U.S. patent application number 10/737324 was filed with the patent office on 2005-06-16 for removable stent-graft.
Invention is credited to Cully, Edward H., Hutchinson, Erin B., Vonesh, Michael J., Watson, Woodrow W..
Application Number | 20050131515 10/737324 |
Document ID | / |
Family ID | 34654083 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050131515 |
Kind Code |
A1 |
Cully, Edward H. ; et
al. |
June 16, 2005 |
Removable stent-graft
Abstract
A removable device such as a stent-graft, intended for
applications where it may be desirable to remove the device at some
time following implantation. The stent-graft of the present
invention includes a helically-wound stent component provided with
a covering of graft material. It is removable by gripping an end of
the helically-wound stent component with a retrieval device and
applying tension to the stent component in the direction in which
it is intended to be withdrawn from the site of implantation. The
use of such a retrieval device allows the stent-graft to be removed
remotely, such as via a catheter inserted into the body at a
different location from the implantation site. The design of the
stent-graft is such that the stent component is extended axially
while the adjacent portion of the graft separates between windings
of the stent component. The axial extension of the stent component,
with portions of the graft still joined to the stent component,
allows the device to be "unraveled" (or "unwound") and removed
through a catheter of diameter adequately small to be inserted into
the body cavity that contained the stent-graft. It is removed
atraumatically, without incurring significant trauma to the body
conduit in which it had been deployed.
Inventors: |
Cully, Edward H.;
(Flagstaff, AZ) ; Hutchinson, Erin B.; (Parks,
AZ) ; Vonesh, Michael J.; (Flagstaff, AZ) ;
Watson, Woodrow W.; (Flagstaff, AZ) |
Correspondence
Address: |
GORE ENTERPRISE HOLDINGS, INC.
551 PAPER MILL ROAD
P. O. BOX 9206
NEWARK
DE
19714-9206
US
|
Family ID: |
34654083 |
Appl. No.: |
10/737324 |
Filed: |
December 16, 2003 |
Current U.S.
Class: |
623/1.13 ;
623/902 |
Current CPC
Class: |
A61F 2250/0071 20130101;
A61F 2/89 20130101; A61F 2/848 20130101; A61F 2220/005 20130101;
A61B 2017/22035 20130101; A61F 2/07 20130101; A61F 2002/072
20130101; A61F 2002/075 20130101; A61F 2/88 20130101; A61F
2002/9528 20130101 |
Class at
Publication: |
623/001.13 ;
623/902 |
International
Class: |
A61F 002/06 |
Claims
1. An endoprosthesis comprising: a stent component having a small
delivery profile and an enlarged deployed profile, said stent
component having adjacent elements with space between adjacent
elements; and a graft material attached to the stent component
covering the space between adjacent stent elements to form a
continuous luminal surface; wherein following deployment, the
endoprosthesis is adapted to be cohesively disassembled to allow
for its remote removal from a patient.
2. The endoprosthesis of claim 1 wherein the graft material tears
during disassembly to facilitate removal of the stent component and
attached graft material.
3. The endoprosthesis of claim 2 wherein the stent component and
attached graft material are removable at a profile less than the
enlarged deployed profile.
4. The endoprosthesis of claim 2 wherein the stent component and
attached graft material are removable at a profile less than the
small delivery profile.
5. The endoprosthesis of claim 1 wherein the endoprosthesis
disassembles in a helical fashion.
6. The endoprosthesis of claim 1 wherein the endoprosthesis
disassembles and removes in a single piece.
7. The endoprosthesis of claim 1 wherein the endoprosthesis
disassembles and removes in multiple pieces.
8. The endoprosthesis of claim 1 wherein the endoprosthesis
disassembles and increases in length by at least 100%.
9. The endoprosthesis of claim 1 wherein the endoprosthesis
disassembles and increases in length by at least 500%.
10. The endoprosthesis of claim 1 wherein the graft material is
impermeable.
11. The endoprosthesis of claim 1 wherein the graft material Is
permeable.
12. The endoprosthesis of claim 1 wherein the endoprosthesis is
adapted to be controllably foreshortenable by at least about
20%.
13. The endoprosthesis of claim 1 wherein the endoprosthesis is
adapted to be controllably foreshortenable by at least about
50%.
14. The endoprosthesis of claim 1 wherein the graft material is
adapted to be cohesively disassembled during removal of the
endoprosthesis from a patient.
15. The endoprosthesis of claim 1 wherein the removal is
atraumatic.
16. The endoprosthesis of claim 1 wherein the graft material
comprises expanded polytetrafluoroethylene.
17. The endoprosthesis of claim 1 wherein the graft material
comprises a tape having a length that is adapted for splitting
along the length of the tape.
18. The endoprosthesis of claim 17 wherein the tape and the stent
component are helically oriented at pitch angles that are
substantially the same.
19. The endoprosthesis of claim 1 wherein the graft material
comprises a tape, and wherein the tape and the stent component are
helically oriented at pitch angles that are substantially the
same.
20. The endoprosthesis of claim 19 wherein the tape has a length
and wherein the tape is adapted for splitting along the length of
the tape.
21. The endoprosthesis of claim 20 wherein the tape comprises
expanded polytetrafluoroethylene.
22. The endoprosthesis of claim 1 wherein the graft material
includes means for splitting.
23. The endoprosthesis of claim 22 wherein the graft material has a
thickness and the means for splitting comprises a row of
perforations extending through at least a portion of the thickness
of the graft material.
24. The endoprosthesis of claim 22 wherein the graft material has a
thickness and the means for splitting comprises a line of reduced
thickness in comparison to the thickness of the remainder of the
graft material.
25. The endoprosthesis of claim 22 wherein the means for splitting
comprises an anisotropic graft material that is tearable in one
direction and resistant to tearing in a direction transverse to the
one direction.
26. An endoprosthesis having a length comprising: a stent
component; a graft material attached to the stent component to form
a continuous luminal surface; wherein the endoprosthesis can be
partially disassembled in situ to shorten the length of the
endoprosthesis.
27. An endoprosthesis comprising: a stent component having a small
delivery profile and an enlarged deployed profile; a graft material
attached to the stent component to form a continuous luminal
surface; wherein following deployment, the stent component is
adapted to be cohesively disassembled from the graft material to
allow for the remote removal of at least a portion of the stent
component from a patient.
28. The endoprosthesis of claim 27 wherein the graft material
remains in situ following removal of the stent.
29. An endoprosthesis comprising: a stent component having a small
delivery profile and an enlarged deployed profile; said stent
component comprising a wire formed into a generally helical winding
having space between adjacent elements of the generally helical
winding, wherein the generally helical winding provides a generally
tubular form to the stent component and wherein the generally
helical winding includes at least one apex; a graft material
attached to the stent component covering the space between adjacent
elements of the generally helical winding, wherein the graft
material provides a continuous luminal surface; and wherein at
least one of said apices is raised to protrude outwardly from said
tubular form and wherein the resulting raised apex is covered by
said graft material.
30. The endoprosthesis of claim 29 wherein following deployment,
the endoprosthesis is adapted to be cohesively disassembled to
allow for its remote removal from a patient.
31. The endoprosthesis of claim 29 wherein the generally helical
winding has a serpentine form with alternating opposing apices.
32. The endoprosthesis of claim 31 wherein following deployment,
the endoprosthesis is adapted to be cohesively disassembled to
allow for its remote removal from a patient.
33. An endoprosthesis comprising: a structural support having a
small delivery profile and an enlarged deployed profile, said
structural support having adjacent elements with space between
adjacent elements; and a graft material attached to the structural
support covering the space between adjacent elements of the
structural support to form a continuous luminal surface; wherein
following deployment, the endoprosthesis is adapted to be
cohesively disassembled to allow for its remote removal from a
patient.
34. A method of making a removable stent-graft having a stent
component and a covering of graft material, comprising: a.)
providing a stent component having a helical orientation having a
pitch; b.) providing the stent component with a graft material that
covers one side of the stent component and covers spaces between
elements of the stent component, wherein the graft material is
splittable in a direction parallel to the pitch of the helical
orientation of the stent component.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of removable
stent-grafts.
BACKGROUND OF THE INVENTION
[0002] Endoluminal stenting has provided a major advancement in
clinical treatment modalities offering a significant reduction in
perioperative treatment times, iatrogenic injury, postoperative
morbidity and healing times. Even with the unprecedented clinical
advantages of these devices, there still remains a number of
limitations and disadvantages of the technologies currently
available. The two primary technologies available for endoluminal
stenting are the use of bare metal stents and stent devices
provided with a covering or lining of a tubular graft material,
i.e., stent-grafts. Either of these technologies may be made to be
deployed via inflation of a catheter balloon (e.g., stainless steel
stents) or to be self-expanding (e.g., nitinol stents). All of
these technologies exhibit a common disadvantage in that none of
the commercially available devices are designed to be removable
after implantation.
[0003] There are numerous applications for which a removable
stent-graft would be highly desirable. Even though great strides
have been undertaken to enhance biocompatibility of these devices,
it is still a synthetic, non-living tissue device that constitutes
a foreign body. As a result, living tissue has a number of
limitations and/or reactions in coping with such a foreign
body.
[0004] The most common of these is infection. Typically, when a
synthetic device becomes infected, or colonized by bacteria, there
is little success in resolving such an infected device or infected
area short of device removal from the patient. In some instances,
if an infected synthetic device cannot be removed enabling the
antibiotic treatment of the effected living tissue, patient
mortality can result due to septic shock.
[0005] Another issue associated with implantation of endoluminal
stents and stent-grafts is foreign body reaction. Endoluminal
stents and stent-grafts are often employed to limit, or control,
the body's normal healing response (restenosis) to vascular,
luminal, or ductal injury due to balloon dilatation. Even though
these devices aid in limiting the amount of restenosis as a result
of vessel or ductal injury, after a period of time the vessel or
duct may generate a hyperplastic tissue (restenotic) or calcific
stone formation response due to the presence of the foreign body.
Consequently, removal of the device after the appropriate
therapeutic period may be desirable.
[0006] Still another application for a removable stent-graft would
involve providing a removable support structure for delivery of
certain other implantable materials or structures (e.g., tubular
structures) which otherwise do not exhibit the necessary mechanical
characteristics for device delivery without the aid of a temporary,
supporting stent component.
[0007] Further, mechanisms for localized drug delivery continue to
be a highly sought after treatment option which offer many
advantages over systemic drug delivery. Two of the key challenges
in local drug delivery are the delivery mechanism and the drug
elution profile or therapeutic window of the drug delivery. These
are not unusually interrelated. By employing one or more
applications of a removable drug eluting stent-graft, therapeutic
windows can be greatly increased providing unlimited drug
application profiles.
[0008] Thus, the array of clinical treatments modalities for such a
removable endoluminal stent-graft includes: malignant and benign
strictures of the biliary tract due to tumor compression,
anastomotic and bile stone nidus; anastomotic and benign strictures
of the colon, small intestine and ureter/urethra; esophagus
collapse syndrome and gastric reflux erosion; strictures of the
tracheal/bronchial tree; treatment of vascular disease or injury;
and localized drug delivery for various chemotherapy
application.
[0009] Various designs for removable stents are known in the art.
For example, Myler et al. in U.S. Pat. No. 5,474,563 describe a
retrievable stent and retrieval tool. The described stent is
removed intact, at its fully deployed dimensions, and may
consequently pose a risk of trauma during removal.
[0010] U.S. Pat. No. 5,782,903 to Wiktor et al. describes a
removable stent system which comprises a continuous serpentine wire
formed into helical coil. The coil after implantation can be
uncoiled by use of a retrieval line. Beyar et al. in U.S. Pat. No.
6,090,115 also describe a temporary stent system comprising a stent
constructed of a helical coil of biocompatible material. Both of
these references teach that the stent is not covered (i.e., is not
a stent-graft) and therefore provides opportunity for tissue
in-growth into the spaces between the coil structure over time.
This in-growth may result in trauma to the implant site during
retrieval.
[0011] U.S. Pat. No. 5,799,384 to Schwartz et al. teaches a stent
similar to the above-described Wiktor et al. stent. It differs from
the Wiktor et al. stent in that a tape of polymeric film is
provided to the stent wire, the length of the tape running parallel
to the length of the wire with the width of the tape being centered
over the stent wire and therefore extending perpendicularly from
the stent wire a short distance from both sides of the wire. When
the wire is wound into a helical form to create a stent structure,
the polymeric tape provides a sort of graft covering. However, this
graft covering is discontinuous and therefore cannot offer the
advantages of a continuous graft covering extending for all or a
major portion of the length of the implantable stent structure.
[0012] Huxel et al. in U.S. Pat. No. 6,494,908 describe a removable
stent in the form of a helical winding wherein adjacent windings
are in direct contact; removal is accomplished by grasping an end
of the helix and unwinding the helical form. The helical form of
the Huxel et al. device is made from a soft, flexible fiber that is
provided with an outer coating of a bioabsorbable material to
render it rigid for insertion into a body conduit. The device
becomes thinner and flexible over time in order to allow the stent
to be removable after a pre-determined time has passed. U.S. Pat.
No. 5,514,176 to Bosley et al. teaches a somewhat similar device in
the form of a removable stent-graft made from a series of helical
windings with the adjacent windings in contact with each other. An
exterior coating of silicone is provided to seal between the
adjacent windings. Removal is accomplished by unwinding the device
whereby the coating is removed simultaneously with the helical
winding.
[0013] Camrud et al., in U.S. Pat. No. 6,258,117, teach a
multi-section stent which incorporates a connecting structure that
can separate. This ability to separate adjacent segments of the
connecting structure however is promoted as a means to add
flexibility to the implanted device rather than as a way to
atraumatically remove portions of it. Removability of the segments
is not taught or suggested. Iwasaka et al. in US Patent Application
Publication No. 2003/0114922 describe a stent-graft having a series
of discrete, ring-like stent structures along its length. The
device is removed from a body conduit by grasping its distal end
with a retrieval device and everting it from the distal end by
pulling it through itself in a proximal direction. The device is
removed in its entirety rather than being removed segmentally.
[0014] WO00/42949 teaches the construction of an impermeable
stent-graft that is primarily intended for biliary applications.
This stent-graft is not described as being removable.
SUMMARY OF THE INVENTION
[0015] The present invention relates to removable, implantable
devices such as removable stent-grafts or removable filter devices
(e.g., embolic filters or vena cava filters). Such devices are
intended for applications wherein it may be deemed necessary to
remove the device at some time following implantation. Such
applications may include stent-grafts for implantation in urethras,
in biliary ducts, in the vascular system, the large or small
intestine, or in the esophagus or trachea. It may be desirable for
a stent-graft to be removable in applications where the stent-graft
has been inserted to prevent obstruction of a duct by anastomotic
stricture or by a tumor, particularly prior to determining if the
tumor is malignant or benign. It may be desirable for such a
stent-graft to be removable if its intended purpose was temporary,
such as for delivery of a therapeutic agent such as drugs or
radioactive materials to a specific site for a limited time. It may
be also be of value to enable the stent-graft to be removed in the
event that it does not effect its intended purpose and must be
replaced by another device.
[0016] Devices of the present invention comprise a structural
support, such as a stent component, provided with a covering of a
graft material. Adjacent elements of the structural support are
spaced apart, i.e., not in continuous direct contact with each
other when the device is in a relaxed state without any deforming
force applied to it. The covering graft material generally extends
between the ends of the device and covers the spaces between the
adjacent elements of the structural support.
[0017] The stent-graft of the present invention has a continuous
luminal surface, meaning that, prior to removal, the graft material
covering the stent component extends in a substantially continuous
fashion between the opposing ends of the device. While the graft
material may be separable between adjacent windings of the stent
component during removal (as by splitting or tearing) as will be
further described, the graft material is substantially integral
prior to removal and does not include gaps between adjacent
windings of the stent component (as shown by, for example, U.S.
Pat. No. 5,799,384) prior to removal. The continuous luminal
surface does not preclude the possibility of openings through
portions of the graft material at desired locations for purposes of
the particular stent application.
[0018] The graft material covering the stent component may be
provided on the exterior surface of the stent component, the
luminal surface of the stent component, or may cover both the
exterior and luminal surfaces.
[0019] The device of the present invention is removable by gripping
an end of the helically-wound structural support with a retrieval
device and applying tension to the structural support in the
direction in which it is intended to be withdrawn from the site of
implantation. The design of the device is such that the structural
support (e.g., stent component) is extended axially while the
adjacent portion of the graft separates between windings of the
structural support. For a stent-graft, for example, the axial
extension of the stent component, with adjacent portions of the
graft still joined to the stent component, allows the device to be
"unraveled" (or "unwound") and removed through a catheter of
diameter adequately small to be inserted into the body cavity that
contained the previously-deployed stent-graft.
[0020] The stent-graft is cohesively removable (i.e., is cohesively
disassembled), meaning that it is removed in its entirety, without
loss of pieces or the formation of separate remnants during the
removal (e.g., the unraveling) process.
[0021] The stent-graft is remotely removable, in that it may be
grasped at one end for removal by a retrieval device inserted from
a more distant point of entry into a body. Further, the removal is
substantially or entirely atraumatic to the body conduit in which
the device had been originally deployed. This is because the
unravelable stent graft lends itself to removal with minimal force
and to being removed through a relatively small diameter
catheter.
[0022] This "unravelable" stent component may also enable the
delivery of an intraluminal graft to an intended site and
deployment of the intraluminal graft securely against the luminal
surface of that site. Following deployment, the stent component may
be removed (simultaneously with the delivery system, or
alternatively, separately removed at a later time), leaving the
graft component implanted at the site.
[0023] In still another embodiment, the stent-graft of the present
invention may be delivered and deployed at a desired site, with
permanently attached but separate stent components also deployed
and intended to be left implanted permanently at, for example, the
ends of the stent-graft. Another stent component extending along
the remaining length of the device not supported by the permanent
stent components may then be removed following successful
deployment and implantation. This temporary stent component may be
useful, for example, to assure that the device is implanted without
twisting or other misalignment, and thus removed once it has served
its temporary purpose.
[0024] Still further, the stent-graft or the stent component
thereof may be made to be removable in lengthwise sections or
segments.
[0025] The stent component is preferably metallic and more
preferably is stainless steel or nitinol. It may be balloon
expandable or self-expanding. The graft material that covers the
stent component may be of a variety of implantable materials such
as nylon, polyethylene terephthalate or polytetrafluoroethylene,
and is preferably of expanded polytetrafluoroethylene (ePTFE) made
as taught by U.S. Pat. No. 3,953,566 to Gore. Alternatively, either
or both of the stent component and the graft component may be made
of any of a variety of resorbable materials. These resorbable
materials may optionally be used in combination with various
non-resorbable materials for particular applications as
desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIGS. 1 and 1A are perspective views of stent-grafts of the
present invention showing the stent component provided with a thin,
flexible covering of graft material.
[0027] FIG. 2 shows a perspective view of the stent-graft during
removal from an implant site by being cohesively disassembled via
pulling the end fitting through a retrieval catheter by use of a
remotely operated instrument.
[0028] FIGS. 3 and 3A-3D show side views of alternate embodiments
of engagement fittings that protrude from either or both ends of
the stent-graft.
[0029] FIGS. 4A-4D show side views of various means of weakening
the graft covering material to allow it to separate between
adjacent windings of the stent component during removal of the
stent-graft.
[0030] FIGS. 5A-5C illustrate side views of a stent-graft having
multiple engagement fittings that coincide with controllably
disruptable patterns in the graft material, allowing the graft to
be removed in lengthwise segments.
[0031] FIGS. 6A-6B show longitudinal cross sections of an
alternative embodiment wherein the stent-graft has a luminal liner
that is removable at a time subsequent to implantation, while the
remainder of the stent-graft is left in place.
[0032] FIG. 7 shows a longitudinal cross section of an alternative
embodiment wherein the stent component is secured to the graft
material by a resorbable adhesive that allows for removal of the
stent component at a time subsequent to insertion and deployment of
the stent-graft.
DETAILED DESCRIPTION OF THE INVENTION
[0033] FIG. 1 is a perspective view of the device 10 of the present
invention wherein the device is composed of a structural component
such as stent component 14, provided with a thin, flexible covering
of graft material 18. The graft material 18 can be either
impermeable or permeable depending upon the needs of the
application. An impermeable material would prevent the transmission
of fluids and/or cells, such as bile and/or tumor or epithelial
cells, through the graft material while a permeable material would
allow the transmission of fluids through the graft material. It is
also possible to laminate one or more layers of a porous or
permeable material to one or more layers of impermeable material.
This may be done, for example, where the porous material is desired
to provide for tissue attachment to one or both surfaces, while
simultaneously providing a construction that is fluid impermeable
through its thickness. Generally, impermeable coverings are
preferred for biliary applications or applications wherein it is
desired to inhibit or preclude cellular ingrowth.
[0034] In the embodiment shown by FIG. 1, the stent component 14
comprises wire which has been formed into a serpentine shape having
apices 22, which shape is also helically wound into a tubular form.
The radii of the apices 22 of the serpentine shape can be as large
or small as desired for an intended application. Minimal radii
result in the serpentine shape having relatively pointed apices 22,
i.e., a zig-zag form. Attached to the wire at the ends are
engagement fittings 26, which extend from either or both ends of
the device 10. These engagement fittings 26 may be grasped by or
attached to a surgical instrument to provide for removing (e.g., by
cohesively disassembling) the device 10 during remote atraumatic
removal of device 10 from a patient in situ through a small
diameter working catheter or sheath. Removal of device 10 will be
described in further detail.
[0035] The wire used to fabricate stent component 14 is preferably
nitinol wire of, for example, about 0.23 mm diameter. A preferred
nitinol wire is wire of this diameter (available from Nitinol
Devices & Components Inc., Fremont Calif.) that has been 45%
cold worked and electropolished. Most preferably, the stent
component is formed from a single length of wire for simplicity and
lowest possible profile. One method of forming the wire into the
desired serpentine shape is to use a mandrel of similar diameter as
the intended diameter of the desired tubular form of the
stent-graft. The mandrel is provided with appropriately located
pins which protrude radially from the exterior surface of the
mandrel in locations corresponding to the intended locations of the
apices of the serpentine shape. A suitable length of the wire is
then wrapped around the pins protruding from the mandrel surface
creating the helically wound serpentine shape that results in the
form of stent component 10. Selected pins pertaining to optional
raised apices 22r may be placed on appropriately elevated surfaces
to achieve the desired amount of elevation. The general form of and
method of making such a wire stent are described in WO 97/21403
(see, e.g., FIGS. 1A-2 of WO 97/21403 for the wire form which for
purposes of the present invention does not require the additional
coupling member 8 or linking member 20). This wire and mandrel
assembly may be placed into an oven for any desired heat-treating.
Immediately following removal from the oven, the wire and mandrel
assembly is quenched in water at about room temperature, following
which the formed stent is removed from the mandrel.
[0036] FIG. 1 also shows how the adjacent windings (or adjacent
elements) of the helically-wound stent component are spaced apart,
with the graft material covering the space between the adjacent
windings. It is not required that the space between adjacent
windings is covered in its entirety by the graft material, although
full coverage of these spaces between the adjacent elements of the
stent component is generally preferred. The space between adjacent
windings or elements of the stent component exists when the stent
is in a relaxed state, not subjected to longitudinal compression
that could force the adjacent elements to be in contact and
therefore no longer spaced apart.
[0037] The use of the serpentine winding of stent component 14
shown in FIG. 1 allows the completed stent to be deployed with
minimal foreshortening. The stent-graft 10 of the present
invention, when deployed from its small, insertion diameter to its
largest, fully deployed diameter, will foreshorten less than about
10% of its insertion length. It is also capable of foreshortening
less than about 8%, 6%, 4%, 2% or even 0% depending on construction
details when properly deployed. Alternatively, if desired, the
stent-graft may be made to be controllably foreshortenable during
deployment, in significant length amounts, in the interest of
making a length-adjustable device. The use of a flexible graft
material in conjunction with the arrangement of adjacent apices in
the windings of the stent component can allow the device to be
controllably shortened in length during deployment, if desired. It
can, for example, be controllably foreshortenable by the physician
during deployment in an amount equal to about 20% or more of the
fully extended length of the device (after being extended by light
manually applied axial tension, followed by removal of the
tension). It is also possible to provide the device in a form that
can be controllably foreshortenable by the physician during
deployment in an amount equal to about 50% or more of the fully
extended length of the device.
[0038] As also shown by FIG. 1, some of the apices 22r of the
serpentine-wound wire may be raised above the tubular form so that
they protrude somewhat above the outer surface of the remainder of
the stent-graft. These protruding or raised apices 22r may be
useful as anchoring means for the covered stent 10 in that they
will protrude slightly into the wall of any body conduit into which
the stent-graft is implanted. In a preferred embodiment for biliary
applications, the raised apices 22r are generally located at
locations other than at the extreme ends of the stent; they are
typically no closer than about 1 mm to the ends of the stent. These
raised apices 22r are preferably formed during the forming of the
stent wire (preferably nitinol wire and more preferably a single
nitinol wire) into the desired serpentine, helically wound shape
used for the stent component 14. Further, as shown by the
perspective view of FIG. 1A, these raised apices 22r, may
optionally be covered with graft material 18 so as to prevent
in-growth of tissue into the wire mesh structure (i.e., overgrowth
or encapsulation of the apice 22r by living tissue). Prevention of
tissue in-growth into the mesh structure would facilitate
atraumatic removal of the device 10, even if the device had not
been made to be removable by unraveling as described below.
[0039] It is apparent that there are a variety of ways of orienting
the raised apices to achieve differing desired amounts of anchoring
of the deployed stent-graft. Variables include the angle of
deviation of apices from parallel to the longitudinal axis of the
stent component, the number of raised apices, the height of raised
apices, and whether all or any portions of particular apices are
raised.
[0040] It is generally preferred that raised apices alternate with
adjacent apices which are not raised (i.e., adjacent on the same
continuous section of stent wire) in the interest of providing a
good bond between the stent component and covering graft material.
This is particularly true with respect to the embodiment of FIG. 1
and is less critical with regard to the embodiment of FIG. 1A.
[0041] Finally, it is apparent that the use of raised apices as
described is only one means of providing anchoring for a
stent-graft. It is further apparent that, for some applications,
anchoring means such as apices may be undesirable.
[0042] The attachment of the covering material to the stent
component may be accomplished by methods including those described
by U.S. Pat. No. 5,735,892 to Myers et al. Mechanical attachment
may be by methods such as by the use of sutures. The covering
material will preferably be attached to the stent using an adhesive
such as, for example, fluorinated ethylene propylene (FEP) which is
effective as a meltable thermoplastic adhesive. It is apparent that
a variety of adhesives may be used (including thermoset adhesives)
as long as the adhesive chosen is adequately biocompatible. The
adhesive may be applied to the stent in either solid (powdered) or
liquid form by various methods including powder coating, dipping or
spraying. Liquid forms may be diluted if desired with appropriate
solvents as necessary for the chosen method of application. The
adhesive-coated stent component may be heated to ensure uniform
coating of the stent component by causing melting of the
thermoplastic adhesive.
[0043] Alternatively, the coating material applied to the ePTFE
film from which the stent covering is made, may also be relied on
for joining of the graft material to the stent component.
[0044] FIG. 2 illustrates the device 10 being cohesively
disassembled during removal from the body conduit into which it was
previously implanted, by means of the end fitting 26 being pulled
through a retrieval catheter 30 by use of a remotely operated
instrument such as removal tool 27.
[0045] As shown, the thin, flexible covering material (graft
material 18) is disrupted by the tensile force applied to the
stent-graft 10 by the remotely operated instrument 27. As the graft
material 18 is disrupted, it remains cohesively attached to the
adjacent portion (or element) of stent component 14 which is
simultaneously being uncoiled. This disruption, or unraveling, of
the graft material 18 and uncoiling of stent component 14, results
in minimal trauma to the vessel from which it is being removed as
the stent coil diameter is reduced from its expanded state during
the disassembling and retrieval process. Further, the graft
material 18, attached to the stent component 14, forms into a thin
ribbon which fits into a capturing catheter that has been
positioned in close proximity to the end of the implanted device
10. This thin ribbon resulting from the unraveling process may have
a length that is 100%, 200%, 300%, 400%, 500% or even greater than
the length of the deployed stent-graft prior to removal.
[0046] The retrieval catheter 30 need only be adequately large
diametrically to accommodate the anticipated width of the strip of
the stent-graft being removed, i.e., adequately large to accept the
substantially straightened serpentine wire form with a small amount
of attached graft material. The catheter thus may be smaller in
outside diameter than the catheter used previously to initially
deliver and implant the device, and likewise smaller than the
compacted diameter of the stent-graft itself during delivery to the
implantation site (prior to diametrical expansion of the
stent-graft during deployment, i.e., the small delivery
profile).
[0047] FIGS. 3 and 3A-3D show alternate embodiments of the
engagement fittings 26 that protrude from either or both ends of
the device 10. These fittings facilitate secure attachment of the
ends of the device 10 to an appropriate tool (e.g., removal tool
27) for use in initiating and completing the cohesive disassembly
of the device 10. Examples of engagement fittings 26 include a ball
as shown in FIG. 3A, a loop as shown in FIG. 3B, a swaged-on end
piece as shown in FIG. 3C and a threaded end as shown in FIG. 3D.
Other shapes, providing the same function of allowing a removal
tool to grasp, attach, or otherwise securely engage onto the
fittings 26, could be used as well. It is apparent that the designs
of the engagement fitting 26 and removal tool 27 (not shown in
FIGS. 3-3D) must be compatible in order to enable the tool 27 to
effectively grasp and apply tension to the engagement fitting
26.
[0048] Numerous means for rendering the graft material 18 able to
be cohesively disassembled can be contemplated. FIG. 4A shows a
device 10 wherein the graft material 18 is selectively weakened in
a prescribed pattern 34. The graft material 18 may be weakened in
those areas 34 by mechanical means such as a cutting with a blade
or compressing die. Alternatively the graft material 18 may be
weakened by use of energy such as with a laser or controlled
heating. While the patterns 34 may extend entirely through the wall
of the graft material 18, it is preferred that they only extend
through a portion of the thickness of the graft material.
[0049] FIG. 4B shows a device 10 wherein the graft material 18 is
selectively weakened by perforating the graft material in an
alternative prescribed pattern 38. The graft material 18 may be
perforated using numerous means, such as with a mechanical cutting
blade, a cutting die, a laser, or heat. Perforations 38 may extend
entirely through the thickness of the graft material 18, or only
extend through a portion of that thickness. When a multi-layer
graft material 18 is used, the perforations can be made through one
layer, but not through all layers, thereby preventing tissue
in-growth through the graft material 18.
[0050] FIG. 4C shows a device 10 wherein a graft material 18 is
provided having a node 42 and fibril 44 microstructure (e.g.,
ePTFE), of which a small sample area 18e, is shown enlarged. This
graft material 18 is oriented so as to be weaker in the
longitudinal direction than in the radial (circumferential)
direction. The ePTFE microstructure shown has a uniaxial
microstructure, meaning that the fibrils are oriented primarily in
a single direction. The graft material is thus amenable to
splitting in the same direction as its direction of greatest
strength (i.e., the direction of orientation of the fibrils). This
orientation allows for the possibility of the graft material 18
splitting or separating between adjacent windings of the stent
component 14 during removal of the stent in the manner previously
described (i.e., cohesively disassembling). A preferred method of
using such a node and fibril microstructure graft material is to
use a film such as an ePTFE film, that has been cut into a long,
narrow tape with the length of the tape parallel to the direction
of the fibrils. This tape can be used as a graft covering either
over or beneath the stent component 14, or both over and beneath
stent component 14, and is applied as a helical wrap with the pitch
of the helix equal to and parallel to that of the helical pitch of
the serpentine stent wire. This allows for disruption of the graft
material 18 parallel to the pitch of the serpentine stent winding
14, by splitting of the tape parallel to its length (i.e., parallel
to the direction of the fibrils) during stent removal, generally as
shown by FIG. 2.
[0051] The use of a covering graft material with anisotropic
strength properties wherein the graft material is oriented with the
direction of greatest strength in the circumferential direction (as
described above with the ePTFE film) provides the resulting
stent-graft with good hoop strength. Following deployment at a
desired site, such a device may be amenable to further expansion
using a balloon catheter if it is deemed necessary by the
physician.
[0052] FIG. 4D shows a device 10 wherein the graft material 18 is
constructed from a composite of resorbable and non-resorbable
materials. The resorbable materials, which may be desirably located
in selected areas of the device 10 such as in a line between and
parallel to adjacent elements of stent component 14 (similar to the
line of perforations 38 of FIG. 4B), are degraded and absorbed by
the body. One such resorbable graft material is taught by U.S. Pat.
No. 6,165,217 to Hayes; this material takes the form of a fibrous
web as shown by the enlargement of 18e.sub.2. Resorbtion times are
typically a function of the resorbable polymer chosen and the
thickness of the material. After the resorbable materials have been
degraded, weakened areas are formed in the remaining non-absorbable
sections of the graft material 18. These weakened areas are more
easily disrupted when longitudinal force is applied to an
engagement fitting 26, allowing the device 10 to be cohesively
disassembled. In addition to the methods described herein, it is
apparent that various other methods of selectively weakening the
graft material may be contemplated.
[0053] Another embodiment of this invention provides for partial
disassembly of the device 10 in situ to allow for shortening of the
overall device length, wherein one or more pieces of the device may
be cohesively disassembled from the remainder of the stent-graft.
FIGS. 5A-5C illustrate a device 10 which has multiple engagement
fittings 26, that coincide with controllably disruptable patterns
in the graft material 18. The amount of force needed to cause
disruption of the graft material 18 and therefore separation of
segments of the device 10 can be varied between segments of the
device. These disruptable patterns could be arranged so as to have
the most easily disrupted pattern 52, closest to the remotely
operated removal instrument, with the next most easily disrupted
pattern 56, further away from the remotely operated removal
instrument. Consistent with this arrangement, the pattern requiring
the most force for disruption 58, would be located furthest away
from the remotely operated removal instrument. Sequential removal
of the segments of the device 10 is described in the sequence shown
from FIG. 5A to FIG. 5C, wherein FIG. 5A shows the device as
implanted with all three segments. FIG. 5B shows the device 10
after removal of the first segment; FIG. 5C shows the device after
removal of the first and second segments. The segments are removed
cohesively, meaning that they separate discretely without loss of
fragments or pieces. It is apparent that such a device may be
provided with a number of segments as desired.
[0054] FIGS. 6A-6B show longitudinal cross sections of an
alternative embodiment wherein the stent-graft 10 has a luminal
liner 18a that is removable at a time subsequent to implantation,
while the remainder of the stent-graft 10 is left in place. Liner
18a is provided with a pull-tab or engagement fitting 26 at the
distal end of liner 18a. As shown by FIG. 6B, engagement fitting 26
may be grasped by a removal tool 27. The application of tension to
engagement fitting 26 via tool 27 allows the liner 18a to be
everted and removed through the lumen of stent-graft 10 and the
body conduit in which the stent-graft 10 has been previously
deployed. This embodiment may be desirable for applications in
which, for example, the luminal graft layer 18a has been provided
with a drug coating intended for delivery to the site of
implantation. It may be desired to subsequently remove layer 18a
following a time suitable for the elution of the drug coating. It
may also be desirable to have this luminal layer 18a removable to
expose the luminal surface of layer 18, which may optionally also
be provided with a drug coating of the same drug, or of an entirely
different drug.
[0055] FIG. 7 shows a longitudinal cross section of an alternative
embodiment wherein the stent component 14 is secured to the graft
material 18 by a resorbable adhesive 72 that allows for removal of
the stent component at a time subsequent to insertion and
deployment of the stent-graft. The material of the resorbable
adhesive may be chosen for a desired time after which the stent
component may be removed. This may be useful if, for example, the
stent component is intended to deliver a drug to the implantation
site and then removed subsequent to elution of the drug coating
applied to the stent. Alternatively, it may be desirable to remove
stent component 14 after graft material 18 has had adequate time to
attach (e.g., via tissue ingrowth) to the luminal surface of the
body conduit into which it has been implanted.
[0056] Other short-term adhesives are also possible, such as
hydrogels (e.g., a 5% solution of polyvinyl alcohol, by weight
volume in water). These may be useful, for example, to join
together parts of a stent-graft where it may be desired to include
components in the construction that are necessary for implantation
and deployment, but not needed functionally following deployment.
Such components might be longitudinally oriented struts that would
ensure that the device is implanted without being twisted. Once
deployed, these longitudinally oriented struts could be removed so
as not to occupy space within the lumen of the device. These
components could be joined to the stent-graft during manufacturing
by a temporary adhesive such as a hydrogel, which would be designed
to dissolve upon exposure to warm body fluids within a relatively
short time such as about 15 minutes, after which they could be
removed from within the device. Removal could be accomplished with
removal devices as previously described.
EXAMPLE
[0057] A stent component was produced by winding a 0.25 mm diameter
nitinol wire (SMA Inc, Santa Clara Calif.) onto an 8 mm diameter
wire forming fixture, creating a stent component as shown in FIG.
1. The wire-wound fixture was then subjected to heat treatment and
quench cycles sufficient to set the wire into the desired form. FEP
powder (Daikin America, Orangeburg N.Y.) was applied to the stent
component by first stirring the powder into an airborne "cloud" in
a standard kitchen-type blender and suspending the frame in the
cloud until a uniform layer of powder was attached to the wire. The
stent component was then subjected a thermal treatment of
320.degree. C. for approximately one minute to cause the powder to
melt and adhere as a coating over the stent component.
[0058] A sacrificial 7 mm inside diameter, 0.1 mm thick ePTFE tube
that had been previously heated above 380.degree. C., was pulled
onto an 8 mm diameter mandrel, which involved slight stretching of
the ePTFE tube. This tube was intended to serve as a release aid
when stripping the final construct from the mandrel and would
subsequently be discarded.
[0059] One layer of a thin ePTFE film provided with a discontinuous
coating of FEP was then wrapped around the sacrificial tube. The
ePTFE film was of a type produced in accordance with U.S. Pat. No.
5,476,589 to Bacino; it has a greater strength in the longitudinal
direction than in the transverse direction. This film was further
modified by application of a discontinuous coating of FEP as taught
in U.S. Pat. No. 6,159,565 to Campbell et al. The film was applied
with the ePTFE side down (toward the mandrel) and with the
direction of greater strength oriented circumferentially (i.e.,
perpendicular to the longitudinal axis of the mandrel). Edges of
the film (parallel to the longitudinal axis of the tube and
mandrel) were slightly overlapped.
[0060] The stent component was carefully fitted over the ePTFE film
and tube covered mandrel. Localized heat from a soldering iron was
then applied to the wire, causing the FEP wire coating to re-flow
and attach to the FEP-coated ePTFE film. When the entire stent
component had been joined to the underlying ePTFE film in this
manner, one additional layer of the same FEP-coated ePTFE/FEP film
is applied over the stent frame. This outer film layer was applied
with the FEP side down toward the stent and with the direction of
greater strength oriented circumferentially (perpendicular to the
longitudinal axis of the mandrel). Longitudinal edges of the film
were again slightly overlapped.
[0061] The mandrel and construct residing upon it was then
subjected to a thermal treatment in an air convection oven set at
320.degree. C. for 5 minutes. After removal from the oven and being
allowed to cool to about ambient temperature, the stent-graft was
stripped from the mandrel and the sacrificial ePTFE tube was
removed from within the stent-graft and discarded. The graft ends
were then trimmed as necessary using scissors.
[0062] The resulting 8 mm diameter stent-graft was chilled by
spraying with Micro Freeze.TM. (Micro Care Corp., Bristol Conn.)
and then diametrically compacted at a temp of -10.degree. C. in a
refrigeration chamber. Compaction was effected using a collet or
iris type of diametrical compaction device, such as taught by U.S.
Pat. No. 6,629,350. The stent-graft was compacted only to a
diameter of about 4 mm, adequate to allow it to be inserted into a
length of silicone tubing was intended to simulate the lumen of a
biliary duct. This silicone tubing (part no. T050PLAT256.times.236,
Jamak Corp., Weatherford Tex.) was of about 6 mm and about 0.25 mm
wall thickness. After insertion of the entire length of the
stent-graft into the lumen of the silicone tubing, the stent-graft
was deployed within the tubing, gripping the luminal surface of the
tubing.
[0063] The resulting 8 mm diameter stent-graft was demonstrated to
be easily and completely removed through the application of a
tensile force applied to the device. Removal was effected using a
Cordis Brite Tip.TM. 5 french guide catheter through the proximal
end of which had been inserted a length of 0.2 mm diameter nitinol
wire that had been doubled back on itself. When the doubled wire
was fully inserted, the doubled end of the wire was allowed to
extend a short distance beyond the distal tip of the catheter while
the two free ends extended from the proximal end. The
wire-containing catheter shaft was then inserted into a length of
translucent polymer tubing of 2.5 mm inside diameter and 0.035 mm
wall thickness. The doubled end of the wire, forming a small loop,
was placed over the engagement fitting located at the end of the
stent component, after which tension was applied to the wire and
catheter assembly by pulling on the proximal end of that assembly
with respect to the translucent polymer tube through which it had
been inserted. During the application of this tensile force to the
stent, the silicone tubing containing the stent was held restrained
(resisting the tensile force) in a human hand. The
wire-and-catheter assembly was slowly withdrawn in a proximal
direction, into the translucent polymer tube. The tensile force,
applied to the engagement fitting located at the end of the stent
component, caused the stent-graft to unravel and be cleanly
withdrawn into the translucent polymer tube, generally as shown by
FIG. 2. This tensile force was applied until the entire stent-graft
had been withdrawn. Withdrawal was accomplished with minimal
distortion or elongation (i.e., minimal trauma) to the silicone
tube. No separate remnants of the stent-graft resulted from the
removal by unraveling process.
[0064] While particular embodiments of the present invention have
been illustrated and described herein, the present invention should
not be limited to such illustrations and descriptions. It should be
apparent that changes and modifications may be incorporated and
embodied as part of the present invention within the scope of the
following claims.
* * * * *