Patent Description:
Self-expanding medical prostheses, frequently referred to as stents, are well known and commercially available. Devices of these types are used within body vessels for a variety of medical applications. Examples include intravascular stents for treating stenosis, stents for maintaining openings in the urinary, biliary, esophageal and renal tracts, and vena cava filters to capture emboli. Further, stents in blood vessels on which aneurysms are developing are currently well known and widely applied. Particularly fine-meshed stents are usually produced as braided stents, which are used, for example, as flow diverters.

Self-expanding stents are formed from a number of resilient filaments which are helically wound and interwoven in a braided configuration. These stents assume a substantially tubular form in their unloaded or expanded state when they are not subjected to external forces. When subjected to inwardly directed radial forces, these stents are forced into a reduced-radius and extended-length loaded or compressed state. A delivery device which retains the stent in its compressed state is used to deliver the stent to a treatment site through vessels in the body. The flexible nature and reduced radius of the compressed stent enables it to be delivered through relatively small and curved vessels. After the stent is positioned at the treatment site, the delivery device is actuated to release the stent, thereby allowing the stent to self-expand within the body vessel. The delivery device is then detached from the stent and removed from the patient. The stent remains in the vessel at the treatment site.

However, there remains a significant problem during placement of stents and during subsequent examination of patients: because of their small size, these stents are extremely difficult to locate with X-ray. The only parts of the stent that appear on imaging are those with sufficient radiopacity, and the mass and thickness of these radiopaque parts decrease with the diameter of the vessels being treated. Accurate placement of the stent is critical to its effective performance. Accordingly, there is a need to visually perceive the stent as it is being placed within a blood vessel or other body cavity. Further, it is advantageous to visually locate and inspect a previously deployed stent. Typically, enhancing the radiopacity of a stent is accomplished by sacrificing other desired mechanical properties, such as strength, ductility, fatigue failure resistance, size, and the like.

<CIT> discloses an implantable braid comprising first filaments formed out of a radiopaque material, second filaments formed out of a support material, and third filaments formed out of a radiopaque material, the first, second and third filaments being braided together.

<CIT> discloses a stent including a sidewall and a plurality of pores in the sidewall that are sized to inhibit flow of blood through the sidewall into an aneurysm to a degree sufficient to lead to thrombosis and healing of the aneurysm when the tubular member is positioned in a blood vessel and adjacent to the aneurysm.

<CIT> discloses an expandable vascular device including a generally tubular sidewall formed of a plurality of braided strands.

It is an object of the present invention to provide a stent with substantially enhanced radiopacity, without any substantial reduction in the favorable mechanical properties of the stent.

The present invention is directed to an implantable braid according to claim <NUM>.

Other and further aspects and features of the disclosed embodiments will become apparent from the ensuing detailed description in view of the accompanying drawings.

The foregoing and other aspects of embodiments are described in further detail with reference to the accompanying drawings, wherein like reference numerals refer to like elements and the description for like elements shall be applicable for all described embodiments wherever relevant, and in which:.

The present invention relates generally to implantable, radially expandable stents having unique braid patterns that enhance the radiopacity of the stent without negatively impacting the mechanical properties of the stent. The stent may be a flow-diverting stent used in treating aneurysms or may be used in other endoluminal applications such as in treating stenosis, maintaining openings, or the like. The unique braid pattern provides enhanced radiopacity while maintaining, or improving, the mechanical properties of the tubular stent, compared to existing stents formed of the same or similar materials. As such, the unique radiopaque patterns of the disclosed device provide additional information to physicians, since physicians can more easily determine length, compaction, diameter reduction, and the like.

Braided stents of the same material, size, quantity of filaments, and size of filaments will create different patterns under X-ray depending on the wire pattern placement on a braider machine. Certain braid patterns result in superior edge definition while maintaining a highly visible cross-hatching pattern. It has been found that unique placement of platinum and drawn filled tube (DFT) radiopaque wires in a braid configuration will create distinct segmented patterns under angiography. A specific alternating pattern of platinum wire, DFT wire, and support wire creates a hybrid braid of enhanced radiopacity without compromising radial pressure or stent performance characteristics, such as opening and apposition.

The stents shown in <FIG> are all made of the same quantity, size, and type of filaments, but have different arrangements of the filaments. The stents are substantially tubular bodies formed by braiding filaments, according to any technique known in the art of braiding tubular bodies. As seen in <FIG>, <FIG>, <FIG>, and <FIG>, the arrangement of the wires in the braid has a substantial effect on the level of detail that can be seen in the imaging, both in the smaller diameter stent (shown in the top portion of <FIG>, <FIG>, <FIG>, and <FIG>) and the larger diameter stent (shown in the bottom portion of <FIG>, <FIG>, <FIG>, and <FIG>). <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> each depict a cross-sectional view of an arrangement of filaments, as viewed from the front of a braider, before braiding begins. The properties of the resulting tubular metallic braid are highly dependent on the starting filament arrangements shown in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>.

The stent shown in <FIG> is a conventional stent <NUM> formed of a plurality of filaments braided together. The plurality of filaments includes a first material <NUM> and a second material <NUM>. As shown in the cross-sectional view of <FIG>, in the starting filament arrangement, the filaments of the second material <NUM> are directly adjacent to the filaments of the first material <NUM> on both sides of the filaments of the first material <NUM>. Cross-hatching and edge patterns do not show up in the imaging, as shown in <FIG>. The edges of the stent <NUM> shown in <FIG> appear as solid lines. In contrast, cross-hatching and edge patterns are more visible in the stent images shown in <FIG>, <FIG>, and <FIG>. In particular, with reference to <FIG>, the edges of the stent appear as alternating areas of light and dark, rather than a solid line.

The stents in <FIG> are formed of the same materials as the stent <NUM> shown in <FIG>. That is, the stents in <FIG> include filaments of the first material <NUM> and filaments of the second material <NUM>, both of which are the same as the first and second materials <NUM>, <NUM> used in the stent <NUM> in <FIG>. However, the stents in <FIG> further include filaments formed of a third material <NUM>, which is a combination of the first material <NUM> and the second material <NUM>. The third material <NUM> is drawn filled tube (DFT) wires that have a core made of the first material <NUM> or the second material <NUM>, covered with a sheath made of the other of the first material <NUM> and the second material <NUM>.

In one exemplary embodiment, the first material <NUM> is a radiopaque material, the second material <NUM> is a monofilament made of a support material that has a higher tensile strength than the radiopaque material, and the third material <NUM> is a DFT wire having a core made of a radiopaque material and a sheath made of a support material. Alternatively, the DFT wire may have a core made of the support material and a sheath made of the radiopaque material. The radiopaque material may be platinum, gold, palladium, tungsten, or the like, or an alloy made of two or more of these materials. The support material has a higher tensile strength than the radiopaque material and may be a cobalt chromium (CoCr) alloy, or the like. Other materials that can be used for a support material include (without limitation) L605, Molybdenum, Titanium, or any relatively high-tensile strength alloy of radiopaque material like platinum. The radiopaque and support materials of the DFT wire may the same as those of the first material and the second material, or may be different radiopaque and support materials. One of ordinary skill in the art would readily understand that the braid filaments can be made of any suitable material which is biocompatible and can be worked into a braid.

The stent <NUM> shown in <FIG> has a starting filament arrangement as shown in <FIG>. Before braiding begins, the filaments are arranged on the braider such that a single filament of the third material <NUM> is on either side of a single filament of the first material <NUM>. Directly adjacent to the other side of the filament of the third material <NUM> is a filament of the second material <NUM>. The pattern of: second material <NUM>, third material <NUM>, first material <NUM>, third material <NUM>, and second material <NUM> is repeated around the stent <NUM>. This is called the "hybrid 8x" configuration. As shown in <FIG>, the hybrid 8x braid pattern provides better visibility of the details of the braid, as compared to the stent shown in <FIG>. That is, a cross-hatching pattern is more visible in the stent <NUM> with the hybrid 8x braid pattern than with the conventional stent <NUM> shown in <FIG>.

In another embodiment, a stent <NUM> includes filaments braided together where the filaments are arranged in the pattern shown in <FIG> before braiding begins. The starting filament arrangement has a group of filaments of the first material <NUM> and a group of filaments of the third material <NUM> positioned directly adjacent to each side of the group of filaments of the first material <NUM>. On the other side of the group of filaments of the third material <NUM> is a group of filaments of the second material <NUM>. In this example, there are two filaments in each group of filaments. However, it should be readily understood that each group may include three or more filaments. The pattern of: two filaments of the second material <NUM>, two filaments of the third material <NUM>, two filaments of the first material <NUM>, two filaments of the third material <NUM>, and two filaments of the second material <NUM> is repeated around the stent <NUM>. This pattern is called the "hybrid double 4x" configuration. As shown in <FIG>, the hybrid double 4x pattern results in better visibility of the cross-hatch pattern and slightly better edge definition, as compared to the stents in <FIG> and <FIG>.

In yet another embodiment, a stent <NUM> includes filaments braided together where the filaments are arranged in the pattern shown in <FIG> before braiding begins. The starting filament arrangement is similar to that shown in <FIG>, except that the third material <NUM> and second material <NUM> are switched. That is, both sides of a group of filaments of the first material <NUM> are placed directly adjacent to a group of filaments of the second material <NUM>. A group of filaments of the third material <NUM> is placed directly adjacent to the other side of the group of filaments of the second material <NUM>. In this example, there are two filaments in each group of filaments. The pattern of: two filaments of the third material <NUM>, two filaments of the second material <NUM>, two filaments of the first material <NUM>, two filaments of the second material <NUM>, and two filaments of the third material <NUM> is repeated around the stent <NUM>. This pattern is called the "hybrid double 8x" configuration. As shown in <FIG>, compared to the other embodiments, the hybrid double 8x pattern results in better visibility of the cross-hatch pattern of the filaments and also results in better edge definition along the sides of the stent <NUM>. That is, the edge of the stent <NUM> appears as alternating areas of light and dark rather than a solid line.

Another example of a starting filament arrangement is depicted in <FIG>. In this example, two filaments of a second material <NUM> are directly adjacent to one side of a single filament of the first material <NUM>, and two filaments of the third material <NUM> are directly adjacent to the other side of the single filament of the first material <NUM>. This pattern of: four filaments of the second material <NUM>, a single filament of the first material <NUM>, four filaments of the third material <NUM>, and a single filament of the first material <NUM> is repeated around the stent. This pattern is called the "hybrid 4x" configuration. While the hybrid 4x braid pattern may result in a stent with enhanced radiopacity, it was found that the braid opening and apposition was abrupt compared to other braid configurations.

In yet another example of a starting filament arrangement for a stent, shown in <FIG>, a single filament of the first material <NUM> is surrounded on both sides by a single filament of the second material <NUM>. The other side of the single filament of the second material <NUM> is directly adjacent to a single filament of the third material <NUM>. This pattern of: single filament of third material <NUM>, single filament of second material <NUM>, single filament of first material <NUM>, single filament of second material <NUM>, and single filament of third material <NUM> is repeated around the stent. This pattern is called the "hybrid 16x" configuration.

It is notable that all the stents shown in <FIG> are made of the same materials and have the same number of filaments. In one example, the materials of the stents are platinum and cobalt chromium alloys. The examples shown in <FIG> further include DFT wires formed of platinum and cobalt chromium alloys. Every filament that forms the stents in <FIG> is made of the first material, the second material, or the third material. Each of the embodiments shown in <FIG> include <NUM> filaments, but one of ordinary skill in the art would readily understand that any number of filaments could be used. Further, one of ordinary skill in the art would understand that other materials besides platinum and cobalt chromium alloys could be used for the filaments of the braided stent. Examples of cobalt chromium alloys that may be used in making the stents include <NUM> CoCr alloy, alloy L605, 35N LT ® Superalloy, and the like.

Depending on the ultimate tensile strength of the third material <NUM> (the DFT wire), the second material <NUM> (the monofilament) may not be necessary. For example, it was found that when the DFT wire was formed of a platinum core having a cross-sectional area that is <NUM>% to <NUM>% of the total cross-sectional area of the DFT wire, and an outer sheath of alloy L605, the monofilament is not necessary. Alloy L605 has a high ultimate tensile strength relative to other alloys, such as <NUM> CoCr alloy. An example of a stent that includes only the first material <NUM> and the third material <NUM> is depicted in <FIG>. Every filament that forms the stent in <FIG> is made of the first material <NUM> or the third material <NUM>. In another embodiment, it was found that when the tubular braid included DFT wire formed of a platinum core having a cross-sectional area that is <NUM>% of the total cross-section of the DFT wire, and an outer sheath of <NUM> CoCr alloy, the second material <NUM> monofilament is necessary in order to enhance the strength of the stent and achieve sufficient radial pressure.

As discussed above, the pattern of the filaments used in the braid of the stent affects the radiopacity of the stent. Some of the braid patterns (e.g., the pattern shown in <FIG>) provide higher definition images of the details of the stent. However, the braid pattern has been shown to have negligible effect on the mechanical properties of the stent. As shown in <FIG> and <FIG>, the braid pattern does not have much, if any, effect on the radial pressure performance of the stent. <FIG> depicts the radial pressures of the <NUM> and <NUM> compressed diameter stents having the braid patterns in accordance with the embodiments discussed above. As shown in <FIG>, the radial pressures of these stents are comparable to that of the conventional stent, which is depicted on the right side of the graph.

Similarly, <FIG> depicts the radial pressures of the <NUM> and <NUM> compressed diameter stents having the braid patterns in accordance with the embodiments described herein. As shown in <FIG>, the radial pressures of these stents are comparable to that of the conventional stent, which is depicted on the right side of the graph.

<FIG> is an image of a conventional stent <NUM>, such as the stent shown in <FIG>. The edges <NUM> of the stent <NUM> appear as a solid line, making it difficult for the physician to see the filaments, and to visualize whether the stent is expanded or compressed. In contrast, <FIG> depicts deployment of a stent <NUM> that has a braid pattern in accordance with the embodiments described herein. The edges <NUM> of the stent in <FIG> appear as alternating dark areas and light areas. As such, the physician is able to see which areas of the stent <NUM> are compressed, and which areas are expanded. The compressed areas <NUM> appear as darker, shorter segments, while the expanded areas <NUM> appear as lighter, longer segments. This visibility is important in, for example, aneurysm treatment in which a forward force may be used to compact the stent lengthwise in the area of the neck of the aneurysm. With the enhanced radiopacity of the braid patterns disclosed herein, the physician can see that the stent is compacted in order to effectively divert blood flow away from the aneurysm. The enhanced radiopacity further allows the physician to see if the device is deployed properly either in terms of position or radial orientation with respect to the entrance to the aneurysm.

Claim 1:
An implantable stent braid (<NUM>), comprising:
a plurality of groups of first filaments, said first filaments being formed out of a radiopaque material (<NUM>);
a plurality of groups of second filaments, each of the second filaments being a monofilament formed out of a support material (<NUM>) having a tensile strength greater than a tensile strength of the radiopaque material; and
a plurality of groups of third filaments, each of the third filaments being a drawn filled tube (DFT) wire (<NUM>) comprising a core formed out of one of a radiopaque material and a support material, and a sheath around the core formed of the other of the radiopaque material and the support material, wherein the support material of the DFT wire has a tensile strength greater than a tensile strength of the radiopaque material of the DFT wire,
wherein the respective groups of first filaments, second filaments, and third filaments are braided together by a braiding machine before braiding begins and are arranged in a starting filament arrangement on the braiding machine in which each group of third filaments is positioned directly adjacent to one of the groups of first filaments.