GB1584803A - Sutures having a bioabsorbable coating - Google Patents

Abstract

The surgical suturing material is characterised by a multi-filament polymer strand. In order to improve the knot running properties and the handling, the strand is provided with a thin, greasy coating. The coating comprises a greasy, biologically absorbable copolymer having polyoxyethylene blocks and polyoxypropylene blocks. The copolymer has a molecular weight such that it is pasty to solid at 25 DEG C.

Description

(54) SUTURES HAVING A BIOABSORBABLE COATING (71) We, AMERICAN CYANAMID COMPANY, a Corporation organized and existing under the laws of the State of Maine, United States of America, of Berdan Avenue, Township of Wayne, State of New Jersey, United States of Anierica, do hereby declare the invention for which we pray that a patent may be granted us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a bioabsorbable or a non-bioabsorbable surgical suture having improved knot run-down characteristics and reduced tissue drag.

In this specification, the term "bioabsorbable" as applied to a suture refers to a suture which is absorbed by living tissue. The term "bioabsorbable" as applied to the suture lubricating coating of this invention (to be described hereafter) refers to a coating which by hydrolytic or enzymatic degradation, or by its inherent characteristics, has such molecular weight and solubility properties that it is absorbed from the surface of the suture and is eliminated by the subject either unchanged or in hydrolyzed or degraded form.

Among the more important of the handling characteristics of surgical sutures are those associated with knot run-down. One technique frequently used is to tie a square kndt that can be run-down from an exterior location where the knot is first tied to lie against tissue with a desired degree of tightness. The knot is snugged down so that it is holding with a degree of firmness chosen by the surgeon for the particular situation and then additional throws are tied down against the first throws of the square knot. In some instances, the first throw is a double twist followed by a single throw to form a surgeons knot, with additional throws to form additional square knots on top as needed.

As contrasted with the ease of placement, is the necessity of knot security.

Even though it is desired that it be easy to tie a knot, it is mandatory that the knot hold without slipping for an acceptable length of time.

Some suture materials are so smooth that a knot runs down very readily and frequently becomes readily untied. Other sutures are of.materials in which the knot tends to "lock-up" or refuse to run-down so that it is difficult to snug-down the throws against the tissue and only a few throws are needed, and security is not a problem. Knots in constantly moving tissue, such as adjacent to the heart, have a much greater chance of becoming untied than knots in quiescent tissue such as knots holding together a wound inside a plaster cast.

United States Patent No. 2,734,502, February 14, 1956, Nichol et al., Silk Sutures and Ligatures, shows poly(alkyl)methacrylate as a coating for silk sutures, and the use of a hot coating die system.

United States Patent No. 3,297,033, January 10, 1967, Schmitt and Polistina, Surgical Sutures, shows synthetic bioabsorbable sutures of polyglycolic acid and discloses that the surfaces of the fiber can be coated with a silicone, beeswax, or the like to modify the handling or the absorption rate.

The coating, coloring and conditioning of surgical sutures with polymeric materials in general is well-known. Silicones, wax, polytetrafluoroethylene, and other polymers have been used. Specific coating materials with unique advantages to give improved sutures are constantly being sought.

In accordance with the present invention there is provided a surgical suture having improved knot run-down characteristics and reduced tissue drag which comprises a polyfilamentary polymer strand having thereon a thin lubricating coating of a lubricating bioabsorbable (as herein defined) copolymer. The lubricating copolymer comprises polyoxyethylene blocks and polyoxypropylene blocks to aid in run-down and handleability, said bioabsorbable copolymer having a molecular weight such that it is pasty-to-solid at 250C.

In a preferred embodiment, the lubricating bioabsorbable copolymer has the formula:

where one of R, and R2 is methyl and the other hydrogen, and n and m are such that the compound is pasty-to-solid at 250C., R is the residue of a reactive hydrogen compound having from 2 to 6 reactive hydrogen atoms and having not over 6 carbon atoms in said compound, and c is the number of reactive hydrogens on the compound forming R.

In one embodiment, the polymer strand is of a bioabsorbable polymer which has glycolic acid ester linkages. In a specific form of this embodiment the polymer is polyglycolic acid.

In an alternative embodiment, the polymer strand is selected from silk, cotton, nylon, a non-bioabsorbable polyester, polypropylene, and polyethylene.

The lubricating coating is preferably 0.1 to 25 percent by weight of the uncoated strand based on the weight of the uncoated strand forming the suture, whereby both chatter and friction are reduced sufficiently that a square knot is movable on the suture with control of a wound edge.

Absorbable polyglycolic acid sutures are described in United States Patent No. 3,297,033, supra. Other synthetic sutures which are absorbable in living tissue may be coated with improved results. At present synthetic bioabsorbable sutures meeting with market acceptance are those in which the degradation or absorption in tissue results from the hydrolytic degradation of glycolic acid ester linkages.

Such materials are presently being sold under the trademarks Dexon and Vicryl.

With synthetic bioabsorbable sutures the problem of a coating to improve knot run-down characteristics is made more difficult by the requirement that the coating must be non-toxic and absorbable.

Non-bioabsorbable sutures are sutures which are resistant to biodegradation in living mammalian tissue and remain in the tissue as a foreign body, unless surgically removed (e.g. skin sutures) or extruded. Non-bioabsorbable sutures retain strength in living mammalian tissue for an extended period, often for the life of the subject.

Non-bioabsorbable sutures used for skin closures with the knot above the surface stage of the healing process. For those in which the knot in the non-bioabsorbable suture is buried in living tissue, and are to be left indefinitely, the present lubricant is absorbed from the non-bioabsorbable suture is less than about 48 hours, and hence the lubricating action ceases, and knot security improves.

Non-bioabsorbable sutures are typically of silk, cotton, nylon, a nonbioabsorbable polyester ("Dacron" -- registered Trade Mark) polypropylene, polyethylene, or linen. Even metals such as stainless steel, monofilament or braided or tantalum or platinum have been used.

The lubricant coating used in the present invention not only aids in the knon run-down characteristics but increases the smoothness and flexibility of the sutures so that they may be more easily drawn through the skin and other tissues during placement of the suture. This reduction in friction is called reduced tissue drag.

The coating that aids in reduced tissue drag, and lubricates in knot placement also causes the knot to slip more readily.

Another unexpected and unobvious advantage of the present lubricant coating in that the lubricant copolymers are absorbed from the suture within a few days so as the wound heals knot security improves.

The bioabsorbable coating used herein is one or more of a group of compounds having blocks of polyoxyethylene and blocks of polyoxypropylene in their structure. For simplicity and ease of description these compounds are taught, drawn and treated as if there were merely two or three blocks in the chain.

However, it is to be understood that non-significant qualities of polyoxypropylene may be present in the polyoxyethylene block and minor quantities of poly oxyethylene may be present in the polyoxypropylene block. From the methods of manufacture it would appear that there may be and probably are such minor admixtures present in the chain. The commercially available grades are acceptable and found to have a low and acceptable degree of toxicity.

The preferred lubricants are, as already indicated, copolymers having the formula:

where one of R, and R2 is methyl and the other hydrogen, and n and m are such that the compound is pasty-to-solid at 250C., R is the residue of a reactive hydrogen compound having from 2 to 6 reactive hydrogen atoms and having not over 6 carbon atoms in said compound, and c is the number of reactive hydrogens on the compound forming R. Those compounds which are at least pasty at 250C. are preferred because they adhere better to the synthetic absorbable polyfilamentary suture. There is not a sharp cut off, but in general as the materials become more pasty or solid, their effectiveness improves.

These lubricating bioabsorbable copolymers are often classed as surface active agents as the polyoxyethylene blocks are predominantly hydrophilic and the polyoxypropylene blocks are predominantly hydrophobic. The materials have been sold by the Wyandotte Chemical Company, Michigan, U.S.A. under the Registered trademark of "PLURONIC" in respect of compounds having the formula:

wherein x, y and z are whole numbers; REVERSE "PLURONIC" in respect of compounds having the formula:

where n, m and o are whole numbers; and TETRONICS in respect of compounds having the formula: where R, is

where q and r are whole numbers.

For the present purposes as synthetic absorbable suture lubricants, the values of x, y, z, n, m, o, q and r are such that the lubricants are pasty-to-solid at 250C. The pastes are opaque semi-solids with melting points above room temperature -- pre- ferably above about 40"C. Those sold under the Registered trademark "Pluronic" are particularly useful for the present invention.

The formulations of certain commercially available products are approximately those shown in Table I.

As all compositions are mixtures, all values are approximate, and values are subject to some rounding.

TABLE I Average M.W. of each Units of M.W. of Poly Molecular Polyoxyethylene each x % Polyoxy- oxypropylene Units of "PLURONIC" Weight Block and z ethylene Block y M.P. C F-38 5000 2000 46 80 930 16 45 F-68 8350 3300 75 80 1.750 30 52 F-77 6600 2300 52 70 2,050 35 48 P-85 4600 1200 27 50 2,250 39 40 F-87 7700 2700 62 70 2,250 39 49 F-88 10800 4300 97 80 2,250 39 54 F-98 13500 5400 122 80 2,750 47 55 F-108 14400 5600 128 80 3,150 54 57 F-127 12500 4300 98 70 3,900 67 56 REVERSE "PLURONIC" M.W. polyethylene M.V. poloxy- Units of units of m block propylene block n and 0 10R8 3,000 2000 45 65% 562 9 46 17R8 4,350 2600 59 60% 870 15 53 25R8 9,000 3250 74 57% 1250 22 56 TABLE I - continued Average Approximate length Approximate Molecu- Molecular Approxi- of chains per block Average lar Weight of In- Approximate mate Weight of In- Approximate % Molecular dividual Polyoxy- % Polyoxy- dividual Polyoxy- Polyoxypro Units of r Units of q TETRONIC Weight ethylene Block ethylene propylene Block pylene 707 12,000 2312 74 673 26 52.5 11 908 26,100 5588 85 923 15 127 15.9 1107 14,500 2438 67 1173 33 55.4 20.2 1307 18,600 3213 69 1423 31 73 24.5 1508 27,000 5063 75 1673 25 115 28.5 In general, the compounds sold under the Registered trademark "Pluronic" with a molecular weight range of from about 4,750 to 16,250 are waxy solids. The polyoxypropylene portion has a molecular weight of 950 to 4,000 and the polyoxyethylene content of about 60-80%.

The pastes in general have a total molecular weight ranging from 3,500 to 5,700 with a polyoxypropylene molecular weight range of 1,750 to 6,500 and polyoxyethylene content of 30-50%. The transitions from wax to paste to liquid are not sharp.

The low toxicity of the polyoxyethylene-polyoxypropylene compounds of the present invention is shown in the following table.

TABLE II TOXICITY Total Physical LD 50 (gm/kg) "Pluronic" No. Molecular Weight Characteristic in Mice F-38 5000 wax > 5 F-77 6600 wax 4.2 F-87 7700 wax 3.75 F--68 8350 wax > 5 F-88 10800 wax > 5 F- 127 12500 wax 2.25 F-98 13500 wax > 5 F108 14400 wax 1.25 P--65 3400 paste 0.83 P-84 4200 paste 0.4 P-85 4600 paste 0.53 P-94 4600 paste 0.6 P-103 4950 paste 1.4 P--104 5850 paste 0.75 P-I 23 5750 paste 2.7 P--105 6500 paste 3 The quantity of the lubricating bioabsorbable copolymer is preferably from 0.1 to 25 percent by weight of the uncoated strand based on the weight of the uncoated strand forming the suture. It is not necessary that the coating be continuous as a discontinuous coating on the surface aids in reducing friction and chatter. A larger quantity may be present if the lubricating bioabsorbable copolymer penetrates inside the strand, with the various filaments themselves being partially or totally covered.

The wide range of coating weight permits adaptation of the present sutures to many varied uses. Because the strand to be coated to form the suture may have considerable variation in surface roughness, due to the mechanical structure, i.e. braid or twist, etc. as well as being made from filaments which are less than 2 denier per filament to more than 6 denier per filament, with the finer filament sizes giving a smoother surface; and because the filaments may be stretched after the suture is manufactured or in heat treatment, the surface roughness basically can vary. The smoother surfaces required less of the lubricating bioabsorbable copolymer for analogous degrees of slippage.

The various surgical techniques used interact with the desired degree of lubrication. For any given type of knot, a larger quantity of lubricant which for a particular technique increases the ease of run-down, also increases the ease of the knot running back or slipping. For some surgical procedures it is highly desirable that the knot be very free in running down, even though the knot slips more readily.

A surgeon in tying knots is confronted with the interaction between the method of tying the knot and the ease of slipping. If a suture is comparatively well lubricated, the surgeon can use a square knot, which is run down readily; with additional squared throws for knot security. On the other hand, if the suture is less well lubricated,-the surgeon can use a double half-hitch or some other type of knot which moves more readily to run the knot down to position, after which the double half-hitch can be pulled to square the knot, or additional throws can be thrown down against the knot to give adequate knot security. Thus the surgeon can either adapt his knot technique to a particular suture, or can get sutures whose surface lubricity is best adapted to the technique which the surgeon desires to use.

Generally, there is an adaptation of each to the other. The surgeon attempts to get a suture whose characteristics are those which he prefers, and then adapts his knot tying techniques to the sutures that he has at the time. Some surgeons make very successful knots with stainless steel wire using a knotting technique that is adapted to such a wire which has a very poor run-down. Others prefer a much more readily run-down well-lubricated suture.

Because the ease of knot run-down and knot security are somewhat opposite, it is necessary for the surgeon to use additional throws or such knots as will hold under the particular conditions of a selected surgical procedure. By changing the quantity of the lubricant bioabsorbable copolymer, the run-down can be modified to suit a using surgeon's preference.

The time of use of the knots can be quite varied.

Because the present lubricating bioabsorbable copolymer is removed from the suture in living tissues, as the lubricant is removed the knot security increases and after 48 hours more or less, knot security is greatly improved.

The requirements of surgery are extremely varied, and various coating weights permit adaptation of sutures of different conditions. In general, if the surgeon desires a better lubricated suture, a larger quantity of the lubricating bioabsorbable copolymer is used and conversely if the surgeon is willing to accept slightly reduced knot run-down and tissue drag characteristics in favour of greater knot security, the coating level is reduced in favour of this particular compromise.

Usually from 2 percent to 8 percent of the lubricant bioabsorbable copolymer gives a useful range of compromise between the ease of knot run-down and knot security.

The use of about 5 percent by weight of "Pluronic" F--68 is a preferred compromise between the knot run-down and knot security requirements for 2 to 6 denier per filament braided sutures of polyglycolic acid.

The examples following should show the effects of certain different coating and quantities under certain conditions.

Example 1.

Run Down and Chatter Test A set of 2/0 US Pharmacopoeia XIX (diameter 0.339 mm, maximum) polyglycolic acid sutures braided from a 2 denier per filament extrusion, was coated with 7 levels of "Pluronic" F--68 and a blank, that is no coating, then subjected to a square knot run-down test.

In this test, the suture is tied with a square knot around a cylinder with a 4 inch periphery. The loop thus formed is slipped off the cylinder and placed in the testing machine jaws. The knot is subjected to running-down by pulling on the original free end in a testing machine which records the pull on a chart as the knot travels down the suture. There is some chatter or variation in knot run-down tension as the knot travels down the suture. This is graphically plotted. Out of a set of runs with various coating levels, the fraction is indicated in which the maximum force for the knot run-down is within the separate ranges given in the table. All of the knots for coated sutures ran down the full length of the suture without breaking. The knot breaking strength of the suture braid was in a range of 7 to 8 pounds. For uncoated braid, the knot locked up and suture broke in 9 out 10 tests.

TABLE III Knot Run-Down on 2/0 Polyglycolic Acid Sutures with "Pluronic" F-68 Lubricant Coating Fraction of trials where maximum resistance was: Level 0-1 1-2 2-3 3-4 4-5 5-6 6-7 lbs.

(percent) 0.0 broke before run-down in 9 out of 10.

1.9 2/10 2/10 4/10 2/10 2.8 2/10 3/10 2/10 3/10 3.9 1/10 1/10 4/10 2/10 2/10 5.0 3/10 2/10 2/10 2/10 1/10 6.2 2/10 3/10 2/10 3/10 7.4 3/11 1/11 4/11 3/11 8.0 5/10 2/10 3/10 The maximum force for run-down decreases steadily with increasing level, Lower coating levels on a different batch of braid showed 0.51% 1/10 2/10 2/10 3/10 2/10 1.09% 5/10 1/10 3/10 1/10 1.53% 5/10 1/10 1/10 1/10 1/10 1/10 For these coatings, the braid was run through a solution of "Pluronic" F-68 at a concentration of about twice the percentage of coating on the suture in chloroform.

With other braid constructions and other sizes, the relative ease of knot rundown may be greater or less for the same quantity of coating, or conversely, the quantity of the coating may be adjusted to give the desired knot run-down values.

The quantity of the "Pluronic" in the solvent may be varied, and solvents other than chloroform may be used.

Other organic solvents such as methyl alcohol, ethyl alcohol, isopropyl alcohol, methylene chloride, warm xylene (about 60 C.), tetrahydrofuran, acetone, dimethylformamide, dimethyl sulfoxide, mixtures thereof, and other slmllar solvents for the lubricant may be used for coating. Flowing the solution onto a moving strand, and letting the surplus drip off is another useful coating technique.

A small amount of water increases the solubility of the lubricants, and aids in coating, but the time of contact with water of the suture should be minimized so that if moisture is present in the coating system, the sutures should be dried and desiccated promptly.

In general it is more convenient to use the solvent coating system at levels below 10 percent pick-up and use a heated die at above about 10 percent pick-up.

Example 2.

A series of runs was made using a coating of either "Pluronic" F-68 or "Pluronic" F-127 on 2/0 size sutures of 6 dpf braided absorbable polyglycolic acid sutures. The coatings were applied by a solution of the "Pluronic" material in chloroform. The concentration of the "Pluronic" material in the solution used for coating is approximately twice that obtained in the braid. A solution containing about 2.8% "Pluronic" F-68 in chloroform results in about 1.4% "Pluronic" F-68 on the braid. An adjustment in concentration can be made to secure any desired level. The strand being coated was braided for a 2/0 size suture using a 6 denier per filament extrusion of polyglycolic acid. An uncoated suture strand of the same lot was used as a control. A standard ATLAB Yarn Friction Tester Model CS--151--026, Custom Scientific Instruments, Inc., Whippany, New Jersey 07981, with a "Hewlett Packard" (registered Trade Mark) Model 321 dual channel amplifier recorder was used to record the tension of the strand feeding into the tester, and coming out of the yarn tester. The chatter factor is the ratio of maximum pull (T3) to the feed tension (T,) minus the minimum pull (T2) to the feed tension, i.e.

T3/T1-T2/T1 The values for friction are of T2 to start slipping.

The values of particular interest are the ratios and percent reduction. With other types of test devices, the numerical values may change, but the relative ratios as an index of improvement are analogous.

In this test, an uncut strand, coated as indicated, was used for the test. For use as a suture, such strand is cut to length, needled, packaged and sterilized using conventional techniques. The friction and chatter are more readily measured on continuous lengths.

Reduction in static friction, chatter and the coefficient of friction are shown for typical coating levels, and sutures in Table IV.

TABLE IV POLYGLYCOLIC ACID BRAID Size 2/0 Coeff. of "Pluronic" Level Static % Chatter % Friction % Run No. Coating % Friction Reduction Factor Reduction x10-2 Reduction 1 Blank 0 3.11 0.50 6.109 2 Blank 0 3.29 0.60 6.284 3 F-68 1.39 2.78 13.1 0.30 45.5 5.766 7.0 4 F-68 1.93 2.55 20.3 0.19 65.5 5.468 11.8 5 F-68 4.44 2.54 20.6 0.31 43.6 4.900 2.9 6 F-68 7.29 2.70 15.6 0.33 40.0 5.084 17.9 7 F-68 8.09 2.59 19.1 0.25 54.6 5.424 12.5 8 F-127 1.38 2.55 20.3 0.33 40.0 4.938 20.3 9 F-127 1.57 2.63 17.8 0.24 56.4 5.539 10.6 10 F-127 2.56 2.97 7.2 0.27 50.9 6.104 1.50 11 F-127 5.37 2.76 13.8 0.32 41.8 5.689 8.2 12 F-127 5.62 2.82 11.9 0.40 27.3 5.617 9.4 13 F-127 5.62 2.87 10.3 0.29 47.3 6.007 3.1 14 F-127 8.14 2.81 12.2 0.29 47.3 5.891 4.9 15 F-127 9.83 2.74 14.4 0.29 47.3 5.621 9.3 Tests on knot security are dependent on the exact technique ot tying knots.

A representative and typical run on knot security showed for a series of tests onsize 2/0 polyglycolic acid sutures of 2 denier per filament construction with 4.79% of "Pluronic" F8 coated thereon and different knots, the force in pounds to slip knots or break without slipping to be: Square Square + Square + Surgeons Surgeons Surgeons Run Knot I Throw 2 Throws Knot + 1 Throw + 2 Throws 1.70 2.95 Broke Broke 7.50 Broke 2 2.05 3.90 Broke 6.15 5.15 Broke 3 4.20 4.05 Broke 3.70 Broke Broke 4 0.70 3.40 Broke Broke 3.35 Broke 5 3.95 Broke Broke 1.40 Broke Broke Average 2.54 - - - - - Example 3.

A series of runs, including blank, were made with solutions of Reverse "PluronicO" R bioabsorbable lubricant copolymers in chloroform, using the procedures of Example 2. The following Table V shows the improvement obtained in chatter and friction with a series of polymers and concentrations.

TABLE V POLYGLYCOLIC ACID BRAID Reverse "Pluronic" Size 2/0 - 6 denier per filament Coeff. of Level Static (%) Chatter (%) Friction (%) Braid Run Coating (%) Friction Reduction Factor Reduction x10-2 Reduction Uncoated 16 3.92 0.31 8.189 Uncoated 17 3.45 0.21 7.503 Uncoated 18 2.87 0.27 6.083 Uncoated 19 2.87 0.18 6.300 10297B 20 10R8 2.05 2.51 23.4 0.28 5.077 28 10297B 21 10R8 3.00 2.33 28.9 0.16 34.1 4.932 31 10297B 22 10R8 3.96 2.31 29.5 0.21 13.6 4.753 33 10297B 23 10R8 5.31 2.41 26.5 0.23 5.3 4.962 30 10297B 24 10R8 7.49 2.39 27.1 0.25 4.843 32 10297B 25 25R8 2.55 2.34 28.6 0.16 34.1 4.962 30 10297B 26 25R8 3.85 2.40 26.8 0.15 38.3 5.162 27 10297B 27 25R8 6.29 2.23 32.0 0.15 38.3 4.662 34 10297B 28 25R8 7.15 2.31 29.5 0.13 46.5 4.990 30 10297B 29 25R8 8.74 2.37 27.7 0.11 54.7 5.175 27 TABLE V - Continued Coeff. of Level Static (%) Chatter (%) Friction (%) Braid Run Coating (%) Friction Reduction Factor Reduction x10-2 Reduction 10297B 30 31R4 2.18 2.53 22.8 0.15 38.3 5.520 22 10297B 31 31R4 3.42 2.53 22.8 0.17 30.0 5.466 23 10297B 32 31R4 4.51 2.57 21.6 0.14 42.4 5.652 23 10297B 33 31R4 5.53 2.61 20.4 0.17 30.0 5.705 20 10297B 34 31R4 7.26 2.51 23.4 0.11 54.7 5.782 19 10297B 35 17R8 2.12 2.45 25.3 0.19 21.8 5.218 27 10297B 36 17R8 3.13 2.45 25.3 0.25 5.019 30 10297B 37 17R8 5.02 2.33 28.9 0.20 17.7 4.782 33 10297B 38 17R8 6.32 2.36 28.0 0.25 4.723 34 10297B 39 17R8 8.60 2.33 28.9 0.15 38.3 4.962 30 Example 4.

A braided polyglycolic acid strand, of a size to form a 2/0 US Pharmacopoeia suture is dipped in a 10% solution of "Pluronic" F-68 in chloroform, and dried.

The pick-up is about 5% by weight of the weight of the strand itself.

The dried coated strand is cut into 54" segments, needled, packaged, sterilized and dried in accordance with conventional procedures.

The thus-prepared sutures were used in surgical procedures. When used to approximate tissue at a wound, a suture is placed in an appropriate location, and tied with a square knot. The square knot readily ran down to pull the edges of the wound to the degree of tightness desired by the using surgeon. The suture shows low tissue drag, and excellent knot run down. When a knot is at a desired final location, three additional squared throws are placed to secure the knot. Knots buried in tissue have the lubricant bioabsorbable copolymer removed from the suture surface within 48 hours, which gives additional knot security. The suture itself maintains tissue retaining strength for at least 15 days, and is substantially absorbed in 90 days.

Whereas exemplified and tested with square knots, the ease of knot run-down and reduced tissue drag are useful in most suture placements and for knot retention. The amount of coating, and the relative values for knot run-down and reduced tissue drag, are variable to suit the requirements of a particular surgical situation.

The needling, packaging and sterilizing of the coated sutures are in accordance with conventional procedcures.

Example 5.

Friction and Chatter Tests A set of 2/0 US Pharmacopoeia XIX (diameter 0.339 mm., maximum) braided silk sutures was coated with 5 levels of "Pluronic" F--68; and 12 levels of "Pluronic" F-I 27.

4 Blanks were run with no coating, on braid from the same lot, for comparison, and an average of these 4 used for comparative values.

Also 5 runs were made using a commercial silicone coated silk suture, see United States Patent No. 3,187,752, supra. for comparative purposes.

For these coatings, the braid was run through a solution of the "Pluronic" material in chloroform at a concentration of about twice the percentage desired for the coating on the suture, and air dried.

A standard ATLAB Yarn Friction Tester Model CS--1511-026, Custom Scientific Instruments, Inc., Whippany, New Jersey, with a "Hewlett" Packard Model 321 dual channel amplifier recorder was used to record the tension of the strand feeding into the tester, and coming out of the yarn tester. The chatter factor is the ratio of maximum pull (T3) to the feed tension (T,) minus the minimum pull (T2) to the feed tension, i.e.

T3 T2 T, T, rhe values for friction are of T2/T1 to start slipping.

The values of particular interest are the ratios and percent reduction. With other types of test devices, the numerical values may change, but the relative ratios as an index of improvement are analogous.

In this test, an uncut strand, coated as indicated, was used for the test. For use as a suture, such strand is cut to length, needled, packaged and sterilized using conventional techniques. The friction and chatter are more readily measured on continuous lengths.

Reduction in static, friction, chatter and the coefficient of friction are shown in Table III.

TABLE III Size 2/0 Silk Braid Coeff.of Level Static % Chatter % Friction % Run No. Coating (%) Friction Reduction Factor Reduction x10-2 Reduction 1 Blank - 3.15 - 0.46 - 6.300 2 Blank - 3.40 - 0.47 - 6.822 3 Blank - 3.32 - 0.46 - 6.690 4 Blank - 3.78 - 0.93 - 6.666 5 Silicone - 3.75 - 0.66 - 7.203 6 Silicone - 3.60 - 0.63 - 6.930 7 Silicone - 3.63 - 0.74 - 6.756 8 Silicone - 3.63 - 0.63 - 7.015 9 Silicone - 3.56 - 0.89 - 6.156 10 F-68 2.46 2.85 16.4 0.13 - 6.370 3.77 11 F-68 3.09 2.46 27.9 0.09 - 5.520 16.6 12 F-68 3.51 2.34 31.4 0.07 - 5.190 21.6 13 F-68 3.51 2.44 28.5 0.08 - 5.466 17.4 14 F-68 4.43 2.49 27.0 0.10 - 5.546 16.2 15 F-127 1.68 2.51 26.4 0.08 77.6 5.652 14.6 16 F-127 1.68 2.41 29.3 0.05 91.4 5.466 17.4 17 F-127 2.57 2.51 26.4 0.06 89.7 5.652 14.6 18 F-127 2.57 2.40 29.6 0.09 84.4 5.329 19.5 19 F-127 4.16 2.53 25.8 0.07 87.9 5.782 12.7 TABLE III - continued Size 2/0 Silk Braid Coeff.of Level Static % Chatter % Friction % Run No. Coating (%) Friction Reduction Factor Reduction x10-2 Reduction 20 F-127 4.16 2.39 29.9 0.05 91.4 5.412 18.2 21 F-127 5.16 2.48 27.3 0.06 89.7 5.626 15.0 22 F-127 5.16 2.38 30.2 0.05 91.4 5.357 19.1 23 F-127 5.95 2.45 28.2 0.10 82.8 5.412 18.2 24 F-127 5.95 2.52 26.1 0.07 87.9 5.705 13.8 25 F-127 5.95 2.43 28.7 0.04 93.1 5.520 16.6 26 F-127 7.72 2.43 28.7 0.08 86.2 5.439 17.8 With other braid constructions and other sizes, the relative ease of knot rundown may be greater or less for the same quantity of coating, or conversely the quantity of the coating may be adjusted to give the desired knot run-down values.

The quantity of the lubricant copolymer in the solvent may be varied, and solvents other than chloroform may be used.

Other organic solvents such as methyl alcohol, ethyl alcohol, isopropyl alcohol, methylene chloride, warm xylene (about 60 C.), tetrahydrofuran, acetone, dimethylformamide, dimethyl sulfoxide, mixtures thereof, and other similar solvents for the lubricant may be used for coating. Flowing the solution onto a moving strand, and letting the surplus drip off is another useful coating technique.

A small amount of water increases the solubility of the lubricants, and aids in coating.

In general, it is more convenient to use the solvent coating system at levels below 10 percent pick-up and use a heated die at above about 10 percent pick-up.

Example 6.

2/0 Nylon Braid Sutures Using the procedures described in Example 1, runs were made on nylon braid, sized for a 2/0 suture. The reduction in friction and chatter factors are shown in Table IV. Both uncoated braids from the same lot, and commercial silicone coated nylon were used for comparison.

The reduction in chatter is particularly outstanding.

TABLE IV 2/0 NYLON BRAID Coeff. of Level Static % Chatter oi/o Friction Run No. Coating (%) Friction Reduction Factor Reduction x 10-2 Reduction 1 Blank - 3.02 - 0.33 - 6.300 2 Blank - 2.89 - 0.53 - 6.205 3 Blank - 3.06 - 0.51 - 5.933 4 Silicone - 2.69 10.0 0.34 26.1 5.466 11.1 5 Silicone - 2.89 3.34 0.42 8.69 5.762 6.25 6 Silicone - 3.43 - 0.55 - 6.734 7 F-68 2.53 2.24 25.1 0.18 @ 60.9 4.632 24.6 8 F68 2.53 2.47 17.4 0.23 50.0 5.162 16.0 9 F8 2.53 2.43 18.7 0.16 65.2 5.218 15.1 10 F-68 4.91 2.41 19.4 0.23 50.0 4.942 19.6 11 F--68 5.60 2.29 23.4 0.18 60.9 4.726 23.1 12 F-68 5.60 2.42 19.1 0.20 56.5 5.077 17.4 13 F-68 5.60 2.46 17.1 0.17 63.0 5.274 14.2 14 F68 6.09 2.54 15.1 0.22 52.2 5.347 13.0 15 F-127 2.83 2.49 16.7 0.19 58.7 5.302 13.7 16 F-127 3.08 2.32 22.4 0.22 52.2 4.783 22.2 17 F-127 3.36 2.36 21.1 0.17 63.0 4.989 18.8 18 F-127 5.60 2.37 20.7 0.17 63.0 4.989 18.8 19 F-127 5.60 2.36 21.1 0.12 73.9 5.133 16.5 20 F-127 5.60 2.38 20.4 0.13 71.7 5.162 16.0 21 F-127 6.21 2.37 20.7 0.15 67.4 5.077 17.4 22 F-127 6.79 2.45 18.1 0.14 69.6 5.329 13.3 23 F-127 7.57 2.65 11.4 0.28 39.1 5.520 10.2 Example 7.

2/0 "Dacron" Braid Sutures - "Dacron" is a Registered Trade Mark Using the procedure of Example 1, runs were made on a polyester braid (Dacron) sized for a 2/0 suture. The reduction in friction and chatter factors are shown in Table V.

Both uncoated braid from the same lot and silicone coated braid were used for comparison. An average of the uncoated braid runs was used as a base to show improvement.

TABLE V 2/0 "Dacron" Braid Coeff. of Level Static % Chatter % Friction Run No. Coating (%) Friction Reduction Factor Reduction x 10-2 Reduction Blank - 2.89 - 0.31 - 6.027 2 Blank - 2.65 - 0.34 - 5.310 3 Blank - 2.54 - 0.28 - 5.189 4 Silicone - 2.14 14 0.19 - 4.263 5 Silicone - 2.20 - 0.17 - 4.478 6 Silicone - 2.40 - 0.27 - 4.800 7 F-127 2.39 2.60 3.45 0.33 - 5.216 5.30 8 F-I 27 5.37 2.47 8.28 0.21 32.3 4.996 9.30 9 F-127 5.12 2.36 12.4 0.21 32.3 4.871 11.6 10 F--68 4.03 2.20 18.3 0.19 38.7 4.269 22.5 11 F68 4.03 2.28 15.3 0.21 32.3 4.628 16.0 12 F--68 5.04 2.45 9.02 0.19 38.7 5.084 7.70 13 F68 6.26 2.24 16.8 0.18 41.9 4.580 16.8 14 Fd8 6.98 2.52 6.42 0.24 22.6 5.247 4.74 15 F--68 8.59 2.26 16.1 0.14 54.8 4.785 13.1 The data in the example are illustrative. Reductions in frictions and improvement in chatter are obtained on all sizes of sutures. With different materials and constructions the results may vary.

The amount of coating and the ease of run-down can be varied to give results desired by the using surgeons.

For sutures, either absorbable or non-absorbable, in which capillarity is a problem, a coating of a phosphatide, preferably purified lecithin, such as taught by United States Patent No. 2,576,576 may be used to reduce capillarity and friction, with the present coating as an additional friction reducer. Lecithin causes tissue irritation under some conditions, particularly if not pure.

Example 8.

A braides silk suture strand, of a size to form a 2/0 USP suture, is dipped in a 10% solution of "Pluronic" F--68 in chloroform, and dried. The pick-up is about 5% by weight of the weight of the strand itself.

The dried coated strand is cut into 54" segments, needled, packaged, sterilized and dried in accordance with conventional procedures.

The thus-prepared silk sutures are used in surgical procedures. When used to approximate tissue at a wound, a suture is placed in an appropriate location, and tied with a square knot. The square knot readily runs down to pull the edges of the wound to the degree of tightness desired by the using surgeon. The suture shows low tissue drag, the excellent knot run-down. When a knot is at a desired final location, three additional squared throws are placed to secure the knot. Knots buried in tissue have the lubricant bioabsorbable copolymer removed from the suture surface within 48 hours, which give additional knot security.

When removed from test animals after 48 hours, a square knot, without additional throws shows markedly greater knot security than immediately after placement.

In human tissue, insofar as can be observed, the knot security increases as the bioabsorbable lubricant coating is absorbed in tissue.

Whereas exemplified and tested with square knots, the ease of knot run-down and reduced tissue drag are useful in most suture placements and for knot retention. The amount of coating, and the relative values for knot run-down and reduced tissue drag, are variable to suit the requirement of a particular surgical situation.

The needling, packaging and sterilizing of the coated sutures is in accordance with conventional procedures.

Claims (7)

WHAT WE CLAIM IS:

1. A surgical suture having improved knot run-down characteristics and reduced tissue drag, comprising a polyfilamentary polymer strand having thereon a thin lubricating coating of a lubricating bioabsorbable (as herein defined) copolymer comprising polyoxyethylene blocks and polyoxypropylene blocks to aid run-down and handleability, said bioabsorbable copolymer having a molecular weight such that it is pasty-to-solid at 250 C.

2. A suture according to Claim 1, in which the lubricating bioabsorbable polymer has the formula:

where one of R, and R2 is methyl and the other hydrogen, and n and m are such that the polymer is pasty-to-solid at 25DC., R is the residue of a reactive hydrogen compound having from 2 to 6 reactive hydrogen atoms and having not over 6 carbon atoms in said compound, and c is the number of reactive hydrogens on the compound forming zing R.

3. A. suture according to Claim I or Claim 2, in which the polymer strand is of a bioabsorbable (as herein defined) polymer containing glycolic acid ester linkages.

4. A suture according to Claim 3, in which the bioabsorbable polymer is polyglycolic acid.

5. A suture according to Claim 1 or Claim 2, in which the polymer strand is selected from silk, cotton, nylon, a non-bioabsorbable polyester, polypropylene and polyethylene.

6. A suture according to any preceding claim, in which the lubricating coating~ is 0.1.to 25 percent by weight of the uncoated strand based on the weight of the uncoated strand forming the suture.

7. A surgical suture, according to Claim I and substantially as described in any one of the Examples herein.