Elastically deformable and resorbable medical mesh implant

The invention relates to a polymeric mesh implant for use in reconstruction of tissue defects, which mesh implant comprises a first set of fibers arranged in a first knit pattern comprising apertures, wherein each aperture, or a subset thereof, comprises an elastic fiber arranged in a first direction of the mesh implant such that when the mesh implant is stretched in this first direction, the elastic fibers are elongated and also exert a restoring force on the first knit pattern.

FIELD OF THE INVENTION

The present invention relates to a resorbable polymeric mesh implant used in the medical reconstruction of soft tissue defects, and particularly to an elastically deformable and resorbable polymeric mesh, and even more particularly to a resorbable polymeric mesh whose knit pattern comprises elastic fibers arranged such that an elastically deformable mesh implant is obtained.

BACKGROUND OF THE INVENTION

Resorbable polymeric mesh implants are known. European Patent No. 1 674 048, which is assigned to the present assignee, describes a resorbable polymeric mesh implant comprising at least two materials, wherein the second material is substantially degraded at a later point in time than the first material following the time of implantation. The mesh implant is adapted to have a predetermined modulus of elasticity that gradually decreases until the implant is completely degraded and subsequently absorbed.

European Patent No. 2 002 800, which is assigned to the present assignee, also describes a resorbable polymeric mesh implant comprising at least two materials having different degradation times. The first material, which has the shorter degradation time, is in the form of a first set of polymer fibers which are arranged in a first knit pattern, and the second material, which has the longer degradation time, is in the form of a second set of polymer fibers which are arranged in a second knit pattern, wherein the fibers of the first knit pattern lock movement of the second knit pattern by traversing apertures of the second knit pattern. When the first set of fibers has degraded, the second knit pattern can move more freely, which results in a more compliant mesh implant. A mesh fabricated according to the specifications of EP 1 674 048 and EP 2 0028 00 is by the present assignee marketed under the trademark TIGR®. This mesh can in its initial, undegraded state be characterized as inelastic, and is in its semi-degraded state, when the polymer fibers of the first set have degraded, be characterized as not reversible deformable. The entire contents of both of these European patents are incorporated herein by reference for the materials, compositions, devices, implants, processes and techniques relating to mesh implants discussed therein.

Although mesh products produced according to the specifications of the patents listed above fulfill their intended purpose very well, the mechanical characteristics of these meshes are for some medical applications not ideal. In particular, the meshes do not exhibit a true elastic behavior, i.e. they are not reversibly deformable.

SUMMARY OF THE INVENTION

A general object of the present invention is therefore to provide an elastic and resorbable medical mesh implant, which after deformation, i.e. stretching, resumes its original shape, or at least almost resumes its original shape.

According to the present invention, a medical mesh implant comprises a first set of fibers having a first degradation time. The fibers of the first set are arranged in a first knit pattern with, inter alia, a predetermined number of openings or apertures per area unit. In all, or optionally some, of these apertures, an elastic fiber is arranged such that when the mesh and thereby the first knit pattern is stretched in a first direction, the elastic fibers are subjected to a force (stress), which causes an elongation or length deformation (strain) of the elastic fibers. When the stretching of the mesh implant is discontinued and the mesh is released and free to relax, the elastic fibers resume their original lengths. The shape of the first knit pattern is thereby restored, and the whole mesh implant will consequently resume its original shape.

In embodiments of the present invention, a mesh is assumed to a have a first direction and a second direction. (In a woven or knitted mesh product, the first and second mesh directions may optionally coincide with the warp direction and weft direction, respectively, or coincide with other “natural” directions.) In a first embodiment, the elastic fibers are arranged in only one direction of the mesh; and in another embodiment the elastic fibers are arranged in two, preferably perpendicular, directions of the mesh. Other directional arrangements for the elastic fibers are also within the scope of the present invention.

In embodiments of the present invention, the elastic fibers are preferably made from a biodegradable and resorbable polymer having a degradation time that can be longer, shorter or comparable to the degradation time of the first set of fibers.

In further embodiments of a mesh implant according to the present invention, a mesh implant comprises elastic fibers which, as in the embodiments described above, are arranged in apertures formed in a first knit pattern of a first set of fibers. In these further embodiments, the fibers of the first set are however supplemented with a second set of fibers whose degradation time is shorter than the degradation time of the elastic fibers. The fibers of the second set can be arranged in a second knit pattern, such that the second knit pattern locks movement of the first knit pattern by traversing the apertures of the first knit pattern. The fibers of the second set can have a high modulus of elasticity such that the mesh initially can be characterized as inelastic. The elastic behaviour of a mesh implant according to these embodiments will thereby come into play once the fibers of the second set have been degraded.

The fibers of the first set and/or the fibers of the second set and/or the elastic fibers can be made from one or more of the materials described in the European Patents described above and/or other suitable materials.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For a better understanding of the present invention, the mechanical behaviour of a conventional medical mesh implant1, which is not the present invention, will first be outlined in conjunction withFIG. 1aandFIG. 1b. The mesh1comprises a number of individual fibers2, which, in accordance with a specific knit pattern, have been knitted together to form a mesh1, which, inter alia, comprises a predetermined number of apertures3.

InFIG. 1a, the mesh1is shown in an initial or relaxed state, i.e. the mesh1is not subjected to any external forces. If a small or at least only moderately large force—denoted with F inFIG. 1b—is applied to the mesh1, a deformation of the mesh1is introduced. More specifically, each of the apertures3of the mesh1undergoes a shape transformation from a more or less quadratic shape to an elongated rhombic shape, as is seen when comparingFIG. 1awithFIG. 1b. Here it should be appreciated that for small forces F this mesh deformation is basically to be attributed to the mesh structure itself, i.e. there is substantially no elongation of the individual fibers2. The latter statement implies consequently that when the force F is removed, there are no significant forces that strive to bring the mesh1back to its original shape. Furthermore, since there is no elongation of the fibers2, it is essentially insignificant whether the fibers2are made from an elastic material or an inelastic material. In other words, a conventional mesh implant like the mesh1does not exhibit an elastic behaviour when it is subjected to a force which only causes a deformation of the mesh structure, and such a mesh implant will not resume its original shape when this force is removed. To merely complete the picture, for large forces F the mesh1would be further deformed, and eventually also the individual fibers2would be stretched. When such a large force is removed, the mesh1would—if the fibers2are made from an elastic material—return to the deformed shape shown inFIG. 1b. The mesh would, however, not resume its original shape shown inFIG. 1a.

FIG. 2aandFIG. 2billustrate a first embodiment of a mesh implant11according to the present invention. The mesh11comprises a first set of fibers12, which are arranged in a first knit pattern such that a number of apertures13are formed in the mesh11. The fibers12are preferably made from a resorbable polymer. Within an aperture13, a fiber14is arranged, such that the fiber14traverses the aperture13and is connected to two points on the perimeter of the aperture13. In this embodiment, each individual fiber14is connected to the corresponding points on the perimeter of an aperture13such that all of the fibers14extend in the same direction of the mesh implant11, which direction may be denoted a first direction of the mesh implant11. The fibers14are made from an elastic and preferably resorbable polymer. InFIG. 2a, the mesh11is shown in an initial or relaxed state, i.e. the mesh11is not subjected to any external forces. Following the same reasoning as in conjunction with the conventional mesh1above, if now a small or moderately large force—denoted F inFIG. 2b—is applied in the first direction of the mesh11, a deformation of the mesh11is introduced. In contrast to the deformation of the conventional mesh1shown inFIGS. 1aand1b, the deformation of the present mesh11involves not only distortion of the mesh structure but also an elongation of the elastic fibers14. Therefore, when the force F is removed, the elongated elastic fibers14will according to Hook's law strive to resume their original lengths. When the elastic fibers14have resumed their original lengths, the whole mesh11has resumed its original shape, as shown inFIG. 2a. In other words, when the mesh11comprises elastic fibers14arranged in a suitable way in apertures13created by a first set of fibers12connected according to a first knit pattern, the mesh11exhibits an elastic behaviour, and an elastically deformable mesh implant11is produced.

In the embodiment shown inFIGS. 2aand2b, each of the apertures13in the mesh11has been provided with a separate elastic fiber14. In an alternative arrangement (not shown in the figures), only a subset (for example, one-half or one-quarter) of the apertures in a mesh implant could be provided with an elastic fiber.

As described above, the mesh11comprises elastic fibers14, which are arranged in only one direction of the mesh11. Other arrangements are also possible, andFIG. 3illustrates a second embodiment of a mesh implant21according to the present invention. The mesh21comprises a first set of fibers22, which are arranged in a first knit pattern such that a number of apertures23are formed in the mesh21. The fibers22are preferably made from a resorbable polymer. Within a first subset of the apertures23, an elastic fiber24is arranged such that the fiber24traverses the aperture23in a first direction and is connected to two points on the perimeter of the aperture23, and within a second subset of the apertures23, an elastic fiber24′ is arranged such that the fiber24′ traverses the aperture23in a second direction and is connected to two points on the perimeter of the aperture23.

In the embodiment shown inFIG. 3, the first direction coincides with the vertical direction of the mesh (as depicted in the figure) and the second direction coincides with the horizontal direction of the mesh (as depicted in the figure). Other directional arrangements are also possible. For example, a third subset of the apertures in a mesh implant could be provided with an elastic fiber that traverses the aperture in a third direction, which is different from both the first direction and the second direction. Any other directional arrangements for the elastic fibers of a mesh implant are also within the scope of the present invention; and it is further possible that some of the apertures lack an elastic fiber. In particular, it may be preferable to let the direction (or directions) of the elastic fibers coincide with the expected direction (or directions) of the load which a mesh implant is designed to be subjected to. It may further be preferred to align the elastic fibers with other “given” directions in a mesh structure, such as the warp direction or weft direction of a woven mesh or corresponding directions in a warp knitted mesh; or the elastic fibers could be arranged more or less perpendicular to such given directions in a mesh structure.

From the above description it should be clear that with elastic fibers arranged in more than one direction of a mesh implant according to the present invention, the mesh will exhibit an elastic behaviour in more than one direction, i.e. the mesh implant will strive to resume its original shape as long as the components of a stretching force are directed along the directions of sufficiently many of the elastic fibers.

In the embodiments described above in conjunction withFIGS. 2a-bandFIG. 3, respectively, an aperture contains at most one elastic fiber. It is however possible that an individual aperture in a mesh contains more than one elastic fiber, e.g. two fibers arranged two different directions.FIG. 4illustrates a third embodiment of a mesh implant31according to the present invention. The mesh31comprises a first set of fibers32, which are arranged in a first knit pattern such that a number of apertures33are formed in the mesh31. The fibers32are preferably made from a resorbable polymer. Within an aperture33, a first elastic fiber34is arranged such that the fiber34traverses the aperture33in a first direction and is connected to two points on the perimeter of the aperture33. Within the same aperture33, a second elastic fiber34′ is arranged such that the fiber34′ traverses the aperture33in a second direction and is connected to two points on the perimeter of the aperture33. In this embodiment, the first direction and the second direction are perpendicular to each other, but other directional arrangements are within the scope of the present invention. For example, within an aperture, a third elastic fiber can be arranged such that the third elastic fiber traverses the aperture in a third direction, which is different from both the first direction and the second direction.

It should be appreciated that although an elastic fiber arranged in a one aperture and an elastic fiber arranged in another aperture have been described as two different elastic fibers, these two elastic fibers could in fact be the same physical fiber; i.e. it is the mesh forming technique (e.g. knitting or weaving) that creates two virtually different fibers. The same applies when there is more than one elastic fiber arranged within one aperture. Further, the term “connected” has herein been used to describe that an elastic fiber extends across an aperture and is connected to two points on the perimeter of the aperture. In a mesh, the apertures as well as the fiber arrangements are created by specific knit patterns, and there are numerous knit patterns that could be utilized to produce a mesh according to the present invention. Thus, the term “connected to” could have any meaning ranging from “being in contact with” to “attached to” or “knitted to”.

FIG. 5illustrates a fourth embodiment of a mesh implant41according to the present invention. The mesh41comprises a first set of fibers42, which are arranged in a first knit pattern such that a number of apertures43are formed in the mesh41. The fibers42are preferably made from a resorbable polymer. Within an aperture43, a fiber44is arranged, such that the fiber44traverses the aperture43and is connected to two points on the perimeter of the aperture43. The fibers44are made from an elastic and preferably resorbable polymer. In contrast to embodiments described above, the mesh implant41comprises further a second set of fibers45, which are arranged in a second knit pattern. The second knit pattern can be designed such that the fibers45of the second set traverse apertures43created in the first knit pattern. The fibers45are preferably made from a resorbable polymer and have preferably a high modulus of elasticity. By suitable choice of first and second knit patterns, the fibers45of the second knit pattern will thereby lock movement of the first knit pattern in a first direction of the mesh implant41. In the embodiment shown inFIG. 5, the fibers45are arranged along the elastic fibers44. By choosing fibers42,44and45such that the first fibers42have the longest degradation time, the high-modulus fibers45have the shortest degradation time, and the elastic fibers44have a degradation time which is between the degradation time of the high-modulus fibers45and the degradation time of the first fibers42, a mesh implant41is achieved which initially can be characterized as inelastic, and which, when the second set of fibers45has degraded, can be characterized as elastically deformable. Instead of providing the high-modulus fibers45alongside the elastic fibers44, the fibers44and fibers45could be interlaced with each other or spun together, such that the mesh implant41is produced (e.g. woven or knitted) with effectively only two different fibers, i.e. the slow resorbing fibers42and the combined fiber composed of fiber44and fiber45.

In the embodiment described in conjunction withFIG. 5, the elastic fibers44and the high-modulus or inelastic fibers45extend in only one direction of the mesh implant41. It is however possible to provide a mesh implant wherein elastic fibers and inelastic fibers, alongside each other, traverse apertures provided in a first knit pattern in more than one direction. Such a mesh would then have the same time-dependent mechanical behaviour as the mesh implant41but in more than one direction of the mesh implant.

A perhaps more imaginative embodiment of a mesh implant according to the present invention is illustrated inFIG. 6. Here, a mesh implant51according to a fifth embodiment comprises a first set of fibers52, which are arranged in a first knit pattern such that a number of apertures53are formed in the mesh51. The fibers52are preferably made from a resorbable polymer. Within an aperture53, a fiber54is arranged such that the fiber54traverses the aperture53in a first direction and is connected to two points on the perimeter of the aperture53. The fibers54are made from an elastic and preferably resorbable polymer. The mesh implant51comprises further a second set of fibers55, which are arranged in a second knit pattern. The second knit pattern is designed such that the fibers55of the second set traverse the apertures53in a second direction of the mesh implant51. The fibers55are preferably made from a resorbable polymer and have preferably a high modulus of elasticity. By suitable choice of first and second knit patterns, the fibers55of the second knit pattern will thereby lock movement of the first knit pattern in the second direction of the mesh implant51. Here it should however be noted that first and second directions are different from each other. By choosing fibers52,54and55such that the first fibers52have the longest degradation time, the high-modulus fibers55have the shortest degradation time, and the elastic fibers54have a degradation time which is between the degradation time of the high-modulus fibers55and the degradation time of the first fibers52, a mesh implant51is achieved which initially can be characterized as elastic in a first direction and inelastic in a second direction of the mesh implant51, and which, at a later point in time when the second set of fibers55has degraded while the elastic fibers54and the first set of fibers52have not degraded, can be characterized as being elastically deformable in the first direction and being non-elastically deformable in the second direction.

The elastic fibers used in a mesh according to some embodiments of the present invention are preferably made from synthetic aliphatic polyesters, carbonates, or mixtures thereof. Non-limiting examples of such materials are those made through ring-opening polymerization of monomers such as lactide, glycolide, ε-caprolactone, trimethylene carbonate, 1,5-dioxane-2-one (para-dioxanone), or 1,5-dioxepane-2-one. To achieve certain elastic properties in such material a prerequisite is that a certain amount of crystalline phase is present in said material to facilitate the fiber spinning process.

Preferably the elastic fiber is made from a block copolymer comprising a soft core, i.e. a glass transition temperature (Tg) below 30° C., and arms that have a certain amount of crystalline phase to facilitate the fiber spinning process. Typical examples of arm materials are those composed of more than 70 mole-% of L,L- or D,D-lactide, glycolide, 1,5-dioxane-2-one and ε-caprolactone, while typical examples of materials for the soft core can be made from any of the above listed monomers to achieve a soft core having a Tg of 30° C., or less.

The block copolymer making up the elastic fiber can be comprised of a linear block copolymer having two arms or a so-called star polymer with three or more arms. The later copolymer can be initiated from a symmetrical or non-symmetrical initiator.

Yet other examples of synthetic resorbable polymers that can be used in part or in whole to form the elastic fiber are various aliphatic polyurethanes, such as polyureaurethanes, polyesterurethanes and polycarbonateurethanes, and also materials such as polyphosphazenes, polyorthoesters, or various copolymers of β-butyrolactones.

Poly-γ-butyrolactone and its various forms as produced in various bacterias, naturally occurring or manipulated, is easily transformed into an elastic fiber that can be used in the present invention as the elastic fiber, or in combination with any of the aforementioned materials, to form an elastic fiber fulfilling the intended purpose.

The first set of fibers according to the present invention is preferably made from synthetic aliphatic polyesters, carbonates, or mixtures thereof. Non-limiting examples of such materials are those made through ring-opening polymerization of monomers such as lactide, glycolide, ε-caprolactone, or 1,5-dioxane-2-one (para-dioxanone). To control the amount of crystalline phase in the material certain amount of trimethylene carbonate or 1,5-dioxepane-2-one can be copolymerized with any of the aforementioned monomers to achieve the material used in the first set of fibers.

Yet other examples of synthetic resorbable polymers that can be used in part or in whole to form the first set of fibers are various aliphatic polyurethanes, such as polyureaurethanes, polyesterurethanes and polycarbonateurethanes, and also materials such as polyphosphazenes, polyorthoesters, or various copolymers of (3-butyrolactones.

The elastic fibers used in the present invention can therefore be made from a plurality of various materials or combinations thereof such as blends to achieve the intended mechanical and degradable characteristic of the mesh. The fiber itself can be a homogeneous material or a bi- or tri-component fiber made from two or three different materials having various cross-sections such as side-by-side, sheath-and-core, island-in-the sea, or segmented structures.

Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent to those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below. It should in particular be noted that terms such as “elastically deformable” should not be interpreted too literally, which means that also a mesh implant provided in accordance with the present invention could exhibit some degree of hysteresis, i.e. the mesh will not necessarily resume exactly its original shape after having been subjected to an external, stretching force. The most important feature of the present invention is that by incorporating elastic fibers in a mesh, a restoring force is introduced which strives to bring the mesh implant back to its original shape after having been subjected to a stretching force. For example, according to some embodiments of the invention, if a mesh material (10 cm×10 cm) is fixed into a ball burst fixture as described in ASTM D3787 and deformed with a force corresponding to 16 Newton per centimeter for no longer than 15 seconds, the mesh will return to a shape where the residual deformation measured as the depth from the ball in its original position before the mesh was deformed and to the mesh surface one minute after load has been removed is less than 25%, or less than 15%, or less than 10%, or less than 5%. The original position of the ball is defined as a position where the ball is touching the surface of the mesh with a pre-load of 0.1 Newton. Also, although the various patterns of fibers described above may be formed by knitting or weaving, other techniques may be used to form the patterns.