JP2008120887A - Flexible biodegradable polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable polymer which improves a hard and brittle property that is a problem of polylactic acid, can be adapted to biological flexible tissues, and has flexibility, to provide a method for producing the same, and to provide a medical treatment material, such as a scaffolding material for regenerating flexible tissues, using the biodegradable polymer. <P>SOLUTION: This flexible biodegradable polymer is characterized by using a biodegradable copolymer comprising hydroxylic acid units and aspartic acid units as a main chain and having mesogenic group-containing side chains on the main chain, and a method for producing the same. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flexible biodegradable polymer having excellent biocompatibility and high elasticity, and a method for producing the same.

  With the innovation and diversification of medical technology, the importance of biodegradable polymers in the medical field is increasing, and degradation controlled drug delivery devices, sutures, bone fixation materials, hemostasis Applications such as adhesives and anti-adhesion membranes that require biodegradable absorbable polymers that can be broken down into non-toxic components in vivo and metabolized and absorbed are increasing. Among them, materials for tissue engineering (regenerative medicine) have attracted particular attention in recent years. In the GTR (guided tissue regeneration) method, which is a tissue engineering technique, cells are cultured using a biodegradable material as a scaffold, and the degradable polymer that provided the scaffold disappears as cells grow and form tissues. Aims to be replaced with normal tissue. (Non-Patent Document 1)

  In this way, medical biodegradable polymer materials can be used for a wide variety of purposes, and the physical properties (biodegradation rate, mechanical properties, bioadhesiveness, etc.) required for each application differ. Yes. For example, temporary substitutes for hard tissues such as bones require the same mechanical properties (hardness and toughness) as bone tissues, whereas materials used in contact with soft tissues such as organs, Flexibility that does not damage the organ when stressed is required. Further, the requirements for cell adhesion are completely opposite between the adhesion-preventing film and the tissue adhesive. Furthermore, the tissue engineering material is required to exhibit a degradation profile suitable for different cell growth rates depending on the target tissue.

  Furthermore, in order to enable recognition from the cell side by specific interaction, it is also an important requirement that chemical modification such as immobilization of a cell affinity ligand is possible. In other words, not only is biocompatibility and safety superior, it is desirable to be able to supply variations in biodegradable materials that satisfy different requirements in terms of biodegradation rate, mechanical and biochemical characteristics, and chemical reactivity. Yes.

  On the other hand, biomedical substances such as collagen, gelatin, and fibrin have been used as medical materials so far, but in recent years, infectious diseases such as bovine spongiform encephalopathy (BSE), Creutzfeldt-Jakob disease, AIDS, and hepatitis. Problems have arisen and it has become clear that natural products are not necessarily safe. There are many voices that manufacturers that provide medical materials make synthetic polymers ideal as materials that do not vary depending on the raw materials, are easy to control quality, and do not contain risk factors derived from living organisms. The biodegradable synthetic polymers that have been most frequently studied and used as medical materials so far are poly-L-lactic acid (PLLA), poly-D-lactic acid (PDLA), and poly-DL-lactic acid (PDLLA). The copolymer is a polylactic acid polymer.

  Polylactic acid is a constituent of the body, lactic acid is a metabolite in the body, is highly safe, has relatively high biocompatibility, is highly crystalline, and can be set to high mechanical strength. The use of has been considered. PLLA, the most common polylactic acid, is synthesized by ring-opening polymerization of L-lactide or direct condensation of L-lactic acid, and has high crystallinity and high strength, so it can be used as a bone support plate and bone fixation screw. It has become. (Non-patent Document 2) However, because PLLA has high crystallinity, depending on the purpose of use, the degradation rate is too slow, and since it is hard and lacks flexibility, it has a drawback that it is poor in adaptability to soft tissues.

  Thus, for example, Patent Document 1 discloses a polymer comprising a sequence based on about 20 to 35 wt% ε-caprolactone and about 65 to 80 wt% glycolide and having a tensile strength of at least 30,000 psi and a Young's modulus of less than 350,000 psi. A sterilized surgical product comprising a molded body and a method for producing the polymer are disclosed. Since the glycolide-caprolactone copolymer disclosed in Patent Document 1 and a surgical product molded from the copolymer have excellent flexibility and mechanical strength, they are used as surgical sutures in the form of monofilaments. There are advantages you can do. However, they are hydrolyzed too quickly and degrade rapidly in vivo. Therefore, it is not satisfactory as a surgical suture or material for an affected part having a long healing period.

  In addition, as a lactide-caprolactone copolymer, for example, Patent Document 2 discloses a biodegradable medical product formed from a copolymer containing 95 to 65 mol% lactic acid units and 5 to 35 mol% caprolactone units. A molded article and a method for producing the same are disclosed. Since the copolymer and the medical molded article disclosed in Patent Document 2 have flexibility, there is an advantage that they can be used as a surgical suture in the form of a monofilament. However, since the mechanical strength is low and the decomposition rate in the living body is too slow, it is not preferable because it exists longer in the living body than necessary. It has already been found that materials that remain in the body for a long time cause many secondary diseases such as inflammation and carcinogenesis.

  Furthermore, the materials that have been developed so far have such low stretchability that it can be said that they have no ability to recover deformation such as tension and compression, and it has become a challenge today to modify this property. . In particular, in the medical field, development of materials having mechanical properties similar to those of tissues and organs in the living body is expected. It has been found that when an artificial material having a mechanical characteristic completely different from that of an organ in a living body is implanted, a biological reaction due to a difference in followability to expansion and contraction occurs in the living body. For example, in the case of an artificial blood vessel, the blood vessel in the living body expands and contracts due to blood pressure. However, in a conventional artificial blood vessel, a material having no stretchability causes a secondary strain at the anastomosis portion between the artificial blood vessel and the blood vessel. It has been found that a natural reaction is induced, and the development of a material having elasticity similar to that of blood vessels is also eagerly desired in a scaffold for revascularization using a biodegradable material. Since the same phenomenon occurs in other organs, the development of biodegradable materials having stretchable properties is expected.

  By the way, while maintaining or improving the excellent properties of polylactic acid polymers such as PLLA, attempts have been made to expand applications and control physical properties by chemical modification. For example, Non-Patent Documents 3 to 6 include polymer synthesis techniques such as random and block copolymerization with a cyclic comonomer having a functional group, a polymerization reaction using a functional molecule having a hydroxyl group as a starting species, and graft polymerization. Utilizing this, lactic acid copolymers having various molecular forms (random, block, graft, branched structure) and chemical properties (reactive functional groups, hydrophilicity / hydrophobicity) have been synthesized.

  Specifically, 1) depsipeptide-lactic acid / random copolymer having a reactive functional group on the side chain (Non-patent Documents 7 to 10), 2) depsipeptide-lactic acid / block copolymer having a reactive functional group on the side chain Polymers (Non-Patent Documents 11 to 12), 3) Comb-shaped polylactic acid (Non-Patent Documents 13 to 14), 4) Hyperbranched polylactic acid (Non-patent Document 15), 5) Polylactic acid grafted polysaccharide (Non-patent Document) 16-17) and the like are synthesized.

In this way, various types of polylactic acid-based polymers have been developed, but they have biocompatibility, can be easily chemically modified, can control biodegradation behavior as needed, and can be applied to soft tissues. At present, no material having flexibility and elasticity that can be adapted has been obtained.
JP 59-82865 JP-A 64-56055 Langer R, et al: Tissue engineering. Science 1993, 260: 920-926, Freed LE, et al: J Biomed Mater Res 1993, 27: 11-23. Hidehito Tsuji et al .: Polylactic acid for medical treatment, pharmaceutical preparation and environment. Kyoto, Kobunshi Shuppankai, 1997, 149-160, edited by Biodegradable Plastics Study Group: Biodegradable Plastics Handbook. Tokyo, N. TS, 1995, 279-291, 666-730. Yuichi Oya: Present status and new development of biodegradable polymers. Artificial organ 1999, 28: 582-589 Yuichi Oya, Goro Ouchi: New polylactic acid polymers as biodegradable biomaterials. Polymer processing 1999, 48: 530 Yuichi Oya: Synthesis of a novel biodegradable polymer based on polylactic acid and its application as a biomaterial. Polymer Papers 2002, 59: 484-498 Ouchi Goro, Oya Yuichi: New polylactic acid-based medical materials. Future materials 2002, 2: 30-35. Ouchi T, et al: Macromol Chem Rapid Commun 1993, 14: 825-831. Ouchi T, et al: Macromol Chem Phys 1996, 197: 1833-1833. Ouchi T, et al: J Polym Sci Part A: Polym Chem 1997, 35: 377-383. Ouchi T, et al: J Poly Sci Part A: Poly Chem 1998, 36: 1283-1290. Ouchi T, et al: Designed Monom Polym 2000, 3: 279-287. Ouchi T, et al: J Polym Sci Part A: Polym Chem 2002, 40: 1218-1225. Tasaka F, et al: Macromolecules 1999, 32: 6386-6389 Tasaka F, et al: Macromolecules 2001, 34: 5494-5500. Tasaka F, et al: Macromol Rapid Commun 2001, 22: 820-824. Ohya Y, et al: Macromolecules 1998, 31: 4662-4665. Ohya Y, et al: Macromol Chem Phys 1998, 199: 2017-2022.

  An object of the present invention is to provide a biodegradable polymer having flexibility that can be adapted to living soft tissue, and a method for producing the same, by improving the hard and brittle nature of polylactic acid. Another object of the present invention is to provide a medical material such as a tissue regeneration scaffold for soft tissue using the biodegradable polymer.

  As a result of intensive studies to solve the above problems, the present inventor has a biodegradable copolymer containing a hydroxy acid unit (for example, a lactic acid unit, a glycolic acid unit, etc.) and an aspartic acid unit as a main chain, It has been found that a biodegradable polymer having a side chain containing a mesogenic group (for example, a group consisting of cholesterol) in the main chain has flexibility and the like that can be adapted to living soft tissue. Based on this knowledge, this has been further developed to complete the present invention.

  That is, the present invention provides the following flexible biodegradable polymer and method for producing the same.

  Item 1. A flexible biodegradable polymer comprising a biodegradable copolymer containing a hydroxy acid unit and an aspartic acid unit as a main chain, and having a side chain containing a mesogenic group in the main chain.

  Item 2. Item 2. The flexible biodegradable polymer according to Item 1, wherein the mesogenic group is a group comprising a cholesterol derivative.

  Item 3. Formula (A):

(Wherein R ¹ and R ² independently represent a hydrogen atom or a methyl group, L represents a spacer, R represents a mesogenic group, x represents 20 to 1000, y represents 0 to 100, z represents 2 to 1000, z / (x + y + z) is 0.002 to 0.5, and the arrangement of each unit of x, y, and z is not limited to the order of the arrangement. The described flexible biodegradable polymer.

  Item 4. The spacer represented by L in the general formula (A) is represented by the general formula (B):

(Wherein, W represents —NH— or —O—, and n represents an integer of 2 to 10.)
Item 4. The flexible biodegradable polymer according to item 3, which is a divalent group represented by the formula:

  Item 5. In the general formula (A), the mesogenic group represented by R is represented by the formula (C):

Item 5. The flexible biodegradable polymer according to item 3 or 4, which is a group represented by:

  Item 6. In the general formula (A), x is 50 to 200, y is 0 to 20, z is 5 to 100, x / (x + y + z) is 0.6 to 0.95, z / Item 6. The flexible biodegradable polymer according to Item 3, 4 or 5, wherein (x + y + z) is 0.05 to 0.4.

  Item 7. Item 7. The flexible biodegradable polymer according to any one of Items 1 to 6, wherein the number average molecular weight (Mn) is 3,000 to 500,000.

  Item 8. Item 8. The flexible biodegradable polymer according to any one of Items 1 to 7, wherein the ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight is 1.0 to 5.0.

  Item 9. Item 9. The flexible biodegradable polymer according to any one of Items 1 to 8, wherein the glass transition temperature is 10 to 40 ° C.

  Item 10. Item 10. The flexibility according to any one of Items 1 to 9, wherein the number average molecular weight decreases by 30 to 70% in 50 days when the biodegradation behavior is immersed in phosphate buffered saline (pH 37) at pH = 7.4. Biodegradable polymer.

  Item 11. The flexible biodegradable polymer is formed into a strip-like film having a thickness of about 100 μm and a width of 7.5 mm. When this is subjected to a tensile test, the breaking strength is 0.1 to 2 MPa, the Young's modulus is 0.1 to 2 MPa, and the strain at break Item 11. The flexible biodegradable polymer according to any one of Items 1 to 10, wherein is from 500 to 1000%.

  Item 12. Formula (A):

(Wherein R ¹ and R ² independently represent a hydrogen atom or a methyl group, L represents a spacer, R represents a mesogenic group, x represents 20 to 1000, y represents 0 to 100, z is 2 to 1000, z / (x + y + z) is 0.002 to 0.5, and the arrangement of each unit of x, y, and z is not limited to the order of the arrangement.) A method for producing a degradable polymer, which is represented by the general formula (F):

(Wherein R ¹ , R ² , x, y and z are the same as above)
A carboxylic acid compound represented by the general formula (G):
HO-LR (G)
(In the formula, L and R are the same as above.)
A production method comprising a condensation reaction with an alcohol represented by the formula:

  Item 13. Item 12. A medical material comprising the flexible biodegradable polymer according to any one of Items 1 to 11.

  The flexible biodegradable polymer of the present invention has a biodegradable copolymer containing a hydroxy acid unit and an aspartic acid unit as a main chain, and has a side chain containing a mesogenic group in the main chain. High flexibility is imparted to the polymer by physically cross-linking mesogenic groups that can be converted (self-association) (see, for example, the schematic diagram of FIG. 1). As a result, the hard and brittle nature of polylactic acid can be greatly improved. Moreover, it has the characteristic that it is excellent in molding processability. Furthermore, taking advantage of the flexibility described above, it can be used as a medical material such as a scaffold material for tissue regeneration.

  In addition, the method for producing a flexible biodegradable polymer of the present invention is characterized in that it can be carried out simply and with good yield, and that the polymer can be modified chemically with variations.

1. Flexible biodegradable polymer The flexible biodegradable polymer of the present invention has a biodegradable copolymer containing a hydroxy acid unit and an aspartic acid unit as a main chain, and has a side chain containing a mesogenic group in the main chain. It becomes.

  Examples of the hydroxy acid constituting the main chain include lactic acid, glycolic acid, tartaric acid, malic acid, and mevalonic acid, and α-hydroxy acids such as lactic acid and glycolic acid are preferred. Hydroxy acid may contain 1 type (s) or 2 or more types.

  The side chain is formed using the side chain carboxylic acid of the aspartic acid unit constituting the main chain as a foothold. The side chain means a mesogenic group, that is, an atomic group (group) which exhibits orientation and plays an essential role in liquid crystal expression. For example, cholesterol derivatives (cholesterol, cholic acid, sitosterol, campesterol, A group containing a tigbenzene skeleton, a group containing a biphenyl skeleton, a group containing an azobenzene skeleton, and the like. It is not limited to these.

  As a specific example of the flexible biodegradable polymer of the present invention, the general formula (A):

(Wherein R ¹ and R ² independently represent a hydrogen atom or a methyl group, L represents a spacer, R represents a mesogenic group, x represents 20 to 1000, y represents 0 to 100, z represents 2 to 1000, z / (x + y + z) is 0.002 to 0.5, and the sequence of each unit of x, y, and z is not limited to the above sequence. It is done. That is, a mesogen derived from a main chain containing a lactide (lactic acid dimer) unit or glycolide (glycolic acid dimer) unit, a lactic acid unit or glycolic acid unit, and an aspartic acid unit, and a side chain carboxylic acid of aspartic acid And a side chain containing a group.

R ¹ and R ² each independently represent a hydrogen atom or a methyl group, preferably R ¹ is a methyl group and R ² is a hydrogen atom. When R ¹ and R ² are methyl groups, the carbon atom to which the methyl group is bonded can be an asymmetric carbon. In the copolymer of the present invention, the configuration of the asymmetric carbon may be (R) isomer, (S) isomer, or a mixture thereof.

Here, x, y, and z represent the average number of each unit in the polymer, and are determined from ¹ HNMR and GPC.

  Further, as described above, the arrangement of each unit of x, y, and z may be random or block.

  X in the polymer of the present invention is 20 to 1000, preferably 50 to 200, and more preferably 100 to 200. The lactide unit and glycolide unit are composed of a dimer of lactic acid and a dimer of glycolic acid, respectively, and are derived from lactide (a cyclic dimer of lactic acid) and glycolide (a cyclic dimer of glycolic acid), respectively. . A lactide unit is preferred. The lactide unit may be composed of either L-lactic acid and / or D-lactic acid, but is composed of a mixture of D-lactic acid and L-lactic acid in which the main chain is amorphous, in particular, an equivalent mixture of both. What is constructed is preferred.

  y is 0-100, Preferably it is 0-20, More preferably, it is 0-10.

  z is 2-1000, Preferably it is 5-100, More preferably, it is 10-20.

  x / (x + y + z) is 0.5 to 0.99, preferably 0.6 to 0.95, and more preferably 0.8 to 0.9. When x is in this range, suitable biodegradability and tissue compatibility are imparted to the polymer of the present invention.

  z / (x + y + z) is 0.002 to 0.5, preferably 0.05 to 0.4, and more preferably 0.06 to 0.2. When z is in this range, physical interaction between mesogenic groups is exhibited and flexibility is imparted to the polymer of the present invention.

  The spacer represented by L is a divalent group that binds the side chain carboxylic acid of aspartic acid constituting the polymer main chain of the present invention to the mesogenic group represented by R, and the mesogenic groups are effectively mutually connected. There is no particular limitation as long as it is a group that can maintain a distance that can act.

  Specifically, for example, the general formula (B):

(Wherein, W represents —NH— or —O—, and n represents an integer of 2 to 10). Among these, W is preferably —NH—, n is preferably an integer of 2 to 8, and more preferably an integer of 4 to 6.

  The mesogenic group represented by R is not particularly limited as long as it is an atomic group (group) that exhibits orientation (liquid crystallinity) and plays an essential role in self-assembly (self-association) expression. Specific examples include groups having a liquid crystalline chemical structure such as cholesterol derivatives, biphenyl derivatives, and azobenzene derivatives. By introducing this group, the side chain forms an orientation domain organized between multiple molecules, and the main chain is physically cross-linked by acting as a cross-linking point. The orientation domain acts like a plasticizer to impart flexibility, and as a result, a biodegradable material having both flexibility and tenacity is obtained.

  Specifically, for example, the formula (C):

A group represented by formula (D):

A group containing a skeleton represented by formula (E):

And a group containing a skeleton represented by: In particular, the temperature range showing the orientation is as wide as room temperature to 180 ° C., and from the viewpoint of safety, a group consisting of cholesterol represented by the formula (C) is preferable.

  Cholesterol is a member of steroids such as bile acids and sex hormones, and is present not only as a component of gallstones but also in human blood and as a component of various animal tissues. The mechanism of cholesterol absorption consists of several successive steps. That is, 1) hydrolysis of cholesterol ester 2) dissolution of free cholesterol in mixed micelles, 3) passage of untreated water layer by diffusion and uptake into absorbed cells, 4) esterification of cholesterol in mucosal cells, 5) Cholesterol and ultralow density lipoprotein (VLDL) release into the lymph, all these steps control cholesterol absorption. As described above, since cholesterol is a substance present in the living body, it is preferable from the viewpoint of safety.

  Cholesterol is excreted mainly in the gall, gallbladder, and intestinal tract. In the liver, cholesterol becomes cholic acid and chenocholic acid, excreted as primary bile, and 95% performs enterohepatic circulation. In the intestine, cholic acid is reduced to deoxycholic acid and chenocholic acid is converted to tricholic acid by intestinal bacteria, resulting in secondary bile acids. The bile acid enterohepatic circulation is 25-30 g / day.

  The number average molecular weight (Mn) of the polymer of the present invention is 3,000 to 500,000, preferably 10,000 to 100,000, more preferably 30,000 to 50,000, and the weight average molecular weight (Mw) is It is 3,000 to 500,000, preferably 10,000 to 100,000, more preferably 30,000 to 50,000. Further, the ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight which is an index of the molecular weight distribution is 1.0 to 5.0, preferably 1.0 to 4.0, more preferably 1.0 to 3. .5. The number average molecular weight and the weight average molecular weight can be measured using a known method such as GPC (solvent: dimethylformamide).

  The glass transition temperature is 10 to 40 ° C, preferably 10 to 30 ° C. Moreover, it is desirable not to show melting | fusing point.

  As the polymer biodegradation behavior of the present invention, when immersed in phosphate buffered saline (pH 37) at pH = 7.4, the decrease rate of the number average molecular weight after immersion for 50 days is 30 to 70%, preferably 40 to 60%. The number average molecular weight is measured using GPC.

  When the polymer of the present invention is formed into a strip-like film having a thickness of about 100 μm and a width of 7.5 mm, and subjected to a tensile test, the breaking strength is 0.1 to 2 MPa, preferably 0.5 to 2 MPa, and the Young's modulus is 0.1 to 2 MPa, preferably 0.1 to 1.0 MPa, and the strain at break is 500 to 1000%, preferably 500 to 700%.

2. Polymer Production Method The flexible biodegradable polymer of the present invention can be produced, for example, as follows.

(In the formula, Bzl represents a benzyl group, and R ¹ , R ² , L, R, x, y and z are the same as above.)
The compound represented by the above (1) can be produced according to, for example, T. Ouchi, et. Al., Macromol. Chem. Phys. 197, 1823-1833 (1996), etc. ) Is a commercially available compound.

Subsequently, the compounds represented by the above (1) and (2) are subjected to ring-opening polymerization using a catalyst (such as tin 2-ethylhexanoate) to obtain the compound represented by the above (3). The side chain benzyl ester is converted to a free carboxylic acid by a catalyst (trifluoromethanesulfonic acid: TFMSA, etc.) or hydrogen reduction (H ₂ , Pd / C, etc.) to convert the carboxylic acid compound represented by (F) above. obtain. This reaction can be carried out using a conventional method.

  Furthermore, the carboxylic acid compound represented by the above (F) is represented by the general formula (G) in the presence of a condensing agent (dicyclohexylcarbodiimide and 1-hydroxybenzotriazole: DCC / HOBt, 4-dimethylaminopyridine: DMAP, etc.). The copolymer represented by the above (A) is obtained by reacting with the alcohol compound.

  In this reaction, the alcohol compound represented by the general formula (G) can be used usually in an amount of 1.1 to 2 equivalents relative to the carboxylic acid compound represented by the above (F). For example, methylene chloride, tetrahydrofuran, or dimethylformamide can be used as the reaction solvent, and the reaction temperature is about 0 to 40 ° C. The condensing agent can usually be used in an amount of 1.1 to 2 equivalents relative to the carboxylic acid compound represented by (F) above. For example, with respect to the carboxylic acid compound represented by (F), DCC is about 1.1 to 2 equivalents, HOBt is about 1.1 to 2 equivalents, and DMAP is a catalytic amount.

  Moreover, when the alcohol compound represented by general formula (G) is a compound represented by general formula (G1), it can manufacture as follows, for example.

(Wherein and W are the same as above.)
The compound represented by general formula (G1) is reacted with cholesterol (5) in the presence of carbonyldiimidazole (CDI) (6) and a catalytic amount of DMAP. Get. The compound represented by the general formula (4) is about 1 to 1.5 equivalents and CDI is about 1 to 1.5 equivalents relative to cholesterol (5). As the reaction solvent, for example, methylene chloride, tetrahydrofuran, or dimethylformamide can be used. The reaction temperature is about 0 to 40 ° C. and may be usually room temperature.

  According to the present invention, a biodegradable material having flexibility can be obtained. This material can be formed into a film, thread, or sponge, and a biodegradable material having flexibility can be developed. These can be applied as, for example, medical materials and medical products, electrical appliances, general shaped articles typified by furniture, plastic bottles, containers for general food and drink industries typified by prepared food containers, and the like.

  The material of the present invention can be suitably used as a medical material (material). For example, because it exhibits high mechanical compatibility with soft tissues and tissues that require flexibility such as blood vessels and muscles (myocardium, skeletal muscle, smooth muscle, etc.), in vivo placement used for regeneration of such tissues Useful as a product. Examples include biodegradable implant materials, tissue regeneration scaffold materials, and use in movable parts in regenerative medicine.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Hereinafter, the polymer of the present invention is also referred to as “polylactic acid-cholesterol conjugate” (PDLLA-cholesterol).
[Example 1]
Synthesis of polylactic acid-cholesterol conjugate (1) 425 mg (1.62 mmol) cyclo [Glc-Asp (OBzl)] and 2,103 mg (14.6 mmol) DL-lactide are placed in a polymerization tube, and 20 μl is used as an initiator. A 6.27 mg (16.2 μmol) tin 2-ethylhexanoate dissolved in THF was added and covered with a two-way cock with a thread. Thereafter, the polymerization tube was taken out from the glove box, and THF was solidified with cooling liquid nitrogen. Subsequently, the polymerization tube was connected to a vacuum line, and degassing and argon substitution were repeated three times to melt the solidified THF. This operation was performed three times in total, and after dehydrating THF was completely removed, the polymerization tube was sealed. The polymerization tube was melted at 160 ° C., which is higher than the melting point of cyclo [Glc-Asp (OBzl)], to make a uniform system, and then copolymerized at 135 ° C. for 24 hours. After a predetermined time, it was dissolved in a small amount of chloroform and precipitated in a large amount of diethyl ether. The obtained precipitate was collected and dried under reduced pressure for 24 hours using a vacuum pump to obtain 660 mg of poly {[Glc-Asp (OBzl)]-random-LA}.
(2) 635 mg (190 μmol) of the compound obtained in (1) above was dissolved in 15 ml of trifluoroacetic acid, and 1.7 ml (1.67 mmol) of 1M-TFMSA was added under ice-cooling and stirred for 1 hour. The reaction mixture was then precipitated into a large amount of cold diethyl ether. The obtained precipitate was collected and dried under reduced pressure for 24 hours using a vacuum pump, to obtain 430 mg of poly [(Glc-Asp) -random-LA].

¹ H NMR (CDCl ₃ ), δ (ppm); 1.5 (3H, CHC H ₃ ), 4.6 (2H, OCH ₂ CO), 4.9 (2H, C H ₂ COOH), 5.1 (1H, C H CH ₃ ) .

(3) After 1,000 mg (2.59 mmol) of cholesterol was placed in an eggplant flask and dissolved in 5 ml of methylene chloride, 504 mg (3.10 mmol) of carbonyldiimidazole (CDI) was added and stirred for 6 hours. Thereafter, 320 mg (3.10 mmol) of 5-amino-1-pentanol and 78 mg (0.64 mmol) of 4-dimethylaminopyridine (DMAP) were added and stirred at room temperature for 12 hours. After stirring, methylene chloride was removed with an evaporator and washed on a glass filter with ultrapure water. The collected white powder was dissolved in 50 ml of chloroform and washed 4 times with 50 ml of saturated brine, and then 10 g of anhydrous magnesium sulfate was added to the extracted organic layer and stirred for 2 hours. After filtering insoluble matter, chloroform was removed using an evaporator to obtain a cholesterol derivative having 970 mg of an alkyl chain (spacer).

TLC [CHCl ₃ / CH ₃ OH (6/4)], detect: iodine, Rf value = 0.72. Melting point: 150-151 ° C. ¹ H NMR (CDCl ₃ ), δ (ppm); 0.68 (3H, cholesterol C-18 H), 1.2-1.7 (2H, (CH ₂ ) ₃ ), 2.19-2.42 (2H, cholesterol C-4 H), 3.18 (2H, CH ₂ NH), 3.64 (2H, CH ₂ OH), 5.37 (1H, cholesterol C-6 H).

(4) After dissolving 500 mg (0.30 mmol) of the compound obtained in (2) above in 10 ml of methylene chloride, 74 mg (0.36 mmol) of dicyclohexylcarbodiimide (DCC) was added as a solid, and the mixture was stirred for 2 hours under ice zero. did. Thereafter, 180 mg (0.36 mmol) of the compound obtained in (3) dissolved in 1 ml of methylene chloride and 12 mg (0.10 mmol) of DMAP were added, and the mixture was stirred at room temperature for 12 hours. The produced DCUre was removed by filtration, and the collected filtrate was added dropwise to n-hexane / ethanol (7/3) to form a precipitate. The collected precipitate was dried under reduced pressure for 24 hours to obtain 491 mg of polylactic acid-cholesterol conjugate.

¹ H NMR (CDCl ₃ ), δ (ppm); 0.68 (3H, C-18 H of cholesterol), 1.2-1.7 (H2, (CH ₂ ) ₃ ), 1.56 (3H, CHC H ₃ ), 2.19-2.42 (2H, C-4 H of cholesterol), 2.82-3.08 (2H, CHC H ₂ CO), 3.18 (2H, C H ₂ NH), 3.64 (2H, C H ₂ OH), 4.67 (2H, OCH ₂ CO ), 4.97 (2H, NHC H ₂ CO), 5.37 (1H, C-6 H of cholesterol).

  When the number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of the obtained copolymer were measured by gel filtration chromatography (α-5000 column manufactured by Tosoh Corporation), Mn = 36,000, Mw / Mn = 3 .2.

Moreover, x, y, and z in the obtained copolymer were 187, 3 and 13 from ¹ H NMR, respectively. See FIG.

  Further, when the obtained copolymer was subjected to differential scanning calorimetry (DSC) measurement (DSC-60, manufactured by Shimadzu Corporation), the glass transition temperature was 20 ° C.

  In addition, from FIG. 3, the conspicuous endothermic peak was not observed in the DSC chart of the carboxylic acid compound (PDLLA-COOH) represented by (F) above, whereas the compound obtained in (4) above In polylactic acid-cholesterol conjugate (PDLLA-cholesterol), several new endothermic peaks were detected in the range of 110 ° C to 140 ° C, indicating that cholesterol groups were stacked in the polymer. .

  When a tensile test of the obtained copolymer was performed using a strip-like film having a thickness of about 100 μm and a width of 7.5 mm, the breaking strength was 1.5 MPa, the Young's modulus was 0.86 MPa, and the strain at break was 620%. It was.

[Comparative Example 1]
A tensile test of polylactic acid having a carboxyl group as a side chain in the main chain (hereinafter also referred to as “PDLLA-COOH”) obtained in Example 1 (2) is a film having a strip shape of about 100 μm in width and 7.5 mm in width. As a result, the breaking strength was 2.9 MPa, the Young's modulus was 360 MPa, and the strain at break was 410%.

[Test Example 1]
Polarized microscope observation of polylactic acid-cholesterol conjugate film
360 mg of PDLLA-cholesterol or 360 mg of PDLLA-COOH (polymer concentration 4 wt%) dissolved in 6 ml of chloroform was cast into a Teflon petri dish (Φ = 50). It dried under reduced pressure for 24 hours and obtained the PDLLA-cholesterol film and the PDLLA-COOH film. The thickness of the obtained PDLLA-cholesterol was about 100 μm and was yellow and transparent. In order to analyze the self-assembly behavior of cholesterol groups, the prepared PDLLA-cholesterol film was observed with a polarizing microscope (FIG. 4).

  As a result, when the polarizer was in a crossed Nicol state, only a dark field was observed in the PDLLA-COOH film, but a birefringence pattern was observed in the PDLLA-cholesterol film, indicating that it was an orientation domain. (See, for example, the schematic diagram of FIG. 5). The domain size was shown to be about 50 μm.

[Test Example 2]
Tensile test of polylactic acid-cholesterol conjugate film In order to analyze the mechanical property change of the film accompanying the formation of physical cross-linking domain of cholesterol group, the prepared PDLLA-cholesterol film and PDLLA-COOH film were cut out to 7.5mm × 25mm, A tensile test was conducted at 1 mm / min (FIG. 6).

  As a result, compared to the PDLLA-COOH film, the maximum stress of the PDLLA-cholesterol film was less than half and the elongation at break increased about 1.3 times. From this, it was shown that by introducing a cholesterol group having a self-association property into the side chain of polylactic acid, it is possible to develop a polylactic acid material having both flexibility and tenacity.

  From the graph (Young's modulus) in the upper right of FIG. 6, the Young's modulus of the PDLLA-COOH film was 360 MPa, while the PDLLA-cholesterol film was 0.86 MPa. This shows that the PDLLA-cholesterol film can follow even weaker stresses.

[Test Example 3]
Biodegradability test of polylactic acid-cholesterol conjugate film Films prepared PDLLA-cholesterol film and PDLLA-COOH film were cut out to 7.0mm × 7.0mm in order to analyze the biodegradation behavior of the film accompanying the introduction of cholesterol groups. The sample was immersed in phosphate buffered saline (37 ° C.) at pH = 7.4. After a predetermined time (1, 2, 4, 7, 14, 28, 50 days), the film was washed out with ultrapure water, lyophilized, freeze-dried, and the film was weighed and GPC measured. The reduction ratio of the weight and number average molecular weight was determined. PDLLA-COOH film was completely dissolved in phosphate buffered saline in the first day, but the supernatant obtained by lyophilizing the supernatant of the phosphate buffered saline and removing the water was measured by GPC. The number average molecular weight was obtained.

  FIG. 7 shows the biodegradable behavior of PDLLA-COOH film and PDLLA-cholesterol film in PBS (pH = 7.4) at 37 ° C. (in vitro). (A) shows the relationship of time-weight reduction rate, and (B) shows the relationship of time-molecular weight reduction rate. The weight reduction rate after t (days) is derived from the following formula.

Weight reduction ratio (wt%) = [(W ₀ −W _t ) / W _0] × 100
W ₀ represents an initial weight (g), and W _t represents a weight (g) after t (days).

  As a result, the weight loss rate of the PDLLA-cholesterol film was significantly reduced as compared with the PDLLA-COOH film. This is considered to be due to the formation of a network of amorphous PDLLA accompanying the self-assembly of cholesterol groups in addition to the decrease in hydrophilic functional groups in the polymer main chain.

It is a schematic diagram of the flexible biodegradable polymer of this invention. The ¹ H NMR chart and representative proton assignments of the polylactic acid-cholesterol conjugate obtained in Example 1 are shown. The differential scanning calorimetry (DSC) measurement result of the polylactic acid-cholesterol conjugate obtained in Example 1 is shown. 2 is a polarizing micrograph of a polylactic acid-cholesterol conjugate (PDLLA-cholesterol) film of Example 1 and a polylactic acid (PDLLA-COOH) film of Comparative Example 1. FIG. 1 is a schematic diagram of a liquid crystal domain of a polylactic acid-cholesterol conjugate (PDLLA-cholesterol) film of Example 1. FIG. The result of the tension test of the polylactic acid-cholesterol conjugate (PDLLA-cholesterol) film of Example 1 and the polylactic acid (PDLLA-COOH) film of Comparative Example 1 is shown. Polylactic acid-cholesterol conjugate (PDLLA-cholesterol) film of Example 1 (▲) and polylactic acid (PDLLA-COOH) film of Comparative Example 1 in PBS (pH = 7.4) at 37 ° C. (in vitro) (■) shows biodegradable behavior.

Claims (13)

  A flexible biodegradable polymer comprising a biodegradable copolymer containing a hydroxy acid unit and an aspartic acid unit as a main chain, and having a side chain containing a mesogenic group in the main chain.   The flexible biodegradable polymer according to claim 1, wherein the mesogenic group is a group comprising a cholesterol derivative. Formula (A):

(Wherein R ¹ and R ² independently represent a hydrogen atom or a methyl group, L represents a spacer, R represents a mesogenic group, x represents 20 to 1000, y represents 0 to 100, z represents 2 to 1000, z / (x + y + z) is 0.002 to 0.5, and the arrangement of each unit of x, y, and z is not limited to the order of the arrangement. The flexible biodegradable polymer described in 1. The spacer represented by L in the general formula (A) is represented by the general formula (B):

(Wherein, W represents —NH— or —O—, and n represents an integer of 2 to 10.)
The flexible biodegradable polymer according to claim 3, which is a divalent group represented by the formula: In the general formula (A), the mesogenic group represented by R is represented by the formula (C):

The flexible biodegradable polymer according to claim 3 or 4, which is a group represented by the formula:   In the general formula (A), x is 50 to 200, y is 0 to 20, z is 5 to 100, x / (x + y + z) is 0.6 to 0.95, z / 6. The flexible biodegradable polymer according to claim 3, 4 or 5, wherein (x + y + z) is 0.05 to 0.4.   The number average molecular weight (Mn) is 3,000 to 500,000. The flexible biodegradable polymer according to any one of claims 1 to 6.   The ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight is 1.0 to 5.0. The flexible biodegradable polymer according to any one of claims 1 to 7.   The flexible biodegradable polymer according to any one of claims 1 to 8, which has a glass transition temperature of 10 to 40 ° C.   The softness according to any one of claims 1 to 9, wherein the biodegradation behavior reduces the number average molecular weight by 30 to 70% in 50 days when immersed in phosphate buffered saline (pH 37) at pH = 7.4. Biodegradable polymer.   The flexible biodegradable polymer is formed into a strip-like film having a thickness of about 100 μm and a width of 7.5 mm. When this is subjected to a tensile test, the breaking strength is 0.1 to 2 MPa, the Young's modulus is 0.1 to 2 MPa, and the strain at break The flexible biodegradable polymer according to any one of claims 1 to 10, which has a content of 500 to 1000%. Formula (A):

(Wherein R ¹ and R ² independently represent a hydrogen atom or a methyl group, L represents a spacer, R represents a mesogenic group, x represents 20 to 1000, y represents 0 to 100, z is 2 to 1000, z / (x + y + z) is 0.002 to 0.5, and the arrangement of each unit of x, y, and z is not limited to the order of the arrangement.) A method for producing a degradable polymer, which is represented by the general formula (F):

(Wherein R ¹ , R ² , x, y and z are the same as above)
A carboxylic acid compound represented by the general formula (G):
HO-LR (G)
(In the formula, L and R are the same as above.)
A production method comprising a condensation reaction with an alcohol represented by the formula:   The medical material containing the flexible biodegradable polymer in any one of Claims 1-11.

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