Synthetic ligament, method of producing same and use thereof

Abstract

A synthetic ligament made of a plurality of polymer filaments comprising two intra-osseous portions (1), within which polymer filaments are oriented only longitudinally and are woven together longitudinally and knotlessly to form a dense weave, and one intra-articular portion (2), located between the two intra-osseous portions (1), which comprises loose filaments and is untwisted around its axis. A method of producing a synthetic ligament in which the step of weaving of the polymer filaments within the intra-osseous portions (1) is carried out by means of longitudinal and knotless weaving to obtain a dense weave, with polymer filaments within the intra-articular portion (2) of a ligament remaining loose. A use of a synthetic ligament as a medical implant for the reconstruction of ligaments and tendons, notably knee ligaments.

Claims

1. A synthetic ligament made of a plurality of polymer filaments comprising two intra-osseous portions, within which the polymer filaments are woven braided together, and one intra-articular portion, located between the two intra-osseous portions, within which the polymer filaments constitute loose filaments, wherein the synthetic ligament comprises 16 to 124 polymer filaments, wherein polymer filaments within the two intra-osseous portions are oriented only longitudinally and are braided together longitudinally and knotlessly to form a dense braid, whereas the one intra-articular portion comprising loose filaments is untwisted around its axis, wherein the polymer filaments consist of UHMWPE filaments, and wherein the synthetic ligament has a form of a braided tube having a hollow core and diameter between 2 and 7.1 mm that upon applying a tensile force assumes a form of a two-layered tape.

2. The synthetic ligament according to claim 1, wherein it comprises 32 polymer filaments and has a diameter of 3 mm.

3. The synthetic ligament according to claim 2, wherein an average maximum force of the synthetic ligament when tested with a method compliant with PN-EN ISO 13934-1:2013-07 standard is 3600 N.

4. The synthetic ligament according to claim 1, wherein the intra-osseous portions have a hydroxyapatite coating.

5. The synthetic ligament according to claim 1, wherein it additionally comprises at least one polymer cap with a guiding strand arranged at a terminal end of the intra-osseous portion.

6. A product comprising a synthetic ligament according to claim 1 as a medical implant for the reconstruction of ligaments and tendons, optionally knee ligaments, including the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL), the lateral collateral ligament (LCL); optionally ligaments of shoulder joint, ligaments of ankle joint, and ligaments of hip joint.

7. The synthetic ligament of claim 1, wherein the synthetic ligament is made by a process comprising preparing polymer filaments, braiding the polymer filaments, and cleaning and sterilising a ligament, wherein the braiding of polymer filaments within the intra-osseous portions is carried out by means of longitudinal and knotless braiding until a dense braid is obtained, with polymer filaments within the intra-articular portion of a ligament remaining loose, until a tubular structure of a ligament is obtained.

8. The synthetic ligament of claim 7, wherein the synthetic ligament exhibits a tear strength greater than a tear strength of a ligament augmentation and reconstruction (L.A.R.S.) ligament of equal diameter and number of filaments when tested with a method compliant with PN-EN ISO 13934-1:2013-07 standard.

9. The synthetic ligament of claim 7, wherein longitudinal and knotless braiding of polymer filaments within the intra-osseous portions of a ligament is carried out in the following steps: a) preparing an even number of polymer filaments and arranging them around a circumference in an alternating layout of even-numbered and odd-numbered filaments, b) gathering spread polymer filaments in a single bundle, maintaining longitudinal orientation of filaments, c) moving even-numbered filaments one place counterclockwise, on the inside of the circumference, with odd-numbered filaments remaining on the outside of the circumference, maintaining longitudinal orientation of all filaments, moving odd-numbered filaments one place clockwise to replace neighbouring, but presently absent, even-numbered filaments, maintaining the longitudinal orientation of all filaments, d) moving even-numbered filaments one place counterclockwise, on the outside of the circumference, with odd-numbered filaments remaining on the inside of the circumference, maintaining longitudinal orientation of all filaments, e) moving odd-numbered filaments one place clockwise to replace neighbouring, but presently absent, even-numbered filaments, maintaining longitudinal orientation of all filaments, to define the starting position analogous as in step c), f) repeating cyclically steps c)-f) to obtain a desired length of knotless braid with longitudinal orientation of filaments for a first intra-osseous portion of a ligament, g) stopping the process of braiding, and spinning a section of loose polymer filaments to obtain an intra-articular portion of a ligament, h) repeating cyclically steps c)-f) to obtain a desired length of knotless braid with longitudinal orientation of filaments for a second intra-osseous portion of a ligament.

10. The synthetic ligament of claim 9, wherein the synthetic ligament comprises 32 polymer filaments and has a diameter of 3 mm.

11. The synthetic ligament according to claim 10, wherein an average maximum force of the synthetic ligament when tested with a method compliant with PN-EN ISO 13934-1:2013-07 standard is 3600 N.

12. The synthetic ligament of claim 9, wherein the intra-osseous portions have a hydroxyapatite coating.

13. The synthetic ligament according to claim 9, wherein it additionally comprises at least one polymer cap with a guiding strand arranged at a terminal end of the intra-osseous portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The subject-matter of the invention has been presented in a drawing wherein

(2) FIG. 1 presents a schematic structure of a synthetic ligament according to the invention,

(3) FIG. 2 presents steps of longitudinal and knotless weaving in a method of producing a ligament according to the invention, and

(4) FIG. 3 presents microscopic images of a synthetic ligament with tissue ingrowth.

(5) The invention has been illustrated with example embodiments described below, which are not intended to limit the scope of invention.

EXAMPLE 1: A SYNTHETIC LIGAMENT ACCORDING TO THE INVENTION

(6) The subject-matter of the invention has been presented in this example in a drawing wherein FIG. 1 presents a schematic anatomical structure of a ligament according to the invention.

(7) A synthetic ligament is made of 32 UHMWPE filaments and comprises two intra-osseous portions (1), within which the polymer filaments are woven together, and one intra-articular portion (2), located between two intra-osseous portions (1), within which the polymer filaments constitute loose filaments. UHMWPE filaments within intra-osseous portions (1) are oriented only longitudinally and are woven together longitudinally and knotlessly to form a dense weave, whereas intra-articular portion (2) comprising loose polymer filaments is untwisted around its axis. Synthetic ligament is made in the form of a tubular structure of polymer filaments, which, upon applying a pulling force, assumes the form of a two-layered tape. The ligament's diameter is 3 mm. Terminal ends of intra-osseous portions (1) are equipped with polymer caps (3) with guiding strands (4).

EXAMPLE 2: A METHOD OF PRODUCING A SYNTHETIC LIGAMENT ACCORDING TO THE INVENTION

(8) To produce a synthetic ligament employing a method according to the invention 32 UHMWPE filaments are prepared, which are then woven together by a longitudinal and knotless weaving technique. Weaving is carried out only in sections corresponding to intra-osseous portions (1) of a ligament, with filaments being left loose (unwoven) in a central section corresponding to intra-articular portion (2).

(9) Longitudinal and knotless weaving of 32 UHMWPE filaments within intra-osseous portions (1) of a ligament has been carried out in the following steps, with steps a)-f) being presented in FIG. 2: a) an even number of UHMWPE filaments were prepared and arranged around a circumference in an alternating layout of even-numbered and odd-numbered filaments, b) spread polymer filaments were gathered in a single bundle, maintaining longitudinal orientation of filaments, c) even-numbered filaments were moved one place counterclockwise, on the inside of the circumference, with odd-numbered filaments remaining on the outside of the circumference, maintaining longitudinal orientation of all filaments, d) odd-numbered filaments were moved one place clockwise to replace neighbouring, but presently absent, even-numbered filaments, maintaining the longitudinal orientation of all filaments, e) even-numbered filaments were moved one place counterclockwise, on the outside of the circumference, with odd-numbered filaments remaining on the inside of the circumference, maintaining longitudinal orientation of all filaments, f) odd-numbered filaments were moved one place clockwise to replace neighbouring, but presently absent, even-numbered filaments, maintaining longitudinal orientation of all filaments, to define a starting position analogous as in step c), g) steps c)-f) were cyclically repeated until a desired length of knotless weave with longitudinal orientation of filaments was obtained for a first intra-osseous portion of ligament, h) the process of weaving was stopped and a section of loose polymer filaments was spun to obtain an intra-articular portion of ligament, i) steps c)-f) were cyclically repeated until a desired length of knotless weave with longitudinal orientation of filaments was obtained for a second intra-osseous portion of ligament.

(10) As a result of carrying out the steps described above, a ligament was obtained in the form of a tube with the diameter of 3 mm. Intra-articular portion (2) comprising loose filaments was left untwisted around its axis. Next, a ligament in the form of a tube of polymer filaments was subject to a pulling force so that it was flattened until it assumed a form of a two-layered tape. At terminal ends of intra-osseous portions (1) polymer caps (3) were secured together with guiding strands (4). Additionally, both intra-osseous portions (1) of ligament comprising woven UHMWPE filaments were coated with hydroxyapatite. Next, a ligament was cleaned and sterilised and packed in a sterile container.

EXAMPLE 3: PRODUCING MODELS OF SYNTHETIC LIGAMENTS ACCORDING TO THE INVENTION HAVING VARIOUS NUMBERS OF FILAMENTS AND DIFFERENT DIAMETERS

(11) Fourteen models of synthetic ligaments having various numbers of filaments and different diameters were produced according to the method described in Example 2. Numbers of filaments and diameters of respective models are shown in Table 1. On the basis of preliminary strength tests a theoretical tear strength was determined for respective models of ligaments, and results are shown in Table 1.

(12) TABLE-US-00001 TABLE 1 Number of Ø of ligament strength Model filaments [mm] [N] 1 22 2.8 2860 2 22 2.8 2860 3 24 3 3600 4 24 3 3600 5 24 3 3600 6 32 3.5 4160 7 32 3.5 4160 8 32 3.5 4160 9 40 4 5850 10 40 4 5850 11 40 4 5850 12 45 4.3 6000 13 45 4.3 6000 14 45 4.3 6000

EXAMPLE 4: STRENGTH TEST FOR A SYNTHETIC LIGAMENT ACCORDING TO THE INVENTION

(13) A synthetic ligament obtained in Example 2 was tested in terms of its tear strength. The test was carried out in The Fabrics and Textile Articles Testing Laboratory of The Textile Institute in Lódź. The test was carried out employing a method compliant with the PN-EN ISO 13934-1:2013-07 standard: “Determination of maximum force and elongation at maximum force using the strip method”.

(14) The test was carried out for ligament samples with diameter of 3 mm made of 32 UHMWPE filaments, cleaned and sterile, which were obtained according to the method described in Example 2.

(15) The test employed a Tinius Olsen H50KS testing machine, jaw type: flat with rubber padding and hydraulic/pneumatic pressure grip. Rate of extension was 100 mm/min, and distance between grips was 30 mm. Ligament strength test results are shown in Table 2.

(16) TABLE-US-00002 TABLE 2 No. of Indicator sample Value Testing method Maximum force for tested 1 2968 PN-EN ISO 13934- samples, [N] 2 4220 1:2013-07 Average maximum force, [N] 3600

(17) As it follows from Table 1, average maximum force for a synthetic ligament with 3 mm diameter made of 32 UHMWPE filaments was 3600 N. However, maximum force for a ligament according to the invention obtained in the test carried out by the Inventors was 4220 N.

(18) This means that a 3 mm, 32-filament ligament according to the invention exhibits the same tear resistance as a 100-filament L.A.R.S. ligament with 9 mm diameter.

EXAMPLE 5: ELASTICITY TEST FOR A SYNTHETIC LIGAMENT ACCORDING TO THE INVENTION

(19) A synthetic ligament obtained in Example 2 was tested in terms of its elasticity. The test was carried out in The Fabrics and Textile Articles Testing Laboratory of The Textile Institute in Lódź. The test was carried out employing a method compliant with the PN-EN ISO 2062:1997 standard: “Determination of breaking force and elongation at break of single strands”.

(20) The test was carried out for ligament samples with diameter of 3 mm made of 32 UHMWPE filaments, cleaned and sterile, which were obtained according to the method described in Example 2.

(21) The test employed an Intron 3365, BM-B 205.00 testing machine. Rate of extension was 100 mm/min, and distance between grips was 30 mm.

(22) Ligament elasticity test results are shown in Table 3.

(23) TABLE-US-00003 TABLE 3 Relative elongation No. of sample Maximum force [cN] at maximum force [%] 1 169 657.9 7.69 2 108 381.1 5.50 3 239 656.8 18.13 4 223 157.6 13.07 5 168 033.5 28.38 6 294 475.6 11.59 7 322 395.9 19.52 8 342 149.8 21.35 9 272 286.6 9.11 Avg. 238 466.1 14.93 Standard deviation  78 087.22 7.44 Coefficient of variation     32.75 49.87 Max. 342 149.8 28.38 Min. 108 381.1 5.50

(24) As it follows from Table 3, average relative elongation at average maximum force for a synthetic ligament with 3 mm diameter made of 32 UHMWPE filaments was 14.93%. However, the maximum observed value was 28.38%.

(25) The above test has shown that a synthetic ligament according to the invention can be deformed up to 15% of its length during stretching and up to this value it retains the ability to return to its original state. Such high elasticity of a ligament according to the invention overcomes the deficiency of previously used ligaments, which are not stretchable.

EXAMPLE 6: BIOCOMPATIBILITY TEST FOR A SYNTHETIC LIGAMENT ACCORDING TO THE INVENTION

(26) In order to test biocompatible properties of a synthetic ligament according to the invention, a reconstructive surgery was carried out to reconstruct a ruptured cruciate ligament in a knee joint of a dog. The surgery was performed in a Mastiff dog, aged 6 years, having a ruptured cruciate ligament. A synthetic ligament according to the invention, obtained as in Example 2, with diameter of 3 mm, made of 32 filaments, cleaned and sterile, was implanted into the dog's knee joint in order to replace a ruptured cruciate ligament. Two months after the surgery, tissues formed at the implantation site were observed under a microscope. Microscopic images of a ligament with tissue ingrowth are presented in FIG. 3.

(27) The microscopic images show visible growth of mature granulation tissue around the present synthetic fibres, with mild exhibition of a granuloma reaction and presence of foreign-body giant cells. It was moreover observed that close to a terminal end of implantation the ground substance was more abundant in connective tissue stroma, there was less collagen fibres, and a focus of osseous metaplasia was also observable in that area. The microscopic image was not discrepant from what is observable around “standard” materials implanted in tissues.

(28) The conducted study confirms that synthetic ligament is neutral for the body, that one's body cells grow into it enabling integration of the implant with the bone and assuring complete tissue regeneration.