ADAPTABLE SLEEVE FOR A MEDICAL IMPLANT

Description

Technical field

[0001] The present invention relates to a flexible shell for a medical implant, which exhibits a high degree of geometric adaptability. In particular, the flexible shells according to the invention can adapt to changing shapes and geometries of the implantation site. Background of the invention

[0002] Medical implants are generally tailored to a patient's individual requirements regarding size and geometry. Particularly for medical implants that interact with organs, a consistently precise fit is crucial for reliable function. This also applies to implants with a shell, such as stent grafts or organ-enclosing implants (e.g., a ventricular assist device). An example of a ventricular assist device is known from WO 01 / 67985.

[0003] Most medical implants cannot adapt to changes in size or geometry at the implantation site after implantation. This can lead to the implants no longer fitting, thus impairing their function. Causes of changes in the shape of the implantation site can include, among other things, disease progression, successful treatment, diurnal variations, or growth in general.

[0004] The object of the present invention is to provide a geometrically adaptable implant with a shell. Summary of the invention

[0005] The present invention relates to various embodiments for an adaptable flexible casing for a cardiac support device.

[0006] A first embodiment of the invention relates to a flexible sheath comprising an auxetic pattern in the form of cuts and / or corrugations, which increases the adaptability of the sheath. The auxetic pattern of the sheath can induce auxetic material behavior. Under uniaxial tensile stress, the sheath can also expand transversely to the tensile direction. Auxetic materials are known, for example, from US 2021 / 052367, WO 2016 / 071823, WO 2005 / 072649 and WO 2019 / 081766.

[0007] The auxetic pattern can include rotating triangles. The auxetic pattern can include a variety of Y-shaped cuts or Y-shaped ripples. The Y-shaped cuts can include one-dimensional incisions. The Y-shaped cuts can include planar cutouts. The planar cutouts can include rounded corners. The cuts or ripples can define predetermined breaking points. Each of the three legs of a Y-shaped cut or Y-shaped ripple can be of the same length. The legs of a Y-shaped cut or Y-shaped ripple can be of different lengths. The majority of the Y-shaped cuts or Y-shaped ripples can have predominantly the same leg length. The majority of the Y-shaped cuts or Y-shaped ripples can have predominantly different leg lengths. The legs of the Y-shaped cuts or Y-shaped ripples can be between 1 mm and 1 cm long.The distance between the centers of two adjacent Y-shaped cuts or Y-shaped corrugations can be between 0.2 cm and 2 cm.

[0008] The auxetic pattern can include rotating quadrilaterals, in particular rotating rectangles or rotating squares. The auxetic pattern can include a plurality of cuts or ripples arranged such that they define at least partial edges of a quadrilateral. The cuts or ripples are arranged approximately at right angles to each other. The cuts can include one-dimensional incisions. The cuts can include planar cutouts. The planar cutouts can include rounded corners. The cuts or ripples can define predetermined breaking points. The cuts or ripples can be of the same length. The cuts or ripples can be of different lengths. The cuts or ripples can be between 1 mm and 1 cm long.The sheath can have a longitudinal axis, and at least some of the sections can be arranged in the same direction as the longitudinal axis. The sheath can have a longitudinal axis, and at least some of the sections can be arranged at an angle of 5° to 45° to the longitudinal axis. The sheath can have a homogeneous auxetic pattern. The sheath can have a heterogeneous auxetic pattern. The auxetic pattern can include rotating triangles and rotating quadrilaterals. The sheath can be part of a cardiac support device. The sheath can include mechanically expandable units. The sheath can be designed to at least partially enclose an organ of the body. The sheath can be designed to at least partially enclose a heart. The sheath can be designed to enclose an organ, with the auxetic pattern of the sheath being designed to compensate for changes in the size of the organ.

[0009] A second embodiment relates to a flexible shell for a medical implant, which includes a foam that increases the adaptability of the shell.

[0010] A third embodiment relates to a flexible shell for a medical implant, comprising one or more folds that can open to increase the adaptability of the shell.

[0011] A fourth embodiment relates to a flexible shell for a medical implant, wherein the shell comprises a mesh structure that increases the adaptability of the shell.

[0012] A fifth embodiment relates to a flexible shell for a medical implant, wherein the shell comprises several layers of different material stiffness, the layers being able to dissolve in order to increase the adaptability of the shell.

[0013] A sixth embodiment relates to a flexible shell for a medical implant, wherein the shell comprises a viscoelastic material that increases the adaptability of the shell.

[0014] A seventh embodiment relates to a flexible shell for a medical implant, wherein the shell comprises an absorbable filling that increases the adaptability of the shell.

[0015] The embodiments are described in more detail below. Overview of the figures

[0016] Figure 1a -d displays various auxetic patterns. Figure 2a -b shows an auxetic pattern with rotating triangles. Figure 3 shows the behavior of an auxetic pattern with rotating triangles during uniaxial tensile stress. Figure 4a -b shows an auxetic pattern with rotating quadrilaterals. Figure 5shows a detail of an auxetic pattern in the form of rotating triangles. Figure 6 shows various arrangements of an auxetic pattern in the form of rotating triangles. Figure 7 shows a cover with an auxetic pattern in the form of flat cuts. Figure 8 shows a shell with an auxetic pattern in the form of ripples. Figure 9 shows a casing that consists primarily of foam. Figure 10 shows a cover that includes a foam and a film. Figure 11a -c shows a cover with folds. Figure 12 shows the tearing open of fastenings using a balloon catheter. Figure 13 shows a shell in the form of a network structure with fuses. Figure 14 shows a shell with several layers of different material stiffness. Figure 15 shows a shell made of a viscoelastic material. Detailed description

[0017] Embodiments are described in more detail below with reference to the figures. The invention is defined by the claims. The flexible sheaths are applicable to any medical implant with a shell. The sheaths are particularly suitable for implants that at least partially enclose organs (e.g., lungs, heart, liver, stomach, small intestine, large intestine, spleen, kidney, gallbladder, pancreas). The sheaths are also suitable for enclosing implants such as stent grafts or breast implants. The various embodiments of the invention are described below with regard to a cardiac support device with a shell designed to at least partially enclose a heart.

[0018] A geometrically adaptable implant shell is particularly beneficial when the organ to be encased (for example, the heart or liver) changes in size or geometry over time. Changes in shape can occur as a result of disease progression (e.g., due to progressive heart failure). Changes in shape can also occur as a result of successful treatment (e.g., a heart may shrink after recovery from acute myocarditis). Changes in shape can also occur cyclically (e.g., during the dynamic cardiac cycle). Changes in shape can also occur due to diurnal variations (e.g., changes in cardiac geometry due to changes in volume status from drinking or urinating). Changes in shape can also occur due to growth of any kind (e.g., cardiac growth in children or proliferation of organs such as the liver or pancreas).Finally, geometrically adaptable implant shells are also advantageous when only a limited number of implant shapes can be provided (e.g., improving the individual fit of shells for standardized heart shapes).

[0019] When used in pediatrics, the adaptable implant shells according to the invention prevent growth restriction of the enclosed organ, e.g., the heart. This means that the adaptability of the shell does not restrict the child's heart growth. Over an implantation period of 12 to 18 months, the expected increase in heart volume of approximately 20-25% can thus be accommodated. The shells according to the invention can enclose an organ (e.g., the heart) or implant either completely or only partially. It is also possible to provide only sections of a shell with the adaptable properties according to the invention. This can be particularly advantageous when different properties are desired along the shell.

[0020] A first embodiment of the invention relates to a flexible shell for a medical implant, wherein the shell comprises an auxetic pattern that increases the adaptability of the shell. The auxetic pattern can, for example, be in the form of cuts and / or corrugations. The auxetic pattern enables the shell to adaptively follow a change in shape (for example, a change in organ size, such as during the growth of a child's heart). In general, auxetic material is characterized by a negative Poisson's ratio, i.e., when a sample is subjected to uniaxial tensile stress, it also expands transversely to the direction of tension, unlike most conventional materials. The patterns shown below are exemplary and induce such auxetic material behavior and are therefore also called auxetic patterns. An auxetic pattern can be formed, among other things, by inset structures ( Figure 1a ), rotating elements ( Figure 1b), chiral structures ( Figure 1c ) and elements with ligaments ( Figure 1d ) can be achieved. What they all have in common is that stretching in the longitudinal or transverse direction is not accompanied by a contraction or constriction of the material in directions perpendicular to the stretching direction. That is, stretching in the longitudinal or transverse direction can also occur simultaneously with stretching in the transverse or longitudinal direction. The materials can expand or contract in the different directions independently of the other directions in the area where the auxetic pattern is present.

[0021] For example, a shell enclosing part of the heart, without auxetic material behavior, would contract along the heart's longitudinal axis when stretched circumferentially. The shell would shorten longitudinally, and the implant would no longer conform to the heart's geometry. A shell without auxetic material behavior would therefore be unable to follow the heart's uniform, natural expansion in all directions. The shell would no longer fit the organ's geometry. With auxetic material behavior, the shell can allow independent expansion in different directions. For example, a shell with auxetic material behavior can accommodate an increase in the heart's geometry both circumferentially and longitudinally. Conversely, if the heart's geometry decreases, the shell can allow contraction in both the circumferential and longitudinal directions.The shell with auxetic material behavior can therefore maintain a good fit even with changing heart geometry.

[0022] The present invention is not limited to a specific pattern and the patterns described in more detail below are only to be understood as serving for further explanation.

[0023] Figure 2a Figure 10 schematically shows a section of a shell comprising an auxetic pattern in the form of "rotating triangles". The triangles can be generated by a variety of Y-shaped cuts or Y-shaped corrugations. As shown in Figure 10. Figure 2b As shown, the Y-shaped cuts can be one-dimensional incisions ( Figure 2b , left ) or flat cutouts ( Figure 2b , center and right) include. A complete cutout of the pattern is advantageous, for example, when the goal is to achieve ingrowth of connective tissue. By utilizing the rapid remodeling process of the ingrown connective tissue, the covering can then expand or contract in line with the growth rate of the organ (e.g., the heart). The complete cutouts can also include rounded corners. ( Figure 2b , right). Rounding the corners can lead to lower stress peaks and increased fatigue strength of the shell. The cuts or corrugations can also define predetermined breaking points ( Figure 2c, right(below). The predetermined breaking points can rupture under a certain load, leading to an enlargement of the shell. To implement this pattern as a predetermined breaking point, one exploits the fact that stress concentrations occur at corners and the predetermined fracture is absorbed by the cut-out circle in the center. The behavior of the rotating triangles during uniaxial tensile stress is described in Figure 3a -c shown. Like the Figures 3a -c As can be seen, the triangular shell surfaces rotate as a result of the tensile stress and enlarge the shell both in the direction of tension and perpendicular to the direction of tension.

[0024] Figure 4aFigure 10 schematically shows a section of a shell comprising an auxetic pattern in the form of "rotating quadrilaterals". The rotating quadrilaterals can be in the form of rotating rectangles or rotating squares, among other forms. The auxetic pattern can comprise a multitude of cuts or corrugations arranged such that they define at least segmental edges of a quadrilateral. The cuts or corrugations can be arranged approximately at right angles to each other in the unstretched material. As already described for the "rotating triangles", the cuts can be one-dimensional incisions ( Figure 4b , left ) or flat cutouts ( Figure 4b , center and right ) include. The flat cutouts can have rounded corners ( Figure 4b , right ) include. The cuts or corrugations can also define predetermined breaking points.

[0025] The following mechanism can lead to good adaptability of the shell, allowing it to follow changes in the organ's shape. The openings created by the (surface) incisions allow for cell integration, so that after implantation, these incisions on the shell are, for example, overgrown by connective tissue. This allows the implant to fuse with the organ. If the organ then undergoes a change in shape, the shell adapts to the new geometry by widening or closing the openings. This is achieved through a rotational movement of shell surfaces (e.g., the triangular surface, see arrow in [reference]). Figure 2a , or the square sub-area, see arrow in Figure 4a ) that the shell material can expand anisotropically and independently in both spatial directions under low material stresses, exhibits auxetic material behavior, and thus leads to an enlargement of the shell in both spatial directions (see also Figure 3This method takes advantage of the frequent remodeling of connective tissue. Connective tissue renews itself at short intervals in a mechanically stress-free state, allowing it to support the widening or closing of openings.

[0026] The mechanical properties, especially the elasticity and anisotropic behavior of the membrane, can be adjusted as needed through the shape and design of the pattern, and the membrane's stretching can be aligned with the organ's main growth directions and main stress directions. In addition to the type of auxetic pattern (re-entering structures, rotating elements, chiral structures, and elements with ligaments, see...), other factors can be considered. Figure 1a -d) There are even more degrees of freedom to design the pattern. For example, the desired material properties can be adjusted by varying the density of the pattern. This can be done as described in... Figure 5The diagram shows that the center-to-center distance A of the Y-cuts and / or Y-ripples can be varied. The density of rotating quadrilaterals can also be adjusted by varying the distance between the cuts and / or ripples. The properties can also be adjusted by changing the length of the cuts. Varying the leg length B of the Y-cuts and / or Y-ripples produces stiffer or more elastic properties. The same applies to rotating quadrilaterals.

[0027] In the rotating triangle pattern, the three legs of a Y-shaped cut or wave can be of the same length or of different lengths. The majority of Y-shaped cuts or waves can have predominantly the same or different leg lengths. The legs of the Y-shaped cuts or waves can be between 1 mm and 1 cm long. The center-to-center distance between two adjacent Y-shaped cuts or waves can be between 0.2 cm and 2 cm. The pattern can also be at least partially aligned with respect to the longitudinal axis. For example, one leg of the Y-structures can run in the direction of the longitudinal axis of the shell ( Figure 6 , left It is also possible to rotate the Y-structures, for example by 15° ( Figure 6 , middle ) or 30° ( Figure 6 , right) or 45° or any other angle to achieve the desired material properties.

[0028] In the rotating quadrilateral pattern, the cuts or ripples can have the same or different lengths. The cuts or ripples can be between 1 mm and 1 cm long. At least some of the cuts can be oriented in the same direction as the longitudinal axis when the shell is in its unstretched state. At least some of the cuts can be oriented at an angle of 5° to 45° to the longitudinal axis.

[0029] An exemplary covering for at least partially enclosing a heart is in Figure 7 This shell comprises an auxetic pattern in the form of rotating triangles, with the Y-structures designed as rounded, planar cutouts with predetermined breaking points (see figure). Figure 2b bottom rightThis covering exhibits a very good adaptability to the human heart and can easily follow changes in the heart's shape.

[0030] Instead of the cuts described above, all shapes can also be designed as waves. If the growth through the covering is not intended, it can be advantageous to design the auxetic pattern as waves instead of (flat) cuts.

[0031] These corrugations can be embossed into the shell material, giving the shell auxetic material behavior. It is also possible to create a shell with cuts and corrugations to achieve desired material properties. An example of a shell for at least partially encasing a heart with Y-structures in the form of corrugations is shown in the Figure 8 The shell exhibits very good auxetic behavior, and the corrugations can prevent the shell from tearing.

[0032] According to the invention, the shell can have a homogeneous auxetic pattern, i.e., the pattern is more or less uniform along the shell. It is also possible to provide a heterogeneous auxetic pattern. Different auxetic patterns can also be combined, for example, rotating triangles with rotating quadrilaterals. A combination with the re-entrant structures described above ( Figure 1a ), rotating elements ( Figure 1b ), chiral structures ( Figure 1c ) and elements with ligaments ( Figure 1d ) is also possible.

[0033] The sheath according to the invention can be part of a cardiac support device. The cardiac support device can comprise mechanically expandable units. The sheath can be designed to at least partially enclose an organ of the body. The sheath can be designed to at least partially enclose a heart. The sheath can be designed to enclose an organ, wherein the auxetic patterning of the sheath is designed to compensate for a change in the size of the organ.

[0034] Materials suitable for a shell with auxetic patterns include polymers such as polyurethane, polyethylene terephthalate (PET) and silicone.

[0035] One advantage of the described auxetic patterns is that a material property (e.g., elasticity) can be adjusted without requiring a change of material. The described sheaths also do not need to be thickened or thinned to precisely adjust the elasticity. The described patterns allow for the introduction of anisotropic material behavior. In particular, the designs with cuts facilitate good tissue ingrowth. The flat cutouts also allow for shrinkage to be accommodated. Another advantage is that the illustrated sheaths can be easily produced by die-cutting and embossing.

[0036] A second embodiment relates to a flexible shell for a medical implant which includes a foam that increases the adaptability of the shell. The shell can be shaped as described in... Figure 9The foam (900) is shown schematically and consists predominantly or exclusively of foam. The foam can envelop the heart or, in particular, the epicardium (500). The foam can be designed to be permeated by connective tissue. Since connective tissue regenerates rapidly, the foam is driven by the shape changes of the connective tissue and follows the shape changes of the organ (e.g., the heart). The foam can be an open-cell foam. Due to its intrinsic property that the cell walls align in the direction of tension under tensile stress, open-cell foam is locally very elastic and adaptive and therefore does not restrict connective tissue and organ / heart growth. The foam can have a pore size of 20 micrometers to 2 millimeters, especially 50 micrometers to 1 mm. The foam can be made of polyurethane, PET, or silicone, among other materials.A shell consisting primarily or exclusively of foam exhibits good adaptability and tissue ingrowth. Due to its very low density, the foam hardly affects natural organ / heart movement.

[0037] The flexible cover can also include a film (1000) in addition to the foam (900). As in Figure 10In schematic terms, the sheath can be designed to enclose an organ, with the foam on the side facing the organ and the film on the side facing away from the organ. The film for the sheath can be dimensioned so that it is oversized relative to the organ / heart being supported at the time of implantation. The resulting space between the film and the epicardium is then filled by the foam. The foam can be rapidly infiltrated by connective tissue. Because soft foam can be compressed with almost no mechanical resistance until it densifies, it accommodates the growth of the organ / heart. Here, too, the fact that the foam adapts to the remodeling of the connective tissue and thus also to the shape changes of the organ / heart is utilized. This represents a shift in perspective from an implant that grows with the organ / heart to one into which the organ / heart grows.A particular advantage here is that organ / heart growth is enabled on the entire implant. The film used represents a comparable pure foam approach (. Figure 9 The necessary dimensional stability is provided. The film can be made of materials such as polyurethane, PET, or silicone.

[0038] A third embodiment relates to a flexible shell for a medical implant, comprising one or more folds that can open to increase the shell's adaptability. The underlying principle of opening the folds is that shell surface is preserved within the fold, which is only released over the course of the implantation period through an opening in the fold. Thus, the implant shell can expand over time. Various approaches to preserving the closed fold can be considered.

[0039] One or more of the folds can be secured with a resorbable adhesive and / or absorbable sutures, i.e., materials that degrade in the body over time. Suitable options include cyanoacrylate-based adhesives, solvent-based adhesives, collagen adhesives, protein-based adhesives, and glutaraldehyde adhesives. Sutures made of polyglycolic acid, polydioxanone, or polyglycolic acid-caprolactone are suitable for resorbable sutures. It is also possible to secure the folds with sutures that are designed to rupture under mechanical stress (for example, due to prolonged stress and material wear). The folds can be secured with sutures and / or adhesive in such a way that they open over time. One or more folds can be secured with sutures positioned so that they can be surgically opened.

[0040] Possible options for fixing the fold with sutures are described in the Figure 11a -cThe fold can be a simple fold as shown in Figure 11a This can be shown. It can be secured with a type 1 fastener (50), which prevents the fold from sticking out. A type 2 fastener (60) can prevent the fold from opening. The fold can also be secured as shown. Figure 11b The illustration shows a double fold pointing outwards. The fold can also be as shown in Figure 11c It is depicted as a double fold facing inwards. Different folds and fastenings can also be combined.

[0041] The folds can also be designed to tear open mechanically under tensile stress. This can be done with the aid of a balloon catheter inserted into the fold. The balloon (70) can be inflated as described in the Figure 12 shown to lead to the tearing of the fastening (50), whereby the fastening may be in the form of a seam or also in the form of another securing device (e.g. adhesive).

[0042] The pleated covers can be made from the same materials as the covers with auxetic patterns described at the beginning.

[0043] A fourth embodiment relates to a flexible shell for a medical implant, wherein the shell comprises a mesh structure that increases the adaptability of the shell. The mesh structure may include resorbable structures such as resorbable sutures and / or clamps. These may be arranged such that the mesh structure can expand after their resorption. For example, some of the resorbable structures may be arranged vertically and / or horizontally to the longitudinal axis. As in Figure 13As can be seen, the network structure (100) comprises horizontal resorbable structures (110) and vertical resorbable structures (120). After resorption of the supporting structures (110, 120), the network structure can expand further. The resorbable structures can also be arranged at an angle of 30° to 60° to the longitudinal axis. A time-controlled envelope growth can be achieved using a network structure with resorbable structures. Another advantage of a network structure is its high permeability, which can lead to good tissue ingrowth. The network structure can be made of threads or wires. Polymers such as polyester, PET, PTFE, ePTFE, polyethylene, and / or metals such as nitinol, steel and iron-based alloys, titanium and titanium alloys, cobalt-based alloys, and nickel-based alloys are particularly suitable for the network structure.

[0044] A fifth embodiment relates to a flexible shell for a medical implant, wherein the shell comprises several layers of different material stiffness, the layers being capable of dissolving to increase the shell's adaptability. The shell may be designed such that the layer on one side dissolves first. As in Figure 14The shell can comprise an inner stable layer (210) with low stiffness and an outer dissolvable layer (212) with high stiffness. A middle layer (211) with medium stiffness can be positioned between these two layers, dissolving more slowly than the outer layer. The layers can dissolve from the outside inwards at different times (e.g., as a result of a hydrolytic reaction). The innermost layer is stable, meaning it does not dissolve, so the shell never completely dissolves. The progressive dissolution of the layers leads to a decrease in the mean stiffness of the shell over the course of the implantation period, and thus to increased shell stretching. This increased stretching results in an enlargement of the implant shell, which can support an enlarged organ / heart geometry over time.The coating can consist of two, three, four, five, six, or more layers with different properties. Suitable materials for the dissolvable layers include polyglycolic acid, polydioxanone, polyglycolic acid-caprolactone, and hydrolytically or oxidatively degradable polyurethanes such as polyether or polyester urethanes. Suitable materials for the stable layers include non-degradable polyurethanes (e.g., polycarbonate urethanes), polyesters, especially PET, and silicones.

[0045] A sixth embodiment relates to a flexible shell for a medical implant, wherein the shell comprises a viscoelastic material that enhances its adaptability. All of the aforementioned plastics are suitable materials. Viscoelastic or viscoplastic materials are characterized by their tendency to exhibit elongation in the form of creep under long-term (often even slight) mechanical stress. Due to this continuously increasing elongation, the implant shell expands, thus enabling the support of organs / hearts with increasing geometries. For example, the shell can accommodate the growth of a child's heart. Only specific areas of the shell can be predominantly composed of the viscoelastic material.Since the greatest strains would occur at the points on the shell where the greatest material stresses are present, but not necessarily at the points where the greatest shape adaptations would be necessary, it makes sense to manufacture only individual areas or strips of the shell from viscoelastic / viscoplastic material. These areas can be in the form of strips. The viscoelastic material can comprise a polymer, such as polyglycolic acid, polydioxanone, polyglycolic acid-caprolactone, polyether or polyester urethanes, and silicones.

[0046] A seventh embodiment relates to a flexible shell for a medical implant, wherein the shell includes an absorbable filling that increases the shell's adaptability. Time-controlled stretching of the shell can be achieved by using dissolvable fillings that are permeably enclosed within the shell. Dissolution of the filling creates space for organ / heart growth. The shell can include a film that at least partially encloses the absorbable filling. The film can include perforations to allow bodily fluids to come into contact with the filling and absorb it. The absorbable filling can be, as in the example of the Figure 15only in areas (310). The filling may also be placed in one or more chambers. The shell may be designed to at least partially enclose an organ, with the absorbable filling located on the inside of the shell. The absorbable filling may comprise a polymer, in particular a polycaprolactone (PCL), polyglycolic acid, polydioxanone, polyglycolic acid-caprolactone, or degenerable polyurethanes (polyester urethane, polyether urethane). The shell may comprise a polyurethane film, in particular thermoplastic polyurethane (TPU), polyester, PET, polyethylene, or silicone. Absorption of the filling creates space for cardiac growth. The inside of the filling (or the chamber) may be corrugated. With a corrugated inside of the filling, shell surface can be stored and then released in a time-controlled manner via dissolution of the filling, thereby increasing the size of the implant shell.The implant shell remains taut at all times, ensuring a good force transmission throughout the entire implantation period.

Claims

1. Flexible sheath for a medical implant, wherein the sheath is part of a cardiac-support device and is designed to at least partially enclose a patient's heart, characterized in that the sheath comprises an auxetic pattern in the form of cuts and / or corrugations, which increase the adaptability of the sheath.

2. Flexible sheath according to Claim 1, wherein the auxetic pattern of the sheath induces an auxetic material behaviour, in particular wherein the sheath, when exposed to uniaxial tensile stress, also expands transversely to the pulling direction.

3. Flexible sheath according to either of the preceding claims, wherein the auxetic pattern comprises rotating triangles.

4. Flexible sheath according to any one of the preceding claims, wherein the auxetic pattern comprises a multiplicity of Y-shaped cuts or Y-shaped corrugations.

5. Flexible sheath according to Claim 4, wherein the legs of the Y-shaped cuts or Y-shaped corrugations are between 1 mm and 1 cm long and / or wherein the centre-to-centre distance between two adjacent Y-shaped cuts or Y-shaped corrugations is between 0.2 cm and 2 cm.

6. Flexible sheath according to any one of the preceding claims, wherein the auxetic pattern comprises rotating quadrilaterals, in particular wherein the pattern comprises rotating rectangles and / or rotating squares.

7. Flexible sheath according to any one of the preceding claims, wherein the auxetic pattern comprises a multiplicity of cuts or corrugations, which are arranged in such a way that they define, at least in part, edges of a quadrilateral.

8. Flexible sheath according to Claim 6 or 7, wherein the cuts or corrugations are arranged approximately at right angles to one another.

9. Flexible sheath according to any one of the preceding claims, wherein the cuts comprise one-dimensional incisions.

10. Flexible sheath according to any one of the preceding claims, wherein the cuts comprise surface-area cutouts.

11. Flexible sheath according to Claim 10, wherein the surface-area cutouts comprise rounded corners.

12. Flexible sheath according to any one of the preceding claims, wherein the cuts or corrugations define predetermined breaking points.

13. Flexible sheath according to any one of the preceding claims, wherein the sheath is designed to at least partially enclose an organ and wherein the auxetic pattern of the sheath is designed to compensate for a change in size of the organ.