Prosthetic porous knit

Abstract

The invention relates to a prosthetic porous knit based on a monofilament of a biocompatible polymer material, the pattern followed for the knitting of said monofilament on a warp knitting machine having two guide bars B1, B2 being the following, according to the ISO 11676 standard: Bar B1: 1.2/4.5/4.3/4.5/4.3/1.0/1.2/1.0// Bar B2: 4.3/1.0/1.2/1.0/1.2/4.5/4.3/4.5// The invention further relates to a method for producing such a knit and to a hernia prosthesis comprising such a knit.

Claims

1. A prosthetic lightweight porous knit for hernia repair comprising a monofilament of a biocompatible polymer, wherein the knit comprises a mass per unit area ranging from about 40 to about 70 g/m.sup.2, an efficient porosity ranging from about 30% to about 70%, and a tear strength in a warp direction of at least 25N and a tear strength in a weft direction of at least 25N.

2. The prosthetic lightweight porous knit of claim 1, wherein the knit comprises a pattern followed for knitting of the monofilament on knitting machine having two guide bars B1, B2 according to ISO 11676 standard, wherein the pattern of bar B1 is: 1.2/4.5/4.3/4.5/4.3/1.0/1.2/1.0//.

3. The prosthetic lightweight porous knit of claim 1, wherein the knit comprises a pattern followed for knitting of the monofilament on knitting machine having two guide bars B1, B2 according to ISO 11676 standard, wherein the pattern of bar B2 is: 3.3/1.0/1.2/1.0/1.2/4.5/4.3/4.5//.

4. The prosthetic lightweight porous knit of claim 1, wherein the biocompatible polymer material is selected from group consisting of polypropylene, polyethylene terephthalate, polyamide, silicone, polyether ether ketone (PEEK), polyarylether ether ketone (PAEK), polylactic acid (PLA), polycaprolactone (PCL), polydioxanone (PDO), trimethylene carbonate (TMC), polyvinyl alcohol (PVA), polyhydroxyalkanoate (PHA), polyglycolic acid (PGA), copolymers of these materials, and mixtures thereof.

5. The prosthetic lightweight porous knit of claim 1, wherein the biocompatible material is polypropylene.

6. The prosthetic lightweight porous knit of claim 1, wherein the diameter of the monofilament is from about 0.10 mm to about 0.15 mm.

7. The prosthetic lightweight porous knit of claim 1, wherein the diameter of the monofilament is about 0.12 mm.

8. The prosthetic lightweight porous knit of claim 1, wherein the knit comprises a plurality of pores having a diameter above 2 mm.

9. The prosthetic lightweight porous knit of claim 1, wherein the efficient porosity of the knit is about 55%.

10. The prosthetic lightweight porous knit of claim 1, wherein the mass per unit area of the knit ranges from about 44 g/m.sup.2 to about 48 g/m.sup.2.

11. The prosthetic lightweight porous knit of claim 1, wherein the knit comprises a tensile breaking strength in a warp direction of at least 200 N.

12. The prosthetic lightweight porous knit of claim 1, wherein the knit comprises a tensile breaking strength in a weft direction of at least 170 N.

13. The prosthetic lightweight porous knit of claim 1, wherein the knit comprises a bursting strength of at least 400 kPa.

14. A prosthetic lightweight porous knit comprising a monofilament of a biocompatible polymer material, wherein the knit comprises a mass per unit area ranging from about 40 to about 70 g/m.sup.2, an efficient porosity ranging from about 30% to about 70%, a tensile breaking strength in a warp direction of at least 200 N, and a tensile breaking strength in a weft direction of at least 170 N.

15. The prosthetic lightweight porous knit of claim 14, wherein the knit comprises a pattern followed for knitting of the monofilament on knitting machine having two guide bars B1, B2 according to ISO 11676 standard, wherein the pattern of bar B1 is: 1.2/4.5/4.3/4.5/4.3/1.0/1.2/1.0//.

16. The prosthetic lightweight porous knit of claim 14, wherein the knit comprises a pattern followed for knitting of the monofilament on knitting machine having two guide bars B1, B2 according to ISO 11676 standard, wherein the pattern of bar B2 is: 3.3/1.0/1.2/1.0/1.2/4.5/4.3/4.5//.

17. The prosthetic lightweight porous knit of claim 14, wherein the biocompatible material is polypropylene.

18. The prosthetic lightweight porous knit of claim 14, wherein the diameter of the monofilament is from about 0.10 mm to about 0.15 mm.

19. The prosthetic lightweight porous knit of claim 14, wherein the knit comprises a plurality of pores having a diameter above 2 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become clearer from the following description and from the attached drawings, in which:

(2) FIG. 1 is a schematic view of the knitting pattern of a knit of the invention,

(3) FIG. 2 is a front view of the knit of the invention obtained with the knitting pattern of FIG. 1,

(4) FIG. 3 is a side view of a schematic configuration of a system for measuring the distribution of the shear forces at fixation points of a knit,

(5) FIG. 4 is an enlarged perspective view of a portion of the system of FIG. 3.

(6) FIGS. 5 and 6 are schematic views of the form used to obtain the average distribution of shear forces at fixation points, as described in at least one embodiments herein.

(7) FIG. 7 is a schematized graph profile of the shear force distribution of a knit.

(8) FIGS. 8-10 are schematized contour profiles of Knits A, B, and C, respectively.

DETAILED DESCRIPTION

(9) With reference to FIG. 1, is shown a graphic representing the knitting pattern of the knit of the invention, namely the following pattern according to the ISO 11676 standard: Bar B1: 1.2/4.5/4.3/4.5/4.3/1.0/1.2/1.0// Bar B2: 4.3/1.0/1.2/1.0/1.2/4.5/4.3/4.5//

(10) The overall pattern repetition size of the knit of the invention is eight courses. FIG. 1 depicts only one thread from guide bar B1 and one thread from guide bar B2 to better show the movement of the thread. The evolution of the threads at the ninth course is the same as at the first course.

(11) With reference to FIG. 2, is shown a photograph of the knit 1 of the invention obtained with the knitting pattern as represented in FIG. 1.

(12) The knit 1 of FIG. 2 was obtained from a monofilament of polypropylene of diameter 0.12 mm.

(13) The knitting pattern of the knit of the invention produces pores greater than about 1.0 mm in diameter. For example, the principal pores 2 of the knit 1 of FIG. 2 have an average size of 2.0×2.4 mm. Such a large size of pores is very favorable for cell colonization and confers to the knit a good transparency allowing a good visibility at the implantation site.

(14) The knit of the invention shows an homogeneous distribution of the shear forces at fixation points. The distribution of the shear forces at fixation points may be evaluated with a system for assessing shear forces distribution at fixation points of textile-based implants, such as an axisymmetrical experimental set-up as described in reference to FIGS. 3 and 4, such a system allowing exhibiting the capability of a textile to distribute shear forces at fixation points without integrating specific geometrical considerations.

(15) Referring now to FIGS. 3 and 4, system 10 includes a tissue model 100, a load simulation device 200, and an analysis system 300 for assessing characteristics of a textile-based implant 400 when fixed to the tissue model 100 and subjected to a load exerted by the load simulation device 200. The tissue model 100 includes a base 110 having an upper surface 112 extending along a plane “P” and having a closed outer perimeter 114 that defines an opening 116 therethrough. The upper surface 112 is configured to mimic the inner surface of an abdominal wall: it is flat and horizontal. The opening 116 defined through the upper surface 112 is configured to mimic a defect in an abdominal wall and may be referred to herein as the “defect”. The opening 116 has a circular shape and a uniform size and dimension through the height “H” of the base 110. In the system of FIG. 3, the opening 116 is an empty circle having a radius of 55 mm with a 10 mm fillet.

(16) The upper surface 112 is covered by a coating 112a having a coefficient of friction that mimics the frictional coefficient of an inner surface abdominal wall against a textile-based implant 400. The coefficient of friction is about 0.3.

(17) The base 110 includes a lower planar surface 118 that is stepped down from the upper planar surface 112 at a pre-determined height “H1” and extends around the upper surface 112.

(18) The base 110 also includes a fixation support under the form of a plurality of rods 120, configured to secure a textile-based implant 400 thereto at two or more fixation points. The plurality of rods 120 are attached to the lower surface 118 at a predetermined distance “D1” of 20 mm from each other and a predetermined distance “D2” of 70 mm from the upper surface 112 extremity. The rods 120 are arranged in a simple circle crown fixation, centered to the opening 116. Each rod 120 includes a first end 120a fixed to the lower surface 118, an elongate body 120b extending from the lower surface 118 towards the upper surface 112 and defining a length “L” of 60 mm, and a second end 120c terminating about or above the plane “P” defined by the upper surface 112. The elongate body 120b extends perpendicularly from the lower surface 118. The rods 120 are threaded rod M3, with an equivalent radius of 2.5 mm and a Young Modulus of 110 Gpa.

(19) The rods 120 are configured for direct fixation to a portion of the textile-based implant 400 when the textile-based implant 400 is placed upon the upper surface 112 of the tissue model 100 over the opening 116 in the upper surface 112. The tension at the fixation points in the textile-based implant 400 is minimum. Markers 122 are attached to the second end 120c of the rods 120 such that the markers 122 are disposed about or above the plane “P” defined by the upper surface 112. Each marker 122 is under the form of a white circle of diameter 5 mm within a black circle of diameter of 10 mm and is localized 8 mm above the textile-based implant 400. Markers 122 provide a visual indication of the position of the rods 120. Markers 122 are distributed on half of the textile-based implant 400 from two warp extremities.

(20) The load simulation device 200 is positioned above the upper surface 112 of the base 110 and is configured to simulate a change in environmental loading conditions surrounding the tissue model 100 such that changes in load are generated about the tissue model 100. The load may be referred to herein as the “intra abdominal pressure equivalent.” As shown, the load simulation device 200 is a plunger 210 including a contacting surface 212 that is hemispherical (diameter 100 mm) and that is centered over the opening 116 defined through the upper surface 112. The plunger 210 is configured to move in a direction perpendicular to the plane “P” of the upper surface 112 and exert a predetermined force, referred to hereinafter as the plunger force, against the textile-based implant 400 so that the implant 400 engages the opening 116 defined within the upper surface 112 of the tissue model 100. The load simulation device 200 is capable of applying a quasi-static pressure (low plunger 210 descent velocity) on the textile-based implant 400 to simulate various physiological conditions. For example, the plunger force applied may be of 147 N, namely 116 mmHg, which corresponds to the intra abdominal pressure when the patient is in a standing valsalva condition. Alternatively, the plunger force applied may be of 304 N, namely 240 mmHg, which corresponds to the intra abdominal pressure when the patient jumps.

(21) The analysis system 300 includes a digital image acquisition and processing component 310 including two cameras 312 for recording the position of the markers 122 in a 3D coordinate system and digital image correlation software 314, namely Vic 3D™ from the company Correlated Solutions for calculating the displacement vector of each of the markers 122 resulting from bending of the rods 120 in response to the loads exerted on the textile-based implant 400 by the load simulation device 200. The analysis system 300 records the plunger displacement 210. The analysis system 300 also includes a mathematical software component 320 that is utilized to calculate the shear force vector at each fixation point where a marker 122 exists using the displacement vector component in the plane “P” of the markers 122 and the continuum mechanics theory applied to the rods 120. Accordingly, each shear force vector is a function of the “intra abdominal pressure equivalent.” The mathematical software component 320 may include any numerical software package, such as, for example, MATLAB® from the company Matchworks.

(22) An indication on the bulging of the textile-based implant 400 through the opening 116 may be given by the assessment of the plunger penetration through the opening 116.

(23) In an exemplary method of use, a textile-based implant 400, such as a prosthetic knit, is placed on the upper surface 112 of the base 110 of the tissue model 100 such that the implant 400 lies along the plane “P” defined by the upper surface 112. The implant 400 is centered placed about the opening 116 in the upper surface 112 and, as should be understood by a person of ordinary skill in the art, the orientation of the fibers of the implant 400 is controlled with respect to the upper surface 112. The textile-based implant 400 is then directly fixed to the plurality of fixation rods 120. A plurality of markers 122 are then affixed to a portion of the fixation rods 120 such that the markers 122 extend between the two warp extremities of the implant 400.

(24) With the implant 400 fixed to the tissue model 100, the analysis system 300 is activated such that the cameras 312 capture the position of the markers 122 in a 3D coordinate system. The acquisition of the position/positional changes of the markers 122 via the cameras 312 is synchronized with the activation of the load simulation device 200 as the forces applied to the implant 400 by the load simulation device 200 is transferred to the rods 120 at the fixation points and results in bending of the rods 120. Accordingly, any movement of the rods 120 results in movement of the markers 122 which is recorded by the cameras 312 and used in determining the shear force vector at each fixation point as described above.

(25) As will appear from the Example below, the system of FIGS. 3 and 4 allows evaluating the properties of prosthetic knits regarding the distribution of shear forces at fixation points, bulging phenomenon and fracture at fixation points.

(26) The advantages of the knit of the invention will appear more clearly in the Example below.

EXAMPLE

(27) Two lightweight knits of the prior art (Knits A and B) and a knit of the invention (knit C) have been produced as described below.

(28) Knit A: knit A is a knit of the prior art as described in WO2011/042811, namely obtained by knitting a monofilament of polyethylene terephthalate of diameter 0.08 mm on a warp knitting machine having two guide bars B1, B2, according to the following pattern, according to the ISO 11676 standard: Bar B1: 1.0/1.2/1.0/2.3/2.1/2.3/4.5/4.3/4.5/3.2/3.4/3.2// Bar B2: 4.5/4.3/4.5/3.2/3.4/3.2/1.0/1.2/1.0/2.3/2.1/2.3//

(29) Guide bars B1 and B2 are threaded 1 full 1 empty and move symmetrically.

(30) Knit B: knit B is a knit of the prior art as described in U.S. Pat. No. 6,408,656, namely obtained by knitting a monofilament of polypropylene of diameter 0.10 mm on a warp knitting machine having two guide bars B1, B2, according to the following pattern, according to the ISO 11676 standard: Bar B1: 5.4/4.3/2.1/0.1/1.2/3.4// Bar B2: 0.1/1.2/3.4/5.4/4.3/2.1//

(31) Guide bars B1 and B2 are threaded 1 full 1 empty and move symmetrically.

(32) Knit C: is a knit of the invention obtained with the knitting pattern of FIG. 1, by knitting a monofilament of polypropylene of diameter 0.12 mm knitted on a warp knitting machine having two guide bars B1, B2, the pattern followed being the following, according to the ISO 11676 standard: Bar B1: 1.2/4.5/4.3/4.5/4.3/1.0/1.2/1.0// Bar B2: 4.3/1.0/1.2/1.0/1.2/4.5/4.3/4.5//

(33) Guide bars B1 and B2 are threaded 1 full 1 empty and move symmetrically.

(34) The following properties of knits A, B and C have been determined as follows: Mass per unit area (g/m.sup.2): measured according to ISO 3801: 1977 «Determination of mass per unit length and mass per unit area», 5 specimens 1 dm.sup.2, pore size (width×height) (mm): knit biggest pores are measured making one measurement on 10 individual samples with a profile projector such as a projector 300V from ORAMA, Bursting strength (kPa): measured according to ISO 13938-2: 1999 “Textiles—Bursting properties of textiles—Pneumatic method for determining the bursting strength and bursting deformation”, 5 samples Tensile strength (N/cm) is measured through a plunger test with a traction testing machine such as the Hounsfield model H5KS (Hounsfield, Redhill, England), crosshead speed: 50 mm/min, 5 samples: the burst pressure can be determined using a circular mesh sample with a radius of R.sub.m=56.4 mm and with a test area of 100 cm.sup.2 clamped at the outward boarder (modified DIN 54307 superseded standard). Then, the mesh is loaded with a spherical stamp of a radius R.sub.s=50 mm, velocity v=50 mm/min until rupture occurs. Based on the measured forces and the resulting stretch, the tensile strength (N/cm) can be calculated; Tear strength (N) in the warp direction and in the weft direction: measured according to ISO 4674:1977 “Textiles covered with rubber or plastic—Determination of the tear strength” Method A2, 5 samples, width: 75 mm, Tear length≤145 mm, crosshead speed: 100 mm/min, Thickness: is measured according to ISO 9073-2: 1997 “Textiles—test methods for nonwovens—Part 2: Determination of thickness”, 10 samples, 100×50 mm, Tensile breaking strength and elongation at break: is measured according to ISO 13934-1: 2013 “Textiles—Tensile properties of fabrics—Part 1: Determination of maximum force and elongation at maximum force using the strip method”, 5 samples, width: 50 mm, Length: 200 mm between the jaws, Crosshead speed: 100 mm/min, Pre-load: 0.5 N, using a traction testing machine such as the Hounsfield model H5KS (Hounsfield, Redhill, England); Effective porosity pores having a diameter above 1 mm are measured with a profile projector such as a projector 300V from ORAMA, 1 sample of 100×50 mm; Suture pull out strength in the warp direction and in the weft direction measured according to NF S94-801: 2007 “Reinforcement implants introduced by the vaginal route for the treatment of stress urinary incontinence and/or of prolapse of the pelvic organs—pre-clinical trials and clinical trials”—§ 5.3.3 5 specimens 50×100 mm, USP 2 suture yarn, crosshead speed: 100 mm/min, using a traction testing machine such as the Hounsfield model H5KS (Hounsfield, Redhill, England).

(35) The results are collected in the following tables:

(36) TABLE-US-00001 TABLE I mechanical properties Knit A Knit B Knit C Warp Weft Warp Weft Warp Weft Tensile breaking strength (N) 175 ± 12 129 ± 2  187 ± 16 149 ± 10 237 ± 6  201 ± 6  Elongation under 50 N (%) 54 ± 0 50 ± 6 43 ± 1 59 ± 1 38 ± 1 46 ± 0 Bursting strength (kPa) 280 ± 19 361 ± 38 463 ± 19 Tear strength (N) 22 ± 1 23 ± 2 23 ± 2 22 ± 3 30 ± 1 37 ± 5 Suture pull out strength (N) 32 ± 4 36 ± 1 33 ± 1 33 ± 2 46 ± 5 42 ± 3 Tensile strength (N/cm) 24 ± 1 40 ± 1 47 ± 1

(37) TABLE-US-00002 TABLE II mass per unit area and porosity Knit A Knit B Knit C Mass per unit area (g/cm.sup.2) 45 36 46 Thickness (mm) 0.4 0.4 0.6 Pore size (mm) (width × 1.5 × 1.5 1.6 × 1.4 2.0 × 2.4 height) Efficient porosity (%) 53 35 55

(38) With reference to Table I above, the knit of the invention (Knit C) shows improved mechanical properties in comparison with the knits of the prior art (Knits A and B). In particular, the knit of the invention shows a higher tensile breaking strength both in warp and weft directions than Knits A and B. The knit of the invention shows a higher bursting strength than Knits A and B. The knit of the invention shows a higher tear strength both in warp and weft directions than Knits A and B.

(39) The knit of the invention (Knit C) shows an improved suture pull out strength both in warp and weft directions compared to the knits of the prior art (knits A and B). The knit of the invention shows a higher tensile strength both in warp and weft directions than Knits A and B.

(40) With reference to Table II above, the knit of the invention further shows an improved efficient porosity compared to Knits A and B.

(41) In addition, the system described at FIGS. 3 and 4 has been utilized to assess the following properties of knits A, B and C under various simulated physiological conditions. For proceeding to these measures, the textile-based implant 400 of FIGS. 3 and 4 is replaced by the knit sample, either Knit A, B or C, to be evaluated.

(42) The following properties have been evaluated:

(43) 1°) The shear forces distribution profile at fixation points of the knit: for each plunger force, namely 147 N respectively 304 N, the marker displacement as described above is transformed into the shear force at each fixation point where markers exist from the initial fixation position, using the mechanical continuum theory applied to the rods implemented in the software MATLAB® from the company Matchworks. The shear force vector is recorded. The Max and min vector norm values are recorded. The average distribution of shear forces at fixation points may be obtained under the form as shown in each of FIGS. 5 and 6, with reference to the following plunger forces, respectively:

(44) Plunger force: 147 N Plunger force: 304 N

(45) The shear forces distribution may be schematized by the graphic profile shown in FIG. 7.

(46) An Average force Min-Max (N) is determined: on the example of the profile above, the Average force Min-Max (N) at a plunger force of 147 N is 3.8-8 and the Average force Min-Max (N) at a plunger force of 304 N is 7.1-13.5

(47) For a knit, when the range of the value of the Average force Min-Max is low, the risks of failure of the knit are decreased. The knit and therefore the abdominal wall repair will be more efficient.

(48) In addition, the more the profile of the shear forces is close to a semi-circle or a semi-ellipse, the more regularly the shear forces are distributed. The risks of tensions in a specific direction are therefore decreased. In addition, the forces being of similar values in all directions, the knit may be implanted without having to check for a specific position of the warp or weft direction of the knit. The knit, or the prosthesis made from the knit, will also be more comfortable for the patient.)

(49) 2°) The bulging indication: corresponds to the distance in mm of penetration of the plunger 210 as described in FIGS. 3 and 4, from an initial position in which its contacting surface 212 is tangent to the sample knit to a final position obtained after application of the plunger force.

(50) A too high bulging indication, like for example above 50 mm at a plunger force of 304 N or for example above 45 mm at a plunger force of 147 N, may mean that the knit/prosthesis may be two soft for ensuring its reinforcement function of the abdominal wall, and/or may generate discomfort and/or aesthetics disturbance.)

(51) 3°) The rupture of knit at fixation: the number of ruptures at fixation points is recorded.

(52) The results are collected in the following table:

(53) The contour profile of Knits A, B, and C are shown in FIGS. 8-10, respectively.

(54) TABLE-US-00003 TABLE III assessment of shear forces Average Average number of bulging Average fracture at Plunder indication force Min- Knit fixation points force (N) (mm) Max (N) Knit A 2 147 48 3.9-4.8 304 58.7 6.5-8.6 Knit B 2 147 44.6 2.2-5.7 304 54.5  4.5-11.2 Knit C 0 147 40.2 3.6-8.sup.  304 48.3  7.1-13.5

(55) As appears from the table above, the knit of the invention (Knit C) shows a regular contour profile very close to a semi-circle. The shear forces are therefore regularly distributed. The knit of the invention may therefore be introduced at the implantation site and implanted without the surgeon having to check previously for a specific positioning of the warp or weft direction of the knit.

(56) In addition, the number of fracture at fixation points is 0 for the knit of the invention, whereas it is 2 for the knits of the prior art (knits A and B). The knit of the invention is therefore more reliable once sutured or tacked to the surrounding biological tissues than the knits of the prior art.

(57) Regarding the bulging indication, the knit of the invention (knit C) shows a better bulging indication at both plunger forces than the knits of the prior art. The knit of the invention will therefore ensure its reinforcement function of the abdominal wall and will be more efficient than the knits of the prior art in physiological conditions such as jumping or coughing.