U.S. patent application number 14/745030 was filed with the patent office on 2015-12-17 for catheter sheath for implant delivery.
The applicant listed for this patent is C. R. Bard, Inc.. Invention is credited to Martin Wubbeling.
Application Number | 20150359651 14/745030 |
Document ID | / |
Family ID | 40262627 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150359651 |
Kind Code |
A1 |
Wubbeling; Martin |
December 17, 2015 |
Catheter Sheath for Implant Delivery
Abstract
A tube of material is disclosed having a seam extending between
a proximal end and a distal end, two edges of the material meeting
and at least partially overlapping along the seam and being sewn
together at the seam by stitches of relatively flexible thread, the
thread of one or more of the stitches passing from a first side of
the overlapped edges of material, through both layers of overlapped
material, crossing a relatively rigid member which is disposed on a
second, opposite side of the overlapped edges of material, and
passing back to the first side. There is further disclosed an
implant delivery catheter incorporating the tube of material, and
associated methods for its manufacture.
Inventors: |
Wubbeling; Martin;
(Mannheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
C. R. Bard, Inc. |
Murray Hill |
NJ |
US |
|
|
Family ID: |
40262627 |
Appl. No.: |
14/745030 |
Filed: |
June 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13132816 |
Aug 19, 2011 |
9060894 |
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PCT/EP2009/066315 |
Dec 3, 2009 |
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14745030 |
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Current U.S.
Class: |
112/475.08 |
Current CPC
Class: |
A61F 2002/9511 20130101;
A61F 2/95 20130101; A61F 2/962 20130101; A61F 2/97 20130101 |
International
Class: |
A61F 2/962 20060101
A61F002/962 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2008 |
GB |
0822110.3 |
Claims
1. A method comprising: forming a seam and a seam allowance by
bringing opposite edges from a same side of a tubing material
together so that the edges overlap to form the seam allowance and
the seam lies along an inside edge of the seam allowance; disposing
a relatively rigid member on a second side of the seam; and
securing the seam by stitching the seam using a relatively flexible
thread from a first side of the seam allowance, through both layers
of the material, across the relatively rigid member and back
through to the first side.
2. The method of claim 1, wherein stitching the relatively flexible
thread includes passing the thread back to the first side from the
second side through both layers of material.
3. The method of claim 2, wherein stitching the relatively flexible
thread further includes crossing the relatively rigid member on the
first side and passing the thread again through both layers to the
second side.
4. The method of claim 3, wherein securing the seam includes
stitching the two ends of the tube material from the proximal end
of the tube to the distal end of the tube.
5. The method of claim 4, wherein securing the seam includes
stitching the two ends of the tube material substantially parallel
to the central axis of the tube.
6. The method of claim 5, wherein stitching the relatively flexible
thread to cross the relatively rigid member on the second side is
done at least at the proximal or distal end of the seam.
7. The method of claim 6, further comprising the step of disposing
the seam and seam allowance inside the tube.
8. A method comprising: at least partially overlapping two ends of
a tube material between proximal and distal ends to form a seam
allowance; securing a seam by passing a relatively flexible thread
from a first side of a seam allowance, through a hole through both
layers of the material, to a second, opposite side of the seam
allowance to form a loop on the second side, whereby the thread of
relatively flexible material passes back to the first side through
the same hole through the two layers; and extending a relatively
rigid member on the second side of the seam allowance through the
loop.
9. The method of claim 8, wherein securing a seam includes forming
a plurality of loops along the seam on the second side of the seam
allowance, and wherein extending a relatively rigid member on the
second side of the seam allowance includes extending the rigid
member through substantially all of the loops.
10. The method of claim 9, wherein securing a seam includes forming
a series of loops along the seam on the second side of the seam
allowance, each loop in the series from one end passing through the
next loop in the series wherein each next loop in the series is
inhibited from being pulled through the hole through the two layers
to the first side, and wherein extending a relatively rigid member
on the second side of the overlapping portion includes disposing
the rigid member to extend through at least the loop at the one
end.
Description
PRIORITY
[0001] This application is a division of U.S. patent application
Ser. No. 13/132,816, now U.S. Pat. No. 9,060,894, which was filed
as a U.S. national stage application under 35 U.S.C .sctn.371 of
International Application No. PCT/EP2009/066315, filed Dec. 3,
2009, claiming priority to United Kingdom Patent Application No.
0822110.3, filed Dec. 3, 2008, each of which is incorporated by
reference in its entirety into this application.
FIELD OF THE INVENTION
[0002] The present invention relates to a tube of material, to
associated methods of manufacturing a tube of material, and to an
implant delivery catheter incorporating such a tube of material.
The tube of material may be of a form that can be used as a
releasable outer sheath for delivering expandable or self-expanding
implants, such as stents.
BACKGROUND
[0003] Numerous implant delivery systems have been devised for
conveying and deploying prosthetic implants in the human body.
Continued development in the field of material science has enabled
an increasingly diverse range of implants to be devised which can
be delivered to and implanted non-invasively at a treatment
location. Such implants will typically have a low-profile delivery
configuration and are expanded to a large-profile operative
configuration at the treatment location. These implants can either
be expanded mechanically to their operative configuration, for
example by the use of balloons or pull-wires to transform the
implants from their delivery configurations to their operative
configuration, or they may be self-expanding implants which will
naturally tend to expand to their operative configurations when
released from the constraints of a delivery device.
[0004] For deployment of implants into luminal body passageways,
catheter based delivery systems have become widely used. A typical
catheter based delivery system is provided with an elongate inner
shaft, with the implant mounted to the distal end portion of the
shaft. An outer sheath surrounds the implant and at least the end
portion of the inner shaft, to constrain the implant in its
delivery configuration prior to being selectively deployed. In a
typical procedure, the distal end of the delivery system is
introduced percutaneously into a patient and advanced along a body
lumen until the implant at the distal end portion is brought to a
treatment location. The outer sheath is then removed to release the
implant to be deployed at the treatment location. Because these
catheter based delivery systems can be made relatively long and of
a small diameter, they are particularly suited for advancement of
implants to treatment locations within the human vasculature, the
urinary tract and the biliary tree.
[0005] Various different arrangements have been devised for
removing the outer sheath so as to release the implant for
deployment at the treatment location. In one common arrangement,
the outer sheath is retractable in a proximal direction relative to
the inner shaft, so that the implant can be gradually released as
the sheath is retracted, exposing the distal end portion of the
inner shaft where the implant is mounted. These systems, however,
are often relatively complex in order to provide the system with
the necessary functionality. For example, the inner shaft has to be
made axially substantially incompressible, so as to allow the shaft
to be advanced along a body passage-way as it is pushed into the
body from the proximal end. At the same time, the shaft has to be
of a small diameter in order to allow it to be advanced through
narrow bodily lumens, and has to be highly flexible so as to enable
it to pass around the tight curvatures encountered in body
passage-ways such as the human vasculature without kinking. The
inner shaft also has to resist compression under the influence of
the axial tensile force that has to be applied in order to retract
the outer sheath. The inner shaft is often provided with a tightly
wound compression spring in order to provide the necessary
resistance to axial compression but the required flexibility
off-axis.
[0006] The outer sheath is often responsible for providing the
necessary force to constrain the implant in its delivery
configuration, in particular where the implant is self-expanding
and tends to exert a radially outward force trying to adopt its
expanded operative configuration. Not only must the outer sheath
resist these radially outward forces, but it must be retractable in
a proximal direction, for which purpose it is preferably relatively
inextensible in the longitudinal direction. A reinforcing
structure, such as braiding, is typically used in the outer sheath
to give it the necessary properties of off-axis flexibility during
advancement of the catheter to the delivery location, and at the
same time the necessary longitudinal strength to be proximally
withdrawn for releasing the implant. The use of these
reinforcements to the inner shaft and outer sheath, to give these
components the necessary structural properties, thus tends to
result in an increase in the thickness and overall diameter of the
components and the system as a whole, which is contrary to the
objective of reducing the system diameter to allow it to be
advanced through narrow bodily lumens. Such systems can also be
costly and time-consuming to manufacture.
[0007] An alternative arrangement for releasing the outer sheath
has been devised, which can potentially reduce the axial forces
associated with sheath retraction and release of the implant. The
sheath is formed as a tube of material, for example ePTFE. This
tube of material has the necessary strength and properties to
constrain the implant in its delivery configuration. The tube is
formed from a sheet of the material, folded so that opposite edges
of the sheath meet and form a seam. The seam is then sewn together
using a suture thread in a manner in which the thread can be
released by pulling on one end of it. In use, the tube of material
functions as the outer sheath during advancement of the end portion
of the delivery system to a treatment location, at which point the
thread is pulled to release the stitching and thus allow the tube
of material to separate at the seam, facilitating deployment of the
implant constrained therein. The sheet of tube material can then
either be retracted along with the delivery system, after the
implant has been deployed, or may be attached to the implant and
left in situ at the treatment: location, held between the implant
and the treatment location to form part of the implant. Examples of
such an implant deployment apparatus are disclosed in U.S. Pat. No.
6,352,561, which is incorporated by reference in its entirety into
this application, to Leopold et al., published on Mar. 5, 2002, in
which the skilled reader will find examples of different stitching
patterns for forming the tube of material as well as discussion of
suitable materials for the outer sheath (restraining member 102)
and suture or sutures (thread-like coupling member 104).
[0008] Such catheter delivery systems are particularly useful for
the delivery of balloon-expandable or self-expandable stents and
stent grafts, as well as valve implants and the like. With the
systems employing a stitched tube of sheet material as the outer
sheath, however, there can be a problem that the suture may snap
before the thread is fully released from the seam of the tube, or
that the stitching may become knotted or tangled at the distal end
prior to complete release of the seam. This is a particular risk
due to the typical length of catheter delivery systems, along which
the proximally extended portion of the suture thread must pass to
reach the proximal end of the delivery system where it can be
manipulated, typically a meter or more in length, and the tight
curvatures around which the delivery system must pass, and in which
the implant may be deployed, within human bodily lumens. If the
thread snaps or becomes entangled after the stitching has been only
partially released, it may not be possible to retract the delivery
system without damaging the bodily lumen through which the catheter
has been inserted, or to fully deploy the implant. Intervention by
open surgery would then be required. On the other hand, if the
suture thread is made thicker, to withstand retraction forces
without snapping, the overall thickness of the seam will be
increased, whilst the potential for entanglement or snagging
remains.
[0009] U.S. Pat. No. 6,019,785, which is incorporated by reference
in its entirety into this application, discloses a device for
delivering a prosthesis held within a sheath in a delivery
configuration. The sheath is held in a retracted delivery
configuration by forming stitches of thread material around the
outer circumference of the sheath, at a diameter at which the
prosthesis internal of the sheath is constrained. In the embodiment
of FIG. 7 of U.S. Pat. No. 6,019,785, a warp thread 78 is used to
secure loops of the thread 75 in place around the circumference of
the sheath. However, there is no indication in U.S. Pat. No.
6,019,785 that the warp thread 78 is of any more or less flexible
material than the thread 75 used to form the constraining loops.
Moreover, the thread 75 in U.S. Pat. No. 6,019,785 does not pass
from a first side of overlapped edges of material, through both
layers of overlapped material, cross a relatively rigid member
which is disposed on a second, opposite side of the overlapped
edges of material, and pass back to the first side.
[0010] WO 2008/140796, which is incorporated by reference in its
entirety into this application, discloses a stent graft having
diameter reducing ties 22, 24 formed so as to progress
circumferentially around the sides of the stent graft from one end
to the other. The diameter reducing ties 22, 24 are tied to release
wires 18, 20, for example as illustrated in FIG. 5A of WO
2008/140796. The release wires 18, 20 are stitched into the
material of the stent graft, to hold them in the desired position
along the length of the stent graft. When the release wires 18, 20
are pulled, they release the diameter reducing ties 22, 24,
allowing the stent graft to expand. The relative rigidity or
flexibility of the release wires 18, 20 is not mentioned. In WO
2008/140796, the suture threads 22, 24 of flexible material are
used to form circumferential loops, and not to form stitches along
a seam at the overlapping edges of a tube of material.
SUMMARY OF THE INVENTION
[0011] According to a first aspect of the present invention, there
is provided a tube of material having a seam extending between a
proximal end and a distal end, two edges of the material meeting
and at least partially overlapping along the seam and being sewn
together at the seam by stitches of relatively flexible thread, the
thread of one or more of the stitches passing from a first side of
the overlapped edges of material, through both layers of overlapped
material, crossing a relatively rigid member which is disposed on a
second, opposite side of the overlapped edges of material, and
passing back to the first side. The relatively rigid member can
resist unwanted small radius, high curvature deflection lateral to
the seam, although is flexible with larger radius, low curvature
deflections of the tube. The relatively rigid member is thus able
to be removed from between the stitches which cross it and the
second side of the overlapped tube material with certainty and
precision, and without risk of breaking as it is manipulated for
removal. The relatively flexible thread is able to adopt the small
radius, high curvature needed to form a stitch, but need only be
strong enough in tension to resist the seam pulling apart in normal
use. The relatively flexible thread need not be strong enough to
allow the one or more stitches to be pulled out from one end of the
tube, and may break or be at risk of breaking under such applied
forces, especially if the thread is long or there are multiple
stitches. The different characteristics of the relatively flexible
thread and relatively rigid member are thus used to render each one
suitable for its own purpose in forming a stitched seam that can be
reliably released. Because each component is selected to have
properties suited to its specific role, dimensions of the
components can be reduced and overall size of the seam structure
substantially minimized.
[0012] In preferred embodiments, the thread passes back to the
first side from the second side through both layers of overlapped
material. This helps to ensure the rigid member is appropriately
constrained in position, at least in the lateral direction, on the
second side. In one preferred form, the thread is formed as a loop
on the second side, and passes back from the second side to the
first side through the same hole through which it passes through
the two layers from the first side to the second side. Besides
constraining the relatively rigid member in position, this helps to
ensure that the seam can be relatively easily pulled open when the
rigid member is removed from within the loops on the second side,
without the loops having to be pulled through the tube material to
separate the seam.
[0013] In further preferred embodiments, the thread also crosses
the relatively rigid member on the first side and passes again
through both layers to the second side. This serves to prevent the
stitches from being pulled through not only from the second side,
on which the relatively rigid member is disposed, to the first
side, but also in the reverse direction from the first side to the
second side, thereby preventing unwanted release of the
stitching.
[0014] In yet further preferred embodiments, the seam extends from
the proximal end of the tube to the distal end of the tube. The
seam can then be released along its whole length, which assists the
tube of material to peel away from any implant carried within the
tube.
[0015] In even further preferred embodiments, the seam extends
substantially parallel to the central axis of the tube. This
facilitates controlled and progressive release of the stitching by
enabling the rigid member to be removed by controlled amounts
corresponding to linear proximal inputs to retract the rigid
member.
[0016] In yet even further preferred embodiments, a series of
stitches are provided along the length of the seam. This can
provide an even seam that is atraumatic during insertion of the
tube in a body without snagging on lumen walls, and ensures a seal
along the seam between the inside of the tube and outside it.
[0017] In still further preferred embodiments, the one or more
stitches which cross the relatively rigid member are provided at
least at the proximal or distal end of the seam. This allows
progressive release of the stitching staring from one end, which
will be most appropriate in most implant delivery applications.
[0018] In still even further preferred embodiments, the relatively
rigid member is disposed on the second side along at least a
proximal or distal portion of the seam. In certain applications,
the rigid member need only be provided at the location where
release of the stitching is to be initiated, where the release of
stitching along the remaining length of the seam will propagate
thereafter in a predictable and regular fashion.
[0019] In yet still further preferred embodiments, the relatively
rigid member is a relatively rigid thread. As a relatively rigid
thread, the relatively rigid member is able to inhibit release of
the stitching when disposed between the stitches and the second
side, but has a low profile which maintains an overall small
diameter for the catheter and can extend beyond the tube to the
proximal end of an associated device, where it can be manipulated
to release the stitching.
[0020] In yet still even further preferred embodiments, the
relatively flexible thread is of material which is more flexible
than the material of the relatively rigid member. Threads can be
made of differing flexibility by altering either the material from
which they are formed or their size and construction. In seeking to
keep dimensions to a minimum, it is preferred that appropriate
different materials be used to give the relatively rigid member and
relatively flexible thread their respective properties.
[0021] In more preferred embodiments, the relatively rigid member
is disposed between the one or more stitches which cross it and the
second side so as to be removable from between them by sliding in a
direction substantially parallel either to the seam or to the
central axis of the tube. Preferably, the relatively rigid member
is removable by sliding under the application of a tensile force,
and is substantially inextensible under the application of the
tensile force. This allows the rigid member to be removed from the
proximal or distal end of the tube by a simple pulling motion, for
releasing the stitches. By the rigid member being inextensible,
retractions at the proximal end are transmitted to the distal end
simultaneously and with precision.
[0022] In yet more preferred embodiments, the relatively rigid
member is of a shape memory or superelastic alloy, preferably a
nickel-titanium alloy, or stainless steel. Shape memory alloys are
particularly useful as they resist plastic deformation, returning
to their memorized configuration after bending, and thus ensure the
rigid member can reliably be withdrawn by simple sliding motion.
These alloys, and stainless steel, are all strong under tension,
and can therefore be made relatively thin whilst still being strong
enough to function. Nickel-titanium alloys in particular have a
failure mode at the point of breaking under tension that is
advantageous; rather than extending substantially linearly with
applied force to a point where the material suddenly fails, the
material first reaches a point where it stretches by a substantial
amount for little increase in applied force. This provides a
warning to the person pulling on the relatively rigid member that
it is about to break, rather than the member appearing to suddenly
snap without warning. Thus, a defect or problem can be identified
prior to critical failure, during the release process, allowing
appropriate remedial action to be taken.
[0023] In still more preferred embodiments, the relatively flexible
thread is of polymer and/or is a surgical suture thread. The
relatively flexible thread has to be able to adopt a tight curve in
order to form the stitches in the seam. Less rigid members are less
suitable for stitching the overlapping layers together.
[0024] In even more preferred embodiments, the two edges of the
tube material which meet and at least partially overlap along the
seam are disposed on the inside of the tube. This keeps the outer
surface of the tube of material smooth, and the tube of material is
thereby effectively rendered atraumatic.
[0025] In yet even more preferred embodiments, the tube material is
a polymer, preferably PTFE, PET, polyamide, polyethylene, or the
like. These materials are not only suitable for use in devices
where biocompatibility is required, but also allow the stitches to
be released by being bulled through the material under application
of an implant release force.
[0026] In still yet even more preferred embodiments, the tube is
formed from a sheet of tube material. Although a larger-diameter
tube of the tube material could be stitched along a seam formed by
pushing together two internal edges along the inner wall surface, a
sheet of material is preferably used to form the tube of material,
as it can be accurately cut to size and stitched along the edges,
thus being easily formed into a tube shape.
[0027] The present invention also provides an implant delivery
catheter comprising a tube of material according to any above
recitation of the first aspect of the invention.
[0028] In embodiments of the implant delivery catheter, the tube of
material is an outer sheath provided over a distal portion the
delivery catheter to house an implant mounted on an inner shaft at
the distal portion of the delivery catheter. The tube protects and
constrains the implant during delivery to the intended treatment
location, as well as protecting the patient's body lumens from
damage by the implant.
[0029] In further embodiments, the rigid member extends or is
coupled to an actuator at the proximal portion of the delivery
catheter, whereby the rigid member can be removed from between the
one or more stitches which cross it and the second side of the
overlapped tube material. The relatively rigid member can extend
proximally beyond the length of the tube of material for connection
to means for its withdrawal, such as a specially designed hand
controller for removing the relatively rigid member from between
the stitches which cross it and the second side.
[0030] In yet further embodiments, when the rigid member is between
the one or more stitches which cross it and the second side of the
overlapped tube material, the one or more stitches which cross it
are inhibited from being pulled through the two layers of tube
material under application of an implant release force, and, when
the rigid member is removed from between the one or more stitches
which cross it and the second side of the overlapped tube material,
the stitches can be pulled through the two layers of tube material
under application of an implant release force. Stitching across the
rigid member on both sides of the overlapped tube material improves
the integrity of the stitched seam and provides for a repeatable
zig-zag pattern that can extend along all or part of the seam
crossing the rigid member.
[0031] In even further embodiments, two or more stitches which
cross the relatively rigid member are provided along at least a
portion of the length of the seam, and the relatively rigid member
is removable from between the two or more stitches in sequence,
whereby an implant within the tube of material can be progressively
released under application of the release force as the rigid member
is sequentially removed. Progressive release of the implant allows
one end of the implant to be positioned accurately, before the
implant is fully released, followed by controlled release of the
remainder of the implant. Thereby, the implant can be accurately
placed at the delivery location, and trauma to the patient can be
avoided by the controlled release without impinging on the
patient's tissue.
[0032] In yet even further embodiments, the implant is of
self-expanding material and is constrained in a delivery
configuration within the tube of material against its tendency to
expand to a release configuration, thereby imparting an implant
release force to the tube of material. The tube of material is
ideally suited to use with self-expanding implants, which will
provide the necessary force to free themselves at the delivery
location, once the rigid member is removed from the stitched seam.
No further means for releasing the stitching then need be provided
to the implant catheter.
[0033] In still preferred embodiments, the implant comprises a
self-expanding stent. The tube of material is particularly suitable
for use in percutaneous delivery applications, widely used for
implanting stents, stent grafts and valve devices into patients'
vasculature or other bodily lumens. In particular, the progressive
release that can be obtained with the tube of material as the seam
is unstitched is useful in accurate stent placement, and the stent
itself can provide the necessary release force to prise open the
tube of material as the rigid member is removed from the
stitches.
[0034] According to a second aspect of the present invention, there
is provided a method of manufacturing a tube of material comprising
the steps of:--at least partially overlapping two ends of the tube
material between proximal and distal ends;--disposing a relatively
rigid member on a second side of an overlapping portion of the
seam; and--forming a seam by stitching a relatively flexible thread
from a first, opposite side of the overlapping portion of the seam,
through both layers of the material, across the relatively rigid
member on the second side and back to the first side. Such a
manufacturing process is simple and can be carried out at
relatively low cost using few components, yet provides a product
that is effective in operation.
[0035] In preferred embodiments, stitching the relatively flexible
thread includes passing the thread back to the first side from the
second side through both layers of overlapped material. This
ensures that the lateral position of the rigid member on the second
side is fixed by the stitching, and serves to hold the stitched
layers of tube material together.
[0036] In more preferred embodiments, stitching the relatively
flexible thread further includes crossing the relatively rigid
member on the first side and passing the thread again through both
layers to the second side. A repetitive zig-zag stitching pattern
can then be produced along at least a portion of the rigid member
disposed on the second side. Crossing the stitching over the rigid
member on the first side also improves the integrity of the
stitched seam against the stitches being pulled through the layers
of tube material in either direction.
[0037] In yet more preferred embodiments, forming the seam includes
stitching the two ends of the tube material from the proximal end
of the tube to the distal end of the tube. When the seam runs the
whole axial length of the tube of material, the tube can be fully
released to a non-tubular shape, facilitating release of an implant
from within the tube. Stitching along the whole length of such a
seam improves the evenness of the seam and provides a stronger seam
to resist forces acting to separate the two overlapped layers of
tube material.
[0038] In still more preferred embodiments, forming the seam
includes stitching the two ends of the tube material substantially
parallel to the central axis of the tube. When the seam is formed
parallel to the tube axis, not only is it simpler to manufacture,
but also the seam will be more uniform and even, and will tend not
to be affected by forces transmitted longitudinally along the tube.
Moreover, removal of the relatively rigid member from the stitches
by sliding in the direction of the seam or tube central axis is
facilitated.
[0039] In even more preferred embodiments, stitching the relatively
flexible thread to cross the relatively rigid member on the second
side is done at least at the proximal or distal end of the seam.
This provides for the relatively rigid member to be removed at or
from one end to release the stitching, and further release will
then be predictable based on the stitching pattern, if any, used on
remaining portions of the seam, or can be controlled by
progressively removing the rigid member from stitches along the
length of the seam, if such are provided to cross the rigid member
along all or a significant part of the seam length.
[0040] Yet still more preferred embodiments further comprise the
step of:--folding the stitched tube of material inside-out so that
the two stitched edges of the tube material which meet and at least
partially overlap along the seam are disposed on the inside of the
tube. By initially forming the stitching on the outside of the
tube, the rigid member can be stitched into the seam of overlapped
tube material without having to access the seam from the inside of
the tube. Turning the tube inside out to place the seam on the
inside presents a relatively smooth and even, atraumatic outer
surface of the tube in the seam region. The stitched seam material
and relatively rigid member are contained inside the tube where
they cannot impinge on and scratch or puncture the wall of a bodily
vessel through which the tube would be advanced.
[0041] According to a third aspect of the present invention, there
is provided a method of manufacturing a tube of material comprising
the steps of:--at least partially overlapping two ends of the tube
material between proximal and distal ends;--stitching a seam by
passing a relatively flexible thread from a first side of an
overlapping portion of the seam, through a hole through both layers
of the material, to a second, opposite side of the overlapping
portion to form a loop on the second side, whereby the thread of
relatively flexible material passes back from the second side to
the first side through the same hole through the two layers;
and--disposing a relatively rigid member on the second side of the
overlapping portion of the seam to extend through the loop.
[0042] In one preferred embodiment, stitching a seam includes
forming a plurality of loops along the seam on the second side of
the overlapping portion; and disposing a relatively rigid member on
the second side of the overlapping portion includes disposing the
rigid member to extend through substantially all of the loops. The
stitching formed in this way can be released progressively by
removing the rigid member from each loop in turn. With this method,
a loop of the relatively flexible thread can be punched through the
two overlapped layers of tube material or pushed through a
pre-formed hole, and the rigid member is simply inserted to inhibit
the loop of thread being pulled back through to the first side.
Stitching formed in this way is easily released by removing the
rigid member from the loop, allowing it to pass back through the
hole and enabling the seam to separate.
[0043] In an alternative preferred embodiment, stitching a seam
includes forming a series of loops along the seam on the second
side of the overlapping portion, each loop in the series from one
end passing through the next loop in the series whereby each next
loop in the series is inhibited from being pulled through the hole
through the two layers to the first side; and disposing a
relatively rigid member on the second side of the overlapping
portion includes disposing the rigid member to extend through at
least the loop at the one end. The stitching formed in this way can
be released simply by removing the rigid member from the loop at
the one end, and progressive subsequent separation of the seam will
occur as the loops in the series release each other
sequentially.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] To enable a better understanding of the present invention,
and to show how the same may be carried into effect, reference will
now be made, by way of example only, to the accompanying drawings,
in which:
[0045] FIG. 1 shows a representative perspective view of a first
embodiment of a tube of material according to the present
invention;
[0046] FIG. 2 shows a representative end view of the first
embodiment;
[0047] FIG. 3 shows a representative end view of the first
embodiment after the tube of material has been turned
inside-out;
[0048] FIG. 4 shows a schematic illustration of an embodiment of an
implant delivery catheter in which the tube of material of the
first embodiment is incorporated;
[0049] FIG. 5 shows a representative perspective view of a second
embodiment of a tube of material according to the present
invention;
[0050] FIG. 6 shows a representative perspective view of a third
embodiment of a tube of material according to the present
invention;
[0051] FIG. 7 shows a representative perspective view of a fourth
embodiment of a tube of material according to the present
invention;
[0052] FIG. 8 shows a representative perspective view of a fifth
embodiment of a tube of material according to the present
invention;
[0053] FIG. 9 shows a representative perspective view of a sixth
embodiment of a tube of material according to the present
invention;
[0054] FIG. 10 shows a representative perspective view of a seventh
embodiment of a tube of material according to the present
invention; and
[0055] FIGS. 11a)-11h) are a series of pictures showing a sequence
of steps a) to h) in the release of a self-expanding stent graft
from an embodiment, of an implant delivery catheter having a tube
of material according to the present invention.
DETAILED DESCRIPTION
[0056] Specific embodiments of the present invention will now be
described, with reference to the illustrated examples shown in the
accompanying drawings. Reference to the drawings is made for
illustrative purposes, and should not to be taken to be limiting of
the scope of the claims.
[0057] In general, embodiments of a tube of material are formed by
folding a sheet of the material so as to bring two edges of the
material together to form a seam. Alternatively, a larger-diameter
tube of the material may be pressed together to bring two portions
of its internal surface together along its length, thereby forming
a smaller-diameter tube with edges in a seam. The material from
which the tube is made can be any suitable biocompatible material,
as is well known to the person skilled in the art for such
applications, including ePTFE, polyethers such as polyterephthalate
(DACRON.RTM. or MYLAR.RTM.), or polyaramids such as KEVLAR.RTM..
Any other suitable polymer, fabric or a foil of metallic material
may be used, as appropriate. Where suitable, the tube of material
may be a composite comprising a combination of any of these
materials, and may include a reinforcing structure, such as
braiding or other wire reinforcement, as required.
[0058] The seam formed by bringing together two edges of the
material is two or more layers thick, and is stitched to hold the
seam together. The seam is preferably formed in such a way as to
lie parallel to the central axis of the tube formed by stitching
the seam, but may instead be formed as a non-parallel seam, for
example extending helically around the wall of the tube between the
proximal and distal ends. Likewise, the seam is preferably formed
along the entire length of the eventual tube from the distal end to
the proximal end, but may also be formed only along part of the
longitudinal length of the tube between the proximal and distal
ends. The seam is stitched by a relatively flexible thread which
may be a surgical suture or any suitable polymer thread capable of
adopting the configuration of closely-spaced, high curvature
stitches. Suitable threads may be formed of ePTFE, polyethers or
polyaramids, or may even be formed of a suitable biocompatible
metal, such as Nitinol, stainless steel or gold, providing that the
thread has the necessary high flexibility. The thread need only
have sufficient strength under tensile forces to hold the seam
together, and may therefore be made of a relatively weak material,
or be made as relatively thin or small-diameter thread of strong
material such Nitinol or stainless steel, to achieve the necessary
degree of flexibility.
[0059] On one side of the seam, a relatively rigid member is
provided interposed between one side of the seam and at least one
of the stitches formed by the relatively flexible thread. The
relatively rigid member may also take the form of a thread and is
preferably formed of a material such as stainless steel or a
nickel-titanium alloy such as Nitinol.RTM.. These materials are
biocompatible and have the necessary rigidity, whilst are strong
under tension to enable the rigid member to be retracted
proximally, even when formed as a thin thread. In other
applications, however, the relatively rigid member may be formed of
a less rigid material having a larger size or diameter to achieve
the required overall rigidity.
[0060] By being relatively rigid, the relatively rigid member
resists forces tending to deflect its shape, meaning that it will
remain relatively straight during insertion of the tube of material
along a curved passage way, facilitating its subsequent retraction
out of the stitch or stitches which cross it on the side of the
seam. The rigid member resists or inhibits the stitches of
relatively flexible thread which cross it from being pulled through
the seam, which would cause the stitching to come apart and allow
the seam to open. Whereas the relatively flexible thread adopts a
low radius high curvature configuration at the stitches, which
inhibits it from being pulled out of the seam from one end, the
relatively rigid member stays more aligned with the seam or the
central axis of the tube of material, allowing it to be reliably
retracted from its position between the seam and the stitches which
cross it. Removing the relatively rigid member out from between the
stitches and the side of the seam in this way will allow the
stitches to come apart. In one variation, the stitches are formed
so as to pass through the seam material through a first hole, to
cross the relatively rigid member, and to pass back to the other
side of the seam through a second different hole. With the rigid
member removed, the relatively flexible thread is able to be pulled
through the seam by tearing through the material interposed between
the two separate holes. In another variation, the individual
stitches are formed as loops which pass through a hole in the two
layers of seam material, around the rigid member and back through
the same hole in the two layers of material at the seam. In this
way, there is virtually no resistance to the seam coming apart
after the rigid member has been removed.
[0061] The use of a relatively rigid member and relatively flexible
thread in combination in order to form the stitched seam can enable
the stitching of the tube of material to be reliably released by
retracting the rigid member in a proximal direction, with little or
no risk of snapping the rigid member by this action due to its
resistance to bending, which will inhibit snagging or tangling of
the member between the stitched tube of material and the proximal
end of the device, and due to the strength of the rigid member
under tension, even when formed as a thin thread. The relatively
flexible thread provides the necessary stitching, able to be
released by removal of the rigid member but otherwise serving to
provide a seam of sufficient strength to resist the seam coming
apart under implant release forces which may be exerted prior to
the rigid member having been removed.
[0062] Turning now to the drawings figures, reference is made to
the specific illustrated embodiments, in which certain components
are shown enlarge as compared with other components, for the
purposes of clear exposition. It will be appreciated that the
relatively flexible thread has been illustrated with the stitches
formed loosely, in order to demonstrate clearly the stitching
pattern used.
[0063] It will be appreciated that the various stitching patterns
and rigid members which are illustrated may be used separately or
in combination with one another, and that more than one illustrated
stitching pattern can be used together along the same seam.
Different portions of the seam may be provided with different
stitching patterns, including those of the illustrated embodiments
of the drawing figures.
[0064] In FIG. 1 there is illustrated a first embodiment of a tube
of material 1 formed from a sheet of material 10. Two edges 10a and
10b of the sheet of material 10 are formed into a seam 12 where
they overlap each other. A relatively rigid member 30 is disposed
on a second side 12b of the seam 12, and extends from the seam in a
proximal direction. A relatively flexible thread 20 passes, at the
proximal end of the seam 12, from a first side 12a of the seam 12,
through a hole 14 through both layers of the seam material, and
crosses the relatively rigid member 30 on the second side 12b of
the seam 12, before passing back through a second hole 14 through
both layers of the seam 12, so as to form a stitch 22a at the
proximal end of the seam 12. The relatively flexible thread 20 then
crosses, on the first side 12a of the seam 12, back under the
position of the relatively rigid member 30, which is on the second
side 12b of the seam 12 before it passes again through a hole 14
through both layers of material in the seam 12 to emerge on the
second side 12b of the seam. The relatively flexible thread 20 then
passes again through a further hole 14 back to the first side,
forming a second stitch 22b on the second side 12b of the seam 12.
This stitching pattern is repeated along the length of the seam 12,
to form a series of stitches 22a-e. It can be seen how, with the
stitches 22a-e pulled tight, the rigid member 30 will be
constrained in its lateral position, but will be free substantially
to slide in proximal and distal directions parallel to the seam 12
or tube central axis.
[0065] FIG. 2 shows an end view of the tube of material 1,
illustrating how the sheet of material 10 is formed into a tube
having a seam 12. Of course, the sheet of material 10 can simply be
folded in half for the purposes of stitching the seam 12, and will
generally form a substantially cylindrical tube shape when an
internal pressure, or a member exerting a radially outwards force,
is provided inside the tube.
[0066] FIG. 2 further illustrates how the relatively flexible
thread 20 passes through both layers of tube material in the seam
12, from the first side 12a to the second side 12b, and crosses the
relatively rigid member 30 on the second side 12b to form a stitch
22, before passing back through both layers of the tube material to
the first side 12a.
[0067] In practice, it is undesirable for the tube of material to
have an outer surface with a seam which projects from the otherwise
smooth surface of the tube, since the seam could damage the
internal surface of a bodily lumen through which the tube of
material is advanced, potentially scratching or rupturing the
bodily lumen or dislodging plaque material from the inside surface
of the lumen.
[0068] As illustrated in FIG. 3, the tube of material formed as
shown in FIG. 2 is then preferably turned inside-out, so that the
stitched seam 12, including the relatively rigid member 30 and the
relatively flexible thread 20 is formed on the inside of the tube
of material 1.
[0069] Because the relatively rigid member 30 is preferably made
from a nickel-titanium alloy having super-elastic properties, it is
able to withstand the process of being turned inside-out and will
then return to its substantially straight configuration along the
seam.
[0070] FIG. 4 shows how a tube of material 1 formed in
substantially the same manner as the tube of material shown in FIG.
3 is employed in an implant delivery catheter 40. Delivery catheter
40 is a system for delivering a stent 50 as the implant.
[0071] Implant delivery catheter 40 is provided with an inner shaft
42 extending from a proximal end of the catheter to a distal end,
and having a central axis X-X. Stent 50 may be a self-expanding
stent or stent graft and is mounted to the inner shaft 42 at a
distal portion of the inner shaft 42, near to the distal end of the
implant delivery catheter 40.
[0072] Tube of material 1 is formed substantially coaxially with
the stent 50 to function as an outer sheath in the implant delivery
catheter 40. Tube of material 1 therefore substantially completely
covers the stent 50 to constrain it in its delivery configuration
mounted to the inner shaft 42.
[0073] FIG. 4 illustrates how the seam 12, formed on the inside of
the tube of material 1, is provided with a series of stitches
22a-h, which cross the rigid member 30 on the second side 12b of
the seam 12. Rigid member 30 extends proximally from the tube of
material 1 and extends along with the inner shaft 42 to a proximal
end of the implant delivery catheter which will remain outside the
body of a patient during an implant delivery procedure. Implant
delivery catheters may be up to 150 cm long, and the relatively
rigid member 30 is thus preferably formed of a material such as a
nickel-titanium alloy or stainless steel, able to transmit tensile
forces all the way from the proximal end of the delivery catheter
40 to the distal tip of the rigid member without snapping. At least
the portion of the relatively rigid member 30 extending proximally
from the tube of material 1 may be formed as a thin thread, able to
adapt to the natural curvature of the bodily lumens through which
the implant delivery catheter 40 may be advanced, but being
relatively rigid to resist adopting high curvature, low radius
configurations similar to the stitches 22a-h formed from the
relatively flexible thread 20.
[0074] Although the relatively rigid member 30 and the relatively
flexible thread 20 are preferably both formed as threads of
relatively rigid and flexible materials, respectively, it is of
course possible to form both the rigid member 30 and the flexible
thread 20 from the same material, but to make the rigid member 30
substantially larger in shape or diameter so as to provide it with
the increased rigidity as compared with the relatively flexible
thread 20.
[0075] Although in the example of FIG. 4 the stent 50 is provided
as a self-expanding stent, the implant delivery catheter 40 could
alternatively be a balloon catheter, having a balloon mounted along
the portion of the inner shaft 42 to which the stent is mounted,
the balloon being inflatable to deploy the stent 50 and to force
open the seam 12 of the tube of material 1, after the relatively
rigid member 30 has been removed from the stitches 22a-h.
[0076] The further illustrated embodiments are variation on the
embodiment of FIGS. 1 to 3, and may be used in the implant delivery
catheter of FIG. 4 in place of the tube of material 1 illustrated
therein.
[0077] In the embodiment shown in FIG. 5, the tube of material 1 is
formed from a sheet 10 folded so that edges 10a and 10b meet to
form a seam 12 which is two layers thick. A flexible thread 20 is
provided, passing from the first side 12a to the second side 12b of
the seam through both layers of material and then back again,
through holes 14 formed through the two layers of the seam 12, to
form a series of stitches 21 along the seam 12. A single stitch 22
is formed at one end of the seam 12 to cross the relatively rigid
member 30, the relatively rigid member 30 preventing this stitch 22
from being pulled through the seam 12 to release the stitching. The
one stitch 22 which crosses the relatively rigid member need not be
a single stitch, it being possible to provide one or more stitches
22 which cross the rigid member 30, as well as one or more stitches
21 which do not cross the rigid member 30, along the second side
12b of the seam 12. Such a stitching arrangement may be used where
the tube of material 1 has a tendency to open from one end, the
relatively rigid member 30 serving the secure the stitch 22 against
opening at that end, and whereby removal of the rigid member 30
allows the stitched seam 12 then to open sequentially from the one
end as the stitches 21 come apart one-at-a-time, thus releasing an
implant from within the tube of material 1 in a progressive
fashion.
[0078] FIG. 6 shows a tube of material 1 formed from a sheet of
material 10 folded to produce a seam 12 where the edges 10a and 10b
of the sheet come together. The relatively flexible thread 20 forms
a series of stitches 22a-c by passing from the first side 12a of
the seam 12 through both layers of material to the second side 12b
through a hole 14 through both layers. The flexible thread 20 then
crosses the relatively rigid member 30 on the second side 12b of
the seam 12, before passing back to the first side 12a of the seam
12 around the edges 10a and 10b of the sheet of material 10,
without passing back through the two layers of the seam material.
This form of stitching is repeated to form the series of stitches
22a-c along the length of the seam 12.
[0079] FIG. 7 shows an embodiment of a tube of material 1 formed
from a sheet of material 10 to have a seam 12 which is two layers
thick where the edges 10a and 10b of the sheet of material 10 come
together. A series of holes 14 are formed through both layers of
the seam 12, along its length. A stitching pattern is formed by
passing loops 24a-d of the relatively flexible thread 20 through
each of the holes 14 in the seam. Each loop 24a-c in the series of
loops 24a-d passes through the next loop 24b-d in the series, on
the second side 126, to effectively lock the loops 24a-d together
on the second side 12b of the seam 12 as a series of stitches. The
relatively rigid member 30 then passes through the first loop 24a
in the series, to lock this first loop against being pulled through
the hole 14 in the seam 12, thereby securing the stitching along
the entire interlocked length of loops of stitches 24a-d.
[0080] In this way, the stitches 24a-d are held firmly in place
until the relatively rigid member 30 is removed from the first loop
24a, allowing the loop 24a to be pulled back to the first side 12a
of the seam 12 through the hole 14 through both layers of the seam
12. This then releases the second loop 24b to pass back through the
next hole 14 in the seam, thus facilitating progressive sequential
release of the seam 12 and allowing the tube of material 10 to open
along the seam 12 in a progressive fashion from one end. The loop
24a which is locked in place by the rigid member 30 may of course
be provided at either end of the seam 12, or may be provided in a
centre portion of the seam 12, if it is desired to provide a seam
12 which opens from the centre progressively outwardly towards each
end thereof.
[0081] FIG. 8 shows another embodiment of the tube of material 1
formed from a sheet of material 10 folded to make a seam 12 where
two edges 10a and 10b of the sheet 10 come together, and having a
series of holes 14 formed through both layers of the seam 12 along
its length. Loops 24 of the relatively flexible thread 20 are
pushed through each hole 14 through the two layers of material in
the seam 12, to form a series of loop stitches 24a-d along the
length of the seam. Relatively rigid member 30 is inserted through
each loop in the series, to lock it against being pulled back
through the seam 12 from the second side 12b to the first side 12a.
When the relatively rigid member 30 is refracted to remove the
member from each loop 24d-a in sequence progressive and controlled
sequential release of the stitching along the length of the seam 12
is achieved. Thus, the seam 12 may come apart up to the point of
the last-released stitch, but is still held closed at the point
where the next stitch in series is locked by the relatively rigid
member 30.
[0082] This facilitates progressive controlled release of an
implant from within the tube of material 1, which aids in the
accuracy of implant placement during a medical procedure, which is
often of benefit when deploying stents along a length of a bodily
lumen, in particular to ensure that the first positioned end of the
stent or stent graft is correctly located.
[0083] FIG. 9 shows an embodiment of a tube of material 1 formed
from a sheet of material 10 by folding the sheet so that opposite
edges 10a and 10b meet to form a two-layer seam 12 along the length
of the tube 1. A series of stitches 22a-d are formed along the
length of the seam 12, to cross the relatively rigid member 30 on
the second side 12b of the seam 12, in the same manner as in the
first embodiment of FIG. 1. In the embodiment of FIG. 9, the
relatively rigid member 30 is formed from a first, proximal section
32 formed as a small diameter thread extending proximally from the
tube of material 1, and having a stitch releasing tip 36 formed at
the distal end thereof. Stitch releasing distal tip 36 is formed as
a larger-diameter end portion of the relatively rigid member 30,
having a tapered transition between the small-diameter thread
portion 32 and the larger-diameter portion 36. As the relatively
rigid member 32 is retracted proximally to remove it from between
the stitches 22a-d and the second side 12b of the seam, along the
length of the seam 12, the stitch releasing tip 36 serves to pull
apart each stitch 22d-a in turn, as the tapered portion and large
diameter portion 36 are pulled through the stitches 22a-d, as
illustrated schematically for the stitch 22d in FIG. 9.
[0084] Stitch releasing tip 36 might alternatively be provided as a
cutting member, for cutting open each stitch in turn, in order to
release the seam 12 to open along its length as the relatively
rigid member is proximally retracted.
[0085] FIG. 10 shows an embodiment of a tube of sheet material 1
formed from a sheet of material 10 folded to bring together
opposite edges 10a and 10b to form a two-layer seam 12 along the
length of the tube 1. Stitches 22 are formed from a relatively
flexible thread 20 to provide a series of stitches 22a-d which
cross relatively rigid member 30 on second side 12b of the seam 12
along the length thereof. In this embodiment, the relatively rigid
member 30 is provided with a thread-like proximal portion 32 which
extends proximally of the tube of material 1, and a wider rigid
portion 34 which is positioned along the length of the seam 12. The
rigidity of the relatively rigid member 30 is thus increased at the
distal portion where it lies between each stitch 22a-d and the
second side 12b of the seam 12, improving resistance to bending and
facilitating smooth proximal retraction to remove the relatively
rigid member 30 from between the stitches 22a-d and the second side
12b of the seam 12. Proximal thread-like portion 32 provides the
necessary flexibility for adopting a curvature in line with the
tortuous shape of a body cavity as the tube of material 1 is
advanced through a bodily lumen such as the human vasculature.
[0086] In the forgoing embodiments, and in embodiments of the
invention in general, it will appreciated that the holes 14 formed
through the two layers of the seam 12 can in every case either be
formed in advance of threading the relatively flexible thread 20
there-through, such as by mechanical punching or using a laser, or
they may be formed using a needle in a conventional stitching
fashion.
[0087] Methods of manufacturing the tube of material 1 according to
the forgoing embodiments include folding the sheet of material 10
to form a seam 12 where the two edges 10a and 10b of the material
overlap; disposing relatively rigid member 30 on the second side
12b of the two overlapped edges of the tube material in the seam
12; and then stitching the relatively flexible thread 20 along the
length of the seam 12 to form the stitches 22 which cross the
relatively rigid member 30. An alternative method involves folding
the sheet of material 10 to bring the opposite edges 10a and 10b
together as a two-layer seam 12; forming a loop 24 or loops 24a-d
of material through holes 14 through the two layers of material in
the seam 12; and then inserting the rigid member 30 through each
loop of material along the seam 12 after it is formed on the second
side 12b of the seam 12. As necessary, each loop of material may
then be pulled tight, once the rigid member 30 has been
inserted.
[0088] In embodiments such as that shown in FIG. 7, each loop 24 is
formed in turn, starting with loop 24d, with each subsequent loop
24c-a being passed through the loop 24d-b previously formed, to
lock the loops 24a-d together, until the end loop 24a is formed and
can be locked in position by the relatively rigid member 30.
[0089] In order to release the implant from within the tube of
material 1 in an implant catheter device 40 such as that shown in
FIG. 4, it will normally be necessary simply to retract the rigid
member 30, after which the restoring force of the self-expanding
implant or a radially outward implant release force, for example
imparted by a balloon of a balloon catheter, will be sufficient to
pull apart the seam 12. In certain embodiments, however, it may be
preferable to extend the relatively flexible thread 20 proximally
from the tube of material 1, so that it can be pulled to assist in
releasing the stitches after the relatively rigid member 30 has
been removed.
[0090] FIGS. 11a) through 11h) show a sequence of steps a) to h) in
the release of a stent 50 mounted to an inner shaft 42 of a
delivery implant catheter. The stent is a self-expanding stent 50
constrained in a delivery configuration by a transparent tube of
material which surrounds it. The transparent tube of material is
stitched together by a relatively flexible thread 20, which can be
seen extending from the distal end of the tube of material 1. Also
visible in step a) of the sequence is the relatively rigid member
30, projecting from the distal end. In the sequence of steps a) to
h), the relatively rigid member 30 is gradually proximally
retracted, and it will be appreciated how this results in the
progressive release of the self-expanding stent 50 as the
relatively rigid member 30 is removed from the distal end to the
proximal end of the tube of material 1.
[0091] It will also be appreciated how the self-expanding stent 50
is incorporated into a stent graft, having a polymeric lining
formed, for example, from ePTFE, to form a covered stent graft in
the expanded operative configuration. It is moreover visible how
the expanded diameter of the stent 50 is in the region of 3 times
the diameter of the delivery configuration, although larger
expansion ratios have been achieved with similar types of
stent.
[0092] It will be appreciated how the spacing of the stitches
affects the release behavior of an implant from within the tube of
material 1. Where the adjacent stitches 22 are relatively widely
spaced, the implant release force exerted by a self-expanding stent
located within the tube of material 1 which each stitch has to
resist is relatively large, since each stitch 22 must hold the seam
together against the expansion force of the stent 50 corresponding
to a relatively long length of the stent. This can ensure that the
stent has a sufficiently large restoring force to pull the
relatively flexible material 20 through the two layers of tube
material in the seam, by tearing the relatively small piece of tube
material between the closely spaced holes through which the two
sides of the stitch 22 pass through the tube material. The stitches
22 may of course be spaced more closely or at greater distance,
depending on the strength of the tube material to resist tearing,
and depending on the strength of the implant releasing force which
will act to pull the seam apart to release the implant.
[0093] The spacing of the stitches will also have an effect on the
release behavior of the stent even where the loops 24 of relatively
flexible material 20 pass through the same hole 14 and the stent 50
does not need to cause the flexible material 20 to rip through the
seam 12 for its release. The release of the stent 50 will still be
progressive, as each stitch is released in turn, and the distance
between adjacent stitches will affect the smoothness of and ability
to control the release, with closer stitches 22 or loops 24
providing a smoother, more gradual release.
* * * * *