US20090171064A1 - Bio-degradable/ absorbable polymer having reduced metal catalyst content, and process for production thereof - Google Patents

Bio-degradable/ absorbable polymer having reduced metal catalyst content, and process for production thereof Download PDF

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US20090171064A1
US20090171064A1 US12/305,104 US30510407A US2009171064A1 US 20090171064 A1 US20090171064 A1 US 20090171064A1 US 30510407 A US30510407 A US 30510407A US 2009171064 A1 US2009171064 A1 US 2009171064A1
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copolymer
metal catalyst
washing
polymer
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Hidetoshi Arimura
Yoshitake Takahashi
Koji Yamauchi
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Gunze Ltd
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Gunze Ltd
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Priority claimed from JP2006178805A external-priority patent/JP5334360B2/ja
Priority claimed from JP2006178808A external-priority patent/JP5354844B2/ja
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/78—Preparation processes
    • C08G63/82—Preparation processes characterised by the catalyst used
    • C08G63/823—Preparation processes characterised by the catalyst used for the preparation of polylactones or polylactides
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L17/00—Materials for surgical sutures or for ligaturing blood vessels ; Materials for prostheses or catheters
    • A61L17/06—At least partially resorbable materials
    • A61L17/10—At least partially resorbable materials containing macromolecular materials
    • A61L17/12—Homopolymers or copolymers of glycolic acid or lactic acid
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/14—Macromolecular materials
    • A61L27/18—Macromolecular materials obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/50—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
    • A61L27/58—Materials at least partially resorbable by the body
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
    • A61L31/14—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
    • A61L31/148—Materials at least partially resorbable by the body
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
    • C08G63/08—Lactones or lactides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/78—Preparation processes
    • C08G63/82—Preparation processes characterised by the catalyst used
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/88—Post-polymerisation treatment
    • C08G63/90—Purification; Drying
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L101/00—Compositions of unspecified macromolecular compounds
    • C08L101/16—Compositions of unspecified macromolecular compounds the macromolecular compounds being biodegradable

Definitions

  • the present invention relates to a biodegradable and bioabsorbable polymer having a low metal catalyst content (residual content), and a process for producing the same. Specifically, the invention relates to a technique for reducing the content of the metal catalyst in the biodegradable and bioabsorbable polymer obtained after synthesis using the metal catalyst.
  • biodegradable and bioabsorbable polymers include polylactic acid, polyglycolic acid, polycaprolactone, trimethylene carbonate, polydioxane, copolymers thereof, and the like. They are degradable and absorbable in vivo, and are thus used in medical implant applications such as sutures, bone-joining materials, etc.
  • the metal catalyst Since a heavy metal-based catalyst such as tin octylate is widely used for the synthesis of such a polymer compound, the metal catalyst remains in the synthesized polymer compound.
  • the metal catalyst When the polymer compound is used as a material for a medical implant application, the metal catalyst is exposed to the body with the degradation of the polymer.
  • the metal catalyst which varies according to species, may have harmful effects on the human body such as immunotoxicity, genetic toxicity, neurotoxicity, etc. when present at a certain concentration or more. Therefore, when the polymer is used in a medical implant application, the metal catalyst residual content must be reduced as much as possible.
  • polymers for implant applications require features of a certain level or more of molecular weight, strength, etc.
  • a metal catalyst of a certain amount or more must be added during the polymerization process; it is thus required to remove the metal catalyst remaining in the polymer after the polymerization reaction.
  • removal of the metal catalyst is not easy, and is often accompanied by industrial difficulties.
  • Patent Document 1 For example, in a method described in Patent Document 1, a polymer compound is first dissolved in an organic solvent, and a metal catalyst is then removed by reprecipitation.
  • This method requires a large amount of solvent, and causes a drastic drop in molecular weight due to the polymer dissolution. Therefore, this is not appropriate for producing materials (e.g., medical devices) that require strength of a certain level or more.
  • materials e.g., medical devices
  • the polymer tends to contain many air bubbles when reprecipitated, the molded product of the polymer is also likely to contain bubbles. Thus, it is not suitable for industrial manufacture.
  • Patent Document 2 discloses a method for producing copolymers of lactide and ⁇ -caprolactone; however, it does not disclose the final metal catalyst content.
  • the publication discloses that the catalyst is used in an amount of 10 ⁇ 7 to 10 ⁇ 3 mol/mol relative to the monomers; however, the Examples merely disclose that a catalyst is added in an amount of 10 ⁇ 5 mol (metal content: 22 ppm) per mol of monomer. The further reduction of the metal catalyst content is not specifically disclosed.
  • Patent Document 3 discloses a method for obtaining a biodegradable and bioabsorbable polymer having a high molecular weight by adding 1 to 20 ppm of a metal catalyst and 0.01 to 0.5 wt % of higher alcohol to lactide and caprolactone, and by conducting polymerization under reduced pressure for 10 to 40 days.
  • a metal catalyst and 0.01 to 0.5 wt % of higher alcohol to lactide and caprolactone
  • the polymer has different properties (e.g., absorbability, safety) than previously used bioabsorbable polymers, and thus various examinations are required.
  • the metal catalyst content used is too small, a long polymerization period is required. It is therefore not industrially preferable.
  • Patent Document 1
  • Patent Document 2
  • Patent Document 3
  • the object of the present invention is to provide a safe biodegradable and bioabsorbable polymer having an extremely low metal catalyst content, while retaining the properties desired for a medical implant or the like; and a process for producing the same.
  • the present invention further aims to provide a method for reducing the content of a metal catalyst in a biodegradable and absorbable polymer that can be applied on an industrial scale.
  • a biodegradable and bioabsorbable polymer that is obtained by copolymerizing lactide (lactic acid cyclic dimer) and ⁇ -caprolactone at a specified molar ratio in the presence of a metal catalyst is capable of having a metal catalyst content of less than 1 ppm in terms of a metal by washing the polymer with the mixed solvent containing acetic acid and isopropanol at a specified volume ratio.
  • the present inventors found that the metal catalyst can be effectively removed, without causing a drastic drop in molecular weight, by copolymerizing lactide (lactic acid cyclic dimer) and ⁇ -caprolactone at a molar ratio ranging from 40/60 to 60/40 using a metal catalyst to produce a copolymer, and washing the copolymer with a mixed solvent comprising acetic acid and isopropanol at a volume ratio ranging from 25/75 to 45/55, and drying the copolymer.
  • lactide lactic acid cyclic dimer
  • ⁇ -caprolactone a metal catalyst to produce a copolymer
  • washing the copolymer with a mixed solvent comprising acetic acid and isopropanol at a volume ratio ranging from 25/75 to 45/55, and drying the copolymer.
  • this invention is sometimes referred to as “First Embodiment”.
  • the present inventors further found that the metal catalyst can be effectively removed, without causing a drastic drop in molecular weight, by copolymerizing lactide (lactic acid cyclic dimer) and ⁇ -caprolactone at a molar ratio ranging from 65/35 to 85/15 using a metal catalyst to produce a copolymer, and washing the copolymer with a mixed solvent comprising acetic acid and isopropanol at a volume ratio ranging from 45/55 to 55/45, and drying the copolymer.
  • lactide lactic acid cyclic dimer
  • ⁇ -caprolactone at a molar ratio ranging from 65/35 to 85/15
  • washing the copolymer with a mixed solvent comprising acetic acid and isopropanol at a volume ratio ranging from 45/55 to 55/45, and drying the copolymer.
  • this invention is sometimes referred to as “Second Embodiment”.
  • the biodegradable and bioabsorbable polymer of the present invention is a lactide/ ⁇ -caprolactone copolymer, which comprises lactide and ⁇ -caprolactone at a molar ratio ranging from 40/60 to 60/40, and preferably 45/55 to 55/45.
  • the biodegradable and bioabsorbable polymer of the invention has a weight average molecular weight (Mw) of about 50,000 to about 800,000, and particularly about 100,000 to about 500,000. Within the range described above, the polymer is suitably used as a medical implant in view of properties such as strength, degradability, and processability.
  • a metal included in the biodegradable and bioabsorbable polymer is derived from a metal catalyst used in a polymerization reaction for producing the biodegradable and bioabsorbable polymer mentioned below.
  • metals include sodium, potassium, aluminium, titanium, zinc, tin, etc.
  • tin octylate when used in the polymerization reaction, tin will be the main metal contained in the polymer.
  • the biodegradable and bioabsorbable polymer of the present invention has an extremely low metal catalyst content of less than 1 ppm in terms of a metal.
  • the content of the metal catalyst (in terms of a metal) in the polymer is preferably 0.1 to 0.95 ppm, more preferably 0.1 to 0.7 ppm, and further preferably 0.1 to 0.5 ppm.
  • the metal catalyst content (in terms of a metal) is measured as follows. A sulfuric acid/nitric acid mixture (1:1, volume ratio) is added to the polymer, and then heated to degrade an organic component. Metal in the resulting mixture is quantified using a plasma emission spectrometry machine with reference to a metal standard solution.
  • Test Example I-1(1) illustrates a measurement example in which tin octylate is used as a catalyst.
  • the biodegradable and bioabsorbable polymer of the present invention having a low metal catalyst content is produced by polymerizing lactide and ⁇ -caprolactone in the presence of a metal catalyst to produce a copolymer, washing the copolymer with a mixed solvent comprising acetic acid and isopropanol at a volume ratio ranging from 25/75 to 45/55, and drying the copolymer.
  • the metal catalyst content (in terms of a metal) in the biodegradable and bioabsorbable polymer can be reduced to less than 1 ppm.
  • metal catalysts include those containing sodium, potassium, aluminium, titanium, zinc, tin, or like groups. Specific examples include sodium ethoxide, potassium-t-butoxide, triethylaluminum, tetrabutyl titanate, tin octylate (II), tin 2-ethylhexanoate, triphenyltin acetate, tin oxide, dibutyltin oxide, tin oxalate, tin chloride, dibutyltin dilaurate, etc. Of these, tin octylate (II) is preferable in view of reactivity and safety in the polymerization reaction.
  • the used amount of the metal catalyst is about 100 to about 1,000 ppm (about 29 to about 290 ppm in terms of a metal), and preferably about 200 to about 700 ppm (48 to 203 ppm in terms of a metal) relative to the mixture weight content of lactide and ⁇ -caprolactone.
  • a copolymer that has a molecular weight, strength, or like properties suitable for implant applications can be produced in a shorter period of time.
  • the amount of metal catalyst to be added is too small, a large number of monomers remain unreacted, or the reaction requires too much time, resulting in a polymer that is unsuitable for industrial manufacture. Further, a polymer having a large polymerization degree (a high molecular weight) cannot be obtained, and it is thus not preferable.
  • the copolymer can be produced by subjecting lactide and 6-caprolactone to a publicly known polymerization reaction such as bulk polymerization, in the presence of a metal catalyst.
  • a publicly known polymerization reaction such as bulk polymerization
  • the lactide and ⁇ -caprolactone are introduced in a reaction vessel, and then the metal catalyst is added thereto such that the metal catalyst is contained in an amount of about 200 to about 700 ppm (48 to 203 ppm in terms of a metal).
  • Bulk polymerization is then carried out under a nitrogen atmosphere, or under reduced pressure according to a known method for 2 to 20 days at 110 to 180° C.
  • the weight average molecular weight (Mw) of the resulting lactic acid- ⁇ -caprolactone copolymer is about 50,000 to about 800,000, and preferably about 100,000 to about 500,000.
  • the content of the metal catalyst (in terms of a metal) in the copolymer is equivalent to the content of the metal derived from the metal catalyst used in the polymerization reaction, i.e., 48 to 203 ppm.
  • the content (bath ratio) of the mixed solvent used in the washing is, for example, not less than 1 L, preferably not less than 3 L, and more preferably in the range of about 3 to about 10 L per washing, relative to 1 kg of dry weight of the polymer.
  • the washing method employed is such that the polymer is immersed in the mixed solvent having a temperature of less than 40° C., and preferably about 15 to about 30° C., and then stirred.
  • the mixed solvent is changed 5 times or more, and preferably about 6 to about 12 times.
  • the washing process takes a total of 48 hours or more, and preferably about 48 to about 96 hours.
  • acetic acid be removed washing the polymer with isopropanol to prevent the molecular weight reduction after long storage.
  • the biodegradable and bioabsorbable polymer of the present invention is produced in the aforementioned process.
  • the metal catalyst content (in terms of a metal) of the biodegradable and bioabsorbable polymer is less than 1 ppm, preferably 0.1 to 0.95 ppm, more preferably 0.1 to 0.7 ppm, and further preferably 0.1 to 0.5 ppm.
  • the weight average molecular weight (Mw) of the biodegradable and bioabsorbable polymer is about 50,000 to about 800,000, preferably about 100,000 to about 650,000, and more preferably about 210,000 to about 500,000.
  • Mw weight average molecular weight
  • the retention rate of the weight average molecular weight of the copolymer after washing relative to that before washing is 75% or more, and further 80% or more. According to the method of the present invention, the molecular weight reduction during the washing process can be suppressed as much as possible.
  • the biodegradable and bioabsorbable polymer of the present invention has an extremely low metal catalyst content of less than 1 ppm (in terms of a metal), and is safe when embedded in the body.
  • Another feature of the invention is its easy general fabrication. Therefore, it is suitably used as a material for a medical device (a medical implant, etc.).
  • medical implants include sutures, bone-joining materials, fracture fixation materials, tissue supplementation materials, tissue reinforcing materials, tissue covering materials, tissue regenerating base materials, tissue prosthetic materials, anti-adhesive materials, artificial blood vessels, artificial valves, stents, clips, fiber cloths, hemostatic materials, adhesives, coating agents, etc., which can be made by known production methods.
  • the biodegradable and bioabsorbable polymer of the present invention is a lactide/ ⁇ -caprolactone copolymer, which comprises lactide and ⁇ -caprolactone at a molar ratio ranging from 65/35 to 85/15, and preferably 70/30 to 80/20.
  • the biodegradable and bioabsorbable polymer of the invention has a weight average molecular weight (Mw) of about 50,000 to about 800,000, and particularly about 100,000 to about 500,000. Within the range described above, the polymer is suitably used as a medical implant in view of properties such as strength, degradability, and processability.
  • a metal included in the biodegradable and bioabsorbable polymer is derived from a metal catalyst used in a polymerization reaction for producing the biodegradable and bioabsorbable polymer mentioned below.
  • metals include sodium, potassium, aluminium, titanium, zinc, tin, etc.
  • tin octylate when used in the polymerization reaction, tin will be the main metal contained in the polymer.
  • the biodegradable and bioabsorbable polymer of the present invention has an extremely low metal catalyst content of less than 1 ppm in terms of a metal.
  • the content of the metal catalyst (in terms of a metal) in the polymer is preferably 0.1 to 0.95 ppm, more preferably 0.1 to 0.7 ppm, and further preferably 0.1 to 0.5 ppm.
  • the metal catalyst content (in terms of a metal) is measured as follows. A sulfuric acid/nitric acid mixture (1:1 volume ratio) is added to the polymer, and then heated to degrade an organic component. Metal in the resulting mixture is quantified using a plasma emission spectrometry machine with reference to a metal standard solution.
  • Test Example II-1(1) illustrates a measurement example in which tin octylate is used as a catalyst.
  • the biodegradable and bioabsorbable polymer of the present invention having a low metal catalyst content is produced by polymerizing lactide and ⁇ -caprolactone in the presence of a metal catalyst to produce a copolymer, washing the copolymer with a mixed solvent comprising acetic acid and isopropanol at a volume ratio ranging from 45/55 to 55/45, and drying the copolymer.
  • the metal catalyst content (in terms of a metal) in the biodegradable and bioabsorbable polymer can be reduced to less than 1 ppm.
  • the copolymer is produced by copolymerizing lactide and ⁇ -caprolactone in the presence of a metal catalyst.
  • a lactic acid forming the lactide may be any one of the following: L-form, D-form, or DL-form, but is preferably L-form.
  • metal catalysts include those containing sodium, potassium, aluminium, titanium, zinc, tin, or like groups. Specific examples include sodium ethoxide, potassium-t-butoxide, triethylaluminum, tetrabutyl titanate, tin octylate (II), tin 2-ethylhexanoate, triphenyltin acetate, tin oxide, dibutyltin oxide, tin oxalate, tin chloride, dibutyltin dilaurate, etc. Of these, tin octylate (II) is preferable in view of reactivity and safety in the polymerization reaction.
  • the used amount of the metal catalyst is about 100 to about 1,000 ppm (about 29 to about 290 ppm in terms of a metal), and preferably about 200 to about 700 ppm (48 to 203 ppm in terms of a metal) relative to the mixture weight content of lactide and ⁇ -caprolactone.
  • a copolymer that has a molecular weight, strength, or like properties suitable for implant applications can be produced in a shorter period of time.
  • the amount of metal catalyst to be added is too small, a large number of monomers remain unreacted, or the reaction requires too much time, resulting in a polymer that is unsuitable for industrial manufacture. Further, a polymer having a large polymerization degree (a high molecular weight) cannot be obtained, and it is thus not preferable.
  • the copolymer can be produced by subjecting lactide and ⁇ -caprolactone to a publicly known polymerization reaction such as bulk polymerization, in the presence of a metal catalyst.
  • a publicly known polymerization reaction such as bulk polymerization
  • the lactide and ⁇ -caprolactone are introduced in a reaction vessel, and then the metal catalyst is added thereto such that the metal catalyst is contained in an amount of about 200 to about 700 ppm (48 to 203 ppm in terms of a metal).
  • Bulk polymerization is then carried out under a nitrogen atmosphere, or under reduced pressure according to a known method for 2 to 20 days at 110 to 180° C.
  • the weight average molecular weight (Mw) of the resulting lactic acid- ⁇ -caprolactone copolymer is about 50,000 to about 800,000, and preferably about 100,000 to about 500,000.
  • the content of the metal catalyst (in terms of a metal) in the copolymer is equivalent to the content of the metal derived from the metal catalyst used in the polymerization reaction, i.e., 48 to 203 ppm.
  • the metal catalyst content (in terms of a metal) is reduced to less than 1 ppm by washing the copolymer obtained above in step (1) in a mixed solvent containing acetic acid and isopropanol at a volume ratio of 45/55 to 55/45 at lower than 40° C.
  • the copolymer be pulverized using a grinder or the like into particles having an average particle diameter of about 0.3 to about 4 mm in order to improve the washing efficiency of the copolymer with a high metal content.
  • the average particle diameter is measured using the following methods: Screening the particles using sieves having various mesh sizes, and calculating the average particle diameter based on the weight ratio of each of the screened portions; or taking a certain amount of the particles, and observing the diameter of each of the particles by means of a microscope.
  • the washing solvent is a mixture comprising acetic acid and isopropanol.
  • the mixed solvent has a function of permeating through the pulverized polymer to allow the acetic acid and metal catalyst to produce a chelate complex, which is to be extracted into the solution.
  • the volume ratio of acetic acid and isopropanol in the mixed solvent is in the range of 45/55 to 55/45, and preferably in the range of 47/53 to 53/47. If necessary, a small amount of ethyl acetate can be added in addition to the isopropanol. In this case, the amount of ethyl acetate is 20% or less by volume, and preferably about 10% by volume relative to the amount of isopropanol.
  • the content (bath ratio) of the mixed solvent used in the washing is, for example, not less than 1 L, preferably not less than 3 L, and more preferably in the range of about 3 to about 10 L per washing, relative to 1 kg of dry weight of the polymer.
  • the washing method employed is such that the polymer is immersed in the mixed solvent having a temperature of less than 40° C., and preferably about 15 to about 30° C., and then stirred.
  • the mixed solvent is changed 4 times or more, and preferably about 5 to about 9 times.
  • the washing process takes a total of 30 hours or more, and preferably about 30 to about 72 hours.
  • the bath ratio of the solvent be relatively increased (for example, about 4 to about 8 L relative to 1 kg of dry weight of the polymer), and/or that the exchange time of the washing solvent be shortened each time.
  • the bath ratio of the solvent be minimized (about 3 to about 6 L relative to 1 kg of dry weight of the polymer), and/or that the washing time be prolonged.
  • the acetic acid be removed by washing the polymer with isopropanol to prevent the molecular weight reduction after long storage.
  • the polymer after washing undergoes a drying process.
  • the drying is conducted at about 15 to about 60° C., and preferably about 20 to about 50° C., for 6 hours or more, and preferably for about 10 to 150 hours, to remove an organic solvent. It is preferable that pre-drying be first performed at about 20 to about 35° C. for about 10 to about 30 hours to remove isopropanol, and then drying be performed at about 35 to about 50° C. for about 40 to about 100 hours. Both drying processes are conducted under normal to reduced pressure (for example, about 0.01 to about 0.1 Pa), and are preferably conducted in vacuo at about 0.01 to about 0.05 Pa. The molecular weight reduction of the polymer can be prevented as much as possible by employing such drying conditions.
  • the biodegradable and bioabsorbable polymer of the present invention is produced in the aforementioned process.
  • the metal catalyst content (in terms of a metal) of the biodegradable and bioabsorbable polymer is less than 1 ppm, preferably 0.1 to 0.95 ppm, more preferably 0.1 to 0.7 ppm, and further preferably 0.1 to 0.5 ppm.
  • the weight average molecular weight (Mw) of the biodegradable and bioabsorbable polymer is about 50,000 to about 800,000, preferably about 100,000 to about 650,000, and more preferably about 210,000 to about 500,000.
  • Mw weight average molecular weight
  • the retention rate of the weight average molecular weight of the copolymer after washing relative to that before washing is 75% or more, and further 80% or more. According to the method of the present invention, the molecular weight reduction during the washing process can be suppressed as much as possible.
  • the biodegradable and bioabsorbable polymer of the present invention has an extremely low metal catalyst content of less than 1 ppm (in terms of a metal), and is safe when embedded in the body.
  • Another feature of the invention is its easy general fabrication. Therefore, it is suitably used as a material for a medical device (a medical implant, etc.).
  • medical implants include sutures, bone-joining materials, fracture fixation materials, tissue supplementation materials, tissue reinforcing materials, tissue covering materials, tissue regenerating base materials, tissue prosthetic materials, anti-adhesive materials, artificial blood vessels, artificial valves, stents, clips, fiber cloths, hemostatic materials, adhesives, coating agents, etc., which can be made by known production methods.
  • a biodegradable and bioabsorbable polymer having a reduced content of metal derived from a metal catalyst used in a polymerization reaction, and a small reduction in molecular weight can be obtained by washing the polymer obtained after a lactide and ⁇ -caprolactone copolymerization reaction with a mixed solvent containing acetic acid and isopropanol at a specified ratio, and drying the polymer.
  • the resulting biodegradable and bioabsorbable polymer is comparable to known polymers in physicochemical properties, and can be processed by a general industrial method. Thus, it is suitably used as a material for a medical application (a medical implant).
  • FIG. 1 is a graph showing the relationship between the drying temperature and the molecular weight retention rate of the polymer obtained in Test Example I-3.
  • FIG. 2 is a graph showing the relationship between the drying temperature and the molecular weight retention rate of the polymer obtained in Test Example II-3.
  • Lactide and ⁇ -caprolactone (50:50, molar ratio) was introduced into a reaction glass tube, and 300 ppm of tin octylate (87 ppm in terms of a tin metal) was added thereto.
  • Polymerization was performed under a nitrogen atmosphere using a known method to thereby obtain a polymer having a weight average molecular weight of 400,000.
  • the polymer was pulverized using a grinder into a granulated polymer having a mean particle diameter of 3.0 mm. The amount of tin remaining in the polymer was 80 ppm.
  • the average particle diameter was determined from the weight ratio using sieves having different mesh sizes.
  • the polymer obtained in Production Example I-1 was immersed in, per 1 kg by weight of the polymer, 5 L of the mixed solution shown in Table 1, and stirred at 20° C. for 4 hours using a stirring device. The solution was replaced and stirred for 4 hours. Further, the solution was replaced, and stirred again for 16 hours. This series of procedures was repeated three times. Specifically, the polymer was washed with a solution having the same components nine times, for 72 hours in total. Subsequently, the polymer was immersed in 5 L of isopropanol, and stirred at 20° C. for one hour. Further, the solution was replaced, and washed under stirring with isopropanol for one hour.
  • the resulting polymer was vacuum-dried at 30° C. for 24 hours (0.01 Pa), and then vacuum-dried at 40° C. for 48 hours to remove a solvent.
  • the resulting polymer was measured for the metal catalyst content (residual tin content) and molecular weight retention rate. The results are shown in Table 1. The measuring methods are as follows.
  • the resulting polymer was added to a sulfuric acid/nitric acid mixture (1:1, volume ratio), and gradually heated to degrade an organic component.
  • a commercially available tin standard solution tin chloride dihydrate, produced by Wako Pure Chemical Industries, Ltd.
  • tin chloride dihydrate produced by Wako Pure Chemical Industries, Ltd.
  • a plasma emission spectrometry machine a CID-AP model, produced by Nippon Jarrell-Ash Co. Ltd.
  • the polymer was dissolved in chloroform, and the weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC) using polystyrene standards.
  • Mw weight average molecular weight
  • GPC gel permeation chromatography
  • the molecular weight retention rate (%) (the weight average molecular weight of the polymer after washing)/(the weight average molecular weight of the polymer before washing) ⁇ 100
  • Table 1 reveals that the polymers of Examples I-1 to I-3 had a reduced residual tin content, which was derived from the metal catalyst, of less than 1 ppm, kept a high molecular weight retention rate after washing, and had no appearance problem. Further, there was little change in physical properties before and after washing.
  • Comparative Examples I-1 and I-2 the molecular weight retention rate was excellent, but the residual tin content became larger.
  • the polymer in Comparative Example I-3 was dissolved because acetic acid was contained in a large amount.
  • the polymer obtained in Production Example I-1 was immersed in, per 1 kg by weight of the polymer, 5 L of the mixed solution of Example I-1 shown in Table 1. Each solution was stirred at 20° C., 30° C., and 40° C. for 4 hours using a stirring device. The solution was replaced and stirred for 4 hours. Further, the solution was replaced, and stirred again for 16 hours. This series of procedures was repeated three times. Specifically, the mixture was washed with a solution having the same components nine times for 72 hours in total.
  • the polymer sampled was immersed in 100 mL of isopropanol, and stirred at 20° C. for one hour using a stirring device. The solution was replaced and stirred for one hour. Specifically, the solution was washed with isopropanol alone for two hours in total. The resulting polymer was vacuum-dried at 30° C. for 24 hours (0.01 Pa), and vacuum-dried again at 40° C. for 48 hours (0.01 Pa) to remove a solvent.
  • the metal catalyst content (the residual tin content) and the molecular weight retention rate of the resulting polymer were measured. The results are shown in Table 2. The measuring method used was the same as that described in Test Example I-1.
  • Table 2 shows temporal changes of the washing temperature and residual tin content.
  • Table 3 shows temporal changes of the washing temperature and molecular weight retention rate.
  • Table 2 reveals that the residual tin content was reduced at any temperature to less than 1 ppm by the washing method of the present invention.
  • the time required for reducing the residual tin content to less than 1 ppm was the shortest when washing was conducted at 40° C.; however, Table 3 reveals that the molecular weight was greatly reduced with time at 40° C.
  • Table 2 shows that there was no remarkable difference in the time required to achieve a residual tin content of less than 1 ppm between the washing temperature of 20° C. and 30° C.
  • Table 3 shows that the molecular weight retention rate at 20° C. was likely higher than at 30° C.
  • the polymer obtained in Production Example I-1 underwent steps before the drying step in accordance with the washing method of Example I-1 of Test Example I-1.
  • the polymer obtained after washing was dried at 30° C. for 24 hours, and then vacuum-dried (0.01 Pa) at 40° C. for 48 hours or at 70° C. for 12 hours to remove a solvent.
  • FIG. 1 reveals that the molecular weight retention rate of the polymer obtained by drying at 40° C. (Example I-1) is 82.2%; however, the molecular weight retention rate of the polymer obtained by drying at 70° C. was greatly reduced to 61.0%.
  • Lactide and ⁇ -caprolactone (75:25, molar ratio) was introduced into a reaction glass tube, and 300 ppm of tin octylate (87 ppm in terms of a tin metal) was added thereto.
  • Polymerization was performed under a nitrogen atmosphere using a known method to thereby obtain a polymer having a weight average molecular weight of 700,000.
  • the polymer was pulverized using a grinder into a granulated polymer having a mean particle diameter of 3.0 mm.
  • the amount of tin remaining in the polymer was 80 ppm.
  • the average particle diameter was determined from the weight ratio using sieves having different mesh sizes.
  • the polymer obtained in Production Example II-1 was immersed in, per 1 kg by weight of the polymer, 5 L of the mixed solution shown in Table 4, and stirred at 20° C. for 4 hours using a stirring device. The solution was replaced and stirred for 4 hours. Further, the solution was replaced, and stirred again for 16 hours. This series of procedures was repeated two times. Specifically, the polymer was washed with a solution having the same components six times for 48 hours in total. Subsequently, the polymer was immersed in 5 L of isopropanol, and stirred at 20° C. for one hour. Further, the solution was replaced, and washed under stirring with isopropanol for one hour.
  • the resulting polymer was vacuum-dried at 30° C. for 24 hours (0.01 Pa), and then vacuum-dried at 40° C. for 48 hours to remove a solvent.
  • the resulting polymer was measured for the metal catalyst content (residual tin content) and molecular weight. The results are shown in Table 4. The measuring methods are as follows.
  • the resulting polymer was added to a sulfuric acid/nitric acid mixture (1:1, volume ratio), and gradually heated to degrade an organic component.
  • a commercially available tin standard solution tin chloride dihydrate, produced by Wako Pure Chemical Industries, Ltd.
  • tin chloride dihydrate produced by Wako Pure Chemical Industries, Ltd.
  • a plasma emission spectrometry machine a CID-AP model, produced by Nippon Jarrell-Ash Co. Ltd.
  • the polymer was dissolved in chloroform, and the weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC) using a polystyrene standard as a standard.
  • Mw weight average molecular weight
  • GPC gel permeation chromatography
  • the molecular weight retention rate (%) (the weight average molecular weight of the polymer after washing)/(the weight average molecular weight of the polymer before washing) ⁇ 100
  • Table 4 reveals that the polymer of Examples II-1 had a reduced residual tin content, which was derived from the metal catalyst, of less than 1 ppm, kept a high molecular weight retention rate after washing, and had no appearance problem. Further, there was little change in physical properties before and after washing.
  • the polymer obtained in Production Example II-1 was immersed in, per 1 kg by weight of the polymer, 5 L of the mixed solution of Example II-1 shown in Table 4. Each solution was stirred at 20° C. or 40° C. for 4 hours using a stirring device. The solution was replaced and stirred for 4 hours. Further, the solution was again replaced, and stirred again for 16 hours. This series of procedures was repeated two times. Specifically, the mixture was washed with a solution having the same components six times for 48 hours in total.
  • Table 5 reveals that the residual tin content was reduced at any temperature to less than 1 ppm by the washing method of the present invention.
  • the time required for reducing the residual tin content to less than 1 ppm was shorter when the washing was conducted at 40° C.; however, Table 6 reveals that the molecular weight was reduced with time at 40° C.
  • the molecular weight retention rate was kept at a high rate (90% or more) at a washing temperature of 20° C.
  • the polymer obtained in Production Example II-1 underwent steps before the drying step in accordance with the washing method of Example II-1 of Test Example II-1.
  • the polymer obtained after washing was dried at 30° C. for 24 hours, and then vacuum-dried (0.01 Pa) at 40° C. for 48 hours or at 70° C. for 12 hours to remove a solvent.
  • FIG. 2 reveals that the molecular weight retention rate of the polymer obtained by drying at 40° C. (Example II-1) is 78.7%; however, the molecular weight retention rate of the polymer obtained by drying at 70° C. is greatly reduced to 54.6%.

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US20080305144A1 (en) * 2005-08-18 2008-12-11 Brown Malcolm Nmi High Strength Devices and Composites
US20090274742A1 (en) * 2005-08-18 2009-11-05 Brown Malcolm Nmi Multimodal high strength devices and composites
US20110236458A1 (en) * 2007-08-07 2011-09-29 David Franklin Farrar Coating
US8722783B2 (en) 2006-11-30 2014-05-13 Smith & Nephew, Inc. Fiber reinforced composite material
US9000066B2 (en) 2007-04-19 2015-04-07 Smith & Nephew, Inc. Multi-modal shape memory polymers
US9120919B2 (en) 2003-12-23 2015-09-01 Smith & Nephew, Inc. Tunable segmented polyacetal
CN104983484A (zh) * 2015-05-26 2015-10-21 中国人民解放军第一0一医院 一种经导管植入高弹性外支架可降解的生物瓣膜系统及制备和应用
US9527955B2 (en) 2013-04-12 2016-12-27 National University Corporation Kyoto Institute Of Technology Method for producing lactide-lactone copolymer
US9770534B2 (en) 2007-04-19 2017-09-26 Smith & Nephew, Inc. Graft fixation
US9815240B2 (en) 2007-04-18 2017-11-14 Smith & Nephew, Inc. Expansion moulding of shape memory polymers
CN112940234A (zh) * 2021-01-28 2021-06-11 中科院长春应化所黄埔先进材料研究院 一种高纯度聚乙丙交酯的制备方法

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WO2019046748A1 (en) * 2017-08-31 2019-03-07 Evonik Corporation ENHANCED RESORBABLE POLYMER PURIFICATION METHOD
GB2568526A (en) * 2017-11-20 2019-05-22 Rebio Tech Oy Composition
SG11202105332YA (en) * 2018-11-27 2021-06-29 Evonik Operations Gmbh Process for preparing a resorbable polyester as a granulate or powder by bulk polymerization

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9120919B2 (en) 2003-12-23 2015-09-01 Smith & Nephew, Inc. Tunable segmented polyacetal
US20080305144A1 (en) * 2005-08-18 2008-12-11 Brown Malcolm Nmi High Strength Devices and Composites
US20090274742A1 (en) * 2005-08-18 2009-11-05 Brown Malcolm Nmi Multimodal high strength devices and composites
US8722783B2 (en) 2006-11-30 2014-05-13 Smith & Nephew, Inc. Fiber reinforced composite material
US9815240B2 (en) 2007-04-18 2017-11-14 Smith & Nephew, Inc. Expansion moulding of shape memory polymers
US9000066B2 (en) 2007-04-19 2015-04-07 Smith & Nephew, Inc. Multi-modal shape memory polymers
US9308293B2 (en) 2007-04-19 2016-04-12 Smith & Nephew, Inc. Multi-modal shape memory polymers
US9770534B2 (en) 2007-04-19 2017-09-26 Smith & Nephew, Inc. Graft fixation
US20110236458A1 (en) * 2007-08-07 2011-09-29 David Franklin Farrar Coating
US9527955B2 (en) 2013-04-12 2016-12-27 National University Corporation Kyoto Institute Of Technology Method for producing lactide-lactone copolymer
CN104983484A (zh) * 2015-05-26 2015-10-21 中国人民解放军第一0一医院 一种经导管植入高弹性外支架可降解的生物瓣膜系统及制备和应用
CN112940234A (zh) * 2021-01-28 2021-06-11 中科院长春应化所黄埔先进材料研究院 一种高纯度聚乙丙交酯的制备方法

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