Patent Description:
In recent years, stent-grafts using expanded polytetrafluoroethylene (ePTFE)-based graft materials have been widely recognized in the field of implantable medical devices, thanks to their advantages including excellent biocompatibility and extra slipperiness. Indications for stent-grafts of this type include peripheral vascular embolization, aorta and branch dissections, true aneurysms in the aorta and branches, false aneurysms in the aorta and branches as well as penetrating ulcers in the aorta and branches. This technique greatly reduces operative mortality and postoperative complications, creates less surgical trauma and allows faster patient recovery. Its therapeutic mechanism is to use a special delivery system to deliver a stent-graft to the target lesion site and then cause it to expand to open a blood vessel blocked by a clot or isolate an aneurysm from the bloodstream, eliminating the risk of death due to massive bleeding caused by an aneurysmal rupture or of aneurysmal compression of surrounding tissues or organs. At present, there have been established products in the world, such as the foreign brands Gore Viabahn and Bard Fluency and the domestic brands Aegis, Ankura, etc..

A conventional stent-graft is often crimped and pushed/pulled into a delivery system and deployed from the delivery system by retracting the stent-graft backward or advancing the stent-graft forward. However, since ePTFE-based materials tend to creep under stress, the conventional loading method is less suitable for stent-grafts using such materials. Specifically, such a stent-graft will deform and remarkably shrink compared to its nominal dimensions upon exposure to a considerable stress occurring during the conventional approach.

In order to overcome this problem, most stent-graft products available on the contemporary market are structurally modified to achieve higher loading performance at the price of compromised flexibility. For example, some of them adopt reinforcing ribs usually in the form of nickel-titanium alloy filaments connecting both ends of the stent. <FIG> shows such a stent-graft <NUM> including a reinforcing rib <NUM>. The reinforcing rib <NUM> has tiny stainless steel eyelets through which it is connected to a stent <NUM>. This structure has enhanced axial rigidity which can prevent the stent-graft <NUM> from experiencing permanent length contraction or expansion. However, the reinforcing rib makes the stent-graft less flexible and thus significantly narrows its application (e.g., fabricating it inapplicable to tortuous blood vessels). In addition, it increases the bulk of the stent-graft, which is unfavorable to the loading.

<CIT> discloses a stent graft which includes a stent and a graft engaged with the stent. The graft can include an inner surface and an outer surface. Further, at least one of the inner surface and the outer surface can include a plurality of protrusions as viewed in cross section extending through a longitudinal axis.

Therefore, there is an urgent need in the art for a stent-graft having both good flexibility and high strength.

It is an objective of the present invention to overcome the problems with the conventional stent-grafts by presenting a stent-graft with both good flexibility and high strength and methods of fabricating such a stent-graft, as set forth in the appended claims.

To this end, the provided stent-graft includes a first graft and a second graft surrounding the first graft, wherein a filament and a stent are disposed between the first and second grafts, and wherein the filament and the first and second grafts are all fastened to the stent.

Optionally, in the stent-graft, the filament may be formed of ePTFE, PTFE or FEP.

Optionally, in the stent-graft, a thickness of the filament measured radially with respect to the stent-graft may be smaller than a width of the filament measured circumferentially with respect to the stent-graft.

The stent-graft has a plurality of filaments, the plurality of filaments spiral in opposite directions at a same angle with respect to a central axis of the stent-graft.

Optionally, in the stent-graft, the filament may be arranged between the first graft and the stent, interlaced within the stent and/or disposed between the stent and the second graft.

Optionally, in the stent-graft, the first and second grafts may be both formed of ePTFE.

The present invention also provides a method of fabricating a stent-graft, including:.

Optionally, in the method, the filament may be formed of ePTFE, PTFE or FEP.

Optionally, in the method, a thickness of the filament measured radially with respect to the stent-graft may be smaller than a width of the filament measured circumferentially with respect to the stent-graft.

In the method, there are a plurality of filaments, the plurality of filaments spiral in opposite directions at a same angle with respect to a central axis of the stent-graft.

Optionally, in the method, arranging the filament and the stent outside the first graft may include:.

Optionally, before subjecting the stent-graft to a shaping process, the method may further include:.

Optionally, in the method, the first and second grafts may be both formed of ePTFE.

The present invention also provides another method of fabricating a stent-graft, including:.

Optionally, in the method, the first graft and the second graft may be respectively formed inside and outside both the filament and the stent by an electrospinning process.

According to the present invention, the filament added between the two grafts is flexible and strong and thus imparts both good flexibility and high strength to the stent-graft. As a result, creep deformation of the stent-graft is effectively avoided at
the price of a minor increase in its outer diameter, while facilitating the loading of the stent-graft into a delivery system. The facilitation includes considerably helping in keeping the intactness of the stent-graft during the loading and release processes and providing a possibility of loading it in smaller catheters so as to leave more room for surgical operations of the physician.

A few embodiment examples of the present invention will be described in detail with reference to the accompanying drawings. Features and advantages of the invention will be more apparent from the following detailed description, and from the appended claims. Note that these figures are presented in a very simple form not necessarily drawn to scale, with the only intention of facilitating convenience and clarity in explaining the examples of the invention. In particular, the figures generally give emphasis on different details and are accordingly drawn to different scales.

Reference is now made to <FIG> and <FIG>, wherein <FIG> is a schematic cross-sectional view of a stent-graft according to Example <NUM>, and <FIG> is a schematic front view of a stent-graft according to Example <NUM>. As shown in <FIG> and <FIG>, the stent-graft <NUM> according to Example <NUM> includes a first graft <NUM> and a second graft <NUM> surrounding the first graft <NUM>. Disposed between the first and second grafts <NUM>, <NUM> are filaments <NUM> and a stent <NUM>. The filaments <NUM>, the first and second grafts <NUM>, <NUM> are all fastened to the stent <NUM>. In this example, both the first and second grafts <NUM>, <NUM> are ePTFE grafts, and the stent <NUM> is a metal stent.

With continued reference to <FIG> and <FIG>, in this example, the filaments <NUM> are
disposed between the first graft <NUM> and the stent <NUM>. That is, the filaments <NUM> are arranged within (inside) the stent.

Preferably, the filaments <NUM> are ePTFE, PTFE or FEP filaments. Additionally, the filaments <NUM> are flat strips, i.e., each of the filaments <NUM> has a thickness, measured radially with respect to the stent-graft <NUM>, that is smaller than a width of the corresponding filament <NUM> measured circumferentially with respect to the stent-graft <NUM>.

The filaments <NUM> are disposed between the two grafts (i.e., the first and second grafts <NUM>, <NUM>). The good flexibility and high strength of the filaments <NUM> impart both good flexibility and high strength to the stent-graft <NUM>. Further, as the filaments <NUM> are flat strips, the stent-graft <NUM> can have a small outer diameter, so that the stent-graft <NUM> is easy to use.

With continued reference to <FIG> and <FIG>, in this Embodiment, the number of the filaments <NUM> is more than one, and each of the filaments <NUM> extends parallel to a central axis of the stent-graft <NUM>. Additionally, the multiple filaments <NUM> are evenly distributed circumferentially with respect to the stent-graft <NUM>. As a result, good flexibility and high strength are obtained throughout the whole stent-graft <NUM>.

Reference is now made to <FIG> and <FIG>, schematic illustrations of the stent-graft in use according to Example <NUM>. As shown in <FIG> and <FIG>, during use, the stent-graft <NUM> is loaded into a delivery catheter <NUM>, advanced by the delivery catheter <NUM> to a target site, such as an occluded portion of the iliac artery <NUM>, and then the stent-graft <NUM> is deployed.

In Example
<NUM>, there is also provided a corresponding method for fabricating the stent-graft <NUM>. <FIG> is a flowchart of the method for fabricating the stent-graft according to Embodiment <NUM> of the present invention. As shown in <FIG>, specifically, the stent-graft <NUM> may be fabricated in the following steps.

In step S10, a first graft is wound over a bobbin. The first graft is an ePTFE film and may be wound one or more turns as practically desired. Moreover, a thickness of the first graft may be adjustable as practically desired.

In this Embodiment, the size of the bobbin can be selected according to a design inner diameter of the stent-graft being fabricated. For example, for a stent-graft with an inner diameter of <NUM>, a cylindrical bobbin having a diameter of <NUM> may be chosen. Preferably, before the first graft is wounded over the bobbin, the bobbin can be washed with alcohol in order to ensure its cleanness. The alcohol may be selected as a <NUM>% alcohol solution. After the washing of the bobbin, the bobbin may be placed in the air until it is dried. More preferably, after the bobbin is washed with alcohol and before the first graft is wound thereon, the bobbin may be wrapped with a dust-proof film, in order to ensure its even higher cleanness, which can lead to higher quality of the stent-graft. The dust-proof film may be a piece of aluminum, tin or silver foil-backed paper.

In step S11, the filaments and the stent are arranged outside the first graft. In this Embodiment, the filaments are arranged inside the stent (i.e., between the first graft and the stent). Accordingly, the arrangement of the filaments and the stent outside the first graft may include the steps of: arranging the filaments outside the first graft; and sleeving the stent over the filaments. This will be described in further detail below.

At first, the filaments are attached to the outer surface of the first graft. Preferably, the filaments are made of ePTFE, PTFE or FEP. The filaments may be arranged into stacks each containing one or more of them to achieve a total thickness as practically desired. In general terms, for an application requiring high strength/tensile and creep resistance of the stent-graft, the multiple filaments may be arranged into a high density of stacks each containing one or more of them to achieve a large total thickness, and for an application not demanding high strength/tensile and creep resistance but requiring high flexibility of the stent-graft, fewer filaments may be used without being stacked so that the density and total thickness of them can be reduced.

Preferably, the filaments are flat strips so that the stent-graft has a smaller outer diameter and is less bulky.

In Example
<NUM>, the number of the filaments is greater than one, and the filaments are circumferentially distributed evenly with respect to the bobbin, i.e., evenly along a circumference of the bobbin (more precisely, an outer circumference of the first graft). Moreover, the filaments extend axially with respect to the bobbin, i.e., having their central axes all parallel to a central axis of the bobbin. For example, six filaments having a length of <NUM> (i.e., the stent-graft being fabricated has a length of <NUM>), a width of <NUM> (i.e., the filaments are <NUM> wide along the circumferential direction of the bobbin) and a thickness of <NUM> (i.e., the filaments are <NUM> thick along the radial direction of the bobbin) are circumferentially arranged evenly with respect to the bobbin so that every adjacent two of them are spaced apart from each other by an angular pitch of <NUM> degrees.

Next, the stent is sleeved over the filaments. The stent may be made of a stainless steel, a cobalt-chromium alloy, a nickel-titanium alloy or another material with desired biocompatibility and mechanical properties. Specifically, the stent sleeved over the filaments may be a mesh frame having a wave pattern and made of a cobalt chromium alloy, a nickel-titanium alloy or the like. Generally, such mesh frames are made beforehand and stored, and upon the fabrication of the stent-graft, a suitable one of them is selected and directly used. In step S12, a second graft is wound around the filaments and the stent to complete the stent-graft. The second graft may be wound one or more turns to achieve a thickness of the second graft as practically desired.

At least, in step S13, the stent-graft is subjected to a shaping process and then removed from the bobbin. In this Embodiment, the shaping process performed on the stent-graft is accomplished with a heat treatment. In other embodiments consistent with the present application, it may also be accomplished with a high-pressure heat treatment, a vacuum extrusion process or an adhesive. More preferably, prior to the performance of the shaping process on the stent-graft, the stent-graft may be wrapped with a dust-proof film and then with a crimp tube. Specifically, the dust-proof film may be a piece of aluminum, tin or silver foil-backed paper, while the crimp tube may be selected as a PTFE heat-shrink tube or the like. The heat treatment may be performed on the stent-graft in an oven at a temperature of <NUM> to <NUM> for <NUM> minutes to <NUM> minutes. In this Embodiment, wrapping the stent-graft with the dust-proof film can prevent the stent-graft from being contaminated with dust or the like, thereby ensuring its quality and reliability. The crimp tube sleeved over the dust-proof film allows the stent-graft to be uniformly pressurized during the shaping (curing) process, thus further increasing the quality and reliability of the stent-graft.

The stent-graft resulting from the above process has both good flexibility and high strength, and can be used as desired after it is removed from the bobbin.

Referring back to <FIG> and <FIG>, Example <NUM> differs from Example <NUM> in that,
in Example
<NUM>, the filaments <NUM> are arranged between the first graft <NUM> and the stent <NUM>, while in Example
<NUM>, the filaments <NUM> are interlaced within the stent <NUM>. In this case,
the filaments <NUM> are often partially inside the stent <NUM> and partially outside the stent <NUM>, i.e., the filaments <NUM> are interlaced within the stent <NUM>. Accordingly, the filaments of Embodiment <NUM> are disposed in a different manner from those of Example <NUM>.

In Example
<NUM>, arranging the filaments and the stent outside the first graft particularly includes the two steps of: sleeving the stent over the first graft; and interlacing the filaments within the stent. The stent may include multiple wave-shaped annular wires (mesh frame) arranged coaxially side-by-side, and each of the filaments may be interlaced over the first annular wire, under the second, over the third, and so forth. That is, each of them extends alternately inside and outside the stent (i.e., going alternately up and down the annular wires).

The resulting stent-graft also has both good flexibility and high strength.

In other examples,
the filaments <NUM> may also be all disposed outside the stent <NUM>, i.e., the filaments <NUM> are disposed between the stent <NUM> and the second graft <NUM>. In this case, arranging the filaments and the stent outside the first graft particularly includes the two steps of: sleeving the stent over the first graft; and attaching the filaments to the outside of the stent.

Reference is now made to <FIG>, a schematic front view of a stent-graft according to Example <NUM>. As shown in <FIG>, the stent-graft <NUM> includes a first graft (not shown in <FIG>) and a second graft (not shown in <FIG>) surrounding the first graft. Filaments <NUM> and a stent <NUM> are disposed between the first and second grafts, and each of the filaments <NUM> terminates at both ends of the stent <NUM>. In this example, the first and second grafts are both ePTFE grafts, and the stent <NUM> is made of a cobalt chromium alloy.

Example <NUM> differs from Example <NUM> in that, in Embodiment <NUM>, the filaments extend parallel to the central axis of the bobbin and are circumferentially distributed evenly with respect to the bobbin, while in Example <NUM>, the filaments spiral outside the first graft axially with respect to the bobbin. Accordingly, the filaments of Example <NUM> are disposed in a different manner from those of Example <NUM>.

In particular, in Example
<NUM>, arranging the filaments outside the first graft include the steps of: spirally winding the filaments outside the first graft in the same direction at the same angle with respect to the central axis of the bobbin. Preferably, each of the filaments spirals at an angle of <NUM>°with respect to the central axis of the bobbin.

In other examples, only one such filament may be spirally wound outside the first graft. Similarly, this filament may spiral at an angle of <NUM>°with respect to the central axis of the bobbin.

In generally, for an application requiring high strength/tensile and creep resistance of the stent-graft, multiple said filaments may be used. For an application not demanding high strength/tensile and creep resistance but requiring high flexibility of the stent-graft, only one such filament may be used.

Reference is now made to <FIG>, a schematic front view of a stent-graft according to the present invention. As shown in <FIG>, the stent-graft <NUM> includes a first graft (not shown in <FIG>) and a second graft (not shown in <FIG>) surrounding the first graft. Filaments <NUM> and a stent <NUM> are disposed between the first and second grafts, and each of the filaments <NUM> terminates at both ends of the stent <NUM>. In this Embodiment, the first and second grafts are both ePTFE grafts, and the stent <NUM> is made of a nickel-titanium alloy.

The present invention differs from Example <NUM> in that, in Example <NUM>, the filaments spiral outside the first graft in the same direction at the same angle with respect to the central axis of the bobbin, while in the present invention,
the filaments spiral outside the first graft in opposite directions at the same angle with respect to the central axis of the bobbin.

For example, two said filaments may be spirally wound outside the first graft both in Example <NUM> and the present invention, wherein the two filaments both lead from the right upper corner of the bobbin in Example
<NUM> (i.e., the unidirectional spiraling configuration), while in the present invention,
one filament leads from the right upper corner of the bobbin and the other from the left upper corner thereof (i.e., the bidirectional spiraling configuration).

In other embodiments, the stent-graft may also be fabricated by a method including: fastening the filaments to the stent; and forming the first and second grafts inside and outside both the filaments and the stent, respectively. The formation of the first and second grafts inside and outside both the filament and the stent may be accomplished by an electrospinning process.

In summary, the filament added between the two grafts is flexible and strong and thus imparts both good flexibility and high strength to the stent-graft. As a result, creep deformation of the stent-graft can be effectively avoided at the price of a minor increase in its outer diameter, while facilitating the loading of the stent-graft into a delivery system.

Claim 1:
A stent-graft (<NUM>), comprising a first graft (<NUM>) and a second graft (<NUM>) surrounding the first graft (<NUM>), wherein a plurality of filaments (<NUM>) and a stent (<NUM>) are disposed between the first graft (<NUM>) and the second graft (<NUM>) in a radial direction, and wherein the plurality of filaments (<NUM>), the first graft (<NUM>) and the second graft (<NUM>) are all fastened to the stent,
characterized in that:
the plurality of filaments (<NUM>) each spiral axially with respect to the stent-graft (<NUM>), the plurality of filaments (<NUM>) spiral in opposite directions at a same angle with respect to the central axis of the stent-graft (<NUM>), and the plurality of filaments (<NUM>) are configured to impart both good flexibility and high strength to the stent-graft.