KR20110088903A - Porous hydroxyapatite scaffolds with controlled designer pore structure for bone tissue engineering applications and their processing route - Google Patents

Abstract

PURPOSE: A porous hydroxyapatite supporter for bone tissue engineering and a manufacturing method thereof are provided to improve mechanical strength by a gel progress. CONSTITUTION: A manufacturing method of a porous hydroxyapatite supporter for bone tissue engineering comprises: a step of forming slurry for freeze casting by adding monomer, dispersing agent, and surfactant to alcohol solution; a step of adding an initiator to the slurry and injecting the slurry into the polymer sponge before gelation occurs; a step of putting the polymer sponge into a mold and forming a freeze specimen by maintaining temperature less than 0 deg.C for 20-40 minutes; a step of drying the frozen specimen at 65-90 deg.C for 20-40 minutes in order to evaporate alcohol solution; a step of raising the temperature of the specimen in an electric furnace in the rate of 1-3 deg.C per a minute and sintering the specimen by heating the specimen at 1200-1500 deg.C for 1-3 hours.

Description

Porous hydroxyapatite scaffolds with controlled designer pore structure for bone tissue engineering applications and their processing route

The present invention relates to a porous hydroxyapatite (HAP) support, a method for preparing the same, and a porous apatite support prepared by the method, and more particularly, to freeze-gel casting / polymer sponge complexation using an alcohol as a solvent. Porous apatite support for bone tissue engineering containing coarse pores and fine pores together with high porosity and excellent mechanical strength, a method for preparing the same, and a porous apatite support prepared by the method It is about.

The support for bone tissue engineering plays an important role in inducing regeneration of damaged osteocytes inserted in vivo. The material used as this support should have good chemical and biological affinity with bone tissue and exhibit bone conductivity.

Bioactive ceramics such as apatite hydroxide (HAP) and β-TCP are widely used as bioactive ceramic materials satisfying these conditions. In addition, the bone tissue support must be porous with sufficient strength and macroporous bi-sized structures that are structurally three-dimensionally interconnected. Process technologies such as replica, sacrificial template, and direct foam have been reported for the manufacture of porous ceramics, but since these have unique advantages and disadvantages, it is difficult to satisfy the structural requirements of bone tissue engineering scaffolds by applying any single process. Development of process technology is necessary.

Among the process technologies for manufacturing porous ceramics, gel casting as a wet molding process has the advantages of uniform microstructure, near net-shape, complex shaped parts, and high strength, which is why It is widely used for manufacturing. Direct coagulation gel casting can directly convert the slurry fluid to a solid object without removing the liquid phase, thus overcoming problems such as dry shrinkage that may occur in conventional wet processes. At this time, the solid content of the slurry is directly related to the molding strength, drying and plastic shrinkage, so that a gel concentration is required as high as possible (> 50%) in order to get closer to the required dimensions of the ceramic part. For this reason, gel casting has generally been recognized as a process technology for the production of molded articles having a high density, but can also be used for the production of porous ceramics by introducing a pore forming material. However, if the molding density is too low, a significant shrinkage occurs during the volatilization of the organic material has a disadvantage that the porosity that can be obtained by gel casting is usually limited to less than 60%. In addition, gel casting of foams enables the production of ceramic supports having high strength, but there is a problem that the size of pores obtained is usually too small, non-uniform, and almost impossible to make structures having interconnected pore meshes.

Freeze drying or freeze casting has been reported as another wet forming technique for producing porous ceramics. This technique includes manufacturing slips, freezing, sublimation drying, calcination and sintering. The frozen solvent acts as a template for the temporary binder and pore channels between the powder particles, and the crystals of the solvent are connected to each other in the dendritic structure surrounded by the frozen ceramic slurry. Removal of solvents by sublimation can minimize drying stresses and shrinkage that can cause defects such as cracking and warping that can occur during normal drying. The final microstructure depends on the lyophilization and sintering conditions, and by controlling the freezing direction and temperature gradient, pore channels and pore gradients can be obtained.

In the freezing casting process, there is a big problem that the ultra-porous molded product obtained when the freezing suspension is sublimed due to low molding strength is extremely weak to handle. In addition, the pore size obtained by this method is several tens of μm or less, there is a problem that it is not enough to use as a bone tissue support.

In order to solve the above problems, an object of the present invention is to provide a porous porous apatite support having a unique property with improved mechanical properties and controlled pore structure for a type of bioactive ceramics (HAP).

In order to solve the above problems, the present invention is to provide a method for producing a porous apatite hydroxide support using a composite process technology of freeze-gel casting / polymer sponge for preparing a porous support for bone tissue engineering The purpose.

In order to achieve the above object, the present invention

As a porous apatite hydroxide support formed by using apatite hydroxide as a starting material,

Coarse pores of 180-360 μm are formed into a mesh;

2 micrometers or less micropores are formed in the said mesh-like support body,

The micropores are arranged regularly to provide a porous apatite hydroxide support, characterized in that to form a connecting pore channel growing in the uniaxial direction.

In order to achieve the above another object, the present invention

Adding a monomer, a dispersant, and a surfactant to an alcohol solvent to form a slurry for freezing casting;

Adding an initiator to the slurry and injecting it into a polymer sponge before gelation occurs;

Placing the polymer sponge in a mold packed with a heat insulating material and maintaining the temperature at 0 ° C. or less for 20 to 40 minutes to form a frozen specimen;

Drying the frozen specimen at a temperature of 65 to 90 ° C. for 20 to 40 minutes to evaporate the solvent of alcohol; And

The dried specimen is placed in an electric furnace to provide a method for producing a porous apatite hydroxide support comprising the step of heating and sintering at 1200-1500 ℃ for 1-3 hours at a temperature increase rate of 1-3 ℃ / min.

In order to achieve the above another object, the present invention

It provides a porous apatite hydroxide support prepared according to the above production method.

Porous hydroxide apatite support according to the present invention can expand the scope of application in the field of biomedical care by selecting HAP having a composition similar to the inorganic components constituting most of the hard tissue of the body and excellent in biocompatibility and bone conductivity as a skeleton structure target material have.

In addition, in order to design a porous support for bone tissue engineering that can withstand the load required in the early stages of bone growth, polymer sponge technology is used to form ultra-porous porous structure with coarse pore network structure, and mechanical process using gel process. The improvement of strength can be ensured.

At the same time, according to the present invention, the microstructure control of the bone structure can be controlled in various ways through the complex process technology combined with the freezing casting process. As a result, it is expected that the characteristics of the surgical medical field for bone tissue reconstruction can be sufficiently satisfied.

Figure 1 shows a scanning electron microscope (SEM) photograph of the starting material HAP in the present invention.
Figure 2 shows a scanning electron microscope (SEM) picture of the polymer sponge used in the present invention.
Figure 3 shows the XRD peak when (a) apatite hydroxide powder, (b) a porous apatite hydroxide support sintered at 1350 ° C, (c) 1450 ° C, and (d) 3% by weight of MgO at 1450 ° C. Illustrated.
4A to 4D show the scanning electrons of the porous support when the apatite hydroxide powder is (a) 5% by volume, (b) 7.5% by volume, (c) 10% by volume, and (d) 12.5% by volume, respectively, with respect to the monomer solution. A micrograph (SEM) photograph is shown.
Figure 5 shows a scanning electron microscope (SEM) photograph of the uniaxial pore structure of the frozen casting sintered body according to an embodiment of the present invention.
Figure 6 shows the relationship between the pore size and the support thickness in the content ratio of the apatite hydroxide powder in one embodiment of the present invention.
7A and 7B illustrate scanning electron microscope (SEM) photographs of the support microstructure according to (a) MgO addition, and (b) 3 wt% MgO addition according to one embodiment of the present invention.
8a to 8c show the porosity of the porous support according to the sintering temperature (a) 1250 ℃, (b) 1350 ℃, (c) 1450 ℃ each in an embodiment of the present invention.
9a to 9c show the compressive strength of the porous support according to the sintering temperature (a) 1250 ° C, (b) 1350 ° C, (c) 1450 ° C in one embodiment of the present invention.

According to one aspect of the present invention, as a porous apatite hydroxide support formed using apatite hydroxide as a starting material, coarse pores of 180 to 360 μm are formed into a mesh, and fine pores of 2 μm or less are formed in the mesh support skeleton. Is formed, and the micropores are arranged regularly and grow in a uniaxial direction to form a porous apatite hydroxide support.

In the porous hydroxide apatite support according to the present invention, coarse pores are formed into a mesh. These coarse pores are the result of using a polymer sponge, and the coarse pore size is preferably about 180-360 μm. The structure and size of these pores serves to effectively grow osteoblasts into the support.

The skeletal structure of the support on which the coarse pores are formed contains micropores having uniaxial orientation. These micropores are formed in a controlled freezing and sublimation / drying process from the bottom to the top of the slurry of apatite hydroxide. The frozen solvent acts as a template for the temporary binder and pore channels between the powder particles, and the crystals of the solvent are connected to each other in the dendritic structure surrounded by the frozen ceramic slurry. The development of pore structures with these properties can contribute to smooth blood flow.

The micropores are arranged regularly and grow in the uniaxial direction to form channels. The final microstructure depends on the lyophilization and sintering conditions, and by controlling the freezing direction and temperature gradient, pore channels and pore gradients can be obtained.

The porosity of the support increased with decreasing content of apatite hydroxide, preferably 55-91%. If the porosity of the micropores is less than 55%, shrinkage occurs during the manufacturing process, so the pore size is too small, uneven and almost impossible to form a structure having interconnected pore meshes, which is undesirable, and if the porosity exceeds 91%, the support Porosity occupies too much of the area, and the strength is very weak, which is undesirable.

According to another aspect of the present invention, by adding a monomer, a dispersant and a surfactant to an alcohol solvent to form a slurry for freezing casting; Adding an initiator to the slurry and injecting it into a polymer sponge before gelation occurs; Placing the polymer sponge in a mold packed with a heat insulating material and maintaining the temperature at 0 ° C. or less for 20 to 40 minutes to form a frozen specimen; Drying the frozen specimen at a temperature of 65-90 ° C. for 20-40 minutes to evaporate the solvent of alcohol; And it provides a method for producing a porous apatite hydroxide support comprising the step of putting the dried specimen in an electric furnace and heated for 1 to 3 hours at 1200-1500 ℃ at a temperature increase rate of 1-3 ℃ / min.

The method for preparing a porous apatite hydroxide support of the present invention simultaneously uses a gel casting method, which is a liquid solidification method, and a lyophilization method (or freeze casting method), which is a wet molding technique for producing porous ceramics, and in addition, a polymer for forming coarse pores. It is characterized by going through a sponge process.

The freeze-drying process in the manufacturing process of the hydroxide apatite support has the advantage of forming micropores, but has a disadvantage of weak strength. Gel casting method, although the strength is improved, it is difficult to have a porous and uniform structure. In addition, the polymer sponge process can obtain coarse pores, but has a weak strength. The present invention provides a porous apatite hydroxide support having coarse pores formed uniformly in the uniaxial direction and exhibiting a significant level of compressive strength while forming coarse pores by taking advantage of each manufacturing method by using each of these steps in each step. do.

In the step of forming the slurry, acrylamide monomer including acrylamide (AM) and N, N'-methylenebisacrylamide (MBAM) is added to an alcohol, preferably tertiary butyl alcohol, to form a monomer solution. It is preferable to inject the apatite hydroxide powder into the monomer solution.

The apatite hydroxide powder is preferably contained in 5 to 15% by volume based on the monomer solution.

The acrylamide monomer is preferably added in an amount of 5 to 15% by weight based on the monomer solution. Here, acrylamide (AM) is used in a considerable excess, and specifically, acrylamide (AM) and N, N'-methylenebisacrylamide (MBAM) monomers can be mixed and used in a content ratio of 10-30: 1, respectively. .

Magnesium oxide (MgO) may be further added to the monomer solution as an additive in the slurry forming step. By adding magnesium oxide, the internal density of the sintered body was densified and the compressive strength was increased as compared with the case without addition. The content of magnesium oxide to be added is preferably set to 2 to 5% by weight based on the monomer solution. If the content of magnesium oxide is less than 2% by weight, it is not preferable because the content is so small that it is difficult to exhibit the effect of addition, and if it is more than 5% by weight, it is not preferable from the viewpoint of biocompatibility.

In the present invention, coarse pores should be formed to have a composition similar to the inorganic component that occupies most of the hard tissue of the body, and a polymer sponge is used to form coarse pores. According to the size and volume of the pore cell of the polymer sponge foam, the pores of the porous apatite hydroxide support may be determined in the future. The polymer sponge is preferably a polyurethane material. It is preferable that the coarse pores of the support formed by the step of sintering are formed into a mesh of 180-360 μm in diameter.

According to another aspect of the present invention, there is provided a porous apatite hydroxide support prepared according to the above-described manufacturing method. The support is preferably micropores of 2 μm or less are formed inside the mesh support, and the micropores are regularly arranged and grown in the uniaxial direction. The microporosity of the support is preferably 55-91%.

Example

material

Apatite hydroxide (HAP) (DC Chemical Co. Ltd., Korea) was used as a starting material. As a solvent, tertiary butyl alcohol (TBA, Junsei Chemical Co. Ltd., Japan) was used. As a process additive, citric acid (Aldrich Chemistry, USA) as a dispersant, ethoxylated acetylenic diol surfactant (Dynol604, Air Products and Chemicals, Inc., USA) as a surfactant, and monofunctional acrylamide (AM) as a monomer for gelation , C ₂ H ₃ CONH ₂ , Aldrich Chemistry, USA) and bifunctional N, N'-methylenebisacrylamide (MBAM, (C ₂ H ₃ CONH) ₂ CH ₂ , Aldrich Chemistry, USA) were used. Ammonium persulfate (APS, (NH ₄ ) ₂ S ₂ O ₈ , Kanto Chemical Co. INC., Japan) was used as the polymer polymerization initiator. The polymer sponge is made of a flexible polyurethane material having a cell size of 75 pores per linear inch (PPI).

Example  One

First, a monomer solution was prepared using a ratio of AM and MBAM in the solvent TBA of 9.6: 0.4 wt%. HAP powder was prepared in a monomer solution prepared in advance so that a mixed solution of 5 vol% solids was dissolved. At this time, 1 wt% of citric acid as a dispersant and dynol604 as a surfactant were used at 0.25 wt% based on the monomer solution. For dispersion stability of the prepared slurry was adjusted to about pH 3 using acetic acid (Junsei Chamical Co. Ltd., Japan). Ball milling for 24 hours for uniform mixing and then defoaming for 3 minutes using a vacuum desiccator. After defoaming, an initiator solution (20 wt% aqueous solution of ammonium presulphate) was added to the slurry, followed by injection into a polyurethane sponge before gelation completely occurred.

After injecting the slurry, the sponge is repeatedly compressed about 5 times to allow the slurry to completely penetrate into the inside of the sponge, and then the bottom and the temperature of the bottom part are kept below 0 ° C by using a mold in which the upper part and the side part are packed by the insulation. Frozen for a minute. The frozen specimen was removed from the mold and held in a dryer at 80 ° C. for 30 minutes to allow rapid and continuous melting of solvent TBA, gelation of AM and evaporation of TBA. Then, it was dried for 24 hours using a freeze dryer. The lyophilized specimens were kept in a dryer at 50 ° C. until there was no change in weight to remove excess solvent. The dried specimen was heated at 1 ° C./min in an electric furnace, maintained at 600 ° C. for 1 hour to remove polyurethane sponges and organics, and heated at 3 ° C./min and sintered at 1250 ° C. for 2 hours to obtain a porous apatite support.

Example 2

The same procedure as in Example 1 was carried out except that HAP powder was prepared to be a mixed solution in which 7.5 vol% was dissolved in the monomer solution.

Example 3

The same procedure as in Example 1 was carried out except that HAP powder was prepared in a monomer solution so that 10 vol% of the mixed solution was dissolved.

Example 4

The same procedure as in Example 1 was carried out except that HAP powder was prepared to be a mixed solution in which 15.0 vol% was dissolved in the monomer solution.

Example 5

It carried out similarly to Example 1 except having set the temperature of sintering to 1350 degreeC in the sintering step.

Example 6

The same process as in Example 1 was carried out except that the temperature of the sintering step was 1450 ° C.

Example 7

Except for preparing a mixed solution by adding 1% by weight of magnesium oxide (MgO) to the monomer solution was carried out in the same manner as in Example 1.

Example 8

Except for preparing a mixed solution by adding 3% by weight of magnesium oxide (MgO) to the monomer solution was carried out in the same manner as in Example 1.

Example 9

Except for preparing a mixed solution by adding 5% by weight of magnesium oxide (MgO) to the monomer solution was carried out in the same manner as in Example 1.

Evaluation and Results

XRD  peak

The crystal phases obtained by the examples were measured through an X-ray diffractometer (XRD, D / max-IIA, Rigaku, Japan). Figure 3 shows the sintered compact XRD peak when (a) apatite hydroxide powder, (b) a porous apatite hydroxide support sintered at 1350 ° C, (c) 1450 ° C, and (d) 3% by weight of MgO at 1450 ° C. Illustrated. Crystals of the hot sintered body also show almost all peaks of apatite hydroxide. However, the peak intensity is stronger when the sintering temperature is high. Also in the case of (d) in which magnesium oxide was added, XRD crystals appeared almost similarly. The results indicate that when sintering at a temperature of 1450 ° C. or less, the support skeleton can be made more compact while other reactions that produce calcium phosphate and the like while maintaining the properties of the apatite hydroxide support are negligible.

SEM  Picture

The properties of the pores and the support were measured using an optical microscope and a scanning electron microscope (SEM, JSA-840A, Jeol, Japan). As a result of examining the effect of the solid loading change on the microstructure formation of the support, the morphology of the pore outer wall also showed a uniform shape from the histological perspective.

1 shows a scanning electron microscope (SEM) photograph of the starting material apatite hydroxide used in the embodiment of the present invention. Figure 2 shows a scanning electron micrograph of the polymer sponge used in the embodiment of the present invention.

Figures 4a to 4d shows that the apatite hydroxide powder (a) 5% by volume (Example 1), (b) 7.5% by volume (Example 2), (c) 10% by volume relative to the monomer solution (Example 3) , (d) A scanning electron microscope (SEM) photograph of the porous support at 12.5% by volume (Example 4) is shown.

FIG. 5 shows a scanning electron microscope (SEM) photograph of a uniaxial pore structure of a freeze-casting sintered compact according to an embodiment of the present invention. Referring to FIG. 5, it can be seen that the pore structure of the freeze-casting sintered body is composed of interconnected uniaxial pore channels regularly arranged along the growth direction of the TBA ice and micropores contained in the skeletal structure.

7A and 7B show scanning electron microscope (SEM) photographs of the microstructure of the support according to Example 1 without MgO and Example 8 with 3% by weight of MgO, respectively, according to one embodiment of the present invention. . Referring to FIGS. 7A and 7B, when 3 wt% MgO was added to improve the strength and densification of the sintered compact, Example 9 had a higher internal density of the sintered compact, compared to 67.8%. Porosity and compressive strength of 3.76 MPa are shown.

Coarse pore size

Figure 6 shows the relationship between the pore size and the support thickness in the content ratio of the apatite hydroxide powder in one embodiment of the present invention. Referring to FIG. 6, in Examples 1 to 5, the range in which coarse pores can be formed is at least 180 μm and at most 360 μm (see FIG. 6). When the amount of apatite hydroxide was added to the monomer solution, the pore size was larger, and when the amount of the apatite hydroxide powder was added, the pore size was smaller. The structure and size of these pores serves to allow osteoblasts to grow inside the scaffold.

Support thickness

Referring to FIG. 6, the range in which the support thickness can be formed is at least 38 μm and at most 118 μm (see FIG. 6). When the amount of the apatite hydroxide powder was added to the monomer solution, the thickness of the support appeared thin, and when the amount of the apatite hydroxide powder was added, the thickness of the support appeared thick.

It can also be seen that the support thickness is inversely proportional to the average pore size, which is due to the constant pore size and volume of the polyurethane foam.

Porosity

8A to 8C are sintering temperatures in one embodiment of the present invention, respectively, at (a) 1250 ° C. (Example 1), (b) 1350 ° C. (Example 5), and (c) 1450 ° C. (Example 6). The porosity of the porous support is shown. 8A to 8C, the porosity of the porous apatite hydroxide support is at least about 55% to at most about 91%. It can be seen that the porosity decreases as the content of the apatite hydroxide powder increases. In addition, the porosity tends to decrease as the amount of magnesium oxide added increases.

Compressive strength

9A to 9C illustrate sintering temperatures according to one embodiment of the present invention (a) 1250 ° C. (Example 1), (b) 1350 ° C. (Example 5), and (c) 1450 ° C. (Example 6) The compressive strength of the porous support is shown. 9A to 9C, the compressive strength of the porous apatite hydroxide support is 0.1 to 6.57 MPa. It can be seen that the compressive strength increases as the content of the hydroxide apatite powder increases. Moreover, the compressive strength of the sintered compact increased when the sintering temperature was 1450 ° C (Example 6) at a high temperature. In addition, it can be seen that the compressive strength also increases as the amount of magnesium oxide added increases.

Claims (13)

As a porous apatite hydroxide support formed using apatite hydroxide as a monomer,
Coarse pores of 180-360 μm are formed into a mesh;
2 micrometers or less micropores are formed in the said mesh-like support body,
The porous microporous hydroxide apatite support, characterized in that the regular arrangement and uniaxial direction to form a channel. The porous apatite hydroxide support according to claim 1, wherein the support has a porosity of 55-91%. Adding a monomer, a dispersant, and a surfactant to an alcohol solvent to form a slurry for freezing casting;
Adding an initiator to the slurry and injecting it into a polymer sponge before gelation occurs;
Placing the polymer sponge in a mold packed with a heat insulating material, and holding the polymer sponge at a temperature of 0 ° C. or less for 20 to 40 minutes to form a frozen specimen;
Drying the frozen specimen at a temperature of 65-90 ° C. for 20-40 minutes to evaporate the solvent of alcohol; And
The dried specimen is placed in an electric furnace and heated at a rate of 1-3 ° C./min, and heated at 1200-1500 ° C. for 1 to 3 hours to prepare a porous apatite hydroxide support. According to claim 3, In the step of forming the slurry, an acrylamide monomer comprising acrylamide (AM) and N, N'- methylenebisacrylamide (MBAM) is added to the alcohol to form a monomer solution, A method for producing a porous apatite hydroxide support, characterized by injecting apatite hydroxide powder into a monomer solution. The method for preparing a porous apatite hydroxide support according to claim 4, wherein the apatite hydroxide powder is contained in an amount of 5 to 15% by volume based on the monomer solution. The method of claim 4, wherein the acrylamide monomer is added in an amount of 5 to 15% by weight based on the monomer solution. The method for producing a porous apatite hydroxide support according to claim 3, wherein the alcohol is tertiary butyl alcohol. The method of claim 3, wherein magnesium oxide (MgO) as an additive in the slurry forming step is further added in an amount of 1 to 5% by weight based on the monomer solution. The method of claim 3, wherein the polymer sponge is a polyurethane material. The method of claim 3, wherein the coarse pores of the support formed by the step of sintering are formed into a mesh of 180-360 μm in diameter. A porous apatite hydroxide support prepared according to the method according to any one of claims 3 to 10. 12. The porous apatite hydroxide support according to claim 11, wherein micropores of 2 µm or less are formed in the mesh support, and the micropores are regularly arranged and grown in the uniaxial direction. 12. The porous apatite hydroxide support according to claim 11, wherein the microporosity of the support is 55-91%.

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