CA1087952A

CA1087952A - Bioabsorbable coating for sutures

Info

Publication number: CA1087952A
Application number: CA286,970A
Authority: CA
Inventors: Vincent A. Perciaccante; Henry P. Landi
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1976-09-20
Filing date: 1977-09-19
Publication date: 1980-10-21
Also published as: PL200938A1; EG12793A; SE459785B; NZ184884A; NO140812B; NL7709548A; RO74976A; GB1584803A; DE2741765C2; JPS6130586B2; FI71666B; GR72957B; IT1090226B; YU218377A; PH17363A; DK153365B; SE7710486L; FI772472A; FI71666C; BR7706201A

Abstract

A B S T R A C T
The handling characteristics, including particu-larly the knot run-down, of surgical sutures and tissue drag characteristics are improved by a coating of a lubricating film of a bioabsorbable copolymer having polyethylene blocks and polyoxypropylene blocks, and which bioabsorbable copoly-mer has a molecular weight such that it is pasty to solid at 25°C.

Description

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This application relates to an absorbable or a non-absorbable surgical suture having improved knot run-down characteristics and reduced tissue drag com-prising a polyfilamentary polymer strand having thereon j .
a thin lubricating coating of a lubricating absorbable .~ 20 copol~mer comprising polyoxyethylene blocks and polyoxy-propylene blocks to aid run-down and handleability, said . . bioabsorbable copolymer having a molecular weight such that it is pasty to solid at 25C.
The lubricating coating is about 0.1 to 25 per-cent 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.
30 This application also relates to a method of :, , .
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1 closing a wound in living tissue which comprises sewing edges of a wound in living tissue with a surgical suture having the lubricating coating described above, tying the suture into a square knot, running down the square knot to approximate the tissues in a desired location, plac-ing additional throws on the square knot, and within less than about 48 hours bioab~orbing and removing the lubricant absorbable copolymer from t~le suture thereby increasing knot security ar~d, leaving the absorbable surgical suture in living tissue until the suture strand is abosrb ed by living tissue during the healing pro-cess, the suture providing useful tissue retention strength for at least 15 days and absorption being sub-stantially complete within 90 days or leaving the non-;~ ~ 15 -absorbable surgical suture in living tissue, thereby reinforcing the tissue.
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 knot 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 firm-ness chosen by the surgeon ~or the particular situation and then additional throws are tied down against the first throws of the square knot. In some instances, the ~ fir~t throw is a double twist followed by a single throw `~' to form a surgeons knot, with additional thro~s to form additional square knots on top as needed.
As contrasted with the ease of placement, is , ,, ~` ~
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1 the neces5ity o~ k~o~ security~ ~ven thc,ugh it is de-sired 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 material~ are so smooth that a knot runs down very readily and frequently becomes read-ily untied. Other sutures are o materials in which the knot tends to "lock-up" or refuse to run-down so that it ; . , .
is dif~icult to snug-down the ~hrows against th~ tissue and only a ~ew throws are needed, and security is nc,t 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, Nichols et al., Silk Sutues and Ligatures, shows poly(alkyl)methacryla~e aR a coating for silk . .. .
sutures, and the use of a hot coating die system.
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~nited States Patent No. 3,2~7,033, January 10, 1967, Schmitt and Polistina, Surgical Sutures, ; shows synthetic surgical sutures of polyglycolic acid and discloses that the surfaces o~ the fiber can be coat-ed with a silicone, beeswax, or the like to modi~y the handling or the absorption rate.
2S United States Patent No. 4,047,533, Septem-`' ber 13, 1977, Perciaccante and Landi, Absorbable Surgi-~ cal Sutures Coated ~ith Polyoxyethylene-Polyoxypropyl-`~ ene Copolymer Lubricant, discloses prior art relating to know run-down, coating, and lubrication in general ; 30 of surgical sutures.
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l surgical ~utures with polymeric materials in general is well-known. Silicones, wax, polytetrafluoroethylene, and other polymers have been used. Speci~ic coating materials with unique advantages to give improves sutures 5 are constantly being sought. ~-The surgical suture having improved knot run--down characteristics and reduced tiSsu~! drag comprises ' ', a polyfilamentary polymer strand having thereon a thin lubricating coating of a lubricating bioabsorbable co-10 polymer. The lubricating copolymer comprises polyoxy- ' ~, ,ethylene blocks and polyoxypropylene blocks to aid in ~-run-down and handleability, said blo'absorbab~e copolymer having a molecular weight such that it is pasty to solid at 25C.
In one embodiment, the lubricating bioabsorb-able copol~mer has the formula:

R[(CH2CHO)n~cH2cHo)mH]c 1~ , Rl R2 , '20 where one of R1 and R2 is methyl and the other hydrogen, and n and m are sufficiently large that t~le compc,und ' is pasty to solid at 25C., R is the residue of a r,ela-tively low molecular weight reactive hydrog,en compound having from 2 to about 6 reactive hydrogen atoms and ` 25 having not over 6 carbon atoms in said compoun~, and c is the number of reactive hydrogens on the compound orming R.
In another embodiment, the polymer strand is of a tissue absorbable polymer subject to hydrolytic degra- ~ -dation to non-toxic tissue compatible absorbable compon-, . . .

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g 952 1 ents, and which polymer has glycolic acid ester link-ages. In yet another embodiment the tissue absorbable polymer is polyglycolic acid In still another embodiment the polymer strand is selected from the group consisting of silk, cotton, nylon, a non-absorbable polyester, polypropylene, and polyethylene.
The lubricating coating is about 0.1 to 25 per-cent by weight of the uncoated strand based on the weight of the uncoated strand forming the suture, whereby both chatter and ~riction are rPduced sufficiently that a square knot is movable on the suture with control of a wound edge.
A method of closing a wound in living tissue comprises sewing edges of a wound in living tissue with the surgical suture having the lubricating coating des-cribed above, tying the suture into a square knot, run-ning down the square knot to approximate the tissue in a desired location, placing additional throws on the square knot, and within less than about ~8 hours bioab- j sorbing and removing the lubricant absorbable copolymer from the suture thereby increasing knot security, and leaving the absorbable surgical suture in living tissue ~;~ until the suture strand is absorbed by livi~g tissue dur-ing the healing process, the suture providin~ useful tis~
sue retention strength for at least 15 days and absorp-tlon being sub~tantially complete within 90 days or leav-ing the non-absorbable surgical su~ure in living tissue, thereby reinorcing the tissue.
Absorbable polyglycolic acid utures are des-. : ~, - ' ' ''... i :: ',- -... . . ~

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1 cribed ~n United States Patent No. 3,297,033, ~upra.
Other synthetic absorbable sutures which absorb in liv-ing tissue may be coated with improved results. At present absorbable sutues meeting with market acceptance are those in which ~he degradation or absorption in tis-sue results from the hydrolytic degradation of glycolic acid ester linkages. Such materials are preRently being ; sold under the trademarks Dexon~ and Vicryl~. The pres-ent invention may be used with other synthetic absorb-able surgical sutures, described in the prior art, and as they are developed. With synthetic absorbable sut-ures the problem of a coating to improve knot run-down characteristics is made more difficult by the require-ment that the coating must be non-toxic and absorbable.
! 15 Non-absorbable sutures are sutures which are ,, .
: resistant to biodegradation in living mammalian tissue ~ and remain in the tissue as a foreign body, unless surg-~ . .
i ically removed (e.g. skin sutures) or extruded. Non--absorbable sutures retain strength in living mammalian tissue for an extended period, often for the life of the subject. Non-absorbable sutures used for skin clos- -UreQ with the knot above the surface of the skin are re-moved by the surgeon at a suitable stage of the healing process~ For those in wl;ich the knot in the non-absorb-able suture is buried in living tissue, and are to be :;
`` left indefinitelyr the present lubricant is absorbed from the non-absorbable suture in less than about 48 hours, and hence the lubricating action ceases, and knot security improves.
Non-absorbable sutures are typically of silk, ; ~ .
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-1 cotton, nylon, a non-absorbable polyester (Dacron~) polypropylene, polyethylene, or linen. ~ven metals such as stainless steel, monofilament or braided or tantalum or platinum have been used.
Absorbable or bioabsorbable as applied to the coating, refers to a coating which by hydrolytic or enzymatic degradation, or by its inherent characteris-tic, 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 hy-drolyzed or degraded form The lubricant coating not only aids in the knot run-down characteristics but increases the smooth-ness 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 reduc~ion in fric- ~
tion is called reduced tissue drag. The coating that ;
aids in reduced ti~sue drag, and lubricates in knot placement also causes the knot to slip more readily.
; 20 Another unexpected and unobvious advantage of the present lubricant coating in that the lubricant co-polymers are absorbed from the suture within a few days so as the wound heals knot security improves.
The absorbable coating is one or more of a group of compounds having blocks of polyoxyethylene and blocks of polyoxypropylene in their structure. For sim-- plicity and ease of description these co~lpounds are taught, drawn and treated as if there were merely two or three blocks in the chain. However, it is to be under-stood that non-significant qualities of polyoxypropylene . .

,, ', l may be preisent in the polyoxyethylene block and minor quantities of polyoxyethylene 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 commercial-', ly available grades are acceptable and found to have a - low and acceptable degree of toxicity.
, The present lubricants may be indicated as hav-;' ' ing the formula:

; R@(CH2CHO)n(CH2CHO)mH]C
Rl R2 , where or!e of Rl and R2 is mekhyl ànd the other hydro-gen, and n and m are sufficiently large that the com-pound is pasty to solid at 25C., R is the residue ofa relatively low molecular weight reactive hydrogen , compound having from 2 to about 6 reacti~e hydrogen ; atoms and having not over 6 carbon atoms in sald com-poundj and c is the number of reactive hydrogens on the ;, ,~ . .
"~ 20 compound forming R. Those compounds which are at least pasty at 25C. are preferred because they adhere better to the synthetic absorbable polyfilamentary suture. ', ~' There is not a sharp cut,off, but in general as the ma-terials become more pasty or solid, their effectivenss i~ 25 improves.
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` These lubricating bioabsorbable copolymers are ' ,~ often clas~ed as surface active agents as the polyoxy-ethylene blocks are predominantly hydrophylic and the '; ' polyoxypropylene blocks are predominantly hydrophobic.

The materials have been sold by the Wyandotte Chemical , ;;;
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1 Cc~mpany, Michigan, U.S.A. under the tradem~rk of PL~RONICS for t}~e formula:

2 2)X~OCllc~2)y~oc~2cH2)zOH

.5 wherein x, y and z are whole numbers;
REVERSE PLURONICS for the formula:

H(oc~lcH2)n(oc~l2c~2)~(ocHcH2~o , ,, , , , ~,, where n, m and o are whole numbers; and :
.~ETRONICS for the formula:
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where q and r are whole numbers.
For the present purposes as synthetic absorb-. able suture lu~ricants, the values o~ x, y, z, n, m, o, ; q and r are such that the lubricants are pasty to solid at 25C. .
. The paste~ are opaque semi-solids with melt-.,j : .
.ing points above room temperature--preferably above about 40C.

` ~ Those clas~ed as Pluronic~. are particularly ` 30 useful for the present invention.

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1The formulations of certain commercially avail-able products is approximately that shown in Table I.
As all compositions are mixtures, all values are approximate, and values are subject to some round-ing.

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1 In general, the Pluronics with a molecular weigh~ range of from about 4,750 to 16,250 are waxy sol-ids. The polyoxypropylene portion has a molecular weight of 950 to 4,000 and the polyoxyethylene content o~ about 60-80~.
The pastes in general have a total molecular weight ranging from 3,500 to 5,700 with a polyoxypro-; pylene~molecular weight range of 1,750 tc, 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-poLy- :
oxypropylene comp~unds of the present invention is shown in the following table.

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1 For a general background description o~ the lubricant compounds and methods o~ manu~acture, see United States Patent No. 4,047,533, Sep~ember 13, 1977.
P~rciaccante and Landi, Absorbable Surqical Sutures Coated with Polyoxyethylene-Polyoxypropylene Copoly-mer Lubricant.
The ~trand of the suture is used as the basis for weight in determining the quantity of material that is placed on the synthetic absorbable polymer strand in forming the absorbable surgical ~utureO
The quantity of the 1ubricating bioabsorbable copolymer is from about 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 ~15 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 var-; ious filaments themselves being partially or totally .
covered.
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~ The wide range of cc.ating weight permits adap-tation of the present sutures to many varied uses. Be-cause the strand to be coated to form the suture may have considerable variation in surface roughness, due to the mechanical qtructure, i.eO braid or twist, etc. as well as being made from filament~ which are less than 2 den-~ ier per filament to more than 6 denier per filament, with - the ~ner filament sizes givin~ a smoother ~urface; and because the filamen1q may be stretched after t~e ~uture is manufactured or ln heat treatment, tha ~urface rough-, :' ', .

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1 ness basically can vary. Th~! smoother surfaces require less of the lubricating ~ioabsorbable copolymer for analogous degrees of slippage.
The various surgical techniques u~.ed interact with the desired degree of lubrication. For any given type of knot, a larger quantity of lubricant which for a particular technique incr~ases the ease of run-dowl, also increases the ease of the knot running back or slipping, called knot security. For some surgical pro-cedures it is highly desirable that the knot be veryfree in running down, ~ven 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 m(,re 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 ade-quate knot security. Thus the sur ~on can either adapt his knot technique to a particular suture, or can get sutures whose urface lubricity is best adapted to the technique which the ~urgeon desires to use. Generally, there i8 an adaptation of each tc tha other. The surgeon attempts to get a suture whose characteristics are those - 30 which he prefers, and then adapts hiw knot typing tech-: . .
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l niques to the sutures that he has at the time. Some surgeons make very successful knots with stainless steel wire using a knotting techrique that is adapted to such - a wire which has very poor run-down. Others prefer a much more readily run~down well-lubri(ated suture.
-Because the ease of knot rlin-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 surg-ical procedure. By changing the quantity o the lubri-cant bioabsorbable copolymer, the run-dc.wn can be modi-fied to suit a using surgeon's preference.
The time of use of the knots can be quire var-ied.
; 15 secause the present lubr1cating bioabsorbable copolymer is removed from the suture in living tissues, as the lubricant is removed the knot Recurity increases and after 48 hours more or less, knot security is greatly - improved.
The requirements of surgery are extremely var-ied, and various coating weights permit adaptat1on of sutures to different conditions. In general, if the surgeon desires a better lubricated sut:ure, 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 character-istics in favor of greater knot security, the cc.ating -level is reduced in favor of this particular compromise.
Usually from 2 percent to 8 percent of the lub-ricant bioabsorbable copolymer gives a useful range of ' :

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1 compromi5e between the ease of knot run-down and knot security.
A usage of about 5 percent b~- weight of Pluronic F-68 is a preferred compromise between ~he --knot run-down and knot security requiremen~s 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 cer-tain conditions.
Example 1 Run Down and Chatter Test A set of 2/0 USP XIX (d.ameter 0.339 mm, max-imum) polyglycolic acid sutures braided ~rom a 2 denier per fiIament extrusion, was coated with 7 levels of Pluronic F-68 and a blank, that is no caoting, then sub-jected to a square knot run-down test~
In this test, the suture is tied with a square knot around a cylinder with a 4 irlch periphery. The loop thus formed ie slipped o~f 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 sut:ure. There is som~: chatter or 25 variation in knot run-down t~,nsion as the knot travels down the suture. This is graphically plotted. Out of a set of runs with various coating levels, the fraction U i8 indicated in which the maximum force for the knot run--down is within the separate ranges g ven in the table.

30 All of the knots for coated sutures ran down tke full .~ . .
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1 length of the suture without br~aking. The knot bre2~k-ing strength of the suture braid was in a range of 7 to 8 pounds. For uncoated braid, the knot locked up and the suture broke in 9 out of 10 tests.

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l 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 chloro-form.
With other braid constructions and other sizes, the relative ease of knot run-down may be greater or lesR for the same quan~ity of ooating, or conversely, the quantity of the coating may be adjusted to give the desired knot run-down values. -; ~ lO 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 chloridel warm xylene (about 60C.), tetrahydrofuran, acetone, di-methylformamide, dimethyl sulfoxide 9 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 i~ another useful coat-ing technique.
A small amount of water increases the solubil-ity of the lubricar.ts, and aids in coating, but the time of contact with water of the suture should be mini-mized so that if moisture is present in the~ coating sys-tem, the sutures should be dried and desiccated promptly.
`~ In genera]. it is more convenient to use the solvent coating ~ystem at leve~s below lO percent pick-up and use a heated die at above about lO percent pick-up.

Example 2 ~ 30 A series of runs was made using a coating of ..;
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1 two commercial Pluronics F-68 and F-121 on 2/0 size sut-ures o~ 6 dpf braided absorbable polyglycolic acid sut-ures. The coatings were applied by a solution of the Pluronic in chloroform. The concentration of the Pluronic in the solution used for coatinc, is approximately twice that obtained in ~,e 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 ln concenl:ra--tion can be made to secure any desi~ed level. The strand being coated was braided for a 2/0 size su~ure using a 6 denier per filament extrusion of polyglycolic acid.
An uncoated sut,lre 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 Model 321 dual channel amE,lifier recorder was used to record the ten-sion of the strand feeding into the tester, and coming out of the yarn tester. The chatter factor i5 the ratio of maximum pull (T3) to the feed tension (Tl) minus the minimum pull (T2) to the feed tension, i.e. T3 - T2.
The values for friction are of T2 to start sllpping.
The values of particular interest are the ratios and percent reduction. With other typect of test . , .
devices, the numerical values may change, but the rela-tive ratios as an index of improvemer,t are analogous.

In this test, an uncut strand, coated as indi-cated, was used for the test. For use as a suture, such ; strand is cut to length, needled, packaged and steriliz-~;~ ed using conventional techniques. The friction and ., ~
`; 30 chatter is more readily measured or, con~inuous leng~hs.
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1 Reduction in st.atic friction, chatter and the coefficient of friction are shown for typical coati~,g levels, and sutures in Table IV.

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l F,xample 3 A series of runs, including blank, were made with solutions of the Pluronic~ R bioabsorbable lubri- :
cant copolymers in chloroform, using the procedures of Example 2. The fol lowing Table V shows the improvement . obtained in chatter and friction with a series of poly-: mers and concentrations.

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1 Example 4 A braided polyglycolic acid strand, of a size to form a 2/0 USP suture is dlpped in a 10% solution of Pluronic F-68 in chloroform, and dried. The pick-up is about 5~ by weight of the weight c,f the strand itself.
The dried coated strand is cut into 54" seg-ments, needled, packaged, sterilized and dried in accord-ance with conventional procedures The thus-prepared sutures were used in surg-ical procedures. When used to approximate tissue at awound, a suture is placed in an appropriate location, and tied with a squar~ knot. The ~quare knot readily ran down to pull the edges of the wound to the degree of tightness desired bv t~e 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 placbd to secure the knot. Knots bur-; ied in tissue have the lubricant bioabsorbalbe copolymer removed from the suture surface within 48 hours, which 20 give additional knot security. The suture itself main-tains tiss~le retaining strength for at least 15 days, and is substantially ahsorbed in 90 days.
Whereas exempliefied and tested with square u knots, the ease of knot run-down and reduced tissue drag '; 25 are useful in most sutur~ placements and for knot reten-tion. The amount of coating, and the relative values for knot run-down and reduced tissue drag, i~ variable ~ to suit the requirements of a particular surgical situa~
; tion.
` 30 The needling, packaging an~ sterilizing of the : . '' ~ - - 31 -., . . : . . . , -, .: : , : .

-~ la~s,~ss2 1 coated sutures is in accordance with cc~nventiOnal proced-ures.
Example 5 .
Friction and Chatter Tests ~ .
A set of 2/0 USP XIX (di~meter 0.339 mm., mc,x-imum) braided silk sutures was coated with 5 levels of Pluronic F-68; and 12 levels of Pluronic F-127.

4 Blanks were run with no coating, on braid from the same lot, for comparison, and an average of ; 10 these 4 used for comparative values.
Also 5 runs were made using a commexcial sili-cone coated silk sutire, 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 in chloroform at a concentra-tion of about twice the percentage desired for the coat-ing on the suture, and air dried.
A standard ATI,AB Yarn Friction Tester Model CS-151-026, Custom Scientiflc Instruments, Inc., Whippany, NeW Jersey, with a Hewlett Packard Model 321 dual channel ampllfier recorder was used to record the tension of the strand feeding into the tester, and com-ing out of the yarn tester. The chatter factor is the ratio of maximum pull (T3) to the feed tension (Tl) minus the minimum pull (T2) to the feed tension, i.e.
T3 - T2 . The values for friction are of T2 to start Tl Tl 1 sIipping.

The values of particular intereRt are the ~ratios and percent reduction. With other types of test device~, th~, numerical value~ may change, but the rela-.
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1 tive ratios as an index of improvement are analogous.
In this t.est, an uncut strand, coated as in-dicated, was used for the test.. For use as a suture;
such strand is cut to length, needled, pac~aged and sterilized using conventional technique~. The friction and chatter is more readily measured on continuous lengths.
Reduction in static,friction, chatter and thecoefficient of friction are shown in Table III.

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With other braid constr~ctions and other sizes, the relative ease cf knot run-down may be greater or less for the same quantity of coating, or conversely the quan-tity of the coating may be adjusted tci 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 slch as methyl alcohol, ethyl alcohol, i9c:propyl alcohol, methylene chloride warm xylene (about 60C.), tetrahydrofuran, acetone, di-, methylformamide, 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 coat-ing technique.
A small amount of water increases the solubil-i~y of the lubricants, and aids in coating.
In general, it is more convenient to use the solvent coating system at levels be]ow 10 percent pick--UE. and use a heated die at above about 10 percent pick-up.
Exam~-le 6 2/0 Nylon Braided Sutures Using the procedures de cribed in Example 1, runs were made on nylon braid, sized for a 2/0 suture.
The reduction in friction and chatter factors ~re shown in Table IV. Both uncoated braid~ ~rom the same lot, and commercial silicone coated nylon were used for com-parison.

The reduction in chatter isparticularly out-standing.
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1 Example 7 2/0 Dacron~ Braid Sutures_ Using the procedur~ of Example 1, runs we~e - made on a polyester braid (Dacron~) sized for a 2/0 sut-ure. The reduction in friction and chatter factors are shown in Table V.
Both uncaated braid from the same lot and ~
cone coated braid were used for ~omparison. An average -of the uncoated braid runs was used as a base to show ~ ~
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1 The data in the example is illu~trative. Re-ductions in frictions and improvement in chatter is ob-; tained on all sizes of sutures. With different materials and constructions the result~ 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, ei~her absorbable or non-absorb-able, in which capillarity is a problem, a coating of a 10 phosphatide, preferably purified lecithin, such as ~ -taught by United States Fatent No. 2,576,576 may be used to reduce capillarity and friction, wi~h the pres-ent coating as an additional friction reductant. Leci-thin causes tissue irri~ation under some conditions, particularly if not pure.
_ample 8 A braided silk s~ture 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" seg~
ments, needled, packaged~ sterilized and dried in ac-cordance 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 `~
~hows low ti~sue drag, and excellent knot run-down. When . . .

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1 a knot is at a de~ired final location, three additional squared throws are placed to secure the knot. Knots bur-ied in tissue have the lubricant bioabsorbab ~ copolymer removed from the suture surface within 48 hours, which gives additional knot security.
When removed from test animals after 48 hours, a square knot, without additional throws shows markedly greater knot securit~ than immediately after placement.
In human tissue, insofar as can be observed, the knot security increases as the bioabsorbalbe lubri-cant coating is absorbed in tissue.
- Whereas exemplified and tested with square knots, the ease of knot run-d~.wn and reduced tissue drag are useful in most suture placements and for knot reten-tion. The amount of coating, and the relative values for knot run-down and reduced tissue drag, is variable to suit the requirement of a particular surgical situa-tion.
The needling, packaging and sterilizing of the coated sutures is in accordance with conventional procedures.

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Claims

1. A surgical suture having improved knot run-down characteristics and reduced tissue drag com-prising a polyfilamentary polymer strand having thereon a thin lubricating coating of a lubricating absorbable copolymer comprising polyoxyethylene blocks and poly-oxypropylene blocks to aid run-down and handleability, said bioabsorbable copolymer having a molecular weight such that it is pasty to solid at 25°C.

2. The suture of Claim 1 in which the lubri-cating bioabsorbable polymer has the formula:

where one of R1 and R2 is methyl and the other hydrogen, and n and m are sufficiently large that the compound is pasty to solid at 25°C., R is the residue of a relative-ly low molecular weight reactive hydrogen compound hav-ing from 2 to about 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.

3. The suture of Claim 1 in which the polymer strand is of a tissue absorbable polymer subject to hy-drolytic degradation to non-toxic tissue compatible absorbable components, and which polymer has glycolic acid ester linkages.

4. The suture of Claim 2 in which the polymer strand is of a tissue absorbable polymer subject to hy-drolytic degradation to non-toxic tissue compatible absorbable components, and which polymer has glycolic acid ester linkages.

5. The suture of Claim 3 in which the tissue absorbable polymer is polyglycolic acid.

6. The suture of Claim 4 in which the tissue absorbable polymer is polyglycolic acid.

7. The suture of Claim 1 in which the polymer strand is selected from the group consisting of silk, cotton, nylon, a non-absorbable polyester, polypropylene and polyethylene.

8. The suture of Claim 2 in which the polymer strand is selected from the group consisting of silk, cotton, nylon, a non-absorbable polyester, polypropylene and polyethylene.

9. The suture of Claim 1 in which the lubri-cating coating is about 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 fric-tion are reduced sufficiently that a square knot is mov-able on the suture with control of a wound edge.

10. The suture of Claim 2 in which the lubri-cating coating is about 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 fric-tion are reduced sufficiently that a square knot is mov-able on the suture with control of a wound edge.

11. The suture of Claim 5 in which the lubri-cating coating is about 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 fric-tion are reduced sufficiently that a square knot is mov-able on the suture with control of a wound edge.

12. The suture of Claim 6 in which the lubri-cating coating is about 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 fric-tion are reduced sufficiently that a square knot is mov-able on the suture with control of a wound edge.

13. The suture of Claim 7 in which the lubri-cating coating is about 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 fric-tion are reduced sufficiently that a square knot is mov-able on the suture with control of a wound edge.

14. The suture of Claim 8 in which the lubri-cating coating is about 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 fric-tion are reduced sufficiently that a square knot is mov-able on the suture with control of a wound edge.

15. A method of closing a wound in living tissue which comprises: sewing edges of a wound in living tissue with the surgical suture of Claim 1, ty-ing the suture into a square knot, running down the square knot to approximate the tissues in a desired lo-cation, placing additional throws on the square knot, and within less than about 48 hours bioabsorbing and removing the lubricant absorbable copolymer from the suture thereby increasing knot security, and leaving the absorbable surgical suture in living tissue until the suture strand is absorbed by living tissue during the healing process, the suture providing useful tissue retention strength for at least 15 days and absorption being substantially complete within 90 days or leaving the non-absorbable surgical suture in living tissue, thereby reinforcing the tissue.