Patent Application
20100070016
This invention relates in one aspect to a method of loading a self-expanding stent device into a delivery sheath, in which the stent device, in a radially contracted delivery configuration, is axially held on an inner catheter and advanced axially into the sheath for delivery to a stenting site in which the sheath is withdrawn to release the stent device for radial expansion. In another aspect, the invention relates to a stent device delivery system comprising a self-expanding stent device within a percutaneous transluminal delivery sheath, where the sheath withdraws proximally to release the stent device at a stenting site, while an inner catheter within the stent device retains the stent device at the site during withdrawal of the sheath.
A stent device is a tubular vascular implant that has structure able to support a segment of a blood vessel or other anatomical lumen against collapse, while allowing blood or other bodily fluid to flow through the lumen of the stent device. The stent device is delivered with a delivery catheter to the site where a diseased segment of blood vessel is located and deployed there to support the blood vessel against radial collapse. The stent device is advanced to the site in a collapsed configuration and expanded to contact the inner wall of the blood vessel upon deployment.
There are stent devices that require forced expansion such as by inflating a balloon inside the lumen of the stent device and self-expanding states that are so made that they automatically expand to the radially expanded configuration once given the radial freedom to do so; that is once the stent device is unconstrained. It is with this latter type of stent device that the present disclosure is concerned.
A stent device includes a tubular framework that is resistant to radial compression so that the blood vessel is maintained open. The stent device may include a cover on the inner and/or the outer surface of the framework, in which case the stent device is often termed a stent graft. If the framework is without inner and outer coverings, the stent device may be labelled a bare stent.
One suitable material for making the framework of the stent device is the nickel titanium shape memory alloy known as NITINOL. Such stents may be put into a collapsed configuration at a low temperature and a memory of a radially expanded configuration is maintained. The nickel titanium material is biologically compatible and returns to the expanded configuration between room temperature and body temperature.
A self-expanding stent device is subjected to axial forces during loading of the stent device into an outer sheath of a delivery system and also during deployment of the stent device from the outer sheath of the delivery system to a site of a vascular lumen where it is to be implanted. During these procedures, the stent device is held axially in position by a stent device pusher and the outer sheath is moved axially relative to the stent device and stent device pusher. The stent device pusher may be the same element for the loading procedure as well as the deployment procedure. The stent device is loaded into the outer sheath in a crimped state. Accordingly, the outer sheath constrains radial expansion of the stent device. Therefore, as the outer sheath slides over the stent device, drag force between the outer sheath and the stent device is translated to axial forces on the stent device that is held by the stent device pusher.
WO 96/39998, which is incorporated by reference into this application, discloses a delivery catheter where the inner catheter has a stop mounted on it axially adjacent a proximal end of the stent device. The stop serves as a stent device pusher, preventing axial movement in the proximal direction as the outer sheath is retracted. For short, axially strong stents, this design is fine. A particular application may require longer stent devices that are desirably flexible so that the tortuous passageways of the vascular system can be traversed. Flexibility and axial strength present a trade-off in properties, where a more flexible stent device is an axially less strong one. In designs of delivery catheters where a stop acts on a proximal end of the stent device, there is a greater risk with more flexible stents of the stent device deforming in the longitudinal direction as friction between the outer sheath and the stent induces axial forces that are focused at the proximal end of the stent.
International patent publication number WO 00/71058, which is incorporated by reference into this application, recognised this problem with low column strength stent devices being axially held on an inner catheter at the proximal end of the stent device. The document discloses to use a stabiliser disposed within the interior of the stent device that is adapted to engage the inner periphery of the stent device. The surface element may be a high friction surface or a plurality of protuberances engaged with the inner surface of the stent device. In one example, the inner catheter may be coated with a pressure-sensitive adhesive. The stabilizer serves to transmit longitudinal force to the stent device, and displaces the stent device relative to the outer sheath without collapsing the low column strength stent device.
International patent publication number WO 2004/096091, which is incorporated by reference into this application, discloses a stent device delivery system that aims to distribute axial forces along the stent device during loading of a self-expanding stent device into an outer sheath or deployment of the stent device out of the outer sheath. This is achieved by the provision of an inner catheter with protrusions and recesses along an outer surface, where the protrusions are embedded within an inner cover layer, made of expanded polytetrafluouroethylene (ePTFE), of a stent device. The embedded protrusions provide a “form fit” between the stent device and the stent device pusher, which means that as the outer sheath is moved relative to the stent device, resultant axial forces on the stent device are effectively distributed along it.
As stent devices become more flexible the relevance increases of uniformly distributing axial forces along and about the stent device during loading and deployment of the stent device.
It is, therefore, an object of the present invention to provide a stent device delivery system and a method of loading the stent device to the delivery system, whereby axial forces caused by an outer sheath moving relative to a stent device axially held on an inner catheter are effectively distributed uniformly along and about the stent device.
In view of the above object, a first aspect of the present invention provides a stent device delivery system, comprising a stent device pusher, a radially self-expandable stent device and an outer sheath. The stent device comprises a lumen and defines a longitudinal axis. The stent device pusher comprises protrusions with axially extending spaces between them. The stent device is constrained in a radially contracted state by the outer sheath so that the protrusions engage an inner surface of the stent device at positions axially distributed along the stent device. The protrusions thus provide a bed for the stent device. The delivery system is characterised by a tacky material axially distributed along the stent device providing tackiness between the stent device pusher and the inner surface of the stent device. The tackiness and the protrusions serve to resist axial movement of the stent device relative to the stent device pusher as the outer sheath slides axially over the stent device. The tacky material is such that it allows the stent device to peel from it and expand to a radially expanded state as the outer sheath slides axially over the stent device to unconstrain/release the stent device.
A method of loading the stent device into an outer sheath of a stent device delivery system is also provided. The method comprises providing a radially self-expandable stent device having a lumen and defining a longitudinal axis. The method also includes providing a stent device pusher comprising protrusions with axially extending spaces between them. The method includes constraining the stent device within the outer sheath so that an inner surface of the stent device engages the protrusions at positions distributed axially along the stent device. The protrusions provide a bed for the stent device. The method is characterised by providing tackiness between the inner surface of the stent device and the stent device pusher with a tacky material. The tacky material is distributed along the stent device. The tackiness and the protrusions serve to resist axial movement of the stent device relative to the stent device pusher as the outer sheath slides over the stent device. The tacky material is so as to allow the stent device to peel from it to expand to a radially expanded state when the outer sheath is retracted and the stent device is thereby unconstrained.
In a second aspect, the present invention provides a stent device delivery system, comprising a stent device pusher, a radially self-expandable stent device and an outer sheath. The stent device comprises a lumen and defines a longitudinal axis. The stent device pusher comprises a compressible bed for the stent device. The stent device is constrained in a radially contracted state by the outer sheath so that the stent device is embedded in the compressible bed so that portions of the compressible bed protrude radially into the stent device at positions axially distributed along the stent device. The delivery system is characterised by a tacky material axially distributed along the stent device providing tackiness between the stent device pusher and the inner surface of the stent device. The tackiness and the protruding portions of the compressible bed serve to resist axial movement of the stent device relative to the stent device pusher as the outer sheath slides axially over the stent device. The tacky material is such that it allows the stent device to peel from it and expand to a radially expanded state as the outer sheath slides axially over the stent device to unconstrain/release the stent device.
A method of loading the stent device into an outer sheath of a stent device delivery system is also provided. The method comprises providing a radially self-expandable stent device having a lumen and defining a longitudinal axis. The method also includes providing a stent device pusher comprising a compressible bed. The method includes constraining the stent device within the outer sheath so that the stent device engages the compressible bed. Portions of the compressible bed protrude radially into the stent device at positions distributed axially along the stent device. The method is characterised by providing tackiness between an inner surface of the stent device and the stent device pusher with a tacky material. The tacky material is distributed along the stent device. The tackiness and the protruding portions of the compressible bed serve to resist axial movement of the stent device relative to the stent device pusher as the outer sheath slides over the stent device. The tacky material is so as to allow the stent device to peel from it to expand to a radially expanded state when the outer sheath is retracted and the stent device is thereby unconstrained.
In both the first and second aspects of the present invention, the protrusions or protruding portions allow a degree of form fit with the stent device. This mixture of form fit and tackiness has been found to be particularly effective in allowing uniform distribution of the compressive force along the stent device as the outer sheath is dragged over the stent device's outer surface. Further, the tackiness will provide some force holding the stent device in the radially contracted state, which serves to reduce the strain on the outer sheath.
In a preferred embodiment, the first and second aspects of the present invention are combined so that the protrusions of the first aspect are compressible and the stent device is embedded in the compressible protrusions so that portions of the compressible protrusions protrude into the stent device at positions distributed axially along the stent device or the compressible bed of the second aspect forms protrusions with axially extending spaces between them.
The protrusions are, by the restraining force of the outer sheath, compressed between the stent device and an inner catheter of the stent device pusher. Thus, the amount of protrusions that are compressed contribute to the crimping force required to load a stent device into an outer sheath and the amount of radial strength the outer sheath needs to restrain the stent device. It can, therefore, be advantageous to reduce the amount of protrusions distributed along the stent device, but a sufficient axial hold on the stent device during retraction of the outer sheath must also be provided. The combination of protrusions and tackiness allows such reduction in the number of protrusions because the tackiness contributes to axial resistance. A number of types of tacky materials can be selected and distributed along the stent device in a number of ways with the aim of distributing the axial forces caused by drag as the outer sheath slides over the stent device, while at the same time ensuring that the tacky material is not so tacky as to prevent the stent device from expanding into its radially enlarged state during deployment.
The tacky material offers a degree of radial force holding the stent device to the stent device pusher and thus offers some resistance to radial expansion of the stent device, requiring the stent device to peel away from it during radial expansion. The tacky material may be a rubber material, a silicone adhesive or an adhesive based on polyether block amides, such as the one sold under the trade name PEBAX. The presently most preferred material is PEBAX 3533. PEBAX 3533 is an extremely soft material (about 35 shore durometer) that has been found to have the right amount of tackiness. The tacky material is an adhesive material in a preferred embodiment, adhesively bonding the stent device pusher to the inner surface of the stent device. The tacky material may be one that can be activated by exposure to radiation for flexibility in manufacturing.
In one preferred embodiment, the tacky material is uniformly distributed along and about the inner surface of the stent device. This provides effective force distribution both along the stent device and about the circumference of the stent device.
One preferred design has the tacky material in a helix about the longitudinal axis of the stent device, the helix extending along the length of the inner surface of the stent device. Such a uniform configuration also facilitates uniformly distributing the axial forces along and about the stent device as the sheath is retracted over the stent device during deployment. This configuration may also be advantageous as it allows a relatively strong tackiness to be used for the purpose of fixing the axial position of the stent device to the stent device pusher, while at the same time offering a sufficiently low radial peel force for the purpose of allowing the stent device to expand as the outer sheath is retracted during deployment.
In a preferred embodiment, there is tackiness between the stent device bed and the inner surface of the stent device by way of the tacky material.
Preferably, the protrusions allow a form fit between the stent device pusher and the stent device serving to resist axial movement of the stent device relative to the stent device pusher by deforming the stent device such that portions of the stent device extend radially inwardly axially between the protrusions.
Engagement between the sides of the protrusions and the portions of the stent device between (along an axial line between the protrusions) them can provide a form fitting axial lock, while the tackiness makes use of the outer surface of the protrusion for resisting axial movement of the stent device relative to the stent device pusher. This mixture of form fitting protrusions and tackiness has been found to allow uniform distribution of the compressive force along the stent device as the outer sheath is dragged over the stent device's outer surface.
The stent device preferably includes a tubular frame for resisting radial forces to support and keep open a vascular portion and an inner cover, such as an ePTFE layer, providing a layer covering an inner surface of the tubular frame. The tubular frame may be in the form of a mesh and so have apertures through the frame. The tubular frame is preferably made of Nitinol. The inner cover may provide a liquid impermeable inner wall to the stent device. In this case, the tacky material adheres to the inner cover. The protrusions deform the inner cover to provide some form fit with the stent device.
Preferably, the tacky material is an adhesive material in that it adhesively bonds to an inner catheter of the stent device pusher. In this way, the tacky material adhesively secures to the inner catheter and also provides tackiness to the inner surface of the stent device.
The tacky material may be radially compressed into a deformed state between the outer sheath and the stent device where the tacky material is resiliently biased radially outwardly. This feature of the tacky material ensures a tight fit between the inner catheter and the stent device so as to ensure strong engagement of the protrusions with the stent device and thus sufficient resistance to axial movement of the stent device relative to the stent device pusher.
In one embodiment, the protrusions are in the form of bands and distributed along the stent device with spaces between them. Alternatively, the protrusions may be in the form of a helix extending along the length of the stent device. In another alternative, the protrusions may be in the form of helices distributed along the stent device with spaces between them. Taking a cross-section of the stent device pusher along the longitudinal axis will reveal how a helix can be considered to give protrusions separated with an axial space between them even though the helix is just one continuous protrusion. The pitch of the helix will determine the space between adjacent protrusions along an axial line.
The pitch of the helix or the density of the bands or helices as well as the height of the protrusions in a radial direction can be determined based on the degree of engagement with the stent device that is needed, while taking into consideration the desire to reduce the crimping force for compressing the protrusions and the resulting restoration force on the outer sheath and results that prove optimal for a particular application.
In an alternative embodiment, the compressible bed may form a continuous layer extending along and about the inner surface of the stent device. The stent device is embedded in the bed. This embodiment may offer manufacturing advantages as compared to embodiments where the compressible bed is formed as protrusions engaging the inner surface of the stent device and distributed along it with spaces positioned axially between the protrusions.
The protrusions or the compressible bed may themselves be formed of tacky material or may be made of some other material with tacky material applied to it for adhering to the inner surface of the stent device. In this latter case, and in the instance of protrusions, the tacky material is preferably also used to secure the non-tacky material to an inner catheter of the stent pusher. Forming the protrusions or compressible bed of the tacky material may be advantageous for reducing manufacturing steps, but other materials may offer greater design flexibility. In particular, the tacky material may be compressible to deform under the constraining force of the outer sheath to provide the tight fit between the stent pusher and the stent device, which means that the non-tacky material is not required to be deformed by the constraining force of the outer sheath.
Preferred embodiments of the present invention will be described in the following with reference to the figures.
A tubular, radially expandable, stent device 2 is shown in
Also shown in
In order to load the stent device 2 onto the stent device pusher 8, the stent device 2 is crimped into its radially contracted state about the stent device pusher 8 so that the stent device pusher 8 extends through the lumen of the stent 6, from one end to the opposite end. The bands 12 will protrude into the inner cover material 4 of the stent device 2 and the inner cover material 4 will protrude into the axial space 14 between the bands 12, thereby providing a form fit. Further, the stent device 2 will be embedded in the bands 12, causing portions of the bands 12 to protrude radially into the stent device 2. This latter effect may be particularly prevalent in bare stent applications. Although there is embedding, the stent device 2 still defines a tubular outer periphery that is radially outward of a tubular outer periphery of the bands 12. Radially extending edges of the inner cover material 4 and the bands 12 will result where the bands begin and end. Further, embedding of the stent device 2 into the bands 12 will cause radially protruding portions of the bands 12 to have radially extending edges engaging radially extending edges of the stent device 2. These interfacing edges provide an axial lock serving to resist relative axial movement between the stent device pusher 8 and the stent device 2. The material of the bands 12 adhesively bonds the bands 12 to the inner catheter 14. The adhesive material also serves to present a tacky surface to the inner surface of the stent device 2 to resist relative axial movement between the stent device 2 and the stent device pusher 8.
The stent device pusher 8, with the contracted stent device 2 mounted on it, is loaded into an outer sheath (not shown) of a stent device delivery system. The outer sheath serves to maintain the stent device 2 in its contracted state while the stent device 2 is delivered to a vascular lumen. The bands 12 are deformed into a compressed configuration by the crimping force of the stent when it is mounted about the stent device pusher 8 and this radially inward force is maintained by the outer sheath. The adhesive material of the bands 12 is resilient in nature and thus provides a radially outward force tending to restore the bands 12 from their compressed configuration. This thus forces the bands 12 into the inner surface of the stent device 2, thereby reinforcing the form fit and the tacky interaction between the stent device 2 and the pusher 8.
The outer sheath slides over the stent device 2 as the stent device 2 is loaded into the outer sheath. The relative position of the stent device pusher 8 and the stent device 2 is maintained as the outer sheath slides over the stent device 2 by the tackiness and the form fit therebetween. The drag of the outer sheath over the stent device 2 causes axial forces on the stent device 2. The mixture of form fit and tackiness has been found to provide a particularly effective way of facilitating distributing of these forces uniformly along the stent device 2 during loading of the stent device 2 into the outer sheath.
A stent device delivery system will be used to position the stent device 2 mounted on the stent device pusher 8 at the desired location along a vascular lumen. The outer sheath is then retracted, which unconstrains the stent device 2 allowing the stent device 2 to progressively, in the axial direction, expand to the expanded state and engage and support the inner wall of the vascular lumen. As the stent device 2 expands, it peels away from the tacky interaction and thus dismounts from the stent device pusher 8. In the expanded state, the form fit with the inner surface of the stent device 2 and the tacky interaction is lost, leaving the stent pusher 8 free to be removed from within the stent device 2 and removed from the body.
The wire is helically wrapped about the inner catheter 24 and adhesively bonded to the inner catheter 24 with an adhesive material. The wire and the adhesive material form axially distributed protrusions 22. The adhesive material also serves to provide a tacky interaction between the protrusion 22 and an inner surface, which is preferably an inner cover of for example ePTFE, of a stent device. The adhesive is preferably PEBAX 3533, which has been found to have the right amount of tackiness. Alternative materials such as silicone adhesive or rubber as described above may be used, provided they offer a radial holding force from which the stent device peels from during expansion.
Only a part of the pusher element 8 is shown in
When the stent device is mounted on the stent device pusher 18, the protrusion 22 embeds within an inner cover of the stent device providing a form fit that serves to resist relative axial movement between the stent device pusher 18 and the stent device. Adhesive material is provided between the inner catheter 24 and the wire to bond them together. The inner cover of the stent device will deform about the protrusion 22 when the stent device is crimped onto the stent device pusher 18, causing the inner cover to be in contact with the adhesive material bonding the protrusion to the inner catheter 14. Accordingly, adhesive material does not necessarily need to be provided on the radial top of the wire. Instead, the inner cover may access the adhesive material from either side of the wire 22 by wrapping the inner cover about the wire 22.
During delivery of the stent device, as the outer sheath is retracted and the stent device is able to expand, the stent device peels away from the tacky interaction and thus dismounts from the stent device pusher 18.
The layer 21 is preferably sprayed on the inner catheter 34 and bonds to the inner catheter 34. Preferably, the layer 21 is made from a rubber material. Alternatively, the layer is made from a silicone glue material or is a polyether block amide based adhesive, such as the one sold under the trade name PEBAX 3533. These materials provide a tacky interaction with the inner surface of the stent device, which the stent device peels away from during radial expansion for deployment.
The thickness of the layer of tacky material 32 or the protrusions 12, 22 made of the tacky material may be in the range of 0.05 mm to 0.25 mm, for example.
In alternative forms to the embodiment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| GB 0816965.9 | Sep 2008 | GB | national |
This application claims the priority benefit to U.S. Provisional Patent Application No. 61/097,337, filed Sep. 16, 2008, and to U.K. Patent Application No. GB 0816965.8, filed Sep. 16, 2008, each of which is incorporated by reference into this application as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 61097337 | Sep 2008 | US |
