Field of the Invention

The present invention relates to a coating composition for surgical sutures and surgical sutures coated with the coating composition.

Description of the Prior Art

Surgical sutures have been coated with lubricating agents to improve their knot slipdown property and bioabsorbability. For example, U.S. Patent No. 3,297,030 discloses polyglycolic acid surgical sutures coated with silicones or waxes; U.S. Patent No. 4,027,676 describes a coating composition for sutures comprising a bioabsorbable film-forming polymer, a hydrophobic material and a bioabsorbable lubricant polyalkylene glycol; and U.S. Patent No. 4,047,533 provides a coating composition for sutures comprising polyoxyethylene-polyoxypropylene copolymer as a lubricant.

However, the coating material in accordance with U.S. Patent No. 3,297,030 is not bioabsorbable and remains in tissues after the suture is absorbed into the body; the coating composition of U.S. Patent No. 4,027,676 is difficult to prepare due to its complexity; and the suture prepared in accordance with U.S. Patent No. 4,047,533 loses the knot slipdown property when wetted with water or blood in surgery.

Accordingly, many studies have been made to search for a suture having an improved knot slipdown property under wet conditions such as in water or blood. U.S. Patent No. 4,624,256 teaches a surgical suture coated with a lubricating agent selected from the group consisting of

polycaprolactone; a copoly er of at least 90% of caprolactone and a biodegradable monomer; and a blend of at least 50% of the polycaprolactone or the copolymer and up to 50% of another biodegradable lubricant. U.S. Patent No. 4,788,979 gives, as a coating agent, a copolymer of 50% to 80% of caprolactone and lactide, lactone or carbonate; and U.S. Patent No. 4,994,074 uses a coating composition comprising a copolymer of a larger amount of caprolactone and a smaller amount of glycolide or glycolic acid. Even though various sutures coated with coating compositions comprising a homopolymer or a copolymer of caprolactone as mentioned above may have improved the knot slipdown property under wet conditions, their knot security has shown the tendency to deteriorate.

Summary of the Invention

Accordingly, an object of the present invention is to provide a coating composition which imparts both improved knot slipdown property and superior knot security to surgical sutures coated therewith.

It is another object of the present invention to provide a suture having both improved knot slipdown property and knot security, which is coated with the present coating composition.

In accordance with one aspect of the present invention, there is provided a coating composition for a surgical suture which comprises at least 50wt% of a surfactant having both hydrophilic and hydrophobic portions and/or a powdery lubricant insoluble in an organic solvent, and at most 50wt% of a polymer component, based on the total weight of the composition, for fixing the surfactant and/or the lubricant onto the surface of the suture.

Detailed Description of the Invention

In general, a surgical suture is coated with a coating composition which includes a part of the main components of the suture, thereby improving the compatibility between the coating composition and the suture. The coating composition so prepared is not easily removable from the suture and imparts a good knot slipdown property to the suture, which may, however, reduce the knot security in the surgical area. In case that the surgical suture is made of a hydrophobic material, a hydrophobic coating composition will be compatible with the suture and the coating layer therefrom may not be easily removable from the suture; whereas a hydrophilic coating composition will not be compatible with the suture and may not be easily coated on the surface of the suture. On the other hand, a coating composition comprising both a hydrophilic component and a hydrophobic component may be compatible with the suture and the coating layer formed therefrom may be easily removable from the suture, depending on the ratio of the two components, regardless of the hydrophilicity or hydrophobicity of the suture.

In accordance with the present invention, therefore, by adjusting the ratio of the hydrophilic and the hydrophobic components in the coating composition, the coating layer formed therefrom may be made easily removable from the suture when the suture is threaded through a surgical area. Thus, the naked suture will lose the knot slipdown property and acquire the knot security, which will facilitate the fixing or securing of the suture at the surgical site.

In accordance with one aspect of the present invention, the coating composition comprises: (A) a surfactant which has both hydrophilic and hydrophobic portions and a polymer which serves to withhold the surfactant when the composition is applied to the surface of a suture and forms a film thereon; (B) a powdery lubricant which is insoluble in an organic solvent and a polymer which serves to withhold the

lubricant onto the surface of the suture when the composition is applied thereon; or (C) a surfactant which has both hydrophilic and hydrophobic portions, a powdery lubricant which is insoluble in an organic solvent, and a polymer which serves to withhold the surfactant and the lubricant onto the surface of the suture. The coating layer of the suture coated with the above coating composition is readily removable from the surface of the suture when the suture is threaded through a surgical area. After the suture loses its coating layer, it hardly slips or moves through the suturing site, that is, its knot security increases .

The surfactant employed in the present coating composition, which has both hydrophilic and hydrophobic groups, may exist as a solid or a liquid at a room temperature. Representative examples of the surfactant are a copolymer of polyethylene oxide and a fatty acid ester and a copolymer of polyethylene oxide and polypropylene oxide, and a copolymer of polyethylene oxide and a fatty acid ester is preferred. Poloxamer 188( utrol* F68, BASF Co.: copolymer of polyethylene oxide and polypropylene oxide) or Polysorbate 80(Tween* 80, I.C.I. Co.: polyoxyethylene sorbitan onooleate) are commercially available.

The powdery lubricant, which is insoluble in an organic solvent and useful in the present coating composition, may be a salt of a fatty acid having six or more carbons, preferably, magnesium stearate.

The preferred polymer which serves to withhold the surfactant and/or the lubricant onto the surface of the suture is polycaprolactone.

The polymer in the present coating composition forms a film on the surface of the surgical suture together with the surfactant and/or the lubricant. The surfactant and/or the lubricant in the present coating composition lowers the friction coefficient of the surface of the surgical suture, therefore, the suture coated therewith slips smoothly. Especially, Polysorbate 80 is effective in smoothing the

surface, and magnesium stearate is effective in facilitating the removal of the coating layer and enhancing the knot security of the suture.

In the present coating composition, the mixing ratio of the surfactant and/or the lubricant to the polymer plays a critical role. The composition comprises at least 50wt% of the surfactant and/or the powdery lubricant and at most 50wt% of the polymer. The polymer is preferably incorporated in an amount ranging from 20 to 50wt%, more preferably, from 40 to 45wt% of the total composition. The surfactant and/or the lubricant is preferably incorporated in an amount ranging from 50 to 80wt%, more preferably, from 60 to 80wt%. In case that a mixture of the surfactant and the lubricant is incorporated in the composition, the amount of the surfactant preferably ranges from 17 to 33wt%, based on the total amount of the surfactant and the lubricant.

Representative examples of the organic solvent, which may be used in accordance with the present invention include aliphatic organic solvents such as methylene chloride, chloroform, 1, 1,2-trichloroethane, acetone, acetonitrile and ethanol, and aromatic organic solvents such as benzene, toluene and xylene.

The surgical suture in accordance with the present invention may be prepared by using a method which comprises dispersing the coating composition in an organic solvent to make a suspension, coating the suspension on the surface of a suture by a conventional method such as spraying or immersion, evaporating the solvent in the coated suspension and drying the suture. To increase the amount of the composition coated on the suture as needs be, the coating and drying steps may be repeated. After the drying, the coating composition remains on the suture preferably in an amount ranging from 6 to 18wt%, based on the weight of the uncoated suture. The coating composition of the present invention may be applied to any suture made of a conventional material including a synthetic bioabsorbable material, e.g., polygly-

colic acid or a copolymer of lactide and glycolide, and a synthetic non-absorbable material, e.g., polyester or polyamide.

The suture may be prepared by melt-spinning the synthetic material into strands and braiding more than, e.g., 3 strands. Conventional surgical sutures are 3, 8, 12 or 16-braided, and, if needed, more than 16 braids are stranded.

The following Examples are intended to illustrate the present invention more specifically, without limiting the scope of the invention. The percentages as used in the Examples are by wt/wt, unless otherwise specified.

Example 1

Chemically pure grade glycolide was polymerized to give polyglycolic acid with a number average molecular weight of 50,000 to 100,000. The polyglycolic acid was melt-spun into strands and the strands were braided into sutures. The sutures were immersed in a coating solution containing 12% of a 4:6 mixture of Polycaprolactone P 300(a number average molecular weight: 15,000, Union Carbide Co. (US)) and Polysorbate 80 (I.C.I. Co.) in methylene chloride, and then dried to evaporate the organic solvent. The Polycaprolac- tone P 300 had a viscosity ranging from 500 to 2,500cps, measured with a B type viscometer at 204°C.

The surgical sutures coated with the above coating composition in accordance with the present, invention had a smooth surface and contained 13% of the coating composition, based on the weight of the uncoated suture. Both the knot slipdown and knot security were good and the removal of the coating layer was easily done.

Knot slipdown property and knot security of the surgical sutures were evaluated under wet conditions measured as follows:

Knot slipdown property

® : slipping down to the target area at once o : slipping down to the target area with one stop Δ : slipping down to the target area with more than two stops x : failure to slip down to the target area

Knot security

© : not slipping down toward the opposite direction after threading o : slipping down toward the opposite direction after threading within 1cm Δ : slipping down toward the opposite direction after threading by 1 to 5cm x : slipping down toward the opposite direction after threading by more than 5cm

The results of the knot slipdown property and knot security of the surgical sutures under wet conditions are given in Table 1.

Examples 2 to 17

The same procedure as in Example 1 was repeated using the same sutures of polyglycolic acid of Example 1 and the coating composition of which the components were given in Table 1. Polycaprolactone P 767 had a number average molecular weight of 43,000, and Poloxa er 188 was manufactured by BASF. The results are given in Table 1.

Examples 18 to 21

The same procedure as in Example 1 was repeated using sutures made of polyethylene terephthalate having a melt viscosity of 3,000 poise at 290°C and the coating compositions of which the components were given in Table 1.

The results are given in Table 1.

Table 1

Coat ing component (A ) (wtx) No. of

Anount of inners ing Anount Snooth-

Ex. Po ly¬ Poly¬ (A ) in the of (A ) ness of

No. Po ly¬ Po loxa- *1 *2 «3 Total nethylene suture in on suture capro¬ capro¬ Magnesiun sorbate ner chloride coating suture surface lactone lactone Stearate 80 188 (wt* ) conpos i - (wtx )

P300 P767 t ion

1 40 60 12 2 13 o o o o ®

2 40 60 12 1 6 o o o o ®

3 40 60 12 2 17 o o o Δ o

4 40 60 11 2 6 ® ® o Δ o

5 40 20 40 11 2 18 o o o Δ o

6 40 40 20 11 2 18 ® o o Δ o

7 40 60 10 2 17 Δ o o ® o

8 40 60 10 1 6 Δ o o ® o

9 35 65 10 2 17 Δ o o ® o

10 35 65 10 1 6 Δ o o ® o

11 30 70 10 2 15 Δ o o © o

12 40 20 40 10 2 18 O o o o ©

13 40 20 40 10 1 6 O o o o ©

14 40 10 50 10 2 18 O o o o ®

15 40 10 50 10 1 6 O o o o ©

16 20 20 60 10 2 18 o o o o ©

17 20 20 60 10 1 6 o o o o ©

18 40 60 11 2 6 ® ® o Δ o

19 40 40 20 11 2 18 ® o o Δ o

20 30 70 10 2 15 Δ o o ® o

21 20 20 60 10 1 6 o o o o ©

© : Exce l lent O : Good Δ : Normal X : Poor

*1 Knot slipdown property under wet conditions *2 Knot security under wet conditions * 3 Removal of coating layer after slipdown

Comparative Examples 1 to 15

The same procedure as in Example 1 was repeated using the same suture of polyglycolic acid of Example 1 and the coating composition of which the components were given in Table 2. The results are given in Table 2.

Comparative Examples 16 to 19

The same procedure as in Example 1 was repeated using the same suture of polyethylene terephthalate of Example 18 and the coating compositions of which the components were given in Table 2. The results are given in Table 2.

Table 2

Coa ing Coaponent(A)(ttx) No. of

Coa. imersing Anount

Sβooth-

Poly¬ Poly¬ (A) in the of (A) Ex. Poly¬ Poloxa- agnesiun ness of »1 »2 «3 capro¬ capro¬ nethylenβ suture in on Total

No. sorbate ner Stearate surface chloride coating suture lactone lactone suture 80 188 (wtx) conposi- (wtx)

P300 P767 tion

1 100 0 12 5 X Δ X O X

2 90 10 12 5 0 X Δ o X

3 80 20 12 5 o X O o X

4 90 10 12 15 0 Δ X 0 X

5 80 20 12 15 0 Δ X o X

6 GO 40 12 15 0 Δ X 0 X

7 100 12 15 0 X O X X

8 100 12 2 19 o X O X X

9 100 12 15 o X O X X

10 90 10 10 13 Δ X Δ 0 X

11 80 20 10 13 Δ X Δ 0 X

12 60 40 10 13 Δ X Δ © X

13 100 10 13 Δ X O 0 X

14 80 10 10 10 13 o Δ X X X

15 60 20 20 10 13 0 Δ X X X

16 100 0 12 5 X Δ X o X

17 100 12 15 0 X 0 X X

18 100 12 2 19 0 X O X X

19 60 20 20 10 1 13 o Δ X X X

@ : Exce l lent O : Good Δ : Normal X : Poor

*1 Knot slipdown property under wet conditions *2 Knot security under wet conditions *3 Removal of coating layer after slipdown

As shown in the above Examples, the removal of the coating layer after slip down was discernible with the naked eyes. The molecular weight of the polycaprolactone was found not to affect the suture properties. The surgical sutures coated with the coating compositions comprising any one of the polymer, surfactant and lubricant did not provide good suture properties such as smooth surface, knot slipdown or knot security, while the present surgical sutures coated with the coating compositions comprising above two or three components as indicated in the above Examples provided excellent suture properties.

While the invention has been described with respect to the specific embodiments, it should be recognized that various modifications and changes may be made by those skilled in the art to the invention which also fall within the scope of the invention as defined as the appended claims.