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Surgical Suture Patent
 

Bioabsorbable surgical suture coating

Surgical suture abstract

A bioabsorbable coating for a surgical suture or ligature is disclosed. The coating is manufactured from a diblock or a triblock copolymer.

Surgical suture claims

We claim:

1. A bioabsorbable coating for a surgical suture or ligature comprising a diblock copolymer having a first block comprising a polyalkylene oxide and a second block consisting essentially of glycolic acid ester and trimethylene carbonate linkages such that said diblock copolymer has a melting point (Tm) less than 65 degrees centigrade and a glass transition temperature (Tg) less than 20 degrees centigrade and is soluble in methylene chloride or chloroform or both.

2. A coating of claim 1 wherein the polyalkylene oxide block is from 5 to 25 percent by weight of the copolymer.

3. A coating of claim 1 wherein the number average molecular weight of the polyalkylene oxide block is from about 4000 to 30000.

4. A coating of claim 1 wherein the polyalkylene oxide block is derived from a polyalkylene oxide terminated on one end by a C.sub.1 to C.sub.6 alkyl group and on the other end by a hydroxyl group.

5. A coating of claim 4 wherein the polyalkylene oxide block is derived from a homopolymer of ethylene oxide.

6. A coating of claim 4 wherein the polyalkylene oxide block is derived from a block or random copolymer of ethylene oxide and a cyclic ether.

7. A coating of claim 6 wherein the cyclic ether is selected from the group consisting of ##STR9## wherein x is 2 to about 9 y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.

8. A coating of claim 4 wherein the polyalkylene oxide block is derived from a block or random copolymer of a first cyclic ether selected from the group consisting of ##STR10## wherein x is 2 to about 9 and a second cyclic ether selected from the group consisting of ##STR11## wherein y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.

9. A coating of claim 5 or 7 or 8 wherein the inherent viscosity of the copolymer, as measured at 30.degree. C. for a 0.5% (w/v) solution in chloroform or methylene chloride, is 0.25 to about 1.50 dl/g.

10. A coating of claim 9 wherein the bioabsorbable surgical suture or ligature is manufactured from a polymer prepared from one or more monomers selected from the group consisting of lactides.

11. A coating of claim 10 wherein the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide.

12. A coating of claim 10 wherein the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide.

13. A coating of claim 11 wherein the suture or ligature is in multifilamentary form.

14. A coating of claim 13 comprising about 1/10 to 5% by weight of the coated suture or ligature.

15. A coating of claim 14 comprising about 1 to 3% by weight of the coated suture or ligature.

16. A bioabsorbable coating for a surgical suture or ligature comprising a triblock copolymer having a middle block and two end blocks, the middle block obtained by removing both terminal hydroxyl hydrogens from either a homopolymer of ethylene oxide, or from a block or random copolymer of ethylene oxide and a cyclic ether, and each end block consisting essentially of glycolic acid ester and trimethylene carbonate linkages such that said triblock copolymer has a melting point (Tm) less than 65 degrees centigrade and a glass transition temperature (Tg) less than 20 degrees centigrade and is soluble in methylene chloride or chloroform or both.

17. A coating of claim 16 wherein the cyclic ether is selected from the group consisting of ##STR12## wherein x is 2 to about 9 y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.

18. A coating of claim 17 having a middle block obtained from a block copolymer of ethylene oxide and a cyclic ether of the formula: ##STR13##

19. A bioabsorbable coating for a surgical suture or ligature comprising a triblock copolymer having a middle block and two end blocks, the middle block obtained by removing both terminal hydroxyl hydrogens from a block or random copolymer of a first cyclic ether selected from the group consisting of ##STR14## wherein x is 2 to about 9 and a second cyclic ether selected from the group consisting of ##STR15## wherein y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group, and each end block consisting essentially of glycolic acid ester and trimethylene carbonate linkages such that said triblock copolymer has a melting points (Tm) less than 65 degrees centigrade and a glass transition temperature (Tg) less than 20 degrees centigrade and is soluble in methylene chloride and/or chloroform.

20. A coating of claim 16 wherein the middle block is from 5 to 25 percent by weight of the copolymer.

21. A coating of claim 20 wherein the number average molecular weight of the middle block is from about 4000 to 30000.

22. A coating of claim 21 wherein the inherent viscosity of the copolymer, as measured at 30.degree. C. for a 0.5% (w/v) solution in chloroform or methylene chloride, is 0.25 to about 1.50 dl/g.

23. A coating of claim 22 comprising a bioabsorbable surgical suture or ligature manufactured from a polymer prepared from one or more monomers selected from the group consisting of lactides.

24. A coating of claim 23 wherein the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide.

25. A coating of claim 24 wherein the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide.

26. A coating of claim 24 wherein the suture or ligature is in multifilamentary form.

27. A coating of claim 26 comprising about 1/10 to 5% by weight of the coated suture or ligature.

28. A coating of claim 27 comprising about 1 to 3% by weight.

Surgical suture description

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to the use of a block hydrogel as a coating and lubricating finish for a surgical suture or ligature.

As early as 1972 R. Perret and A. Skoulious, Makromol. Chem. 156 143-156 (1972); Makromol. Chem. 162 147-162 (1972); and Makromol. Chem. 162 163-177 (1972) disclosed the synthesis and characterization of thermoplastic poly(caprolactone)-poly(ethylene oxide)-poly(caprolactone) (PCL-PEO-PCL) ABA triblock copolymers. The purification and crystallization behavior of these materials was extensively discussed. However, no mention was made as to the biodegradability of these polymers, their swelling behavior, or to any medical use such as suture materials or as suture coatings. Pitt and Schindler, U.S. Pat. No. 4379138 have published extensively on the biodegradability of PCL; therefore, the PCL-PEO-PCL triblock polymers should make attractive biodegradable hydrogel materials but this use was never mentioned.

Reed, Ph.D. Dissertation, Univ. of Liverpool (1978) has disclosed the synthesis of poly(lactide)-PEO-poly(lactide) (PLA-PEO-PLA) ABA triblock copolymers. The biodegradability of these materials was recognized; however, there was no mention of their potential hydrogel nature, or the use of these materials as suture coatings.

Casey, et al., U.S. Pat. No. 4452973 (6/5/84) disclosed the synthesis of poly(glycolic acid)-PEO-poly(glycolic acid) (PGA-PEO-PGA) thermoplastic biodegradable ABA triblock polymers. The intended use for these materials was as absorbable sutures having the required flexibility for use as a monofilament. The patent discloses the use of trimethylene carbonate in combination with glycolide to prepare the A portion of the ABA triblock polymer.

Churchill, et al., U.S. Pat. No. 4526938 (9/2/85) also disclosed the use of degradable ABA triblock polymers as hydrogels. In this case, the middle block was also PEO and the endblocks were generally PLA or PLA/PGA copolymers although the use of PGA, PCL or poly(3-hydroxy-butyric acid) was mentioned with no specific experimental details given. No mention was made to using Gly/TMC endblocks for these hydrogels, or to using these materials as suture coatings.

Mattei (U.S. Pat. No. 4027676 to Ethicon, June 7 1977) has disclosed suture coatings consisting of blends of absorbable copolymers of glycolide and lactide as a film forming resin, polyalkylene glycols as a lubricant, and a hydrophobic material such as a fatty acid or an ester of a fatty acid to improve tie-down performance. However, no mention was made of using block polymers formed from poly(alkylene glycols) and absorbable polymers. A particular disadvantage of the Mattei method of using blends of poly(alkylene glycols) with absorbable copolymers is the tendency for the poly(alkylene glycols) to dissolve prematurely if exposed to an aqueous environment (see, e.g., Example 4 of U.S. Pat. No. 4027676) rendering the coating less effective.

Mattei (U.S. Pat. No. 4201216 to Ethicon May 6 1980) has also disclosed the use of an absorbable copolymer of glycolide and lactide as a film former blended with salts of C.sub.6 or higher fatty acids as suture coatings. No mention was made of using block polymers with poly(alkylene glycols) for this application.

Mattei has also disclosed the use of polyvalent metal fatty acid salt gels as suture coating materials (U.S. Pat. No. 4185637 to Ethicon Jan. 29 1980). No mention is made of using block copolymers of poly(alkylene glycols) for this application.

Conventional hydrogels which are made by crosslinking water soluble polymers have several drawbacks which are associated with their crosslinked nature. These include a lack of both solubility and processability. In contrast the block copolymers of this invention are thermoplastic. They are soluble in common organic solvents and are fusible.

The biodegradable thermoplastic hydrogels of this invention are useful as a suture coating material for surgical sutures or ligatures. Their solubility in common organic solvents allows for a coating composition to be applied by conventional solution techniques. When applied in this manner the coating polymer will improve tie-down performance and lubricity of the surgical suture as compared to an identical uncoated surgical suture. The polymers of this invention will also degrade to non-toxic low molecular weight materials capable of being eliminated from the body without adverse reaction or response.

A bioabsorbable coating for a surgical suture or ligature comprising a diblock copolymer has been invented. The copolymer has a first block comprising a polyalkylene oxide and a second block consisting essentially of glycolic acid ester and trimethylene carbonate linkages. In one embodiment, the polyalkylene oxide block is from 5 to 25 percent by weight of the copolymer. In another embodiment, the number average molecular weight of the polyalkylene oxide block is from about 4000 to 30000. In yet another embodiment, the polyalkylene oxide block is derived from a polyalkylene oxide terminated on one end by a C.sub.1 to C.sub.6 alkyl group and on the other end by a hydroxyl group.

In a specific embodiment of any of the above embodiments, the polyalkylene oxide block is derived from a homopolymer of ethylene oxide. In another specific embodiment of any of the above, the polyalkylene oxide block is derived from a block or random copolymer of ethylene oxide and a cyclic ether. In a more specific embodiment, the cyclic ether is selected from the group consisting of ##STR1## wherein x is 2 to about 9 y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.

In yet another specific embodiment, the polyalkylene oxide block is derived from a block or random copolymer of a first cyclic ether selected from the group consisting of ##STR2## wherein x is 2 to about 9 and a second cyclic ether selected from the group consisting of ##STR3## wherein y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.

In a more specific embodiment (to the above specific embodiments), the inherent viscosity of the diblock copolymer, as measured at 30.degree. C. for a 0.5% (w/v) solution in chloroform or methylene chloride, is 0.25 to about 1.50 dl/g.

In a still further embodiment, the surgical suture or ligature containing the bioabsorbable diblock copolymer coating is also bioabsorbable. The suture or ligature is manufactured from a polymer. The polymer is prepared from one or more monomers selected from the group consisting of lactides. In one embodiment, the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide. In another embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide. In a specific embodiment, the suture or ligature is in multifilamentary form. In a more specific embodiment, the coating comprises about 1/10 to 5% by weight of the coated suture or ligature. In a most specific embodiment, the coating comprises about 1 to 3% by weight of the coated suture or ligature.

A bioabsorbable coating for a surgical suture or ligature comprising a triblock copolymer has also been invented. The middle block (of the triblock copolymer) is obtained by removing both terminal hydroxyl hydrogens either form a homopolymer of ethylene oxide, or from a block or random copolymer of ethylene oxide and a cyclic ether. In one embodiment, the cyclic ether is selected from the group consisting of ##STR4## wherein x is 2 to about 9 y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group. In a specific embodiment, the middle block is obtained from a block copolymer of ethylene oxide and a cyclic ether of the formula: ##STR5##

Further, a bioabsorbable coating for a surgical suture or ligature comprising an alternative triblock copolymer has been invented. The middle block is obtained by removing both terminal hydroxyl hydrogens from a block or random copolymer of a first cyclic ether selected from the group consisting of ##STR6## wherein x is 2 to about 9 and a second cyclic ether selected from the group consisting of ##STR7## wherein y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.

In a further embodiment of any of the above embodiments, each end block of the triblock copolymer consists essentially of glycolic acid ester and trimethylene carbonate linkages. In a specific embodiment, the middle block is from 5 to 25 percent by weight of the copolymer. In a more specific embodiment, the number average molecular weight of the middle block is from about 4000 to 30000.

In a most specific embodiment (to the above specific embodiments), the inherent viscosity of the copolymer, as measured at 30.degree. C. for a 0.5% (w/v) solution in chloroform or methylene chloride, is 0.25 to about 1.50 dl/g. In a still further embodiment, the surgical suture or ligature containing the bioabsorbable bioabsorbable triblock copolymer coating is also bioabsorbable. The suture or ligature is manufactured from a polymer. The polymer is prepared from one or more monomers selected from the group consisting of lactides. In one embodiment, the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide. In another embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide.

In a specific embodiment, the suture or ligature is in multifilamentary form. In a more specific embodiment, the coating comprises about 1/10 to 5% by weight of the coated suture or ligature. In a most specific embodiment, the coating comprises about 1 to 3% by weight of the coated suture or ligature.

DESCRIPTION OF THE INVENTION

This invention relates to the use of degradable thermoplastic hydrogels consisting of block polymers as a coating and lubricating finish for surgical articles including sutures and ligatures. These materials will impart lubricity to, and improve the tie-down properties of a multifilament absorbable suture or ligature in both wet and dry state. The suture or ligature can be manufactured from a homopolymer (e.g., Dexon.TM., American Cyanamid Co., NJ, USA) or copolymer (e.g., Vicryl.TM., Ethicon, Inc., NJ, USA) of glycolic acid. In addition, these materials are capable of being completely degraded and eliminated from the body over a period of time. A particular advantage of these materials is their thermoplastic nature, that is, they can be applied to sutures by conventional solution or thermal techniques.

Recently, there has been interest in using hydrogels in a wide variety of biomedical applications such as contact lenses, burn dressings, blood and tissue compatible implants, lubricant coatings for surgical implants, and drug delivery devices. In some of these areas, crosslinked hydrogel materials have met with great success. However, these materials suffer drawbacks, such as a lack of processibility, which are a consequence of their crosslinked nature.

Our approach to this problem was to investigate the use of block copolymers as thermoplastic biodegradable hydrogels for suture coating applications. In an ABA triblock example of these block polymers, the middle (B) block is a water soluble polymer such as a poly(alkylene oxide) and the end blocks (A) are comprised of degradable random copolymers of glycolide (Gly) and trimethylene carbonate (TMC). The middle and end blocks of this block copolymer are chemically incompatible and the result is a phase separated system with poly(alkylene oxide) regions dispersed throughout the Gly/TMC matrix. When exposed to an aqueous environment, the block polymer picks up an amount of water which is a function of the composition and molecular weight of the various block structures. The thermoplastic nature of the block polymers allows for lubricant coatings to be applied by known solution or melt processes. The crystalline poly(alkylene oxide) segments serve, in the dry state, as temperature dependent crosslinks which hold the coating securely in place and minimize coating flow on storage of the surgical suture.

The method of choice for preparing the above block copolymers is the melt phase ring-opening copolymerization of glycolide and trimethylene carbonate using specially purified, commercially available difunctional or monofunctional poly(alkylene glycols) as initiators. These polymerizations are conducted in a stirred reactor at about 165.degree. C. under nitrogen. When maximum melt viscosity has been reached, the polymer is discharged and allowed to cool to room temperature. Oligomeric material can be removed by reprecipitation from methylene chloride solutions into methanol or ethanol.

Samples of the above polymers are extruded at 60.degree.-100.degree. C. with an extruder to yield fibers of 1.5 mm average diameter. The fibers are then cut into 1" lengths and several are placed in deionized water at room temperature. At various time intervals, the fibers are withdrawn, wiped thoroughly to remove any surface liquid, and the water uptake is measured gravimetrically. Alternatively, the uptake can be measured from thin films (0.6 mm) prepared by compression molding the polymer at 90.degree. C., or by casting thin films of the polymer from solution.


Packaging for surgical suture material
Packaging for surgical suture material

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