KR101786645B1

KR101786645B1 - A preparation method for a magnesium substrate with improved anti-corrosive property by dual coating with bioceramic and biodegradable polymer

Info

Publication number: KR101786645B1
Application number: KR1020150052048A
Authority: KR
Inventors: 김현이; 이성미; 정인권; 마틸드 디에즈
Original assignee: 서울대학교산학협력단; 주식회사 제노스
Priority date: 2015-04-13
Filing date: 2015-04-13
Publication date: 2017-10-19
Also published as: KR20160122347A

Abstract

The present invention relates to a magnesium-containing substrate; A crystalline bioceramics layer formed on the substrate by precipitation; And a biodegradable polymer layer coated on the bioceramics layer. The present invention also relates to a method of manufacturing the magnesium base, and a bone graft implant having the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesium substrate having improved corrosion resistance by bi-coating with a bioceramic ceramic and a biodegradable polymer,

BACKGROUND OF THE INVENTION [0002] Artificial organs or grafts have been used to replace and / or repair injured parts in the human body due to the recent development of medical technology, which are collectively referred to as implants. Implants can be used as fixation means for supporting or attaching tissue under treatment, such as molded parts that can be implanted in an organ / organ, such as membranes, fixed thin plates, other solid or spatial components, screws, pins, rivets, For separating the tissue from other neighboring tissues, and the like. The application range of the implant is gradually widening, and accordingly, a lot of research is being carried out for the development of the implant. Typical materials used for the purpose of medical treatment include metals, ceramics, and polymers. However, due to the nature of implantation in the body, the material of the implant must have biocompatibility, have blood compatibility when in contact with blood, and in contact with tissues or cells other than blood, tissue compatibility, the materials that can be used in implants are very limited.

In particular, metallic implants are excellent in mechanical properties and processability, but may cause stress shielding, image degradation, and implant migration. Ceramic implants are relatively biocompatible, There is a possibility of breakage due to impact and it is difficult to process, and the polymer implant has a disadvantage that it is relatively weak in strength.

For example, a bone plate for bone joining and a screw, which are a kind of implants, are used for the purpose of treating internal fractures. Since the apparatus for supporting and fixing the bone fragments requires high mechanical strength together with biocompatibility, And is made of a non-decomposable metal base material such as titanium or a stainless steel alloy is widely used.

Plates or screws of such non-degradable metal materials are permanently retained in the body after healing, so if the metal is corroded or exposed in the body, there is a risk of infection, the plate may be touched during the acceleration, or may protrude even when viewed by the naked eye, As the bone tissue grows, there is a risk that the inserted plate or screw will be embedded inside. In addition, since most of metal materials have elastic modulus higher than that of bone tissue, it may cause stress shielding and cause bone damage. It is preferable to remove the metal plate or screw after the bone tissue has been cured. However, And the economic and psychological burden that follows.

Therefore, the present plate of the biodegradable polymer material may be used instead of the main plate of these metallic materials. Polylactic acid, polyglycolic acid, and polylactic acid-glycolic acid copolymer thereof, which are mainly used, are disadvantageous in that these polymers have significantly lower strength than metals. Therefore, in order to be able to withstand the same load, plates and screws of a larger size are used, so that the procedure becomes difficult and the decomposition speed may become too long. In addition, biodegradable polymers are difficult to control the rate of absorption and have a short period of time until the loss of strength, but it takes a very long time to completely decompose and absorb the polymer.

In order to overcome such disadvantages, magnesium, which is a biodegradable metal material, can be used. The biodegradable magnesium has a remarkably high strength compared with the biodegradable polymer, and is light and excellent in workability, and has a remarkably low modulus of elasticity as compared with other medical metal materials, so that it is possible to prevent the stress shielding, which is a practical problem of the metal material. However, since the magnesium material exhibits a very rapid initial corrosion rate in a biological aqueous solution containing a large amount of chlorine ions, various methods for overcoming this have been developed. In order to control the rate of biodegradation of magnesium, various studies have been made to improve the corrosion resistance by coating the magnesium surface with biodegradable ceramics or polymers, or to improve the corrosion resistance by alloying with other metals .

By coating hydroxyapatite, a biocompatible ceramic used to control the rate of biodegradation of magnesium, the corrosion rate can be easily controlled, but the flexibility inherent in the metal is limited. In addition, when a polymer or ceramic is directly coated on a magnesium magnesium substrate, it can be easily peeled off due to lack of interfacial bonding force, so that it is difficult to sufficiently exhibit a desired effect.

The present inventors have made intensive researches to improve the corrosion resistance of a magnesium-containing substrate by introducing a biodegradable polymer or a ceramic coating layer but to overcome the weak flexibility of the ceramic coating layer and the poor interfacial bonding strength of the polymer coating layer. As a result, When the biodegradable polymer layer is introduced on the bioceramics layer in the same or larger thickness than the biodegradable polymer layer, the corrosion resistance of the magnesium-containing base material is improved by the coating of the biodegradable material, And the present invention has been completed.

According to a first aspect of the present invention, there is provided a magnesium-containing substrate, A crystalline bioceramics layer formed on the substrate by precipitation; And a biodegradable polymer layer coated on the bioceramics layer, wherein the biodegradable polymer layer has improved corrosion resistance.

A second aspect of the present invention is a method for manufacturing a magnesium-containing substrate, comprising: a first step of coating a bio-ceramic layer on a magnesium-containing substrate; And a second step of coating a biodegradable polymer layer on the bioceramics layer according to the first aspect of the present invention.

A third aspect of the present invention provides an implant for bone fixation comprising a magnesium base with improved corrosion resistance according to the first aspect of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention relates to a combination of a biocompatible ceramic and / or a polymer coating layer for delaying initial corrosion, which is a weak point of a magnesium-containing substrate, in order to overcome the weak flexibility of the ceramic coating layer and the weak interface- And a method for producing the same. Specifically, first, a bioceramics layer was coated on a magnesium-containing substrate through a precipitation process, and a biodegradable polymer layer was further coated thereon. Unlike a metal or a polymer layer that provides a smooth surface, the bio-ceramic layer formed by precipitation has a needle-like crystal form. Therefore, in order to uniformly apply the polymer to the uneven surface and coat the bio- The process of coating the biodegradable polymer layer can be carried out by pressure dip coating.

The magnesium-containing substrate may be an alloy substrate containing at least 90% of magnesium.

The bio-ceramic layer may be coated to a thickness of 1 to 5 탆. When the thickness of the bioceramics layer is less than 1 占 퐉, it may be difficult to achieve a desired effect of improving the corrosion resistance and / or increasing the interfacial adhesion force with the polymer layer to be introduced later. If the thickness is more than 5 占 퐉, It may take longer than necessary to be thickened and completely decomposed and absorbed.

The biodegradable polymer layer may be coated to a thickness of 1 to 500 μm. Considering the introduction of a more flexible polymer layer in order to compensate for the fact that the bioceramic is cracked when the stimulus is applied from the outside to the base material such as the deformation force and the corrosion of the magnesium is not further prevented, It may be preferable to form the bioceramic layer to be thicker so as to completely cover the crystal-type bio-ceramic layer coated therein. For example, when the biodegradable polymer layer is formed to a thickness of less than 1 μm, the exposed portion of the biocompatible ceramic layer may not completely cover the surface of the biocompatible ceramic layer formed by the irregularly shaped needle crystals. The magnesium-containing base material is cracked and exposed through the crack to cause secondary corrosion, and when it is formed to have a thickness exceeding 500 탆, it is excessively thick than necessary and it may take a considerable time to be completely decomposed and absorbed have.

The magnesium-containing substrate in which the bioceramics and biodegradable polymer coating layers of the present invention are formed may have improved biocompatibility as compared with the magnesium-containing substrate not containing these coating layers. Bioceramic and biodegradable polymers are all biocompatible and can promote the engraftment and / or proliferation of tissue cells by introducing these coating layers.

A magnesium-containing substrate having improved corrosion resistance according to the present invention can be produced by coating a bioceramics layer on a magnesium-containing substrate and coating the biodegradable polymer layer on the bioceramics layer.

For example, in the case of using an alloy mainly containing magnesium as a magnesium-containing base material and containing another metal, these other metals are mainly distributed at grain boundaries, and therefore, in order to deposit them into the inside of particles to form a uniform surface, The method may further include a step of heat-treating the substrate containing magnesium at 370 ° C to 550 ° C for 1 to 8 hours prior to the coating, but the present invention is not limited thereto, and if the magnesium-containing substrate has an already uniform surface This step can be omitted.

The second step may be performed by a pressure dip coating method. As described above, since the bioceramics layer formed by precipitation is formed in a crystalline form, for example, a needle shape, it is close to a form in which the thin and pointed pillars having different elevations are densely gathered rather than a uniform surface. Therefore, it is preferable to perform the pressure dip coating method rather than the general dip coating method to introduce the biodegradable polymer layer so as to completely cover the gap between the pillars of the bioceramics layer. However, the present invention is not limited thereto.

The second step may include a second step of preparing a biodegradable polymer solution at a concentration of 1 to 30% by weight; A second step of immersing the magnesium base material coated with the bioceramics layer in the prepared polymer solution and maintaining a vacuum degree of 0.1 to 1 MPa; And a step 2-3 in which the sample is dried at a temperature of from 10 캜 to 35 캜 at a rate of 300 to 1000 탆 / sec. However, the present invention is not limited thereto.

Step 2-2 may be carried out while maintaining a vacuum of 0.3 to 1.7 MPa. More preferably 0.5 MPa. However, the present invention is not limited thereto and may be appropriately selected depending on the type of the polymer and the solvent. However, if the degree of vacuum is too low, the polymer solution may not penetrate completely between the crystalline hydroxyapatite layers. If the degree of vacuum is too high, the polymer solution may be boiled and coating may not be possible.

As described above, the bioceramics layer may be coated to a thickness of 1 to 5 탆, and the biodegradable polymer layer may be formed to have a thickness of 1 to 500 탆 so as to cover the bioceramics layer completely.

The magnesium substrate improved in corrosion resistance according to the present invention can be used in bone graft implants. Since it has an appropriate strength based on a magnesium-containing base material, which is metal, it is advantageous for enduring the load, and the corrosion and corrosion resistance is improved through the bio-ceramic and the biodegradable polymer coating so that strength and shape can be maintained for a predetermined time, And thus may be suitable for use as an implant for use to fix damaged bone.

According to the present invention, a magnesium-containing base material having improved corrosion resistance is coated with a combination of a bioceramics layer and a biodegradable polymer layer, thereby remarkably lowering strength due to abrupt initial erosion, which is a disadvantage of a magnesium- It can be used effectively as a graft for bone fixation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view illustrating a process for producing a bi-layer ceramic coating layer of bioceramics HA and biodegradable polymer PLLA according to the present invention.
FIG. 2 is a diagram showing the surface microstructure of the magnesium alloy before (left) and after (right) heat treatment. FIG.
3 is a diagram showing the surface microstructure of a magnesium alloy surface on which a coating layer is formed. The left side shows the microstructure of the surface after bioceramic HA coating, and the right side shows the surface microstructure after further coating biodegradable polymer PLLA on the HA coating layer.
4 is a diagram showing SEM and focused ion beam (FIB) images of a cross section of a dual coating layer according to the present invention.
5 is a diagram showing an X-ray diffraction pattern of a WE43 alloy (lower end) and a bioceramics HA (upper end) coated on the alloy.
FIG. 6 is a graph showing the measurement results of the interfacial bonding force of the double coating layer according to the present invention.
FIG. 7 is a graph showing a result of polarization voltage measurement for confirming the corrosion resistance of an implant to which the dual coating layer according to the present invention is applied.
FIG. 8 is a graph showing changes in pH with time of immersion for confirming corrosion resistance of an implant to which a dual coating layer according to the present invention is applied.
Figure 9 is a SEM and FIB image showing the microstructure after 6% stretching to confirm the flexibility of the dual coating layer according to the present invention. (a) shows the results for HA single coating layer, which is a bioceramic ceramic, and (b) shows the results for a dual coating layer of bioceramics HA and polymer PLLA.
10 is a graph showing a graph of Mg ion concentration for confirming corrosion resistance after tensile of an implant to which a dual coating layer according to the present invention is applied.
11 is a graph showing the result of evaluation of mechanical strength deterioration due to post-tensile corrosion of an implant to which a dual coating layer according to the present invention is applied.
12 is a view showing an image of cell attachment on the surface of an implant to which a dual coating layer according to the present invention is applied.
13 is a diagram showing cell proliferation on the surface of an implant to which a dual coating layer according to the present invention is applied.
14 is a view showing a bone plate for bone fixation, which is an example of an implant manufactured by applying the double coating layer of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are for further illustrating the present invention, and the scope of the present invention is not limited by these examples.

Example 1: Preheating of magnesium alloy

WE43, a magnesium alloy, was used as a biodegradable implant according to the present invention. The WE43 is an alloy containing about 4% of yttrium, neodymium and about 3% of rare-earth metal elements in addition to magnesium as a main component. As shown in the microstructure, the alloy element has a grain boundary (Fig. 2 (a)). In order to ensure the uniformity of the surface prior to coating, it was precipitated into the particles through heat treatment (Fig. 2 (b)).

Specifically, the temperature condition was set in a box furnace in the range of 370 ° C to 550 ° C and performed for 1 to 8 hours. As a result of conducting a series of experiments by controlling the temperature and time in the above range, the most uniform microstructure was obtained when the treatment was carried out at 525 ° C for 5 hours.

Example 2: Bioceramic coating

Hydroxyapatite (HA) was coated on the WE43 magnesium alloy prepared by the heat treatment in the method of Example 1 above. Specific experimental methods are described in J. Biomed . Mater . Res . Part A , 2014, 102 (2): 429-441.

At this time, the coating solution was prepared by mixing a calcium-based compound and a phosphoric acid-based compound, maintaining the temperature of the mixed solution at 90 ° C, and then precipitating magnesium to form a coating layer. Ethylenediaminetetraacetic acid calcium disodium salt hydrate was used as the phosphate compound, and the pH of the mixed solution was adjusted to 9.3 by using an aqueous solution of sodium hydroxide. After the HA coating layer was introduced through the above process, the surface microstructure was confirmed by an electron microscope and the results are shown in FIG. 3 (left side in FIG. 3). As shown in the photograph on the left side of FIG. 3, it was confirmed that the HA crystal phase was uniformly formed in a needle-shaped manner on the surface of the magnesium alloy.

Example 3: biodegradable polymer coating

In Example 2, a bioabsorbable polymer, poly-L-lactic acid (PLLA), was further coated on a magnesium alloy substrate having a surface coated with a bioceramic material having excellent interfacial adhesion. As a process for coating the biodegradable polymer, a general dip coating process can be used. However, in order to form a biodegradable polymer coating layer more densely on a nail-shaped HA coating layer, a pressure-dip coating process Respectively. Specifically, the PLLA was dissolved in dichloromethane (DCM) at a concentration of 10%, the magnesium alloy was immersed, and a vacuum degree of about 0.5 MPa was maintained using a vacuum pump. The specimens were then taken out at a speed of 500 μm / sec and dried at room temperature.

The biodegradable polymer coating layer formed through the above method penetrated into the previously formed needle-shaped HA crystal phases and was continuously formed, and a smooth surface image was shown as shown on the right side of FIG. For more detailed microstructural analysis, a cross-sectional scanning microscope and a focused ion beam (FIB) for finer observation were observed, and the results are shown in FIG. As shown in the left side of FIG. 4, a biodegradable polymer component permeated through the needle-like HA crystal phase to form a continuous coating layer without gaps. As shown in the right side of FIG. 4, the FIB measurement showed that the needle- It was confirmed that a homogeneous double layer was formed by introducing biodegradable polymer PLLA layer uniformly at a thickness of about 3 μm on the bioceramic coating layer.

Experimental Example 1: X-ray diffraction Pattern measurement

The X-ray diffraction pattern was measured to confirm the HA crystallinity of the sample prepared in Example 2, and the results are shown in FIG. As a control group, a magnesium alloy base material not coated with HA was used (FIG. 5, bottom; WE43). As shown in Fig. 5, additional HA diffraction patterns appeared well on the diffraction pattern of the magnesium alloy, indicating that the HA layer was successfully coated and image-formed on the magnesium substrate.

Experimental Example 2: Interfacial adhesion strength measurement

The interfacial adhesion of the magnesium alloy substrate having the coating layer introduced by the method of Example 2 was confirmed, and the results are shown in Fig. Specifically, a small metal rod with adhesive polymer is fixed on a coated substrate to be tested, and the metal rod is attached to the coating layer by holding at 150 ° C. for 1 hour. Then, the metal rod is pulled with a tension device to measure the strength Respectively. As a result, it showed an interfacial bonding force of 16 MPa or more, which is similar to the interfacial bonding force of 20 MPa, which is measured when a conventional pure magnesium substrate is coated with a bioceramics, indicating that a stable ceramic coating layer is formed on the WE43 substrate .

Experimental Example 3: Evaluation of corrosion resistance

3.1. Polarization curve Measure

In order to comparatively evaluate the corrosion resistance, four types of specimens were prepared, and the polarization curves thereof were measured. The results are shown in FIG. 7: WE43, bioceramic HA coated WE43, biodegradable polymer PLLA coated WE43 , And bioceramic HA and biodegradable polymer PLLA. Specifically, the voltage was plotted against the logarithm of current for each specimen measured by an electrochemical measurement method. At this time, the higher the voltage and the lower the current density, the higher the corrosion resistance of the specimen. As shown in FIG. 7, in the case of the specimen coated with the biodegradable polymer PLLA alone, the graph was shifted in the direction of decreasing the corrosion current density compared with the corrosion resistance of the magnesium alloy itself, so that the PLLA coating layer also provided some corrosion resistance Respectively. In the case of specimens coated with HA, which is a bioceramic material, the measured current density was decreased and the measured corrosion voltage was increased. This indicates that HA coating alone can improve the corrosion resistance. On the other hand, in the specimens coated with HA and PLLA, additional current density and corrosion voltage were observed. In other words, it was confirmed that corrosion resistance was remarkably improved by synergistic corrosion resistance in specimens coated with bioceramics and biodegradable polymers through polarization curves.

3.2. pH Change measurement

Further, as another method for confirming the corrosion resistance, each of the specimens was immersed in a simulated body fluid (SBF) at 37 ° C for a predetermined time, and the pH change of the solution was measured. Specifically, the pH increase due to the generation of hydroxide ions and hydrogen gas produced by the corrosion of magnesium was measured. The pH change was measured according to immersion time, and the results are shown in FIG. As shown in FIG. 8, after 7 days after immersion in SBF, the pH of WE43 increased to 9.5 or more, while the amount of base coated with bioceramics HA decreased to 8.0 and the amount of base coated with biodegradable polymer PLLA decreased to 8.5 . On the other hand, HA and PLLA were introduced in succession, and in the case of the double layer coated magnesium specimen, the pH change remained almost unchanged at 7.5, indicating excellent corrosion resistance.

Experimental Example 4: Flexibility evaluation

4.1. transform( strain ) Microstructure confirmation after

In order to confirm the flexibility of the magnesium specimen in which the bioceramic and / or biodegradable polymer coating layer was introduced through Examples 1 to 3, a 6% strain was applied to the uncoated or coated magnesium specimen and the surface microstructure was confirmed And the results are shown in Fig. As shown in Fig. 9 (a), when the bio-ceramic HA alone was coated, the surface was cracked due to the applied deformation. Indicating that sufficient flexibility was not ensured by the coating layer formed. On the other hand, as shown in FIG. 9 (b), it was confirmed that the HA / PLLA double layer coated specimen did not crack at all due to the flexibility added by the biodegradable polymer even after 6% strain was applied.

4.2. Evaluation of Corrosion Resistance after Deformation

Further, in order to confirm the corrosion characteristics of the specimens after the deformation was applied, the magnesium ion concentration was confirmed immediately after immersing each of the specimens subjected to the 6% strain in SBF and after 1 day, 4 days and 7 days, Respectively. As shown in FIG. 10, in the case of a specimen containing only a magnesium alloy specimen, a bioceramics HA, or a biodegradable polymer PLLA monolayer not containing a coating layer, the concentration of magnesium ions in the solution was remarkably increased with an immersion time in the solution . On the other hand, the increase rate of magnesium ion concentration in HA / PLLA bilayer coated specimens was significantly decreased. In connection with the results of Experimental Example 4.1, it can be deduced that the corrosion rate was increased by the cracks formed on the surface due to the stress applied to the specimen.

4.3. Analysis of mechanical strength degradation after deformation

In addition, to evaluate the stability of the magnesium material for insertion into the medical device, the mechanical strength of the test piece was confirmed after immersing in SBF for 7 days. The maximum tensile strength of WE43 itself was about 200 MPa, but after 7 days immersed in SBF, the strength of WE43 decreased to 120 MPa. In the case of specimens coated with HA alone, the measured strength was the weakest at 40 MPa . This is because the bioceramic coating layer primarily acts to prevent corrosion as a whole, but when the cracks are generated due to the application of the deformation force, the local corrosion of the area is seriously eroded and the strength is rapidly reduced. On the other hand, PLLA coated specimens with flexible biodegradable polymer showed relatively high strength, and HA / PLLA double coated specimens showed little decrease in strength. From this, it was confirmed that the introduction of a double coating layer, in which bioceramics and a biodegradable polymer were sequentially coated in order to secure the flexibility of the magnesium alloy material and to provide corrosion resistance, was confirmed.

Experimental Example 5: Biocompatibility assessment

5.1. cell Attachment

MC3T3 cell line, pre-osteoblast, was placed on the surface of the specimen at a density of 1.5 × 10 ⁴ cells / ml and cultured for 3 days. The cells were observed by SEM to see if they were attached to the surface of the specimen. Respectively. As shown in FIG. 12, it was observed that the cells were not attached properly on the magnesium alloy specimen that does not include the coating layer, and some cells were rounded. However, in the HA coated PLLA, PLLA coated specimen and HA / PLLA coated specimen, Were uniformly adhered to each other. This indicates that the biocompatibility lacking in the magnesium alloy itself can be provided by introducing HA and / or PLLA coatings.

5.2. Cell proliferation

In addition, the proliferation rate of osteoclasts on the above specimens was confirmed. MC3T3 cells were plated on the surface of each specimen at a density of 0.25 × 10 ⁴ cells / ml, cultured for 1 day and 4 days, and then the cells were collected and the amount of DNA was measured. In the case of the WE43 specimen, the DNA content was measured at about the same level as in the case of culturing for 4 days. In other words, the number of cells did not increase almost even on day 4 compared to day 1, but rather decreased slightly. On the other hand, when HA and / or PLLA were coated, a remarkable increase in DNA amount was observed after 4 days incubation compared with 1 day. This indicates that the HA and PLLA coating layers provide an environment suitable for cell culture and propagation. When HA or PLLA monolayer was coated, cell proliferation was also observed when PLLA was coated. Especially, cell proliferation was observed in HA coated specimen. Furthermore, the specimens containing HA and PLLA coated with double coating layer exhibited higher growth rate than the HA monolayer coated specimen due to the synergistic effect.

A bone plate for bone fixation was prepared as an example of an implant to which the HA / PLLA double coating layer was applied, and an image thereof is shown in FIG.

Claims

A magnesium-containing substrate; A crystalline bioceramics layer formed on the substrate by precipitation; And a biodegradable polymer layer coated on the bioceramics layer, the magnesium base having improved corrosion resistance,
Wherein the crystalline bioceramics layer has a needle-like crystalline form, and the biodegradable polymer layer is uniformly injected onto a non-uniform surface of a needle-shaped crystalline bioceramics layer by pressure dip coating,
Wherein the bio-ceramic is hydroxyapatite, and the polymer is poly-L-lactic acid.

The method according to claim 1,
Wherein the magnesium-containing base material contains magnesium in an amount of 90% or more.

The method according to claim 1,
Wherein the bioceramics layer is coated to a thickness of 1 to 5 占 퐉.

The method according to claim 1,
Wherein the biodegradable polymer layer is coated to a thickness of 1 to 500 占 퐉.

The method according to claim 1,
Wherein the biocompatibility is improved as compared with a magnesium-containing substrate containing no crystalline bioceramics layer, biodegradable polymer layer or both.

A first step of coating a crystalline bioceramics layer on the magnesium-containing substrate by precipitation; And
And a second step of coating a biodegradable polymer layer on the bioceramics layer by pressurized dip coating. The method of any one of claims 1 to 5, wherein the biodegradable polymer layer is coated on the bioceramics layer by pressure dip coating.

The method according to claim 6,
Further comprising the step of heat treating the substrate containing magnesium prior to the bioceramic coating at 370 ° C to 550 ° C for 1 to 8 hours.

delete

The method according to claim 6,
The second step
2-1) preparing a biodegradable polymer solution at a concentration of 1 to 30% by weight;
A second step of immersing the magnesium base material coated with the bioceramics layer in the prepared polymer solution and maintaining a vacuum degree of 0.1 to 1 MPa; And
And (2-3) drying the specimen at a temperature of 10 to 35 占 폚 at a rate of 300 to 1000 占 퐉 / sec.

The method according to claim 6,
Wherein the bioceramics layer is coated to a thickness of 1 to 5 μm and the biodegradable polymer layer is formed to a thickness of 1 to 500 μm thicker than the bioceramics layer.

A graft implant for bone grafting comprising a magnesium substrate having improved corrosion resistance according to any one of claims 1 to 5.