In-situ magnesium hydroxide nanosheet layer modified magnesium alloy and preparation and application thereof

Abstract

The present invention relates to a magnesium alloy material, which is an in situ magnesium hydroxide nanosheet layer modified magnesium alloy. The material is prepared from a magnesium alloy through a hydrothermal reaction under alkaline condition. The protective effect of the in situ formed magnesium hydroxide nanosheet layer structure results in remarkably enhanced corrosion resistance of the magnesium alloy, meanwhile the biocompatibility can also be significantly improved since the release rate of magnesium ion can be significantly reduced. In addition, the two-dimensional nanolayer structure has a non-releasing physical antibacterial property depending on contact. Therefore, the magnesium alloy material according to the present invention has an extremely great application prospect in the field of medical implant.

Claims

1. A preparation method of a magnesium alloy material, wherein the preparation method comprises the step of conducting a hydrothermal reaction of a magnesium alloy under an alkaline condition to form a magnesium hydroxide nanosheet layer in situ; wherein a temperature of the hydrothermal reaction is from 60 to 200 C.; a reaction time of the hydrothermal reaction is more than 30 minutes; and a heating rate of the hydrothermal reaction is 1-30 C..Math.min.sup.1; wherein the magnesium alloy material comprises a magnesium alloy body and a magnesium hydroxide nanosheet layer on the surface; the magnesium hydroxide nanosheet in the magnesium hydroxide nanosheet layer has an area between 1 nm.sup.2 and 10 m.sup.2 and a thickness between 1 nm and 1 m; wherein the magnesium alloy body is a magnesium alloy having a magnesium content greater than 85 wt %.

2. The preparation method according to claim 1, wherein the temperature of the hydrothermal reaction is from 80 to 180 C.; the reaction time is more than 2 hours.

3. The preparation method according to claim 1, wherein the alkaline condition refers to a pH value between 8 and 14.

4. The preparation method according to claim 3, wherein the pH value of the hydrothermal reaction is controlled using an aqueous solution of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide or aqueous ammonia.

5. The preparation method according to claim 1, wherein the magnesium hydroxide nanosheet has the area between 50 nm.sup.2 and 5 m.sup.2 and the thickness between 5 nm and 1 m.

6. The preparation method according to claim 1, wherein the magnesium alloy body is a magnesium alloy having a magnesium content greater than 90 wt %.

7. The preparation method according to claim 1, wherein the magnesium alloy body is a magnesium alloy having a magnesium content greater than 92 wt %.

8. The preparation method according to claim 1, wherein the temperature of the hydrothermal reaction is from 90 to 160 C.; the reaction time is between 4 and 72 hours.

9. The preparation method according to claim 1, wherein the heating rate of the hydrothermal reaction is 2-20 C..Math.min.sup.1.

10. The preparation method according to claim 1, wherein the alkaline condition refers to a pH value between 8 and 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the micromorphologies of the surface and cross-section after 12 hours of hydrothermal treatment under a scanning electron microscope (scale=1 m); wherein, a represents the untreated magnesium alloy (Mg); b represents the magnesium alloy after 4 hours of hydrothermal treatment (HT4); c represents the magnesium alloy after 8 hours of hydrothermal treatment (HT8); and d represents the magnesium alloy after 12 hours of hydrothermal treatment (HT12).

(2) FIG. 2 shows the morphology and crystal form of HT12 by a high-resolution transmission scanning electron microscopy analysis (scale=100 nm; scale of the partial enlarged view=2 nm).

(3) FIG. 3 shows the comparison of XRD patterns of various samples.

(4) FIG. 4 shows the Mg 1 s spectrum in high resolution XPS.

(5) FIG. 5 shows the micromorphology of the sample surface after 3 hours of immersion (scale=1 m); wherein a represents the untreated magnesium alloy; and b represents HT12.

(6) FIG. 6 shows the polarization curves for various samples.

(7) FIG. 7 shows the impedance spectroscopies of various samples.

(8) FIG. 8 shows the analysis of biocompatibility.

(9) FIG. 9 shows the antibacterial rates against Escherichia coli in a 100 L system.

(10) FIG. 10 shows the antibacterial rates against Staphylococcus aureus in a 100 L system.

(11) FIG. 11 shows the detection of anti-biofilms.

(12) FIG. 12 shows the test of antibacterial effect in a 1 mL system.

(13) FIG. 13 shows the treated Escherichia coli under a scanning electron microscope (scale=1 m).

(14) FIG. 14 shows the computer-simulated interaction between bacteria and the materials.

(15) FIGS. 15a-e show the results wherein FIG. 15a represents the antibacterial results 3 days after the implantation (wherein implant indicates the results at the implant; tissue indicates the results at the surrounding tissues); FIG. 15b represents the antibacterial results 7 days after the implantation; FIG. 15c represents the antibacterial results 10 days after the implantation; FIG. 15d represents the antibacterial results 14 days after the implantation; and FIG. 15e represents the anti-inflammatory results 3-14 days after the implantation (scale=200 m).

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example 1

(16) Magnesium sheets with a lengthwidthheight of 10 mm10 mm5 mm were polished and grinded, and washed well with alcohol. The samples were placed into a reaction kettle with a volume of 25 mL, and 10 mL of aqueous sodium hydroxide solution of pH=12 was added. The reaction kettle was screwed and placed in a muffle furnace, wherein the heating rate was 10 C. min.sup.1, the reaction temperature was 120 C., and the reaction time was 4 h, 8 h and 12 h. After the reaction was completed, the micromorphologies of various samples were observed by scanning electron microscope respectively. As can be seen in FIG. 1, a magnesium hydroxide micro-nanosheet layer with a surface area of 1 m.sup.2 and a thickness of 5 nm was formed on the surface of the magnesium alloy after 12 h of hydrothermal reaction.

Example 2

(17) The surfaces of the samples obtained by the treatment of Example 1 were subjected to crystallography and chemical element analysis. The results from high resolution TEM (FIG. 2) showed that HT12 had a magnesium hydroxide crystal form with (101) crystal plane. The main peak of magnesium hydroxide can be seen from the XRD results (FIG. 3). The XPS results showed that a conversion of the MgMg bond to the MgOH bond occurred as the treatment time increased (FIG. 4). The above results indicate that a dense magnesium hydroxide nanosheet layer can be obtained through in situ growth by 12 hours of hydrothermal reaction.

Example 3

(18) The corrosion resistance property of the samples was analyzed by an immersion method and an electrochemical analysis method. After immersion of the untreated magnesium block, there were many cracks on the surface, but the surface of the magnesium alloy modified by the magnesium hydroxide sheet layer had no change in structure (FIG. 5). The weight loss analysis showed that the weight loss of the magnesium alloy modified by the nanosheet was significantly reduced compared with that of the magnesium block. The polarization curves showed that as the hydrothermal reaction time increased, the corrosion current gradually decreased (FIG. 6). The impedance spectroscopy showed that the longer the hydrothermal reaction time, the greater the impedance (FIG. 7).

Example 4

(19) The samples obtained in Example 1 were sterilized and osteoblasts were cultured on the surface. The proliferation of the cells was examined by MTT. The results showed that the cell proliferation with HT12 was more evident (FIG. 8). It showed that the biocompatibility of the magnesium alloy after 12 hours of hydrothermal treatment was significantly improved compared with that of the untreated magnesium block.

Example 5

(20) The samples obtained in Example 1 were used in the antibacterial (Staphylococcus aureus and Escherichia coli) test. The antibacterial effect was evaluated by the spread plate and count method, and the results were shown in FIG. 9 and FIG. 10. A bactericidal rate of 90% could be achieved for both bacteria by treating for 1 h in a 100 L system (bacterial concentration being 10.sup.5 mL.sup.1), and 100% antibacterial rate could be achieved as the treatment time was prolonged to 6 hours (FIG. 9). By increasing the initial colony concentration to be 10 times larger and culturing for 24 hours, the dead bacteria were evidently detected and no continuous biofilm was formed, indicating that HT12 can still effectively inhibit the formation of biofilm (FIG. 11).

Example 6

(21) By increasing the volume of the antibacterial system to 1 mL, it was found that the antibacterial effect of HT12 decreased significantly and the group of magnesium block did not change significantly (FIG. 12), indicating that the antibacterial effect of the samples after hydrothermal treatment depends on the surface contact, suggesting that this may be a non-release type antibacterial process. Morphological observation of the treated bacteria by scanning electron microscopy showed that the cell membrane of Escherichia coli after HT12 treatment was significantly stretched (FIG. 13). A molecular dynamics model was established to simulate the physical interaction between the bacteria and the interface. It showed that the shear force applied to the bacterial surface could cause the bacterial membrane to be stretched and the membrane area to be increased. When the shear force was 40.5 dyn cm.sup.1, the collapse of bacterial membrane appeared, suggesting that the bacterial cell membrane was torn (FIG. 14).

Example 7

(22) The samples of Example 1 were implanted into the subcutaneous tissues of mice as implants, and the untreated magnesium blocks and titanium blocks were used as the control groups. The wounds were carefully sutured after implantation. The implants were taken out on the 3rd, 7th, 10th, and 14th days to detect the bacterial contents at the implant and at surrounding tissues by the spread plate and count method. At the same time, the tissues surrounding the implants were fixed and sliced for H&E staining to verify the effect. The results showed that HT12 can effectively kill the bacteria at the implants and at their surrounding environment. In addition, the inflammatory response of the tissue in the HT12 group was weaker compared with the two control groups (FIGS. 15a-e). These preliminarily demonstrated the feasibility of HT12 as an implant.