Polypropylene multifilament warp knitted mesh and its use in surgery

Abstract: A surgical mesh of warp knit construction is fabricated from a polypropylene multifilament yarn.

Description: BACKGROUND OF THE INVENTION This invention relates to a textile material and, in particular, to a nonabsorbable surgical mesh of warp knit construction fabricated from a polypropylene multifilament yarn. Knitted and woven fabrics constructed from a variety of synthetic fibers and the use of the fabrics in surgical repair are known from, among others, U.S. Patent Nos. 3,054,406; 3,124,136; 4,193,137; 4,347,847; 4,452,245; 4,520,821; 4,633,873; 4,652,264; 4,655,221; 4,838,884; 5,002,551; and, European Patent Application No. 334,046. Hernia repairs are among the more common surgical operations which employ a mesh fabric prothesis. A mesh constructed from polypropylene monofilament, while it induces a good fibroblastic response ensuring its prompt fixation and integration with tissue at the surgical repair site, is considered to be too stiff for some types of hernioplasties, e.g., giant prosthetic reinforcement of the visceral sac (GPRVS). While a warp knitted surgical mesh constructed from a nonabsorbable polyester multifilament yarn (e.g., Mersilene of Ethicon, Inc.) has been indicated to be a particularly desirable prosthesis for a GPRVS procedure due to its suppleness and elasticity (Wantz, "Atlas of Hernia Surgery", Raven Press, 1991, p. 102), were it not for the aforementioned stiffness associated with a polypropylene monofilament mesh, the later would likely be the material of choice due to its greater strength and chemical inertness. SUMMARY OF THE INVENTION It is an object of the present invention to provide a surgical mesh fabricated from polypropylene multifilament yarn which exhibits an appreciably greater flexibility than a surgical mesh constructed from polypropylene monofilament. It is another object of the invention to provide a polypropylene multifilament warp knitted surgical mesh exhibiting a flexibility which is at least comparable to that of a nonabsorbable polyester multifilament surgical mesh of similar construction but possessing greater mechanical strength than the latter. It is yet another object of the invention to provide a surgical mesh with a color pattern which facilitates the orientation and/or installation of the mesh at a surgical repair site. Another specific object of the invention is the provision of a thermoplastic surgical mesh which is cut to size with an ultrasonic slitter. Still another specific object of the invention is the provision of a surgical mesh coated on one side with a material that prevents or minimizes organ adhesions. In keeping with these and other objects of the invention, there is provided a warp knitted surgical mesh fabricated from polypropylene multifilament yarn, wherein the polypropylene is an isotactic polypropylene resin having a melt flow index, g/10min, of from 2.0 to 6.0. The foregoing mesh is considerably more flexible than any of the known surgical mesh materials constructed from monofilament. Thus, e.g., the mesh of this invention can be more easily passed through a trocar and into a body cavity. The greater flexibility of the mesh makes it more maneuverable and easier to be installed at the desired surgical site than a monofilament mesh of otherwise similar construction. Compared to a nonbioabsorbable surgical mesh knitted from polyester multifilament yarn, the polypropylene multifilament mesh of this invention possesses much greater strength but at no loss of flexibility and suppleness. The mesh of this invention finds application in a number of surgical procedures including the repair of hernias, anatomical defects of the abdominal wall diaphragm, and chest wall, correction of defects in the genitourinary system, repair of traumatically damaged organs such as the spleen, liver or kidney, and so forth. DESCRIPTION OF THE PREFERRED EMBODIMENTS The surgical mesh of this invention is fabricated from a yarn formed from a polypropylene resin (isotactic index of at least about 90), preferably one which is already accepted for use as a suture material, e.g., a polypropylene resin having a melt flow index in g/10 min (ASTM D 1231-82) of from about 2 to about 6, preferably from about 2.1 to about 5.0 and most preferably from about 2.5 to about 4.6. Known and conventional apparatus and procedures can be used for the production of polypropylene multifilament yarns from which the mesh of this invention is constructed. Properties of the individual polypropylene filaments and the yarns manufactured therefrom are advantageously as set forth in Table I below: TABLE I PROPERTIES OF MONOFILAMENTS AND AND YARNS CONSTRUCTED THEREFROM Broad Range Preferred Range Most Preferred Range Denier per Filament 0.5-6 1-4 2-3 Filaments per Yarn 10-60 20-40 25-35 Denier per Yarn at least 10 40-80 50-70 During the spinning process, after the individual polypropylene filaments have been brought together to provide the yarn, it is conventional practice to apply a spin finish to the yarn. The spin finish typically contains lubricant, antistatic and adhesive components to hold the yarn together and improve its processability, e.g., drawability. One spin finish composition which is known to provide generally good results is Lurol 1187 (Goulston Inc., 700 N. Johnson Street, Monroe, NC 28110) which can be applied to the yarn from solution prepared with a suitable solvent, e.g., as a 5-35 weight percent solution in isopropyl alcohol. Following spinning, the multifilament yarn is ordinarily subjected to further mechanical processing, e.g., twisting, air entanglement, etc., in order to further enhance its processability. Thus, e.g., the yarn can be ring twisted at a rate of from about 1 to about 5 turns per inch (25.4 mm) or air entangled at a level of at least about 50 nodes per meter prior to being knitted into mesh. In a preferred melt spinning process for obtaining yarn to be knitted into the surgical mesh of this invention, the isotactic polypropylene resin, melt spinning equipment and ranges of operating conditions set forth below in Table II can be advantageously employed: TABLE II: MELT SPINNING OF POLYPROPYLENE MULTIFILAMENT YARNS A. Polypropylene Resin The preferred polypropylene resin is a surgical suture grade resin having an isotactic index of about 95 or greater and a melt flow rate of from about 2.5 to about 4.6. b. Melt Spinning Apparatus and Operating Conditions Range of Apparatus Component Operating Parameter Operating Condition Extruder barrel temp., zone 1 °C 230-250 Extruder barrel temp., zone 2 °C 230-270 Extruder barrel temp., zone 3 °C 230-270 Extruder barrel pressure, (psi)Pa (1000-2000) 6.9-10 6 Extruder barrel melt temp., °C 230-275 13.8-10 6 Pump size, cc per rev .16-.584 Pump rpm 25-35 for size .16 pump 6-10 for size .584 pump Pump temp., °C 220-250 Pump pressure, (psi)Pa (400-1000) 2.7-10 6 Pump melt temp., °C 215-255 6.9-10 6 Block temp., °C 220-250 Clamp temp., °C 220-250 Adapter temp., °C 220-250 Candle filter, screen, microns 10-100 No. of spinneret orifices 10-200 Diameter of spinneret orifices (.001 in)mm (5-30) 0.127-0.762 Spinneret temp., °C 220-250 Spinneret pressure, (psi)Pa (400-1500) 2.7-10 6 Spinneret melt temp., °C 215-255 10.3-10 6 cc/hr output, per spinneret orifice 5-20 First pair of godets, °C 40-90 First pair of godets, mpm 100-300 Second pair of godets,°C 70-130 Second pair of godets, mpm 300-1000 Draw (stretch) ratio 2-4 Third pair of godets, °C ambient Third pair of godets, mpm 250-1000 Shrinkage (relaxation), percent 5-15 C. Properties of Individual Filaments and Polypropylene Yarns Obtained Therefrom Property Range of Property Denier per Filament .3-20 Filaments per Yarn 10-200 Denier per Yarn 3-300 The surgical mesh of this invention can be fabricated from these and similar multifilament polypropylene yarns employing known and conventional warp knitting apparatus and techniques, e.g., the tricot and Raschel knitting machines and procedures described in "Warp Knitting Production" by Dr. S. Raz, Melliand Textilberichte GmbH, Rohr-bacher Str. 76, D-6900 Heidelberg, Germany (1987), the contents of which are incorporated by reference herein. As is well known in the art of warp knitting, the number of courses and wales per inch (25.4 mm) in a knitted material is affected by a number of machine operating variables such as the rate at which the fabric is drawn away from the needles, the number of needles per inch (25.4 mm), the amount of tension applied to the warp yarns and other variables after the fabric leaves the machine, e.g., the heat setting conditions. The structure of the knitted mesh of this invention can be defined for any given yarn in terms of the number of courses and wales per inch (25.4 mm) and the knit design for which there can be a great number of variations. Advantageously, the polypropylene multifilament yarns of Table II can be warp knitted, preferably tricot knitted on a 2 bar set-up, to provide surgical meshes possessing the structural characteristics set forth in Table III as follows: TABLE III STRUCTURAL CHARACTERISTICS OF SURGICAL MESHES Broad Range Preferred Range Most Preferred Range Courses per Inch (25.4mm) 20-80 25-60 30-50 Wales per Inch (25.4mm) 12-40 18-34 20-24 Following knitting, the mesh is cleaned to remove the spin finish and thereafter heat set to stabilize the fabric. For the latter operation, the mesh can be secured to a tenter frame which maintains the mesh at a predetermined width, the frame then being passed through an elongate heating zone at a temperature of from about 120 to about 180°C, preferably at a temperature of from about 120 to about 150°C, at a rate providing a dwell time of from about 10 to about 55 seconds and preferably from about 20 to about 50 seconds. On a smaller scale, the mesh can be mounted upon a stationary frame which is then placed in an oven for about 5 to about 12 minutes at from about 125 to about 140°C. Following heat setting, the mesh is cut to size, packaged and sterilized. The mesh can be cut to any desired configuration, e.g., a square or rectangular shape, of appropriate dimensions. Two suitable configurations are a square of 101.6mm (4 inches) and a rectangle measuring 228.6mm (9 inches) by 355.6mm (14 inches). In cutting the mesh to size, it has been found advantageous to employ an ultrasonic slitter or cutter, various types of which are commercially available. Unlike the result one obtains when cutting with a blade, i.e., frayed yarn ends, or when the yarn ends are heat-sealed, i.e., bead-like formations, cutting the mesh to size with an ultrasonic cutter avoids both frayed and beaded ends. The polypropylene multifilament warp knitted mesh of this invention possesses a ball burst strength (ASTM D 3787-80A) of at least about 50 kg, preferably at least about 50 kg and most preferably at least about 80 kg. Even at only 50 kg ball burst strength, the mesh of this invention is considerably stronger, e.g., up to 100 percent stronger, than a nonabsorbable polyester multifilament warp knitted mesh of otherwise comparable construction. For some applications, particularly those involving laparoscopic procedures, it may be desirable to partially stiffen the mesh so that the mesh can be rolled up for easy passage through a trocar and into a body cavity and once inside the body, spring back to its previous flattened condition. One way of accomplishing this partial stiffening effect is to coat the mesh with a polymer such as poly(hydroxymethyl methacrylate). The amount of polymer applied to the mesh to achieve a particular stiffening effect can, of course, be determined employing simple and routine experimentation. Stiffening can also be achieved by heating the mesh at a temperature which is higher and/or for a period of time which is longer than the aforementioned heat setting conditions. Thus, heating at from about 160 to about 180°C for from about 30 minutes to about 2 hours will cause the mesh to stiffen. It can also be advantageous to provide the surgical mesh of this invention with a clearly visible color pattern, e.g., In the form of a grid of two differently colored yarns such as dark blue and light blue, dark blue or light blue and clear or natural, etc., as such a pattern will tend to facilitate the proper orientation and/or installation of the mesh at the surgical repair site. The mesh can contain yarn of one color in the machine direction, yarn of the other color being incorporated into the mesh fabric after knitting. In the case where the mesh is manufactured on a weft insertion warp knitter, both the knitting and the insertion of the weft can be accomplished in a single operation. The following example is illustrative of the surgical mesh of this invention and its fabrication. EXAMPLE The surgical mesh of this invention was manufactured from a 96 percent isotactic polypropylene having a melt flow index of about 3.3 g/10 min, a weight average molecular weight of 283,000 and a number average weight of 61,000 as reported by the supplier (Resin F040A Natural of Aristech Chemical Corporation, Pittsburgh, PA). The conditions of melt spinning the polypropylene multifilament yarn, warp knitting the yarn to provide the surgical mesh and the properties of the mesh and its heat setting conditions are set forth in Table IV below: TABLE IV: SURGICAL MESH MANUFACTURING CONDITIONS A. Melt Spinning Apparatus and Operating Conditions Apparatus Component, Operating Parameter Operating Condition Extruder barrel temp., zone 1 °C 240 Extruder barrel temp., zone 2 °C 260 Extruder barrel temp., zone 3 °C 260 Extruder barrel pressure, (psi)Pa (1500) 10.3-10 6 Extruder barrel melt temp., °C 260 Pump size, cc per rev 0.16 Pump rpm 32 Pump temp., °C 240 Pump pressure, (psi)Pa (500-750) 3.4-10 6 Pump melt temp., °C 240 5.2-10 6 Block temp.,.°C 240 Clamp temp., °C 240 Adapter temp., °C 240 Candle filter, screen, microns 40 No. of spinneret orifices 30 Diameter of spinneret orifices (.001 in)mm (10)0.254 Spinneret temp., °C 240 Spinneret pressure, (psi)Pa (400-800) 2.7-10 6 Spinneret melt temp., °C 240 5.5-10 6 Spinneret melt temp., °C 215-255 10.3-10 6 cc/hr output, per spinneret orifice 10.2 First pair of godets, °C 65 First pair of godets, mpm 160 Second pair of godets, °C 90 Second pair of godets, mpm 510 Draw (stretch) ratio 2.9 Third pair of godets, °C ambient Third pair of godets, mpm 465 Shrinkage (relaxation), percent 9 Spin Finish 35 wt% isopropyl alcohol solution of Lurol 1187, as needed B. Properties of Polypropylene Multifilament Yarn Denier per Filament: 2 Filaments per Yarn: 30 Denier per Yarn: 60 C. Tricot Knitting Conditions Knitting Machine: 20 gauge (20 needle) 2-bar tricot knitter (Mayer Textile Machine Corporation, Clifton, NJ) Courses per Inch (25.4mm) 40 Wales per Inch (25.4mm) 22 Knit Design: Back Bar Front Bar 1/0 0/1 4/5 1/0 D. Properties of the Surgical Mesh Fabric Width: 1.2 meters (48 inches) Fabric Weight: 2.5-2.8 ox./sq. yd. Ball Burst Strength: 58 kg The mesh was heat set by being clamped to a frame and placed in an oven heated to 130° for 10 minutes. Within their scope, the claims which follow define embodiments of the invention additional to those specifically described above.

Claims: A warp knitted surgical mesh fabricated from polypropylene multifilament yarn, wherein the polypropylene is an isotactic polypropylene resin having a melt flow index, g/10 min, of from 2 to 6. A mesh as daimed in claim 1 wherein the polypropylene is an isotactic polypropylene resin having a melt flow index, g/10 min, of from 2.1 to 5.0. A mesh as claimed in claim 2 wherein the polypropylene is an isotactic polypropylene resin having a melt flow index, g/10 min, of from 2.5 to 4.0. A mesh as claimed in any one of the preceding claims wherein the yarn is made from filaments of from 0.5 to 6 denier, the yarn is constructed with from 60 to 10 filaments and the yarn possesses a denier of at least 10. A mesh as claimed in claim 4 wherein the yarn is made from filaments of from 1 to 4 denier, the yarn is constructed with from 20 to 40 filaments and the yarn possesses a denier of from 40 to 80. A mesh as claimed in claim 5 wherein the yarn is made from filaments of from 2 to 3 denier, the yarn is constructed with from 25 to 35 filaments and the yarn possesses a denier of from 50 to 70. A mesh as claimed in any one of the preceding claims wherein the mesh possesses from 20 to 80 courses per inch (25.4 mm) and from 12 to 40 wales per inch (25. 4 mm). A mesh as claimed in claim 7 wherein the mesh possesses from 25 to 60 courses per inch (25.4 mm) and from 18 to 32 - 34 wales per inch (25. 4 mm). A mesh as claimed in any one of the preceding claims exhibiting a colour pattern to facilitate its orientation and/or installation at the surgical repair site. A mesh as claimed in any one of the preceding claims and heat set or heat stiffened. A mesh as claimed in any one of the preceding claims and coated for enhanced stiffness. A mesh as claimed in claim 11, the coating comprising poly(hydroxymethacrylate). A mesh as claimed in any one of the preceding claims, cut to size and with the cut ends of the yarns being sealed but unbeaded. A method of making surgical mesh wherein a polypropylene multifilament yarn is produced by a process which comprises melt spinning an isotactic polyopropylene having a melt flow index, g/10 min, of from about 2 to about 6 employing an extruder equipped with a spinneret and downstream of the extruder a draw frame possessing three pairs of godets, the extruder being operated in one or more zones thereof at a temperature of about 230 to about 270°C, the pressure of the extruder being from about 6.9.10 6 (1000) to about 13.8.10 6 Pa (2000 psi), the temperature of the spinneret being from about 220 to about 250°C, the first pair of godets being operated at a temperature of from about 40 to about 90°C and an mpm of from about 100 to 300, the second godet being operated at a temperature of from about 70 to about 130°C and an mpm of from about 300 to about 1000 and the third godet being operated at ambient temperature and an mpm of from about 250 to about 1000, the draw ratio of the yarn being from about 2 to about 4 and the shrinkage of the yarn being from about 5 to about 15 percent. A method of making surgical mesh characterised in that the mesh is as claimed in claim 1.

Inventors: HAIN MATTHEW E, LIU CHENG-KUNG, HAIN, MATTHEW E., LIU, CHENG-KUNG
Applicants: UNITED STATES SURGICAL CORP, UNITED STATES SURGICAL CORPORATION
Application year: 1992
Main classification: A61L31
IPC codes: A61F2, A61L31