NO772382L - SURGICAL SUTUR. - Google Patents

Description

Surgical sutures can be broadly divided into two classes, namely absorbable sutures, such as catgut or polyglycolic acid which are absorbed into the human body, and sutures of non-absorbable materials which remain largely unchanged under the influence of the body's tissues and fluids. Such non-absorbable sutures are often removed after the repaired tissues have healed. There are, however, several cases, e.g. in heart operations or cardiovascular surgery, where the tissue that is healed never becomes self-supporting

they and where the sutures must ensure continuous and fail-safe support.

Among the various proper features of sutures for such applications are (a) the resistance to longitudinal creep or expansion under continuous stress which may eventually lead to failure of the repaired portion and (b) the ability to withstand sustained, continuous bending, f .ex. in such a vessel as the aorta, and where the bending is due to a continuous pulsation of the blood flow. The same can be the case after heart surgery, where constant bending occurs as a result of the heartbeat. Although bending resistance and creep resistance are inherent properties of properly manufactured braided sutures, there are a number of reasons why surgical

ger rather prefers to use a monofilament suture for many of the aforementioned applications.

The sutures in accordance with the invention are produced on

similar manner of filaments made as described below. This means that the filaments are attached to a needle, wound, packaged and sterilized in the usual way. The flexibility and creep resistance of dis-

se sutures is special for each individual suture of a certain size, which will be evident from the following examples.

As usually non-absorbable sutures, one has in hay

degree used sutures of linear polyethylene with high density. However, it has been shown that such sutures have failed during use after heart surgery and cardiovascular surgery presumably as

resulting in poor service life which in turn is due to poor resistance to repeated bending. Polypropylene sutures available on the market have creep resistance properties that are inferior to the suture according to the invention.

It has been found that it is possible to produce a polypropylene suture with a significantly longer life and better resistance to creep and which is suitable for use in wound repair without having to sacrifice other important advantages of isotactic polypropylene sutures by making the monofilament under specific process conditions. In accordance with the invention, essentially isotactic polypropylene is extruded with an average molecular weight of approximately 350,000, although higher or lower molecular weight can be used, using a conventional extruder, at an extrusion temperature between 218°C and 280°C, after which the liquid cooled to approximately 52-80°C. The filaments are then stretched from 1 to about 5 times in a stretching device. After the first stretching device, the yarn is passed by means of another stretching device through a 1.8 m long tank of hot water at 96°C for further stretching from 5 times to about 8 times. This double drawn yarn is then stretched once more through a 1.8 m long infrared chamber, where the yarn is heated to about 150-230°C and the final draw ratio is from about 0.95 to about 1.6. The filaments are then collected and cut to specific lengths. Filaments produced in this way have good bending fatigue properties and great creep resistance, which is much better than for polyethylene otherwise and better than for polypropylene sutures that can currently be obtained on the market. By "essentially isotactic" is meant here that polypropylene can contain up to approximately 15% atactic configurations, but is preferably as completely isotactic as possible.

Pellets of isotactic polypropylene, either naturally colored or dyed, such as with copper phthalcyanine blue, are placed in a hopper of a conventional extruder for polymer material and, as a result of gravity, flow into the extruder's water-cooled throat, where the material is driven through the extruder's tube by means of ex- the auger which is driven from a drive unit with variable speed. The extruder cylinder's temperature is kept at 218-288°C by means of three electrically heated zone blocks that surround the cylinder and are controlled from a control table. Molten polymer material flows from the extruder under pressure into the spinning head, which is heated and controlled from a control unit. The flow of molten polymer is regulated by a pump for precision feeding by means of a variable speed drive. The pump forces precisely measured quantities of the melt continuously through a multi-hole spinning die. The molten polymer stream passes through a cooling bath of liquid at about 52-80°C and is drawn over two submerged rolls and a guide using a draw station with inclined rolls for stretching the filaments to about five times<p>g subsequent solidification. The filaments are then passed through a drawing tank with heated water which is 1.8 m high and which is heated electrically and through another stretching device with a greater surface speed than the first. Here the filaments are stretched up to approximately 8 times, so that the filament material is partially oriented and there is a marked reduction in the filament diameter and an increase in the filament strength. From the second drawing device, the filaments are drawn to an infrared chamber with a temperature of about 149-232°C by means of a third drawing device where the drawing ratio can be from about 0.95 to 1.6 times.

The filaments are then separated and wound on coils in a known manner, i.e. that the individual filaments are guided through guides, over rollers, tension arms and reciprocating transverse guides for winding onto coils. These coils are stored for later processing, such as cutting, needling, packing, sterilization etc.

As mentioned above, the filaments made essentially of isotactic propylene can be made in their natural color or can be mechanically colored by mixing pellets of polymer fed to the extruder with a pigment, such as copper phthalcyanine blue in an amount of about 1% or less. Softeners and stabilizers may also be added.

Certain monofilaments are preferred as sutures according to the invention. Multifilaments can, however, be used in a twisted or braided construction of a type known per se. The sutures can be round, oval, flat, square, triangular or have other cross-sectional shapes.

The sutures can be dry packed in glass tubes or plastic packs because they are relatively stable. However, a conditioning fluid can be used to prevent rusting of the needle and ensure sterility. The packaged sutures can be sterilized with ethylene oxide or other sterilizing gas and sealed, or the package can be sealed first and then sterilized by heat or radiation.

As mentioned, the new sutures according to the invention possess exceptionally high resistance to bending fatigue fracture and high creep resistance compared to previously known polypropylene sutures. The effective service life of the sutures in living bodies is therefore considerably longer, which is due to their resistance to creeping and bending as a result of the body's movement, e.g. pulsation of the blood vessels, etc. Moreover, they possess other advantageous features that polypropylene sutures have, such as strength, non-absorption, lack of toxicity, etc., i.e. properties required for a permanent or semi-permanent surgical structure.

More particularly, the new suture of the invention is largely of isotactic material and has a diameter of from about 0.064 mm to about 0.762 mm, a denier of about 30 to 3000 and otherwise the following properties:

Extension attempt

Elongation tests were performed in an Instron apparatus manufactured by Instron Corporation of Canton, Massachusetts.

The method was ASTM D-2256 66T (see the 1971 ASTM book, Part 24). In order to avoid too frequent twine breakage at the slopes, a twine and cord type clamp was used. The 20 seconds to break was reached using a sample length of 25.4 cm under the crosshead speed of 25.4 cm per second. minute. The cell size was as appropriate for the suture size under test.

Static creep

This experiment was carried out to investigate the filament's ability to maintain constant length in an environment under tension. This was done by keeping the filament in a water tank at a temperature of 36°C and under constant tension. The initial length of approximately 12.7 cm was marked with two silicone balls and the increase in length between the balls was noted every day for five days.

The applied tension was varied according to the diameter or transverse dimension of the suture in question and the load was approximately 0.625 gpd. The results are set up. as an extension in % of the original length.

Bending fatigue resistance

The purpose of this test is to provide a device for determining the resistance of the filaments to continuous voltage changes and bending, as may be the case in a blood vessel branch e.1.

The experiment was carried out in a bending tester of the Tinius-Olsen type MIT with the opportunity to vary the number of cycles per min, the bending angle and the load. Tests were performed at approximately 175 cycles/min, 270° bend angle and approximately 1.25 gpd load as indicated in the following table. For sutures of small sizes, a clamp of 2.5 x 10 mm was used--4 -4 tet and for large sutures 5.08 x 10 mm. The results indicated as the number of cycles are breaks or failures.

Young's modulus

The module is determined using the Instron apparatus equipped with yarn and cord trays and an appropriate load cell. The measuring length was 25.4 cm and the speed of the crosshead 25.4 cm/min. The curve card speed was 50.8 cm/min and the modulus is calculated as the angle of the line CE of the classical stress-strain curve.

Knot strength

The knot strengths were determined in a Scott IP-4 inclined plane apparatus according to the method described in U.S. Pharmacopeie, Volume XVII, page 291, using a specimen of 127 mm length and appropriate weight load and a standard surgeon's knot.

The following examples are set out only to illustrate the invention and do not represent a limitation of the invention. If something else is not specified, the percentage values are specified in weight percent.

Example 1

Suture with dimension 2/0 is made of isotactic polypropylene. with an average molecular weight of 352,000.

4540 parts of polymer are mixed with 449 parts of stock mixture containing 5% copper phthalcyanine blue and stirred for k -1 hour in a small drum mixer. The mixture is transferred to an extruded hopper dryer and dried for 15-18 hours at 71°C.

The polymer is then extruded through a standard screw-kee extruder at a rate of 1.5 kg/hour. The extruder has three cylinder zones respectively kept at 233, 230 and 249°C. The pump and file-

the teret is kept at 229°C and the spinneret at 279°C. The spinning nozzle has four holes with a diameter of 1.52 mm. The filaments which are extruded from the nozzle are passed through a cooling bath at 66°C and drawn away with a drawing device having a rotational speed of approximately 11 m/min. for the first stretch of about 2.5. From this stretching device draw

the yarn is drawn using another stretching device with a high-speed

hot at 79.4 m/min. through a hot water tank that has a length of

1.8 m and a temperature of 96 o C for stretching with a stretch ratio of 7.2. The yarn is then fed to a third stretching device at a speed of approx. 83 m/min. through a second chamber heated to 204°C for further stretching at a strain ratio of 0.96.

The yarn is then separated into 4 single filaments and wound

onto spools like monofilaments. At the end of the collection, the filaments are unwound on drums of suitable size and clip-

pes into strings of the desired length for the manufacture of sutures. The properties of the manufactured filaments are then determined as

indicated above. The results are listed in the table below

IN.

Example 2-

Polypropylene suture of dimension 3/0 is manufactured from isotak-

tical propylene with a molecular weight of approximately 352,000.

4540 parts polymer is mixed with 449 parts of a. stock mix containing 5% copper phthalcyanine blue and stirred for 1 hour in a small drum mixer. The mixture is transferred to a drier and dried for 15-18 hours at 71°C.

The polymer is then extruded through a standard screw extruder at a rate of 1.63 kg/hour. The extruder has three cylinder zones which are held at 233, 230 and 249°C. The top of the extrusion

the vessel containing the pump and filter is kept at 229°C and the nozzle at 279°C. The nozzle has 8 holes with a diameter of 0.89 mm. The filaments extruded from the die pass through an aqueous cooling bath

at 66°C and is pulled away with a stretching device with a peripheral speed of 11.6 m/min., which gives the filaments a first stretch with a stretch ratio of 1.65. The yarn is then drawn using another tensioning device which rotates at a peripheral speed of 79.4 m/min. at the same time as it is passed through a hot water bath in a 1.8m long tank heated to 96°C, where the yarn is given a stretch of 6.9. The yarn is then removed by a third tensioner rotating at a circumferential speed of 76.2 m/min. through another chamber heated to 204°C, where the additional stretch ratio imparted to the yarn is approximately 0.96.

The yarn is then collected into 8 separate filaments which

■winds up as monofilaments. These monofilaments are wound on suitably large drums and cut to suitable lengths for making sutures. The properties of the filaments can be found in Table I below.

Example 3

A suture with dimension 4/0 is made from isotactic po-

r lypropylene with an average molecular weight of approximately 352,000 as follows: 4540 parts of polymer are mixed with 449 parts of stock mix containing 5% copper phthalcyanine blue and stirred in a mixing chamber-

flour for a \-\ hour. The mixture is transferred to an extruder dryer and dried for 15-18 hours at 71°C.

The polymer is extruded through a standard extruder at a rate of 1 kg/hour. The extruder has three cylinder zones which are held at 233, 230 and 249°C. The pump and filter unit is kept at 229°C and the spinneret at 279°C. The spinning nozzle has 8 holes with dia-

meter 0.89 mm. The filaments which are extruded are passed through a cooling bath at 66°C and drawn away by means of a stretching device which rotates at a peripheral speed of 11.6 m/min. and imparts filamén-

have a stretch ratio of 2.5. From there, the yarn is drawn using another stretching device which rotates at 79.4 m/min., as it is passed through a 1.8 m long tank filled with hot water at 96°C and the yarn is given a stretch ratio of 6.9. The yarn is then drawn by means of a third drawing device, the peripheral speed of which is 76.2 m/min., through another chamber' heated to 232 o Cr and where the drawing ratio is 0.96.

The yarn is then collected as 8 individual filaments

which are wound up as monofilaments on suitable drums and cut into strands of suitable length for the production of

sutures. The properties of these filaments appear from the table I mentioned below.

Example 4

A suture with dimension 5/0 is produced from isotactic polypropylene with an average molecular weight of 352,000.

4540 parts of polymer are mixed with 449 parts of stock mix

which contains 5% copper phthalcyanine blue and is stirred for h~ l hour in a small mixing drum. The mixture is then transferred to the extruder dryer and dried for 15-18 hours at 71°C.

The polymer is then extruded through a standard extruder, at a rate of 0.59 kg/hour. The extruder has three cylinder zones which are held at 233, 230 and 249°C. The extruder top,

which contains the pump and filter, is kept at 229°C and the spinning nozzle at 279°C. The nozzle has 8 holes and the hole diameter is 0.89 mm. Filamén-

The fibers extruded from the nozzle are passed through an aqueous cooling bath at 66°C and drawn away by means of a rotating stretching device.

which has a peripheral speed of 10.7 m/min and which stretches

ker the yarn 4.3 times. From there, the yarn is drawn using another tensioning device which rotates at a circumferential speed of

79.4 m/min. and which leads the yarn through a tank with a length of 1.8 m

and which contains water with a temperature of 9 6°C, where the stretch increases to 6.9 times. This yarn is then drawn with the help of a third tensioning device whose peripheral speed is 76.2 m/min. at the same time as the yarn passes through another chamber with a temperature of 2 32°C, and where the stretch ratio is measured at 0.96 times.

The yarn is then separated into 8 single filaments which collect

read separately on suitable drums and cut to suitable lengths

there for the production of sutures. The filament properties appear in table I below.

Example 5

Size 6/0 suture is made from isotactic polypropylene with an average molecular weight of approximately 352,000.

4540 parts of polymer are mixed with 449 parts of stock mix

containing 5% copper phthalcyanine blue and stirred for ^-1 hour i

a small drum mixer. The mixture is transferred to a drier and

dried for 15-18 hours at 71°C.

The polymer is then extruded through a standard screw extruder at a rate of 0.25 kg/hour. The extruder has three cylinder zones which are held at 233, 230 and 249°C. The spinning nozzle has 8 holes with a diameter of 0.51 mm. The filaments from the nozzle are passed through an aqueous cooling bath at 66° C. and stretched 2.8 times at

by means of a stretching device which rotates at a circumferential speed of

9.3 m/min. The yarn is then stretched using another stretching device which rotates at a speed of approx. 61 m/min., while the yarn is passed through a 1.8 m long tank of water at 96°C, and where the yarn is stretched 6.1 times. The yarn is then pulled further by means of a third tension device, which rotates at 76.2 m/

my. and passes another chamber heated to 168°C, where the yarn is further stretched with a stretch ratio of 1.35.

The yarn is then separated into 8 individual filaments and collected

each separately as monofilaments. The monofilaments are wound on suitable drums and cut to suitable lengths for manufacturing

ling of sutures. The filament properties appear in table I below.

Example 6

A size 7/0 suture is made from isotactic polypropylene with an average molecular weight of 352,000.

4540 parts of polymer are mixed with 449 parts of stock mix

which contains 5% copper phthalcyanine blue and is stirred for 30 minutes in a small drum mixer. The mixture is transferred to a drier and dried for 15-18 hours at 71°C.

The polymer is then extruded through a standard ex-

truder of the screw type with a quantity of 0.136 kg/hour. The extruder has three cylinder zones which are held at 233, 230 and 249°C. The top of the extruder, which contains the pump and filter, is kept at a temperature of 229°C and the spinneret at 279°C. The nozzle has 8 holes and the diameter of the holes is 0.51 mm. The filaments extruded through the die are passed through an aqueous cooling bath at 66°C and stretched

kes using a stretching device that rotates at a peripheral speed of approx. 10 m/min., so that the stretch ratio is approximately 4.8. The yarn is then drawn further by means of another stretching device whose peripheral speed is 49 m/min. as the water passes

fills a tank of length 1.8 m with hot water heated to 96°C,'

and where the yarn is given a stretch of 5.3. This yarn is then drawn

away by means of a third stretching device whose rotational speed

heat or circumferential speed is 76.2 m/min., as the yarn passes through another chamber heated to 154°C, and where a further stretch of approximately 1.55 is imparted to the yarn.

The yarn is then separated into 8 single filaments which are collected on single spools as monofilaments and after collection are wound on suitable drums and cut to suitable lengths for the production of sutures. The test results showing the properties of these filaments can be found in Table I below.

In table II below, values have been set up for the same characteristic data as in table I, but for corresponding sutures that are available on the market and are made of isotactic polypropylene and have the same size.

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Claims (5)

1. Suture of substantially isotactic polypropylene having a denier of from about 30 to about 3000, characterized by Tensile strength gpd 4.3-7.5 Knot strength gpd 3.0-5.0 Elongation to break in % 20.0-30.0 2 5 5 Young's modulus kg/cm 0.38x10 - 0.67 x1 <0> Bending fracture resistance (F) .(Number of cycles to failure) as defined F- l,251x 10 <8> xD~ <1>,<77> where D stands for denier Static creep - % elongation below 8.0. 2. Surgical suture with needle comprising a suture of largely isotactic polypropylene and attached to a surgical needle, where the needle and suture are sterile and the polypropylene has properties according to claim 1. 3. Surgical suture package comprising a sterile wrapper and therein a sterile surgical suture with a needle comprising a substantially isotactic polypropylene suture attached to the needle, wherein the polypropylene has properties according to claim 1. 4. Suture according to claim 1, characterized in that the suture is monofilament. 5. Method for producing the suture according to claim 1, characterized by the following features: a) extrusion of essentially isotactic polypropylene at a temperature from about 232°C to about 288°C into a filament, b) liquid cooling of the filament at a temperature from about 52°C to about 80°C while simultaneously stretching the filament from 1.0 to about 5.0 times) passing the cooled and drawn filament through a heating and stretching zone at a temperature of about 96°C for imparting a stretch of 5.0 to about 8.0 to the filament, d) passing said heated and drawn filament through another heating and stretching zone at a temperature of from about 149 to about 232°C to impart a final stretch from about 0.95 to about 1.6, and e) collecting the produced suture.