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Patent 2475058 Summary

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(12) Patent: (11) CA 2475058
(54) English Title: MEDICAL STENTS FOR BODY LUMENS EXHIBITING PERISTALTIC MOTION
(54) French Title: EXTENSEURS MEDICAUX POUR LES LUMIERES DE L'ORGANISME DOTEES DE MOUVEMENT PERISTALTIQUE
Status: Deemed expired
Bibliographic Data
(51) International Patent Classification (IPC):
  • A61F 2/95 (2013.01)
  • A61F 2/90 (2013.01)
(72) Inventors :
  • ANDERSEN, ERIK (Denmark)
  • STRECKER, ERNST PETER (Germany)
  • HESS, KATHLEEN L. (United States of America)
  • URHOJ, SUSAN (United States of America)
(73) Owners :
  • BOSTON SCIENTIFIC CORPORATION (United States of America)
(71) Applicants :
  • BOSTON SCIENTIFIC CORPORATION (United States of America)
(74) Agent: SMART & BIGGAR LLP
(74) Associate agent:
(45) Issued: 2008-12-02
(22) Filed Date: 1993-10-13
(41) Open to Public Inspection: 1994-06-09
Examination requested: 2004-08-17
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data:
Application No. Country/Territory Date
07/960,584 United States of America 1992-10-13

Abstracts

English Abstract





A stent (100) for reinforcement of the lumen of a peristaltic organ, and
methods for forming, shaping and heat-treating of such a
stent. The stent (100) is formed by knitting preferably a nitinol wire into a
pattern of overlapping loops selected such that from a relaxed
state each row of loops may shift axially relative to and independently of the
rows on either side. A stent is also shown which comprises
two resilient cylindrical mesh layers (532,534) and a semi-permeable compliant
membrane (530) such as expanded polytetrafluoroethylene,
sandwiched between. A method is also shown of manufacturing a delivery
system for a resilient tubular device such as a stent so that the
device can be inserted into the body in a substantially reduced diameter.


Claims

Note: Claims are shown in the official language in which they were submitted.



-34-
WHAT IS CLAIMED IS:

1. A method for manufacturing a system for delivering a
resilient tubular device into a body by reducing said tubular
device from a rest diameter to a substantially reduced
diameter, the method comprising the steps of:
providing a confining block having a bore at least as
large as said reduced diameter and a slot in a side of said
confining block, said slot having an end at said bore;
pinching a flat line in said tubular device;
inserting the pinched portion of said tubular device
into said confining block, the pinched line of said tubular
device lying in said slot and a contiguous portion of said
tubular device lying in said bore;
inserting a first mandrel into the portion of said
tubular device lying inside said bore;
inserting a second mandrel into said bore but outside
said tubular device;
revolving said mandrels relatively about each other to
roll said tubular device on itself until said tubular device
is entirely rolled and has said reduced diameter within said
bore; and
removing said tubular device from said bore while
restraining said tubular device in its reduced diameter
condition.

2. The method of claim 1, wherein said removing step
comprises:
slowly pushing said tubular device from an end of said
bore and restraining said tubular device as it emerges.

3. The method of claim 2, wherein said restraining
comprises wrapping a wire around said tubular device.


-35-

4. The method of claim 1, 2, or 3, wherein said slot is
tangent to said bore of said confining block.

5. The method of any one of claims 1 to 4, wherein said
tubular device comprises a stent knit of an elastic filament.
6. The method of claim 5, wherein said first mandrel
comprises an elongated delivery carrier for said stent.

Description

Note: Descriptions are shown in the official language in which they were submitted.


. ..~~,.,~~ .,~...,.., ~. ,. .. , ..
CA 02475058 2008-04-15

- 1 -

--MEDICAL STENTS FOR BODY LUMENS EXHIBITING PERISTALIC MOTION--

-

Field of the Invention
This invention relates to endoprosthetic stents that
are placed within body lumens that exhibit physiologic
motion such as peristaltic motion.

Background of the Invention
Medical stents are tubular endoprostheses placed
within the body to perform a function such as maintaining
open a body lumen, for example, a passageway occluded by
a tumor. Typically, the stent is delivered inside the
body by a catheter that supports the stent in a compacted
form as it is transported to the desired site. Upon
reaching the site, the stent is expanded so that it
engages the walls of the lumen. The expansion mechanism
may involve forcing the stent to expand radially outward,
for example, by inflation of a balloon carried by the
catheter, to inelastically deform the stent and fix it at
a predetermined expanded position in contact with the
lumen wall. The expansion balloon can then be deflated
and the catheter removed.


CA 02475058 2004-08-17

- 2 -

In another technique, the stent is formed of a highly
elastic material that will self-expand after being compacted.
During introduction into the body, the stent is restrained in
the compacted condition. When the stent has been delivered
to the desired site for implantation, the restraint is
removed, allowing the stent to self-expand by its own
internal elastic restoring force.

Strictures of the esophagus often produce obstructive
dysphagia resulting in debilitating malnutrition. To date,
the theoretical advantages of placing a plastic stent to

restore the patient's ability to swallow have been offset by
technical difficulty of placement, morbidity and mortality
associated with the procedure, and poor long-term prosthesis
performance. In particular, previous stents have

transmitted the force and deformation of peristaltic waves
inappropriately, for instance causing the stent to creep
toward the stomach, perforate the esophagus, or rupture the
aorta.

Summary of the Invention

In a first aspect, the invention features a method for
providing reinforcement to the lumen of a peristaltic organ.
The stent is formed by knitting a filament into interknit

loops, the pattern of the loops selected such that from a
relaxed state each row of loops may shift axially relative to
and independently of the rows on either side. The local
lengthening and shortening allowed by the shifting allows the
stent to accommodate the peristalsis of the organ without

migrating within the organ.
Preferred embodiments of the stent feature the
following. The lumen treated is the esophagus. The
elongation factor e by which the stent can locally lengthen


CA 02475058 2004-08-17

- 2a -

by shifting is related to the angle 6 at which the lumen can
incline inward by the relationship: g= 1.0 / cos e. The
stent is knitted of metal wire to be self-expandable such that
the stent expands outward against the body lumen wall by an
elastic restoring force of the wire. The stent is knitted from
nitinol wire having a diameter of about 0.15 mm. The stent, in
its free state, has a point of constricted cross-section. The
constriction may have a valve.
Various embodiments of this invention provide a method for
manufacturing a system for delivering a resilient tubular device
into a body by reducing said tubular device from a rest diameter
to a substantially reduced diameter, the method comprising the
steps of: providing a confining block having a bore at least as
large as said reduced diameter and a slot in a side of said
confining block, said slot having an end at said bore; pinching
a flat line in said tubular device; inserting the pinched
portion of said tubular device into said confining block, the
pinched line of said tubular device lying in said slot and a
contiguous portion of said tubular device lying in said bore;
inserting a first mandrel into the portion of said tubular
device lying inside said bore; inserting a second mandrel into
said bore but outside said tubular device; revolving said
mandrels relatively about each other to roll said tubular device
on itself until said tubular device is entirely rolled and has
said reduced diameter within said bore; and removing said
tubular device from said bore while restraining said tubular
device in its reduced diameter condition.
Various embodiments of this invention provide a method of
manufacturing a wire medical device, the method comprising:
providing an elastic metal wire; forming said wire so it
defines, generally, a tube that has a predetermined geometry and
length, said tube being formed by bending said wire in a
substantially regular pattern that forms the walls of said tube
over said length, and thereafter shaping the tube to form a

device having a different, desired geometry by applying a


CA 02475058 2004-08-17

-2b-
mechanical deforming force to said tube so it conforms to said
desired geometry and, while maintaining said deforming force,
heating and then cooling said tube such that said tube retains
said desired geometry when said mechanical deforming force is
removed.

Various embodiments of this invention provide a method of
manufacturing a wire medical device, the method comprising:
providing an elastic metal wire; forming said wire so it defines
a medical device generally in the form of a tube that has a
predetermined geometry and length, said tube being formed by
bending said wire in a substantially regular pattern to form the
walls of said tube over said length, said pattern including
portions in which the wire is in overlapping, pressure contact,
and heating said tube for a prescribed period in the manner that
pressure between wire portions in overlapping contact, created
during said bending, is substantially relieved to improve the
capability of said device to adaptively respond to change in the
configuration of surrounding tissue.
Various embodiments of this invention provide a method of
manufacturing a wire medical stent device, the method
comprising: providing an elastic metal wire; forming said wire
so it defines, generally, a tube that has a predetermined first
geometry and length, said tube being formed by knitting said
wire in a substantially regular pattern that forms the walls of
said tube over said length. Also provided is a medical stent
device formed by this method.
Various embodiments of this invention provide a medical
device for use in a body lumen, comprising: a tube formed by a
flexible wire bent in a substantially regular pattern to form
the walls of said tube over a desired length, said pattern being
configured to allow relative motion of adjacent portions of wire
when said tube is subject to the physiologic motions of a body
lumen, said tube having a shape of a varying geometry along its
length, said shape being selected to improve the functioh of
said device in the lumen in which said device is to be used.


CA 02475058 2004-08-17

- 2c -

Various embodiments of this invention provide a valve
device for izaplantation into a lumen of an organ of a body,
comprising: a tube formed by a flexible wire bent in a regular
pattern to form the walls of said tube over a desired length,
said pattern being configured to allow relative motion of
adjacent portions of wire when said tube is subject to the
physiologic motions of a body lumen, a portion of the tube
having a much reduced diameter, and being provided with a
material that is substantially impermeable to body fluid,
said device being capable of impeding the flow of body fluid
through said reduced diameter portion until the pressure of said
body fluid is sufficient to elastically widen said portion and
allow flow therethrough, said portion of said device relaxing to
said reduced diameter when the pressure of said bodily fluid
decreases thereafter.
Various embodiments of this invention provide a medical
stent device for use in a body lumen, comprising: a tube formed
by a flexible wire knitted in a substantially regular pattern to
form the walls of said tube over a desired length, said pattern
being configured to allow relative motion of adjacent portions
of wire when said tube is subject to the physiologic motion of a
body lumen, a flare to larger diameter and an end extending over
multiple knit row loops and a smaller diameter portion adjacent
said flared end, said smaller diameter portion selected to
conform to the diameter of said lumen and said flare serving to
anchor said device in said lumen.


CA 02475058 2004-08-17

- 3 -

A stent according to the invention offers the
following advantages. The stent exerts a constant,
gentle radial force on the wall of the lumen that
lo maintains lumen patency and actively resists compression,
as by a tumor. The inherent flexibi.lity of the knitted
stent adapts to peristalsis, transmitting the peristaltic
wave to the lumen, but without changing overall length or
creeping. This reduces complications and promotes long-
is term stability, patency, and patient comfort. The force
exerted by the stent against the lumen is sufficient to
compress the capillaries of the organ so that growth into
the lumen is retarded. The stent can be delivered via a
low-profile delivery system which is smallar than a
20 standard endoscope. The small diameter of the delivery
system simplifies implantation by elimi.nating the need
for pre-dilating the stricture, and allows placement even
in patients with tortuous esophageal aaatomy or
strictures prone to perforation by plastic stents.
25 In a second aspect, the invention features a stent
for providing reinforcement to a selected region of a
selected body lumen. The stent comprises two resilient
cylindrical mesh layers and a semi-permeable compliant
membrane sandwiched between.
30 Preferred embodiments of the invention feature the
following. The two mesh layers may be knit of a flexible
filament, and the knit may be configured so that the
stent can adapt to peristalsis of the body lumen. The
membrane is composed of expanded polytetrafluoroethylene.
35 The invention or preferred embodiments thereof may
feature the following advantages. The semi-permeable


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94/12136 PCT/US93/0971:
- 4 -

membrane prevents cell ingrowth of the stent. The force
exerted by the stent against the lumen is sufficient to
compress the capillaries of the organ so that growth into
the lumen is retarded.
s In a third aspect, the invention features a method of
manufacturing a delivery system for a resilient tubular
device so that the tubular device can be inserted into
the body in a substantially reduced diameter. The method
uses a confining block having a bore and a slot leading
io into the bore. The tubular device is pinched and
inserted into the bore and the slot. Two mandrels are
inserted into the bore, one inside the tubular device and
one outside. The mandrels are revolved about each other
to roll the tubular device on itself until the tubular
device is entirely rolled and confined at the reduced
diameter within the bore. The tubular device is removed
from the bore while being restrained in the reduced
diameter.
Preferred embodiments of the method of manufacture
feature the following. The removing step may be
accomplished by pushing the tubular device from the end
of the bore and restraining the tubular device as it
emerges. The restraining my be by means of wrapping a
wire around the tubular device. The slot may be tangent
to the bore of the confining block. The tubular device
may be a stent knit of an elastic filament. One of the
mandrels may be part of the delivery system that will be
used to deliver the stent.
The inventive method of manufacturing the stent
features the following advantages. Certain prior methods
required several operators to simultaneously hold and
constrain the resiliency of the stent and hurt the
fingers of the operators. The method of the invention
requires only one operator and is comfortable to execute.
The stent delivery systems produced by the method are
more uniform than those manufactured by previous methods,


CA 02475058 2004-08-17

= WO 94/12136 PCT/US93/00
- 5 -

both in distribution of stresses within a single stent
and in variation between stents, thus avoiding
deformation of the stent during manufacture and allowing
the physician to place the stent more precisely in the
patient. A stent delivery system manufactured according
to the method has a small profile, and thus minimizes
trauma to the patient during implantation.
In a fourth aspect, the invention features a method
of manufacturing a wire medical device. The mettiod
io includes the steps of: bending an elastic wire in a
regular pattern so it defines, generally, the valls of a
tube that has a substantially constant outer diameter and
geometry and extends over a desired axial length; and
shaping the tube to form a device having a different,
desired diameter or geometry by applying a mechanically
deforming force to the tube so it conforms to the
diameter or geometry and, while maintaining the deforming
force, heating and then cooling the tube such that the
tube retains the desired diameter or geometry whett the
mechanical deforming force is removed.
Preferred embodiments of this method of maaufacture
may include the following features. The mechanical
deforming force is exerted by confining the tube within a
cavity of a die having a smaller diameter than the tube,
2s and/or by stretching the tube over a mandrel having a
larger diameter than the tube. The deformed shape may
define a stent having one or both ends flared to a larger
diameter than other portions of the stent. The deformed
portion of the tube may extend over at least about 10% of
its length.
In a fifth aspect, the invention features a method of
manufacturing a wire medical device, including the steps:
bending an elastic wire in a regular pattern to define
the walls of a generally tubular medical device that has
a desired outer diameter and geometry and extends over a
desired axiai length, the pattern including portions in


CA 02475058 2004-08-17

0094/12136 PCT/US93/0971 i+
- 6 -

which the wire is in overlapping contact; and relieving
stresses in the portions of overlapping contact by
heating the tube for a proscribed period and then cooling
the tube, the stresses in the portions of overlapping
s contact that were created during the bending being
relieved to improve the capacity of the device to respond
by internal motion when subject to the physiologic
motions of a body lumen.
Preferred embodiments of this method of iaanufacture
io may feature the following. The tube is formed by
knitting the wire. The knitting machine may have a
knitting head formed from a durable, low-fri ction
polymeric material, for instance delrin or nylon.
Portions of the knitting needles in contact with the wire
is during knitting include a durable, low frict ion polymeric
material. The wire is selected from the group consisting
of a nickel-titanium alloy and molybdenum- o= barium-
containing highly elastic stainless steel. The tube is
heated to about 400-500 C for about 20 to 30 minutes.
20 In a sixth aspect, the invention features a medical
device for use in a body lumen. The medical device
includes a tube formed by a flexible wire bent in a
regular pattern to form the walls of the tube over a
desired length, the pattern being configured to allow
2s relative motion of adjacent portions of wire when the
tube is subject to the physiologic motions of a body
lumen. The tube has a shape of a varying outer diameter
or geometry along its length, the shape being selected to
improve the function of the device in the lumen in which
30 the device is to be used.
Preferred embodiments of this sixth aspect may
include the following features. The selected shape
complements the inner wall of the lumen in which the
device is to be used. The tube shape has a 1 arger
35 diameter for part of its length for contacting a portion
of the lumen having a corresponding large di ameter and a

SURS i! i ViTC SHEG t


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WO 94/12136 PCTIUS93/0
- 7 -

smaller diameter for the rest of its length for
contacting a portion of the lumen having a corresponding
to smaller diameter. The tube shape has a flare to
larger diameter at one or both ends and a smaller
diameter portion adjacent the flared end(s), the smaller
diameter portion=selected to conform to the diameter of
the lumen and the flare serving to anchor the device in
the lumen. The flare extends to a diameter about 10-25%
larger than the reduced diameter portion and has a length
3.o of about 15-25% of the length of the tube. The tube
shape has a secondary flare formed by the wire at the end
of the pattern. The bent regular pattern is formed by
knitting.
In a seventh aspect, the invention features a valve
device for implantation into a lumen of an organ of a
body. The device is formed by a flexible wire bent in a
regular pattern to form the walls of the tube over a
desired length, the pattern being configured to allow
relative motion of adjacent portions of wire when the
tube is subject to the physiologic motions of the body
lumen. A portion of the tube has a much reduced
diameter, and is provided with a material that is
substantially impermeable to body fluid. The device is
capable of impeding the flow of body fluid through the
reduced diameter portion until the pressure of the body
fluid is sufficient to elastically widen the portion and
allow flow therethrough, the portion of said device
relaxing to its reduced diameter when the pressure of the
bodily fluid decreases thereafter.
In preferred embodiments, this valve is configured as
a valve for the urethra.
Other advantages and features of the invention wil.l
become apparent from the following description'of a
preferred embodiment, and from the claims.

Brief Descriution of the Drawinas


CA 02475058 2004-08-17
.vo 94/12136 PCT/US93/09719
- 8 -

Figs. 1 and ic are perspective views of a stent
according to the invention.
Fig. la is an end elevation view of the stent.
Figs. ib, ld-lh, 4a, 6, and llg are detail views of
s the knitted loops of a knitted stent.
Figs. 2, 2a, 3, and' 3a-3e are sectional views of a
body, showing effects and operation of a stent in the
esophaqus.
Fig. 4 is a sectional view of a peristaltic organ.
Figs. 5, 5a, and 5b are schematic representations of
alternate embodiments of the stent.
Fig. 5c is a partially broken-away view of an
alternate embodiment.
Figs. 6a, 7, 7a, 7c-7j, 71, 7m, 7p-7s, l0a-lOc, 11,
and lla-lif are perspective views of tools and a time
sequence of steps in processes for manufacturing a
delivery system for the stent.
Fig. 6b is a perspective view of a.m alternate
embodiment.
Figs. 7b, 7k, 7n, and 7o are, crass-sectional views
taken during the process of manufacturing the delivery
system.
Fig. 7t is a sectional view of the delivery system.
Fig. 7u is a perspective view of the delivery system,
cut away.
Figs. 8 and 8a-8e are a time sequence of sectional
views of an esophagus showing delivery of a stent.
Figs. , 9a, and 9b are a time sequence of cutaway
views of an alternate delivery method.
Fig. 10 is a perspective view, partially cut-away, of
a die and a stent being formed in the die.

Descrir)tion of Preferred -Embodiments
Referring to Figs. 1 and la, a stent 100 according to
a preferred embodiment is formed of a knit cylinder with
length L and diameter D. The knitting forms a series of


CA 02475058 2004-08-17

WO 94/12136 ACT/US93/0:~
-s-
loosely-interlocked knitted loops (e.g., as indicated by
adjacent loops 132 and 134 in Fig. lb) that may slide
with respect to each other. This sliding or shifting
allows the stent to adapt to the movement of the organ
without moving axially in the organ. The adaptation is
accomplished with mere bending of the stent filament.
The stent maintains its axial working length L when
locally radially compressed, by locally lengthening or
shortening due to shifting of the rows of loops relative
io to each other. Fig. lc shows a region 130 of the stent
not under radial compression where adjacent loops 132 and
134 are in an overlapping, relaxed configuration, and the
heads of the loops are separated by a short distance s.
in the case of an esophagus, a large piece of food
i5 distends the esophagus. At the first instant of the
expansion, the wall may be deflected by an angle e, but
the diameter of the organ will not have changed
appreciably. In such a region, 140 in Fig. ic, the local
length of the wall elongates by a factor 1/cos6. The
2o rows of loops of the stent shift axially with elastic
deformation of the wire of the loops so that the
separation of the heads increases to a loop length 11, as
shown in Fig. le. In the region of maximum expansion
150, the length of each portion of the esophagus returns
25 to its rest length, but the diameter is extended. The
knit loops of the stezlt can widen, as shown in Fig. lf ,
to accommodate this extension. Returning again to
considering any peristaltic organ, the organ contracts (c
of Fig. ic) to compress a region. In a region 160 where
30 the wall is at an angle of deflection e but the diameter
is essentially equal to the rest diameter, the length of
the wall of the organ will elongate by a factor 1/cose,
and the loops will again pass through a state where their
width is essentially the same as the rest width, but, by
35 relative shifting of the rows of _oops axially, they are
extended to length 1i, the stat-e shown in Fig. le. In a


CA 02475058 2004-08-17

oj'O 94/12136 PCT/US93/0971*
- 10 -

region of maximum compression 170, the wall of the organ
is at its rest length, but the circumference is much
reduced. In this region, the loops of the stent deform
into the configuration of Fig. ig, where the length of
the loops is s but the width is compressed. Finally, as
the peristalsis relaxes, the wall of the organ returns to
its rest length and rest circumference, region 190 of
Fig. lc, and the loops of the stent return to the
overlapped rest configuration of Fig. id.
In the case of organs that can constrict almost
closed, as the lumen compresses radially the
circumference shortens, and thus part of the length of
the filament that contributes to the circumference of the
stent in its rest state is freed to contribute to length,
1s and thus the loops can lengthen to length 12, as shown in
Fig. lh.
The lengthening from s to 12 all occurs without
significant elongation of the filament of the steat
itself, only by elastic bending deformation and sliding
of the rows of loops against one other. The ratio of the
maximum local length to the relaxed local length, 12/s,
is determined by the configuration of the loops and the
elastic limit of the material of the filament.
Referring again to Fig. ic, the local lengthening in
2s regions of radial extension, compression or slope does
not substantially affect the loops in nearby regions that
are not exposed to the radial compression, which are in
turn free to elongate, contract or widen in response to
the movements of their own local portions of the organ.
Thus, the stent maintains its overall working length L
even when locally extended or compressed. When the
radial compression is released, the elasticity of the
filament causes the stent to expand back to its original
rest diameter D without change of the overall length,
?s since adjacent loops in the region of compression slide
bac}: to the relaxed overlapped state, separated by


CA 02475058 2004-08-17

WO 94112136 PCT/US93/010
- 11 -

distance s. Because the stent maintains point-for-point
contact with the organ, averaged over a local area about
the size of one loop, the stent maintains its placement
in the organ, and does not migrate with the peristalsis.
s A further property of the stent is that the state
characterized by all adjacent loops being separated by
distance s is the stable equilibrium between the elastic
restoring forces of the wire and the compressive force of
the esophagus. Thus, the stent automatically adjusts to
1o overall length L regardless of the initial configuration
of the loops and length of the stent. For example, if
the loops are in extended positions as in Fig. le or lh,
then upon compression the loops adjacent the compressed
region draw axially inward to the relaxed configuration
ls in Fig. ib, thus drawing the proximal end (120 of Fig. 1)
and distal end 122 inward. When the compression
releases, the loops in the region of the compression also
shorten, since the ends 120 a.nd Z22 of the stent have
been drawn inward and adjacent loops slide inward to
2o adjust for the reduced overall Length. Once the stent
has settled into this equilibrium state, the overall
length and position within the lumen are stable.
These features are enabled in the preferred stents of
the invention by a sliding motion of adjacent filament
25 loops, which in turn is enabled by the method of knitting
that reduces overlap of the loops, as shown, and the
elasticity of the filament and the shape of the loops.
The sliding motion allows local axial lengthening or
shortening of the stent substantially independently of
30 other remotely located portions of the stent. The
elasticity of the stent filament allows the stent and
lumen to return to their desired patency when the
compacting force is removed, without inelastic*
deformation. The loops are configured so that the sten-,
35 assumes its desired diameter and overall length as the
elastic restoring forces seek their minimum stress, the


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so 94/12136 PCTIUS93/097170
- 12 -

relaxed state of Fig. lb. This minimization occurs when
adjacent loops touch at their widest points, as for
instance point 136 between loops 132 and 134.
These features are particularly useful in body
passages in which physiologic function includes motion of
the lumen walls, such as peristaltic motion of the
esophagus. For example, referring to Fig. 2, an
esophagus 200 is occluded by a tumor 202. In Fig. 2a,
after insertion of the stent 100, the lumen's patency is
io restored. Once implanted in the esophagus, the stent is
held in a rest diameter that is slightly compressed by
the esophagus from its free diameter when outside the
body. It is the elastic restoring force of the stent
resisting this compression that holds the stent in place.
A stent for an organ like the esophagus, according to
the invention, not only holds the lumen open but allows
the organ to maintain its physiologic motion. Further,
the stent adapts to this motion without itself being
subject to the peristaltic force -- it does not crtep
toward the stomach with each esophageal contractioa, nor
does the overall length change. The operation of the
elastic knitted stent is illustrated in Figs. 3 and 3a-
3e. A food particle 310 is.urged through the lumen 320
by a peristaltic wave 322 that propagates down the
esophagus 200. The wave is induced by circumferential
contraction of the muscular tissue surrounding the lumen,
a consequence of which is radial inward extension of the
wall. Before the wave reaches the stented portion, the
stent lies between points T and B, with length L between.
As the wave reaches point T and the portion of the
esophagus reinforced by the stent 100, the stent complies
with the radial contraction, as shown in Figs. 3a-3e. As
shown in Fig. 3e, after passage of the peristaltic wave
the stent has not migrated from points T and B, and
maintains its overall length L. The adjustment and
restoration feature allows the stent to maintain its


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~ WO 94/12136 PCTIUS93/0
- 13 -

position in the lumen, without migrating axially as might
occur with a unitary structure in which stresses in one
portion are substantially transmitted to other portions.
Referring to Figs. 4 and 4a, the configuration of the
knit loops of the stent may be determined based on the
degree of radial motion and consequent axial lengthening
imposed by the peristaltic motion. Generally, the loop
length of the stent in its extended position 1 can be
expressed as:
1 = es (1)
where s is the axial length of the portion of the body
lumen over which two adjacent loops of the stent extend,
and c is the factor by which the stent must elongate in
response to local lengthening of the body lumen wall. It
will be seen that the maximum local lengthening will
occur over the portion of the wall that lies at the
largest angle 8 from the at-rest position. In a worst-
case limit, the entire peristaltic wave can be
approximated as having a wall at angle e, thus distending
2o a portion of the lumen that has rest length a to a
triangular wave with hypotenuse b. Thus,
b/a = 1/cos 8 (2)
This ratio, b/a, is the elongation factor by which the
loops must lengthen from their relaxed length s to their
2s extended length 1 to accommodate the lengthening of the
lumen wall at the incline of the peristaltic wave. Thus,
b/a = 1/cos 8= 1/s = E (3)
For the stent as a whole to maintain point-for-point
contact with the wall of the lumen and thus for the stent
3o as a whole to remain stationary along the axis of the
lumen, the heads of the loops are allowed to slide
locally in the region of peristaltic compression by a
distance (1-s)/2.
It will be noted that the stent will accommodate the
35 elongatlion of the lumen wall if it is capable of local
elongation e equal to 1/cose, independent of the amount

SU4 ~"? ! U 7 E SH oc-i


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ab 94112136 PCT/US93/097170
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of deflection c, even in the extreme case where the organ
is capable of constricting completely shut -- deflection
c in Fig. 4a being equal to the radius D/2 of the lumen.
The amount of force exerted by the stent against the
lumen wall is chosen to exceed the blood pressure within
the capillaries of a typical tumor, and thereby prevent
the tumor from further growth into the lumen of the
esophagus. The exerted force is determined by the
coefficient of elasticity of the filament, by the
configuration of the loops and density of the knit (loops
per unit of axial length), and by the diameters of the
lumen and the stent. For instance, a stent design would
exert more force against the lumen wall by choosing a
stiffer material for the filament, by knitting the stent
ls with more, smaller loops per unit of length (decreasing
s, and reconfiguring the loops to maintain the ratio
1/s), or by knitting the stent to a larger rest diameter
D. The radial force exerted is bounded at the point
where the loops reach the relaxed configuration of Fig.
lb and the stent's diameter reaches diameter D -- the
forces sum to zero at the contact points 136, and the
force exerted on the lumen itself falls to zero. Thus,
the diameter p of the stent must be slightly larger than
the diameter of the lumen if the stent is to retain its
place in the lumen.
Referring again to Figs. 1, la and lb, a particular
embodiment for use as an esophageal stent is knitted of
nitinol wire of about 0.15 millimeters in diameter to
have a diameter D of about 18mm, though diameters of 14mm
to 25mm may be useful. The proximal end 120 is flared to
20mm, to secure fixation to the esophageal wall. Stents
manufactured in overall lengths varying from 5 to 15cm
allow selection of a stent tailored to the patient's
needs. The relaxed loop length s is about 0.80-0.85mm,
3s and the maximum loop length 1 attained without
significantly distorting the loops is about 1.05-1.15 mm.


CA 02475058 2004-08-17
~ M

- 15 -

This elongation factor of about 1.4 is close to d2,
allowing for a maximum angle 6 of about 450. The peak-
to-peak height p of the loops is about 2.2mm when the
loops are in their rest state.
Examples of filament materials include shape memory
metals, for example, nitinol, tantalum steel, stainless
steel or other elastic metals, or plastics such as
polyester, polypropylene, or carbon fiber. The filament
may be selected to have a sufficiently high elastic limit
lo to allow the delivery system to rely entirely on this
elasticity, rather than, for example, the balloon 820 of
Fig. 8e to expand the stent. The filament may be formed
of a two-component metal wire system.that exhibits
desirable physical properties such as enhanced
is radiopacity along with desirable mechanical properties,
such as extreme elasticity. A full discussion of
composite medical wires will be found in
WO 93/19803 and WO 93/19804. The stent may be knit of two or more filaments.
As shown in Fig. 4a, the stent is knitted of a single
filament. This view shows only the front half of the
stent. The loops that appear in this view as independent
rows in fact are a single spiral-wrapped sequence, much
as a common screw has only one ridge from head to tip.
in alternate embodiments of the stent, multiple filaments
or other knits could be used, so long as the knit
structure allows a single row to elongate without forcing
the two adjacent rows to shift. The last loop of the
3o wire is cut 440. To prevent the stent from unravelling,
the last three loops (two shown, 450 and 452) of the
stent are coated in urethane, as shown in Fig. 4b. The
coating also covers the sharp ends of the filament.
It will be realized that the stent is applicable to
malignant or benign obstructions of many other organs.
Stents to treat biliary duct obstructions, for instance


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00/12136 PCT/US93/09710
- 16 -

when treating liver sclerosis or bleeding, would be about
8 to 1 0mm in diameter and 4 to 8cm in length. Stents for
the ureter would be about 6 to 10mm in diameter and about
2 to l0cm in length. Urethral stents would be about 10
to 20mm in diameter and about 2 to 6 cm in length.
Stents for the prostatic urethra would be about 10 to
20mm'in diameter and about 2 to 6cm in length. Colonic
stents would be about 10 to 20mm in diameter and about 4
to 10 cm in length. Stents for hemodialysis shunts would
io be about 6 to 8mm in diameter and about 2 to 6cm in
length. Stents for the porta canal would be about 8 to
14mm in diameter and 4 to 8 cm in length. Stents for the
trachea and bronchi would be about 8mm to 25mm in
diameter and 1 to 8 cm in length. Stents for gastric
outlet obstructions would be about 8 to 20mm in diameter
and 1 to 25 cm in length. Peristaltic stents may also be
configured for aortic aneurysms or dissections
(preferably weaving the filament material with a covering
such as dacron), and treatment of superior vena cava
syndrome and venous restrictions. The invention is also
useful in lumens in which compression is caused by some
outside force, for example in blood vessels compressed by
muscular contraction, movement of an extremity, or
pressure exerted by an object external to the body.
Figs. 5, 5a, and 5b represent alternate forms for
stents. (Showing the knit loops in these projections
would obscure the shape; these figures represent only
shapes of the stents.) The stent could be shaped to
include, in its free and rest states, a narrowing at a
point in its length. This narrowing would accommodate
the stent to the anatomy of a natural sphincteric
structure, for instance the pylorus or the cardia. A
stent so narrowed would enable the organ to close, for
instance to prevent reflux. The narrowing could be
shaped at one of the ends, for instance for use in the
SUBSTITUTE SH~E_


CA 02475058 2004-08-17
WO 94/12136 PCT/L-S93/0.0
- 17 -

rectum at the anus or in the common duct for a Papilla of
Vater.
The narrowing could be shaped conically, as in Fig. 5
for use in sphincter organs. Fig. 5a shows a stent
s incorporating a flattening, with the circumference in the
area of the flattening reduced so that the width remains
constant. The latter embodiment could be used in an
occlusion with two lips such as the vocal cords. In
either case, it may be desirable to form the loops in the
lo region of the constriction so that their free state is
similar to one of the compressed configurations, e.g.
Fig. ig, so that the constriction is capable of opening
to the rest diameter D.
As shown in Fig. 5b, the margins of the narrowing
is could incorporate a valve to ensure complete closure of
the stented organ, as for instance the reinforced=lips
520. This valve could be opened and closed either by the
muscles normally surrounding the point of constriction,
or by a manually-operated control extended to outside the
20 body. This would allow the use of the stent, for
instance, across the aortic valve or as a replacement for
the urinary sphincter. It may be desirable to reinforce
the point of the constriction, e.g., with a stiff wire,
especially in conjunction with the flattened constriction
25 of Fig. 5a. It may also be desirable to provide a valved
stent with a watertight membrane, similar in form to that
discussed below and shown in Fig. 5c.
The stent can be made to exert varying force along
its length, for instance by varying the gauge of the wire
30 or the density of the knit. In the narrowed stents
discussed above, it may be desirable to make the stent
particularly flexible in the region of the narrowing.
Some tumors are so invasive that the stent is quickly
ingrown by the tumor. As shown in Fig. 5c, the stent may
35 be manufactured with an elastic semi-permeable membrane
530 of porosity less than 50 microns and of very low

SUSSTfTUTEE SHEET


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00 94/12136 PCT/US93/0971710
- 18 -

modulus of elasticity, sandwiched between two knit
layers. The membrane may advantageously be of expanded
polytetrafluoroethylene (teflon) or latex. The inner
layer 532 is essentially identical to the single-layer
s stent, providing most of the elastic force against the
lumen. The outer knit layer 534, which acts to retain
the membrane, is typically constructed of thinner wire,
for instance 0.07mm diameter, or a less-resilient
material such as polypropylene or polyethylene. The
io outer knit layer is slightly shorter in length than the
inner layer.
The stent is knit on a conventional knitting machine,
very similar to that used to knit stockings. During the
knitting process, the wire is deformed past its elastic
is limit. Referring to Fig. 6, on some knitting machines,
or for stents of some diameters, it may be convenient to
produce a knit with the "up loops" 610 of a different
shape than the "down loops" 612. In some applications,
for instance the aorta, it is important that the loops be
20 uniform so that the stent exerts uniform pressure along
the lumen wall. During the knitting process, the wire
will be under tension, and thus the loops will be in a
tight configuration, similar to Fig. le, or possibly to
Fig. if or ih depending on the geometry and setup
25 parameters of the knitting machine itself.
The knitting machine produces a long "rope" of knit
loops. The rope is cut into lengths somewhat longer than
the final length of the stent. The extra length allows
for the shortening of the stent that will occur as the
30 loops are shortened from the elongated state in which
they emerge from the knitting machine to the rest state
of Fig. lb, and allows for some trimming. As shown in
Fig. 6a, after knitting, the stent is mounted on a
mandrel 620 for annealing, to relieve the strains induced
35 by the plastic deformation of knitting and to produce
greater elasticity in the wire. The mandrel is in the

SUBSTITUTE SHE E T


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= WO 94/12136 PCTJL'S93/0-*
- 19 -

free shape of the stent, 18mm in diameter with a flare
622 to 20mm at one end.
To achieve the constricted embodiments of Figs. 5 and
5a, the mandrel would have a constriction formed in it,
s and an external restraint would be applied to the stent
so that the annealed shape would be as shown in those
figures. As the stent is loaded onto the mandrel, the
operator shortens the overall length so that the loops
assume the relaxed, shortened state of Fig. lb. The
stent is annealed at approximately 450 C for about 15
minutes.
After annealing, the stent is cut to its final
length, and the three loops at each end of the stent each
receive a drop of urethane (450 of Fig. 4a or Fig. 6) to
zs prevent unravelling.
Alternately, the stent may be knit of interlocking
pre-formed sinusoidal rings, two of which 630, 632 are
shown in Fig. 6b.
The stent itself is packaged into a delivery catheter
2o as shown in Figs. 7 and 7a-7u. The center of the
delivery catheter is a carrier tube 700, shown in Fig. 7.
The carrier is a flexible tube of Pebax, a
polyether/polyamide-12 resin from Atochimie with
desirable flexibility/rigidity characteristics, 2.5mm in
25 diameter and approximately 80cm long. The carrier has
several radiopaque 0-rings 704,706 mounted along the
most-distal 20cm. The preferred radiopaque material is
tantalum.
The preferred process of mounting the stent on the
30 carrier tube 700 uses several tools: a confining block,
two mandrels, and a pusher. The confining block 710,
shown in Figs. 7a-c, is cylindrical, somewhat longer than
the stent itself at about 20cm, and formed of a rigid
plastic with low friction characteristics, preferably
35 deirin or nylon. The block has a drilled bore 712 of 8mm
diameter, with a imm-wide slot 714 cut from the top of
SUES TI iTU ; E SHEET


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.0 94/12136 PCT/US93/0971 0
- 20 -

the outside of the block and meeting the inner bore 712
at a tangent. The slot and bore may have a guideway 718
formed, to make the following steps easier. The block
may also have flats 716 milled in the bottom so that the
s block may be mounted in a vise. A first mandrel 720,
shown in Fig. 7d, is a simple rod approximately 30cm long
and about 3mm in diameter. A second mandrel 722, shown
in Fig. 7e, has a shaft of about 3mm diameter and length
longer than the confining block, two handles 724, each
io about 10mm in diameter, with center bores that friction
fit on the ends of the mandrel shaft, and slots 726 of
width to accommodate the carrier tube. Both mandrels
have rounded ends so that they will not catch on the
loops of the stent. A third tool is a pusher 728, shown
ls in Fig. 7f, with a shaft 729 of slightly less than 8mm
diameter and a bore 730 somewhat larger than the outer
diameter of the carrier 700. The bore may either be the
full length of the pusher, or as shown in Fig. 7f, may
have a breech hole 732. A fourth tool, which will be
20 seen in Fig. 7q, is a soft copper wire with a silicone
sheath 760 (silastic) over it. The sheathed wire is
about 50cm long, and the sheath is about 1-2mm in
diameter.
Referring to Fig. 7g, the confining block 710 is
25 securely mounted, as in a vise 750. An operator squeezes
a stent 100 flat and works it into the slot 714
preferably starting at a corner 752, and bottoms it in
the bore 712. Referring to Fig. 7h, the stent is
positioned in the confining block so that the proximal
3o end 120 of the stent extends from the end of the
confining block. The first mandrel 720 is inserted into
the distal end of the carrier 700, and then the mandrel
and carrier tube are passed through the center of the
stent. The operator slides the stent to the center of
35 the confining block, as shown in Fig. 7i. Referring to
Fig. 7j, the stent is slid back so that the flared


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~ WO 94/12136 PCT/L'S93/0*
- 21 -

proximal end again extends from the end of the confining
block. One handle of the second mandrel is removed, and
the shaft 722 of the second mandrel inserted through the
bore of the confining block but outside the stent.
Referring to Fig. 7k, the first mandrel 720 lies inside
the carrier tube 700, which in turn lies inside the stent
100. The lower portion of the stent and the second
mandrel 722 lie inside the bore 712 of the confining
block. Referring to Fig. 71, the stent is slid back to
zo the center of the confining block. The several slides
forward and back equalize the distribution of the knit
loops evenly over the length of the stent. The second
handle of the second mandrel is affixed to the shaft of
the second mandrel, and the slots 726 of the handles
engaged with the carrier tube 700 and/or first mandrel
720. The operator can center the 0-rings 704,706 within
the stent so that the carrier will be axially positioned
roughly correctly within the stent. Referring to Fig.
7m, the operator twists the handles, revolving the two
2o mandrels about each other and winding the stent about the
two mandrels. Fig. 7n shows the configuration of the
stent and the two mandrels after about half a revoiution.
The operator continues winding until the stent is
completely rolled on itself in the bore of the confining
block. The operator removes a handle from the second
mandrel and removes the second mandrel from the confining
block. The stent is held in the wound conformation by
the confining block, as shown in Fig. 7o.
Referring to Fig. 7p, the operator threads the pusher
728 over the proximal end of the carrier, with the shaft
729 distal. The pusher will be used to slowly push the
stent out of the bore of the confining block.
Referring to Fig. 7q, using the pusher the stent is
pushed out of the confining block by about lcm. The
operator makes any final adjustments required to center
the radiopaque 0-rings within the stent. The operator


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0094/12136 PCTIUS93/0971 ~
- 22 -

wraps several turns of the copper wire and silicone
sheath 760 around the exposed distal end 122 of the
stent, with about a lmm gap between turns, and lays the
bight of the sheathed wire into the slot of the confining
s block. Referring to Fig. 7r, the operator gradually
feeds the stent out of the confining block using the
pusher, and wraps the sheathed wire around the stent to
keep it confined to a diameter of about 8mm. The
operator maintains a roughly uniform imm spacing between
lo wraps.
After the stent is fully bound in the copper wire
760, the pusher is removed back over the proximal end of
the carrier tube and the carrier tube is pulled out of
the bore of the confining block, the stent and
is silastic/copper wrap is dipped in U.S.P. grade dissolving
gelatin, and the gelatin is allowed to set. The copper
wire can then be unwrapped; the silicone sheath acts as
a release surface so that the gelatin peels off the wire
and remains set on the stent in a lmm-wide "threaded"
20 strip, 770 in Fig. 7s, confining the stent.
Referring to Figs. 7t and 7u, the stent delivery
system catheter 799 is completed by affixing a nose piece
772 onto the distal end of the carrier 700, and
surrounding the entire assembly in a cylindrical sheath
25 774. Both the carrier and sheath are essentially rigid
in the axial direction, so that they can be used to push
or pull the catheter to position it, and so that handles
782 and 784 can be squeezed together to retract the
sheath from over the stent. Also shown in Fig. 7t are
30 the radiopaque markers 704,706 and in Fig. 7u graduation
markings 778 on the sheath, both of which will be used
during implantation to guide positioning. The inner pair
of the markers indicate the length the stent will assume
at its 18mm fully-expanded diameter, and the outer pair
35 indicate the length of the stent when compressed to 8mm
SUBS T(T? 711 E :tiEET


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= WO 94112136 PC?NS93/0910
- 23 -

diameter. A guidewire 778 will be threaded through the
center bore 776 of the carrier during implantation.
The process of implanting the stent is illustrated in
Figs. 8 and 8a-8e. Referring to Fig. 8, using an
endoscope 810, the proximal margin 812 of a stricture 814
is identified. The guidewire 778 is advanced across and
beyoind the stricture. In Fig. 8a, an 8cm-long balloon
820 is advanced over the guidewire and inflated to 12mm
diameter, dilating the stricture to 12mm. After
lo examining the stricture endoscopically and
fluoroscopically, a gelatin-encased stent 4- 6cm longer
than the stricture is chosen. The delivery system 799 is
passed over the guidewire and advanced until the distal
inner radiopaque marker 704 is 2-3cm below the distal
is margin 832 of the stricture.
Referring to Fig. 8c, The outer sheath is retracted
by squeezing together handles 782 and 784 (see Fig. 7u),
and the stent begins to deploy. The gelatin will
immediately begin to dissolve, allowing the stent to
2o expand under its own elastic restoring force. The
material of the stent filament, nitinol, is chosen so
that even the fairly severe deformation required to
compact the stent into the delivery system does not
exceed the elastic limit. Referring to Fig. 8d, after
25 the proximal 120 and distal ends 122 of the stent have
expanded and firmly attached to the esophageal wall, the
catheter 799 can be removed. Referring to Fig. 8e,
depending on the patient, a 12mm-diameter balloon 820 may
be inflated within the stent to ensure that the occlusion
30 is opened to the desired patency, to affix the stent
firmly to the esophageal wall, and to ensure adequate
esophageal lumen size for endoscopic examination.
Peristaltic contractions of the esophagus will allow the
stent to "settle" into its most-relaxed configuration.
35 Referring to Fig. 9, in another delivery system, the
stent 100 is formed of an elastic filament material that


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=iO 94/12136 PCT/US93/09710
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is selected so compaction produces internal restoring
forces that allow the stent to return to its rest
diameter after the compacting restraint is removed. The
stent may be compressed onto a catheter 900 that includes
a sleeve 902; the sleeve holds the stent in a relatively
compacted state. The compaction is typically achieved by
rolling the stent upon itself using two mandrels, as in
Figs. 7g-7o. In other cases, the stent may be positioned
coaxially over the catheter. The catheter is positioned
io within the lumen at the region of the tumor 202. In Fig.
9a, the sleeve is removed from about the stent, for
example, by withdrawing axially in the direction of arrow
910, thus allowing the stent 100 to radially expand by
release of its internal restoring force. As shown in
Fig. 9b, the axial force exerted by the stent is
sufficient to dilate the lumen 200 by pushing the tumor
growth 202 outward, or in some cases to compress the
occlusion against the lumen wall. The catheter can then
be removed.
An aspect of the invention is to form stents that
have a shape or profile along their length that is
adapted for a particular application in a particular body
lumen. The profile is effected by knitting a stent of
constant diameter and geometry, mechanically deforming
the stent into a desired shape with a different diameter
or geometry, and then heat treating the stent so it
maintains that shape after the mechanical deforming force
is removed. The deforming force, applied prior to heat
treatment, is usually less than that required to
3o plastically deform the stent wire. However, plastic
deformation prior to heat treatment may also be used in
some cases.
The shape of the stent can be selected to have a
variable diameter such as a flare at one end that helps
anchor the stent in a lumen that has inherent physiologic
lumen wall movement such as peristalsis. The transition
SUBSTlTUTE SHIEET


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. 1* /12136 PCT1US93/040
- 25 -

between the larger diameter flare and smaller diameter
portion can be a gradual taper. In an esophageal stent,
the flare is usually positioned upstream of the smaller
diameter portion. The larger diameter of the flare and
the taper provide a smooth transition to the smaller
diameter portion., which reduces the likelihood that food
particles will be caught on the stent. The flare is
preferably of a considerable length extending over
multiple knit-loop rows. The flare may be, e.g. about 5-
3.o 25-t of the overall length of the stent, and also of
considerable width, extending for example, to diameters
5-35% larger than the diameter of the main body of the
stent. The flare may be of a non-uniform diameter, for
instance, similar to a trumpet bell.
The stent can also be shaped to complement the
varying diameter of a body lumen. For example, a stent
for the bronchial tract includes a portion of e.g., 15mm
diameter, that is positioned in the trachea, and a
smaller diameter portion, e.g. 11mm, that extends into a
2o bronchus (side branch). The stent has a tapered
transition region about 1 cm long between the two
portions. For use in the colon, the stent can have a
flare at both ends, to affix the stent to the lumen wall
at both ends. Other important lumens include the biliary
2s duct, the prostatic urethra, and the vascular system,
where the axial stretching motion of, e.g., the wall of a
coronary artery or aorta, is accommodated by the movement
of the knit loops in a manner similar to the discussion
above with respect to radial narrowing in peristalsis.
30 Referring to Fig. 10, a shaped stent may be formed by
applying a confining force to a uniform stent at desired
locations along its length using a die 1000. Die 1000 is
formed of heat resistant material, such as a piece of
1mm-thick 360 stainless steel tubing. Die 1000 includes
35 a portion 1002 of inner diameter e.ssentially equal to the
desired rest outer diameter D of stent 100, with enlarged
SU~ST1 i U ; ~ SHE~'


CA 02475058 2004-08-17

- 26 -

portion 1004 of inner diameter equal to the outer
diameter of the desired flare. The die has a portion
1003 that has a gradual transition between the larger and
smaller diameter portions. The non-flared end 1006 of
the stent is extended beyond the die, wrapped around the
outside of the die, and held in place with a retaining
wire 1008. The assembly is heat treated. After heat
treatment, the wrapped end 1006 is cut off so the stent
can be removed from the die. After it is removed, the
io stent retains the shape of the die. (Alternately, the
die may have a constricted portion 1002 of cross section
equal to the desired cross section of a dssired
constriction, as shown in Figs. 5 and 5a.)
An advantage of using a die to confine the stent is
that the end loops of the stent can be formed having the
same diameter as the adjacent loops of the body of the
stent. Typically, after heart treatment over a mandrel,
the erid loops 1070 of the knit extend outwardly because
of residual stress, forming a short end loop flare, as
shown in Fig. lOc. This short end loop flare is an
advantage in many cases, such as for esophageal stents,
to help anchor the stent and prevent food particles from
collecting on the end loops. The short end loop flare is
most useful as a secondary flare on the upstream end of
the stent, at the end of the main anchoring flare. In
other applications this flare may not be needed or could
damage tissue in the lumen wall. The secondary flare is
also particularly useful with delivery systems that
attach to loops of the stent, for instance that disclosed
in WO 94/27667.

Referring to Fig. loa, in another embodiment, one end
the stent 101 is confined within a die 1010 and the other
end is stretched over a mandrel 1012. After heat
:3.z treatment,. the maintains a shape having one large
diameter end, larger than the original knit diameter, and


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V 0 94/12136 PCT/US93/0se
- 27 -

one small end, smaller than the original knit diameter,
with a transition region in between.
Referring to Fig. lOb, in another embodi_ment, both
ends of a stent are stretched over separate aandrels
1014, 1015. After heat treatment, the mandrels are
removed from the ends and the stent maintains flares of
enlarged diameter at either end with a midsection having
a diameter that corresponds to the original knit
diameter.
Stents having various shapes can be constructed using
these techniques. The cross-sectional geometry of the
stent can be varied by varying the geometry of the die or
mandrel. The shaping technique can be used to form
medical devices other than stents. For example, in a
i5 particular embodiment, the knit tube is formed into a
vascular valve, e.g. for the heart, by shaping the stent
to have a large diameter approximating a lumen diameter
at one end and a neck-down to very small dia=aeter at the
other end. After shaping, the knit-form is covered with
2o a blood impermeable polymer such as silicon or urethane.
The device is implanted in a blood vessel with the large
diameter end anchoring the device to a blood vessel and
the small diameter end oriented downstream. The small
diameter end substantially obstructs the flow of blood
25 until sufficient blood pressure builds to force it open,
allowing a large flow of blood to pass until the pressure
again subsides and the end of the device again relaxes to
its small diameter state. The polymer thickness and
elasticity may, but need not, be selected to enhance the
30 opening and closing of the small end of the device. in
another embodiment, a valve of this construction can be
implanted in the prostate to treat incontinence. The
valve prevents urine from passing until sufficient
pressure builds. The valve may be constructed so that it
35 can be opened by the patient relaxing the muscles in the
urinary tract that prevent urine flow.

+ U ; = SHE= 7
SUEST;


CA 02475058 2004-08-17

0094112136 PCT/US93/0971
- 28 -

Another important feature of the invention is to heat
treat the knit medical devices to reduce the stress
caused by the knitting process and therefore make the
device, e.g. a stent, more compliant and longer lasting.
s As illustrated in Figs. ld-lh, adjacent rows of knit
loops have portions that overlap and are in contact.
During the knitting process that forms this structure,
the metal filament is bent, which introduces stress that
can create in the stent a certain stiffness. At the
lo portions of overlap this stiffness can cause one row of
knit loops to hinder the motion of the adjacent row and
therefore reduce the compliance of the stent and reduce
its ability to conform to the physiological motion of the
lumen wall in which it was placed. Moreover, the
15 stiffness also can cause increased abrasion at the
overlap regions, which can reduce the stent lifetime.
These concerns can be alleviated by proper heat treatment
to reduce the stress created in the overlap regions by
the knitting and increases elasticity. The stress can
2o also be alleviated by coordinated selection of the
diameter of the knitting wire and the amount of curvature
of the knit loops. Generally, the smaller the knitting
wire and the larger the loop size, the less stiffening-
type stress in the resulting knitted device. The heat
25 treatment may as well vary with these parameters.
The heat treating not only reduces the stresses in
the overlap regions but recovers the tensile strength of
the stent wire. The heat treating conditions are
dependent on the degree of work hardening incurred during
30 knitting which weakens the wire. The more bending, the
greater the work hardening. For example, for a wire
having a tensile strength of 250,000 - 300,000 psi may
have a tensile strength of 70-90,000 psi, after knitting
into an esophageal stent. After heat treating, the
35 tensile strength is recovered, for example, to 180-
190,000 psi. The heat treatment to reduce the stress in
overlap regions and recover tensile strength can be


CA 02475058 2004-08-17

= WO 94/12136 PCT/US93/090
- 29 -

effected simultaneously with the heat treatment to shape
the stent. The heat treatment to reduce the stress in
the overlap regions and recover tensile strength is
useful even when the stent is not shaped.
The performance of the knitted medical device can be
improved=by manufacture on a knitting machine constructed
to limit abrasion of the knitting wire during knitting.
Referring to Fig. 11, a knitted stent may be manufactured
on a conventional circular knitting machine 1100, very
io similar to that used to knit stockings. The knitting
machine includes a knitting head 1102 for guiding a
series of needles 1104 which are axially extended and
retracted by a rotating (arrow 1106) contoured platen
1108.
i5 The portions of the machine that contact the knitting
wire are constructed of a low friction durable polymer to
reduce abrasion. The knitting head 1102, conventionally
of iron or steel, is preferably constructed for medical
device applications from a low friction durable member
20 such as nylon or delrin (polyacetate) which reduces
abrasion, scratching and nicking of the stent wire as it
is drawn into the knitting head, as discussed in more
detail below. The needle heads 1120 may also be formed
of or coated with such a polymer.
25 The wire 1110 feeds from a spool 1112 to the needles
during the knitting operation. The knit stent 100 is
produced around a polymeric mandrel 1114 which is drawn
downward in the direction of arrow 1116. Referring
particularly to Figs. Ila-lid, each needle 1104 includes
3o a needle head 1120 and a pivoted needle tongue 1122.
During the upstroke of the needle (Fig. ila), the head
1120 grasps the wire 1110, the tongue 1122 being
initially in the downward position. On the downstroke
(Fig. llb), the tongue 1122 is deflected upward as it
35 engages the portion of the knitting head 1102, thus
enclosing the strand within the head. The downstroke
(Fig. 11C) continues for a selected length within the
SUS'3TE7Vj 1, y.,.. V ~ L. ~F-'cL.c-'


CA 02475058 2004-08-17

0094/12136 PCT/US93/0971
- 30 -

knitting head, deforming wire 1110 past its elastic
limit, forming a loop 610 in the wire. On the upstroke
(Fig. lld), the strand deflects the tongue 1122 downward,
thus releasing the strand from the needle head 1120.
Because the stent 100 is being pulled down (arrow 1116),
loop 610 is pulled (arrow 1116) so that it ends up
pointing up. The cycle is repeated as the platen 1108
rotates. As shown in Fig. lie, on some knitting
machines, or for stents of some diameters, it may be
lo convenient to produce a knit with the "up loops" 610 of a
different shape than the "down loops" 612. In some
applications, for instance the aorta, it is important
that the loops be uniform so that the stent exerts
uniform pressure along the lumen wall. During the
is knitting process, the wire will be under tension, and
thus the loops will be in a tight configuration, similar
to Fig. le, or possibly to Fig. if or lh depending on the
geometry and setup parameters of the knitting machine
itself.
20 Referring to Figs. lle and llf, many of the geometric
parameters of the knit stent are determined by the
configuration of the knitting head 1102. Knitting head
1102 is generally a frustum of a cone, with a central
throughbore and a plurality of slots 1160 down the side.
25 The number of loops 610 around the circumference of the
stent is determined by the number of needles 1104 that
travel in slots 1160 of the knitting head. The overall
diameter D of the stent is nearly equal to the diameter
1162 of the throughbore of the knitting head. The width
30 1154 of the up loops 610 is related to the diameter of
needles 1104 and the width of knitting head slots 1160: a
smaller needle in a narrower slot forms a narrower loop
since the strand bends more acutely around the narrower
needle head. The width 1156 of down loops 612 is related
35 to the width 1164 of the lands between knitting head
slots 1160. The amount of compressibility of the stent,
for instance to compress the stent from its working rest
~
S! [EST--! aT~ S~-~PET


CA 02475058 2004-08-17

= WO 94/12136 PCT/US93/00
- 31 -

diameter to the diameter required for packaging into a
compact delivery system, is most strongly influenced by
dimension 1156, the width of the down loops 612. For
instance, a stent can be made more compressible while
retaining its diameter by reducing the number of loops in
its circumference but widening dimension 1156. As shown
in Fig. lig, when such a stent is compressed, the down
loops 612 bow and the shoulders of the loops can be
forced to overlap, as shown in region 1170.
io The knitting machine produces a long "rope" of knit
loops. The rope is cut into lengths somewhat longer than
the final length of the stent. The extra length allows
for the shortening of the stent that will occur as the
loops are shortened from the elongated state in which
is they emerge from the knitting machine to the rest state
of Fig. lb, and allows for some trimming. The knitted
tube, of constant diameter is then stress relieved and
shaped as discussed above.
Accordingly, using the methods and teaching above, in
20 preferred embodiments, the wire may be 0.002" to 0.010"
in diameter, obtained from, for example, Shape Memory
Applications of Sunnyvale, CA, which was drawn by Fort
Wayne Metals from, for example, 1/4", nickel-titanium
alloy wire with an Af equal to -5 to +10 C, available
25 from Furukawa Electric Company of Japan. After drawing,
the wire has a tensile strength of about 250,000 psi to
300,000 psi. The knitted tube for an esophageal stent is
heat treated at 400 C in vacuum for 20 minutes, then
cooled by a nitrogen flow to 100 C in one minute, and
30 then to room temperature over twenty minutes. The heat
treatment may vary, as discussed above. For example, for
a biliary stent the maximum temperature is 450 C. For
the prostate stent, the maximum temperature is 500 C for
30 minutes. Other materials include highly elastic
35 stainless steel alloys such as those including molybdenum
or cobalt.

~~~~ 7-7i..1' jr~ ~~=--
~T ~ ~
SJ~~


CA 02475058 2004-08-17

94/12136 PCTlUS93/097170
- 32 -

As discussed, particular applications have preferred
specifications and dimensions. These preferred
dimensions are shown in TABLE 1. For example, a
preferred esophageal stent is formed of wire whose
diameter is 0.006"; the overall diameter D is 18mm with a
flare 62Z to 20 to 22mm at one end, and has 16 loops
around its circumference. The flare is preferably 20mm
in diameter and 1.5cm in length. A stent for the biliary
duct is not flared at either end. A stent for the colon
lo would be about 10 to 20mm in diameter and about 4 to 10
cm in length, and may have flared diameters at both ends.
Vascular stents are particular embodiments. The wall
of a blood vessel stretches and contracts a small amount
with each heartbeat but does not substantially extend
radially inward. If the blood vessel is in an extremity,
especially if it is near a joint, the length and bend of
the blood vessel undergoes large changes. Vascular
stents would be about 6mm in diameter. The radial force
of the stent must be sufficient to maintain the lumen
open and not inhibit blood flow. The wire diameter and
composition would be selected to have high fatigue
resistance, to compensate for the demands described
above.

:-DVBSTITUTE SHEFT


CA 02475058 2004-08-17
33

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Other embodiments are within the following claims.

Representative Drawing
A single figure which represents the drawing illustrating the invention.
Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 2008-12-02
(22) Filed 1993-10-13
(41) Open to Public Inspection 1994-06-09
Examination Requested 2004-08-17
(45) Issued 2008-12-02
Deemed Expired 2011-10-13

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Request for Examination $800.00 2004-08-17
Registration of a document - section 124 $100.00 2004-08-17
Application Fee $400.00 2004-08-17
Maintenance Fee - Application - New Act 2 1995-10-13 $100.00 2004-08-17
Maintenance Fee - Application - New Act 3 1996-10-14 $100.00 2004-08-17
Maintenance Fee - Application - New Act 4 1997-10-14 $100.00 2004-08-17
Maintenance Fee - Application - New Act 5 1998-10-13 $200.00 2004-08-17
Maintenance Fee - Application - New Act 6 1999-10-13 $200.00 2004-08-17
Maintenance Fee - Application - New Act 7 2000-10-13 $200.00 2004-08-17
Maintenance Fee - Application - New Act 8 2001-10-15 $200.00 2004-08-17
Maintenance Fee - Application - New Act 9 2002-10-15 $200.00 2004-08-17
Maintenance Fee - Application - New Act 10 2003-10-14 $250.00 2004-08-17
Maintenance Fee - Application - New Act 11 2004-10-13 $250.00 2004-08-17
Maintenance Fee - Application - New Act 12 2005-10-13 $250.00 2005-09-16
Maintenance Fee - Application - New Act 13 2006-10-13 $250.00 2006-09-19
Maintenance Fee - Application - New Act 14 2007-10-15 $250.00 2007-09-18
Final Fee $300.00 2008-07-21
Maintenance Fee - Application - New Act 15 2008-10-13 $450.00 2008-09-18
Maintenance Fee - Patent - New Act 16 2009-10-13 $450.00 2009-09-17
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
BOSTON SCIENTIFIC CORPORATION
Past Owners on Record
ANDERSEN, ERIK
HESS, KATHLEEN L.
STRECKER, ERNST PETER
URHOJ, SUSAN
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Description 2004-08-17 36 1,822
Claims 2004-08-17 8 290
Drawings 2004-08-17 21 595
Abstract 2004-08-17 1 52
Representative Drawing 2004-09-29 1 10
Cover Page 2004-11-03 1 43
Claims 2007-07-24 2 48
Description 2008-04-15 36 1,823
Cover Page 2008-11-18 1 44
Correspondence 2004-08-31 1 43
Assignment 2004-08-17 3 120
Prosecution-Amendment 2007-01-24 3 77
Prosecution-Amendment 2007-07-24 3 55
Correspondence 2008-03-13 1 20
Correspondence 2008-04-15 3 69
Correspondence 2008-07-21 1 34