WO2000004847A1

WO2000004847A1 - Braided absorbable implant

Info

Publication number: WO2000004847A1
Application number: PCT/EP1999/004854
Authority: WO
Inventors: Christoph Walther; Barbara Schuldt
Original assignee: Ethicon Gmbh
Priority date: 1998-07-21
Filing date: 1999-07-12
Publication date: 2000-02-03
Also published as: DE19833796B4; DE19833796A1

Abstract

A braided absorbable implant is in the form of tape or cord and has at least two cores (10) which are separated from one another by a braided jacket (12) and covered by a braided jacket (12). The contribution of the cores (10) to the tear strength of the implant is the range from 30 % to 70 %.

Description

Braided absorbable implant

The invention relates to a braided absorbable implant in the form of tape or cord.

Absorbable implants of high tear strength are employed in particular for treatment of defects in the support and locomotion apparatus , e.g. for traction strapping of bone defects or for torn ligaments . Such implants are in the form of tapes or cords which are made e.g. of poly-p-dioxanone, glycolide/lactide copolymer or of polyglycolides .

Absorbable cords of high tear strength are as a rule constructed as braid, and in particular predominantly as circular braid, which usually comprises a core and jacket. After implantation, such an implant cord not only must absorb high traction forces, but is also exposed to constant stress from frictional forces which act on the jacket of the implant cord. Some of the jacket may tear here due to friction. As a result, the residual tear strength of the implant cord is reduced relatively severely, depending specifically on the braid construction chosen. A typical circular braid comprises e.g. three parts of core and sixteen parts of surrounding braiding or jacket (the "parts" relating to the number of bobbins during the braiding operation), so that e.g. tear strength is reduced by 4/19 if four parts of the surrounding braiding tear due to friction. If the surrounding braiding was originally symmetrical in structure, tearing of some parts of the surrounding braiding manifests itself particularly adversely, so that the tear strength may become even smaller than that resulting from the ratio of the number of torn parts to the total number of parts of the implant . Implants of high tear strength in the form of tapes are often woven tapes , for which various types of weave are suitable . However, tapes can also be braided. Woven tapes are constructed from weft and warp threads . The strength of the commercially available absorbable tapes results chiefly from the warp threads . The warp threads are indeed in principle protected from friction by the weft thread on top. However, the weft thread easily shifts when exposed to pressure, depending on the type of weave, so that the warp threads can be chafed through at the place where they are exposed. The commercially available surgical braided tapes have a relatively low resistance to chafing, since they comprise only a relatively small or even no content of core. The tear strength therefore decreases sharply if part of the surrounding braiding is rubbed through.

It is an object of the invention to provide an absorbable implant in the form of tape or cord which is particularly suitable for intended uses which require a high tear strength, and which is substantially insensitive to exposure to friction.

This object is achieved by a braided absorbable implant having the features of claim 1. Advantageous embodiments can be seen from the sub-claims .

The braided absorbable implant according to the invention is in the form of tape or cord and has at least two cores which are separated from one another by a braided jacket and are covered by a braided jacket. The contribution of the cores to the tear strength of the implant is in the region of 30% to 70%.

The term "braided jacket" is to be understood here quite generally as continuous braiding and is not limited to a hollow cylindrical structure . The implant according to the invention can have one or more braided jackets which, taken in themselves and in their interaction, are such that on the one hand they separate the cores of the implant from one another, and on the other hand they cover them so that only the braided jacket (or the braided jackets) appears on the outside of the implant.

The cores are covered by the surrounding braiding and are therefore adequately protected from losses in tear strength due to friction. The contribution of the cores to the tear strength of the implant of not less than 30% is relatively high, so that the tear strength is not reduced unacceptably severely if part of the surrounding braiding should be rubbed through. On the other hand, the contribution of the cores to the tear strength of the implant is not more than 70%, which means that the surrounding braiding, i.e. the braided jacket or jackets, is relatively thick, so that the cores lie relatively far inside the implant and as a rule are not exposed to attack even if part of the surrounding braiding is damaged. Since several cores are distributed over the implant, there is a high probability that even in the event of very adverse friction effects, one or more cores remains completely undamaged and ensures an adequate residual tear strength of the implant.

In a preferred embodiment, the implant is in the form of a tape and has at least three cores, which are arranged side by side and are separated from one another and covered by a common braided jacket. Such an implant can be constructed e.g. as a flat braid, which is produced as a strip braid with e.g. six cores. A larger or smaller number of cores is also possible.

In another preferred embodiment, the implant is in the form of cord and has at least four cores which are separated from one another and covered by a common diagonally braided jacket. The cores here are preferably arranged in a configuration which is invariant to rotations around the implant axis through 90°. Preferably, a central core is arranged along the implant axis, which can be thicker than the other cores and the tear strength of which is e.g. at least 20% of the tear strength of the implant . A core can have several elements arranged side by side which are not separated from one another by a surrounding braiding. Such a structure of a core is known.

At least one of the cores can have its own braided material which covers the core and separates it from adjacent cores . The other cores can likewise have such a braided jacket, so that the implant in total has several braided jackets which are held together with one another, e.g. by a common outer braided jacket which surrounds all the cores, including the braided jackets assigned to the individual cores. Overall, many embodiments of the implant according to the invention are conceivable which embodiments have the common feature that several cores are present which are protected by a surrounding braiding and contribute 30% to 70% of the tear strength of the implant.

Poly-p-dioxanone or a glycolide/lactide copolymer (preferably polyglactin 910, a copolymer of glycolide and lactide in a ratio of 9:1, or a copolymer with 5 parts glycolide per 95 parts L- lactide) e.g. are possible as the material for the braided absorbable implant . The use of pure polyglycolides or several different absorbable materials is also conceivable. It may be advantageous here if different materials are employed for the cores and the braided jacket (or the braided jackets), in which case, for example, the material of the cores may be absorbed more slowly than the material of the braided jacket.

The invention is explained in more detail below with the aid of embodiment examples . In the drawings :

Figure 1 shows a diagram of a cross-section through an implant according to the invention in the form of tape,

Figure 2 shows in part (a) a diagram of a cross-section and in part (b) a side view of an implant according to the invention in the form of cord with five cores, Figure 3 shows in part (a) a diagram of a cross-section and in part (b) a side view of an implant according to the invention in the form of cord with nine cores,

Figure 4 shows in part (a) a diagram of a cross-section and in part (b) a side view of an implant according to the invention in the form of cord with seventeen cores ,

Figure 5 shows a diagram of a view of the arrangement of the cores over the cross-section of an implant according to the invention with a central core which is thicker than the other cores , and

Figure 6 shows a force-elongation diagram in which the behaviour of two conventional implants (a, b) and that of an implant ( c ) according to the invention are compared with one another.

Figure 1 shows a cross-section of an embodiment of a braided absorbable implant in the form of tape (band) . The implant has six cores 10, which are arranged side by side, run substantially parallel to one another and, in the embodiment example, contribute 50% of the tear strength of the implant. Each of the cores 10 can be multifilamentous, i.e. have several or many elements arranged side by side. The six cores 10 are surrounded by a braided jacket 12, which is shown in diagram form in figure 1 and has an outline 13. In the embodiment example, the braided jacket 12 is a continuous surrounding braiding around the six cores 10, which on the one hand separates the cores 10 from one another and on the other hand covers them, so that they are protected from the outside by the braided jacket 12.

The implant tape according to figure 1 is distinguished by a high flexibility and high tear strength, and, in respect of its tear strength, is resistant to friction and chafing. Figures 2 , 3 and 4 show embodiments of a braided absorbable implant in the form of cord, and in particular in part (a) in cross-section and in part (b) in a side view, the braided jacket being partly omitted in order to allow a view of the cores.

The implant according to figure 2 has a central core 20 which is arranged along the implant axis. The central core 20 is surrounded by four outer cores 21 arranged at the corners of a square . A configuration which is invariant to rotations around the implant axis through 90° thereby results. The cores 20, 21, which preferably each have several elements arranged side by side, are surrounded by a common diagonally braided jacket, which separates the cores 20, 21 from one another and keeps them spaced and covers them, as a result of which cores 20, 21 are protected from external influences .

In the implant according to figure 3, a central core 30 is surrounded by eight outer cores 31. The arrangement of the cores 30, 31 is again invariant to rotations around the implant axis through 90°. A common diagonally braided jacket 32 is also provided in this embodiment.

Figure 4 shows an embodiment of the braided absorbable implant in which a central core 40 is surrounded by a total of sixteen further cores 41. The further cores 41 are arranged in four rows and four columns in cross-section, and the distance between the central core 40 and one of the inner further cores 41 is shorter than the distance of one of the outer further cores 41 to another further core 41. Here also, the arrangement of the cores 40, 41 is invariant to rotations around the implant axis through 90°. The total of seventeen cores 40, 41 are in a common diagonally braided jacket 42.

Figure 5 shows a variant of the embodiment according to figure 3. The braided absorbable implant shown in figure 5 has a central core 50 which is thicker than the eight outer cores 51. The braided jacket of the embodiment according to figure 5 can be in the form as in the embodiment according to figure 3, but is not shown in figure 5. The central core 50 contributes at least 20% of the tear strength of the implant in the embodiment example. The outer cores 51 likewise have a considerable proportion of the tear strength of the implant, and furthermore protect the central core 50, additionally to the braided jacket. In this embodiment, the central core 50, which carries the greatest proportion of the tear strength of the implant, thus proves to be particularly effective against harmful external influences, in particular as a result of friction and chafing.

As in the other embodiment examples, the central core 50 can have several elements arranged side by side. In one variant, it is additionally protected by its own braided jacket in the form of a circular braid. This braided jacket defines the outline of the central core 50 drawn in figure 5. This embodiment furthermore has the previously described common diagonally braided jacke .

The braided absorbable implants in the form of cords are also flexible, have a high tear strength and as a result of the structure described are stable to friction.

All the embodiments described are suitable e.g. for use on the AC joint (acromioclavicular joint) .

Poly-p-dioxanone or glycolide/lactide copolymers, in particular a copolymer of glycolide and L-lactide in a ratio of 90:10 (polyglactin 910) or a copolymer of glycolide and L-lactide in a ratio of 5:95, are suitable, for example, as the material for the braided absorbable implant. It may be advantageous here if different materials are employed for the cores and the braided jacket (or the braided jackets), in which case, for example, the material of the cores may be absorbed more slowly than the material of the braided jacket. This is illustrated below with the aid of two further embodiment examples .

In the first example, both the cores and the braided jacket or the braided jackets are made of a copolymer of glycolide and L- lactide in a ratio of 5:95. An implant of this material which has been constructed according to the invention has an increased stability to friction as a result of the core being covered by the braided jacket or the braided jackets . The absorption time is about two to four years . The tear strength in vivo is still approx. 40% to 70% after half a year, and still approx. 15% to 35% of the original (initial) tear strength after one year. This slow breakdown profile allows a relatively small implant volume if the original tear strength and the tear strength in vivo after approx. eight to twelve weeks are not to differ substantially. Such conditions are sufficient for care of an acromioclavicular rupture, since natural ligament structures, which slowly develop a high strength again, have formed to a sufficient extent after approx. eight to twelve weeks.

In contrast, conventional implants, for example conventional tapes or conventional circular braids Of e.g. poly-p-dioxanone yarns, show a loss in tear strength of approx. 50% to 65% within eight weeks solely due to normal in vivo degradation, without the influence of friction. In addition, a loss in tear strength occurs in implants of this braid construction due to friction, which is not inconsiderable, depending on the site of the implant, the nature of the implant and the frictional area, and which e.g. may decrease the residual tear strength by another factor of 2 after an implant time of several weeks . The initial tear strength must therefore be correspondingly high in conventional implants, which necessitates a larger implant mass and therefore leads to an undesirable, more severe foreign body reaction. In the second example, the cores are made of a material which can be absorbed slowly and the braided jacket or braided jackets (surrounding braiding) are made of a material which can be absorbed rapidly. A possible material which can be absorbed slowly is, for example, a copolymer of glycolide and lactide, in particular a copolymer of glycolide and L-lactide in a ratio of 5:95 (absorption time approx. two to four years). A suitable material which can be absorbed rapidly is, for example, polyglactin 910 (absorption time approx. 70 to 80 days) or poly- p-dioxanone (absorption time approx. 180 days). The advantage here is that there is an adequate stability to friction over a period of several weeks due to the surrounding braiding. The element which is actually load-bearing, that is to say the cores which can be absorbed slowly, is effectively protected by the surrounding braiding from losses in tear strength as result of friction in this critical initial phase, and shows only a slow loss in tear strength. On the other hand, the overall implant mass is reduced relatively rapidly as a result of the breakdown of the surrounding braiding, which benefits the healing process.

Figure 6 shows a force-elongation diagram in which the behaviour of two conventional implants (a, b) and that of an implant (c) according to the invention are compared with one another. The dimensions of the implants are such that when a tensile force of 100 N is applied, an elongation of 100% occurs, that is to say the length of the particular implant doubles .

The conventional implants are a circular braid without a core (a) and a circular braid which comprises three parts of core and sixteen parts of surrounding braiding (b) .

The implant (c) according to the invention is constructed as a strip braid with a basic structure as in figure 1. The cores are made of a high-stretched multifilament yarn and each have several or many load-bearing elements arranged side by side. The core proportion here is 50% of the total mass of the implant. The force-elongation behaviour of the implant according to the invention is characterized by the high core proportion in the region of small elongations. This implant (c) has a significantly higher rigidity than the two comparison implants (a, b) in the region of small elongations. (The rigidity is defined as the change in force which occurs under linear tension per change in length, based on the initial length) . For certain indications, for example the care of an AC rupture (acromioclavicular rupture), high rigidities are desired. The rigidity can be controlled or determined, for example, by the material employed as the core .

Claims

1. Braided absorbable implant which is in the form of tape or cord and has at least two cores (10; 20, 21; 30, 31; 40, 41; 50, 51) which are separated from one another by a braided jacket (12; 22; 32; 42) and covered by a braided jacket (12; 22; 32; 42), the contribution of the cores (10; 20, 21; 30, 31; 40, 41; 50, 51) to the tear strength of the implant being in the range from 30% to 70%.

2. Implant according to claim 1, characterized in that the implant is in the form of tape and has at least three cores (10) which are arranged side by side and are separated from one another and covered by a common braided jacket (12).

3. Implant according to claim 1, characterized in that the implant is in the form of cord and has at least four cores (20, 21; 30, 31; 40, 41; 50, 51) which are separated from one another and covered by a common diagonally braided jacket (22; 32; 42).

4. Implant according to claim 3, characterized in that the cores (20, 21; 30, 31; 40, 41; 50, 51) are arranged in a configuration which is invariant to rotations around the implant axis through 90┬░.

5. Implant according to claim 3 or 4 , characterized by a central core (20; 30; 40; 50) which is arranged along the implant axis .

6. Implant according to claim 5, characterized in that the central core (50) is thicker than the other cores (51).

7. Implant according to claim 5 or 6 , characterized in that the tear strength of the central core (20; 30; 40; 50) is at least 20% of the tear strength of the implant.

8. Implant according to one of the preceding claims , characterized in that at least one of the cores (10; 20, 21; 30, 31; 40, 41; 50, 51) has several elements arranged side by side.

9. Implant according to one of the preceding claims, characterized in that at least one of the cores (50) has its own braided jacket.

10. Implant according to one of the preceding claims, characterized in that the implant comprises poly-p-dioxanone.

11. Implant according to one of the preceding claims, characterized in that the implant comprises a glycolide/lactide copolymer, preferably a copolymer of 90 parts glycolide per 10 parts L-lactide or a copolymer of 5 parts glycolide per 95 parts L-lactide.

12. Implant according to one of the preceding claims, characterized in that at least one core (10; 20, 21; 30, 31; 40, 41; 50, 51) is made of a material different to that of a braided jacket (12; 22; 32; 42).

13. Implant according to claim 12, characterized in that at least one core (10; 20, 21; 30, 31; 40, 41; 50, 51) is made of a material which can be absorbed more slowly than the material of a braided jacket (12; 22; 32; 42).