Radiopacity vascular prosthesis

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]

[0001] (Related Applications) This application claims priority to, and is a nonprovisional application of, U.S. Provisional Application No. 62 / 768,803, entitled "Stent," filed November 16, 2018, which is hereby incorporated by reference in its entirety. [Background technology]

[0002] Vascular prostheses, such as stents and stent grafts, are used in the vascular system for a variety of reasons, a non-exhaustive list including: holding open diseased or blocked vessels to promote blood flow, flow diversion, including diverting flow away from a target area such as an aneurysm, and retaining material (e.g., embolic material) within a treatment site to promote localized occlusion in the area.

[0003] Visualization is important for vascular prostheses so that surgeons can confirm proper placement of the device in the vasculature. Traditional metal stents utilize good shape memory materials, such as Nitinol, which allow the stent to easily assume its expanded state upon delivery to the treatment site. Metal stents are heat set in an expanded shape so that the stent easily assumes this expanded shape when released from its compressed state in the delivery catheter. However, these metals are not radiopaque, making imaging difficult. One possible solution is to utilize radiopaque metal wires in making these stents, but in practice, such materials are often difficult to handle and can 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 so that the physician can determine proper placement of the device in the vasculature. These radiopaque components are distinct from the actual prosthesis itself (e.g., a separate radiopaque layer or component separately attached to the stent). The use of these separate radiopaque components can lead to complications as they thicken the stent, making it more difficult to deploy and affecting whether these stents can effectively treat smaller vessels, such as those present in the neurovasculature. 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 inner core and an outer jacket. DFTs can be constructed with radiopaque materials (e.g., a radiopaque inner core with a non-radiopaque outer jacket, or vice versa) to combine the advantages of good shape memory metal wires with the radiopacity / imaging advantages of radiopaque materials. These DFT wires can then be used to design vascular prostheses that do not require a separate radiopaque material. In this way, DFTs can be used for the metal layers that make up stents / stent grafts, allowing the device to be visualized without the inclusion of a separate radiopaque material. However, DFT wires have different mechanical properties than traditional metal wires, creating a different type of engineering challenge in creating a usable vascular prosthesis incorporating DFT wires.

[0006] What is needed is a usable DFT stent that combines the benefits of DFT imaging while addressing the unique design challenges posed by DFT wires. Summary of the Invention

[0007] The present invention relates to a vascular prosthesis comprised of one or more DFT wires, which offers advantages in imaging of the device.

[0008] In one embodiment, the vascular prosthesis consists of a single DFT wire braided back and forth within itself to form a generally tubular shape. In other embodiments, multiple DFT wires can be used. In one embodiment, the single or multiple 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 are sized and angled to allow snug contact with the vessel and resist movement at the implant location. In one embodiment, the longer loops utilize coils or marker coil elements to help the delivery pusher grip the prosthesis during prosthesis delivery. In one embodiment, the shorter loops are configured to overlap the longer loop coils when the DFT prosthesis is in its compressed delivery state.

[0010] The DFT prosthesis includes a plurality of pores along the vasculature of the prosthesis. The pores are formed by the intersection of one or more wires that make up the DFT prosthesis. In one embodiment, the pores are sized to allow placement of a microcatheter and / or embolic material therein to occlude a target treatment location (such as an aneurysm).

[0011] In one embodiment, a delivery system for a DFT prosthesis includes a pusher with two expansion bands and a recessed area therebetween. The DFT prosthesis includes a plurality of proximal end loops having a longer loop and a shorter loop, where the longer loop utilizes a coil or marker coil. The coil engages with the expansion band to form a thickened area for driving the stent during delivery. The shorter loop is sized and positioned to overlap a portion of the coil or marker coil when the DFT prosthesis is in its compressed delivery state, preventing the coil from being captured when the DFT prosthesis is introduced into and delivered from the delivery catheter, thereby allowing for a smoother delivery. In one embodiment, the pusher system is configured such that all of the ends of the shorter proximal end loop and the longer proximal end loop are contained within the recessed area 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 wound coil. In another embodiment, the reinforcing element is a tube. The reinforcing element increases stiffness along the relevant region of the stent and helps the stent open upon deployment. [Brief description of the drawings]

[0013] These and other aspects, features and advantages of which embodiments of the invention are possible will become apparent and elucidated from the following description of embodiments of the invention, which proceeds with reference to the accompanying drawings.

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

[0015] [Diagram 2] FIG. 2 illustrates a DFT stent, according to one embodiment.

[0016] [Diagram 3] FIG. 3 shows the mandrel used to wind the DFT stent.

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

[0018] [Diagram 5] FIG. 5 shows a loop wrapped around the enlarged end of the mandrel of FIG.

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

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

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

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

[0023] [Figure 10] FIG. 10 shows a marker coil used in the end loops of a DFT stent, according to one embodiment.

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

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

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

[0027] [Figure 15] FIG. 15 illustrates a DFT stent weave pattern, according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be complete and complete, and will fully convey the scope of the present invention to those skilled in the art. In that regard, the elements and functionality of one embodiment are not necessarily limited to that embodiment, but can be combined with other embodiments shown herein in any manner 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, including between different embodiments, like numbers refer to like elements.

[0029] The embodiments presented herein address the creation of vascular prostheses (e.g., stents or stent-grafts) with usable drawn-fill tubes (DFTs). DFTs are particularly advantageous in visualization when radiopaque materials are used to form the drawn-fill tubes, as described above. In some examples, these drawn-fill tubes can be used to create wire or filament elements with radiopaque inner components (e.g., platinum, gold, tantalum, palladium, or other similar materials) and metallic outer jackets / outer components (e.g., nitinol, stainless steel, cobalt chrome, or other shape memory materials).

[0030] In an embodiment of the present invention, DFT wire is used in the structural layers that define the stent, such that the stent is physically constructed from one or more DFT wires. In this way, since the stent itself is constructed from DFT wire, no separate radiopaque components are required with the stent, and therefore it can be easily visualized in-vivo. DFT wire presents challenges in use because it has different mechanical properties than metal (e.g., nitinol, stainless steel, cobalt chrome) wires traditionally used to make stents. Therefore, there are unique design challenges in making a usable DFT stent. An embodiment of the present invention addresses these issues by providing a unique design and configuration for making a usable DFT stent.

[0031] There are several issues specific to the use of DFT wire that must be considered when designing a DFT stent. One of the main advantages of using DFT wire 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 traditional stents, since no additional radiopaque components or layers are required for visualization. This has the advantage of allowing for easier deployment and allowing these stents to fit (and treat) smaller vessels, including those of the distal neurovasculature.

[0032] Despite these advantages, there are several design challenges in using DFT wire and fabricating DFT stents. First, because DFT wire is a composite of two different materials, it may not have the shape memory properties of a traditional shape memory metal (e.g., Nitinol) stent, meaning it may not have the same heat-set expansion properties as a traditional metal stent. Second, the inclusion of a radiopaque element or layer on a traditional metal stent generally increases the stiffness of the stent, which increases properties such as apposition and resistance to migration upon implantation. Because DFT stents do not require this additional radiopaque material for visualization, the resulting reduction in stiffness may affect apposition and migration.

[0033] Moreover, one surprising problem with using DFT wires is that when heat treated / heat set, these materials tend to soften more than pure metal shape memory wires. This is generally unexpected since the radiopaque core or inner material (depending on which specific material is used) can be stiffer compared to the metal shape memory outer jacket. However, using two different materials when creating a single wire can change the material properties of the combined wire shape. Due to these properties, when DFT wires are used in a stent, the mechanical properties of the stent must be tailored to provide sufficient strength to promote proper deployment of the DFT stent at the treatment site and to promote proper attachment of the DFT stent to prevent stent migration. The embodiments presented herein address these and other issues to create a usable DFT stent.

[0034] 1 shows a cross section of a DFT wire 100 utilizing a radiopaque inner wire component 102 and a metallic outer jacket 104. Elements that can be used for the radiopaque inner element are those discussed above and include platinum, gold, tantalum, or palladium. The metallic outer jacket material, also discussed above, preferably utilizes a strong shape memory material such as Nitinol (currently preferred as a particularly useful shape memory material), stainless steel, cobalt chrome, and the like.

[0035] The shape memory jacket allows for good shape memory properties to be imparted to the wire, useful for imparting the heat-formed expanded configuration of the stent, while the use of a radiopaque inner component allows for visualization. In some embodiments, this configuration can be reversed to utilize a radiopaque outer jacket and a non-radiopaque inner element. In other embodiments, three or more concentrically arranged radial wire elements can be used, including various combinations of shape memory metals and radiopaque components.

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

[0037] When heat set, an extended shape memory is imparted to the material via a heat treatment process. Either before or after the heat set process, one or more of the DFT wires are electropolished to make them smooth and facilitate implantation within the vasculature.

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

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

[0040] FIG. 2 illustrates a DFT stent 110, according to one embodiment. The stent 110 is comprised 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 comprised 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 long flares or loops 114 and short flares or loops 118. These flares or loops provide attachment to the vessel, help resist migration at the treatment site, and aid in the stent delivery process, as described below.

[0041] A stent is braided onto a mandrel such that one or more wires that make up the stent are braided onto the mandrel to form the stent shape. In one embodiment, the stent utilizes a single DFT wire 112, which is braided or woven back and forth onto the mandrel to form the shape shown in Figure 2. This involves wrapping from one end of the mandrel to the other in a particular direction (clockwise or counterclockwise) and longitudinally in an over-under pattern with other portions of the wrapped wire, continuing this process back and forth from one end of the stent to the other.

[0042] The single wire configuration has several advantages. For example, forces are better transmitted along a single wire than along multiple, connected or braided wires, since there are no attachments that can affect the transmission of forces. This is advantageous when pushing the stent through a delivery catheter, and also helps the stent to expand radially when it is released from the delivery catheter on which it is placed. This single wire configuration can also be advantageous when used with DFT stents, which, as mentioned above, tend to be softer and less rigid than typical metal stents. While this softness is beneficial for stents that conform to the shape of tortuous anatomical sites, they can also be difficult to deliver and attach, and thus the single wire can transmit and retain forces in a more efficient manner.

[0043] In another embodiment, the stent utilizes multiple DFT wires 112 (e.g., 2 or more, 4-48, 6-24, 12-24, to provide various examples). The multiple wires that make up the braid are welded or otherwise attached to one another (e.g., crimped or via a mechanical cap), with one wire attached to another at one or more locations along the stent or at the flared end regions of the stent.

[0044] The mandrel 120 used to wind the stent is shown in FIG. 3 and utilizes a cylindrical inner or "middle" section 122 around which the majority of the stent is wrapped, forming a cylindrical tubular shape that constitutes the majority of the stent. In one embodiment, this middle section 122 may utilize a number of pins around which the wire or wires that make up the stent are wrapped. In another embodiment, a number of protrusions, recesses, or laser cut guide components are utilized to guide the placement of the wire or wires as they are wound around the mandrel. In another embodiment, no pins are used and the user simply wraps the wires in a clockwise, counterclockwise, or mixed manner longitudinally and circumferentially around the mandrel.

[0045] Expansion mandrel sections 124a and 124b are at either end of this intermediate section 122. Each expansion mandrel section 124a, 124b utilizes its own tapered region 126a, 126b that is used to wind the flares or loops 114, 118 of the stent 110. Tapered region 126a (which is similar in configuration to region 126b) is shown in more detail in FIG. 4. Although it is shown as being flat in FIG. 4, in a true perspective view it would be shown as tapered such that the radially inner, more central portion protrudes outwardly relative to the radially outer, more peripheral portion. The flat shape as shown is merely for ease of illustration.

[0046] The tapered regions 126a, 128b include an inner pin 128 extending radially closer to 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 is wrapped around the inner pin 128 and the longer flare 114 is wrapped around the outer pin 130. In one illustrated example, the inner pin is lined up with the outer pin, meaning that the inner and outer pins share the same line or angle if a line is drawn from the pin to the center of the "flattened" tapered region 126a.

[0047] As shown in Figure 1, each shorter loop is immediately next to a longer loop, so that each loop is offset from the other. In practice, this means that the shorter loop 118 is wound on the inner pin 128, unwound on the other side of the mandrel, comes back and is wound on the next outer pin 130 to form a longer loop, wound on the mandrel, comes back and is wound on the next inner pin 128 to form a short loop, comes back and is wound on the next outer pin to form a long loop, and so on. This is shown in Figure 5, where the long loop is next to the short loop. In practice, this means that only one pin of each "pair" of pins (either the inner pin 128 or the outer pin 130) is used to wind either the short loop or the 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 and four long loops are created, with each loop offset by an equal distance amount (e.g., 45 degrees, whereby a short loop is offset 45 degrees from an adjacent long loop and vice versa). The pin "pairs" of the inner and outer pins are preferably equally spaced, so that in the context of Figure 4, each pin "pair" is spaced 45 degrees from an adjacent pin "pair," meaning that each loop is spaced 45 degrees from each other loop. To create a six-loop configuration of three short and three long loops, six pin "pairs" spaced 60 degrees from each other are used on the tapered regions 126a, 126b.

[0049] As discussed above, a tapered portion of the mandrel is used to form a flare. In one example, this taper is about 50 degrees to 60 degrees, and in a more specific example, about 60 degrees. With respect to tapered portion 126b, this angle represents the angle between tapered portion 126b and a horizontal line drawn to the right of the tapered portion (e.g., a horizontal line drawn through the center of enlarged mandrel 124b). This angle represents the approximate angle of the plane defined by stent loops 114, 118, or in other words, the degree of bend angle defined by the stent loops. Thus, the short and long loops are tapered at about 50 to 60 degrees, or in a more specific example, about 60 degrees. Different dimensions may be utilized in different embodiments. However, this angle may have particular utility in allowing the short loops in a particular sized profile to contact the vessel wall without collapsing, thereby promoting proper attachment to the vessel and providing a firm anchor point within the vessel. That is, the 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 in more detail the configuration of the flare or loops at the end of the stent. Figures 6-9 show a linear type flare with the configuration shown for ease of illustration. These figures can be thought of as representing the circumferential area formed by the stent end if the flare were to be laid flat along one plane after one cut had been made. Each long loop 114 is adjacent to a short loop 118 such that the long loop 114 has a short loop 118 on either side of it, while the short loop 118 has a long loop 114 on either side of it.

[0051] Figures 6 and 8 show a 6-loop configuration, where each end of the stent has three alternating long and three short loops, and Figures 7 and 9 show an 8-loop configuration, where each end of the stent has four alternating long and four short loops.

[0052] In Figures 5 and 6, in one embodiment of the flare / loop configuration, the loops / flares are positioned substantially adjacent 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 as the wires making up the loops contact adjacent wires / loops during stent expansion, resulting in an overlapped configuration. Note that different numbers of flares / loops are possible. For example, each end of the stent may have 4 to 24 loops.

[0053] The short flare 118 is preferably sized similarly 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 provides support without collapsing as a result of oversizing relative to the vessel diameter.

[0054] As mentioned above, since DFT wires are generally softer than shape memory metal wires, the short flares 118 are carefully tailored to promote adhesion in the 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 they do not compress downward (e.g., if oversized by a significant amount compared to the vessel size).

[0055] As mentioned above, the long flare 114 and the short flare 118 can each be oriented at an angle of about 60 degrees (relative to a horizontal plane extending through the axial / radial midsection of the stent). The size of the flare / loop can also vary depending on the size of the stent. In various examples, the stent is sized at about 2.5-5 mm in diameter. This particular size fits into neurovascular arteries that are smaller than the arteries that make up the majority of the vasculature and has the advantage as a scaffold stent used to support against the neck region of the aneurysm for subsequent devices (e.g., embolic coils or other occluding agents) used to fill the aneurysm. Proper attachment of the stent is important in this targeted treatment regimen to ensure that the stent does not migrate from the aneurysm site, which allows embolic material to migrate if it becomes dislodged without a supporting scaffold.

[0056] In some instances, a stent having a fully expanded / deployed width of about 0.1 inches (about 2.5-3 mm) has a short flare 118 of about 0.015-0.025 inches and a long flare 114 of about 0.04-0.05 inches. A stent having a fully expanded / deployed width of about 0.12 inches (about 3-3.5 mm) has a short flare of about 0.015-0.025 inches and a long flare of about 0.04-0.05 inches. A stent having a fully expanded / deployed width of about 0.14 inches (about 3.5-4 mm) has a short flare of about 0.015-0.025 inches and a long flare of about 0.04-0.05 inches. A stent having a fully expanded / deployed width of about 0.162 inches (about 4 to 4.5 mm) will have a short flare measuring about 0.015 to 0.025 inches and a long flare measuring about 0.04 to 0.05.

[0057] It should be noted that the fully expanded / deployed width of the stent represents the outer diameter of the tubular portion of the stent (i.e., not including the flared end), and the flare length represents the length of the flare extending from this tubular portion. Furthermore, it should be noted that the relatively consistent sizing of the short and long flares, regardless of the size of the stent, i.e., relatively small compared to the overall stent diameter, ensures that the stent maintains adequate contact with the vessel wall to support attachment (via the short flare 118 intended to be in 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 a smoother delivery since the loops do not significantly hang over the stent, resulting in less contact friction against the catheter. The length of the stent may vary based on the size and intended use (e.g., the size of the treatment area, such as the aneurysm being treated). In some instances, the overall length of the stent can range from about 0.27 inches (about 7 millimeters) to about 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. Note that in the above range, the long loops 114 are not excessively large compared to the short loops 118, which are not excessively large compared to other portions of the stent. Thus, in some embodiments, the working length of the stent can also include the portion of the stent that includes the short loops 118, thereby increasing the percentage of the stent available to perform the procedure. By way of example, the above short loop 118 size range would add approximately 1 mm overall to the "working length" of the stent. If the stent length is 7 mm (representing the lower end of the given range), this 1 mm increase can be significant. Even if the stent length is 18.55 mm (representing the upper end of the given range), this 1 mm is still relatively significant.

[0059] The above discussion discusses some of the softness characteristics of DFT stents, some of which are due to the lack of radiopaque components added to the stent (e.g., either radiopaque wire wrapped around the stent, separate radiopaque layers, or radiopaque elements added to select portions of the stent) and the tendency for inclusion of these layers to increase the associated stiffness in conventional stents, as well as observable phenomena involving the metal processing and heat treatment of the DFT wire.

[0060] Due to this increased softness, delivery of the DFT stent may require more force to track the DFT stent through the overlying delivery catheter. The above discussion discusses the sizing of short flare 118 and long flare 114 and how they are sized relatively similarly such that long flare 114 is not significantly longer than short flare 118. One additional advantage of this design is that short flare 118 and long flare 114 are located relatively close together when the stent is in a collapsed, deployed state when delivered through an overlying catheter.

[0061] FIG. 10 shows the configuration of the longer flare 114 in more detail. The longer flare 114 includes a wound marker coil 132 that wraps around the structural DFT wire that makes up the stent. The shorter flare 118 can optionally include a marker coil 132 as well. The marker coil 132 can be a wound tantalum, platinum, palladium or gold wire that is wound around the structural DFT wire of the stent. The one or more marker coils 132 on the longer flare 118 are not necessarily used for visualization purposes, since the entire stent is radiopaque (although enhanced radiopacity may help visualize both ends of the stent in more detail). Here, they are used to help grip the stent during delivery, as described below.

[0062] The use of a radiopaque marker coil 132 at the flare of the stent provides various advantages. While the stent itself is constructed from DFT wire and is therefore radiopaque, the inclusion of the marker coil 132 along the flare aids in visualizing the ends of the stent. In this manner, the ends of the stent can be made prominent and the physician or operator can determine the location of the stent ends relative to the target area to confirm placement. This is particularly useful in situations where a particular facility utilizes relatively poor imaging technology, as it provides greater visibility at least to the ends of the stent.

[0063] The use of coils 132 as elements has some advantages for DFT wires, given their flexibility, since a wrapped coil typically exerts less force on the underlying wire. Nevertheless, in some embodiments, the marker elements 132 can take the form of a tube compressed over the loop. This can make sense if the DFT wire is particularly thick, or if the overall diameter of the DFT stent is smaller so that there is more strength built into the DFT stent.

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

[0065] As described below, the marker coil element 132 is particularly advantageous in increasing the thickness of the loop portion and helping to engage the stent during the delivery process. In this manner, the marker coil 132 also functions as a strut thickening element. In these ways, the marker coil 132 can also be considered a non-radiopaque coil, a radiopaque or non-radiopaque tube, and / or a thickening / reinforcing / expansion member 132 for increasing the strut thickness of a portion of the loop portion of a DFT stent. That is, in various embodiments, any of these terms can be used to describe the element 132.

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

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

[0068] When the stent is restrained within the delivery catheter, the collapsed configuration of the stent is shown in FIG. 11, particularly showing 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 a user can push or pull to manipulate the stent connected to the pusher 142 out through the catheter 140. The pusher 142 includes a pair of expansion bands 144, 146 along a distal portion of the pusher 142. In one embodiment, the expansion bands 144, 146 are radiopaque (e.g., tantalum, gold, platinum, or palladium) to aid in visualization during delivery, and thus function as marker bands. In some situations (e.g., based on stent sizing or imaging technique), the inclusion of a very large amount of radiopaque material (recall that the entire stent is radiopaque with DFT wire) can make visualization more difficult as there is little to see apart. Thus, in some embodiments, the expansion bands 144, 146 are non-radiopaque (eg, nitinol or stainless steel).

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

[0070] It should be noted that various stent embodiments, as discussed above, have various combinations of short and long loops, and for ease of illustration, two short and two long loops are shown, but this is meant to represent that all proximal loops (both long and short) are constrained within this enlarged pusher band region. That is, if a stent configuration utilizes six proximal loops (three short, three long), all six of these proximal loops will be located within this region / space defined between the two enlarged bands 144, 146. Similarly, if a stent configuration utilizes eight proximal loops (four short, four long), all eight of these proximal loops will be located within this region, etc.

[0071] The marker coil 132 on the long loop serves an important function as it helps keep the loop constrained in this region and also ensures that the enlarged bands 144, 146 can engage the stent. The marker coil 132 on the loop (note that each loop can utilize two marker coils 132, but the marker coils 132 on the loop are only shown along a portion of the long loop) provides an enlarged contact surface to aid in engagement with the stent. In one embodiment (shown in FIG. 11), the proximal band 144 engages the end of the longer flare 114 to move the stent forward, and the distal band 146 engages the marker coil 132 to pull the stent back proximally. In the context of FIG. 11, pushing the stent forward involves moving the stent toward the left, with the proximal band 144 engaging the end of the long loop 114. Pulling the stent back involves moving the stent to the right, with the distal band 146 engaging the marker coil 132 to engage 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 of the proximal loops are located within the region between the enlarged pusher bands 144, 146 provides multiple advantages. For example, because all of the loops / marker coils are located within this region, each expansion band is more likely to come into contact with one or more marker coils, thereby providing a higher pushing force as each expansion band engages with a marker coil to drive the movement of the stent. The increased pushing force has advantages that aid in delivering the stent, especially considering the material properties of the DFT stent discussed above. Additionally, the stacked configuration (with all of the looped ends within this region) also provides a backup system in the event one of the stent loops becomes disengaged relative to the pusher 142, so that each enlarged pusher band 144 or 146 can still contact one of the other proximal loops / marker coils to engage the stent.

[0073] 11, it should be noted that since the short loop 118 is shorter than the long loop 114, the short loop 118 will always be 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 (e.g., the marker coil can be located relatively close to the "end" of the short loop) such that the expansion band 146 can engage the marker coil 132 of the short loop 118 to engage the stent. In this manner, the distal expansion band 146 can engage the marker coil 132 of only the short loop 118, only the marker coil 132 of the long loop 114, or the marker coils 132 of both the short loop 118 and the long loop 114.

[0074] A stacked configuration in which all of the loops are contained within the area defined between the pusher bands 144, 146 has additional advantages. For example, in many configurations, the pusher bands engage the marker coils 132 of the longer loops 114 because these loops 114 are larger (i.e., have a larger surface area and extend a greater distance) than the shorter loops 118. The stacked configuration ensures that the marker coils 132 along the longer loops 114 are partially protected by the shorter loops 118, thereby reducing the likelihood that the marker coils 132 will get caught on the delivery catheter during placement from the introducer device into the catheter or during delivery from the catheter into the blood vessel. In the context of FIG. 11, this protection is provided by the short loops 118 actually being positioned over or around the marker coils 132 of the longer loops to protect them.

[0075] Another configuration utilizes an arrangement in which the ends of the proximal loops are all stacked or restrained within the area defined between the pusher bands 144, 146, but instead of engaging the ends of the long loops 114, the proximal band 144 engages the marker coil 132 to drive the stent forward. In this configuration, the position of the long loops 114 differs from that shown in FIG. 11, instead a portion of the long loops 114 hangs slightly over the expansion bands 144, 146, and the proximal band 144 engages the marker coil 132 to drive the stent, rather than the ends of the long loops 144. In some embodiments, the short loops 118 may also utilize marker coils 132, which may be configured such that the expansion band 144 also contacts these marker coils.

[0076] By way of example, the space or spacing between bands 144, 146 (see FIG. 11) is approximately 1.5-2 mm (approximately 0.06 to 0.08 inches) in length. Because there is no significant difference in length between long loops 114 and short loops 118 (the sizing dimensions are, by way of example only, approximately 0.015-0.025 inches for the short loops and approximately 0.04-0.05 inches for the long loops), such spacing between the expansion bands leaves sufficient room for all of the ends of the proximal (short and long) loops 114, 118 to be located within this region while the stent is in the delivery configuration.

[0077] It should be noted that the configuration shown in FIG. 11 and described above with respect to how all of the ends of the proximal loops at the proximal end of the stent are contained in the area between the two expansion bands 144, 146 has been described as being particularly useful in enhancing delivery forces that are beneficial for delivering DFT stents, which tend to be softer than conventional stents. It should be noted that this same approach can also be used to deliver non-DFT stents in situations where an enhanced delivery force would be beneficial. Thus, this delivery configuration can be used with either DFT or non-DFT stents.

[0078] The above discussion often discusses that DFT stents are less stiff than conventional stents. This is due to some properties of DFT, as well as the lack of a separate radiopaque material (which tends to be hard and brittle), which makes the resulting DFT stent softer or less stiff than a conventional stent. Softer / less stiff stents have some advantages in that they are flexible and can conform to tortuous areas. However, softer / less stiff stents also have lower retention strength and may be difficult to fully open or deploy in certain situations, such as opening across bends in a tortuous vessel where there are complex forces applied to the stent. Furthermore, DFT wire cross sections also contain non-shape memory components, which makes DFT stents less inherently shape memory than conventional stents, making the stent more difficult to open in some cases.

[0079] These complications are compounded at the proximal end of the stent, which is the last region of the stent to be exposed / expanded upon deployment from the delivery catheter. These complications also increase for larger stents, which require greater radial force and inherent shape memory to properly expand. As discussed above with respect to flare angle, length and shape, the design of long and short flares is important to help maximize attachment to the vessel wall. The following discussion discloses methods of increasing the opening strength in one or more regions of a DFT stent.

[0080] 12 illustrates one embodiment of a DFT stent 150. As with 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 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] With braided stents, it can be difficult to fully expand the proximal end of the stent once the remainder of the stent has been deployed. This is due to the high forces associated with stent deployment in the vasculature, which is more pronounced in more tortuous anatomical structures. This problem is exacerbated when the stent is designed to be less stiff and more flexible. Thus, introducing a reinforcing element 154 along the proximal region of the stent increases the opening force along this region, making deployment easier.

[0082] The reinforcing element 154, in one embodiment, comprises a coil, as shown in detail in FIG. 13, which is wound around the DFT wire 152 of the stent. In other embodiments, the reinforcing element 154 may comprise a tube disposed on the DFT wire 152 along one or more regions of the stent. In one embodiment, the reinforcing element 154 is attached (e.g., by adhesive or welding) to the wire to fix its position. In another embodiment, the reinforcing element 154 is unattached and free to move. In another embodiment, the reinforcing element 154 is a separate linear wire element that is attached to a portion of the DFT wire 152 to "thicken" the associated DFT wire segment.

[0083] The reinforcing element 154, in one example, is made of a strong shape memory material. A preferred example is Nitinol (e.g., either a Nitinol coil or Nitinol tubing), although other examples may include Cobalt Chrome or Stainless Steel.

[0084] When the reinforcing element 154 is a coil, as shown in FIG. 13, the coil has an associated stiffness or k-value associated with it. This stiffness / k-value depends on several attributes including the material composition, the thickness of the coil, and the closeness of the turns (i.e., pitch) of the reinforcing coil. Higher k-values ​​can be achieved, for example, by using a relatively stiff material (e.g., a radiopaque material such as gold, platinum, tungsten, palladium, tantalum, or a hard non-radiopaque metal), using a tightly wound pitch in the coil, and / or adjusting the coil properties (e.g., the thickness of the wire comprising the coil, the overall width of the coil, and the overall length of the coil reinforcing element 154).

[0085] The wire portion 152 underlying the reinforcing element 154 has its own associated k-value stiffness since the wire forming the reinforcing element 154 has a corresponding "springiness" due to being wound helically longitudinally along the stent. Note that this "springiness" increases as the stent is compressed and helps open the stent during deployment. The k-value of the wire 152 depends on the associated stiffness of the DFT wire, the diameter of the wire, and the pitch of the wires that make up the DFT stent (i.e., the helical / longitudinal winding pattern used to mechanically wind the stent).

[0086] The region of the stent shown in FIG. 13 where the reinforcing coil 154 is located on the wire 152 can be thought of as two parallel springs, with corresponding stiffnesses resulting from Hooke's Law. If the wire 152 has an associated stiffness k1 and the reinforcing coil 154 has an associated stiffness k2, then the overall stiffness of this region will be (k1+k2), i.e., the combined stiffness will be high. In this manner, the reinforcing element 154 serves to increase the associated stiffness in that region. This increased stiffness has certain benefits, such as reinforcing certain regions of the stent to increase deployment forces (aiding in stent opening) and promoting attachment to the vessel wall along the reinforced sections.

[0087] Another advantage is that the increased stiffness and increased area that the reinforcing elements occupy over the underlying wires helps adjacent cells of the stent to open: if adjacent cells cannot fully open, they will come into contact with the reinforcing elements (which have a higher surface area than the surrounding underlying wires 152) and this contact force can help these other cells open.

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

[0089] The reinforcing element 154 can be added to the DFT wires of the stent in a variety of ways. The following technique can be used whether the DFT stent is made up of only one DFT wire or multiple DFT wires. In one embodiment, the reinforcing element 154 is slid onto 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 will be 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 FIG. 14, where a wire 152 comprises two segments 152a, 152b connected at location 156. The two wire segments 152a, 152b could represent a location where a length of wire is cut into two segments and then reconnected, or it could represent a location where two separate wires are attached / connected near the reinforcing element 154. One advantage of locating this wire attachment location near the reinforcing element 154 is that it thickens the associated wire segment, which helps to maintain the reinforcing element 154 in a particular position and prevents it from moving around.

[0091] In some instances, the reinforcing element 154 or an increased number of reinforcing elements 154 can be used in larger DFT stents (e.g., those sized at about 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 third of the stent by loading the reinforcing element 154 over two (as shown in FIG. 12) or more winding positions. In one example, the reinforcing element 154 is a Nitinol coil having an inner diameter of about 0.003 inches and an outer diameter of about 0.0065 inches. When multiple reinforcing elements 154 are used, they can be positioned in various ways, for example, one turn of wire can separate the two elements 154 (as shown in FIG. 12), multiple turns of wire can separate the two elements, or the elements 154 can be positioned directly adjacent to each other in any of the adjacent turns.

[0092] Figure 15 shows in more detail the winding pattern of the DFT stent, where one or more of the wires that make up 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 windings of the wire along a first direction (e.g., left to right along the mandrel) and the gray wires reflect multiple windings of the wire along a second direction (e.g., right to left along the mandrel).

[0093] As shown, the wire windings are woven in an over-under pattern. In the context of FIG. 15, wire winding element 164a is first wound over element 162a, then under the next element 162b, then over the next element 162c, etc. While some type of over-under pattern is necessary to prevent fraying of the stent, various embodiments can use different over-under patterns (e.g., 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 mentioned above, there is a certain over-under pattern that is used to wind the stent, so that if the reinforcing element 154 used is long enough, the reinforcing element will also go over and under a particular wire segment. For example, if a reinforcing element 154 is used along wire element 164b in FIG. 15 and extends the entire length of the illustrated wire element 164b, the reinforcing element will go in an over-under pattern with its associated wire 164b. Because of its larger size, the reinforcing element helps to increase the spacing between the overlying or underlying wire segments, which increases the movement of the wires as the stent expands, and also helps the stent assume its expanded shape when delivered from the catheter.

[0095] The above discussion has referred to having the reinforcing element 154 either attached to a wire or float (meaning not connected to the associated wire region). Each design has its advantages. For example, by having the reinforcing element 154 attached, the desired expansion characteristics can be limited to a particular segment of the stent. However, by not having the reinforcing element 154 attached (i.e., it can "float" or have some movement), the reinforcing element can have some degree of movement adjustment, or slight movement adjustment if desired, which can be beneficial during expansion where the stent is exposed to complex forces from various directions.

[0096] 12 along a defined segment along one "plane" of the stent, the reinforcing elements 154 can be longer or shorter as desired. Thus, a longer reinforcing element 154 can span multiple windings / picks / turns of the wire that makes up the DFT stent.

[0097] Although the reinforcing element 154 and its associated advantages are discussed with respect to the DFT stent embodiments presented herein, the reinforcing element 154 may also be incorporated along more conventional (non-DFT) stents and has its own utility in adjusting stiffness along one or more portions of a conventional stent, i.e., this idea may also be used in conjunction with other stent designs to incorporate these advantages into other stent designs.

[0098] As described in the embodiments presented thus far, the DFT stent can be used for a variety of purposes (e.g., to keep a blood vessel open, to divert flow away from a target area such as an aneurysm, or to retain an embolus within a target area). In one embodiment, the DFT stent is a coil-assisted stent that acts as a scaffold to retain an embolic coil within a target treatment site, such as an aneurysm, to retain embolic material within the aneurysm treatment site. In one example, the pores of the DFT stent (diamond-shaped pattern in FIG. 15) are sized to allow a microcatheter to pass through it, such that the DFT stent is first positioned adjacent to the aneurysm, and then the microcatheter is delivered through the pores of the DFT stent into the aneurysm, where embolic material is then delivered through the microcatheter into the aneurysm to occlude the aneurysm. In one example, the pores are approximately 0.3-0.5 mm in size when the stent is in its expanded configuration.

[0099] The above discussion included reference to the short flare 118 and how, in some embodiments, the short flare is considered part of the "working length" of the stent. In these embodiments, the pore size of the short flare is similar to the pore size of the remainder 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, diverting stents have a relatively large PPI because a denser wire cross section is needed to divert blood flow away from the target area (e.g., aneurysm). On the other hand, coil-assisted stents, which help retain embolic material within the target area (e.g., aneurysm), generally have a lower PPI because these stents perform more of a scaffolding function and larger pores may be needed to provide access for the embolic delivery catheter.

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

[0102] Although the present invention has been described with respect to specific embodiments and applications, those skilled in the art may, in light of this teaching, generate additional embodiments and modifications without departing from the spirit or beyond the scope of the claimed invention. It is therefore to be understood that the drawings and descriptions herein are provided by way of example to facilitate understanding of the invention and should not be construed as limiting its scope.

Claims

1. 1. A stent delivery system comprising: a pusher including a pair of bands; a stent including a body portion and a plurality of end loops, the stent being adjustable between a collapsed configuration and an expanded configuration; A stent delivery system, wherein in the collapsed configuration, the plurality of terminal loops of the stent are positioned between the pair of bands of the pusher.

2. The stent delivery system of claim 1 , wherein the pair of bands are disposed along a distal portion of the pusher.

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

4. The stent delivery system of claim 3 , wherein the stent is constructed from a radiopaque material.

5. The stent delivery system of claim 4 , wherein the stent is constructed from a single drawn filled tube (DFT) wire.

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

7. The stent delivery system of claim 1 , wherein the plurality of terminal loops comprises a plurality of short loops and a plurality of long loops.

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

9. The stent delivery system of claim 8 , wherein in a proximal movement configuration, a distal band of the pair of bands engages the marker coil to retract the stent proximally.

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

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

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

13. The stent delivery system of claim 1 , wherein the stent comprises a DFT stent.

14. The stent delivery system of claim 1 further comprising a reinforcing element attached to the body portion of the stent.

15. The stent delivery system of claim 14 , wherein the reinforcing element is comprised of a coil wound around a DFT wire of the body portion of the stent.

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