Polybutylene succinate copolymer

Abstract

To provide a resin material that can suppress occurrence of inflammation even when used as a material for a medical device to be disposed in a human body and to generate abrasion powder due to slide during its use.SOLUTION: A polybutylene succinate copolymer comprises at least one of a repeat unit of a formula (1) and a repeat unit of a formula (2), and a repeat unit of a formula (3), with R1 being a zwitterionic group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polybutylene succinate copolymer having biocompatibility.

Background Art

[0002] One method for treating nerve disorders caused by damaged or deformed intervertebral discs due to injuries or diseases is artificial intervertebral disc replacement. In artificial intervertebral disc replacement, the damaged or deformed intervertebral disc is removed from between the vertebrae, and an artificial intervertebral disc is installed there. The artificial intervertebral disc includes, for example, a pair of metal end plates fixed to the upper and lower vertebrae of the removed intervertebral disc, respectively, and a polymer spacer disposed between the pair of end plates to connect the end plates. The spacer has spherical seating surfaces on the upper and lower sides, and the end plate has a recess in which the seating surface is slidably accommodated. By accommodating the seating surface of the spacer in the recess of the end plate, the pair of end plates are rotatably connected to the upper and lower sides of the spacer via the spacer, and the movement between the vertebrae at the location where the artificial intervertebral disc is installed is reproduced (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the artificial intervertebral disc is installed in the living body, titanium alloy and polyethylene, which have excellent biocompatibility and high mechanical strength, are used as the materials for the end plate and the spacer, respectively. However, in the artificial intervertebral disc having the above configuration, there is a problem that wear powder is generated on the surface of the spacer due to the sliding of the spacer in the recess of the end plate as the vertebrae move, and inflammation is caused by the wear powder.

[0005] The problem to be solved by the present invention is to suppress the occurrence of inflammation even when used as a material for a medical device that is placed and used in a human body and generates wear powder due to sliding during use, and to provide a resin material that is excellent in biocompatibility and has high mechanical strength.

Means for Solving the Problem

[0006] The present invention made to solve the above problems includes at least one of a repeating unit (U1) represented by the following formula (1) and a repeating unit (U2) represented by the following formula (2),

Chemical Formula

Chemical Formula

Chemical Formula

[0007] In the polybutylene succinate copolymer according to the present invention, the amphoteric ion group is preferably at least one betaine group selected from the group consisting of a carboxybetaine group, a sulfobetaine group, and a phosphobetaine group. In particular, it is preferable that the betaine group is represented by the following formula (4).

Chemical Formula

[0008] The polybutylene succinate copolymer according to the present invention can be represented by any of the following formulas (5) to (7).

Chemical Formula

[0009] Further, the present invention made to solve the above problems is a method for producing the above polybutylene succinate copolymer, a first step of generating a copolymer having the repeating unit (U1) and the repeating unit (U2); reacting the copolymer with an amphoteric ion compound having a functional group that reacts with a double bond site of the repeating unit (U1) of the copolymer, whereby an amphoteric ion group R 1 a second step of generating a copolymer containing the repeating unit (U3) having and at least one of the repeating unit (U1) and the repeating unit (U2).

[0010] According to the above production method, the amphoteric ion group R 1 can be easily introduced into the main chain of the polybutylene succinate skeleton.

Advantages of the Invention

[0011] The polybutylene succinate copolymer according to the present invention has excellent biocompatibility in addition to the high mechanical strength and biodegradability of PBS because the surface of polybutylene succinate (PBS) is chemically modified with an amphoteric ion. Therefore, when an artificial intervertebral disc having a spacer formed using a molding material containing the polybutylene succinate copolymer is implanted into a human body, even if wear powder is generated on the surface of the spacer, the wear powder is decomposed in the living body and does not stay in the living body for a long time, so that the occurrence of inflammation can be suppressed.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0013] Hereinafter, some embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[0014] The polybutylene succinate copolymer according to one embodiment contains at least one of the repeating unit (U1) represented by the following formula (1) and the repeating unit (U2) represented by the following formula (2), and the repeating unit (U3) represented by the following formula (3). In formula (3), R 1 is an amphoteric ion group.

Chemical formula

Chemical formula

Chemical formula

[0015] Polybutylene succinate (PBS), which is a polymer of the repeating unit (U2), is known as a plastic having mechanical strength equivalent to that of polyethylene and biodegradability. The polybutylene succinate copolymer according to one embodiment (hereinafter referred to as "PBS copolymer") is obtained by introducing an amphoteric ion group as a side chain into the polymer main chain of such PBS. "Amphoteric ion" refers to a molecule having a positive unit charge and a negative unit charge at different positions within one molecule and having a structure in which the charges are neutralized. An amphoteric ion is a kind of bipolar compound and is also called an "inner salt".

[0016] By chemically modifying PBS with zwitterionic groups, the PBS-based copolymer becomes biocompatible in addition to the high mechanical strength and biodegradability that PBS inherently has, and is useful as a material for medical devices that are placed and used in the living body such as artificial intervertebral discs. In addition, a molding material containing a PBS-based polymer having a zwitterionic group as a side chain may be able to suppress either or both of cell adhesion and protein adsorption. A PBS-based copolymer with suppressed cell adhesion or / and protein adsorption is useful, for example, as a material for stents, implant materials, and artificial intervertebral disc materials that are installed in blood vessels to expand stenosed sites of blood vessels.

[0017] That is, the molding material containing the above PBS-based copolymer can be used to manufacture medical devices that are placed and used in the living body of humans such as artificial intervertebral discs and stents. The molding material may contain appropriate components as required in addition to the PBS-based copolymer. Examples of other components include crosslinking agents, photoinitiators, light stabilizers, reinforcing agents, antibacterial agents, preservatives, and the like.

[0018] In the PBS-based copolymer according to one embodiment, the zwitterionic groups contained in each repeating unit (U3) may be of the same type or different types. Examples of zwitterionic groups include at least one betaine group selected from the group consisting of carboxybetaine groups, sulfobetaine groups, and phosphobetaine groups, and particularly a sulfobetaine group represented by the following formula (4) can be used.

Chemical formula

[0019] The sulfobetaine group represented by formula (4) can be easily introduced into the double bond site of the repeating unit (U1) by reacting the thiol compound represented by the following formula (4-1) with the repeating unit (U1).

Chemical formula

[0020] The zwitterionic group R of the repeating unit (U3) 1 Examples of the PBS-based copolymer in which 1 is a betaine group represented by the formula (4) include those represented by the following formula (5), (6), or (7). In these formulas (5) to (7), n, m, and p each independently represent an integer of 2 or more. [Chemical formula]

[0021] From the viewpoint of imparting biodegradability, the proportion of the repeating unit (U3) in the PBS-based copolymer represented by the formulas (5) to (7) is preferably 5 mol% to 20 mol%, more preferably 10 to 20 mol%, based on all the repeating units constituting the PBS-based copolymer.

[0022] The PBS-based copolymer according to one embodiment includes a first step of generating a copolymer having a repeating unit (U1) and a repeating unit (U2), and reacting the copolymer with a zwitterionic compound having a functional group that reacts with a double bond site of the repeating unit (U1) of the copolymer, thereby obtaining a repeating unit (U3) having a zwitterionic group R 1 and a second step of generating a copolymer including at least one of the repeating unit (U1) and the repeating unit (U2). The PBS-based copolymer can be produced by a method including these steps.

[0023] According to the above production method, by changing the charged amount of the repeating unit (U1) when generating the copolymer in the first step, the proportion (mol%) of the repeating unit (U3) in the PBS-based copolymer can be changed. [Examples]

[0024] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[0025] [Example 1] A round-bottom flask was charged with cis-2-butene-1,4-diol and 1,4-butanediol in a total amount of 100 mol, and 100 mol of succinic acid was added thereto and mixed. Further, tin octylate (Sn(Oct)2) was added to the round-bottom flask as a catalyst at a ratio of 0.5 mol% per ester group, and 4-methoxyphenol was added as a radical quencher at a ratio of 0.5 wt% based on the mixture. While heating the mixture in the round-bottom flask to 180 °C, the reaction was carried out for 5 hours under atmospheric pressure (1 atm) in a nitrogen atmosphere to effect esterification.

[0026] After the esterification was completed, the pressure was reduced to 40 mbar and the temperature was raised to 220 °C to completely remove by-products and unreacted monomers, and the polycondensation step was continued for 4 hours to produce a copolyester. The obtained copolyester was dissolved in chloroform, precipitated with methanol, and then vacuum dried at 30 °C for 24 hours. Thus, a white solid sample was obtained. The obtained sample contains at least one of the repeating unit (U1) represented by the following formula (1) and the repeating unit (U2) represented by the following formula (2).

Chemical formula

Chemical formula

[0027] In the following description, a polymer containing only the repeating unit (U2) is denoted as "PBS", a polymer containing only the repeating unit (U1) is denoted as "PcBS", and a copolymer containing both the repeating units (U1) and (U2) is denoted as "PBS-PcBS" or "PcBS-PBS". Table 1 shows the amounts of compounds used in the synthesis of each sample obtained in this example, the yields, etc. In Table 1, A, B, and C represent succinic acid, cis-2-butene-1,4-diol, and 1,4-butanediol, respectively.

[0028]

Table 1

[0029] In addition, the reaction formulas for each sample are shown below. In the following reaction formulas, n and m represent integers of 0 or 2 or more. When n = 0 and m is an integer of 2 or more, the polymer is PBS, and when m = 0 and n is an integer of 2 or more, the polymer is PcBS. Further, when both n and m are integers of 2 or more, the copolymer is PBS-PcBS or PcBS-PBS.

Chemical formula

[0030] [Example 2] A sulfobetaine (SB-SH) having a thiol functional group was synthesized by the following reaction using 3-dimethylamino-1-propyl chloride hydrochloride as a starting material. Hereinafter, for convenience of explanation, the substances used for the synthesis of SB-SH are labeled with the symbols D to H used in the following formula.

Chemical formula

[0031] (1) Synthesis of 3-(dimethylamino)propyl thioacetate (F). 43.87 g (278 mmol) of 3-dimethylamino-1-propyl chloride hydrochloride (D) was placed in a three-necked round-bottom flask equipped with a stir bar and a reflux condenser, and 150 mL of chloroform (CHCl3) was added thereto. Subsequently, the mixture in the round-bottom flask was bubbled with nitrogen in an ice bath to obtain a suspension. This suspension was cooled to 0 °C, 84.42 mL (334 mmol) of triethylamine (NEt3) was added dropwise to the suspension, and then the temperature of the reaction mixture was maintained at about 10 °C, and 117 mL (835 mmol) of thioacetic acid (E) was further added dropwise. The reaction mixture obtained as described above was maintained in an ice bath for a while and then slowly heated to 65 °C by refluxing in an oil bath for 20 hours. The bubbling operation with nitrogen was stopped when the reflux became stable.

[0032] The reaction mixture in the round-bottom flask was cooled to room temperature and extracted three times with ice-cooled 1 N sodium hydroxide (NaOH) solution, followed by extraction with pure water. The extraction layer with pure water was further extracted twice with chloroform. After combining these two extracts, they were washed with 1 N saturated saline. After the separation was completed, the chloroform extract was dried twice with anhydrous magnesium sulfate for 20 minutes each. Subsequently, it was filtered through Celite® and evaporated under reduced pressure to obtain 41.96 g of a slightly yellow oily reaction product. The yield was 93.6%. The structure of the reaction product was 1 Analyzed by 1H NMR, as shown below, it was confirmed that 3-(dimethylamino)propylthioacetate (F) was obtained. 1 1H NMR (500 MHz, CDCl3, δ): 2.90 (t, 2H, CH2S), 2.32 (s, 3H, COCH3), 2.31 (t, 2H, CH2N), 2.21 (s, 6H, N(CH3)2), 1.73 (m, 2H, CH2CH2CH2).

[0033] (2) Synthesis of sulfobetaine thioacetate (H) In a round-bottom flask, 21.62 g (246 mmol) of 1,3-propanesultone (G) was dissolved in 300 mL of dry acetone under nitrogen, and then 3-(dimethylamino)propylthioacetate (F) (41.96 g, 260 mmol) was added dropwise thereto. The mixture was stirred at room temperature for 48 hours. After filtration and washing with acetone, the solid was dried with a vacuum pump. Finally, the dried solid was dissolved in 10 mL of methanol and then crystallized with 700 mL of dry acetone. 57.75 g of a pure reaction product was obtained as a white solid. The yield was 78.3%. The structure of the reaction product was 1 Analyzed by 1H NMR, as shown below, it was confirmed that sulfobetaine thioacetate (H) was obtained. 11H NMR (500 MHz, D2O, δ): 3.34 - 3.27 (m, 4H, SO3CH2CH2CH2N, 2H, NCH2CH2CH2SCO), 2.98 (s, 6H, N(CH3)2), 2.85 (m, 4H, SO3CH2CH2N, 2H, NCH2CH2CH2SCO). 85(m,4H,SO3CH2CH2CH2N、NCH2CH2CH2SCO),2.28(s,3H,COCH3),2.09 - 1.97(m,4H,NCH2CH2CH2SCO、SO3CH2CH2CH2N).

[0034] (3) Synthesis of SB-SH In a round-bottom flask, 20.07 g (70.82 mmol) of sulfobetaine thioacetate was dissolved in 15 mL of methanol under nitrogen, and then 400 mL of 1 M sodium hydroxide (NaOH) solution was added dropwise. The mixture was stirred at room temperature for 90 minutes while bubbling with nitrogen. Then, 1 M sodium hydroxide solution was added to adjust the pH to 5.0. After removing the solvent by evaporation, the crude product was dissolved in a large amount of acetonitrile and methanol, and the resulting mixture was filtered and evaporated to obtain a white solid reaction product. The yield was 86.3%. The structure of the reaction product was 1 Analyzed by 1H NMR, as shown below, it was confirmed that SB-SH was obtained. 1 1H NMR (500 MHz, D2O, δ): 3.36 (t, 2H, NCH2CH2CH2SH), 3.35 (t, 2H, SO3CH2CH2N), 3.00 (s, 6H, N(CH3)2), 2.87 (t, 2H, SO3CH2CH2CH2N), 2.87(t, 2H, SO3CH2CH2CH2N), 2.51(t, 2H, NCH2CH2CH2SH), 2.12 - 1.97(m, 4H, NCH2CH2CH2SH、SO3CH2CH2CH2N).

[0035] Table 2 shows 3-(dimethylamino)propylthioacetate (F), sulfobetaine thioacetate (H), SB-SH, the amounts (g, moles) and ratios of the compounds used in each synthesis, the yield, etc.

Table 2

[0036] [Example 3] By a thiol-ene click reaction, a sulfobetaine group, which is an amphoteric ion group, was introduced into the PcBS-PBS backbone. For the reaction, a mixed solvent of hexafluoro-2-propanol (HFIP) and chloroform mixed at 5:1 was used, and tris(bipyridine)ruthenium(II) chloride (Ru(bpy)3Cl2) and N-dimethyl-p-toluidine (DMPT) were used as a catalyst and a photoinitiator, respectively. The molar ratio of each component charged was [allyl]0:[SB-SH]0:[Ru(bpy)3Cl2]0:[DMPT]0 = 1.0:6.0:0.005:0.05.

[0037] (1) In a 10 mL flask, 0.701 g of PcBS-PBS, 0.634 g of SB-SH, 1.5 mg of Ru(bpy)3Cl2, and 2.2 mg of DMPT were placed and dissolved in 4.2 mL of the mixed solvent. Then, the reaction mixture was irradiated with UV light (λmax = 448 nm) for 5 hours. After diluting the obtained crude product with water, it was dialyzed for 2 days to remove the remaining catalyst, photoinitiator, and unreacted SB-SH, and the product was filtered to obtain a powdery composite. The yield was 83%. The composite contains a polybutylene succinate-based copolymer (hereinafter referred to as "PcBS-PBS-S-SB") represented by the following formula.

Chemical formula

[0038] Also, the reaction formula of PcBS-PBS-S-SB is shown below.

Chemical formula

Chemical formula

[0039] (3) In addition to (1) and (2) described above, by changing the amounts of each component and using the same method as in (1) and (2), a composite containing PcBS-PBS-S-SB was obtained. Tables 3-1 and 3-2 summarize the component amounts and the like of the composites obtained by the above methods (1) to (3).

Table 3-1

Table 3-2

[0040] (4) Using the compounds shown in Table 3, a disk-shaped film with a diameter of 8 mm (thickness 1 mm) and a weight of 40 mg was compression-molded using a mold. Also, using PcBS and PcBS-PBS obtained in Example 1, similarly, a disk-shaped film with a diameter of 8 mm (thickness 1 mm) and a weight of 40 mg was compression-molded using a mold, and the surface of this film was covered with a solution in which 0.344 g of SB-SH, 0.9 mg of Ru(bpy)3Cl2, and 1.3 mg of DMPT were each dissolved in methanol, and a thiol-ene click reaction was carried out. The film obtained using the compounds shown in Table 3 is called a bulk film, and the film in which a thiol-ene click reaction was carried out on the surface of the PcBS and PcBS-PBS films to introduce a sulfobetaine group is called a surface-modified film. The amounts of the components contained in the surface-modified film are shown in Table 4 below. Also, the molar ratio of each component charge was [allyl]0:[SB-SH]0:[Ru(bpy)3Cl2]0:[DMPT]0 = 1.0:6.0:0.005:0.05.

Table 4

[0041] After irradiating the film after the reaction with UV light (λmax = 448 nm) for 2 hours, the film was washed with water, immersed in water for 10 minutes to remove the excipient, and dried under vacuum overnight.

[0042] (5) Evaluation (5-1) Cell Adhesion and Proliferation Mouse fibroblasts (L-929) purchased from RIKEN Cell Bank (Saitama, Japan) were cultured in Dulbecco's modified Eagle's medium (DMEM, Nacalai Tesque, Japan) containing 10% fetal bovine serum (FBS) and 1% antibiotic in the usual manner. Cells fluorescently labeled with CellTracker green were used in the following experiments. TM green, were used in the following experiments. After sterilizing the film obtained in (4) above with UV light overnight, it was washed with ethanol and immersed in phosphate-buffered saline (PBS) overnight. 4.0×10 TM green) fluorescently labeled3 Individual cells were seeded on the surface of the film and cultured at 37°C in a 5% CO2 atmosphere for a predetermined period of time. After culturing, the cells were washed with PBS, transferred to DMEM (10% FBS) for storage, and observed under a fluorescence microscope. From the observation images of the fluorescence microscope, the number of cells adhered to the film and the number of proliferated cells were counted and compared. As a comparative example, films made of polybutylene succinate (PBS) without the introduction of zwitterionic groups, films made of polyethylene terephthalate (PET), and films made of polyethylene (PE) were used.

[0043] Figure 1 shows the fluorescence microscope observation images of some of the films used in the evaluation experiment. Also, Figure 2 shows the results of measuring the number of adhered cells and the number of proliferated cells for some of the films used in the evaluation experiment. As can be seen from Figure 1 and Figure 2, the number of adhered cells of the bulk film (UTN1_0086, 096) and the surface-modified film (UTN1_098) was very small compared to the PBS film, PET film, and PE film.

[0044] (5-2) Adsorption of proteins A film with a diameter of 2.8 mm and a thickness of 0.8 mm was prepared, and the amount of protein adsorbed to it was examined. Bovine serum albumin (BSA) was used as the protein, and a BCA (bicinchoninic acid) protein assay reagent was used for protein detection.

[0045] First, the films of the examples and comparative examples were washed with ethanol and immersed in phosphate-buffered saline (PBS, pH 7.3 - 7.4) at room temperature overnight. Next, each film was immersed in 900 μL of bovine serum albumin (BSA) / PBS solution (4.5 mg / mL) at 37 °C for 4 hours. Then, the film was washed 3 times with PBS and immersed in 1 mL of SDS / PBS solution (10 mg / mL) at 37 °C for 4 hours to peel off the proteins on the film surface. 400 μL of the SDS / PBS solution containing the proteins peeled off from the film was mixed with 400 μL of BCA protein assay reagent, and this mixture was incubated at 37 °C for 2 hours. The UV (570 nm) absorbance of the incubated mixed solution was measured using an absorbance microplate reader (MTP-310lab, Corona Electric), and the amount of protein adsorbed on the film surface was determined.

[0046] The results of the experiment are shown in Fig. 3. As can be seen from Fig. 3, the protein adsorption amount of the films of the examples (UTN1_121, 120, 119, 114, 118, 107) was equal to or more than that of the PET film, but less than that of the PE film and the PBS film.

[0047] (5 - 3) Compression experiment The compression strengths of PBS, PcBS, PBS-PcBS, and PcBS-PBS-S-SB were measured using an EZ-SX texture analyzer (manufactured by Shimadzu Corporation). For the measurement, compression test pieces of 1 mm × 1 mm × 0.8 mm were used, and the measurement was repeated 3 times under the conditions of a sensitivity of 50% and a speed of 0.1 mm / min.

[0048] Figure 4 shows the experimental results. In Figure 4, "PBS75cBS25" represents that the ratio of PBS to PCBS is 75:25, and "PBS25cBS75" represents that the ratio of PBS to PCBS is 25:75. As can be seen from this Figure 4, compared with PBS, the compressive strengths of PcBS, PBS-PcBS, and PcBS-PBS-S-SB are low, but it was found that the compressive strength changes due to the difference in the ratio of PBS to PCBS in PBS-PcBS. From this, it was considered that the compressive strength of PBS-PcBS could be adjusted by setting the ratio of PBS to PCBS to an appropriate value.

Claims

1. At least one of the repeating unit (U1) represented by the following formula (1) and the repeating unit (U2) represented by the following formula (2), 【Chemical Formula 1】 【Chemical Formula 2】 and the repeating unit (U3) represented by the following formula (3), 【Chemical Formula 3】 A polybutylene succinate copolymer in which R1 in formula (3) is a zwitterionic group.

2. The polybutylene succinate copolymer according to claim 1, wherein the zwitterionic group is at least one betaine group selected from the group consisting of a carboxybetaine group, a sulfobetaine group, and a phosphobetaine group.

3. The betaine group is represented by the following formula (4) 【Chemical Formula 4】 The polybutylene succinate copolymer according to claim 2.

4. Represented by any of the following formulas (5) to (7) 【Chemical Formula 5】 A polybutylene succinate copolymer, wherein in the above formulas (5) to (7), n, m, and p are each independently an integer of 2 or more.

5. A molding material for a medical device, comprising the polybutylene succinate copolymer according to any one of claims 1 to 3.

6. Represented by each of the following formulas (5) to (7) 【Chemical Formula 5】 A molding material for a medical device, comprising one or more selected from three kinds of polybutylene succinate copolymers, wherein in the above formulas (5) to (7), n, m, and p are each independently an integer of 2 or more.

7. A method for producing the polybutylene succinate copolymer according to claim 1, A first step of producing a copolymer having the repeating unit (U1) and the repeating unit (U2); A second step of reacting the copolymer with an amphoteric ion compound having a functional group that reacts with a double bond site of the repeating unit (U1) of the copolymer, thereby producing a repeating unit (U3) having an amphoteric ion group R1 and a copolymer containing at least one of the repeating unit (U1) and the repeating unit (U2). A method for producing a polybutylene succinate copolymer.

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