Expandable tube for deployment within blood vessel

Abstract

To provide an expandable tube for deployment within a blood vessel that has improved performance.SOLUTION: According to the present invention, there is provided an expandable tube for deployment within a blood vessel, 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 comprising braided filament, and a second frame connected to the first frame and overlapping with the first frame in the radial direction, the second frame comprising a network of non-overlapping elements, the non-overlapping elements being non-overlapping with respect to each other in the radial direction. The network of non-overlapping elements has an interconnected structure comprising a plurality of sub-units that repeat in the longitudinal direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to an expandable tube for deployment within a blood vessel, particularly for use in diverting blood flow away from an aneurysm sac. [Background technology]

[0002] Intracranial aneurysms are weak areas in the arterial wall within the brain where dilation or expansion of the arterial wall can occur. Histologically, disease in the arterial media, middle muscularis, and internal elastic lamina causes structural defects. These defects, combined with hemodynamic factors, result in an aneurysmal sac. Intracranial aneurysms are fairly common, with a prevalence ranging from 1 to 5 percent in the adult population based on autopsy studies. In the United States alone, 10 to 12 million people may have an intracranial aneurysm.

[0003] Current methods for treating intracranial aneurysms include surgical clipping and endovascular coiling. Surgical clipping involves opening the patient's skull and placing a surgical clip across the neck of the aneurysm to stop blood flow into 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 packed with coils. This helps induce thrombus formation inside the aneurysm. Although endovascular coiling is considered safer than surgical clipping, it has its own limitations. First, the aneurysm remains its original size after being filled with coils. As a result, the pressure exerted by the aneurysm on the surrounding tissue is not relieved. Second, this procedure is less effective in cases of wide-necked aneurysms, where the coils may intrude into the parent vessel. This problem can be alleviated by using stents in combination with coil embolization, but the procedure is difficult and time consuming.

[0004] Treating aneurysms using an expandable tube alone, sometimes called a stent, is a promising approach that avoids the aforementioned challenges. In this method, an expandable tube with a relatively low porosity region is placed across the aneurysm neck to divert blood flow away from the sac and induce thrombus formation within the aneurysm. Because the aneurysm naturally clots itself, the risk of rupture is low. Furthermore, because this method does not involve any coils, the aneurysm gradually shrinks as the thrombus is absorbed, thus relieving pressure on the surrounding tissue. However, manufacturing an expandable tube with optimal properties for this application is difficult. The expandable tube must provide low enough porosity to divert blood flow away from the aneurysm to a sufficient extent, while also being flexible enough to navigate and conform to the highly tortuous blood vessels in the brain.

[0005] A known type of expandable tube is formed from braided filaments, e.g., wire. The filaments are braided together to form a mesh tube. This type of expandable tube can be radially contracted and longitudinally expanded within a catheter for placement within a blood vessel. When properly positioned relative to the neck of an aneurysm, the expandable tube expands radially and longitudinally upon deployment from within the catheter, thereby placing it within the blood vessel and occluding blood flow to and from the aneurysm. However, a challenge with braided filament expandable tubes is that the numerous contact points between the filaments in the braided structure create friction. Furthermore, each filament moves freely relative to other intersecting filaments, resulting in insufficient radial force. This causes the braided filament expandable tube to radially expand slowly and inconsistently upon deployment from a catheter, thereby making proper placement of the expandable tube relative to the neck of an aneurysm more difficult and less reliable.

[0006] Another existing type of expandable tube is formed from a network of interconnecting, non-overlapping elements. This can be formed, for example, by laser cutting from a thin tube of material such as a shape memory alloy. These laser-cut tubes have the advantage that there are no contact points between the braided filaments that create friction, and their deployment can be more consistent. However, it can be difficult to design this type of tube with a low enough porosity to adequately occlude varicose veins. Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to provide an expandable tube for deployment within a vessel that has improved performance, particularly with respect to deployment of the expandable tube. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided an expandable tube for deployment within a blood vessel, 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 having braided filaments; and a second frame connected to the first frame and radially overlapping the first frame, the second frame comprising a network of non-overlapping elements that are radially non-overlapping with respect to one another, the non-overlapping elements having an interconnected structure having a plurality of longitudinally repeating sub-units.

[0009] By using an expandable tube with a hybrid structure that includes both a braided filament frame and a frame with a network of non-overlapping elements, it is possible to combine the advantages of each frame, such as consistent deployment and low porosity. The non-overlapping element frame provides additional force to expand the braided frame. Combining the two types of frames requires careful design of the two tubes so that their different expansion characteristics do not interfere with their proper operation. Furthermore, the advantageous expansion characteristics of the non-overlapping element frame allow the braided filament frame to be fabricated using filaments with smaller diameters. This allows the braided filament frame to be constructed with additional filaments while remaining compatible with necessary accessory devices (e.g., microcatheters used to deliver the expandable tube into a blood vessel). A higher filament count reduces the size of the individual pores between the filaments in the wall of the expandable tube, which is associated with greater flow reduction within the aneurysm sac and more rapid re-endothelialization across the aneurysm neck.

[0010] In one embodiment, the non-overlapping network of elements includes a plurality of longitudinally and / or circumferentially deformable elements. In one embodiment, the non-overlapping network of elements includes a plurality of longitudinally deformable elements that effect longitudinal expansion and contraction of the second frame, and a plurality of circumferentially deformable elements that effect radial expansion and contraction of the second frame. This allows the frame to change both its radial and longitudinal dimensions, which may allow the expansion / contraction ratio of the tube to be increased, thereby allowing the tube to be more easily inserted into a microcatheter for deployment.

[0011] In one embodiment, the longitudinally deformable element is configured to be expanded or contracted longitudinally substantially without any substantial shape change of the circumferentially deformable element. In one embodiment, the circumferentially deformable element is configured to be expanded or contracted circumferentially substantially without any substantial shape change of the longitudinally deformable element. By designing the longitudinally deformable element and the circumferentially deformable element to be able to expand and contract substantially independently, it is easier to design a second frame whose expansion characteristics match those of the first frame.

[0012] In one embodiment, the second frame is configured to urge the expandable tube from the radially contracted and longitudinally expanded state to the radially expanded and longitudinally contracted state. Using a second frame to urge the expansion of the first frame helps to more consistently and reliably deploy the tube, thereby reducing the likelihood of deployment failure.

[0013] In one embodiment, the second frame is configured to urge the expandable tube from the radially contracted and longitudinally expanded state to the radially expanded and longitudinally contracted state by applying a radial force to the first frame, which means that the first frame will quickly expand to its full diameter upon release from a deployment catheter and therefore can be more easily properly deployed.

[0014] In one embodiment, the non-overlapping element network is integrally formed, which reduces the complexity of the manufacturing process by eliminating the need to bond elements of the network, and also reduces imperfections or irregularities in the surface of the second frame that result from bonding between elements.

[0015] In one embodiment, the second frame comprises a shape memory alloy material, preferably Nitinol, which is an advantageous material choice because it is designed to return to a desired shape when released from a constraint, thereby eliminating the need to apply an external force to the tube to radially expand the shape memory alloy.

[0016] In one embodiment, the second frame has a porosity of at least 70%. The relatively high porosity of the second frame allows the first frame to be the primary determinant of the porosity of the expandable tube, simplifying the overall design of the expandable tube's properties.

[0017] In one embodiment, the length of the second frame is at least 50% of the length of the first frame. In one embodiment, the second frame overlaps with 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 uniform behavior of the expandable tube.

[0018] In one embodiment, the second frame is connected to the first frame at at least one end of the second frame. Connecting the two frames together ensures that the frames do not move relative to each other and that the expandable tube behaves consistently and predictably.

[0019] In one embodiment, the second frame is further connected to the first frame at one or more points along the length of the second frame, meaning that the interaction of the first and second frames is uniform along the length of the expandable tube and is not simply constrained at both ends of the expandable tube.

[0020] In one embodiment, the second frame is connected to the first frame by at least one of welding, crimping, adhesive or encapsulation, which are particularly advantageous joining methods where the first frame is formed from braided filaments.

[0021] In one embodiment, the second frame has a plurality of filament-receiving apertures, and one or more connecting filaments are woven into the first frame, each passing through one or more of the filament-receiving apertures. The use of connecting filaments reduces the profile of the bond between the first and second frames compared to other methods, such as crimping or welding, resulting in a more uniform surface for the expandable tube.

[0022] In one embodiment, the connecting filaments comprise the filaments of the first frame, meaning that no additional filaments are added, keeping the dimensions of the expandable tube the same as without the connecting filaments.

[0023] In one embodiment, one or more radiopaque markers are attached to one or more of the connecting filaments, which are convenient attachment points for radiopaque markers that improve visibility of the expandable tube upon deployment.

[0024] In one embodiment, the plurality of filament-receiving apertures include filament-receiving apertures in longitudinal end regions of the second frame, thereby securing the two frames together over their entire lengths.

[0025] In one embodiment, the plurality of filament-receiving apertures includes filament-receiving apertures spaced along the length of the second frame. Including additional apertures spaced along the second frame enhances attachment of the first and second frames to one another and reduces the likelihood of the two frames separating.

[0026] In one embodiment, a second frame is positioned within the first frame. Having the braided filaments on the outside of 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 on the first frame than if the second frame were located outside the first frame, thereby further promoting proper deployment of the expandable tube.

[0027] In one embodiment, the radius of the second frame when the second frame is not connected to the first frame and in a radially expanded, longitudinally contracted, unconstrained state is greater than the radius of the first frame when the first frame is not connected to the second frame and in a radially expanded, longitudinally contracted, unconstrained state. Oversizing the second frame so that its unconstrained radius is greater than the unconstrained radius of the first frame helps ensure that the second frame can facilitate deployment of the expandable tube while minimizing the risk of radial separation between the two frames, especially when deployed in tortuous anatomical structures. This also means that fewer fixation points are required to securely join the two frames together.

[0028] In one embodiment, the first extensibility of the first frame is within 25% of the second extensibility of the second frame, the first extensibility being the ratio of the length of the first frame in a radially expanded, longitudinally contracted, unconstrained state when the first frame is not connected to the second frame to the length of the first frame in the radially contracted, longitudinally expanded state, and the second extensibility being the ratio of the length of the second frame in a radially expanded, longitudinally contracted, unconstrained state when the second frame is not connected to the first frame to the length of the second frame in the radially contracted, longitudinally expanded state. Previous designs of expandable tubes with braided filaments have included expansion rings at one or both ends of the expandable tube to promote proper deployment of the ends of the braided tube. However, increasing the length of the expansion ring relative to the braided stent to promote proper deployment throughout its length is challenging due to the different expansion characteristics of the two types of frames. Matching the elongation ensures that the first frame or the second frame do not wrinkle or buckle when the expandable tube is deployed, thereby reducing the potential for complications from deployment. This also allows the second frame to be longer relative to the first frame, further improving the consistency of deployment of the expandable tube.

[0029] In one embodiment, the non-overlapping network of elements includes a plurality of longitudinally deformable elements that effect longitudinal expansion and contraction of the second frame, each subunit of the non-overlapping network of elements having a first longitudinal length in an unconstrained state in which the second frame is not connected to the first frame and the second frame is in a radially expanded and longitudinally contracted state, the ratio of the first length to a path length along each longitudinally deformable element being within 25% of the first extensibility. By appropriately selecting the path length along the longitudinally deformable elements, the longitudinal expansion of the second frame is determined to match the first extensibility of the first frame.

[0030] In one embodiment, the first frame comprises a shape memory alloy material, preferably Nitinol, which is an advantageous material choice because it is designed to return to a desired shape when released from a constraint, thereby eliminating the need to apply an external force to the tube to radially expand the shape memory alloy.

[0031] In one embodiment, when the expandable tube is positioned across the opening against the aneurysm sac in a radially expanded and longitudinally contracted state in use, the first frame has a porosity that diverts blood flow away from the aneurysm sac and thereby promotes thrombus formation within the aneurysm sac, ensuring that the expandable tube is operative in inducing thrombus formation within the aneurysm.

[0032] In one embodiment, the first frame has a porosity of at most 90% in the 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 allowing thrombus formation within the aneurysm.

[0033] In one embodiment, the first frame has at least 48 filaments. A higher filament count helps increase pore density, which improves the ability of the expandable tube to occlude an aneurysm.

[0034] In one embodiment, the filaments of the first frame have a diameter of at most 30 μm. Smaller diameter filaments allow for ever increasing filament counts while remaining compatible with appropriately sized microcatheters.

[0035] In one embodiment, the first frame has at least 30 pores / mm 2 The higher the pore density, the better the ability of the expandable tube to occlude the aneurysm and promote endothelialization of the tube.

[0036] In one embodiment, in a radially contracted and longitudinally expanded state, the expandable tube has a maximum radial dimension that is at least 30% less than the maximum radial dimension of the expandable tube in the radially expanded and longitudinally contracted state, allowing for sufficient compression of the expandable tube so that it can be inserted into a catheter for deployment.

[0037] In one embodiment, the elongation of the expandable tube in the longitudinal direction caused by switching from the radially expanded and longitudinally contracted state to the radially contracted and longitudinally expanded state is at least 10%. By providing longitudinal expansion and contraction, the extent to which the expandable tube can radially expand and contract is increased.

[0038] In one embodiment, 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 routinely used to treat cerebral aneurysms, and therefore compatibility with this catheter size is desirable.

[0039] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which corresponding reference symbols indicate corresponding parts and in which: [Brief explanation of the drawings]

[0040] [Figure 1] 1 is a schematic diagram of an expandable tube in a radially expanded and longitudinally contracted state. [Figure 2] 1 is a schematic diagram of an expandable tube in a radially contracted and longitudinally expanded state. [Figure 3] 1 is a schematic diagram of an expandable tube having a first frame and a second frame in a radially expanded and longitudinally contracted state. [Figure 4] 1 is a schematic diagram of an expandable tube having a first frame and a second frame in a radially contracted and longitudinally expanded state. [Figure 5] FIG. 1 shows an expandable tube having a first frame and a second frame, where the first frame is connected to the second frame at an end of the first frame and at an end of the second frame. [Figure 6] FIG. 1 shows an expandable tube having a first frame and a second frame in a radially expanded and longitudinally contracted state. [Figure 7] 1A and 1B show an expandable tube having a first frame and a second frame in an intermediate state during expansion or contraction of the expandable tube. [Figure 8] FIG. 1 shows an expandable tube having a first frame and a second frame in a radially contracted and longitudinally expanded state. [Figure 9] FIG. 10 shows details of the design of the non-overlapping element network of the second frame. [Figure 10] FIG. 10 shows details of an alternative design of the element network of the second frame. [Figure 11] FIG. 10 shows details of a further alternative design of the element network of the second frame. [Figure 12] FIG. 12 is a schematic diagram of the element network design of the second frame of FIG. [Figure 13] FIG. 10 shows an aperture at the edge of the second frame that can be used to connect the first and second frames. [Figure 14] FIG. 11 shows details of the use of apertures and bonding filaments to connect the first and second frames. [Figure 15] FIG. 15 shows details of an alternative design to that of FIG. 14 in which the filaments of the first frame are used as joining filaments connecting the first and second frames. [Figure 16] 10 shows an embodiment in which the aperture is along the entire length of the second frame. [Figure 17] FIG. 10 illustrates the addition of radiopaque markers to the bonding filament. [Figure 18] FIG. 10 illustrates the shape change of the spaces between braided filaments in the first frame between a radially expanded and longitudinally contracted state and a radially contracted and longitudinally expanded state. [Figure 19] 10A-10C illustrate the dimensions of an expandable tube in a radially expanded and longitudinally contracted state and in a radially contracted and longitudinally expanded state. [Figure 20] 10 shows the path length along the longitudinally deformable elements and the length of the sub-units of the non-overlapping element network for the network design of FIG. 9. FIG. [Figure 21] 1 is a schematic diagram of the deployment of an expandable tube from a catheter. DETAILED DESCRIPTION OF THE INVENTION

[0041] 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 treating aneurysms. In particular, the designs herein are suitable for use in methods for treating cerebral aneurysms, where the vessels into which the expandable tube must be deployed are narrow and tortuous.

[0042] Figure 1 shows the outer geometry of expandable tube 2 in a radially expanded and longitudinally contracted state. Figure 2 shows the outer geometry of expandable tube 2 in a radially contracted and longitudinally expanded state. Expandable tube 2 is reversibly switchable from the radially contracted and longitudinally expanded state shown in Figure 2 to the radially expanded and longitudinally contracted state shown in Figure 1. As will be discussed further, expandable tube 2 has a first frame 10 having braided filaments and a second frame 12 having a network of non-overlapping elements.

[0043] The expandable tube 2 is elongated relative to the extension axis 4. The expandable tube 2 can be, for example, cylindrical. If the expandable tube 2 is cylindrical, the maximum lateral dimension is the same (i.e., equal to the diameter) at all positions and angles. If the expandable tube 2 is not cylindrical, the maximum lateral dimension can be different at various positions and / or angles. The maximum lateral dimension defines the smallest inner diameter of a cylindrical tube (e.g., a delivery catheter) into which the frame can be inserted.

[0044] In its radially contracted state, the expandable tube 2 is substantially thinner than in its radially expanded state. Preferably, in its radially contracted and longitudinally expanded state, the expandable tube 2 has a maximum radial dimension that is at least 30% smaller, and more preferably at least 50% smaller, than the maximum radial dimension of the expandable tube 2 in its radially expanded and longitudinally contracted state. 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, particularly when access to the deployment site requires navigation through tortuous regions of the vasculature, as may often be the case, for example, when treating a cerebral aneurysm.

[0045] In the following discussion, the term porosity ρ will be understood to refer to the ratio of the surface area of ​​the free space to the total exterior 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 (described further below). The total exterior surface area is the sum of the surface area of ​​the free space and the surface area of ​​the area occupied by the material of the expandable tube 2 or frame. If the expandable tube 2 or frame is a cylinder, the total exterior surface area is simply 2πRL, where R is the radius of the cylinder and L is the length of the cylinder.

[0046] Considering the second frame 12 of the expandable tube 2, the second frame has elements that cannot overlap each other in the radial direction. The second frame 12 has a porosity ρ in its fully radially expanded state. The minimum radius R that the second frame 12 can achieve in its radially contracted state is defined by the state where the porosity is zero when the radius and length of the second frame 12 in its fully radially expanded state are R0 and L0, respectively. min teeth,

number

[0047] This relationship indicates that if the length of the second frame 12 is not significantly altered, then only the radius can be reduced by a factor of ρ. Because ρ needs to be fairly low (e.g., less than 90%, preferably less than 80%, at least in low-porosity regions, such as those intended to be positioned across the opening to the aneurysm sac during use), this represents a significant limitation to the extent to which the second frame 12 can be thinned for insertion into a delivery catheter. For example, if the porosity ρ of the second frame 12 is 20% and the length of the second frame 12 is not altered during radial contraction, i.e., L1 = L0, then the second frame 12 can achieve a radius reduction of up to 20%. Allowing for length increase is also important for frames with braided filaments, such as the first frame 10. If the first frame 10's length cannot be changed due to its braided structure, then radius reduction is not possible; the greater the possible length increase, the greater the possible radius reduction.

[0048] Providing the expandable tube 2 with a frame that can expand longitudinally when it assumes a radially contracted state is based on this understanding, allowing much greater radius reductions to be achieved. For example, if the length is doubled, i.e., L1 = 2L0, the second frame 12 can achieve a 60% radius reduction for a porosity of 20%. For this reason, the elongation of the expandable tube 2 (or a frame forming part of the expandable tube 2) in the longitudinal direction caused 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%.

[0049] FIG. 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 with braided filaments and a second frame 12. FIG. 4 shows the expandable tube 2 of FIG. 3 in a radially contracted and longitudinally expanded state. In FIG. 4, both the first frame 10 and the second frame 12 are radially contracted and longitudinally expanded compared to their states in FIG. 3. An illustration of one embodiment of the expandable tube 2 of FIGS. 3 and 4 is shown in FIG. 5. The structure of the braided filaments of the first frame 10 and the second frame 12 can be clearly seen.

[0050] FIGS. 6-8 demonstrate the process by which the expandable tube 2 transitions from the radially expanded and longitudinally contracted state shown in FIG. 4 to the radially contracted and longitudinally expanded state shown in FIG. 3. The interfilament spacing of the first frame 10 changes from a diamond shape, with the long axes of the filaments circumferentially oriented, to a diamond shape, with the long axes of the filaments longitudinally oriented. The elements of the second frame 12 contract circumferentially and expand longitudinally. In the state shown in FIG. 6, the expandable tube 2 has its maximum diameter so that it can engage the wall of the vessel in which it is deployed. In the intermediate state shown in FIG. 7, the porosity of the expandable tube 2 is at its maximum because the interfilament spacing of the first frame 10 has the maximum area of ​​the filaments. In the state shown in FIG. 8, the expandable tube 2 has its minimum diameter so that it can be inserted into a catheter for deployment into a vessel.

[0051] The first filament 10 comprises braided filaments. The first filament 10 can have multiple filaments braided together. As seen in FIG. 5 , the first frame 10 has filaments arranged in multiple helices. The first frame 10 has filaments arranged in both right-handed and left-handed helices of equal diameter. In this manner, filaments of opposing helices overlap each other radially to form the braided structure of the first frame 10. To form the braided structure, individual filaments of the first helices can alternately pass over and under filaments of a second helices (different from the first helices) (over and under being interpreted as being radially adjacent to and separated from each other relative to the axis of the expandable tube 2). Other arrangements are also possible. For example, filaments of the first helices can alternately pass over and under pairs of filaments of opposing helices, or over and under more sets of filaments, such as three, four, or more filaments. Passing multiple filaments over and under opposing wound helices can be advantageous to reduce deformation of individual filaments and reduce strain and friction between the filaments, however, passing over and under too many filaments at once can reduce the integrity of the first frame 10.

[0052] The first frame 10, and more particularly the filaments of the first frame 10, can comprise a shape memory alloy material, preferably Nitinol. The shape memory alloy material can be configured to bias itself toward a radially expanded state, which is advantageous for facilitating the radial expansion of the first frame 10. Alternatively, the first frame 10 can comprise a polymer or other biocompatible material. In some embodiments, the first frame 10 can be independently self-expanding. That is, the first frame 10 is configured to self-expand from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state even when the first frame 10 is not connected to the second frame 12.

[0053] The filaments of the first frame 10 can comprise a radiopaque material, such as platinum. In one embodiment, the filaments of the first frame 10 have a core of radiopaque material within a covering of another material. The covering can be a shape memory alloy, preferably nitinol. For example, the filaments of the first frame 10 can comprise a drawn-fill-tube nitinol wire with a platinum core. Such an embodiment allows the first frame 10 to be radiopaque, thereby significantly improving visibility of the expandable tube 2 during deployment and increasing the accuracy with which the expandable tube 2 can be deployed. The covering material can also be selected to have improved biocompatibility relative to the radiopaque core. The covering material can also be selected to have other advantageous properties, such as the self-expanding properties of a shape memory alloy.

[0054] An important characteristic of stents used to treat aneurysms is their pore density, i.e., the number of pores in the vessel wall per unit area. Increased pore density is associated with greater flow reduction within the aneurysm sac and more rapid endothelialization of the stent by the vessel, both of which result in better and more reliable patient outcomes. Therefore, for some time, a goal of stent designers has been to increase the pore density in stents.

[0055] For frames made from braided filaments (such as the first frame 10), 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 stiff, and frames made from thinner filaments have poorer expansion properties. Therefore, attempts to increase the pore density of a braided frame by using thinner filaments typically worsen the already less-than-ideal expansion properties of the braided frame.

[0056] Increasing the filament count without decreasing the filament diameter may provide some benefit without compromising expansion characteristics, but it increases the diameter of the stent in its radially contracted state. This makes the stent incompatible with standard-sized catheters used to deploy stents to treat intracranial aneurysms, which are widely available and well understood by practitioners. Thus, the problem of increasing pore density in a stent without increasing the stent's radially contracted diameter has remained unsolved for some time.

[0057] As discussed further below, in the present invention, the second frame 12 can expand more easily and consistently than the first frame 10. Thus, the second frame 12 can be configured to urge the expandable tube 2 from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state, i.e., the expansion characteristics of the expandable tube 2 are primarily determined by the second frame 12. The advantageous expansion characteristics of the second frame 12 allow the first frame 10 to be made using filaments having a smaller diameter because the first frame 10 is not relied upon to cause the expansion of the expandable tube 2. The use of smaller diameter filaments allows the filament count of the first frame 10 to be increased relative to conventional braided stents without requiring an increase in the diameter of the expandable tube 2 in its radially contracted and longitudinally expanded state.

[0058] This, in turn, increases the pore density of the first frame 10 while still allowing the expandable tube 2 to be compatible with widely available standard-sized catheters for deploying the expandable tube 2 to treat intracranial aneurysms. For example, in one embodiment, in a radially contracted and longitudinally expanded state, 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 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 inch) or 0.53 mm (0.021 inch) or smaller.

[0059] In one embodiment, the first frame 10 has at least 48 filaments, preferably at least 64 filaments, more preferably at least 72 filaments, and most preferably at least 96 filaments. In one embodiment, the filaments of the first frame 10 have a diameter of at most 30 μm, preferably at most 25 μm, and more preferably at most 20 μm. In one embodiment, the first frame 10 has at least 30 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 The pore density is

[0060] Another important characteristic of the first frame 10 is the braid 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 braid pitch decreases (i.e., as the braid angle increases). This is advantageous in allowing the expandable tube 2 to conform to the tortuous anatomical structure of blood vessels without exhibiting kinking. A higher braid angle improves bending flexibility, allows for smaller pores (allowing for a higher pore density), and improves longitudinal flexibility. In some embodiments, the braid angle is at least 50°, preferably in the range of 50-80°.

[0061] Existing stent designs generally achieve a filament count of only 48 filaments or at most 64 filaments, with a maximum of 20 or at most 30 pores / mm. 2 Attempts to further increase the filament count in prior art devices did not maintain compatibility with standard 0.69 mm (0.027 inch) catheters and required custom and / or larger sized catheters for deployment.

[0062] Dual-layer stents have been considered previously. However, in existing designs, both layers are made from conventional braided filament layers. Such designs offer several advantages. However, two braided layers do not have the same improvement in expansion reliability and consistency provided by the present design, one braided frame and one frame of non-overlapping elements.

[0063] Furthermore, in the braided frame, each filament overlaps with another filament at the intersection. * The cross-sectional profile of the filament diameter (i.e., the effective thickness of the wall of the frame in the radial direction) is obtained. If the double-layer device has only a braided frame, the cross-sectional profile is further calculated by dividing the inner frame by two. * Filament diameter + outer frame diameter 2 *filament diameter is increased. This increase in cross-sectional profile is undesirably associated with higher thrombus formation. The present invention allows for the use of thinner filaments and for a reduced cross-sectional profile by including a second frame with non-overlapping elements. When the expandable tube 2 is positioned across the opening against the aneurysm sac in use in a radially expanded and longitudinally contracted state, the first frame 10 can have a porosity that diverts blood flow away from the aneurysm sac and thereby promotes thrombus formation 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 the radially expanded and longitudinally contracted state of the expandable tube. If the porosity of the first frame 10 alone is low enough to divert blood flow away from the aneurysm, this reduces design constraints on the second frame 12, allowing the second frame to have a higher porosity.

[0064] The expandable tube 2 further includes a second frame 12. The second frame 12 includes a network of non-overlapping elements, which are radially non-overlapping relative to one another. This is not true for the braided filaments of the first frame 10, which radially overlap one another. An exemplary design for a network of non-overlapping elements is shown in FIG. 9. By having a network of non-overlapping elements for the second frame 12, friction between these elements that would otherwise occur at the overlap points is avoided. This, in turn, reduces resistance to radial expansion of the second frame 12, allowing the second frame 12 to expand quickly and consistently upon release from the catheter during deployment.

[0065] The network of non-overlapping elements is integrally formed, i.e., the non-overlapping elements are connected together to form the network such that there are no material interfaces between any of the elements. This can be achieved, for example, by forming the second frame 12 by laser cutting a hollow tube or by other techniques known in the art for manufacturing such structures. Forming the network of non-overlapping elements integrally is preferred because there are no joints between the elements that could increase friction, create failure points, etc. However, this is not essential, and in some embodiments, the network of non-overlapping elements can be formed, for example, by welding multiple individual elements together.

[0066] The second frame 12, specifically the non-overlapping elements, can comprise a shape memory alloy material, preferably Nitinol. In some embodiments, the second frame 12 can have a porosity of at least 70%, preferably at least 80%, more preferably at least 90%, and most preferably at least 95%. This allows the second frame 12 to have a low-density network of non-overlapping elements, thereby reducing the likelihood of elements interfering with each other during frame expansion and contraction and simplifying the network design. This also allows the porosity of the expandable tube 2 as a whole to be more completely determined by the first frame 10 alone, thereby simplifying the determination of the overall properties of the expandable tube 2. In some embodiments, the second frame 12 can be independently self-expanding. That is, the second frame 12 is configured to self-expand from a radially contracted and longitudinally expanded state to a radially expanded and longitudinally contracted state even when the second frame 12 is not connected to the first frame 10.

[0067] FIG. 9 shows an enlargement of one design of the second frame 12 in which the non-overlapping element network has multiple longitudinally and / or circumferentially deformable elements. Such multiple elements allow the second frame 12 to expand and contract longitudinally and / or radially to accommodate dimensional changes in the first frame 10. In the example of FIG. 9, the non-overlapping element network has multiple longitudinally deformable elements 8, which provide longitudinal expansion and contraction of the second frame 12, and multiple circumferentially deformable elements 6, which provide radial expansion and contraction of the second frame 12. The high degree of longitudinal contraction and elongation allowed by the non-overlapping structure of the second frame has many advantages. For example, using a small braid pitch (preferred in neurovascular applications where high longitudinal flexibility is particularly desirable) results in significant longitudinal contraction of the first frame 10 between a radially contracted and longitudinally expanded state and a radially expanded and longitudinally contracted state (and vice versa). The non-overlapping design of the second frame 12 allows the second frame 12 to accommodate changes in the length of the first frame 10 even with short braid pitches.

[0068] As noted above, the longitudinal elongation of the expandable tube 2 (or the frame forming part of the expandable tube 2) resulting from switching from a radially expanded and longitudinally contracted state to a radially contracted and longitudinally expanded state is preferably at least 10%. High longitudinal flexibility is particularly desirable for neurovascular applications where the vessels are thin and tortuous. To provide high longitudinal flexibility in these applications, the longitudinal elongation of the expandable tube 2 resulting from switching from a radially expanded and longitudinally contracted state to a radially contracted and longitudinally expanded state should be at least 20%, preferably at least 30%.

[0069] The network of elements in Figure 9 is such that the longitudinally deformable elements 8 are configured to expand or contract longitudinally without any substantial change in shape of the circumferentially deformable elements 6. In one embodiment, the deformation of the longitudinally deformable elements 8 occurs without substantially any deformation of the circumferentially deformable elements 6 for at least a portion of the deformation. Furthermore, the network of elements in Figure 9 is such that the circumferentially deformable elements 6 are configured to expand or contract circumferentially without any substantial change in shape of the longitudinally deformable elements 8. In one embodiment, the deformation of the circumferentially deformable elements 6 occurs without substantially any deformation of the longitudinally deformable elements 8 for at least a portion of the deformation. This independence of the two types of deformation allows the second frame 12 to smoothly and consistently follow any deformation in the first frame 10.

[0070] Other designs of non-overlapping element networks are possible. Figure 10 shows a design similar to that of Figure 9, but in which the circumferentially deformable elements 6 are circumferentially repeated. In other words, the circumferentially deformable elements 6 are connected around the periphery to form "rings". Each ring is connected by a connecting longitudinally deformable element 8.

[0071] In the design of FIG. 9, each circumferentially deformable element 6 joins two longitudinally deformable elements 8 having the same longitudinal position along the expandable tube 2. In contrast, in the design of FIG. 10, each circumferentially deformable element 6 joins two longitudinally deformable elements 8 having different longitudinal positions along the expandable tube 2.

[0072] Preferably, as shown by the dashed lines in FIG. 10, the angle between the longitudinally deformable elements 8 joined by each circumferentially deformable element 6 matches the braid angle of the braided filaments of the first frame 10.

[0073] 11 and 12 show another design in which the circumferentially deformable elements 6 form closed rings around the extension axis 4 of the expandable tube 2. Each closed ring consists entirely of circumferentially deformable elements 6, and each circumferentially deformable element 6 is generally V-shaped. Thus, each closed ring consists of multiple Vs connected together at the outer ends of the arms of each V. FIG. 11 shows the mesh in the radially expanded and longitudinally contracted state of the expandable tube 2, where the closed rings of circumferentially deformable elements 6 overlap each other longitudinally. FIG. 12 shows the mesh of FIG. 11 in the radially contracted and longitudinally expanded state of the expandable tube 2.

[0074] The non-overlapping element network has an interconnected structure with multiple sub-units that repeat longitudinally. This feature has the advantage that the length of the expandable tube 2 can be easily modified to suit any particular application by adding more sub-units. The longitudinally repeating sub-units may themselves have multiple circumferentially repeating cells. In this case, the structure of the non-overlapping element network can itself repeat both longitudinally and circumferentially. The circumferential repetition of cells allows the radius of the expandable tube to be easily adjusted according to the requirements of a particular application.

[0075] The second frame 12 radially overlaps (overlaps) the first frame 10. That is, for at least some points along the extension axis 4, a line perpendicular to the extension axis 4 passes through both the first frame 10 and the second frame 12. The second frame 12 may overlap 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 example of FIGS. 3-5, the first frame 10 and the second frame 12 overlap substantially along their entire length. Having substantial overlap between the first frame 10 and the second frame 12 ensures that the properties of the expandable tube 2 are the same along the expandable tube 2, thereby making the behavior of the expandable tube 2 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.

[0076] 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 example of Figures 3-5, the first frame 10 and the second frame 12 have approximately the same length. This can help ensure that the properties of the expandable tube 2 are consistent along the length of the expandable tube 2. The overlap requirement and the relative lengths of the first frame 10 and the second frame 12 also allow for connecting the first frame 10 and the second frame 12 together at both ends of the expandable tube 2, which can be preferred in some embodiments.

[0077] The second frame 12 is connected to the first frame 10. The connection can be achieved in any suitable manner. For example, the second frame 12 can be connected to the first frame 10 by at least one of welding, crimping, adhesive, or encapsulation. Connecting the first frame 10 and the second frame 12 at a point by encapsulation can be achieved by locally coating both the first frame 10 and the second frame 12 in a continuous section of a suitable material, such as a biocompatible polymer (e.g., PTFE).

[0078] In a preferred embodiment, the second frame 12 is connected to the first frame 10 using connecting filaments 16. To facilitate this, the second frame 12 has a plurality of filament receiving apertures 18. One or more connecting filaments 16 are woven into the first frame 10, with each connecting filament 16 passing through one or more of the filament receiving apertures 18.

[0079] An advantage of using connecting filaments 16 is that they reduce the profile of the bond between the first frame 10 and the second frame 12 compared to other methods, such as crimping or welding, thereby creating a more uniform surface for the expandable tube 2. The filaments also allow for the bonding of laser-cut structures to continuous braids (i.e., braids with a continuous pitch). Furthermore, the filaments 16 can deform during expansion and contraction of the expandable tube 2. The use of connecting filaments 16 thereby allows for a smooth transition between a radially contracted and longitudinally expanded state and a radially expanded and longitudinally contracted state while securing both the first frame 10 and the second frame 12 at some locations within the filament-receiving apertures 18.

[0080] FIG. 13 shows an example of a longitudinal end region of the second frame 12 in an embodiment in which the plurality of filament receiving apertures 18 are located within the longitudinal end region of the second frame 12. The longitudinal end region can include an area within a distance of 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 a filament receiving aperture 18 within one or both end regions of the expandable tube 2. The filament receiving aperture 18 in the embodiment of FIG. 13 is located in the longitudinally most distal element of the interconnected element network of the second frame 12. Although not shown, the filament receiving aperture 18 in the embodiment of FIG. 13 is also located in the longitudinally most proximal element of the interconnected element network of the second frame 12.

[0081] As shown in FIGS. 14 and 15, one or more connecting filaments 16 are woven into the first frame 10, with each connecting filament 16 passing through one or more of the filament receiving apertures 18.

[0082] 13, the second frame 12 has 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 braid angle of the braided filaments of the first frame 10. This causes the connecting filaments 16 passing through the filament receiving apertures 18 in the same element of the second frame 12 to extend parallel to the filaments of the first frame 10. This makes it easier to weave the connecting filaments 16 into the first frame 10.

[0083] The connecting filaments 16 are woven into the first frame 10. Thus, the connecting filaments 16 pass alternately over and under the filaments of the first frame 10 (interpreted as being radially adjacent to and away from the axis of the expandable tube 2). Other arrangements are possible. For example, the connecting filaments 16 can pass alternately over and under multiple pairs of filaments of the first frame 10, or over more sets of filaments, such as three, four, or more filaments. Passing over and under multiple filaments of the first frame 10 can be advantageous for reducing assembly time. The arrangement of the connecting filaments 16 may match or differ from the arrangement of the filaments of the first frame 10. For example, if the connecting filaments 16 have a larger diameter than the filaments of the first frame 10, it may be desirable for the connecting filaments 16 to pass over and under more sets of filaments of the first frame 10 than the filaments of the first frame 10 themselves.

[0084] In embodiments in which the plurality of filament-receiving apertures 18 are located within the longitudinal end regions of the second frame 12, the connecting filament 16 can be woven around the first frame 10. One example of such an embodiment is shown in FIG. 14. In this case, the connecting filament 16 is bent at equal intervals to follow the alternating right-handed and left-handed helical filaments of the first frame 10. To facilitate this, the connecting filament 16 can be bent into the desired shape before being woven into the first frame 10. This helps to retain the bend in the proper position and angle after the connecting filament 16 is woven into the first frame 10. If the connecting filament 16 comprises a wire, the wire can be shaped to achieve the bend in the desired position to facilitate the transition between the radially contracted and radially expanded configurations. Embodiments in which the connecting filaments 16 are woven around and into the first frame 10 can also improve the expansion characteristics of the expandable frame 2, as the connecting filaments 16 at the ends of the expandable tube 2 can help promote radial expansion when the expandable tube 2 is deployed from the catheter.

[0085] The connecting filaments 16 can have the same material and / or the same diameter as the filaments of the first frame 10. In one embodiment, the connecting filaments 16 comprise the filaments of the first frame 10. Such an embodiment is shown in FIG. 15. In such an embodiment, joining the first frame 10 and the second frame 12 together can include unwinding one or more filaments of the first frame 10 for use as the connecting filaments 16. The connecting filaments 16 are then threaded through apertures 18 in the second frame 12 and woven back into the other braided filaments of the first frame 10.

[0086] Alternatively, the connecting filament 16 may have a different diameter or be made of a different material than the filament of the first frame 10. The connecting filament 16 may comprise Nitinol wire. The connecting filament 16 may comprise a material commonly used for medical sutures. In this embodiment, the two ends of the suture may be knotted together to secure the two frames together.

[0087] In some embodiments, the plurality of filament receiving apertures 18 includes filament receiving apertures 18 spaced apart along the length of the second frame 12. One example of such an embodiment is shown in FIG. 16. The filament receiving apertures 18 can be spaced apart, preferably equally spaced apart, along the length of the second frame 12. The spacing between the filament receiving apertures 18 can be at most 50%, preferably at most 25%, and more preferably at most 10% of the length of the expandable tube 2. In some embodiments, each longitudinally expandable element 8 of the second frame 12 has a filament receiving aperture.

[0088] The inclusion of spaced filament-receiving apertures 18 along the second frame 12 enhances the attachment of the first frame 10 and the second frame 12 to one another and reduces the likelihood of the two frames separating. This also means that the connecting filament 16 does not need to bend in the manner shown in FIG. 14 but can instead follow the helical path of the braided filament of the first frame 10 along its entire length. This is advantageous because the connecting filament 16 is subjected to less tension than if it were bent. As shown in FIG. 16, multiple connecting filaments 16 can be provided that follow both the right-handed and left-handed helices of the braided filament of the first frame 10.

[0089] Preferably, the apertures 18 are positioned so that each connecting filament 16 follows the braid angle of the braided filaments of the first frame 10 as it passes through the aperture 18. To accomplish this, if multiple 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 braid angle of the braided filaments of the first frame 10. This also reduces unnecessary bending of the connecting filaments 16 and reduces tension in the connecting filaments 16.

[0090] The connecting filaments 16 can contribute to increasing the visibility of the expandable tube 2 during deployment. For example, the connecting filaments 16 can comprise a radiopaque material. Alternatively, as shown in FIG. 17, one or more of the connecting filaments 16 can have one or more radiopaque markers attached to them.

[0091] The connection shall be accomplished in a manner that is biocompatible, so as not to affect the ability of the expandable tube 2 to be inserted into the human or animal body. The expandable tube 2 may remain in the body for extended periods of time, generally indefinitely, after deployment. It is therefore important that any materials used in the connection be biocompatible as well.

[0092] The second frame 12 can be connected to the first frame 10 at at least one end of the second frame 12. Connection at one end of the second frame 12 can be convenient because an end of an element of the second frame 12 can be bonded to the first frame 10, e.g., to an end of a filament of the first frame 10. The second frame 12 can also be connected to the first frame 10 at one or more points along its length. Joining the first frame 10 and the second frame 12 at additional points along the length of the second frame 12 helps prevent the first frame 10 and the second frame 12 from separating, 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 could result in improper deployment of the expandable tube 2 or damage to the tube. However, joining at multiple points along the length of the expandable tube 2 increases the complexity of manufacturing the expandable tube 2 and, therefore, may not be preferred in all embodiments.

[0093] 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, in FIG. 5 , the ends of the braided filaments of the first frame 10 and the ends of the elements of the second frame 12 are housed within termination elements 14. The termination elements 14 are configured to reduce the possibility of damaging the interior of the blood vessel, for example, by preventing any sharp points or other sharp surfaces on the ends of the filaments from contacting the interior wall of the blood vessel. The termination elements 14 themselves can have smooth and / or curved surfaces to prevent any damage to the blood vessel.

[0094] In some embodiments, 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 discussed above, a challenge with prior art expandable tubes comprised solely of braided filaments is that they 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 radially expand and longitudinally contract, the behavior of the expandable tube 2 can be made more reliable and consistent. In some embodiments, 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 for the expandable tube 2 to expand to its final size and engage the inner wall of the vessel in which it 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 urging of the expandable tube 2 to radially expand is then only indirect and may not provide much improvement in the consistency of radial expansion during deployment.

[0095] In one embodiment, the radius of the second frame 12 in its unconstrained, radially expanded and longitudinally contracted state, when the second frame 12 is not connected to the first frame 10, is greater than the radius of the first frame 10 in its unconstrained, radially expanded and longitudinally contracted state, when the first frame 10 is not connected to the second frame 12. Both the first frame 10 and the second frame 12 are configured to bias themselves toward their radially expanded and longitudinally contracted states and have maximum radii that they reach when in their unconstrained states. When the first frame 10 and the second frame 12 are connected together to form an expandable tube, their respective maximum radii in the radially expanded and longitudinally contracted states of the expandable tube 2 are constrained to be the same, i.e., the smaller of the radii of the first frame 10 and the second frame 12 in their unconstrained states. By designing the second frame 12 so that its unconstrained radius is larger than the unconstrained radius of the first frame 10, the second frame 12 encourages the first frame 10 to expand to its maximum radius, minimizing the risk of radial separation between the two frames, especially when deployed in tortuous anatomy. This improves the consistency of the radial expansion of the first frame 10 with its braided filaments. This feature also means that fewer fixation points are required to securely join the two frames together.

[0096] In some embodiments, at least one of the first frame 10 and the second frame 12 may be provided with a hydrophilic and / or anti-thrombogenic coating.

[0097] This layered expandable tube 2 design, having a first frame 10 and a second frame 12, relies on the first frame 10 and the second frame 12 expanding and contracting longitudinally and radially together. The extent of longitudinal and radial expansion and contraction of the expandable tube 2 is determined primarily by the braided structure of the first frame 10, with the second frame 12, including, for example, longitudinally and circumferentially independent elements, matching the longitudinal and radial movement of the braided structure.

[0098] In one embodiment, the first extensibility of the first frame 10 is within 25%, preferably within 15%, more preferably within 10%, and most preferably within 5% of the second extensibility of the second frame 12. The first extensibility 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 radially contracted and longitudinally expanded state. The unconstrained length of the first frame 10 is the length of the first frame 10 in a radially expanded and longitudinally contracted unconstrained state, i.e., when the first frame 10 is not connected to the second frame 12. The second extensibility is the ratio of the unconstrained length of the second frame 12 to the length of the second frame 12 in a radially contracted and longitudinally expanded state. The unconstrained length of the second frame 12 is the length of the second frame 12 when it is not connected to the first frame 10 and is in its unconstrained, radially expanded and longitudinally contracted state. The radially contracted and longitudinally expanded state referred to refers to the state of the first frame 10 or second frame 12 when it is part of (i.e., connected to) the expandable tube 2 and the expandable tube 2 is in its radially contracted and longitudinally expanded state. This may be, for example, when the expandable tube 2 is inside a catheter ready to be deployed. Previous designs of expandable tubes with braided filaments have included expansion rings at one or both ends of the expandable tube to promote proper deployment of the braided tube ends. However, increasing the length of the expansion ring relative to a braided stent to promote proper deployment throughout its full length is challenging due to the different expansion characteristics of the two types of frames. Matching the first and second elongation rates ensures that there is a reduced likelihood of buckling of the first frame 10 or the second frame 12 or separation between the first frame 10 and the second frame 12. This further allows the second frame to be longer relative to the first frame, further improving the consistency of deployment of the expandable tube.

[0099] To determine the dimensional inputs for designing the second frame 12, the elongation rate of the first frame 10 must be analytically determined. 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 so that the second elongation rate matches the first elongation rate to the desired extent. The first method outlines a detailed approach by determining the change in length and height of a single pore in the first frame 10 between a radially expanded and longitudinally contracted state and a radially contracted and longitudinally expanded state. The pore is a single space defined by adjacent filaments in the first frame 10, as illustrated schematically in FIG. 18. The radially contracted and longitudinally expanded state is sometimes referred to as the loaded state, since this is the state of the expandable tube 2 when it is loaded onto a catheter prior to deployment within a blood vessel. The second method provides a simpler approach to assess the change in overall length of the first frame 10 between a radially expanded and longitudinally contracted state and a radially contracted and longitudinally expanded state.

[0100] The first method is to measure the diameter φ of the expandable tube 2 in its radially expanded but longitudinally contracted state, as seen in FIG. expanded and braid angle θ braid Start with the braid angle θ braid is the angle between the longitudinal direction of the first frame 10 and the individual filaments of the first frame 10. This angle varies depending on whether the expandable tube 2 is in a radially expanded and longitudinally contracted state or a radially contracted and longitudinally expanded state. Therefore, the circumference C of the expandable tube 2 can be calculated using Equation 1: C=πφ expanded equation 1

[0101] Circumferential distance D between filaments in the first frame 10 c can be calculated using Equation 2.

number

[0102] The pores of the first frame 10 have a rhomboid 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 Figure 18, resulting in the pore height decreasing and the pore length increasing.

[0103] Longitudinal length of pore L pore is calculated using Equation 3. L pore =2a sin(90°-θ braid ) Equation 3

[0104] Circumferential height of the hole H pore can be calculated using Equation 4. H pore =2a cos(90°-θ braid ) Equation 4

[0105] Total number of pores around the periphery N c can be calculated using Equation 5.

number

[0106] The total number of holes N in a single row along the length of the first frame 10 h can be calculated using Equation 6.

number

number

number

[0107] Then, the longitudinal length L of each pore in the loaded state loaded pore can be calculated using Equation 9. L loaded pore =2a cos(90°-θ loaded ) Equation 9

[0108] As can be seen in FIG. 19, 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

[0109] Finally, the first elongation rate ε can be determined using Equation 11:

number

[0110] The second method is a simpler approach that is applied to evaluate the elongation of the first frame 10 when the length of each individual filament in the first frame 10 is assumed to be equal to the length of the first frame 10 in the loaded state.

[0111] The first step is to use Equation 12 to determine the known braid angle θ braid and the pitch P of a helix with circumference C.

number

[0112] A given length L in a state where the tube is radially expanded and longitudinally contracted expanded , the number of turns N per filament in the first frame 10 turns can be found using Equation 13.

number

[0113] If we assume that the length of the filament in the first frame 10 is equal to the length of the first frame in the loaded state, then equation 14 can be applied.

number

[0114] For the first method, Equation 11 can be used to determine the first elongation rate. Furthermore, by applying Equation 15, the number of cells N cells can be obtained.

number

[0115] It should be noted that the number of cells in the second frame 12 shall be an integer, and this must be taken into consideration when selecting the parameters of the first frame 10 to ensure that the length remains the same for the first frame 10 and the second frame 12 in both the radially expanded and longitudinally contracted state and the radially contracted and longitudinally expanded state.

[0116] Knowing the first elongation rate of the first frame 10, it is possible to determine the geometry of the individual cells of the second frame 12, as shown in Figure 20. This is done for an embodiment in which a sub-unit of the non-overlapping element network of the second frame 12 has a plurality of circumferentially repeating cells (as described above) that repeat themselves longitudinally.

[0117] In such an embodiment, the non-overlapping element network includes a plurality of longitudinally deformable elements 8 that provide longitudinal expansion and contraction of the second frame 12. Each sub-unit of the non-overlapping element network has a first longitudinal length in an unconstrained state in which the second frame 12 is not connected to the first frame 10 and the second frame 12 is radially expanded and longitudinally contracted.

[0118] The longitudinally deformable elements 8 have a path length L along each longitudinally deformable element 8. path and the first length (i.e., the length of each cell in a radially expanded and longitudinally contracted state) L cell is designed to match the elongation of the first frame 10 by ensuring that the first length is proportional to the first elongation rate of the first frame 10. In one embodiment, 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.

[0119] The expandable tube 2 can be configured for use in a delivery system 20, such as the delivery system shown in FIG. 21 . The delivery system 20 includes a tubular member 24, also referred to as a catheter, and an elongated body 22, also referred to as a guidewire. 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 internally engages the elongated body 22 and externally engages the tubular member 24. The delivery system 20 is positioned within a blood vessel at a suitable location near the aneurysm, 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 that the expandable tube similarly moves longitudinally and deploys from the tubular member 24. The expandable tube 2 expands radially and contracts longitudinally, thereby releasing it from the elongate body 22 and deploying it into the blood vessel. Once the expandable tube 2 is fully deployed from the tubular member 24, the delivery system 20 can be withdrawn from the blood vessel, leaving the expandable tube 2 in place.

[0120] 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 also be deployed using a delivery system that does not have an elongated body externally engaging the expandable tube 2. The expandable tube 2 can also be deployed using a delivery system that pushes the expandable tube 2 from its proximal end. This type of delivery system is often not suitable for expandable tubes having a non-overlapping network of elements. This is especially true when those expandable tubes are designed for high longitudinal flexibility and therefore low longitudinal stiffness, for example, for use 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 due to the higher filament density provided by the first frame 10.

[0121] Various examples of aspects of the present disclosure are described below as numbered clauses (1, 2, 3, etc.) for convenience, and are provided as examples and not as limitations on the subject technology. [Article 1] 1. An expandable tube for deployment within a blood vessel, 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 having braided filaments; a second frame connected to the first frame and radially overlapping the first frame, the second frame having a network of non-overlapping elements, the non-overlapping elements being radially non-overlapping with respect to one another; and The non-overlapping element network is an expandable tube having an interconnected structure with multiple sub-units that repeat longitudinally. [Clause 2] 10. The expandable tube of claim 1, wherein the non-overlapping element network has a plurality of longitudinally and / or circumferentially deformable elements. [Article 3] The expandable tube described in clause 2, wherein the non-overlapping element network has a plurality of longitudinally deformable elements that cause longitudinal expansion and contraction of the second frame and a plurality of circumferentially deformable elements that cause radial expansion and contraction of the second frame. [Article 4] 4. The expandable tube of clause 3, wherein the longitudinally deformable element is configured to be longitudinally expanded or contracted without any substantial shape change of the circumferentially deformable element. [Article 5] 5. The expandable tube of clause 3 or 4, wherein the circumferentially deformable element is configured to be expanded or contracted circumferentially without any substantial shape change of the longitudinally deformable element. [Article 6] 6. The expandable tube of any one of clauses 1 to 5, wherein the second frame is configured to move the expandable tube from the radially contracted and longitudinally expanded state to the radially expanded and longitudinally contracted state. [Article 7] The expandable tube described in clause 6, wherein the second frame is configured to apply a radial force to the first frame to bring the expandable tube from the radially contracted and longitudinally expanded state to the radially expanded and longitudinally contracted state. [Article 8] 8. The expandable tube of any one of clauses 1 to 7, wherein the non-overlapping element network is integrally formed. [Article 9] 9. The expandable tube of any one of clauses 1 to 8, wherein the second frame comprises a shape memory alloy material, preferably Nitinol. [Article 10] 10. The expandable tube of any one of clauses 1 to 9, wherein the second frame has a porosity of at least 70%. [Article 11] 11. The expandable tube of any one of clauses 1 to 10, wherein the length of the second frame is at least 50% of the length of the first frame. [Article 12] 12. The expandable tube of any one of clauses 1 to 11, wherein the second frame overlaps with the first frame over at least 50% of the length of the expandable tube. [Article 13] 13. The expandable tube of any one of clauses 1 to 12, wherein the second frame is connected to the first frame at at least one end of the second frame. [Article 14] 14. The expandable tube of clause 13, wherein the second frame is further connected to the first frame at one or more points along the length of the second frame. [Article 15] 15. The expandable frame of any one of clauses 1 to 14, wherein the second frame is connected to the first frame by at least one of welding, crimping, adhesive, or encapsulation. [Article 16] the second frame has a plurality of filament-receiving apertures; one or more connecting filaments are woven into the first frame; 16. The expandable tube of any one of clauses 1 to 15, wherein each connecting filament passes through one or more of the filament receiving apertures. [Article 17] 17. The expandable tube of clause 16, wherein the connecting filaments comprise filaments of the first frame. [Article 18] 18. The expandable tube of clause 16 or 17, wherein one or more of the connecting filaments have one or more radiopaque markers attached to them. [Article 19] 19. The expandable tube of any one of clauses 16 to 18, wherein the plurality of filament receiving apertures comprises filament receiving apertures in longitudinal end regions of the second frame. [Article 20] 20. The expandable tube of any one of clauses 16 to 19, wherein the plurality of filament receiving apertures comprises filament receiving apertures spaced along the length of the second frame. [Article 21] 21. The expandable tube of any one of clauses 1 to 20, wherein the second frame is positioned within the first frame. [Article 22] 22. The expandable tube of any one of clauses 1 to 21, wherein the radius of the second frame in an unconstrained state in which the second frame is not connected to the first frame and is radially expanded and longitudinally contracted is greater than the radius of the first frame in an unconstrained state in which the first frame is not connected to the second frame and is radially expanded and longitudinally contracted. [Article 23] a first elongation rate of the first frame is within 25% of a second elongation rate of the second frame; the first elongation rate is a ratio of a length of the first frame in an unconstrained state in which the first frame is not connected to the second frame and is radially expanded and longitudinally contracted, to a length of the first frame in the radially contracted and longitudinally expanded state; 23. The expandable tube of any one of clauses 1 to 22, wherein the second elongation rate is the ratio of the length of the second frame in an unconstrained state in which the second frame is not connected to the first frame and is radially expanded and longitudinally contracted, to the length of the second frame in the radially contracted and longitudinally expanded state. [Article 24] the non-overlapping element network having a plurality of longitudinally deformable elements that effect longitudinal expansion and contraction of the second frame; each sub-unit of the non-overlapping element network has a first length in a longitudinal direction in the unconstrained state in which the second frame is not connected to the first frame and the second frame is radially expanded and longitudinally contracted; 24. The expandable tube of clause 23, wherein the ratio of the first length to the path length along each longitudinally deformable element is within 25% of the first elongation. [Article 25] 25. The expandable tube of any one of clauses 1 to 24, wherein the first frame comprises a shape memory alloy material, preferably Nitinol. [Article 26] An expandable tube as described in any one of clauses 1 to 25, wherein when the expandable tube is positioned across an opening against an aneurysm sac in use in the radially expanded and longitudinally contracted state, the first frame has porosity such that it diverts blood flow away from the aneurysm sac, thereby promoting thrombus formation within the aneurysm sac. [Article 27] 27. The expandable tube of any one of clauses 1 to 26, wherein the first frame has a porosity of at most 90% in the radially expanded and longitudinally contracted state of the expandable tube. [Article 28] 28. The expandable tube of any one of clauses 1 to 27, wherein the first frame has at least 48 filaments. [Article 29] 29. The expandable tube of any one of clauses 1 to 28, wherein the filaments of the first frame have a diameter of at most 30 μm. [Article 30] The first frame has at least 30 pores / mm 2 30. The expandable tube of any one of clauses 1 to 29, having a pore density of [Article 31] 31. The expandable tube of any one of clauses 1 to 30, wherein the first frame has a braid angle of at least 50°. [Article 32] 32. The expandable tube of any one of clauses 1 to 31, wherein 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. [Article 33] 33. The expandable tube of any one of clauses 1 to 32, wherein the longitudinal elongation of the expandable tube resulting from switching from the radially expanded and longitudinally contracted state to the radially contracted and longitudinally expanded state is at least 10%. [Article 34] 34. The expandable tube of any one of clauses 1 to 33, wherein 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.

Claims

1. 1. An expandable tube for deployment within a blood vessel, 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 having braided filaments; a second frame connected to the first frame and radially overlapping the first frame, the second frame having a network of non-overlapping elements, the non-overlapping elements being radially non-overlapping with respect to one another; and the non-overlapping element network has an interconnect structure having a plurality of longitudinally repeating sub-units; and The network of non-overlapping elements is an expandable tube having a plurality of longitudinally deformable elements.

2. The expandable tube of claim 1 , wherein the network of non-overlapping elements comprises a plurality of circumferentially deformable elements.

3. 3. The expandable tube of claim 2, wherein the non-overlapping element network comprises a plurality of longitudinally deformable elements that effect longitudinal expansion and contraction of the second frame and a plurality of circumferentially deformable elements that effect radial expansion and contraction of the second frame.

4. a) the longitudinally deformable element is configured to be longitudinally expanded or contracted without any substantial shape change of the circumferentially deformable element; and b) the circumferentially deformable element is configured to be expanded or contracted circumferentially without any substantial change in shape of the longitudinally deformable element; 4. The expandable tube of claim 3, characterized by one or both of:

5. 5. The expandable tube of claim 1, wherein the second frame is configured to move the expandable tube from the radially contracted and longitudinally expanded state to the radially expanded and longitudinally contracted state.

6. 6. The expandable tube of claim 5, wherein the second frame is configured to apply a radial force to the first frame to cause the expandable tube to transition from the radially contracted and longitudinally expanded state to the radially expanded and longitudinally contracted state.

7. The expandable tube of claim 1 , wherein the non-overlapping element network is integrally formed.

8. a) the second frame comprises a shape memory alloy material, preferably Nitinol; b) the second frame has a porosity of at least 70%; c) the length of the second frame is at least 50% of the length of the first frame; and d) the second frame overlaps the first frame over at least 50% of the length of the expandable tube.

8. The expandable tube according to claim 1, characterized in that:

9. a) the second frame is connected to the first frame at at least one end of the second frame; b) the second frame is connected to the first frame at at least one end of the second frame and at one or more points along the length of the second frame; and c) the second frame is connected to the first frame by at least one of welding, crimping, adhesive, or encapsulation.

9. The expandable tube according to claim 1, characterized in that:

10. the second frame has a plurality of filament-receiving apertures; one or more connecting filaments are woven into the first frame; 10. The expandable tube of claim 1, wherein each connecting filament passes through one or more of the filament-receiving apertures.

11. a) the connecting filaments comprise filaments of the first frame; b) one or more radiopaque markers are attached to one or more of said connecting filaments; c) the plurality of filament receiving apertures include filament receiving apertures in longitudinal end regions of the second frame; and d) the plurality of filament receiving apertures includes filament receiving apertures spaced along a length of the second frame; 11. The expandable tube of claim 10, characterized by one or more of:

12. The expandable tube of claim 1 , wherein the second frame is positioned within the first frame.

13. 13. The expandable tube of claim 1, wherein the radius of the second frame in an unconstrained state in which the second frame is not connected to the first frame and is radially expanded and longitudinally contracted is greater than the radius of the first frame in an unconstrained state in which the first frame is not connected to the second frame and is radially expanded and longitudinally contracted.

14. a first elongation rate of the first frame is within 25% of a second elongation rate of the second frame; the first elongation rate is a ratio of a length of the first frame in an unconstrained state in which the first frame is not connected to the second frame and is radially expanded and longitudinally contracted, to a length of the first frame in the radially contracted and longitudinally expanded state; 14. The expandable tube of claim 1, wherein the second elongation is a ratio of a length of the second frame in an unconstrained state in which the second frame is not connected to the first frame and is radially expanded and longitudinally contracted, to a length of the second frame in the radially contracted and longitudinally expanded state.

15. the non-overlapping element network having a plurality of longitudinally deformable elements that effect longitudinal expansion and contraction of the second frame; each sub-unit of the non-overlapping element network has a first length in a longitudinal direction in the unconstrained state in which the second frame is not connected to the first frame and the second frame is radially expanded and longitudinally contracted; 15. The expandable tube of claim 14, wherein the ratio of the first length to the path length along each longitudinally deformable element is within 25% of the first elongation.

16. 16. The expandable tube of claim 1, wherein when the expandable tube is positioned across an opening against an aneurysm sac in the radially expanded and longitudinally contracted state in use, the first frame has porosity that diverts blood flow away from the aneurysm sac, thereby promoting thrombus formation within the aneurysm sac.

17. a) the first frame comprises a shape memory alloy material, preferably Nitinol; b) the first frame has a porosity of at most 90% in the radially expanded and longitudinally contracted state of the expandable tube; c) the first frame has at least 48 filaments; d) the filaments of the first frame have a diameter of at most 30 μm; e) the first frame has at least 30 pores / mm ２ and f) the first frame has a braid angle of at least 50°; 17. The expandable tube according to claim 1, characterized in that:

18. 18. The expandable tube of claim 1, wherein 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.

19. 19. The expandable tube of claim 1, wherein the longitudinal elongation of the expandable tube caused by switching from the radially expanded and longitudinally contracted state to the radially contracted and longitudinally expanded state is at least 10%.

20. 20. The expandable tube of claim 1, wherein 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.

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