CA1098668A

CA1098668A - Isotactic polypropylene surgical sutures

Info

Publication number: CA1098668A
Application number: CA282,245A
Authority: CA
Inventors: Percival W. Cummings, Jr.; John H. Goodman, Iii
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1976-08-10
Filing date: 1977-07-07
Publication date: 1981-04-07
Also published as: CH618608A5; NO772382L; IT1079280B; AR213315A1; IL52415A0; NL7708777A; DK354677A; AU512915B2; FR2361119A1; DE2735452A1; IL52415A; ES461501A1; FI772392A7; GB1588031A; DE2735452C2; JPS6130585B2; BE857612A; PT66884A; DD132635A5; SE7709022L

Abstract

Abstract of the Disclosure An isotactic polypropylene suture having good long range flex life and creep resistance is disclosed. Specifically, the suture has a denier of from about 30 to about 3000 and the following characteristics:

Tensile Strength-gpd 4.3-7.5 Knot Strength-gpd 3.0-5.0 Percent Elongation to Break 20.0-30.0 Young's Modulus-psi 5.4x105-9.5x105 Flexural Fatigue Resistance (F) (Cycles to break), as defined by, F=1.251x108xD-1.77 where D=denier Static Creep - % Elongation <8.0 To produce the suture, isotactic polypropylene is extruded at a temperature between about 425°F. and about 550°F. into a filament, and is then liquid quenched at about 125°F. to about 175°F. with simultaneous stretching thereof to about 1.0X to about 5.0X. The filament is then passed through a heating and drawing zone at about 205°F. to give from about a 5.0X to about 8.0X
draw ratio. This twice-drawn filament is then passed through a second heating and drawing zone at a temperature of about 300 to about 450°F. at a final draw of from about 0.95X to about 1.6X. The fils are then collected and cut to the required length.

Description

24,595 BACKGROUND OF THE INVENTION
Surgical sutures are divided into -two broad classes, absorbable sutures such as catgut or polyglycolic acid which are absorbed in the human body, and non-absorbable sutures which remain essentially unchanged by action of the body tissues and fluids. Such nonabsorbable sutures are frequently removed after the repaired tissues are healed, However, there are also many occasions, such as in heart repair or cardio-vascular surgery, where tissue healing never becomes self--supportive, and the sutures must provide continual non-fail-ing support. Among the several important characteristics of sutures used in such applications are (a) resistance to "creep"
or longitudinal elongation under continued stress, possibly permitting failure of a repaired section, and (b) the abili-ty of the suture to withstand long-time continued flexing such as would occur in a vessel such as the aorta due to continuous pulsation resulting from blood flow, or in heart repair, due to continuous flexing due to heart beat. Although flex and creep resistance are inherent in well made braided sutures, there are a number of reasons why surgeons prefer to use a ~ ~ monofilament suture rather than a braid suture in many of these ;~ ~ applications. Other requisities and advantages of monofila-ment sutures,~ especially oriented isotactic polypropylene ~; sutures, are reclted in U. S. Patent 3,359,983, and over whlch the instant invention is a d~stinct imProve~
ment.
; The su~ures of the present invention are prepared ; from the fil.~ments, prepared as described below, in the con-ventional manner. That is to say, the filaments are attached to a needle,Wulld , packaged and sterili2ed as is known in the art. The flex life and creep resistance of these sutures is unique for each individual suture of a specific size, as :

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sho~n more fully in the examples hereinbelow.
Due to the advantages of s~eriLe inert polyolefin su-tures, as described in U.S. Patent 3,359,983, sutures of high density linear poly-ethylene have been used to a large degree as general non-absorbable sutures.
'lowever, it ilas been reported that application of these sutures in areas such as heart repair and cardiovascular surgery has failed, presumably due to a poor long time flex life. Polypropylene sutures now being marketed are also found to have creep and flex resistance inferior ~o the novel sutures of the present invention.
SUMMARY OF THE INVENTION
.
We have now found that a polypropylene suture with a markedly superior long range flex life and an improved creep resis-tance, which renders it desirable for wound repair, can be made without sacrifice of other import-ant features attributable to iso~actic polypropylene sutures by ~he prepar-ation of the monofilament under proper process conditions. According to our invention, substantially isotactic polypropylene having a weight average molecular weight of about 350,000, although higher or lower molecular weight material may be used, is extruded at a temperature between about 425F. and about 550F. into a filament, and is then liquid quenched at about 125F
-to about 175F with simultaneous stretching thereof to about l.OX to about 5.0X. The filament is then passed through a heating and drawing zone at ; - about 205F. to give from about a 5.0X to about 8.0X draw ratio. This twice-drawr. filament is then passed through a second heating and drawing zone a~
a temperature of about 300 ~o about 450F. at a final draw of from about 0.95X to about 1.6X. The fils are then collected and cut to the required

2-.~ .

. - .. :

24,595 length. Filamen-ts made in this manner have a flex life and creep resistance far superior to polyethylene and to presently commercially available polypropylene sutures.
By "substantially iso~actic" used herein is mean~ that the polypropylene may contain up to about 15~ at~ctic confi~uration but is preferably as completely isotactic as possible.
DESCRIPTION OF THE INVENTION
INCLUDING PREFERRED EMBODIMENTS
Isotactic polypropylene pellets, either natural or colored, such as with copper phthalocyanine blue ! see U. S.
Patents No. 15 3,133,893; 3,159,498; 3~630l205; are placed into the feed hopper of a conventional polymer extruder and flow by gravity into the water-cooled extruder hopper throat where they are propelled forward through the extruder barrel by the extruder screw which is driven by a variable speed drive unit. The temperature of the extruder barrel is con-trolled at about 425-550F. by three electrically heated zone blocks surrounding the barrel, with the controller units mounted in a panel board. From the extruder, the molten polymer flows under pressure into the spin head which is heated and controlled by a heater-controller unit. The flow of the molten polymer is regulated by a precision metering pump driven by a variable speed drive. The pump forces precisely measured quantities of melt continuously through a multi-hole spin jet. The molten streamspass through a temperature controlled liquid quench bath at about 125-175F. -and are pulled over two submerged rollers and a guide-wiper unit by a godet station consisting of skewed godets to thereby stretch the filaments from about 1.0X to about 5.0X
and subsequently solidify them. They then pass through an electrically heated and controlled six-foot hot water draw tank to a second set of yodets rotatïng at a faster surface speed than the fir~t godet unit.

- 3 -24,595 This faster speed rate imparts a stretch or draw of from about 5.0X to about 8.0X to the filaments thus partially orienting them and causing a marked decrease in diameter and increase in strength. From the second godet assembly, the filaments are clrawn through a heated in~rared chamber at a temperature of from about 300-450qF. by a third godet assembly to give a draw ratio o from about 0.95-1.6X.
The filaments are then separated and wound onto spools in a manner known to those skilled in the art, i.e., the individual fils are separated through guides, passed over rollers, tension arms and reciprocating traverse guides, and are ultimately wound on spools. These spools are stored for further processing such as cutting, needling, packaging, sterilizing, etc.
As mentioned above, the substantially isotactic polypropylene filament, produced as described above, can be prepared in its natural color or can be colored by mechanically blending the pellets of polymer charged to the sxtruder with a pigment such as copper phthalocyanine blue in quantities of about 1% or lessO Plasticizers and stabilizers may also be incorporated for purposes and in a manner known to those skilled in the artO
Single strand or monofilaments are preferred as the sutures of the instant invention. Ho~ever, multi-filaments can also be used in a twisted or braided construction as i~
known in thle art. The suture~ may be of round, o~al, ~lat, square, triangular or other configurations, the specific shape thereof not forming any part of the in~tant invention The sutures may be dry-p~cked in glas~ tubes or plastic pac;kages since they are relatively stable. Howe~er,

- 4 ~

24,595 a conditioning fluid ma~ be used so as to prevent needle rust-c~ ~
ing and insure s-terility The ~ s sutures may be ~teri-lized with ethylene oxide or other sterilizincJ gas and sealed, or the package may be sealed ~irst and then sterilized by heat or radiation As mentioned above, the novel sutures of the instant invention have an exceptional:Ly long-range fle~ life, and a substantially improved creep resistance when compared to those polypropylene sutures currently commercially available.
Our sutures, therefore, possess a longer useful suture life in living bodies due to their superior resistance to creep and flexion resulting from body movement, e.g. pulsation of blood vessels, etc. They also retain tho~e other attributes of known polypropylene sutures such as strength, non-absorption, lack of toxicity, etc. which are required of a permanent or semipermanent surgical suture.
As mentioned briefly above, the unique properties of the sutures of the present invention are represented primarily by their static creep and fatigue or flex life values.
More precisely, our novel sutures comprise an essentially isotactic suture, the diameter of which ranges from about 0.0025 to about 0.030 inches, a denier of about 30 to about 3000, having the following characteristics Tensile Strength 4.3-7.5 gpd Knot Strength 3,0-5.0 gpd Break Percent Elongation 20~30 Young~s Modulus 5.4~9.5 x 10 psi or 50 80 gpd Flexural ~atigue Resistance (F) as defined F-1.251 x 10 x D 1.77 wherein D=denier Static CFeep - % Elongation ~ 8 7 0 24,595 LONGATION TESTING
The Break Percent Elongation tests in the following tables are run on a table model constant rate of extension -tensile tester manu~
factured bv the I~stron Corporation of Canton, Massachusetts.
The test method is ASTM D-2256 66T (see 1971 book, part 24). In order to eliminate excessive jaw breaks a yarn and cord style clamp is used. The 20 seconds to break is approximated by using a 10" gauge length and 10"/min. cross head speed. The cell size used is that which ~pproximates ~he su-ture size under test.
STATIC CREEP
The static creep test is designed to test the filament's ability to maintain a constant length while in a body environment under stress. This is accomplished by holding the filament in a tank of water at body temperature (36C.) under a constant stress. The original length of approximately 5" is marked by two silicone balls, and the increase in length between the balls is noted daily for 5 days.
- ~ The applied stress is varied according to the gauge of the suture under test, the loads being approximately 0.625 ~, :
gpd. The results are reported as % Elongation based on original length.
FLEXURAL FATIGUE Rh'SISTANCE
TI~e purpose of this test is to provide an accelerat- -ed means fo:r characterizing the resistance of the filament to contlnued stress~changes and flexing such as would be encountered in a vascular graft or similar operation, me test is carried out using a Tinius~Olsen MIT

6 ~

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, 24,595 Eolding endur~nce tester modified to allow variations in cycles/min,, angle of flex, and load stress. The tests cited were run at 175 cycles/min,, 270~ ~lex and approximately 1.25 gpd load according to the following table. For small suture si.zes a .010 mil clamp is used and a ,020 mil clamp for larger sizes~ The results are reported as cycles to break or failure.
Suture SizeTest Load _(grams)

5/0 75 : 3/0 500 : 15 1/0 ~317.5 MODULUS ~YOUNG~S) Sa~
r9~ ~ The Modulus is also determined using the~table model : 20 ~mstr~ tensile tester equipped with yarn and cord jaws and the appropriate cell. A 10" gauge length and a 10"/min.
cross head speed are used with a ~0"/min, chart speed. The Young's Modulus i5 calculated as the slope of the line CE
in a cIasslcal Stress-Strain curve.

_ Knot trength~ are determined on a 5cott IP-4 ~nclined Plane Te ter following the method described in ~he U.S.
Pharmacopeia, Vol. XVII, page 291, using a 127 mm gauge length : and the appropriate carriage-weight combination and a standard surgeon's knot.
The foliowlng examples are set forth for purposes of ; illustration only and are not to be construed as limitations 24r595 on the present inven-tion except as set ~orth in the appended claims. All parts and percentages are by welght unless otherwise specified.

A size 2/0 polypropylene suture is prepared from isotactic polypropylene with a weight average molecular weight of about 352,000 as follows:
4540 parts of polymer are mixed with 449 parts of a masterbatch containing 5% of copper phthalocyanine blue pigment in polymer and tumbled for 1/2-1 hour in a small drum tumbler. The blend is then transferred to an extruder hopper dryer and dried 15-18 hours at 160F, The polymer is then extruded through a standard plasticating screw extruder at 3,3 lbs./hr. The extruder has three barrel zones held at 451F., 446~F, and 481F. The head containing the pump and filter is held at 445F. and the spin jet at 535F. The spin jet has 4 holes with 60 mil diameter capillaries. The filaments extruding from the jet pass through an aqueous quench bath held at 150F. and are pulled away by a godet assembly rotating at 36 fpm to give a primary draw down of about 2.5X.Fromthis godet the filaments are drawn by a second godet rotating at 260.5 fpm through a hot water draw tank six feet long heated to 205~F. to give about a 7.2X draw ratio. The drawn filaments are drawn away 25 from the second godet by a third godet rotating at 250 fpm through a second-chamber hea-ted to;400F. to give an -additional dr;aw ratio of 0.96X.
Thefilaments are then separated into the ~ individual ~ -filaments and collected on takeup spools as individual mono-fils, At the end;~of a collection period the monofils are wound off onto appropriate si~e drums and then cut to give strands of the desired length ~or suture manufacture. The ) :

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24,595 properties of the resultant filaments are then determined as described above. The results are set forth in Table I, below.
EX~MPLE 2 A size 3/0 polypropylene suture is prepared from isotactic polypropylene with a weight average molecular weight of about 352,000 as follows:
4540 parts of polymer are mixed with 449 parts of a masterbatch containing 5% of copper phthalocyanine blue pig-ment in polymer, and tumbled for 1/2~1 hour in a small drum tumbler. The blend is then transferred to the extruder hopper dryer and dried 15-18 hours at 160~F~
The polymer is then extruded through a standard plasticating screw extruder at 3.6 lbs./hr. The extruder has three barrel zones held at 451~F., 446~F., and 481F. The head containing the pump and filter is held at 445~F. and the spin jet at 535~F. The spin ~et has 8 holes with 35 mil dia-meter capillaries~ The filaments extruding from the jet pass through an aqueous quench bath held at 150~F. and are pulled away by a godet assembly rotating at 38 fpm to give a primary draw down of about 1.65X.Fromthis godett~efilaments are drawn by a second godet rotating at 260,5 fpm through a hot water draw tank six feet long heated to 205QF. to give about a 6.9X draw ratio.The drawn filaments are dra~m a~7a~fromthe second godet by a third godet rotating at 253 fpm through a second chamber heated to 400F. to give an additional draw ratio of ;
about 0.96X.
The filaments arethen separatedintothe 8 individual filaments and collected on takeup spools as individual monoflls. At the end of a collection period the monofils 3Q are wound off onto appropriate size drums and then cut to give strands of the desired length for suture manufacture.

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i8 24,595 the properties of these filaments are set forth in Table I, below.
_AMPLE 3 A size 4/0 polypropylene suture is prepared from isotactic polypropylene with a weight avera~e molecular weight of about 352,000 as follows:
4540 parts of polymer are mixed with 449 parts of masterbatch containing 5~ of copper phthalocyanine blue pigment in polymer and tumbled for 1/2--1 hour in a small drum tumbler. The blend is then transferred to the extruder hopper dryer and dried 15-18 hours at 160~F.
The polymer is then extruded through a standard plasticating screw extruder at 2.2 lbs./hr. The extruder has three barrel zones held at 451F., 446~F.~ and 481F. The head containing the pump and filter is held at 445~F. and the spin jet at 535F. The spin ~et has 8 holes with 35 mil di-ameter capillaries, The filaments extruding from the jet pass ~hrough an aqueous quench bath held at 150~F. and are pulled away by a godet assembIy rotating at 38 fpm to give a primary draw down of about 2.5X. From this godet the filaments aredrawn by a second godet rotating at 260.5 fpm through a hot water draw tank 6 fee-t long heated to 205~F. to give about a 6.9X
draw ratio. The drawn filaments are drawnawav fromthe second godet by a third godet rotating at 250 fpm through a second chamber heated to 450~F. to give an additional draw ratio of about 0.96X.
The filaments arethense~aratedinto 8indiviaual filaments and collected on takeup spools as indivi~dual monofils.
At the end cf ~a colleckion period the monofils are wound off onto aPPrOPriate size drums and then cut to give strands of the desired~length for~suture manufacture. The properties of I ~ ~ 1 0 ~

- . . .

24,595 these filaments are determined and set forth ln Table I~ below.

A size 5/0 polypropylene suture is prepared from isotactic polypropylene with a weight average molecular weight of about 352,000 as follows;
4540 parts of polymer are mixed with 449 parts of masterbatch containing 5~ of copper phthalocyanine blue pigment in polymer and tumbled for 1/2 1 hour in a small drum tumbler. The blend is then transferred to the extruder hopper dryer and dried 15-18 hours at 160F.
The polymer is then extruded through a standard plasticating screw extruder at 1.3 lbs./hr. The extruder has three barrel zones held at 451F., 446F., and 481F.
The head containing the pump and filter is held at 445F. and the spin jet at 535F. The spin jet has 8 holes with 35 mil diameter capillaries. The filaments extruding from the jet pass through an aqueous quench batch held at 150F. and are pulled away by a godet assembly rotating at 35 fpm to give a primary draw down of about 4.3X. From this godet the ~laments are drawn by a second godet rotating at 260.5 fpm through a hot water draw tank six feet Iong heated to 205~F. to give about a 6.9X
draw ratio. The drawn filaments aredrawn away from the second ~ godet by a third godet rotating at 250 fpm through a second -` chamber heated to 450F. to give an additional draw ratio of ; 25 about 0.96X.
The filamentsc~ethen separatedintothe 8 individual filaments and collected on takeup spools as individual mono-fils. At the end of a collection period the monofils are would off onto appropriate size drums and then cut to give strands of the de~ired length ~or suture manufacture. Ta~le I, below~ sets forth the properties o~ these ~ilaments, ;

~ ~ 11 ~ ' 24,595 `EXAMPLE 5 A size 6/0 polypropylene suture is prepared from isotactic polypropylene with a weight avexage molecular weight of about 352,000 as follows~
4540 parts of polymer are mixed with 449 parts of masterbatch containing 5% of cop~er phthalocyanine blue pigment in polymer and tumbled for 1~2=1 hour in a s~all drum tumbler. The blend is then transferred to the extruder hopper dryer and dried 15-18 hours at 160~F, - 10 The polymer is then extruded through a standard plasticating screw extruder at 0.5 lbs./hr. The extruder has three barrel zones held at 451~F., 446F., and 481F. The spin jet has 8 holes with 20 mil diameter capillaries. The filaments extruding from the jet pass through an aqueous quench bath held at 150F. and are pulled away by a godet assembly rotating at 30.5 fpm to give a primary draw down of about 2.8X. From this godet the filaments aredr-awnby a second godet rotating at 185 fpm through a hot water draw tank six feet long heat~ed to 205F. to give about a 6.1 draw ratio.
The drawnfilaments aredrawnaway from-the second~odet by a third godet rotating at 250 fpm through ~ second chamber heated to 3~5F. to give an additional draw ratio of about 1.35X.
Thefilaments arethenseparatedinto the 8 individual filaments and collected on takeup spools as individual monofils.
At the end of a collection period the monofils are would off onto appropriate size drums and then cut to give strands of the desired length for suture manufacture. The properties of these ~ilamehts are set forth in Table I, below.
~ EXAMPLE 6 A size 7/0 polypropylene suture is prepared from isotactic pol~propylene With a weight average molecular weight - : :

~ ~ 12 ~ -~9B~

24,595 of about 352,000 as ~ollows~
~5~0 parts of pol~mer are mixed with 449 parts of masterbatch containing 5% of copper phthalocyanine blue pigment in polymer and tumbled for 30 minutes in a small drum tumbler. The blend is then transferred to the extruder hopper dryer and dried 15~18 hours at 150~F~
The polymer is then extruded through a standard plasticating screw extruder at 0.3 lbs./hr. The extruder has three barrel zones held at 451F., 446F., and 481~F. The head containing the pump and filter i5 held at 445F. and the spin jet at 535F. The spin jet has 8 holes with 20 mil diameter capillaries. The filaments extruding from the jet pass through an aqueous quench bath held at 150F. and are pulled away by a godet assembly rotating at 30.5 fpm to give a primary draw down of about 4.8X.F~omthisgcdett~efilaments are drawn by a second godet rotating at 161 fpm through a hot water draw tank six feet long heated to 205F~ to give about a 5.3X draw ratio. The drawn filaments aredrawnaway from the second godet by a third godet rotating at 250 fpm through a second chamber heated to 310F. to give an additional draw ratio of about 1.55X.
- m e filaments ~rethen separatedin-tothe 8 individual filaments and collected on takeup spools as individual mono-fils. ~t the end of a collection period the monofils are wound off onto appropriate size drums and then cut to give strands of the desired length ~or suture manufacture. The results of tests conducted to determine the properties of ; ~ these filaments are set forth in Table I, below, in addition to proper~ties of size 1/0, 01 and 02 sutures prepared as described above~in Examples 1-6.
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24,595 The corresponding properties of a commercially available isotactic polypropylene suture of identical size are set forth in Table II, below.

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H Z C~ E-, ~ * a P~ ~! ~
u~ ~ C~ H ~ I¢ ~ 1:~ O ~ E~ z; ~1 ~ E~ ~ C :~ ~ u~ ~ R
E E~ E C~ ~ O æ ~ ~ ~ tn -,1 r~ E-l E I
,~ u~ ~:1 ~ 1 C~ ~? E~ -~ :~ {~ IY ~ 1 ~ ~ ~ ~4 1_ ,~ P. ~ ~ m E~ ~ H al ~Z; cn E~
U~ ~ ~ ~ ~~ U~ ~ ~~ ~ O ~ U~ .
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An essentially isotactic polypropylene suture having a denier of from about 30 to about 3000, said suture having the following characteristics:

Tensile Strength-gpd 4.3-7.5 Knot Strength-gpd 3.0-5.0 Percent Elongation to Break 20.0-30.0 Young's Modulus-psi 5.4x105-9.5x105 Flexural Fatigue Resistance (F) (Cycles to break) as defined by, F=1.251x108xD-1.77 where D=denier Static Creep - % Elongation < 8.0

2. The suture of claim 1 in the form of a monofilament.

3. A method of preparing the suture of claim 1 which comprises extruding essentially isotactic polypropylene at a temperature ranging from about 425 F. to about 550°F. into a filament, liquid quenching said filament at a temperature ranging from about 125°F. to about 175°F. with a simultane-ous stretching thereof of about 1.0 to about 5.0X, passing said quenched and stretched filament through a heating and drawing zone at a temperature of about 205°F. to impart thereto about a 5.0 to about an 8.0 draw, passing said heated and drawn filament through a second heating and drawing zone at a temperature ranging from about 300°F. to about 450°F. to impart thereto a final draw of from about 0.95 to about 1.6 draw and recovering the result-ant suture.