Stents with increased flexibility

Stents that are adapted to be balloon expanded and include adjacent supports connected by connecting portions. The configurations, materials, and/or dimensions of at least one of the supports and connection portions allows the stents to be expanded to a greater extent, and optionally with reduced foreshortening.

INCORPORATION BY REFERENCE

FIELD

Described herein are expandable intraluminal grafts (“stents”) for use within a body passageway or duct which are particularly useful for repairing blood vessels narrowed or occluded by disease. The stents described herein are configured to change size over a large range, while minimizing the strain on the stent.

BACKGROUND

Intravascular stents may be used in coronary arteries and other body lumens of human patients. Stents are generally tubular-shaped devices which function to hold open a segment of a blood vessel or other body lumen such as a coronary artery. They also are suitable for use to support and hold back a dissected arterial lining that can occlude the fluid passageway. At present, there are numerous commercial stents being marketed throughout the world. For example, prior art stents typically have multiple cylindrical rings connected by one or more connecting links. While some of these stents are flexible and have the appropriate radial rigidity needed to hold open a vessel or artery, there typically is a tradeoff between flexibility and radial strength and the ability to tightly compress or crimp the stent onto a catheter so that it does not move relative to the catheter or dislodge prematurely prior to controlled implantation in a vessel.

Intravascular stents are known and there are numerous structural designs in commercial use. One well known structural pattern includes a tubular stent having rings connected by links. Typically, there are two or more links connecting adjacent rings. While stents having two links between adjacent rings (two-link stents) offer the benefit of low crimp profile and high flexibility, these benefits come with a trade-off in terms of longitudinal stability. Further, peak-to-peak stent patterns (in which the peaks on adjacent rings point toward each other and are essentially axially aligned) offer dense packing of stent rings, which in turn allows for a stent pattern with high radial strength and high radial stiffness. One stent pattern that incorporates these design features is the 2 link offset peak-to-peak style stent. While this stent pattern performs well in terms of traditional stent metrics, it experiences one key tradeoff, namely it will excessively shorten under modest longitudinal compressive loads.

Two-link stents, specifically offset peak-to-peak, where the peaks of adjacent rings point toward each other but are slightly offset circumferentially, excessively shorten under modest (clinically relevant) longitudinal compressive loads. This creates unwanted implications for safety and efficacy of the stent implant. Offset and angled link designs lend readily to collapse behavior, as links do not provide resistance in direction of load, and in addition offset link designs create a bending moment effect, which encourages the bar arms adjacent to link structures to bend and swing excessively (stress is focused in these bar arms).

SUMMARY OF THE DISCLOSURE

The present disclosure relates to stents, such as balloon-expandable vascular prosthesis. In addition to vascular applications, these devices may be used for tracheal, bronchial patency and/or in iliac or renal arteries.

The stents described herein have greater flexibility than prior art stents and expand with less foreshortening, based in part upon a combination of factors, including the configuration of one or more portions of the stent, material properties, and dimensions of one or more portions of the stents.

The stents can include a plurality of annular supports (rings) that are adjacent and extend transversely (e.g., at 90 degrees, but including +/− 15 degrees) to the longitudinal distal-to-proximal axis of the device. The rings may be coupled together by a connecting portion, which can include one or more connectors (and in particular, omega-shaped connectors).

At least some of the supports (e.g., rings) may have a configuration that has a repeating pattern (e.g., a biphasic pattern) of a pair of flat-ended, open trapezoidal shapes (which may be rounded at the corners) that are circumferential offset but face each other and may be connected at their ends by connecting members that may be straight or curved (e.g., S-shaped). The trapezoidal shapes may be square, rectangular, isosceles (e.g., a wide-mouthed isosceles in which the open end of the trapezoid would be the longer parallel side, or narrow-mouthed isosceles, in which the open end of the trapezoid would be the shorter parallel side).

Typically, as the stent device is expanded, the flat end of the open trapezoidal shapes stay approximately the same (e.g., same length, and may remain substantially parallel with each other), while the connecting members may bend relative to the flat ends. In some variations, the legs of the open trapezoidal shapes (the legs forming the open ends) may bend relative to the connecting members and/or the flat end(s).

As mentioned, the connectors may be configured as omega connectors, which may include an arc region (e.g., semi-circular or 180 degree arc, 170 degree arc, 190 degree arc, 200 degree arc, 210 degree arc, etc.) from which a pair of straight legs may extend from either side of the ends of the arc region, e.g., in a single line. For example, each omega-shaped connector may include includes an arc region and a pair of linear sections extending from the arc regions on either side of the arc region. One or both ends of the connector may be L-shaped. For example, the omega connector may include a first an L-shaped end connecting to the second side of one of the first open trapezoidal portions of the plurality of biphasic cells and a second L-shaped end connecting to the fifth side of one of the second open trapezoidal portions of the plurality of biphasic cells.

In general, the apparatuses described herein may be configured as balloon-expandable stent grafts that may be used in percutaneous transluminal angioplasty (PTA) procedures, including in particular in peripheral arteries such as tibial, femoral and iliac. Balloon-expandable stents are Endovascular prostheses and may be metallic tubular meshes that expand radially by means of inflation of a balloon. The stent grafts describe here may have a frame (e.g., a cobalt chrome tubular frame/mesh, Nitinol tubular frame/mesh, stainless steel tubular frame/mesh, etc.), embedded into sleeve formed from a polymer matrix. The sleeve may be porous.

For example, this apparatuses and methods described herein relate to stent grafts (“stents”) having radiused struts that may be embedded and/or enveloped in a polymer matrix. The stent graft may comprise rings that form radiused struts in sinusoidally (“s-shaped”) shaped segments. The rings may be connected by omega-shaped crosslinks, e.g., connectors or crosslinks that may have an omega (Ω) shape. The stent struts may be embedded and/or enveloped into a polymer matrix of a composite, such as a composite of ePTFE that may enhance its mechanical properties. The improved properties may permit the stent to go through tortuous paths of injured peripheral arteries with the required flexibility and with the proper radial stability to open the vascular vessel and recover the blood flow.

For example, described herein are stent devices having a length extending in a distal to proximal direction, the device comprising: a plurality of adjacent rings arranged transverse to a length of the device, wherein each ring is a ring comprising length of material arranged radially around the length of the stent device as a plurality of repeating biphasic cells, each biphasic cell comprising a first open trapezoidal portion having a first side, a second side and a third side forming a proximal-facing opening, and a second open trapezoidal portion having a fourth side, a fifth side and a sixth side forming a distal-facing opening, wherein the second side and the fifth side are parallel, further wherein the third side of the first open trapezoidal portion is connected to the fourth side of the second open trapezoidal portion by a first connector region extending at a first angle relative to the third side, and wherein the first side of the first open trapezoidal portion connects to a sixth side of an adjacent biphasic cell in the ring by a second connector extending at a second angle relative to the first side; and a plurality of omega-shaped connectors connecting each ring that is adjacent to a more distal ring to the more distal ring, wherein each omega-shaped connector connects the second side of one of the first open trapezoidal portions of the plurality of biphasic cells in the ring that is adjacent to the more distal ring to the fifth side of one of the second open trapezoidal portions of the plurality of biphasic cells of the more distal ring; wherein the stent device has a first configuration in which the plurality of adjacent rings have a first diameter, and the stent device has a second configuration in which the plurality of adjacent rings have a second diameter that is greater than the first diameter, and wherein the second side and the first side remain parallel as the stent device is expanded from the first configuration to the second configuration.

A stent device having a length extending in a distal to proximal direction may include: a plurality of adjacent rings arranged transverse to a length of the device, wherein each ring is a ring comprising length of material arranged radially around the length of the stent device as a plurality of repeating biphasic cells, each biphasic cell comprising a first open trapezoidal portion having a first side, a second side and a third side forming a proximal-facing opening, and a second open trapezoidal portion having a fourth side, a fifth side and a sixth side forming a distal-facing opening, wherein the second side and the fifth side are parallel, further wherein the first open trapezoidal portion is radially offset from the second open trapezoidal portion and the third side of the first open trapezoidal portion is connected to the fourth side of the second open trapezoidal portion by a first connector region extending at a first angle relative to the third side, and wherein the first side of the first open trapezoidal portion connects to a sixth side of an adjacent biphasic cell in the ring by a second connector extending at a second angle relative to the first side; and between one and three omega-shaped connectors connecting each ring that is adjacent to a more distal ring to the more distal ring, wherein each omega-shaped connector connects the second side of one of the first open trapezoidal portions of the plurality of biphasic cells in the ring that is adjacent to the more distal ring to the fifth side of one of the second open trapezoidal portions of the plurality of biphasic cells of the more distal ring, further wherein an omega-shape of each of the omega-shaped connectors connecting the plurality of adjacent rings is oriented in the same distal to proximal direction; wherein the stent device has a first configuration in which a first diameter of the plurality of adjacent rings is between 0.5 mm and 4 mm and a second configuration in which a second diameter of the plurality of adjacent rings is between 3 mm and 7 mm, and wherein the second side and the first side remain parallel but the first and second angles change as the stent device expands from the first configuration to the second configuration.

As mentioned, the plurality of omega-shaped connectors may comprises between 1 and 3 omega-shaped connectors. In some variations, the plurality of omega-shaped connectors has a maximum of 2 omega-shaped connectors.

Typically, the first open trapezoidal portion (or at least the flattened top of the open trapezoidal portion) is radially offset from the second open trapezoidal portion (e.g., the flattened top of the open trapezoidal portion). This offset may increase as the device transitions from the first (un-expanded configuration) into the second (expanded) configuration, while the flattened top remains essentially the same shape and size. Thus, the radial offset between the first open trapezoidal portion and the second open trapezoidal portion may increase as the stent device transitions from the first configuration to the second configuration.

In general, the length of any of the devices described herein may be between about 10 mm and about 40 mm (e.g., between about 12 mm and about 39 mm, between about 12 mm and 38 mm, e.g., 40 mm or less, 39 mm or less, 38 or less, etc.). The first diameter (e.g., the outer diameter of each ring in the un-expanded configuration) may be between about 0.5 mm and about 4 mm and the second diameter (e.g., the outer diameter of the rings in the expanded configuration) may be between about 3 mm and about 7 mm.

The frame (e.g., the length of material) may comprises one or more of: an alloy of chromium cobalt, a nickel titanium alloy (e.g., Nitinol), a stainless steel and a magnesium alloy.

Any of these devices may include a sleeve bonded to and/or encapsulating the frame (e.g., the plurality of connected rings). The sleeve may be a polymeric matrix in which the plurality of rings is encapsulated. For example, the sleeve may be ePTFE. The sleeve material may be electrospun onto the frame. The sleeve may comprise a porous material. In some variations, the sleeve may have a thickness of between about 0.005 and 0.001 inches.

In any of the stent devices described herein the omega connectors may be oriented so that an omega-shape (the approximately “Ω” shape) of each of the omega-shaped connectors connecting the plurality of adjacent rings are all in the same distal to proximal direction, e.g., so that they all face distally or proximally.

As mentioned above, the first open trapezoidal portion may be an open rectangle, open isosceles trapezoid, etc. The open trapezoidal portions (first and second) may generally include a flattened end with square or rounded corners extending into a pair of legs. The legs forming the open end may be straight or curved (including sinusoidal). The legs may bend as the device expands from the first (un-expanded) to the second (expanded) configuration. In some variations the second open trapezoidal portion may be the same shape as the first open trapezoidal shape, or different. For example, the first and third sides may be parallel and in some variations the fourth and sixth sides are not parallel. The first and second open trapezoidal shapes have opposite open ends that face different each other (e.g., one faces distally while the other faces proximally). Either or both the first open trapezoidal portion and the second open trapezoidal portion may have rounded edges.

The width of the length of material forming the repeating biphasic cells (the rings) may be constant or it may vary. For example, the width may be between about 0.05 and about 0.5 mm (e.g., between about 0.1 and about 0.3, between about 0.1 and about 0.2, etc.).

The plurality of adjacent rings are typically separated from each other by a ring offset. The connector (e.g., the omega-shaped connector) may sit within this ring offset. The ring offset may be a distance of between 0.1 and 1 mm (e.g., between about 0.1 mm and about 0.8 mm, between about 0.1 mm and 0.6 mm, etc.) along the distal to proximal length of the stent device. In general, the distal to proximal height of each ring may be between about 0.5 mm and about 4 mm (e.g., between about 0.5 mm and about 3.5 mm, between about 1 mm and about 3 mm, etc.).

The stent devices described herein, because of the dimensions and arrangement of the frame (e.g., the repeating biphasic cell configuration) and the connectors (e.g., the omega-shaped connectors) may permit the device to have particularly advantageous properties, including resistance to kinking. For example, the stent device may bend at least 90 degrees along its length in the first configuration without kinking. The device may foreshortens less than 7% (e.g., less than 6%, less than 5.5%, etc.) when expanding from the first configuration to the second configuration. For example, the device may foreshorten less than 7% (e.g., less than 6%, less than 5.5%, etc.) when the second diameter of the plurality of adjacent rings is greater than 2.9 times the first diameter of the plurality of adjacent rings.

The first open trapezoidal portions of the repeating biphasic cells in each of the rings may be aligned with the first open trapezoidal portions in the other rings along the proximal to distal length of the device. Similarly the second open trapezoidal portion of the repeating biphasic cells may be aligned with each other along the length (proximal to distal) of the device.

The patterns forming the rings may alternatively be described herein as a repeating pattern of alternating flattened tops and flattened bottoms, wherein the flattened tops extend transverse to the length of the device and wherein the flattened bottoms extend transverse to the length of the device and further wherein the flattened tops and flattened bottoms are connected by sigmoid-shaped connectors so that each flattened top forms part of a distal-facing U-shape and each flattened bottom forms part of a proximal-facing U-shape. Each flattened top and a portion each of two sigmoidal-shaped connectors to which it is attached may form a first open trapezoidal portion having a proximal-facing opening and each flattened top and a portion each of two sigmoidal-shaped connectors to which it is attached forms a second open trapezoidal portion having a distal-facing opening.

Thus, described herein are stent device comprising: a plurality of adjacent rings arranged transverse to a length of the device in a proximal to distal direction, wherein each ring comprises a length of material arranged radially around the length of the stent device in a repeating pattern of alternating flattened tops and flattened bottoms, wherein the flattened tops extend transverse to the length of the device and wherein the flattened bottoms extend transverse to the length of the device and further wherein the flattened tops and flattened bottoms are connected by sigmoid-shaped connectors so that each flattened top forms part of a distal-facing U-shape and each flattened bottom forms part of a proximal-facing U-shape; a plurality of omega-shaped connectors connecting each ring that is adjacent to a more distal ring to the more distal ring, wherein each omega-shaped connector connects one of the flattened tops the ring that is adjacent to the more distal ring to a flattened bottom of the more distal ring; wherein the stent device has a first configuration in which the plurality of adjacent rings have a first diameter, and the stent device has a second configuration in which the plurality of adjacent rings have a second diameter that is greater than the first diameter, and wherein the flattened tops and the flattened bottoms remain parallel to each other as the stent device is expanded from the first configuration to the second configuration.

The plurality of omega-shaped connectors may comprise between 1 and 3 omega-shaped connectors. The plurality of omega-shaped connectors may have a maximum of 2 omega-shaped connectors. The flattened tops of each ring may be radially offset from the flattened bottoms. The radial offset may increase as the stent device transitions from the first configuration to the second configuration. As mentioned above, an omega-shape of each of the omega-shaped connectors connecting the plurality of adjacent rings may be oriented in the same proximal to distal direction.

For example, a stent device may include: a plurality of adjacent rings arranged transverse to a length of the device in a proximal to distal direction, wherein each ring comprises a length of material arranged radially around the length of the stent device in a repeating pattern of alternating flattened tops and flattened bottoms, wherein the flattened tops extend transverse to the length of the device and wherein the flattened bottoms extend transverse to the length of the device and further wherein the flattened tops and flattened bottoms are connected by sigmoid-shaped connectors so that each flattened top forms part of a distal-facing U-shape and each flattened bottom forms part of a proximal-facing U-shape; between one and three omega-shaped connectors connecting each ring that is adjacent to a more distal ring to the more distal ring, wherein each omega-shaped connector connects one of the flattened tops the ring that is adjacent to the more distal ring to a flattened bottom of the more distal ring, further wherein an omega-shape of each of the omega-shaped connectors is oriented in the same proximal to distal direction; wherein the stent device has a first configuration in which the plurality of adjacent rings have a first diameter, and the stent device has a second configuration in which the plurality of adjacent rings have a second diameter that is greater than the first diameter, and wherein the flattened tops and the flattened bottoms remain parallel to each other and the shape of the sigmoidal-shaped connectors extends radially as the stent device is expanded from the first configuration to the second configuration.

As mentioned above, the first diameter may be between 0.5 mm and 4 mm and the second diameter may be between 3 mm and 7 mm.

DETAILED DESCRIPTION

Described herein are stent apparatuses with improved flexibility for greater expansion without fracture. This allows the stents to be expanded to greater diameter sizes when in use, which provides an exemplary benefit of being able to use a single stent for a greater variety of uses (e.g., different vessel sizes) without having to use a differently sized stent. The stents described herein are also adapted such that foreshortening of the stent during expansion is reduced, preventing a variety of complications.

The stents herein generally have a collapsed delivery configuration, and are adapted to be expanded. The “collapsed” configurations may be referred to herein as delivery, collapsed, initial, or other similar term. The delivery configuration can be the configuration the stent has after being manufactured, such as by laser cutting a tubular element or 3-D printing the stent. The stents herein are described as being expanded by balloon expansion, but the stents could be adapted to be able to at least partially self-expand.

Any of the stents herein can include one or more coverings over any portion of the stent.

The stents include a plurality of supports, optionally annular, wherein each of the plurality of supports are connected to at least one adjacent support by one or more connecting portions, which can include one or more connectors.

There are several factors that influence the flexibility of the stents herein and provide the stents with the ability to expand to larger outer dimensions without fracturing. The following are examples of factors that can influence the flexibility of the stents: the configuration of the annular supports and connectors; the dimensions of the annular supports and connectors; and the materials of the annular supports and connectors.

FIG. 1Aillustrates a side view of exemplary stent10in an un-expanded (e.g., delivery) configuration, stent10having a first end12(e.g., proximal end) and a second end14(e.g., distal end) and a length, L; thus stent10has a longitudinal axis L extending through a lumen defined by the stent. Stent10includes a plurality of annular supports22(“rings”) transverse to the long axis and generally axially spaced from at each other; the individual regions are connected by at least one connector20(e.g., omega connector). In this example, an annular support is “adjacent” to another annular support if it is the next annular support when moving towards either the first end12or the second end14. In this example, the annular supports22(which may also be referred to herein as “rings”) are connected to at least one adjacent support22by a connecting portion20(omega connector). The rings22may be described herein as being “connected” to adjacent rings; it is understand that this may include one or more (e.g., two) omega connectors20that may be integrally formed with the rings, such as if the entire stent may be manufactured from a single piece of starting material, e.g., by laser cutting a cylindrical piece.

Each of the rings22in this embodiment has a wave configuration, with a plurality of peaks and valleys, repeating in a pattern (only some peaks and valleys are labeled for clarity). In this embodiment, peaks of the supports may extend to the same location along the length of the stent. Valleys of supports (rings) also extend to the same location along the length of the stent. Thus, the peaks (e.g., the flattened top regions24) may be aligned along the length of the stent device, shown, and the valleys (e.g., the flattened bottom regions24′) may also be aligned along the length of the stent. Peaks and valleys of the waves may define flattened, or squared, ends. Between the peaks and valley are intermediate sections28(connecting regions), and in this embodiment the intermediate sections have S-shapes, as can be seen in the side view ofFIG. 1A. This embodiment is an example of at least one annular support with a repeating wave pattern having flattened ends connected by curvilinear intermediate sections, such as S-shaped intermediate regions.

In this embodiment, the annular supports all have the same configuration along the length of the stent. Peaks24(which are described in additional detail below, and may be referred to herein as a first open trapezoidal portion having a first side, a second side and a third side forming a proximal-facing opening) of adjacent rings may therefore be circumferentially aligned, and valleys (which are described in additional detail below and may be referred to herein as a second open trapezoidal portion having a fourth side, a fifth side and a sixth side) of adjacent rings may be circumferentially aligned.

In alternative embodiments, not every annular support has the same configuration as every other annular support.

Adjacent annular supports22are connected together by connecting portion20.FIG. 1Dillustrates a flattened/planar view of an example of a stent device10, which illustrates the connections between adjacent rings. In this embodiment, the connecting portions20(e.g., omega connectors) between adjacent rings22include at least two connectors, shown inFIG. 1Cas Detail A shown inFIGS. 1A and 1D.FIG. 1Cillustrates a connector that connects adjacent rings22(only a portion of rings are shown). The connector has a configuration, at least a portion of which has a general “omega” configuration. In this embodiment, the general “omega” configuration is defined by arc region (e.g., dome region)32and radial regions33generally extending radially outward from arc or domed region32. In this embodiment, radial regions have linear configurations and may be L-shaped, but in other embodiments they could include some curvature. The connector (e.g., omega connector) may also include axial regions34which may extend generally axially from radial regions33and may be parallel to the longitudinal axis LA of the device (e.g., forming the L-shaped ends, mentioned above). Axial regions33of the connector are linear but could, in some embodiments, have some curvature to them. One of the axial regions34extends further toward first end12than the other axial region34. Radial regions of a connector may generally be aligned when they have linear configurations (and are also aligned with other radial regions of the other connector that connects the two adjacent supports), and axial regions34are parallel to each other, and to the longitudinal axis LA.

The “omega” shape is generally defined by an arc or domed region32and radial regions33. While domed region32and radial regions33do not form an exact, traditional, “omega” Greek letter, it is understood that they form a general “omega” shape of the connector. Domed regions32and radial sections36can have slightly varying configurations and that portion of the connector can still have a general “omega” configuration as that term is used herein.

The connector extends from a flattened top region (e.g., of the open trapezoidal ‘peak’ region24) of a first ring22to a flattened top (e.g., of the next open trapezoidal ‘valley’ region24′) of an adjacent ring22, as can be seen inFIGS. 1A and 1D. The first open trapezoidal portion (e.g., peak) and second open trapezoidal portion (valley) from which the connector extends are not circumferential aligned. For example, a connector extends from a first open trapezoidal portion24on a first ring22to a second open trapezoidal portion24′ on an adjacent ring, as shown inFIGS. 1A, 1C and 1D.

As can be seen inFIG. 1D, the arc regions of all of the omega-shaped connectors have similar configurations, and are all oriented in the same direction. In this embodiment, each pair of adjacent supports is coupled together by two omega-shaped connectors, each of which has the configuration shown inFIG. 1C. As can be seen inFIG. 1D, the omega-shaped connectors in any given connecting portion are not circumferentially aligned with the connectors in the adjacent connecting portion, but they are circumferentially aligned with the connectors in the next adjacent connecting portion. In this embodiment, the position of the omega connectors are in an A-B-A-B pattern, with every-other ring having connectors that are circumferentially aligned.

The first and second open trapezoidal potions of the repeating biphasic shapes forming each ring are connected by an intermediate section (e.g., connecting the peak and a valley regions) as described above. InFIG. 1D, the connecting intermediate section is a length that extends in an angle between the open trapezoidal portions; this connection may be straight or curved (e.g., sinusoidal, including s-shaped). As will be described in greater detail below, this intermediate section, and in some variations the ‘legs’ of the open trapezoidal portions (forming the openings) may change their angle relative to the flattened top region when the stent devices expand (e.g., when driven by a balloon to expand).

InFIG. 1Dthe two omega-shaped connectors20extend from adjacent peaks24′ and20, on an adjacent rings. In this embodiment the two connectors extend from adjacent flattened top (or bottom) regions. In the example shown inFIGS. 1A-1D, there are three flattened top regions (peaks) between some of the omega-shaped connectors (from which no connector extends), and on flattened top region (peak) on the other side (radially) between the two omega-shaped connectors. Thus, in the space between each set of rings, two omega-shaped connectors are connect the adjacent rings, and this connecting pattern is offset and alternating with every other ring, as shown inFIGS. 1A-1D.

In some variations, only three or fewer (e.g., two) connectors are used to connect adjacent rings. For example, by having only two connectors in each connecting region, there is less area of material than in some other stent designs. This smaller area may allow the stent to have more flexibility and can expand to a greater extent when forces are applied on the stent such as by an expansion balloon. In alternative embodiments, however, there could be more than two connectors in a connecting portion, and the desired flexibility could still be maintained by modifying one or more other aspects, such as, for example without limitation, one or more dimensions (e.g., thickness, radius), configuration, or material.

In general, each ring may be formed of a length of material, such as a metal (e.g., a nickel titanium alloy, a chromium alloy, a stainless steel alloy, etc.). The length of material may be a strip of material formed into a rectangular or square cross-section (e.g., which may be formed by laser cutting from a tube of the material), or in some variation it may be formed of a wire.

The dimensions of the rings are one factor that may influence the flexibility and may provide for greater expansion of the stents herein. Less area of the stent material generally increases the flexibility and allows the stent to expand to greater outer dimensions without fracture.FIG. 1Dshows exemplary dimensions and radii for portions of at least one of the rings. In some embodiments the thickness of the support material is from 0.08 mm to 2.0 mm, such as from 0.1 mm to 1.8 mm, such as from 1.2 mm to 1.6 mm (e.g., 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm).

The configuration of the ring, including the arrangement of the repeating biphasic cells (e.g., the first and second open trapezoidal portions) of the rings is another factor that influences the flexibility and provides for greater expansion of the stents herein. The plurality of adjacent rings (e.g., annular supports)22generally have a wave-like configuration, with squared (flattened) end and S-shaped intermediate sections in between these flattened ends (forming peaks and valleys). As shown in the exemplaryFIG. 1D, the connecting regions28between the open trapezoidal portions (or more specifically, between the flattened tops) are not aligned with the longitudinal axis of the stent. That is, they are at an angle relative to the longitudinal axis. This angle can increase the flexibility of the stent and allow for greater expansion.

As mentioned above, the dimensions of the omega-shaped connectors are an additional factor influences the flexibility and provides for greater expansion of the stents herein.FIG. 1Cshows exemplary dimensions (e.g., thicknesses and radii) that can be used for any of the omega-shaped connectors herein. In some embodiments, one or more omega-shaped connectors have a thickness from about 0.02 mm to about 1 mm, such as about 0.02 mm to about 0.8 mm (e.g., about 0.02 mm about 0.03 mm, about 0.04 mm, about 0.05 mm, about 0.06 mm, about 0.07 mm, about 0.08 mm, etc.).

The configuration and number of the omega-shaped connectors are other factors that influence the flexibility and provides for greater expansion of the stents herein. As set forth herein, at least a portion of the omega-shaped connectors may have a general omega configuration, including an arc (e.g., domed) section. The omega configuration provides for added flexibility in the connecting portions. Additionally, in some embodiments the connecting portions only include two omega-shaped connectors, which reduces the area of the connecting portions and increases the flexibility.

FIG. 1Eillustrates an expanded configuration (top) of the stent10fromFIGS. 1A-1D. The bottom configuration inFIG. 1Eis the same stent device10as shown inFIG. 1A. The top inFIG. 1Eillustrates the stent10(which has an initial, unexpanded outer diameter of approximately 2.76 mm-seeFIG. 1B) expanded to an outer diameter of about 8 mm, about 2.9 times the initial outer dimension.FIG. 1Ealso illustrates the foreshortening that the stent undergoes as it is expanded. The initial length is 18 mm, and the length when expanded is about 16.9 mm, shortening by about 1.1 mm. In this embodiment the stent foreshortened by not more than about 6.2% when expanded to about 2.9 times an initial outer diameter. The ability to expand this much with so little foreshortening is due in part to the configuration of the rings and omega-shaped connectors, the dimensions of the rings and omega-shaped connectors, and the material(s) forming the stent.

As can also be seen in the top view ofFIG. 1E, when the stent is expanded, the flattened top of the first open trapezoidal portion (peak)24is rotated along the radius of the stent, e.g., away from the longitudinal axis of the stent, with the flattened tops (or bottoms) of the next open trapezoidal portion (valley)24′ also rotated, but still parallel with the first flattened top24. The plane of each ring is shown rotated by angle (β) relative to the long axis (LA) compared to the initial configuration shown in the bottom ofFIG. 1E, showing the unexpanded configuration. The flatten tops of peaks24and may be individually flared radially outward relative to the flattened tops of the valleys24′ when the device is expanded. The angle of rotation can be anywhere from 5 degrees to 60 degrees, such as from 10 to 45 degrees.

As is also shown in the bottom ofFIG. 1E, each ring may have an axis or plane E′ that is orthogonal to the longitudinal axis (LA). When the stent is expanded, in this example the annular supports (rings) expand in such a manner than the axis rotates with respect to the longitudinal axis, and as shown in the expanded top configuration, the plane of the rings has rotated relative to the longitudinal axis. The angle β is less than 90 degrees (compared with the original angle of β′ which is approximately 90 degrees in this example).

FIG. 1Fillustrates the initial80and expanded82configurations fromFIG. 1Eoverlaid on top of each other, which can further highlight the disclosure described with respect toFIG. 1E.

It is understood that not every features show in the embodiments herein is necessary to increase the flexibility of the stents herein. For example, in alternative embodiments, some connecting portions can have three connectors, and the stent may still be able to expand to desired outer dimensions for some applications.

As set forth above, one of the exemplary advantages of stents herein is that they can be mounted on different diameter expansion balloons and can be expanded to a greater variety of outer dimensions. This can reduce the number of stents that must be available for use for a particular medical application.

FIGS. 2A-2Cillustrate an exemplary stent that is similar in many ways to the exemplary stent inFIGS. 1A-1E. The general configurations of the annular supports and connectors is the same to those inFIGS. 1A-1E. One difference is that the initial outer dimension of the stent is shown as 2.83 mm (see, e.g.,FIG. 2B), as opposed to 2.76 mm in the embodiment inFIG. 1A-1E. The initial larger outer dimension allows the stent in this embodiment to be expanded to larger outer dimensions without fracturing. Another difference is the distance between peaks in one circumferential region of the stent. As shown inFIG. 2C, one distance between the peaks in the center of the stent is 1.90 mm, whereas inFIG. 1A-1Eit was 1.70 mm (seeFIG. 1D). Any of the other features described with respect to the embodiment inFIGS. 1A-1Ecan be incorporated in this embodiment as well.

FIGS. 3A-3Cillustrate an exemplary stent that is similar in many ways to the exemplary stent inFIGS. 1A-1E and 2A-2C, and any feature therein can be incorporated into this embodiment as well. This embodiment is longer than the embodiments inFIGS. 1A-1E and 2A-2C, with the exemplary length of 38 mm. The outer dimension of 2.76 mm shown inFIG. 3Dis the same as in the embodiment inFIG. 1A-1E. The distance between adjacent peaks is slightly different than the embodiments inFIGS. 1A-1E and 2A-C, as shown inFIG. 3C. The connectors can have any of the dimensions of any of the connectors herein. Other exemplar dimensions are also provided inFIG. 3C.

The stents can generally be any appropriate length and have any appropriate initial outer dimension.

Exemplary materials for any of the stents herein include cobalt-chrome alloys (e.g., L605) y 316 L stainless steel. Expandable polytetrafluorethylene (ePTFE) and polyester (PET, dracon) are examples of materials that can be used for one or more sleeves, coatings or coverings on the stent, if included.

FIG. 4Aillustrates a pressure versus diameter graph for the stent shown inFIGS. 1A-1E, illustrating a pressure applied by an internal expansion balloon. When plotting applied pressure vs corresponding outer diameter values, stent expansion progresses gradually until reaching approximately 7.5 bar pressure. From this pressure, more accelerated expansion starts, being more susceptible to expansion as pressure increases, until reaching about 8 mm, a maximum expansion value. It is noted that this exemplary stent is configured to be able increase its diameter in approximately 2.9 times without showing fracture hazard. When removing applied pressure, a slight stent recovery occurs due to initial elastic deforming. Similarly,FIG. 4Bshows an example of a stress vs. strain curve for a stent device such as those shown inFIGS. 1A-1F, 2A-2C and 3A-3C. In this example, the stress (in MPa) vs. strain (mm/mm) follows a similar profile to that shown inFIG. 4Afor applied pressure vs. diameter over the ranges examined.

As mentioned, any of the stent devices descried herein may include a sleeve, cover, coating or the like. For example,FIG. 5illustrates an exemplary stent device (which can be any of the stents described herein), at least a portion of which is covered by a sleeve505. In this example, the ends of the stent frame503are uncovered by the sleeve. Examples of sleeves that may be used are described in greater detail below.

FIG. 6is a perspective view illustrating an exemplary catheter system600for delivering any of the stents601described herein. This system may include a connector603connected to an elongate lumen605for inserting the stent device601over an expandable balloon607. The balloon may be inflated by applying fluid through the catheter (e.g., one of the lumen of the catheter605). One or more imaging markers609may be included to aid in visualizing the stent when in the body, e.g., using fluoroscopy. The tip611of the device may be open and a lumen through the device may be used for advancement over a guidewire (not shown).

The devices described herein may be used anywhere appropriate in the body, including, but not limited to, the peripheral vasculature. For example, a merely exemplary location for placement of the stents herein can be in tibial arteries, such as for injury to such arteries. The primitive iliac artery has a diameter between about 5 and 8 mm, and may be well suited for stents herein.

EXAMPLES

FIG. 7shows another example of a stent700as described herein. The stent may include a sheath or cover703. For example the stent device frame, formed of a plurality of interconnected rings, as described above, may be embedded in a polymeric matrix703, such as Bioweb® (Zeus Industrial Products Inc). The layers of this polymeric matrix may be applied, e.g., by electrospinning to the entire structure of the stent frame, providing a great deal of flexibility and structural stability. This may also improve its radial proprieties and allow the vascular vessel to open and recover the blood flow.

FIG. 13illustrates one example of a sleeve encapsulating a stent frame. In this example, the sleeve is formed of a porous material (such as ePTFE) that is applied to the frame in an average thickness of between, e.g., about 0.001 inches to about 0.010 inches (e.g., between about 25 micrometers to about 250 micrometers, between about 40 to about 80 micrometers, between about 50 to about 70 micrometers, etc.). The pores may be a variety of different sizes, depending upon the needs. In some variations the sleeve may be formed by electrospinning the material onto the stent frame, using polymer fibers with thicknesses ranging from nanoscale to microscale. Fabrics with complex shapes can be electrospun from solutions, producing a broad range of fiber and fabric properties. This technique has the ability to create encapsulation technology, spin membrane/sheet, and develop 3-D structures for coating substrates of varying shapes and sizes.

Returning toFIGS. 8A-8C, in general, the rings are formed of a length of material (e.g., metallic and or polymeric material) that forms, around the radius of the stent, a pattern of repeating biphasic cells, as shown inFIG. 8B. The repeating biphasic cells801typically include a pair of flattened top regions803,805that are connected by an intermediate region807. In some variations the flattened top region forms a pair of open trapezoidal portions, such as shown inFIG. 8C. InFIG. 8C, the open trapezoidal portion (dashed box809) includes a first side or leg811, a second side (corresponding to the flattened top803), and a third side or leg815. This open trapezoidal portion has a distal-facing opening817. Similarly, a second open trapezoidal portion819, oriented 180 degrees off of the first open trapezoidal portion809, includes a fourth side821, a fifth side (corresponding to the flattened top805), and a sixth side or leg823. The second open trapezoidal portion has a proximal-facing opening818. The first and second open trapezoidal portions may be connected by intermediate regions807. For example, the third side815of the first open trapezoidal portion may be connected to the fourth side of the second open trapezoid portion by a connector region807, as shown, and the first side of the first open trapezoidal portion is connected to the sixth side of a second open trapezoidal portion of the next biphasic cell.

The first open trapezoidal portion and the second open trapezoidal portion may have different ‘trapezoidal’ shapes. For example, inFIG. 8B, the first and second open trapezoidal shape is approximately rectangular809, and open on one side, as shown inFIG. 8C. Both the first and second open trapezoidal portions in the exemplary biphasic cell shown inFIG. 8Care the same general shape.FIGS. 9A-9Cillustrate another example of a repeating biphasic cell forming a ring of a stent device as described herein, in which the first biphasic cell is an open trapezoidal portion having an isosceles (or keystone) shape905, while the second open trapezoidal portion907has a more rectangular shape, at least in the un-expanded shape (shown inFIG. 9A). The dimensions of the open trapezoidal portions (e.g., the lengths of the flattened top regions901,903) are approximately the same.

FIGS. 10A-10Billustrate another example of a repeating biphasic cell1001in with the first and second open trapezoidal portions1005,1007are approximately the same (e.g., isosceles) shape. As shown inFIG. 10B, the open trapezoidal portion1005in this example includes first1009, second (flattened top1011) and third1013sides. The first1009and third1013sides are angled inwards forming the open isosceles trapezoidal shape. The angle (α) shown provides and angle of the first or third sides relative to the intermediate connector1017.

As shown in all of these examples the open trapezoidal shapes may have rounded (curved) edges. In some variations the open trapezoidal shapes may have straight edges (e.g., angled edges). In addition, the flattened tops (e.g.,803,805,901,903) may be flat or approximately flat, as shown. Thus, they may be curved slightly (typically <15 degrees of curvature, e.g., <12 degrees, <10 degrees, <8 degrees, etc.). The flattened tops of the first and second open trapezoidal portions shown are parallel, where in the context of the flattened (e.g., slightly curved) tops, the term parallel means substantially, parallel, so that an average vector through the flattened top portion of the first open trapezoidal portion (see, e.g.,832,FIG. 8A) is parallel to an average vector through the flattened top portion of the second open trapezoidal portion.

FIGS. 8B-8C, 9A-9C and 10A-10Bschematically illustrate the repeating biphasic cells; in practice the cells may be formed of a length of material having a width, w, as shown inFIG. 8A. In this example, the width is constant; in some variations the width may be narrower, e.g., in the intermediate region connecting the open trapezoidal regions. InFIG. 8A, the exemplary portion of the repeating biphasic cell shows an open trapezoidal portion819having a proximal-facing opening818and half of the adjacent open trapezoidal portions809,819′ having distal-facing openings.FIG. 8Aalso shows an example of an omega-shaped connector851that is connecting to the flattened top of the open trapezoidal portion819at a middle region. The omega connector includes an arc (“domed”) region853and two laterally extending arms extending from the arc855. The ends of the omega-shaped connectors may be L-shaped857,857′ so as to connect perpendicularly to the flattened top(s).

In general, the repeating biphasic cells forming the rings may have a generally interconnected “U” shape, with the U-shapes alternating as distal-facing and proximal facing radially around the circumference of the stent in each ring. As shown and described above, the generally U-shaped geometry may also be described an open trapezoidal portion. Thus, the U-shapes may have an inwards curved part in the beginning of the figure and afterwards an outwards curve. The tops of the U′s may be connected to each other by an intermediate region, which may be angled or curved, as shown. Thus, the repeating biphasic cell may be formed of a pair of connected U-shapes.

The repeating biphasic cell shapes allow the stent to expand adequately and give the stent enough stability to expand and maintain the peripheral vascular vessel open. The radial stability and homogeneity of the stent may be improved by including a sheath, e.g., embedding it in a membrane, as described above.

FIGS. 9A-9Cillustrate the effect of expansion of the stent on a portion of a ring, showing the movement of the intermediate region909and/or the legs of the open trapezoidal region(s) as the device transitions from an unexpanded configuration (shown inFIG. 9A) to an expanded configuration (shown inFIG. 9C). For example, inFIG. 9Athe repeating biphasic cell pattern is shown in the unexpanded configuration, and the first and second open trapezoidal portions905,907are shown with the first911and third913sides and fourth915and sixth917sides angled slightly inwards and the first and second open trapezoidal portions905,907are connected to each other by an intermediate region909(adjacent repeating biphasic cells are also connected by intermediate regions909′).FIG. 9Bshows a schematic of the repeating biphasic cell ofFIG. 9Aafter the ring formed by the repeating biphasic cell has begun to expand, e.g., by applying an expansion force from a balloon. InFIG. 9B, the first and third sides of the proximal-facing open trapezoidal portion901have opened slightly (e.g., expanding the open trapezoidal shape) and the angle of the intermediate regions909,909′ has changed as well. Similarly, the fourth915and sixth917sides have also opened slightly. As expansion continues, inFIG. 9Cthe first911and third913sides and the fourth915and sixth917sides have opened relative to the flattened tops901,903even more, resulting in the expansion (without substantial foreshortening) of the repeating biphasic cells.

FIGS. 11 and 12illustrate an example of a stent device similar to those described above. InFIG. 11, a portion of a stent frame1100encapsulated in a sleeve1103is shown. The frame is in an un-expanded configuration.FIG. 11shows an omega-shaped connector1104connected via an L-shaped connector1101to a flattened top of a first open trapezoidal portion1111having a distal-facing opening (the distal direction1121is ‘up’ inFIG. 11). The opposite end of the omega-shaped connector1109is a second L-shaped connector (e.g., a right-angled connector) that is connected to a flattened top of another open trapezoidal portion1113having a proximal-facing opening on an adjacent ring of the stent.

A stent such as the one shown inFIG. 11is shown in an expanded view inFIG. 12. In this example, similar to that shown inFIG. 9C, above, the stent frame1200is expanded so that the sides of the open trapezoidal portions forming the distal- and proximal-facing openings are spread further apart and the angle between the interconnecting intermediate regions and the flattened top regions is larger, while the flattened top regions remain parallel, and essentially unchanged from the un-expanded configuration. InFIG. 12, the distance between the flattened ends1203is much larger than in the un-expanded configuration. The omega-shaped connector(s)1205continue to connect the adjacent rings together, while bending to minimize foreshortening of the stent, even when the diameter of the stent increases more than twice its un-expanded diameter.

As described above, the rings forming the stent are interconnected through the omega-shaped crosslinks that build up the stent. Every cylindrical ring may be connected to another cylindrical ring through two crosslinks. The crosslinks may be placed every two connections points, as shown inFIG. 1A-1F, above. The crosslinks are not typically placed on the same connection point as the adjacent rings, but (as shown) may repeat the pattern every other ring. The omega shape may give the stent flexibility when it has to expand. For example, the crosslinks design may allow them to be embedded in a material (e.g., ePTFE) as well as to be crimped and uniformly expanded without ruptures. This type of crosslinks may allow the stent to crimp in the catheter without overlapping each other. As will be described below inFIGS. 16A-16B, the rings may not overlap when the stent is compressed and/or bent in the catheter. The crosslinks may be identical and may have the same organization (orientation) along the stent's length. The stent can be compressed to a diameter that is smaller than the one it was designed in, in order to be placed correctly on the balloon, to obtain a thin profile when placed on the catheter and/or to avoid the stent migration when introduced in the tortuous paths of the vascular vessels.

Thus, in some variations, the membrane, together with the repeating biphasic cell pattern that forms the stent, may make the stent flexible, and the crosslinks position may improve the stent's flexibility, giving a uniform flexibility in the whole structure when the stent graft is bent or kinked. The uniform flexibility may be assisted by the sleeve (e.g., membrane) and the link between the rings through the omega-shaped connectors (crosslinks).

The stent devices described herein are highly flexible, and may be bent over a tight radius of bending without kinking. For example,FIGS. 14A and 14Billustrate the resistance to crushing of these stents. InFIG. 14A, the graph illustrates compression at 50% of the diameter of the stent, which occurs when a force of about 7.5 N is applied. The test shown inFIG. 14Awas performed until the stent was compressed approximately 50% of its length. As shown inFIG. 14B, the maximum force reached was about 9.5 N.

The mechanical properties, including the flexibility and resistance to kinking, was apparent when compared to other prior art stents having similar dimensions. For example,FIG. 15A-15Cillustrate various prior art stents in which the flexibility was examined when bending the stents 90 degrees with a very short radius of bending (bending at almost a right angle). For example,FIG. 15Ashows bending of a first prior art stent1501, showing an 8×58 mm stent (“LifeStream” covered stent by CR Bard, having a sinusoidal stent pattern with an offset connector between adjacent rows of sinusoids). This stent kinked1503at tight bend radius, as shown. Similarly,FIG. 15, showing an 8×59 mm prior art stent1505(“Advanta V12” covered stent by Getinge is a PTFE covered stent having an open cell pattern of adjacent zig-zags interconnected by longitudinal links); this stent also kinked1507. The prior art stent1509inFIG. 15C(“BeGraft” covered stent by Bentley, having a repeating pattern of curly bracket-shapes) also kinked1511, though less than the devices inFIGS. 15A and 15B.

In contrast the stent devices described herein do no appreciably kink. For example a covered stent device having a plurality of adjacent rings arranged transverse to a length of the device, wherein each ring is a ring comprising length of material arranged radially around the length of the stent device as a plurality of repeating biphasic cells, as described above, when bent 90 degrees over the same bend radius did not kink, as shown inFIGS. 16A and 16B. InFIG. 16A, the 5×38 mm stent1601did not kink at the bend1603, in contrast to the prior art devices. Similar result were seen with a 6×38 mm stent1605, as shown inFIG. 16B.

Because the stents described herein also have both a high flexibility, high resilience and a high resistance to kinking, these stents are highly navigable, able to navigate even the most tortious vessels. Navigability testing was performed on the exemplary stent devices described herein. The navigability test consists of introducing a catheter with the stent covered with ePTFE in a device that simulates the peripheral arterial vasculature, such as the device (“jig”) shown schematically inFIG. 17A. The test was performed by a physician specialized in stenting technique. The result of the tests is qualitative, but showed extremely high degrees of navigability and flexibility. The devices described herein were successfully deployed in vessels having diameters of between 3-8 mm (e.g., 3, 4, 6 and 8 mm respectively). For example,FIG. 17Bshows an example of a navigability test in which a catheter including a stent1701was navigated through a tortious model of a vessel relatively easily. The model used has more complex trajectories than typical peripheral human anatomy. A catheter with a stent graft was navigated smoothly through the device, including through regions of high tortuosity without damage and remained positioned in the catheter. The stent graft has adequate flexibility to traverse complex trajectories, including 30 degree, 45 degree, 60 degree and 90 degree bends.

In general, the stents described herein may be any appropriate size (e.g., unexpanded diameter, expanded diameter, and length). The configuration of repeating biphasic cells and omega-shaped connectors described herein may be particularly well suited for smaller diameter (e.g., 7 m or less) and/or smaller length (e.g., 40 mm or shorter) devices.FIGS. 18A-18Deach provide example parameters for four different examples of stents as described herein. All of these exemplary stents were made as covered stents, with an ePTFE sheath (in this case the sheath encapsulated the stent frame as described above). For example,FIG. 18Adescribes a 5×18 mm stent graft having an initial (unexpanded) diameter of 2.1 mm and final (30 seconds after removal of the balloon) diameter of 5.0 mm.FIG. 18Bdescribes a similar 5×38 mm device, having a starting diameter of about 2.2 mm and a final (30 seconds after removal of the balloon) of about 4.9 mm.FIG. 18Cshows an example of a 6×18 mm stent, andFIG. 18Dshows an example of a 6×38 mm stent device. In general, all of these devices went from an unexpanded configuration to an expanded configuration of greater than 2×the unexpanded configuration yet had less than 7% foreshortening (e.g., less than 6.5%, less than 6%, less than 5.5%, etc.).