KR20040015854A - Improvement of calcium phosphate formation in simulated body fluid by polarizing barium titanate thin film on titanium substrate - Google Patents

Abstract

PURPOSE: A method for producing calcium-phosphate in a bioavailable solution by polarizing a barium titanate thin film coated on titanium surface is provided to produce the calcium-phosphate crystals fast and minutely in the bioavailable solution. CONSTITUTION: The method for producing calcium-phosphate in the bioavailable solution by polarizing a barium titanate thin film coated on titanium surface comprises the steps of: preparing the ferroelectric barium titanate thin film by spin coating metal naphthenate on a titanium substrate and heat treating; polarizing the barium titanate thin film to apply the negative electric charge to the surface of the thin film; and settling the barium titanate thin film into the bioavailable solution.

Description

Improvement of calcium-phosphate formation in bioavailable solution by polarization of barium titanate thin film coated on titanium surface {Improvement of calcium phosphate formation in simulated body fluid by polarizing barium titanate thin film on titanium substrate}

The present invention relates to the enhancement of calcium-phosphate production in a biouse solution by forming and polarizing a barium titanate thin film on titanium.

Titanium, most widely used as a bone material for bone implants, forms an extremely stable oxide film on the surface and has excellent corrosion resistance. Excellent biocompatibility and low elastic modulus compared to other metals results in less bone stress and fracture resistance. It is relatively good and is most often used as a dental intraosseous implant material. However, the initial osteogenic capacity around the implant is lower and the rate of contact with the fibrous tissue is higher than the bioactive and in vivo disintegrating materials.

Accordingly, the surface of titanium used as an implant is coated with hydroxyapatite (abbreviated as 'HAP'), and an implant having biocompatibility and mechanical strength is used in orthopedics and dentistry. HAP-coated implants are mainly used for plasma spraying, but this method is to apply HAP to plasma flame of 6,000 ℃ or higher and collide with metal surface in electric field to coat in thin layer within a short time. However, because it is performed at extremely high temperatures, HAP can be decomposed and partially vitrified or denatured, and it is difficult to apply uniform coatings on large materials or implants with complex shapes, and the thermal spraying equipment is extremely expensive, and material loss There is a disadvantage that the additional cost is large because a large amount of material is required. Flame spraying, which is performed at a lower temperature than plasma spraying, and which has a lower price, has less defects in HAP, but a sufficient welding strength is not obtained.

As described above, the HAP-coated implant has problems due to microstructural defects, deterioration of adhesion force that may occur during the long-term use of the implant material, and the amorphousness of the HAP during the coating process.

In addition, the method of physically treating the surface morphology of the metal or polymer material to form HAP in the bio-used solution, etc., has been steadily studied, but in practice, the adhesion strength between the thin film and the base metal, the mechanical properties of the thin film and the thin film Due to microstructural defects, clinical applications are limited.

As for the effect of electrical stimulation on bone formation, it was reported that microcurrent stimulation was continuously applied to rabbit's femur for several weeks and bone was added around electrode (Yasuda I. et al., J. Bone. Joint. Surg. 37, 1292-1293 (1995)), and there have been studies on the effects of different types of electrical stimulation on bones, and it is well known that when electrical stimulation is applied to bones, significant bone formation occurs around the cathode (Buch F. et al., Biomaterials, 5, 341-346 (1984); Friedenberg ZB et al., Surg. Gynecol. Obstet., 131, 894-899 (1970); Liboff AR et al., Clin. Orthop. Relat. R , 106, 330-335 (1975). Currently, the electrical stimulation method has been applied to promote healing by using together as an auxiliary means of treatment when bone union does not occur at the site of fracture or in pseudoarthritis.

It is an object of the present invention to form a polarized barium titanate thin film on a titanium surface and to polarize it, thereby facilitating the production of much faster and dense calcium-phosphate crystals than in the case of ordinary titanium in a biofuel solution.

1 is a schematic diagram illustrating the process of the present invention

2 is a polarization device for polarization treatment

Figure 3 is a scanning electron microscope and elemental analysis of the crystal formed on the polarized barium titanate and non-polarized barium titanate thin film after deposition test in a bio-use solution

Figure 4 is a scanning electron microscope and elemental analysis of the crystal formed after the deposition test in the bio-use solution on the titanium surface on which titanium and the oxide layer formed

5 is a scanning electron microscope and elemental analysis photographs of crystals formed after deposition test in MEM solution on polarized barium titanate and non-polarized barium titanate thin film;

FIG. 6 is a scanning electron microscope and elemental analysis photograph of crystals formed after deposition test in a MEM solution on a titanium surface on which titanium and an oxide layer were formed;

In the barium titanate thin film used in the present invention, after the spin coating using a metal naphthenate on a titanium substrate, the electrothermal treatment is repeated to obtain a ferroelectric barium titanate thin film having a desired thickness, and the final heat treatment is performed under an argon atmosphere of 750 ° C. By heat treatment for 10 minutes, titanium oxide was not produced in the thin film, and the thin film having the best crystallinity of barium titanate was formed. The thin film thus prepared is polarized to negatively charge the surface of the barium titanate thin film, thereby facilitating the production of calcium-phosphate crystals when deposited in the biouse fluid.

Hereinafter, with reference to the accompanying drawings, a specific embodiment of the present invention will be described in more detail for the calcium-phosphate production in the bio-use solution by the polarization treatment of the barium titanate thin film on the titanium surface, but the following examples It is only illustrative, and the content of the present invention is not limited to the following examples.

Example

Hereinafter, with reference to the accompanying drawings, a specific embodiment of the present invention will be described in more detail the calcium-phosphate production in the bio-use solution by polarization treatment of barium titanate, but the present invention is not limited thereto.

Step of manufacturing ferroelectric barium titanate thin film

Pure titanium rods with a diameter of 10 mm were cut to 1 mm thickness using a low speed cutter. The cut titanium discs were polished using a grinder on # 240, 600, 800, 1500 and 2000 SiC abrasive paper, and the final polishing was 0.3 μm and 0.05 μm alumina powders sequentially. The starting solution for thin film production was used by mixing barium naphthenate and titanium naphthenate sol in a ratio of 1: 1 molar ratio of barium: titanium. To prepare a homogeneous thin film, the amount of toluene was changed to adjust the viscosity and concentration of the starting solution. The concentration of sol was prepared by adjusting to 15.1 mg metal / g coating solution. Since the stoichiometry of the thin film is likely to be broken due to excessive atomic diffusion from titanium during the heat treatment between the titanium surface and the barium titanate thin film, a titanium oxide layer is formed on the titanium substrate to serve as a buffer layer to maintain the stoichiometric ratio of the thin film. After that, a barium titanate thin film was formed. To this end, the titanium substrate was heat-treated at 600 ° C. for 5 minutes to form a titanium oxide layer on the surface of the titanium substrate. The starting solution was added dropwise to the surface of the titanium substrate on which the oxide layer was formed, followed by spin coating at 3500 rpm for 15 seconds. By evaporating the organic material on the coated specimens and repeating coating and heat treatment, a homogeneous thin film of a desired thickness can be prepared. At this time, the organic material is sufficiently volatilized to prevent crystal growth, thereby forming a homogeneous thin film by repeated coating. In order to achieve this, proper heat treatment temperature should be used. Therefore, thermal analysis of barium and titanium naphthenate sol used as starting solution was performed. Thermal analysis was performed using a thermogravimetric / differential thermal analyzer at a temperature rise rate of 5 ° C / min in an air atmosphere at a temperature range of 30 to 800 ° C. The heat treatment was performed under the condition of preheating at 500 ° C. for 10 minutes, which was found as a result of the thermal analysis, thereby minimizing the generation of pores and defects in the coating thin film after the final heat treatment. In the thin film having a thickness of 0.3 μm or less, polarization under high voltage was difficult, so that the coating thickness was increased by repeating the coating and the heat treatment 20 times. The final heat treatment is performed at 600, 650, 700, 750, 800 and 850 ° C, respectively, and then subjected to X-ray diffraction analysis. As a result, 750 ° C with the best crystallinity without the presence of heterogeneous titanium oxide is used as the final heat treatment temperature. The final heat treatment was performed for 10 minutes in an argon atmosphere.

Polarization step of barium titanate

In order to polarize the barium titanate thin film, a silver paste used at room temperature was applied to the surface of the specimen and dried at room temperature for 3 hours. The specimen was subjected to a high temperature polarization treatment in which a specimen was cooled in a drying chamber in air for 2 hours at room temperature at 160 ° C., which is a temperature higher than Curie temperature. At this time, the applied voltage was 5V / ㎛. 2 shows an example of the polarization treatment apparatus. When the Curie temperature of barium titanate is 120 ° C and polarization treatment is lower than the Curie temperature, stress between the divisions is difficult to align the electric dipoles, and after the polarization treatment, the electric dipoles return to their original state within a short time. However, if the polarization treatment is performed at a temperature above the Curie temperature, the partition wall becomes a dielectric and the stress between the partition walls disappears. When polarized with a low electric field, the dipoles can be easily aligned, and the dipoles can be aligned for a long time. Therefore, in this study, high temperature polarization treatment was performed in which the polarization conditions were cooled to room temperature above the Curie temperature.

Deposition test step in bio-use solution of barium titanate

The negatively charged barium titanate thin film, the unpolarized barium titanate thin film, the titanium substrate, and the titanium substrate heat-treated at 600 ° C. for 5 minutes were washed with acetone and distilled water, respectively. After the surface was completely dried, the specimens were deposited in a polyethylene test tube containing 50 ml of the bioavailability solution and soaked in a 37 ° C. thermostat for 15 days. Specimens from each of the same experimental groups were stored for 15 days in the same manner in 20 ml of Eagel's MEM (abbreviated as 'MEM') solution (Life Technologies, U.S.A.). In order to keep the ionic concentration of the solution as constant as possible, fresh solutions were exchanged every day. After the deposition test, the specimens were washed with running distilled water and dried at room temperature. Table 1 shows the composition of the prepared bio-use solution.

Table 1

Order of addition reagent Amount g / dm3 H2O One (CH2OH) 3CNH2 6.005 2 NaCl 7.995 3 NaHCO3 0.353 4 KCl 0.224 5 K2HPO4, 3H2O 0.228 6 MgCl2, 6H2O 0.305 7 CaCl2 · 2H2O 0.368 8 Na2SO4 0.071 9 2 mol / dm 3 HCl 20 ml

After the polarized barium titanate thin film and the non-polarized barium titanate thin film were immersed in a bioused solution for 15 days, the surface of the specimen was analyzed by scanning electron microscope and EDX.

Crystals were produced in the non-polarized specimens deposited for 15 days, but the results of EDX analysis showed that the crystals were not calcium-phosphate crystals, that is, Cl- and NaCl crystals. In the polarized specimens deposited for 15 days, the branched crystals and the black areas surrounding them were observed, unlike the non-polarized specimens, and EDX analysis showed that calcium-phosphate crystals were formed on the surface. It became. It is thought that the formation of crystals is different due to the different ions initially adsorbed according to the charged polarity of the barium titanate thin film surface with or without polarization. Figure 4 shows the result of analyzing the surface of the specimen by scanning electron microscope and EDX after immersing the titanium substrate and titanium substrate heat-treated for 5 minutes at 600 ℃ in air for 15 days. After 15 days of immersion in a titanium substrate, the titanium substrate showed a tendency to form crystals of NaCl similar to an unpolarized barium titanate thin film with or without heat treatment, which was also formed on the surface by ions initially adsorbed on the surface. It is thought that the decision to be made is different. Inferring the mechanism of calcium-phosphate crystal formation in the biouse solution from the adsorption order of the adsorbable cations and anions according to the charged polarity, the surface of the negatively charged barium titanate thin film is polarized to the Ca 2+ cation in the biouse solution. It is adsorbed quickly. On the other hand, Cl- group is adsorbed on the surface of the barium titanate which has not been polarized. Ca2 + cations adsorbed on the polarized barium titanate surface begin to attract HPO42- or OH- ions in the bioused solution, so the Ca2 + ions first adsorbed on the polarized barium titanate surface act as calcium-phosphate generating nuclei. Would have done. However, the surface of the non-polarized barium titanate is adsorbed with Cl- first and exerts repulsion on anions such as HPO42- or OH- so that calcium-phosphate is not formed and Na + cations are adsorbed to form NaCl crystals. In the bioavailable solution, K + and Mg2 + cations exist in addition to Na + cations, and Cl- anion mainly binds to Na + cation because Na + ions have the highest electrical positiveness, and they are more easily ion-bonded with Cl- anions than other cations. It would be because

In FIG. 5, after the polarized barium titanate thin film and the nonpolarized barium titanate thin film were immersed in MEM solution for 15 days, the surface of the specimen was analyzed by scanning electron microscope and EDX. The polarization treatment resulted in dense and uniform crystals on the negatively charged surface. EDX analysis showed that the calcium-phosphate crystals were very thick, and the calcium-phosphate layer grew very thickly compared to the non-polarized specimens. . Non-polarized thin films also produced calcium-phosphate crystals, but EDX analysis showed strong peaks of barium titanate, whereas in polarized and negatively charged specimens, barium titanate was grown due to the growth of thick calcium-phosphate layers. It can be seen that the peak appears relatively low. And it can be seen that the calcium-phosphate layer formed on the non-polarized thin film is not densely formed. Therefore, it was confirmed that calcium-phosphate crystals were formed on the surface of the negatively charged barium titanate thin film, and that the negatively charged barium titanate thin film was formed by polarization rather than the non-polarized barium titanate thin film. I could see that the ability is higher.

In FIG. 6, after the titanium substrate and the titanium substrate having an oxide layer formed by heat treatment at 600 ° C. for 5 minutes in the air were deposited for 15 days in a MEM solution, the specimen surface was analyzed by scanning electron microscope and EDX. In the titanium substrate, NaCl crystals were formed in the same way as the result of immersion in the biouse solution when immersed in MEM.However, in the case of a titanium substrate heat-treated for 5 minutes at 600 ° C in air, a calcium-phosphate layer containing NaCl crystals was formed on the surface Formed.

According to the present invention, when the barium titanate thin film is formed on the titanium surface and then polarized, the following effects can be obtained. Efforts to improve bone adhesion by altering the surface shape of materials as well as attempting to obtain chemical bonds with bone using bioactive materials such as crystalline HAP or green glass as a way to increase the bone adhesion of implants However, the HAP coating has problems such as peeling and dissolution of the implant surface due to the inherent brittleness of the ceramic. In the present invention, a barium titanate thin film was formed on the titanium using a sol-gel method. Since the ceramic containing titanium component was selected, the bonding force between the substrate and the ceramic thin film was increased, and the polarization treatment negatively charged the surface of the barium titanate thin film to promote the formation of calcium-phosphate crystals when deposited in the bioavailable solution. .

Claims (6)

A manufacturing process in which a thin film of ferroelectric material is formed on a titanium surface as an implant material. The manufacturing process according to claim 1, wherein the ferroelectric material on the surface of the implant is polarized. A polarization apparatus according to claim 1, which can be used at room temperature when polarizing a ferroelectric thin film. The high temperature polarization method of claim 2, wherein the thin film of barium titanate is cooled to room temperature from 150 to 170 ° C. above the Curie temperature. The polarization method according to claim 2, wherein the application voltage ranges from 3V / µm to 7V / µm during polarization of the thin film. A manufacturing process in which a surface is negatively charged by coating and polarizing a ferroelectric thin film to enhance calcium-phosphate production on titanium.