Expandable tube for deployment within a blood vessel

Abstract

An expandable tube for intravascular deployment that can be reversibly switched from a state of being contracted in the radial direction and expanded in the longitudinal direction to a state of being expanded in the radial direction and contracted in the longitudinal direction. The expandable tube includes a first frame and a second frame connected to the first frame and overlapping the first frame in the radial direction. The second frame includes reticulated non-overlapping elements that are non-overlapping with respect to each other in the radial direction. The reticulated non-overlapping elements have an interconnected structure including a plurality of sub-units that repeat in the longitudinal direction. Each sub-unit of the second frame defines a closed cell, and in a state of being expanded in the radial direction and contracted in the longitudinal direction, the closed cell has a bulbous region where the closed cell spreads away from the circumferential central region of the closed cell towards the circumferential end of the closed cell.

Description

Technical Field

[0001] The present invention relates to an expandable tube for deployment within a blood vessel, and particularly for use in diverting blood flow from an aneurysm sac.

Background Art

[0002] An intracranial aneurysm is a weak site in the arterial wall within the brain, where dilation or bulging of the arterial wall can occur. Histologically, a reduction in the arterial media, the intermediate muscular layer, and the internal elastic lamina causes a structural defect. These defects, in combination with hemodynamic factors, cause an aneurysm sac. Intracranial aneurysms are a fairly common disease with a prevalence in the adult population in the range of 1 to 5 percent according to autopsy studies. In the United States alone, 10 to 12 million people may have intracranial aneurysms.

[0003] Current methods for treating intracranial aneurysms include surgical clipping and endovascular coiling. In the surgical clipping method, the patient's skull is opened and a surgical clip is placed across the neck of the aneurysm to stop blood flow from entering the aneurysm sac. The risks of this method are relatively high, especially for elderly or medically complex patients. Endovascular coiling is a minimally invasive method that involves placing one or more coils delivered through a catheter into the aneurysm until the aneurysm sac is completely filled with coils. This helps to induce thrombosis inside the aneurysm. Endovascular coiling is considered to be safer than surgical clipping, but it has its own limitations. First, the aneurysm remains at its original size after being filled with coils. As a result, the pressure on the surrounding tissue exerted by the aneurysm is not removed. Second, this procedure is not very effective in the case of wide-neck aneurysms where the coils may penetrate into the parent blood vessel. This problem can be alleviated by using a stent in combination with coil embolization, but the procedure is difficult and time-consuming.

[0004] Treating an aneurysm using an expandable tube, sometimes called a stent, alone is a promising way to avoid the problems described above. In this method, an expandable tube having a region of relatively low porosity is placed across the aneurysm neck so as to divert blood flow from the sac and induce the formation of thrombus within the aneurysm. Since the aneurysm coagulates naturally by itself, the risk of its rupture is low. Furthermore, since there are no coils involved in this method, the aneurysm gradually shrinks as the thrombus is absorbed. Thus, the pressure exerted on the surrounding tissue can be removed. However, it is difficult to manufacture an expandable tube having the optimal properties for this application. The expandable tube needs to have a porosity low enough to divert blood flow from the aneurysm to a sufficient extent, while at the same time being flexible enough to pass through the very tortuous blood vessels in the brain and conform to their shape.

[0005] Known types of expandable tubes are formed from braided filaments, for example of wire. The filaments are braided together to form a mesh tube. This type of expandable tube can be radially contracted and longitudinally expanded inside a catheter for placement within a blood vessel. When the expandable tube is in the proper position relative to the aneurysm neck and is deployed from inside the catheter, it expands radially and contracts longitudinally, thereby being retained within the blood vessel and occluding the blood flow into and out of the aneurysm. However, the problem associated with expandable tubes of braided filaments is that the numerous contact points between the filaments in the braided structure cause friction. Furthermore, as a result of each filament being free to move relative to other intersecting filaments, an insufficient radial external force is generated. This causes the expandable tube of braided filaments to expand radially slowly, erratically and without consistency when deployed from the catheter, thereby making the proper placement of the expandable tube relative to the aneurysm neck more difficult and less reliable.

[0006] Another existing type of expandable tube is formed from a network of interconnected non-overlapping elements. This can be formed, for example, by laser cutting from thin tubes of materials such as shape memory alloys. These laser-cut tubes have the advantage that there are no contact points that cause friction between the braided filaments, and the deployment of those tubes can be more consistent. However, it may be difficult to design this type of tube with a porosity low enough to adequately occlude an aneurysm.

[0007] Any of these types of expandable tubes further have the limitation that they often cannot adapt to tight bends within tortuous anatomical structures and may twist or not expand properly. Such tortuous anatomical structures are particularly common within the brain where many small blood vessels are densely packed together.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] An object of the present invention is to provide an expandable tube for intravascular deployment with improved performance, particularly with respect to the deployment of expandable tubes.

MEANS FOR SOLVING THE PROBLEMS

[0009] According to one aspect of the present invention, there is provided an expandable tube for intravascular deployment, the expandable tube being reversibly switchable from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state, the expandable tube comprising a first frame and a second frame connected to the first frame and overlapping the first frame in the radial direction, the second frame including reticulated non-overlapping elements that are non-overlapping with respect to each other in the radial direction, the reticulated non-overlapping elements having an interconnected structure including a plurality of sub-units repeating in the longitudinal direction, each sub-unit of the second frame defining a closed cell, and in a state of being radially expanded and longitudinally contracted, the closed cell having a bulbous region where the closed cell expands away from a circumferential central region of the closed cell towards a circumferential end of the closed cell.

[0010] The use of a frame defining a closed cell having a bulbous region results in a longer path length of the non-overlapping elements around the cell. This improves the bending flexibility to allow the expandable tube to bend around tighter bends without twisting.

[0011] Optionally, the closed cell includes two bulbous regions at opposite circumferential ends of the closed cell. The two bulbous regions provide greater symmetry and further improve flexibility.

[0012] Optionally, the closed cell is a region around the periphery of the second frame surrounded by non-overlapping elements. The closed cell defines a region on the circumferential surface of the expandable tube.

[0013] Optionally, the network of non-overlapping elements includes a plurality of longitudinally extending members that define an interconnected structure, with circumferentially adjacent longitudinally extending members connected at connection points. Using longitudinally extending members provides greater longitudinal flexibility, which contributes to improved bending flexibility by enabling the closed cells to expand or contract longitudinally around bends.

[0014] Optionally, in a radially expanded and longitudinally contracted state, the path along each longitudinally extending member reverses longitudinally between consecutive connection points. Doubling back on themselves the longitudinally extending members creates bulbous regions and increases the path length along those members.

[0015] Optionally, in a radially expanded and longitudinally contracted state, preferably a circumferential line located at the midpoint between consecutive connection points of the longitudinally extending members and intersecting the longitudinally extending members three or more times exists for each sub-unit. This ensures that the longitudinally extending members fold back to create bulbous regions and increase the path length along those members.

[0016] Optionally, the longitudinally extending members are longitudinally deformable. Deforming the longitudinally extending members to expand them is a simple mechanism for longitudinal expansion, which reduces manufacturing complexity.

[0017] Optionally, each sub-unit defines a plurality of closed cells around the perimeter of the second frame, with circumferentially adjacent closed cells connected at connection points. In a state where the longitudinal extension member extends radially and contracts longitudinally, the radius of curvature of the longitudinal extension member decreases in a direction away from the connection point. Connecting the longitudinal extension members together increases the torsional rigidity and torsional resistance of the expandable tube. The decrease in the radius of curvature in a direction away from the connection point allows a bulbous region to be formed as the longitudinal extension member folds back on itself. Further, a larger radius adjacent to the connection point promotes less mechanical strain in a state where it contracts radially and expands longitudinally.

[0018] Optionally, the closed cells have mirror symmetry in a plane parallel to the longitudinal axis of the expandable tube and / or in a plane perpendicular to the longitudinal axis of the expandable tube. Optionally, circumferentially adjacent sub-units have mirror symmetry in a plane perpendicular to the longitudinal axis of the expandable tube. Mirror symmetry between the various levels of the structure enhances the uniformity of the behavior of the expandable tube.

[0019] Optionally, each sub-unit defines a plurality of closed cells around the perimeter of the second frame, with circumferentially adjacent closed cells connected at connection points. Connecting the longitudinal extension members together increases the torsional rigidity and torsional resistance of the expandable tube.

[0020] Optionally, circumferentially adjacent closed cells have mirror symmetry in a plane parallel to the longitudinal axis of the expandable tube. Mirror symmetry between the various levels of the structure enhances the uniformity of the behavior of the expandable tube.

[0021] Optionally, circumferentially adjacent closed cells are connected to the connection points by bridges, and optionally, the bridges are rigid bridges. Optionally, the bridges extend circumferentially. Using bridges allows adjacent cells to remain independent and reduces the effect of the connection on the ability of non-overlapping elements to deform around the connection points.

[0022] Optionally, the bridge has a longitudinal length of at most 0.1 mm, preferably at most 0.08 mm. Optionally, the bridge has a circumferential length of at most 0.2 mm, preferably at most 0.1 mm. These dimensions have been found to be effective in joining adjacent cells while providing excellent torsional rigidity.

[0023] Optionally, the non-overlapping element includes a straight portion at the connection point. The straight portion minimizes deformation of the non-overlapping element around the connection point, which can cause excessive mechanical strain that accelerates fatigue or damage to the connection.

[0024] Optionally, the radius of curvature of the non-overlapping element adjacent to the straight portion is at least 0.3 mm, preferably at least 0.5 mm, and most preferably at least 0.7 mm. This ensures that the increase in curvature occurs at an appropriate rate in the direction away from the straight portion.

[0025] Optionally, the length of the straight portion is at least 0.05 mm, preferably at least 0.1 mm. This length has been found to be effective in reducing strain at the connection point.

[0026] Optionally, the closed cell extends at least 20%, preferably at least 40%, more preferably at least 60% in the bulbous region. This level of extension provides sufficient additional path length to achieve improved bending flexibility of the expandable tube.

[0027] Optionally, the second frame is configured to urge the expandable tube from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state. Using the second frame to promote the expansion of the first frame helps to deploy the tube more consistently and reliably, thereby reducing the likelihood of deployment failure.

[0028] Optionally, the second frame is configured to urge the expandable tube from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state by applying a radial force to the first frame. Applying a radial force means that when the first frame is released from the deployment catheter, it rapidly expands to its full diameter, and thus can be more easily and properly positioned.

[0029] Optionally, the mesh non-overlapping elements are integrally formed. This reduces the complexity of the manufacturing process by eliminating the need to join the elements of the mesh. This also reduces defects or irregularities on the surface of the second frame resulting from the joining between elements.

[0030] Optionally, the second frame is connected to the first frame at least at one end of the second frame. Connecting the two frames together ensures that they do not move relative to each other and that the expandable tube behaves consistently and predictably.

[0031] Optionally, the second frame is further connected to the first frame at one or more points along the length of the second frame. This means that the interaction between the first frame and the second frame is uniform along the length of the expandable tube and is not restricted only at the two ends of the expandable tube.

[0032] Optionally, the second frame is connected to the first frame by at least one of welding, crimping, adhesive, or encapsulation. These are particularly convenient joining methods when the first frame is formed from braided filaments.

[0033] Optionally, the second frame includes a plurality of filament receiving apertures, and one or more connecting filaments are woven into the first frame, with each connecting filament passing through one or more of the filament receiving apertures. By using connecting filaments, the profile of the joining of the first frame and the second frame is reduced compared to other methods such as crimping or welding, resulting in a more uniform surface of the expandable tube.

[0034] Optionally, the connecting filaments include filaments of the first frame. This means that no additional filaments are added and the dimensions of the expandable tube are kept the same as in the case without the connecting filaments.

[0035] Optionally, one or more radiopaque markers are attached to one or more of the connecting filaments. The connecting filaments are convenient attachment points for radiopaque markers that improve the visibility of the expandable tube during deployment.

[0036] Optionally, the plurality of filament receiving apertures include filament receiving apertures in the longitudinal end regions of the second frame. This fixes the overall lengths of the two frames together.

[0037] Optionally, the plurality of filament receiving apertures include filament receiving apertures spaced along the length of the second frame. Including additional apertures spaced along the second frame enhances the attachment of the first frame and the second frame to each other and reduces the possibility of these two frames separating.

[0038] Optionally, the length of the second frame is at least 50% of the length of the first frame. Optionally, the second frame overlaps the first frame over at least 50% of the length of the expandable tube. These requirements ensure that the second frame can interact with the first frame over most of its length, thereby creating a uniform behavior of the expandable tube.

[0039] Optionally, the second frame is positioned within the first frame. Having a braided filament outside the expandable tube means that a uniform sheath is provided along the length of the expandable tube. This results in a greater radial expansion force being applied to the first frame than when the second frame is provided outside the first frame, thereby further facilitating the proper deployment of the expandable tube.

[0040] Optionally, the radius of the second frame in an unconstrained state where the second frame is not connected to the first frame and the second frame is expanding radially and contracting longitudinally is greater than the radius of the first frame in an unconstrained state where the first frame is not connected to the second frame and the first frame is expanding radially and contracting longitudinally. Oversizing the second frame such that its unconstrained radius is greater than that of the first frame can help ensure that the second frame can facilitate the deployment of the expandable tube and, in particular, minimize the risk of radial separation between the two frames when deployed within a tortuous anatomical structure. This also means that fewer fixation points are required to securely join the two frames together.

[0041] Optionally, the first elongation rate of the first frame is within 25% of the second elongation rate of the second frame, and the first elongation rate is the ratio of the length of the first frame in an unconstrained state where the first frame is not connected to the second frame and the first frame expands radially and contracts longitudinally, to the length of the first frame in a state where it contracts radially and expands longitudinally, and the second elongation rate is the ratio of the length of the second frame in an unconstrained state where the second frame is not connected to the first frame and the second frame expands radially and contracts longitudinally, to the length of the second frame in a state where it contracts radially and expands longitudinally. Previous designs of expandable tubes containing braided filaments included expansion rings at one or both ends of the expandable tube to facilitate proper deployment of the ends of the braided tube. However, increasing the length of the expansion ring for a braided stent to facilitate proper deployment over its full length is a challenge because the expansion characteristics of the two types of frames are different. Matching the elongation rates ensures that no wrinkles or buckling occur in the first or second frame when the expandable tube is deployed, thereby reducing the potential for complications from deployment. This further enables the second frame to be longer relative to the first frame and further improves the consistency of deployment of the expandable tube.

[0042] Optionally, the reticulated non-overlapping elements include a plurality of longitudinally deformable elements that effect longitudinal expansion and contraction of the second frame, and each smallest repeating unit of the reticulated non-overlapping elements has a first length longitudinally in an unconstrained state where the second frame is not connected to the first frame and the second frame expands radially and contracts longitudinally, and the ratio of the first length to the path length along each longitudinally deformable element is within 25% of the first elongation rate. By appropriately selecting the path length along the longitudinally deformable elements, the longitudinal expansion of the second frame is determined to match the first elongation rate of the first frame.

[0043] Optionally, the first frame comprises a shape memory alloy material, preferably nitinol. Shape memory alloys are designed to return to a desired shape when released from restraint, thereby eliminating the need to apply an external force to the tube to radially expand the shape memory alloy, making it a convenient material choice.

[0044] Optionally, when an expandable tube is positioned across an opening relative to an aneurysm sac in a radially expanded and longitudinally contracted state during use, the first frame can have a porosity such that it deflects blood flow away from the aneurysm sac, thereby promoting thrombosis within the aneurysm sac. This ensures that the expandable tube acts to cause thrombosis within the aneurysm.

[0045] Optionally, the first frame has a porosity of at most 90% in a radially expanded and longitudinally contracted state of the expandable tube. Limiting the porosity of the first frame reduces the porosity of the expandable tube, thereby enabling thrombosis to occur within the aneurysm.

[0046] Optionally, the first frame comprises braided filaments. Braided filament frames are well known and their manufacture is well established. These frames can also provide good porosity values suitable for aneurysm occlusion.

[0047] Optionally, the first frame comprises at least 48 filaments. A higher filament count helps increase pore density, thereby enhancing the ability of the expandable tube to occlude the aneurysm.

[0048] Optionally, the filaments of the first frame have a diameter of at most 30 μm. Smaller diameter filaments allow for an increased filament count while maintaining compatibility with a suitably sized microcatheter.

[0049] Optionally, the first frame has a braiding angle of at least 50°. This is advantageous in that it allows the expandable tube 2 to conform to the tortuous anatomical structure of the blood vessel without showing torsion. The higher the braiding angle, the better the bending flexibility, the smaller the pores (allowing for a higher pore density), and the greater the longitudinal flexibility.

[0050] Optionally, the first frame has a pore density of at least 20 pores / mm 2 . The higher the pore density, the better the ability of the expandable tube to occlude the aneurysm and the more it promotes endothelialization of the tube.

[0051] Optionally, the second frame comprises a shape memory alloy material, preferably nitinol. Shape memory alloys are designed to return to a desired shape when released from restraint, thereby eliminating the need to apply an external force to the tube to radially expand the shape memory alloy, making it a convenient material choice.

[0052] Optionally, the second frame has a porosity of at least 70%. The relatively high porosity of the second frame makes the first frame the main determinant of the porosity of the expandable tube, simplifying the design of the overall characteristics of the expandable tube.

[0053] Optionally, in the radially contracted and longitudinally expanded state, the expandable tube has a maximum radial dimension that is at least 30% smaller than the maximum radial dimension of the expandable tube in the radially expanded and longitudinally contracted state. This allows for sufficient compression of the expandable tube so that it can be inserted into a catheter for deployment.

[0054] Optionally, the longitudinal elongation of the expandable tube resulting from switching from a radially expanded and longitudinally contracted state to a radially contracted and longitudinally expanded state is at least 10%. By providing longitudinal expansion and contraction, the degree to which the expandable tube can expand and contract radially is increased.

[0055] Optionally, in the radially contracted and longitudinally expanded state, the maximum radial dimension of the expandable tube is such that the expandable tube can be inserted into a catheter having an inner diameter of at most 1.0 mm. Catheters of this size are widely available and are routinely used in the treatment of cerebral aneurysms, and thus compatibility with this catheter size is desirable.

[0056] According to a second aspect of the present invention, there is provided an expandable tube for intravascular deployment, the expandable tube being reversibly switchable from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state, the expandable tube including a frame including reticulated non-overlapping elements, the non-overlapping elements being non-overlapping with respect to each other radially, the reticulated non-overlapping elements having an interconnected structure including a plurality of sub-units repeating in the longitudinal direction, each sub-unit defining a closed cell, in the radially expanded and longitudinally contracted state, the closed cell having a bulbous region where the closed cell spreads away from the circumferential central region of the closed cell towards the circumferential ends of the closed cell, the closed cell having mirror symmetry in at least one of a plane parallel to the longitudinal axis of the expandable tube and a plane perpendicular to the longitudinal axis of the expandable tube.

[0057] The use of the bulbous regions and the symmetric closed cells enables the expandable tube to have improved flexibility for navigating tortuous anatomical structures and improved longitudinal stiffness for easier deployment.

[0058] Here, embodiments of the present invention will be described merely by way of example with reference to the accompanying drawings, in which corresponding reference numerals indicate corresponding parts.

Brief Description of the Drawings

[0059]

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DETAILED DESCRIPTION OF THE INVENTION

[0060] The present disclosure provides an expandable tube suitable for deployment within a blood vessel. The expandable tube, which may also be known as a stent, is suitable for use in methods for the treatment of aneurysms. In particular, the design herein is suitable for use in methods for the treatment of cerebral aneurysms where the blood vessel into which the expandable tube must be deployed is thin and tortuous.

[0061] FIG. 1 shows the outer geometry of an expandable tube 2 in a radially expanded and longitudinally contracted state. FIG. 2 shows the outer geometry of the expandable tube 2 in a radially contracted and longitudinally expanded state. The expandable tube 2 can be reversibly switched from the state shown in FIG. 2, which is radially contracted and longitudinally expanded, to the state shown in FIG. 1, which is radially expanded and longitudinally contracted. As will be further discussed, the expandable tube 2 includes a first frame 10 that optionally includes braided filaments and a second frame 12 that includes a network of non-overlapping elements.

[0062] The expandable tube 2 is elongated with respect to the elongation axis 4. The expandable tube 2 can be, for example, cylindrical. When the expandable tube 2 is cylindrical, the maximum transverse dimension is the same at all positions and angles (i.e., equal to the diameter). When the expandable tube 2 is not cylindrical, the maximum transverse dimension can vary at various positions and / or angles. The maximum transverse dimension defines the minimum inner diameter of a cylindrical tube (e.g., a delivery catheter) into which the frame can be inserted.

[0063] In the radially contracted state, the expandable tube 2 is substantially thinner than in the radially expanded state. Preferably, in the state of being radially contracted and longitudinally expanded, the expandable tube 2 has a maximum radial dimension that is at least 30% smaller, more preferably at least 50% smaller, than the maximum radial dimension of the expandable tube 2 in the state of being radially expanded and longitudinally contracted. Radially contracting the expandable tube 2 allows the expandable tube 2 to be inserted into a thinner delivery catheter for deployment at the target site. It is generally desirable for the delivery catheter to be as thin as possible. This is especially the case when navigation of tortuous regions of the vasculature is required for access to the deployment site. This can often be the case, for example, when treating a cerebral aneurysm.

[0064] In the following discussion, the term porosity ρ is understood to refer to the ratio of the surface area of the void region to the total outer surface area occupied by the expandable tube 2, the portion of the expandable tube 2 being described, or the frame of the expandable tube 2 (further described below). The total outer surface area is the sum of the surface area of the void region and the surface area of the region occupied by the material of the expandable tube 2 or the frame. When the expandable tube 2 or the frame is cylindrical, the total outer surface area is simply 2πRL, where R is the radius of the cylinder and L is the length of the cylinder.

[0065] Considering the second frame 12 of the expandable tube 2, the second frame includes elements that cannot overlap each other radially. The second frame 12 has a porosity ρ in a fully radially expanded state. If the radius and length of the second frame 12 in a fully radially expanded state are R0 and L0, respectively, the minimum radius R that the second frame 12 can achieve in a radially contracted state, defined by the state where the porosity becomes zero. min is

Number

[0066] This relationship indicates that when the length of the second frame 12 cannot be significantly changed, only the radius can be reduced by the coefficient of ρ. Since ρ needs to be quite low (for example, less than 90%, preferably less than 80% in at least a low porosity region such as a region intended to be positioned across the opening with respect to the aneurysm sac during use), this represents a significant limitation to the extent that the second frame 12 can be thinned for insertion into the delivery catheter. For example, if the porosity ρ of the second frame 12 is 20% and the length of the second frame 12 cannot be changed during radial contraction, i.e., L1 = L0, the second frame 12 can achieve a maximum radius reduction of 20%. Allowing for length increase is also important for frames including braided filaments. If the length of a braided frame cannot be changed due to its braided structure, radius reduction is impossible, and the greater the possible length increase, the greater the possible radius reduction.

[0067] Providing an expandable tube 2 with a frame that can expand longitudinally when in a radially contracted state is based on this understanding, and much greater radius reduction can be achieved. For example, when the length is doubled, i.e., L1 = 2L0, the second frame 12 can achieve a 60% radius reduction for a 20% porosity. For this reason, the elongation of the expandable tube 2 (or the frame forming part of the expandable tube 2) in the longitudinal direction, which occurs by switching from a radially expanded and longitudinally contracted state to a radially contracted and longitudinally expanded state, is preferably at least 10%, more preferably at least 20%, and most preferably at least 30%.

[0068] Figure 3 shows further details of the expandable tube 2 in a radially expanded and longitudinally contracted state. The expandable tube 2 includes a first frame 10 and a second frame 12, preferably including braided filaments. Figure 4 shows the expandable tube 2 of Figure 3 in a radially contracted and longitudinally expanded state. In Figure 4, both the first frame 10 and the second frame 12 are radially contracted and longitudinally expanded compared to their states in Figure 3.

[0069] An example of an embodiment of the expandable tube 2 of Figures 3 and 4 is shown in Figure 5. Figure 5 shows the expandable tube in a radially expanded and longitudinally contracted state, i.e., the state schematically shown in Figure 3. The structure of the first frame 10, which includes braided filaments, and the second frame 12 can be clearly seen.

[0070] The first frame 10 preferably includes braided filaments. The first filament 10 can include a number of filaments braided together. As seen in Figure 5, the first frame 10 includes filaments arranged in a plurality of spirals. The first frame 10 preferably includes filaments arranged in both right-handed and left-handed spirals of equal diameter. In this way, filaments of opposing spiral turns overlap radially with each other to form the braided structure of the first frame 10. The filaments of the first frame 10 can have substantially the same diameter. Alternatively, the filaments may include a mixture of filaments having various diameters and / or materials. For example, a mixture of filaments of various diameters can provide advantageous mechanical properties. Alternatively or additionally, some filaments made of a radiopaque material, optionally filaments of a larger diameter, provide radiopacity to enable the expandable tube to be more easily positioned during an implantation procedure, for example using fluoroscopic visualization.

[0071] To form the braided structure, the individual filaments of the first helix can alternately pass above and below the filaments of the second helix (different from the first helix), where above and below are interpreted as being respectively away from and in contact with the axis of the expandable tube 2 in the radial direction. Other arrangements are also possible. For example, the filaments of the first helix can alternately pass above and below a plurality of pairs of filaments of the opposing helices, or more sets of filaments such as three, four or more filaments. Passing above and below a plurality of filaments of the opposing helices can be advantageous for reducing the deformation of the individual filaments and reducing the strain and friction between the filaments. However, passing above and below too many filaments at once may reduce the integrity of the first frame 10.

[0072] The first frame 10, specifically the filaments of the first frame 10, can include a shape memory alloy material, preferably nitinol. Since the shape memory alloy material can be configured to bias itself into a radially expanded state (self-expansion), it is advantageous for promoting the radial expansion of the first frame 10. Alternatively, the first frame 10 may include a polymer or other biocompatible material. Optionally, the first frame 10 may independently be self-expanding. That is, the first frame 10 is configured to self-expand from a state where it is radially contracted and longitudinally expanded to a state where it is radially expanded and longitudinally contracted even when the first frame 10 is not connected to the second frame 12.

[0073] The filaments of the first frame 10 can include a radiopaque material, such as platinum. Optionally, the filaments of the first frame 10 can include a core of radiopaque material within a coating of another material. The coating can be a shape memory alloy, preferably nitinol. For example, the filaments of the first frame 10 can include drawn and filled tube nitinol wires having a platinum core. Such an embodiment enables the first frame 10 to be radiopaque, thereby significantly improving the visibility of the expandable tube 2 during deployment and improving the accuracy with which the expandable tube 2 can be deployed. The coating material can also be selected to have improved biocompatibility with respect to the radiopaque core. The coating material can also be selected to have other advantageous properties, such as the self-expanding properties of a shape memory alloy.

[0074] An important property of a stent used to treat an aneurysm is its pore density, i.e., the number of pores in the wall of the tube per unit area. An increase in pore density is associated with a greater flow reduction within the aneurysm sac and a more rapid endothelialization of the stent by the blood vessel, both of which result in a better and more reliable patient outcome. Thus, for some time, the goal of stent designers has been to increase the pore density in stents.

[0075] In the case of a frame (such as the first frame 10) made from braided filaments, the pore density can be increased by using thinner filaments and increasing the filament count (the total number of filaments around the diameter of the frame). However, thinner filaments are less rigid, and a frame made from thinner filaments has insufficient expansion characteristics. Thus, attempts to increase the pore density of a braided frame by using thinner filaments typically degrade the already less than ideal expansion characteristics of the braided frame.

[0076] Increasing the filament count without decreasing the filament diameter can provide some benefits without degrading the expansion characteristics, but it will increase the diameter of the stent in the radially contracted state. This makes the standard-sized catheter, which is widely available and well understood by practicing physicians, and the stent incompatible when used to deploy the stent for treating intracranial aneurysms. Therefore, the problem of increasing the pore density in the stent without increasing the diameter of the stent in the radially contracted state has remained without a sufficient solution for some time.

[0077] As further discussed below, in the present invention, the second frame 12 can expand more easily and consistently than the first frame 10. Therefore, the second frame 12 can be configured to urge the expandable tube 2 from a state of being radially contracted and longitudinally expanded to a state of being radially expanded and longitudinally contracted, that is, the expansion characteristics of the expandable tube 2 are mainly determined by the second frame 12. Due to the advantageous expansion characteristics of the second frame 12, it becomes possible to fabricate the first frame 10 using filaments having a smaller diameter, because the first frame 10 does not rely on causing the expansion of the expandable tube 2. By using filaments with a smaller diameter, it is possible to increase the filament count of the first frame 10 compared to conventional braided stents without requiring an increase in the diameter of the expandable tube 2 in a state of being radially contracted and longitudinally expanded.

[0078] Similarly, this still enables the expandable tube 2 to be compatible with a standard-sized catheter widely used to deploy the expandable tube 2 for treating intracranial aneurysms, while increasing the pore density of the first frame 10. For example, in a radially contracted and longitudinally expanded state, the maximum radial dimension of the expandable tube 2 can be such that the expandable tube 2 can be inserted into a catheter having an inner diameter of at most 1.0 mm. Preferably, the maximum radial dimension of the expandable tube 2 is such that the expandable tube 2 can be inserted into a catheter having an inner diameter of 0.69 mm (0.027 inches) or 0.53 mm (0.021 inches) or less.

[0079] Optionally, the first filament 10 includes at least 48 filaments, preferably at least 64 filaments, more preferably at least 72 filaments, and most preferably at least 96 filaments. Optionally, the filaments of the first frame 10 have a diameter of at most 30 μm, preferably at most 25 μm, more preferably at most 20 μm. Optionally, the first frame 10 has at least 20 pores / mm 2 , preferably at least 40 pores / mm 2 , more preferably at least 50 pores / mm 2 , most preferably at least 60 pores / mm 2 pore density.

[0080] Another important characteristic of the first frame 10 is the braiding angle, i.e., the angle between the longitudinal direction of the first frame 10 and the individual filaments of the first frame 10. The bending flexibility of the braided filaments of the first frame 10 increases as the braiding pitch decreases (i.e., as the braiding angle increases). This is advantageous in that it allows the expandable tube 2 to conform to the tortuous anatomical structure of blood vessels without showing torsion. The higher the braiding angle, the better the bending flexibility, the smaller the pores (allowing for a higher pore density), and the better the longitudinal flexibility. Optionally, the braiding angle is at least 50°, preferably in the range of 50-80°.

[0081] Existing stent designs generally achieve a filament count of only 48 filaments, or at most 64 filaments, and a pore density of up to 20 or at most 30 pores / mm 2 . Attempts to further increase the filament count in prior art devices did not maintain compatibility with a standard size 0.69 mm (0.027 inch) catheter and required custom-made and / or larger size catheters for deployment.

[0082] Double-layer stents have been previously considered. However, in existing designs, both layers are made from conventional braided filament layers. Such designs provide some advantages. However, the two braided layers do not have the same improvement in expansion certainty and consistency brought about by having one as a braided frame and one as a frame of non-overlapping elements.

[0083] Furthermore, in a braided frame, each filament overlaps with other filaments at the intersections. This results in a cross-sectional profile of 2 * filament diameters (i.e., the effective thickness of the frame wall in the radial direction). If a double-layer device has only a braided frame, the cross-sectional profile is further 2 * filament diameters of the inner frame + 2 *The filament diameter is increased. This increase in the cross-sectional profile is associated with higher thrombosis and is undesirable. The present invention can use thinner filaments and can have a reduced cross-sectional profile by including a second frame 12 including non-overlapping elements. When the expandable tube 2 is positioned across the opening with respect to the aneurysm sac in a radially expanded and longitudinally contracted state during use, the first frame 10 can have a porosity such that it deflects blood flow from the aneurysm sac, thereby promoting thrombosis within the aneurysm sac. For example, the first frame 10 can have a porosity of at most 90%, preferably at most 80%, more preferably at most 70%, more preferably at most 60%, and most preferably at most 50% in a radially expanded and longitudinally contracted state of the expandable tube. The porosity can be expressed in terms of a surface coverage rate that is inversely proportional to the porosity (i.e., a surface coverage rate of 90% indicates a porosity of 10%). If the porosity of the first frame 10 alone is low enough to deflect blood flow from the aneurysm, this reduces the design constraints regarding the second frame 12 and allows the second frame to have a higher porosity.

[0084] The expandable tube 2 further includes a second frame 12. The second frame 12 includes a network of non-overlapping elements that are non-overlapping with respect to each other radially. This does not apply to the braided filaments of the first frame 10 that overlap with each other radially. Exemplary designs of the network of non-overlapping elements are shown in FIGS. 6 and 8. By having a network of non-overlapping elements for the second frame 12, the friction between these elements that would otherwise occur at the overlap points is avoided. Similarly, this reduces the resistance to radial expansion of the second frame 12, so that the second frame 12 can expand rapidly and consistently when released from the catheter during deployment.

[0085] The non-overlapping elements of the network can be integrally formed, i.e., the non-overlapping elements are connected together so that there is no material interface between any of them to form a network. This can be achieved, for example, by laser cutting a hollow tube or by other techniques known in the prior art for manufacturing such structures, by forming the second frame 12. Integrally forming the non-overlapping elements of the network is preferred because there is no joint between them that would cause defects or the like that could increase friction. However, it is not essential, and for example, the non-overlapping elements of the network can be formed by welding a plurality of individual elements together.

[0086] The second frame 12, specifically the non-overlapping elements, can include a shape memory alloy material, preferably nitinol. Optionally, the second frame can have a porosity of at least 70%, preferably at least 80%, preferably at least 85%, more preferably at least 90%, and most preferably at least 95%. This enables the second frame 12 to have a low-density network of non-overlapping elements, thereby reducing the likelihood that these elements will interfere with each other during expansion and contraction of the frame and simplifying the design of the network. This also means that the porosity of the expandable tube 2 is more completely determined overall by the first frame 10 alone, thereby making it possible to simplify the determination of the overall characteristics of the expandable tube 2. Optionally, the second frame 12 can be independently self-expanding. That is, the second frame 12 is configured to self-expand from a state where it is radially contracted and longitudinally expanded to a state where it is radially expanded and longitudinally contracted even when the second frame 12 is not connected to the first frame 10.

[0087] The reticulated non-overlapping elements of the second frame 12 have an interconnected structure that includes a plurality of sub-units that repeat longitudinally. This feature has the advantage that the length of the expandable tube 2 can be easily changed to suit any particular application by adding more sub-units. Adjacent sub-units in the longitudinal direction may have mirror symmetry in a plane perpendicular to the longitudinal axis of the expandable tube 2.

[0088] Each sub-unit of the second frame 12 defines a closed cell 32. FIG. 6 shows two adjacent closed cells 32 of the second frame 12. The closed cell 32 is an area surrounded by non-overlapping elements around the second frame 12. In other words, the closed cell 32 is a portion of the outer surface area of the second frame 12 bounded by the reticulated non-overlapping elements.

[0089] In the radially expanded and longitudinally contracted state, the closed cell 32 has a bulbous region 34 where the closed cell 32 spreads away from the circumferential central region of the closed cell 32 towards the circumferential ends of the closed cell 32. The closed cell 32 can spread at least 20%, preferably at least 40%, more preferably at least 60% in the bulbous region 34.

[0090] The circumferential ends refer to the ends of the closed cell 32 in the circumferential direction around the second frame 12, i.e., around the outer surface of the second frame 12. Similarly, the circumferential central region is the region between the circumferential ends of the closed cell 32 in the circumferential direction (e.g., approximately equidistant between the circumferential ends). As shown in FIG. 6, the closed cell 32 may include two bulbous regions 34 at the opposing circumferential ends of the closed cell 32. In the example of FIG. 6, the reticulated non-overlapping elements include a series of s-shaped sections to define the bulbous regions 34 of the closed cell 32. The closed cell design of the second frame 12 provides greater torsional stiffness and torsional resistance.

[0091] The closed cell 32 may have mirror symmetry in one or both of a plane parallel to the longitudinal axis of the expandable tube 2 and a plane perpendicular to the longitudinal axis of the expandable tube 2. In the example of FIG. 6, the closed cell 32 has mirror symmetry in a plane defined by the longitudinal axis of the expandable tube and a line drawn through every other connection point 30 along the longitudinal extension member. The closed cell 32 of FIG. 6 also has mirror symmetry in a plane perpendicular to the longitudinal axis of the expandable tube 2 drawn through the connection points 30 at the opposing circumferential ends of the closed cell 32.

[0092] The network of non-overlapping elements may include a plurality of longitudinal extension members 8 that define an interconnected structure. Preferably, the longitudinal extension members 8 are deformable longitudinally. In the example of FIG. 6, this means that each closed cell 32 is defined by two circumferentially adjacent longitudinal extension members 8.

[0093] The longitudinal extension members may be configured such that the angle "A" labeled in FIG. 6 is greater than 180 degrees. This means that in a radially expanded and longitudinally contracted state, the path along each longitudinal extension member 8 reverses longitudinally between successive connection points 30. In a radially expanded and longitudinally contracted state, there is a circumferential line that intersects the longitudinal extension members 8 three or more times for each sub-unit. The circumferential line is preferably located midway between successive connection points 30 of the longitudinal extension members 8, but generally exists within a range of longitudinal positions around the midpoint depending on the degree to which the longitudinal members fold back between connection points.

[0094] The angle "A" being greater than 180 degrees allows for a longer path length of the longitudinal extension member 8 to be achieved. This s-shaped configuration between successive connection points 30 thereby causes the longitudinal extension member 8 to reverse its bending direction, resulting in better bending flexibility, longitudinal flexibility, and a lower magnitude of strain on the non-overlapping elements.

[0095] Each sub-unit of the second frame 12 can define a plurality of closed cells 32 around the second frame 12 such that the closed cells 32 repeat circumferentially. Adjacent closed cells 32 in the circumferential direction can be connected at connection points 30 (i.e., non-overlapping elements defining the boundaries of adjacent closed cells 32 in the circumferential direction are connected at the connection points). When the second frame 12 includes a plurality of longitudinally extending members 8, adjacent longitudinally extending members 8 in the circumferential direction are connected at connection points 30. In this case, the structure of the network of non-overlapping elements can itself repeat in both the longitudinal and circumferential directions. The circumferential repetition of the cells allows the radius of the expandable tube 2 to be easily adjusted according to the requirements of a particular application.

[0096] The non-overlapping elements can include a straight portion 36 at the connection point 30. In the example of FIG. 6, the straight portion 36 has a length "L". The straight portion 36 minimizes the deformation of the non-overlapping elements at the connection point 30. This can significantly reduce fatigue-related failures of the expandable tube 2 since additional material and / or joints at the connection point 30 cannot bend very much. The length of the straight portion 36 can be at least 0.05 mm, preferably at least 0.1 mm. The straight portion 36 is preferably centered around the connection point 30. The straight portion 36 does not need to be exactly straight, but the radius of curvature of the non-overlapping elements in the straight portion 36 should be substantially larger, e.g., 25% larger, preferably 50% larger, more preferably 100% larger than the radius of curvature of the non-overlapping elements outside the straight portion 36. Preferably, the non-overlapping elements do not bend too much immediately from the straight portion 36 to further reduce the strain at the connection point 30. The radius of curvature of the non-overlapping elements adjacent to the straight portion 36 can be at least 0.3 mm, preferably at least 0.5 mm, most preferably at least 0.7 mm.

[0097] Adjacent closed cells 32 in the circumferential direction in each sub-unit may have mirror symmetry in a plane parallel to the longitudinal axis of the expandable tube 2. In the examples of FIGS. 5 and 6, the closed cells have mirror symmetry in such a plane defined by the longitudinal axis of the expandable tube and a line drawn through every other connection point along the longitudinal extension member 8.

[0098] When the sub-unit includes a plurality of closed cells 32 connected at the connection point 30, the second frame 12 may be configured such that in a radially expanded and longitudinally contracted state, the radius of curvature of the longitudinal extension member 8 decreases in a direction away from the connection point 30. The decrease in the radius of curvature may be substantially continuous or may be brought about by two or more sections of the longitudinal extension member 8 having different radii of curvature.

[0099] In the example of FIG. 6, the two sections are shown as R1 and R2. The radius of curvature of section R1 is greater than the radius of curvature of R2. This minimizes the strain in the longitudinal extension member at R1, as well as at and near the connection point 30. As a result, the deformation of the longitudinal extension member 8 is mainly brought about by the R2 section. Using this design with two or more radii of curvature allows for lower strain values in non-redundant elements.

[0100] Closely adjacent closed cells 32 (or longitudinal extension elements 8 defining the closed cells 32) in the circumferential direction can be connected at connection points 30 by bridges. The bridges are preferably rigid bridges. Using a closed cell design where the bridges connect the longitudinal extension members 8 gives greater longitudinal rigidity to the second frame 12. This can enable the expandable tube 2 to be more easily extruded from the delivery catheter by a delivery guide wire and also enable the expandable tube 2 to be more easily and consistently delivered from a wider range of designs of the delivery system. The bridges preferably extend circumferentially. The bridges can have a longitudinal length of at most 0.2 mm, preferably 0.1 mm, more preferably at most 0.08 mm, and most preferably at most 0.05 mm. The bridges can have a circumferential length of at most 0.1 mm.

[0101] FIG. 7 shows the process by which the expandable tube 2 switches from the radially expanded and longitudinally contracted state shown in FIG. 5 to the radially contracted and longitudinally expanded state schematically shown in FIG. 4. In FIG. 7, the expandable tube 2 is disposed inside a tapered glass funnel, so that its behavior at various levels of radial contraction and longitudinal expansion can be observed.

[0102] In the state shown in FIG. 5, the expandable tube 2 has its maximum diameter, so that the expandable tube 2 can engage the wall of the blood vessel in which it is deployed. This corresponds to the state in the radially expanded region 40 of FIG. 7.

[0103] In the intermediate region 42 in FIG. 7, the porosity of the expandable tube 2 is maximum because the space between the filaments of the first frame 10 has its maximum area. The closed cells 32 of the second frame 12 extend longitudinally and contract circumferentially, and thus no longer show the bulbous regions 34 that exist in the radially expanded and longitudinally contracted state.

[0104] In the radially contracted region 44 in FIG. 7, the expandable tube 2 has its minimum diameter and can thus be inserted into a catheter for deployment within a blood vessel. During this process, the space between the filaments of the first frame 10 changes from a rhombus in which the major axes of those filaments are circumferentially oriented to a rhombus in which the major axes of those filaments are longitudinally oriented. The closed cells 32 of the second frame 12 contract further circumferentially and expand longitudinally. As can be seen, most of the deformation of the longitudinal extension member 8 occurs away from the connection point 30, thereby reducing the mechanical strain around the connection point 30.

[0105] FIG. 8 shows some of the beneficial effects of the second frame 12 having closed cells 32 with bulbous regions 34. The closed cell structure provides greater torsional rigidity to resist torsion in tortuous anatomical structures. An open cell design has the potential for elements of the frame (struts) to protrude into the vascular lumen around bends. This can result in partial occlusion of the vascular lumen and can cause thromboembolic complications. In contrast, the closed cell design also provides improved adherence of the expandable tube 2 in tortuous anatomical structures, which is particularly useful in neurovascular applications.

[0106] In a closed-cell design, the longer path lengths of non-overlapping elements provided by the bulbous region 34 improve the bending flexibility with respect to the outer curve without requiring any substantial change in the diameter of the expandable tube 2. As shown in FIG. 8, the closed cell 32 can open with respect to the outer curve and close with respect to the inner curve without the elements protruding significantly into the surrounding space. FIG. 8 also shows that the second frame 12 can have a flared end (i.e., the diameter of the second frame 12 is increasing in one or both end regions of the second frame 12). The flared end improves the engagement of the second frame 12 with the vessel wall while maintaining wall contact around the curve and preventing the "fish mouth" of the first frame 10. This is the case where the ends of the first frame 10 are not fully radially expanded as a result of insufficient radial force and insufficient compliance of the structure (especially when the first frame 10 includes braided filaments).

[0107] The second frame 12 is described herein as part of the expandable tube 2 that includes both the second frame 12 and the first frame 10. However, the second frame 12 may be provided independently of the first frame 10 as an expandable tube for intravascular deployment. This may be preferred in some situations, for example, when a low porosity of the expandable tube is not overly important. The second frame 12 can have any of the applicable structural features described herein when provided as an expandable tube independently of the first frame 10.

[0108] When the second frame 12 is provided together with the first frame as part of the expandable tube 2, it radially overlaps with the first frame. That is, for at least some points along the elongation axis 4, a line perpendicular to the elongation axis 4 passes through both the first frame 10 and the second frame 12. The second frame 12 can overlap with the first frame 10 over at least 50%, preferably at least 60%, more preferably at least 70%, and most preferably at least 80% of the length of the expandable tube 2. In the examples of FIGS. 3 to 5, the first frame 10 and the second frame 12 overlap substantially over their entire lengths. By having substantial overlap between the first frame 10 and the second frame 12, it is ensured that the characteristics of the expandable tube 2 are the same along the expandable tube 2, and thus the behavior of the expandable tube 2 is predictable. In FIG. 3, the second frame 12 is positioned within the first frame 10. However, this is not essential, and in other embodiments, the first frame 10 may be within the second frame 12. If the first frame 10 is within the second frame 12, this may further require that the second frame 12 be connected to the first frame 10 at one or more points along the length of the second frame 12.

[0109] The length of the second frame 12 can be at least 50%, preferably at least 60%, more preferably at least 70%, and most preferably at least 80% of the length of the first frame 10. In the examples of FIGS. 3 to 5, the first frame 10 and the second frame 12 have substantially the same length. This can contribute to ensuring that the characteristics of the expandable tube 2 are consistent along the length of the expandable tube 2. The requirements regarding the overlap and the relative lengths of the first frame 10 and the second frame 12 also make it possible to connect both the first frame 10 and the second frame 12 at both ends of the expandable tube 2, which may be preferred in some embodiments.

[0110] The second frame 12 is connected to the first frame 10. The connection can be achieved in any suitable way. For example, the second frame 12 can be connected to the first frame 10 by at least one of welding, crimping, adhesives, weaving or knitting, or encapsulation. Connecting the first frame 10 and the second frame 12 at a certain point by encapsulation can be achieved by locally covering both the first frame 10 and the second frame 12 in a continuous portion of a suitable material such as a biocompatible polymer (e.g., PTFE).

[0111] In a preferred embodiment, the second frame 12 is connected to the first frame 10 using a connecting filament 16. FIGS. 9-12 show various ways of connecting the frames together using the connecting filament 16. The design of the non-overlapping elements of the mesh of the second frame 12 is different in FIGS. 10-12 from the design discussed with respect to FIGS. 6-8. However, the method of connecting the two frames is equally applicable to any design of the second frame 12.

[0112] To facilitate the connection between the two frames, the second frame 12 includes a plurality of filament receiving apertures 18. One or more connecting filaments 16 are woven into the first filament 10, and each connecting filament 16 passes through one or more of the filament receiving apertures 18.

[0113] The advantage of using the connecting filament 16 is to reduce the profile of the joint between the first frame 10 and the second frame 12 compared to other methods such as crimping or welding, thereby making the surface of the expandable tube 2 more uniform. These filaments also enable the joining of the laser cutting structure to a continuous braid (i.e., a braid with a continuous pitch). Further, the filament 16 can deform during the expansion and contraction of the expandable tube 2. Thereby, by using the connecting filament 16, both the first frame 10 and the second frame 12 are fixed at several positions of the filament receiving aperture 18, while enabling a smooth transition between a radially contracted and longitudinally expanded state and a radially expanded and longitudinally contracted state.

[0114] FIG. 9 shows an example of a longitudinal end region of the second frame 12 in an embodiment in which a plurality of filament receiving apertures 18 are included in the longitudinal end region of the second frame 12. The longitudinal end region may include a region within a certain distance from one end of the expandable tube 2 that is at most 10%, preferably at most 5%, of the length of the expandable tube 2. The second frame 12 can include the filament receiving apertures 18 within one or both end regions of the expandable tube 2. The filament receiving apertures 18 in the embodiment of FIG. 9 are located at the most distal element in the longitudinal direction of the networked interconnecting elements of the second frame 12. Although not shown, the filament receiving apertures 18 in the embodiment of FIG. 9 are also located at the most proximal element in the longitudinal direction of the networked interconnecting elements of the second frame 12.

[0115] As shown in FIGS. 10 and 11, one or more connecting filaments 16 are woven into the first frame 10, and each connecting filament 16 passes through one or more of the filament receiving apertures 18.

[0116] In the example of FIG. 9, the second frame 12 includes two filament receiving apertures 18 in the same element of the second frame 12. In this case, the angle between the line between the filament receiving apertures 18 in the same element and the longitudinal axis 4 of the expandable tube 2 is preferably the same as the braiding angle of the braided filaments of the first frame 10. Thereby, the connecting filament 16 passing through the filament receiving apertures 18 in the same element of the second frame 12 extends parallel to the filaments of the first frame 10. This facilitates the weaving of the connecting filament 16 to the first frame 10.

[0117] The connecting filament 16 is woven into the first frame 10. Thus, the connecting filament 16 alternately passes above and below the filaments of the first frame 10 (above and below are interpreted as being respectively separated from and in contact with the axis of the expandable tube 2 in the radial direction). Other arrangements are also possible. For example, the connecting filament 16 can alternately pass above and below a plurality of pairs of filaments of the first frame 10, or more sets of filaments such as three, four or more filaments of the first frame 10. Passing above and below a large number of filaments of the first frame 10 can be advantageous for shortening the assembly time. Alternatively, passing above and below fewer filaments of the first frame 10 can be advantageous for increasing the bonding strength between the first frame 10 and the second frame 12. The arrangement of the connecting filament 16 may or may not coincide with the arrangement of the filaments of the first frame 10. For example, if the connecting filament 16 has a larger diameter than the filaments of the first frame 10, it would be desirable for the connecting filament 16 to pass above and below more sets of the filaments of the first frame 10 than the filaments of the first frame 10 themselves pass through.

[0118] In embodiments where a plurality of filament receiving apertures 18 are included within the longitudinal end regions of the second frame 12, the connecting filament 16 can be woven into the first frame 10 around the first frame 10. An example of such an embodiment is shown in FIG. 10. In this case, the connecting filament 16 is bent at equal intervals so as to alternately follow the right-handed and left-handed helical filaments of the first frame 10. To facilitate this, the connecting filament 16 can be bent into a desired shape before being woven into the first frame 10. This helps to maintain the bending at the proper position and angle after the connecting filament 16 has been woven into the first frame 10. If the connecting filament 16 includes a wire, the wire can be shaped to achieve bending at a desired position to facilitate transition between a radially contracted configuration and a radially expanded configuration. Embodiments where the connecting filament 16 is woven around the first frame 10 into the first frame 10 can also improve the expansion characteristics of the expandable frame 2, since the connecting filament 16 at the end of the expandable tube 2 can contribute to promoting radial expansion when the expandable tube 2 is deployed from the catheter.

[0119] The connecting filament 16 can comprise the same material as the filaments of the first frame 10 and / or can have the same diameter as the filaments. Optionally, the connecting filament 16 comprises filaments of the first frame 10. Such an embodiment is shown in FIG. 11. In such an embodiment, joining both the first frame 10 and the second frame 12 can include unweaving one or more filaments of the first frame 10 for use as the connecting filament 16. The connecting filament 16 is then passed through the apertures 18 in the second frame 12 and woven back into the other braided filaments of the first frame 10.

[0120] Alternatively, the connecting filament 16 may have a diameter different from that of the filaments of the first frame 10 or may be made of a material different from that of the filaments. The connecting filament 16 can have a nitinol wire. The connecting filament 16 can have a material commonly used for medical sutures. In this embodiment, the two ends of the suture can be tied together to fix the two frames together.

[0121] Optionally, the plurality of filament receiving apertures 18 include filament receiving apertures 18 spaced along the length of the second frame 12. The filament receiving apertures 18 can be spaced along the length of the second frame 12, preferably at equal intervals. The spacing between the filament receiving apertures 18 can be at most 50%, preferably at most 25%, more preferably at most 10% of the length of the expandable tube 2. Optionally, each longitudinally expandable element 8 of the second frame 12 includes a filament receiving aperture.

[0122] Including the filament receiving apertures 18 spaced along the second frame 12 enhances the attachment of the first frame 10 and the second frame 12 to each other and reduces the possibility of these two frames separating. This also means that the connecting filament 16 does not need to be bent in the manner shown in FIG. 10 and instead can follow the helical path of the braided filaments of the first frame 10 along the entire length of the first frame 10. This is advantageous because the connecting filament 16 is subjected to a lower tension than when it is bent. A plurality of connecting filaments 16 can be provided that follow both the right-handed helix and the left-handed helix of the braided filaments of the first frame 10.

[0123] Preferably, the aperture 18 is arranged such that when the connecting filament 16 passes through the aperture 18, each connecting filament 16 follows the braiding angle of the braiding filaments of the first frame 10. To achieve this, when a plurality of filament receiving apertures 18 are provided in the same element of the second frame 12, the angle between the line between the filament receiving apertures 18 in the same element and the longitudinal axis 4 of the expandable tube 2 is preferably the same as the braiding angle of the braiding filaments of the first frame 10. This also reduces unnecessary bending of the connecting filaments 16 and reduces the tension in the connecting filaments 16.

[0124] The connecting filaments 16 can contribute to enhancing the visibility of the expandable tube 2 during deployment. For example, the connecting filaments 16 can include a radiopaque material. Alternatively or additionally, as shown in FIG. 12, one or more radiopaque markers 19 can be attached to one or more of the connecting filaments 16.

[0125] The connection is achieved in a biocompatible manner such that it does not affect the ability of the expandable tube 2 to be inserted into the body of a human or animal. The expandable tube 2 can generally be left in the body indefinitely after deployment for an extended period of time. Thus, it is also important that any material used for the connection is biocompatible.

[0126] The second frame 12 can be connected to the first frame 10 at least at one end of the second frame 12. The connection at one end of the second frame 12 can be convenient because the end of an element of the second frame 12 can be joined to the first frame 10, for example, the end of a filament of the first frame 10. The second frame 12 can be further connected to the first frame 10 at one or more points along the length of the second frame 12. Joining the first frame 10 and the second frame 12 at additional points along the length of the second frame 12 contributes to preventing separation, or buckling or wrinkling, at any point along the length of the expandable tube 2. This is particularly relevant when the expandable tube 2 is expanding or contracting. Separation of the first frame 10 and the second frame 12 can cause improper deployment of the expandable tube 2 or damage to the tube. However, joining at a plurality of points along the length of the expandable tube 2 increases the complexity of manufacturing the expandable tube 2 and can therefore be undesirable in all embodiments.

[0127] The connection between the first frame 10 and the second frame 12 can also be designed to reduce the possibility of damaging the blood vessel in which the expandable tube 2 is deployed. For example, the ends of the braided filaments of the first frame 10 and the ends of the elements of the second frame 12 can be received within a terminal element. The terminal element is configured to reduce the possibility of damaging the interior of the blood vessel, for example, by preventing any sharp points or other sharp surfaces at the ends of the filaments from contacting the inner wall of the blood vessel. The terminal element itself can have a smooth and / or curved surface to prevent any damage to the blood vessel.

[0128] Optionally, the second frame 12 is configured to urge the expandable tube 2 from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state. As described above, a problem associated with prior art expandable tubes consisting of only braided filaments is that those expandable tubes do not always expand uniformly or reliably due to friction between the filaments. By including a second frame 12 configured to urge the expandable tube 2 to expand radially and contract longitudinally, the behavior of the expandable tube 2 can be made more reliable and consistent. Optionally, the second frame 12 is configured to urge the expandable tube 2 from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state by applying a radial force to the first frame 10. Consistent radial expansion is important so that the expandable tube 2 expands to its final size and engages the inner wall of the blood vessel in which the expandable tube 2 is deployed. In other embodiments, the second frame 12 can urge the expandable tube 2 from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state by applying a longitudinal force to the first frame 10. However, this is generally not preferred because the drive to expand the expandable tube 2 radially is only indirect in that case and may not contribute much to the consistency of the radial expansion during deployment.

[0129] Optionally, the second frame 12 is not connected to the first frame 10, and the radius of the second frame 12 in the unconstrained state where the second frame 12 expands radially and contracts longitudinally is greater than the radius of the first frame 10 in the unconstrained state where the first frame 10 is not connected to the second frame 12 and the first frame 10 expands radially and contracts longitudinally. Both the first frame 10 and the second frame 12 are configured to bias themselves into a state of expanding radially and contracting longitudinally and have a maximum radius that they reach when in the unconstrained state. When the first frame 10 and the second frame 12 are both connected to form an expandable tube, their respective maximum radii in the state of expanding radially and contracting longitudinally of the expandable tube 2 are constrained to be the same, that is, constrained to the smaller of the radius of the first frame 10 and the radius of the second frame 12 in their unconstrained states. By designing the second frame 12 such that its radius in the unconstrained state is greater than the radius of the first frame 10 in the unconstrained state, the second frame 12 encourages the first frame 10 to expand to its maximum radius and minimizes the risk of radial separation between the two frames, especially when deployed within a tortuous anatomical structure. This improves the consistency of the radial expansion of the first frame 10, which includes braided filaments. This feature also means that fewer fixation points are required to firmly join the two frames together.

[0130] Optionally, at least one of the first frame 10 and the second frame 12 can be provided with a hydrophilic coating and / or an antithrombotic coating.

[0131] The design of this laminated expandable tube 2, which includes a first frame 10 and a second frame 12, relies on the first frame 10 and the second frame 12 that expand and contract longitudinally and radially together with each other and expand and contract radially. The degree of longitudinal and radial expansion and contraction of the expandable tube 2 is mainly determined by the braided structure of the first frame 10. For example, the second frame 12, which includes elements independent in the longitudinal and circumferential directions, adapts to the longitudinal and radial movement of the braided structure.

[0132] Optionally, the first elongation rate of the first frame 10 is within 25%, preferably within 15%, more preferably within 10%, and most preferably within 5% of the second elongation rate of the second frame 12. The first elongation rate of the first frame 10 is the ratio of the unconstrained length of the first frame 10 to the length of the first frame 10 in a state of contracting radially and expanding longitudinally. The unconstrained length of the first frame is the length of the first frame 10 in an unconstrained state where the first frame 10 is not connected to the second frame 12 and the first frame 10 is expanding radially and contracting longitudinally. The second elongation rate is the ratio of the unconstrained length of the second frame 12 to the length of the second frame 12 in a state of contracting radially and expanding longitudinally. The unconstrained length of the second frame 12 is the length of the second frame 12 in an unconstrained state where the second frame 12 is not connected to the first frame 10 and the second frame 12 is expanding radially and contracting longitudinally. The state of contracting radially and expanding longitudinally as mentioned refers to the state of the first frame 10 or the second frame 12 when the first frame 10 or the second frame 12 is part of the expandable tube 2 (i.e., connected to the second frame 12) and the expandable tube 2 is in a state of contracting radially and expanding longitudinally. This can be the case, for example, when the expandable tube 2 is inside the catheter in a state ready to be deployed. Previous designs of expandable tubes including braided filaments included expansion rings at one or both ends of the expandable tube to facilitate proper deployment of the ends of the braided tube. However, increasing the length of the expansion ring for a braided stent to facilitate proper deployment over its full length is a challenge because the expansion characteristics of the two types of frames are different. Matching the first elongation rate and the second elongation rate ensures that the possibility of buckling of the first frame 10 or the second frame 12 or separation between the first frame 10 and the second frame 12 is reduced. This further enables the second frame to be longer relative to the first frame and further improves the consistency of the deployment of the expandable tube.

[0133] To determine the dimensional inputs for designing the second frame 12, it is necessary to analytically determine the elongation rate of the first frame 10. Two methods for determining the first elongation rate of the first frame 10 are outlined below, and the elements of the second frame can be designed such that the second elongation rate matches the first elongation rate to the required extent. The first method outlines a detailed approach by determining the changes in the length and height of a single pore of the first frame 10 between a state of radially expanding and longitudinally contracting and a state of radially contracting and longitudinally expanding. A pore is a single space defined by adjacent filaments in the first frame 10, as schematically illustrated in FIG. 13. The state of radially contracting and longitudinally expanding may sometimes be referred to as the loaded state because this state is the state of the expandable tube 2 when the expandable tube 2 is loaded into the catheter before deployment into the blood vessel. The second method provides a simpler approach of evaluating the overall length change of the first frame 10 between a state of radially expanding and longitudinally contracting and a state of radially contracting and longitudinally expanding.

[0134] The first method begins with the diameter of the expandable tube 2 in a state of radially expanding and longitudinally contracting, as seen in FIG. 14(a)

Number

Number

[0135] The circumferential distance D between filaments in the first frame 10 c can be calculated using Equation 2.

Number

[0136] The pores of the first frame 10 have a rhombus shape in which the length of each side of the pore remains constant as the diameter of the first frame 10 decreases, as shown in FIG. 13(b). As a result, the height of the pore decreases while the length of the pore increases.

[0137] The longitudinal length L of the pore pore is calculated using Equation 3. L pore = 2αsin(90° - θ braid ) Equation 3

[0138] The circumferential height H of the pore pore can be calculated using Equation 4. H pore = 2αcos(90° - θ braid ) Equation 4

[0139] The total number of pores N around the circumference c can be calculated using Equation 5.

Number

[0140] The total number of pores N in a single row along the length of the first frame 10 h can be calculated using Equation 6.

Number

Equation

Equation

[0141] Then, the longitudinal length L of each pore in the loaded state loaded pore can be calculated using Equation 9 L loaded pore = 2α cos(90° - θ loaded ) Equation 9

[0142] As shown in FIG. 14(b), the length L of the first frame 10 in the loaded state loaded can then be calculated using Equation 10 L loaded = N h L loaded pore Equation 10

[0143] Finally, the first elongation rate ε can be obtained using Equation 11

Equation

[0144] The second method is a simpler technique applied to evaluate the elongation rate of the first frame 10 when the length of each filament in the first frame 10 is equal to the length of the first frame 10 in the loaded state.

[0145] The first step is to calculate the pitch P of a helix having a known braiding angle θ braid and a circumference C using Equation 12.

Equation

[0146] For a predetermined length L in a state of being radially expanded and longitudinally contracted, the number of turns N per filament in the first frame 10 expanded can be obtained using Equation 13. turns

Equation

Equation

[0147] When the length of the filament in the first frame 10 is equal to the length of the first frame in the loaded state, Equation 14 can be applied.

Equation

[0148] Regarding the first method, Equation 11 can be used to obtain the first elongation rate. Further, by applying Equation 15, the number of sub-units N cells can be obtained.

Equation

[0149] It is assumed that the number of sub-units in the second frame 12 is an integer, which must be taken into account when selecting the parameters of the first frame 10 so as to ensure that the lengths of the first frame 10 and the second frame 12 remain the same in both the state of expanding in the radial direction and contracting in the longitudinal direction and the state of contracting in the radial direction and expanding in the longitudinal direction.

[0150] When the first elongation rate of the first frame 10 is known, as shown in FIG. 15, it is possible to determine the geometric shape of the smallest repeating unit of the second frame 12. The second frame 12 is designed to match the change characteristics of the diameter and length of the first frame 10 in order to ensure the uniform performance of the expandable tube 2. This is done for embodiments in which the sub-units of the net-like non-overlapping elements of the second frame 12, which repeat itself longitudinally, include a plurality of cells that repeat circumferentially (as described above).

[0151] FIG. 15 shows the smallest repeating unit of the closed-cell design shown in FIGS. 5-9. This repeating unit is repeated longitudinally to form the longitudinal extension member 8, and the longitudinal extension member 8 itself is repeated circumferentially to form the complete second frame 12. For this reason, it should be noted that the smallest repeating unit is not the same as the sub-unit of the second frame 12 because each smallest repeating unit does not define the closed cell 32 alone. The length L of the cell cell is

Number

Number

[0152] Thus, the longitudinal extension member 8 has a path length L along each longitudinal extension member 8 path and a first length L cell (i.e., the longitudinal length of each smallest repeating unit in the radially expanded and longitudinally contracted state) is designed to match the elongation of the first frame 10 by ensuring that it is proportional to the first elongation rate of the first frame 10. Optionally, the ratio of the first length to the path length along each longitudinally deformable element 8 is within 25%, preferably within 15%, more preferably within 10%, and most preferably within 5% of the first elongation rate.

[0153] The expandable tube 2 can be configured for use in a delivery system 20 such as the delivery system shown in FIG. 16. The delivery system 20 includes a tubular member 24, also called a catheter, and an elongated body 22, also called a guide wire. The elongated body 22 is positioned within the tubular member 24, and the expandable tube 2 is positioned between the tubular member 24 and the elongated body 22. The expandable tube 2 engages the elongated body 22 on the inside and the tubular member 24 on the outside. The delivery system 20 is positioned at an appropriate location near an aneurysm within a blood vessel, and the elongated body 22 extends beyond the end of the tubular member 24. The longitudinal engagement forces between the elongated body 22 and the expandable tube 2 and between the expandable tube 2 and the tubular member 24 are such as to move the expandable tube longitudinally as well as deploy it from the tubular member 24. The expandable tube 2 expands radially and contracts longitudinally, thereby being released from the elongated body 22 and deploying into the blood vessel. When the expandable tube 2 is fully deployed from the tubular member 24, the delivery system 20 can be withdrawn from the blood vessel while leaving the expandable tube 2 in place.

[0154] Figure 17 shows the deployment of the expandable tube 2 into a blood vessel model using a delivery system such as the delivery system of Figure 16. In Figure 17(a), the expandable tube is still fully contained within the tubular member 24. In Figure 17(b), the distal portion of the expandable tube 2 has deployed from the tubular member 24, while the proximal portion remains within the tubular member 24. To deploy the expandable tube 2, the elongated body 22 extends further beyond the end of the tubular member 24. In Figure 17(c), the expandable tube 2 is fully deployed and completely released from the delivery system. The tubular member 24 and the elongated body 22 can then be withdrawn from the blood vessel while leaving the expandable tube 2 in place.

[0155] While this type of delivery system is preferred, the expandable tube 2 can also be used with other suitable types of conventional delivery systems. For example, the expandable tube 2 can be deployed using a delivery system that does not include an elongated body that engages the expandable tube 2 externally. The expandable tube 2 can also be deployed using a delivery system that pushes the expandable tube 2 from the proximal end. This type of delivery system is often not suitable for expandable tubes that include a network of non-overlapping elements. This is particularly true when those expandable tubes are designed to be highly flexible in the longitudinal direction, and thus have low longitudinal rigidity, for use, for example, in neurovascular applications. However, the hybrid design of the expandable tube 2 of the present invention allows for deployment using this type of delivery system because the filament density provided by the first frame 10 is higher.

[0156] Further aspects of the expandable tubes disclosed above can be described by the following numbered clauses. These are not the claims of the present application, which follow under the heading of the claims. However, these clauses present further aspects that can be combined with the features in the claims. Clause 1. An expandable tube for intravascular deployment, wherein the expandable tube is reversibly switchable from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state, the expandable tube comprising a first frame and a second frame connected to the first frame and overlapping the first frame in the radial direction, the second frame including a reticulated non-overlapping element, the non-overlapping elements being non-overlapping with respect to each other in the radial direction, the reticulated non-overlapping element having an interconnected structure including a plurality of sub-units repeating in the longitudinal direction, each sub-unit of the second frame defining a closed cell, and in the state of being radially expanded and longitudinally contracted, the closed cell having a bulbous region that expands away from the circumferential central region of the closed cell towards the circumferential ends of the closed cell. Clause 2. The expandable tube according to Clause 1, wherein the second frame is configured to urge the expandable tube from a state of being radially contracted and longitudinally expanded to a state of being radially expanded and longitudinally contracted. Clause 3. The expandable tube according to Clause 2, wherein the second frame is configured to urge the expandable tube from a state of being radially contracted and longitudinally expanded to a state of being radially expanded and longitudinally contracted by applying a radial force to the first frame. Clause 4. The expandable tube according to any one of Clauses 1 to 3, wherein the reticulated non-overlapping elements are integrally formed. Clause 5. The expandable tube according to any one of Clauses 1 to 4, wherein the second frame is connected to the first frame at least at one end of the second frame. Clause 6. The expandable tube according to Clause 5, wherein the second frame is further connected to the first frame at one or more points along the length of the second frame. Clause 7. The second frame is the expandable tube according to clause 5 or 6, which is connected to the first frame by at least one of welding, crimping, adhesive, weaving or knitting, or encapsulation. Clause 8. The second frame includes a plurality of filament receiving apertures, and one or more connecting filaments are woven into the first frame, and each connecting filament passes through one or more of the filament receiving apertures. The expandable tube according to any one of clauses 1 to 7. Clause 9. The connecting filament includes the filament of the first frame. The expandable tube according to clause 8. Clause 10. One or more radiation-opaque markers are attached to one or more of the connecting filaments. The expandable tube according to claim 8 or 9. Clause 11. The plurality of filament receiving apertures include filament receiving apertures in the longitudinal end regions of the second frame. The expandable tube according to any one of clauses 8 to 10. Clause 12. The plurality of filament receiving apertures include filament receiving apertures spaced along the length of the second frame. The expandable tube according to any one of claims 8 to 11. Clause 13. The length of the second frame is at least 50% of the length of the first frame. The expandable tube according to any one of clauses 1 to 12. Clause 14. The second frame overlaps the first frame over at least 50% of the length of the expandable tube. The expandable tube according to any one of clauses 1 to 13. Clause 15. The second frame is positioned within the first frame. The expandable tube according to any one of clauses 1 to 14. Clause 16. The radius of the second frame in the unconstrained state where the second frame is not connected to the first frame and the second frame is radially expanded and longitudinally contracted is greater than the radius of the first frame in the unconstrained state where the first frame is not connected to the second frame and the first frame is radially expanded and longitudinally contracted. An expandable tube according to any one of Clauses 1 to 15. Clause 17. The first elongation rate of the first frame is within 25% of the second elongation rate of the second frame. The first elongation rate is the ratio of the length of the first frame in the unconstrained state where the first frame is not connected to the second frame and the first frame is radially expanded and longitudinally contracted to the length of the first frame in the state where it is radially contracted and longitudinally expanded. The second elongation rate is the ratio of the length of the second frame in the unconstrained state where the second frame is not connected to the first frame and the second frame is radially expanded and longitudinally contracted to the length of the second frame in the state where it is radially contracted and longitudinally expanded. An expandable tube according to any one of Clauses 1 to 16. Clause 18. The reticulated non - overlapping elements include a plurality of longitudinally deformable elements that cause longitudinal expansion and contraction of the second frame. Each smallest repeating unit of the reticulated non - overlapping elements has a first length in the longitudinal direction in the unconstrained state where the second frame is not connected to the first frame and the second frame is radially expanded and longitudinally contracted. The ratio of the first length to the path length along each longitudinally deformable element is within 25% of the first elongation rate. An expandable tube according to Clause 17. Clause 19. The first frame includes a shape - memory alloy material, preferably nitinol. An expandable tube according to any one of Clauses 1 to 18. Clause 20. When the expandable tube is positioned over the aneurysm sac at the time of use in a state where it is expanded in the radial direction and contracted in the longitudinal direction, the first frame has a porosity such that it deflects blood flow away from the aneurysm sac, thereby promoting thrombus formation in the aneurysm sac, and is an expandable tube according to any one of Clauses 1 to 19. Clause 21. The first frame has a porosity of at most 90% in a state where the expandable tube is expanded in the radial direction and contracted in the longitudinal direction, and is an expandable tube according to any one of Clauses 1 to 20. Clause 22. The first frame includes a braided filament, and is an expandable tube according to any one of Clauses 1 to 21. Clause 23. The first frame includes at least 48 filaments, and is an expandable tube according to Clause 22. Clause 24. The filaments of the first frame have a diameter of at most 30 μm, and are an expandable tube according to Clause 22 or 23. Clause 25. The first frame has a braiding angle of at least 50°, and is an expandable tube according to any one of Clauses 22 to 24. Clause 26. The first frame has a pore density of at least 20 pores / mm 2 and is an expandable tube according to any one of Clauses 1 to 25. Clause 27. The second frame includes a shape memory alloy material, preferably nitinol, and is an expandable tube according to any one of Clauses 1 to 26. Clause 28. The second frame has a porosity of at least 70%, and is an expandable tube according to any one of Clauses 1 to 27. Clause 29. In a state where it is contracted in the radial direction and expanded in the longitudinal direction, the expandable tube has a maximum dimension in the radial direction that is at least 30% smaller than the maximum dimension in the radial direction of the expandable tube in a state where it is expanded in the radial direction and contracted in the longitudinal direction, and is an expandable tube according to any one of Clauses 1 to 28. Clause 30. The expandable tube according to any one of Clauses 1 to 29, wherein the longitudinal elongation of the expandable tube caused by switching from a state of expanding in the radial direction and contracting in the longitudinal direction to a state of contracting in the radial direction and expanding in the longitudinal direction is at least 10%. Clause 31. The expandable tube according to any one of Clauses 1 to 30, wherein in a state of contracting in the radial direction and expanding in the longitudinal direction, the maximum dimension in the radial direction of the expandable tube is such that the expandable tube can be inserted into a catheter having an inner diameter of at most 1.0 mm.

Claims

1. An expandable tube for deployment within a blood vessel, wherein the expandable tube is reversibly switchable from a state of radial contraction and longitudinal expansion to a state of radial expansion and longitudinal contraction, and the expandable tube is The first frame and A second frame connected to the first frame and overlapping with the first frame in the radial direction, wherein the second frame includes a mesh of non-overlapping elements, and the non-overlapping elements are non-overlapping with respect to each other in the radial direction, Includes, The aforementioned mesh-like non-overlapping elements have an interconnection structure that includes a plurality of sub-units that are repeated in the longitudinal direction. Each sub-unit of the second frame defines a closed cell, In the state of being radially expanded and longitudinally contracted, the closed cell has a bulbous region that extends toward the circumferential end of the closed cell, away from the circumferential central region of the closed cell. The aforementioned mesh-like non-overlapping elements include a plurality of longitudinally extendable members defining the interconnection structure, and the circumferentially adjacent longitudinally extendable members are connected at connection points, forming an expandable tube.

2. (a) The closed cell includes two bulbous regions at opposing circumferential ends of the closed cell, (b) The closed cell is the area around the second frame, enclosed by the non-overlapping elements. An expandable tube according to claim 1, comprising one or both of the features of the above.

3. (a) In the state of being radially expanded and longitudinally contracted, the path along each longitudinally expanding member reverses its longitudinal direction between consecutive connection points. (b) In the radially expanded and longitudinally contracted state, preferably, for each sub-unit, there exists a circumferential line located at the midpoint between the continuous connection points of the longitudinally expandable member, which intersects the longitudinally expandable member three or more times. (c) The longitudinally stretchable member is deformable in the longitudinal direction. (d) Each sub-unit defines a plurality of closed cells around the second frame, and adjacent closed cells in the circumferential direction are connected at connection points. In the state in which it is expanded radially and contracted longitudinally, the radius of curvature of the longitudinally extended member decreases in the direction away from the connection point. An expandable tube according to claim 1, comprising one or more of the features of the above.

4. The expandable tube according to claim 1, wherein the closed cell has mirror symmetry in a plane parallel to the longitudinal axis of the expandable tube and / or in a plane perpendicular to the longitudinal axis of the expandable tube.

5. The expandable tube according to claim 1, wherein adjacent subunits in the longitudinal direction have mirror symmetry in a plane perpendicular to the longitudinal axis of the expandable tube.

6. Each subunit defines a plurality of closed cells around the second frame, and adjacent closed cells in the circumferential direction are connected at the connection points. The expandable tube according to any one of claims 1 to 5, wherein, optionally, adjacent closed cells in the circumferential direction have mirror symmetry in a plane parallel to the longitudinal axis of the expandable tube.

7. Adjacent closed cells in the circumferential direction are connected at the connection point by a bridge, and optionally the bridge is a rigid bridge, optionally (a) The bridge extends in the circumferential direction, (b) The bridge has a longitudinal length of at most 0.1 mm, preferably at most 0.08 mm. (c) The bridge has a circumferential length of at most 0.2 mm. The expandable tube according to claim 6, comprising one or more of the features of the above.

8. The non-overlapping elements include a straight portion at the connection point, and optionally, (a) The radius of curvature of the non-overlapping element adjacent to the straight portion is at least 0.3 mm, preferably at least 0.5 mm, and most preferably at least 0.7 mm. (b) The length of the straight portion is at least 0.05 mm, preferably at least 0.1 mm. An expandable tube according to claim 6, comprising one or both of the features of the above.

9. The expandable tube according to claim 1, wherein the closed cell extends by at least 20%, preferably at least 40%, and more preferably at least 60% in the bulbous region.

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