.

EXAMPLE 4

[0054] A coating, which was capable of controlling the degradation of magnesium alloys, was prepared on a surface of an LZ91 magnesium alloy bar through the following steps.

[0055] (1) The LZ91 magnesium alloy was processed into a sample with a size of Φ3×10 mm, which was sanded sequentially with 800#, 1200#, 2000# sandpapers, and subjected to ultrasonic cleaning in anhydrous acetone for 5 min to remove surface oil and blow drying.

[0056] (2) A solution containing magnesium dihydrogen phosphate (0.35 mol/L) was prepared, adjusted to pH 3.0 with phosphoric acid, and heated to 75° C. in water bath.

[0057] (3) The LZ91 magnesium alloy sample obtained in step (1) was soaked into the solution prepared in step (2) for reaction for 60 min, rinsed with deionized water, and dried to obtain a magnesium phosphate conversion layer-coated LZ91 magnesium alloy.

[0058] (4) A solution containing ethylenediaminetetraacetic acid calcium disodium salt (EDTA-Ca) (0.15 mol/L) and sodium dihydrogen phosphate (0.15 mol/L) was prepared and adjusted to pH 7.5 with sodium hydroxide.

[0059] (5) The magnesium phosphate conversion layer-coated LZ91 magnesium alloy sample obtained in step (3) was soaked into the solution prepared in step (4) and heated to 80° C. in a water bath for reaction for 12 h. After the reaction, the sample was taken out, cooled, rinsed with deionized water and dried to obtain an LZ91 magnesium alloy sample with a uniform and complete surface coating.

[0060] (6) The bonding strength between the coating and the substrate was measured to be 73 MPa by a universal mechanical testing machine.

EXPERIMENTAL EXAMPLE 1

[0061] The samples prepared in the Examples 1 and 2 and uncoated AZ31 magnesium alloy sample were soaked into a solution containing 3% (w/w) sodium chloride at 37° C. to perform an accelerated degradation test. The uncoated AZ31 magnesium alloy sample was the same as the samples prepared in the Examples 1 and 2 in sizes. The solution was changed every 3-4 days, and all the samples were weighed every week. The surface corrosion and overall degradation of each sample were observed simultaneously to obtain a resulting weight loss curve shown in FIG. 1. As shown in FIG. 1, the weight of the uncoated magnesium alloy sample was greatly reduced by more than 50% after soaking for 30 days, while the weight of each of magnesium alloy samples prepared in Example 1 and 2 was only reduced by about 10% after soaking for 30 days, indicating that the coating greatly decelerated the degradation of the magnesium alloy.

EXPERIMENTAL EXAMPLE 2

[0062] The AZ31 magnesium alloy was processed into a bone screw shape. The bone nail made of coated AZ31 magnesium alloy was prepared according to the method in Example 1, and the bone nail made of uncoated AZ31 magnesium alloy was taken as a control example. The bone nail made of coated AZ31 magnesium alloy and the bone nail made of uncoated AZ31 magnesium alloy were respectively implanted into a tibial plateau of the left leg and a tibial plateau of a right leg s of a goat, and then scanned by computerized tomography (CT) scanning at 3, 6, 12, and 18 months to observe the degradation of magnesium alloy bone nails. As shown in FIG. 2, the bone nail made of uncoated magnesium alloy began to degrade and generate a large amount of gas after implantation, such that cavities were formed in the bone tissue (marked by white arrow in FIG. 2). 6 months after implantation, the bone nail made of uncoated magnesium alloy was basically degraded. 12 and 18 months after implantation, the bone nail made of uncoated magnesium alloy could not be seen. However, 12 months after the implantation, the bone nail made of coated magnesium alloy provided herein still could be clearly seen, and the thread structure of the bone nail almost remains unchanged. Referring to FIG. 2, 18 months after implantation, the bone nail made of coated magnesium alloy almost disappeared. Moreover, the bone nail made of coated magnesium alloy provided herein was rarely degraded within 12 months, and the degradation was completed within 12 to 18 months. It can be concluded that the surface coating for the magnesium alloy provided herein effectively controlled the degradation of magnesium alloy in vivo, and the degradation time is controlled within 12 to 18 months.

[0063] Described above are merely preferred embodiments of this application, which are not intended to limit this application. It should be understood that various modifications, replacements and changes made by hose skilled in the art without departing from the spirit of the application should still fall within the scope of the present application defined by the appended claims.