Radiopaque vascular prostheses

Abstract

To provide a vascular prosthesis formed of one or more DFT wires for imaging of a device.SOLUTION: Provided is a vascular prosthesis using a drawn filled tube (DFT) wire 112 for supporting visualization of the prosthesis without requiring a supplemental radiopacity material.SELECTED DRAWING: Figure 2

Description

Technical Field

[0003]

[0001] (Related Application) This application claims priority to U.S. Provisional Application No. 62 / 768,803, filed November 16, 2018, under the name "Stent," and is the non-provisional application thereof, which is hereby incorporated by reference in its entirety.

Background Art

[0002] Vascular prostheses such as stents and stent grafts are used in the vascular system for various reasons. A non-exhaustive list includes opening diseased or occluded blood vessels to promote blood flow, flow diversion including diverting flow from a target area such as an aneurysm, and retaining a material (e.g., an embolization material) within a treatment site to promote local occlusion within the area.

[0003] Visualization is important for vascular prostheses so that a surgeon can confirm proper placement of the device within the vascular system. Conventional metal stents utilize a good shape memory material such as nitinol, and the stent readily assumes its expanded state upon delivery to the treatment site. The metal stent is heat set to the expanded shape so that when released from its compressed state within the delivery catheter, the stent readily assumes this expanded shape. However, since these metals are not radiopaque, imaging is difficult. One possible solution is to utilize radiopaque metal wires when fabricating these stents, but in practice, such materials are difficult to handle and often become brittle once heat treated.

[0004] To address this issue, many stents and stent grafts may utilize one or more radiopaque components to facilitate visualization, allowing physicians to verify that the device is properly positioned in the vascular system. These radiopaque components are distinct from the actual prosthesis itself (e.g., they are separate radiopaque layers or components attached separately to the stent). The use of these separate radiopaque components can complicate matters by thickening the stent, thereby making deployment more difficult and affecting whether these stents can effectively treat smaller vessels, such as those present in the neurovascular system. These separate radiopaque components also affect the overall mechanical properties of the stent, thereby creating engineering challenges.

[0005] Drawn-filled tubes (DFTs) utilize dissimilar materials, including an internal core and an external jacket. DFTs can be constructed from radiopaque materials (e.g., a radiopaque internal core with a non-radiopaque external jacket, or vice versa) to combine the advantages of good shape-memory metal wires with the radiopaque / imaging advantages of radiopaque materials. These DFT wires can then be used to design vascular prostheses that do not require separate radiopaque materials. In this way, DFTs can be used in the metal layers constituting stents / stent grafts, allowing for device visualization without the inclusion of separate radiopaque materials. However, DFT wires have different mechanical properties than conventional metal wires, creating different kinds of engineering challenges when fabricating usable vascular prostheses incorporating DFT wires.

[0006] There is a need for a usable DFT stent that combines the advantages of DFT imaging with addressing the unique design challenges inherent in DFT wires. [Overview of the project]

[0007] The present invention relates to a vascular prosthesis composed of one or more DFT wires that offers advantages in imaging devices.

[0008] In one embodiment, the vascular prosthesis consists of a single DFT wire braided anteriorly and posteriorly within itself to form a substantially tubular shape. In other embodiments, multiple DFT wires can be used. In one embodiment, one or more DFT wires utilize a platinum or tantalum core surrounded by a nitinol jacket.

[0009] In one embodiment, the DFT prosthesis utilizes multiple terminal loops on either end of the prosthesis, thereby utilizing shorter and longer loops. The shorter loops have a size and angle that allows for tight contact with blood vessels and resists movement at the implant site. In one embodiment, the longer loops utilize coil or marker coil elements to help the delivery pusher grasp the prosthesis during delivery. In one embodiment, the shorter loops are configured to overlap with the longer loop coil when the DFT prosthesis is in its compressed delivery state.

[0010] A DFT prosthesis contains multiple pores along the blood vessels of the prosthesis. The pores are formed by the intersections of one or more wires that make up the DFT prosthesis. In one embodiment, the pores are made large enough to allow a microcatheter and / or embolic material to be placed inside in order to occlude a target therapeutic site (such as an aneurysm).

[0011] In one embodiment, a delivery system for a DFT prosthesis includes a pusher comprising two expansion bands and a recessed region between them. The DFT prosthesis includes multiple proximal end loops having longer and shorter loops, where the longer loops utilize a coil or marker coil. The coil engages with the expansion bands to form a thickened region for driving the stent during delivery. The shorter loops are sized and positioned to overlap with a portion of the coil or marker coil when the DFT prosthesis is in its compressed delivery state, preventing the coil from becoming trapped when the DFT prosthesis is introduced into the delivery catheter and delivered from there, thereby enabling smoother delivery. In one embodiment, the pusher system is configured such that all ends of the shorter and longer proximal end loops are contained within the recessed region between the two expansion bands.

[0012] In one embodiment, the DFT prosthesis utilizes one or more reinforcing elements on one or more wire segments of the prosthesis. In one embodiment, the reinforcing element is a coiled coil. In another embodiment, the reinforcing element is a tube. The reinforcing element increases rigidity along the relevant region of the stent, helping the stent open during deployment. [Brief explanation of the drawing]

[0013] These and other possible embodiments, features and advantages of the present invention will become apparent and clarified from the following description of embodiments of the present invention with reference to the accompanying drawings.

[0014] [Figure 1] Figure 1 shows the DFT wire used in the DFT stent.

[0015] [Figure 2] Figure 2 shows a DFT stent according to one embodiment.

[0016] [Figure 3] Figure 3 shows the mandrel used to wrap the DFT stent.

[0017] [Figure 4] Figure 4 shows a detailed view of the enlarged end region of the mandrel of Figure 3.

[0018] [Figure 5] Figure 5 shows the loop wound around the enlarged end of the mandrel of Figure 4.

[0019] [Figure 6] Figure 6 is a plan view of a DFT stent end loop configuration according to one embodiment.

[0020] [Figure 7] Figure 7 is a plan view of a DFT stent end loop configuration according to another embodiment.

[0021] [Figure 8] Figure 8 is a plan view of a DFT stent end loop configuration according to another embodiment.

[0022] [Figure 9] Figure 9 is a plan view of a DFT stent end loop configuration according to another embodiment.

[0023] [Figure 10] Figure 10 shows a marker coil used for the end loop of a DFT stent according to one embodiment.

[0024] [Figure 11] Figure 11 shows a DFT stent end loop configuration for a pusher system according to one embodiment.

[0025] [Figure 12] Figure 12 shows a DFT stent utilizing a reinforcing element according to one embodiment.

[0026] [Figure 13] Figure 13 shows an enlarged view of the reinforcing element of Figure 12. [Figure 14]Figure 14 shows an enlarged view of the reinforcing element in Figure 12.

[0027] [Figure 15] Figure 15 shows a DFT stent weave pattern according to one embodiment. [Modes for carrying out the invention]

[0028] Specific embodiments of the present invention will be described below with reference to the drawings. However, the present invention can be carried out in many different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided so as to make this disclosure complete and self-contained and fully convey the scope of the invention to those skilled in the art. In this regard, the elements and functionality of one embodiment are not necessarily limited to that embodiment and can be combined with other embodiments shown herein in any way that results in a functional embodiment. The terms used in the detailed description of the embodiments shown in the accompanying drawings are not intended to limit the present invention. In the drawings, between different embodiments, similar numbers refer to similar elements.

[0029] The embodiments presented herein deal with the fabrication of vascular prostheses (e.g., stents or stent grafts) using usable drawn-fill tubes (DFTs). DFTs are particularly advantageous in terms of visualization when the drawn-fill tubes are formed using radiopaque materials, as described above. In some examples, these drawn-fill tubes can be used to fabricate wire or filament elements having radiopaque internal components (e.g., platinum, gold, tantalum, palladium, or other similar materials) and a metallic outer jacket / external component (e.g., nitinol, stainless steel, cobalt-chromium, or other shape memory materials).

[0030] In embodiments of the present invention, DFT wires are used in a structural layer defining the stent such that the stent is physically composed of one or more DFT wires. In this way, since the stent itself is composed of DFT wires, it does not require a separate radiopaque component with the stent and can therefore be easily visualized in vivo. DFT wires have different mechanical properties from metal wires (e.g., nitinol, stainless steel, cobalt-chromium) conventionally used to fabricate stents, which presents challenges in their use. Therefore, there are specific design challenges in fabricating usable DFT stents. Embodiments of the present invention address these problems by providing specific designs and configurations for fabricating usable DFT stents.

[0031] There are several issues specific to the use of DFT wires that need to be considered when designing DFT stents. One of the main advantages of using DFT wires is that the stent itself can be visualized without the need for a separate radiopaque imaging material. Another advantage is that DFT stents can be smaller in size than conventional stents because no additional radiopaque components or layers are needed for visualization. This has the advantage of allowing for easier deployment and enabling these stents to be fitted into (and treated) smaller vessels, including those of the distal neurovascular system.

[0032] Despite these advantages, there are several design challenges in using DFT wires and fabricating DFT stents. Firstly, because DFT wires are a composite of two different materials, they may not possess the shape memory properties of conventional shape memory metal (e.g., nitinol) stents, meaning they may not have the same heat-set expansion properties as conventional metal stents. Secondly, including a radiopaque element or layer on top of a conventional metal stent generally increases the stiffness of the stent, which enhances properties such as resistance to apposition and migration during implantation. Since DFT stents do not require this additional radiopaque material for visualization, the resulting decrease in stiffness can affect apposition and migration.

[0033] Furthermore, one surprising issue when using DFT wires is that, upon heat treatment / heat setting, these materials tend to soften more than pure metal shape memory wires. This is generally unexpected, as the radiopaque core or internal material (depending on which specific material is used) can be rigid compared to the metal shape memory outer jacket. However, using two different materials when creating a single wire can alter the material properties of the combined wire shape. These properties mean that when DFT wires are used in stents, the mechanical properties of the stent must be tuned to provide sufficient strength to facilitate proper deployment of the DFT stent at the treatment site and to promote proper adhesion of the DFT stent to prevent stent migration. Embodiments presented herein address these and other issues in order to fabricate usable DFT stents.

[0034] Figure 1 shows a cross-section of a DFT wire 100 utilizing a radiopaque internal wire component 102 and a metal external jacket 104. The elements that can be used for the radiopaque internal component are those described above, and include platinum, gold, tantalum, or palladium. Similarly, the metal external jacket material described above preferably utilizes a strong shape memory material such as nitinol (generally preferred as a particularly beneficial shape memory material), stainless steel, or cobalt-chromium.

[0035] The shape memory jacket allows for the imparting of good shape memory properties to the wire and is useful for providing a thermoformable expansion structure for the stent, while the use of radiopaque internal components allows for visibility. In some embodiments, this configuration can be reversed to utilize a radiopaque outer jacket and radiopaque internal components. In other embodiments, three or more concentrically arranged radial wire elements can be used, including various combinations of shape memory metal and radiopaque components.

[0036] The internal component 102 can be of various shapes, such as a rectangle, but is preferably circular, elliptical, or egg-shaped (e.g., wire-shaped). The external component / jacket 104 has an inner diameter that closely matches the outer diameter of the internal component 102 and can be considered a hollow component that surrounds the internal component in a jacket-like configuration. The use of a radiopaque internal component 102 facilitates the visualization of the DFT wire, while the external jacket 104 (made of a metallic shape memory material) allows for good flexibility of the stent, so that once the stent is deployed or released from the delivery catheter, it can easily adopt a heat-set expansion configuration.

[0037] During heat setting, extended shape memory is imparted to the material through a heat treatment process. Before or after the heat setting process, one or more DFT wires are electropolished to smooth them and facilitate implantation into the vascular system.

[0038] Depending on the stent size and the targeted treatment procedure (which affects the required structural stability, stent opening pore size, etc.), various dimensions of the DFT wire can be used. In one example, the internal components of the DFT are made of platinum or tantalum, and the external components are made of nitinol-1 or nitinol-2. In some examples, the overall wire size is approximately 0.001 inches to 0.004 inches, or approximately 0.0025 to 0.003 inches. Note that these dimensions represent the overall diameter of wire 100 shown in Figure 1. In some examples, the internal radiopaque core is approximately 0.0005 inches to 0.001 inches, or approximately 0.0008 to 0.0009 inches.

[0039] The total cross-sectional area of ​​wire 100 is the sum of the area of ​​the inner component 104 and the area of ​​the outer component 102. In one example, the cross-sectional area ratio is such that the radiopaque core accounts for approximately 10% of the total area of ​​wire 100. The electropolishing process further reduces the area of ​​the nitinol jacket, as the nitinol jacket is an outer section, and in some examples, the radiopaque core after electropolishing accounts for approximately 18-20% of the total area of ​​wire 100. In some examples, the diameter of the DFT wire after electropolishing is approximately 0.0018-0.0022 inches. Essentially, this means that while electropolishing reduces the area of ​​the outer jacket and the overall cross-sectional area of ​​the wire, the area of ​​the radiopaque inner component remains generally unchanged due to the presence of the shape memory metal outer jacket over it.

[0040] Figure 2 shows a DFT stent 110 according to one embodiment. The stent 110 is composed of one or more DFT wires 112 wound to form the shape shown, where the DFT wire composition is as described above. In one embodiment, the stent 110 is composed of only one DFT wire 112. In another embodiment, multiple DFT wires 112 are braided together to form the stent shape. Both ends of the stent utilize flares, including a long flare or loop 114 and a short flare or loop 118. These flares or loops provide adhesion to the blood vessel, help resist migration at the treatment site, and assist in the stent delivery process, as described later.

[0041] The stent is braided on a mandrel such that one or more wires constituting the stent are braided on the mandrel to form the stent shape. In one embodiment, the stent utilizes a single DFT wire 112, and the single DFT wire constituting the stent is braided or woven back and forth on the mandrel to form the shape shown in Figure 2. This involves winding the wire from one end of the mandrel to the other, in a specific direction (clockwise or counterclockwise) and longitudinally, with the other parts of the wound wire in an over-under pattern, and continuing this process back and forth from one end of the stent to the other.

[0042] A single-wire configuration offers several advantages. For example, because there are no attachment points that could affect force transmission, force is transmitted better along a single wire than along multiple, connected, and braided wires. This is advantageous when pushing the stent with a delivery catheter and also helps the stent expand radially when released from the delivery catheter over it. This single-wire configuration can also be advantageous when used with DFT stents, which, as mentioned above, tend to be more flexible and less rigid than typical metal stents. While this flexibility is beneficial for stents conforming to the shape of curved anatomical sites, it can also make delivery and attachment difficult, and therefore, a single wire can transmit and retain force in a more efficient way.

[0043] In another embodiment, the stent utilizes a plurality of DFT wires 112 (for example, two or more, 4 to 48, 6 to 24, or 12 to 24 wires to provide various embodiments). The plurality of wires constituting the braid are welded together or attached to one another (for example, by crimping or via mechanical caps), with one wire attached to another at one or more locations along the stent or in the flared end region of the stent.

[0044] The mandrel 120 used to wind the stent is shown in Figure 3 and utilizes a cylindrical inner section, or "intermediate" section 122, around which the majority of the stent is wound. This section forms the cylindrical tubular shape that constitutes the majority of the stent. In one embodiment, this intermediate section 122 may utilize multiple pins around which one or more wires constituting the stent are wound. In another embodiment, multiple protrusions, recesses, or laser-cut guide components are used to guide the placement of one or more wires as they are wound around the mandrel. In yet another embodiment, no pins are used, and the user simply winds the wires in a mixed manner, clockwise, counterclockwise, or longitudinally and circumferentially around the mandrel.

[0045] The enlarged mandrel sections 124a and 124b are located at both ends of this intermediate section 122. Each enlarged mandrel section 124a, 124b utilizes its own tapered regions 126a, 126b, which are used to wind the flares or loops 114, 118 of the stent 110. The tapered region 126a (which is similar in configuration to region 126b) is shown in more detail in Figure 4. Although it is shown as flat in Figure 4, in a true perspective view it would be shown as tapered such that the radially inward, more central portion protrudes outward compared to the radially outward, more peripheral portion. The flat shape as shown is simply for illustrative purposes.

[0046] The tapered regions 126a and 128b include an inner pin 128 extending radially near the center of the tapered region and an outer pin 130 extending radially away from the center of the tapered region 126a. The shorter flare 118 of the DFT stent wraps around the inner pin 128, and the longer flare 114 wraps around the outer pin 130. In the illustrated example, the inner pin is aligned with the outer pin, meaning that if a line is drawn from the pin to the center of the "flattened" tapered region 126a, the inner and outer pins share the same line or angle.

[0047] As shown in Figure 1, each shorter loop is right next to the longer loop, so each loop is offset from the other. In practice, this means that the shorter loop 118 is wound around the inner pin 128, unwound to the other side of the mandrel, comes back and wound around the next outer pin 130 to form the longer loop, wound on the mandrel, comes back and wound around the next inner pin 128 to form the shorter loop, comes back and wound around the next outer pin to form the longer loop, and so on. This is shown in Figure 5, where the longer loop is next to the shorter loop. In practice, this means that only one pin (either the inner pin 128 or the outer pin 130) of each "pair" of pins is used to wind either the short or long loop.

[0048] In the context of Figure 4, eight sets of inner and outer pins are used, meaning that in this pattern, four short loops and four long loops are created, with each loop offset by an equidistant amount (e.g., 45 degrees, so that each short loop is offset by 45 degrees from its adjacent long loop, and vice versa). The pin "pairs" of inner and outer pins are preferably spaced equally apart, and therefore, in the context of Figure 4, each pin "pair" is spaced 45 degrees apart from its adjacent pin "pair," meaning that each loop is spaced 45 degrees apart from each other. Six pin "pairs" spaced 60 degrees apart from each other are used on tapered regions 126a, 126b to create a six-loop configuration of three short loops and three long loops.

[0049] As described above, the tapered portion of the mandrel is used to form a flare. In one example, this taper is approximately 50 to 60 degrees, and in a more specific example, approximately 60 degrees. With respect to the tapered portion 126b, this angle represents the angle between the tapered portion 126b and a horizontal line drawn to the right of the tapered portion (for example, a horizontal line drawn through the center of the expanding mandrel 124b). This angle represents the approximate angle of the plane defined by the stent loops 114, 118, or in other words, the degree of the bending angle defined by the stent loops. Thus, the short and long loops are tapered at approximately 50 to 60 degrees, or in a more specific example, approximately 60 degrees. Different dimensions may be used in different embodiments. However, this angle may have particular utility in allowing the short loop in a profile of a certain size to contact the vessel wall without collapsing, thereby promoting proper adhesion to the vessel and providing a firm anchor point within the vessel. In other words, this angle is carefully adjusted to maximize the adhesion of the stent to the vessel wall, taking into account the unique properties of the DFT stent.

[0050] Figures 6-9 show the flare or loop configuration at the end of the stent in more detail. Figures 6-9 show a linear type of flare configuration shown for ease of explanation. These figures can be thought of as representing the circumferential region formed by the stent end when the flare is laid flat along a plane after one cut has been made. Each long loop 114 is adjacent to a short loop 118, such that the long loop 114 has short loops 118 on both sides, and the short loops 118 have long loops 114 on both sides.

[0051] Figures 6 and 8 show a 6-loop configuration, in which each end of the stent is arranged alternately in three long loops and three short loops. Figures 7 and 9 show an 8-loop configuration, in which each end of the stent is arranged alternately in four long loops and four short loops.

[0052] In Figures 5 and 6, in one embodiment of the flare / loop configuration, the loops / flares are arranged substantially adjacent to each other or aligned with one another. In Figures 7 and 8, in another embodiment of the flare / loop configuration, the loops / flares overlap slightly. This overlap may be formed during the heat treatment process, or it may occur naturally during stent expansion as the wires constituting the loops come into contact with adjacent wires / loops, resulting in an overlapping configuration. Note that different numbers of flares / loops are possible. For example, each end of a stent may have 4 to 24 loops.

[0053] The short flare 118 is preferably made to be similar in size to the diameter of the vessel being treated. In this way, when fully expanded, the short flare 118 directly contacts and adheres to the vessel wall, helping to provide a restraining force to prevent stent migration. In this way, the short flare 118 is supported without collapsing as a result of being oversized relative to the vessel diameter.

[0054] As mentioned above, DFT wires are generally softer than shape memory metal wires, so the short flares 118 are carefully adjusted to promote adhesion in the blood vessel, thereby helping to prevent stent migration after implantation. The short flares 118 have a certain angle, length, and shape (as described above) to maximize adhesion to the vessel wall so that these short flares are not compressed downward (for example, if they are oversized to a significant amount compared to the size of the vessel).

[0055] As described above, the long flare 114 and the short flare 118 can each be oriented at an angle of approximately 60 degrees (with respect to the horizontal plane extending through the axial / radial center of the stent). The flare / loop size can also vary depending on the size of the stent. In various examples, the stent is approximately 2.5–5 mm in diameter. This particular size is suitable for the neurovascular arteries, which are smaller than the arteries that make up the majority of the vascular system, and has the advantage of being used as a scaffold stent to support the neck region of the aneurysm for subsequent devices (e.g., embolic coils or other occlusive agents) used to fill the aneurysm. Proper stent attachment is important in this targeted therapy regimen to ensure that the stent does not move away from the aneurysm site, thereby allowing the embolic material to move if it were to detach without a supporting scaffold.

[0056] In some examples, a fully extended / unfolded stent with a width of approximately 0.1 inches (approximately 2.5–3 millimeters) has a short flare 118 measuring approximately 0.015–0.025 inches and a long flare 114 measuring approximately 0.04–0.05 inches. A fully extended / unfolded stent with a width of approximately 0.12 inches (approximately 3–3.5 millimeters) has a short flare measuring approximately 0.015–0.025 inches and a long flare measuring approximately 0.04–0.05 inches. A fully extended / unfolded stent with a width of approximately 0.14 inches (approximately 3.5–4 millimeters) has a short flare measuring approximately 0.015–0.025 inches and a long flare measuring approximately 0.04–0.05 inches. A fully extended / unfolded stent with a width of approximately 0.162 inches (approximately 4-4.5 millimeters) has a short flare of approximately 0.015-0.025 inches and a long flare of approximately 0.04-0.05 inches.

[0057] Note that the fully expanded / unfolded width of the stent represents the outer diameter of the tubular portion of the stent (i.e., excluding the flared end), and the flare length represents the length of the flare extending from this tubular portion. Furthermore, note that the relatively consistent sizing of the short and long flares, regardless of the stent size—that is, relatively small compared to the total stent diameter—ensures that the stent maintains proper contact with the vessel wall and supports adhesion (via the short flares 118 intended to make direct contact with the vessel), while the longer flares 114 (slightly larger compared to the vessel diameter) further ensure that they do not collapse as much because they are not significantly oversized. This relative sizing also helps ensure smoother delivery, as the loop does not significantly overlap the stent and there is less contact friction with the catheter. The length of the stent may vary based on its size and intended use (e.g., the size of the treatment area, such as an aneurysm being treated). In some cases, the overall length of the stent can range from approximately 0.27 inches (about 7 millimeters) to approximately 0.73 inches (about 18.5 millimeters).

[0058] The "working length" of a stent refers to the portion of the stent that can be used for its intended therapeutic purpose. Within the range described above, it should be noted that the long loop 114 is not significantly larger than the short loop 118, and the short loop 118 is not significantly larger than the rest of the stent. Thus, in some embodiments, the working length of the stent may include portions of the stent containing the short loop 118, thereby increasing the proportion of the stent available for performing the procedure. For example, the size range of the short loop 118 described above adds approximately 1 mm to the "working length" of the stent overall. If the stent length is 7 mm (representing the lower limit of a given range), this 1 mm increase may be significant. Even if the stent length is 18.55 mm (representing the upper limit of a given range), this 1 mm is still relatively significant.

[0059] The above description discusses some of the characteristics of the softness of DFT stents. Some of these are due to the absence of radiopaque components added to the stent (e.g., radiopaque wire wrapped around the stent, a separate radiopaque layer, or radiopaque elements added to selected parts of the stent), the tendency for the inclusion of these layers in conventional stents to increase the associated stiffness, and observable phenomena including metalworking and heat treatment of the DFT wire.

[0060] Due to this increased flexibility, delivering the DFT stent may require additional force to track it through the delivery catheter above it. The above description discussed the sizing of the short flare 118 and the long flare 114, and how they are sized to be relatively similar so that the long flare 114 is not significantly longer than the short flare 118. One further advantage of this design is that the short flare 118 and the long flare 114 are located relatively close together when the stent is in a collapsed deployed state after being delivered through the catheter above it.

[0061] Figure 10 shows the configuration of the longer flare 114 in more detail. The longer flare 114 includes a wound marker coil 132 that is wrapped around the structural DFT wire that constitutes the stent. The shorter flare 118 may also optionally include a marker coil 132. The marker coil 132 may be a wound wire of tantalum, platinum, palladium, or gold that is wrapped around the structural DFT wire of the stent. One or more marker coils 132 on the longer flare 118 are not necessarily used for visualization purposes because the entire stent is radiopaque (although enhanced radiopaqueness may help visualize both ends of the stent in more detail). Here, they are used to help grasp the stent during delivery, as described below.

[0062] Using radiopaque marker coils 132 on the stent flare offers several advantages. While the stent itself is composed of DFT wire and therefore radiopaque, the inclusion of marker coils 132 along the flare helps visualize the stent's edge. In this way, the stent's edge can be made more prominent, allowing the physician or surgeon to determine its location in comparison to a target area to confirm its placement. This is particularly useful in situations where certain facilities utilize relatively poor imaging techniques, as it provides at least better visualization of the stent's edge.

[0063] Because the wound coil typically exerts less force on the wire beneath it, using the coil 132 as an element offers several advantages for the DFT wire, given its flexibility. Nevertheless, in some embodiments, the marker element 132 can take the form of a compressed tube across the loop. This is particularly meaningful when the DFT wire is thicker, or when the overall diameter of the DFT stent is smaller, so that greater strength is incorporated into the DFT stent.

[0064] In some embodiments, the marker element 132 can be radiopaque, in which case, for example, the stent is oversized compared to the target region and many of the DFT components overlap. In this situation, having a radiopaque end actually helps to make the stent end more visible. Therefore, in some embodiments, the marker element 132 can take the form of a radiopaque metal (e.g., nitinol, stainless steel, or cobalt-chromium) coil or tube.

[0065] As described below, the marker coil element 132 has particular advantages in increasing the thickness of the loop portion and helping to engage with the stent during the delivery process. Thus, the marker coil 132 also functions as a strut thickening element. In these ways, the marker coil 132 can also be considered a thickening / reinforcement / enlargement member 132 for increasing the strut thickness of a portion of the loop portion of a radiopaque coil, a radiopaque or radiopaque tube, and / or DFT stent. In other words, in various embodiments, any of these terms can be used to describe the element 132.

[0066] Figure 2 shows the marker coils 132 along the longer flares 114. Note that, although not shown, the shorter loops 118 can also utilize the marker coils 132. In one example, one marker coil 132 is used for each long flare 114; in another example, two marker coils 132 are used for each flare (one for each "V" that makes up the flare shape); in yet another example, one marker coil 132 is used for each short and long flare 114, 118; and in yet another example, two marker coils 132 are used for each short and long flare 114, 118.

[0067] The configuration of the long flare 114 and marker coil 132 is shown in more detail in Figure 10, which represents the extended configuration of the stent (similar to Figure 2). As previously mentioned, opposing "V" shaped segments on the longer flare 114 can also utilize the marker coil 132, although this is not shown exemplarily.

[0068] When the stent is restrained within the delivery catheter, the collapsed configuration of the stent is shown in Figure 11, particularly the proximal end loop portion of the stent. A pusher 142 is used to push the stent through the catheter 140. The pusher has a proximal end that the user can push and pull to manipulate the stent, which is connected to the pusher 142, out through the catheter 140. The pusher 142 includes a pair of expanding bands 144, 146 along the distal portion of the pusher 142. In one embodiment, the expanding bands 144, 146 are radiopaque (e.g., tantalum, gold, platinum, or palladium) to aid visualization during delivery and thus function as marker bands. Depending on the situation (e.g., based on stent sizing or imaging techniques), if a very large amount of radiopaque material is included (remember that the entire stent is radiopaque due to the DFT wire), visualization may be more difficult as there will be little that appears separated. Therefore, in some embodiments, the expanding bands 144, 146 are radiopaque (e.g., nitinol or stainless steel).

[0069] When the stent is anchored within the delivery catheter 140, the proximal loop of the stent is positioned as shown in Figure 11, and all the short loops 118 (shown as solid loops) and long loops 114 (shown as dashed loops) at the proximal end of the stent are contained within the region defined between the two expansion bands 144, 146.

[0070] As described above, various stent embodiments have various combinations of short and long loops. For the sake of clarity, two short loops and two long loops are shown, but it should be noted that this means all proximal loops (both long and short loops) are constrained within this expanding pusher band region. That is, if the stent configuration utilizes six proximal loops (three short loops and three long loops), all six of these proximal loops are located within this region / space defined between the two expanding bands 144 and 146. Similarly, if the stent configuration utilizes eight proximal loops (four short loops and four long loops), all eight of these proximal loops are located within this region, and so on.

[0071] The marker coil 132 on the long loop plays a crucial role in helping the loop remain constrained within this region and ensuring that the expanding bands 144, 146 can engage with the stent. Note that while each loop can utilize two marker coils 132, the marker coils 132 on the loop are shown only along a portion of the long loop. The marker coil 132 on the loop provides an expanded contact surface and assists in engagement with the stent. In one embodiment (shown in Figure 11), the proximal band 144 engages with the end of the longer flare 114 to move the stent forward, and the distal band 146 engages with the marker coil 132 to pull the stent back proximal. In the context of Figure 11, pushing the stent forward involves moving the stent to the left, with the proximal band 144 engaging with the end of the long loop 114. Pulling the stent back involves moving the stent to the right, with the distal band 146 engaging with the marker coil 132 and engaging with the stent. Although the marker coil 132 is shown only on the longer loop 114, in different embodiments, the marker coil 132 may be utilized only along both the longer loop 114 and the shorter loop 118.

[0072] The fact that all proximal loops are located within the region between the expanding pusher bands 144 and 146 offers several advantages. For example, because all loops / marker coils are located within this region, each expanding band is more likely to come into contact with one or more marker coils, thereby providing a higher pressing force when each expanding band engages with a marker coil to drive the stent's movement. The increased pressing force is particularly advantageous given the material properties of the DFT stent described above, as it helps in delivering the stent. Furthermore, the laminated configuration (all loop-shaped ends are within this region) also provides a backup system in case one of the stent loops becomes disengaged from the pusher 142, so that each expanding pusher band 144 or 146 can still come into contact with one of the other proximal loops / marker coils and engage with the stent.

[0073] As shown in Figure 11, since the short loop 118 is shorter than the long loop 114, it should be noted that the short loop 118 is always slightly offset compared to the long loop. However, in configurations where the short loop 118 also utilizes a marker coil, the position of the marker coil can still be adjusted so that the expansion band 146 can engage with the marker coil 132 of the short loop 118 and engage with the stent (for example, the marker coil may be positioned relatively close to the "end" of the short loop). In this way, the distal expansion band 146 can engage with only the marker coil 132 of the short loop 118, only the marker coil 132 of the long loop 114, or with the marker coils 132 of both the short loop 118 and the long loop 114.

[0074] A layered configuration in which all loops are contained within a region defined between pusher bands 144, 146 offers further advantages. For example, in many configurations, the pusher bands engage with the marker coils 132 of the longer loops 114 because these loops 114 are larger than the shorter loops 118 (i.e., they have a larger surface area and extend over a longer distance). The layered configuration ensures that the marker coils 132 along the longer loops 114 are partially protected by the shorter loops 118, thereby reducing the likelihood of the marker coils 132 snagging on the delivery catheter during placement from the introduction device to the catheter or delivery from the catheter to the blood vessel. In the context of Figure 11, this protection is provided by the shorter loops 118 actually being positioned on or around the marker coils 132 of the longer loops.

[0075] Another configuration involves all ends of the proximal loop being stacked or constrained within a defined area between pusher bands 144, 146, but utilizing an arrangement where the proximal band 144 engages with the marker coil 132 instead of the end of the long loop 114 to drive the stent forward. In this configuration, the position of the long loop 114 differs from that shown in Figure 11, with a portion of the long loop 114 slightly overlapping the expansion bands 144, 146, and the proximal band 144 engaging with the marker coil 132 instead of the end of the long loop 144 to drive the stent. In some embodiments, the short loop 118 may also utilize the marker coil 132, and these marker coils may be configured so that the expansion band 144 also contacts these marker coils.

[0076] For example, the space or gap between bands 144 and 146 (see Figure 11) is approximately 1.5–2 mm (approximately 0.06–0.08 inches) in length. Since there is no significant length difference between the long loop 114 and the short loop 118 (the sizing dimensions, as mentioned above as an example, are approximately 0.015–0.025 inches for the short loop and approximately 0.04–0.05 inches for the long loop), such a gap between the expanding bands leaves enough space for the ends of the proximal (short and long) loops 114 and 118 to be located within this region while the stent is in its delivery configuration.

[0077] Note that the configuration described above, shown in Figure 11, in which all of the ends of the proximal loop at the proximal end of the stent are included in the region between the two expanding bands 144 and 146, is described as being particularly useful in enhancing delivery force, which is beneficial for delivering DFT stents, which tend to be softer than conventional stents. Note that this same approach can also be used to deliver non-DFT stents in situations where enhanced delivery force would be beneficial. Therefore, this delivery configuration can be used with either DFT or non-DFT stents.

[0078] The above explanation often discusses the fact that DFT stents are less rigid than conventional stents. This is due to several properties of DFT, plus the absence of a separate radiopaque material (which tends to be hard and brittle), resulting in DFT stents being softer or less rigid than conventional stents. Softer / less rigid stents have some advantages in that they are flexible and can conform to curved regions. However, softer / less rigid stents also have lower retention strength, which can make it difficult to fully open or deploy them in certain situations, such as opening across bends in curved blood vessels where complex forces are applied to the stent. Furthermore, because the DFT wire cross-section also contains non-shape-memory components, DFT stents have less inherent shape memory than conventional stents, which can make it difficult to open the stent in some cases.

[0079] These complexities increase at the proximal end of the stent, which is the last region of the stent exposed / expanded during deployment from the delivery catheter. These complexities also increase for larger stents, requiring greater radial force and inherent shape memory for proper expansion. As mentioned above regarding flare angle, length, and shape, the design of long and short flares is important to help maximize adhesion to the vessel wall. The following discussion discloses methods for increasing opening strength in one or more regions of a DFT stent.

[0080] Figure 12 shows one embodiment of the DFT stent 150. Similar to the previous embodiment, the stent utilizes short loops 118 and long loops 114 at each end of the stent. One or more wires 152 are wound around it to form the stent shape. One or more regions of the stent 152 include reinforcing elements 154 to introduce increased strength and stiffness along the stent.

[0081] In braided stents, once the rest of the stent is deployed, it can be difficult to fully expand the proximal end of the stent. This is due to the high forces involved in stent deployment in the vascular system, which are more pronounced in more convoluted anatomical structures. This problem is even greater if the stent is designed to be low in rigidity and high in flexibility. Therefore, introducing reinforcing element 154 along the proximal region of the stent increases the opening force along this region, making deployment easier.

[0082] In one embodiment, the reinforcing element 154 comprises a coil, as shown in detail in Figure 13, which is wound around the DFT wire 152 of the stent. In other embodiments, the reinforcing element 154 may comprise a tube positioned on the DFT wire 152 along one or more regions of the stent. In one embodiment, the reinforcing element 154 is attached to the wire (e.g., by adhesive or welding) to fix its position. In another embodiment, the reinforcing element 154 is not attached and is free to move. In yet another embodiment, the reinforcing element 154 is another linear wire element attached to a portion of the DFT wire 152 to "thicken" the relevant DFT wire segment.

[0083] The reinforcing element 154 is, in one example, made of a strong shape memory material. A preferred example is nitinol (e.g., either a nitinol coil or a nitinol tube), but other examples may include cobalt-chromium or stainless steel.

[0084] If the reinforcing element 154 is a coil, as shown in Figure 13, this coil has a corresponding stiffness or a corresponding k-value. This stiffness / k-value depends on several attributes, including the composition of the material, the thickness of the coil, and the tightness of the windings of the reinforcing coil (i.e., pitch). A higher k-value can be achieved, for example, by using a relatively hard material (e.g., radiopaque materials such as gold, platinum, tungsten, palladium, tantalum, or hard, non-radiopaque metals), by using a tightly wound pitch for the coil, and / or by adjusting the coil properties (e.g., the thickness of the wires constituting the coil, the overall width of the coil, and the overall length of the coil reinforcing element 154).

[0085] The wire forming the reinforcing element 154 has corresponding "springiness" due to being wound spirally along the stent in the longitudinal direction, so the wire portion 152 beneath the reinforcing element 154 has its own associated k-value stiffness. Note that this "springiness" increases as the stent is compressed, helping to open the stent during deployment. The k-value of wire 152 depends on the associated stiffness of the DFT wire, the wire diameter, and the pitch of the wires constituting the DFT stent (i.e., the spiral / longitudinal winding pattern used to mechanically wind the stent).

[0086] The stent region shown in Figure 13, where the reinforcing coil 154 is located on the wire 152, can be considered as two parallel springs, and according to Hooke's Law, corresponding stiffnesses arise. If the wire 152 has a corresponding stiffness k1 and the reinforcing coil 154 has a corresponding stiffness k2, then the overall stiffness of this region becomes (k1 + k2), i.e., the combined stiffness is increased. In this way, the reinforcing element 154 plays a role in increasing the corresponding stiffness in that region. This increased stiffness has certain advantages, such as strengthening specific areas of the stent to increase deployment force (assisting stent opening) and promoting adhesion to the vessel wall along the strengthened portion.

[0087] Another advantage is that the increased stiffness and increased area occupied by the reinforcing element across the underlying wire helps adjacent cells of the stent open. If adjacent cells cannot open sufficiently, these cells come into contact with the reinforcing element (which has a higher surface area than the surrounding wire 152 below it), and this contact force can help these other cells open.

[0088] The reinforcing elements 154 can be positioned in one or more regions along the DFT stent. For example, to promote consistent expansion and consistently increased stiffness throughout the stent, the reinforcing elements can be positioned at approximately equidistant intervals (or at random locations) along the length of the stent. Alternatively, to increase the strength and opening of the proximal portion of the stent, the reinforcing elements can be positioned at one or more locations along the proximal portion of the stent, or only along the proximal portion of the stent (as shown in Figure 2).

[0089] The reinforcing element 154 can be added to the DFT wire of the stent in various ways. The following techniques can be used whether the DFT stent consists of only one DFT wire or multiple DFT wires. In one embodiment, the reinforcing element 154 is slid over each wire segment before or during the winding procedure used to wind the stent.

[0090] In another embodiment, the wire can be cut near the area where the reinforcing element 154 is added to the wire, and once the reinforcing element 154 is properly positioned, the wire is then soldered or welded to the other cut portion of the wire to reattach the two wire segments. This is shown in Figure 14, where the wire 152 comprises two segments 152a, 152b connected at position 156. The two wire segments 152a, 152b can also represent a location where one wire is cut into two segments and then reconnected, or they can represent a location where two separate wires are attached / connected near the reinforcing element 154. One advantage of placing this wire attachment location near the reinforcing element 154 is that it thickens the associated wire segments, thereby keeping the reinforcing element 154 in a specific position and preventing it from moving around.

[0091] In some examples, reinforcing elements 154 or an increased number of reinforcing elements 154 can be used in larger DFT stents (e.g., those with a size of approximately 4-4.5 mm or larger) because these stents are more difficult to fully open. In various configurations, reinforcing elements can be added to the proximal 1 / 3 of the stent by loading reinforcing elements 154 across two or more winding positions (as shown in Figure 12). In one example, the reinforcing element 154 is a nitinol coil with an inner diameter of approximately 0.003 inches and an outer diameter of approximately 0.0065 inches. When multiple reinforcing elements 154 are used, they can be arranged in various ways, for example, one turn of wire can separate two elements 154 (as shown in Figure 12), multiple turns of wire can separate two elements, or the elements 154 can be placed directly adjacent to each other in either of the adjacent windings.

[0092] Figure 15 shows in more detail the winding pattern of a DFT stent where one or more wires constituting the DFT stent are wound in an over-under pattern. This pattern forms multiple diamond-shaped cells along the length of the stent, as shown in Figures 12 and 15. The black wires reflect multiple turns of wire along a first direction (e.g., left to right along the mandrel), and the gray wires reflect multiple turns of wire along a second direction (e.g., right to left along the mandrel).

[0093] As shown in the figure, the wire windings are woven in an over-under pattern. In the context of Figure 15, wire winding element 164a is first wound over element 162a, then under the next element 162b, and then over the next element 162c, and so on. Some kind of over-under pattern is necessary to prevent the stent from fraying, but various embodiments may use different over-under patterns (for example, over one wire segment and under two wire segments, or vice versa, over one wire segment and under three wire segments, or vice versa, etc.).

[0094] As described above, there is a certain over-under pattern used to wrap the stent, so if the reinforcing element 154 used is long enough, the reinforcing element will also extend above and below a particular wire segment. For example, if the reinforcing element 154 is used along wire element 164b in Figure 15 and extends over the entire length of the illustrated wire element 164b, the reinforcing element will extend in an over-under pattern along with its associated wire 164b. Because of its larger size, the reinforcing element helps to increase the spacing between wire segments located above or below it, which increases the movement of the wire as the stent expands and further helps the stent take on its expanded shape when delivered from the catheter.

[0095] The above description referred to methods of attaching the reinforcing element 154 to either a wire or a float (meaning it is not connected to the associated wire area). Each design has its advantages. For example, by attaching the reinforcing element 154, the desired expansion characteristics can be limited to a specific segment of the stent. However, by not attaching the reinforcing element 154 (i.e., it can "float" or have some movement), the reinforcing element can make some or as needed slight movement adjustments, which can be beneficial during expansion when the stent is subjected to complex forces from various directions.

[0096] In Figure 12, the reinforcing element 154 is shown along a defined segment along one "face" of the stent, but the reinforcing element 154 can be longer or shorter as needed. Thus, longer reinforcing elements 154 may extend to multiple windings / picks / rotations of the wires constituting the DFT stent.

[0097] While the reinforcing element 154 and its associated advantages are discussed in relation to the DFT stent embodiment presented herein, the reinforcing element 154 can also be incorporated along more conventional (non-DFT) stents and has its own utility in adjusting stiffness along one or more parts of conventional stents. In other words, this idea can also be used in conjunction with other stent designs to incorporate these advantages into other stent designs.

[0098] As described in the embodiments presented to date, DFT stents can be used for a variety of purposes, such as keeping blood vessels open, diverting flow away from a target area like an aneurysm, or retaining an embolization within a target area. In one embodiment, the DFT stent is a coil-assisted stent that acts as a scaffold for holding embolization coils within a target treatment site, such as an aneurysm, in order to retain embolization material within the aneurysm treatment site. In one example, the pores of the DFT stent (diamond-shaped pattern in Figure 15) are made large enough to allow a microcatheter to pass through them, so that the DFT stent is first positioned adjacent to the aneurysm, and then the microcatheter is delivered into the aneurysm through the pores of the DFT stent, where then the embolization material is delivered into the aneurysm through the microcatheter to occlude the aneurysm. In one example, when the stent is in its expanded configuration, the pores are approximately 0.3–0.5 mm in size.

[0099] The above discussion included references to the short flare 118 and how, in some embodiments, the short flare is considered part of the stent's "working length." In these embodiments, the pore size of the short flare is similar to the pore size of the rest of the stent.

[0100] The PPI of a stent is generally calculated as the number of wire crossings or "picks" per inch along the length of the stent. The PPI of a stent depends on its intended use. For example, diversion stents have a relatively high PPI because a denser wire cross-section is needed to bypass blood flow from a target area (e.g., an aneurysm). On the other hand, coil-assisted stents, which help hold embolic material within a target area (e.g., an aneurysm), generally have a low PPI because these stents may need larger pores to provide more scaffolding and access to the embolic delivery catheter.

[0101] It should be understood that different embodiments of the embodiments described herein are interchangeable and can be combined with one another. That is, additional embodiments are also specifically conceived by combining different features from different embodiments. Therefore, although certain embodiments are shown in the figures, the present invention is not necessarily intended to be limited to these specific combinations.

[0102] While the present invention has been described in relation to specific embodiments and uses, those skilled in the art can, in light of this teaching, generate additional embodiments and modifications without departing from the spirit of the claimed invention or exceeding the scope of the claimed invention. Therefore, it should be understood that the drawings and description herein are provided as examples to facilitate understanding of the invention and should not be construed as limiting its scope.

Claims

1. A stent delivery system, A pusher including a pair of bands, A stent comprising a main body and a plurality of end loops, wherein the stent is adjustable between a collapsed configuration and an expanded configuration. The stent comprises a reinforcing element fixed along a portion of the length of the wire of the main body, The reinforcing element is wrapped around the wire of the main body of the stent. In the aforementioned collapsed configuration, the plurality of end loops of the stent are located between the pair of bands of the pusher in the stent delivery system.

2. The stent delivery system according to claim 1, wherein the pair of bands are arranged along the distal portion of the pusher.

3. The stent delivery system according to claim 1, wherein the pair of bands are radiopaque.

4. The stent delivery system according to claim 3, wherein the stent is made of a radiopaque material.

5. The stent delivery system according to claim 4, wherein the stent is composed of a single drawn-filled tube (DFT) wire.

6. The stent delivery system according to claim 1, wherein the plurality of terminal loops are located at the proximal end of the main body.

7. The stent delivery system according to claim 1, wherein the plurality of terminal loops are composed of a plurality of short loops and a plurality of long loops.

8. The stent delivery system according to claim 7, wherein each of the plurality of long loops includes a marker coil.

9. The stent delivery system according to claim 8, wherein in a proximal movement configuration, the distal band of the pair of bands engages with the marker coil to pull the stent back to the proximal side.

10. The stent delivery system according to claim 9, wherein in a distal movement configuration, the proximal band of the pair of bands engages with the plurality of long loops to advance the stent.

11. The stent delivery system according to claim 8, wherein each of the plurality of short loops includes a second marker coil.

12. The stent delivery system according to claim 11, wherein the second marker coil is located at or near the end of each of the plurality of short loops.

13. The stent delivery system according to claim 1, wherein the stent is composed of a DFT stent.

14. The stent delivery system according to claim 1, wherein the reinforcing element is composed of a coil wound around the wire of the main body of the stent.

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