CA2158757C

CA2158757C - Covered stent and stent delivery device

Info

Publication number: CA2158757C
Application number: CA002158757A
Authority: CA
Inventors: Joseph E. Laptewicz Jr.; Paul J. Thompson
Original assignee: Schneider USA Inc
Current assignee: Schneider USA Inc
Priority date: 1993-04-23
Filing date: 1994-02-01
Publication date: 2000-01-04
Anticipated expiration: 2014-02-01
Also published as: JPH08504650A; JP2735389B2; EP0695152A1; WO1994024961A1; CA2158757A1

Abstract

A radially self-expanding stent (10) is disclosed that is circumscribed with a matrix (15) of flexible poly-meric material. This matrix (15) pro-vides a barrier to tissue and/or tumor ingrowth. A deployment device (20) for the stent (10) includes an inte-rior tube (30) on which the stent (10) may be placed and a hose (55) folded on itself surrounding and compress-ing the stent (10) on the interior tube (30).

Description

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p 1 f 1 _ ., ' ~ A 1 1 1 -~t~E, Pi~J i~J Ti;~ ~~.:~~d~C~. 21 5 8 7 5 7 TEXT 'FR~i~t3tAit9~1 COVERED STENT AND STENT DELIVERY DEVICE
Background of the Invention The present invention relates to a st mt which can be used within a vessel of the body of a living animal or a living human. This invention also relates to a device for delivering the stmt to the treatment site. The stmt includes a flexible tubular body which has a specific diameter at an unloaded state but which can be contracted to a smaller diameter by the application of force such as by radially compressing the stmt or by pulling the ends of the stent apart. This feature makes the stent particularly useful for mechanical transluminal implantation in biliary ducts, respiratory tracts, the esophagus, blood vessels or the like. The stmt delivery device includes a first tube having a central lumen for accommodating a guidewire and a flexible hose folded over itself and removably surrounding the first tube. The stmt is placed around the first tube and held in a radially contracted state by the flexible hose. In this manner, the stent can be delivered percutaneously and transluminally to a treatment site in a body vessel.
The stmt is deployed by rolling the flexible hose off of the stent to allow the stent to radially self-expand. Once the stent is deployed, the stmt delivery device can be withdrawn.
Prior radially self-expanding stents have an open mesh construction. After positioning such a stent in a body vessel, tissue may grow through the spaces between the wires of the stent. In many applications, such an occurrence is not detrimental to the efficacy of the stent. Indeed in many cases such tissue ingrowth is desirable because it helps to I~M~N~ ~~
A

. .. .

keep the stent in place preventing migration of the stmt .
However, in certain applications, tissue ingrowth could be detrimental. For example, if the stmt is to be placed in a body passage that has tumor growth therein to maintain the patency of the body passage, tumor ingrowth through the stmt would limit the effectiveness of the stmt. Indeed tumor ingrowth could completely block the body vessel. In addition, such tumor ingrowth would permanently "lock" the stmt in place. In certain applications where the ability to remove the stmt is a consideration, that is undesirable.
Prior delivery devices for radially self-expanding stems generally perform in accordance with their intended purposes. Typical prior delivery devices have a moveable tubular member that constrains the stmt in a contracted state on an inner catheter. The tubular member is removed from contact with the stmt to allow the stmt to be deployed. In certain devices, the tubular member is folded over itself to form a double-walled section.
However, such prior delivery devices may not be totally effective in delivering a stmt to a treatment site. For instance, friction between the walls of the double-walled section of the moveable tubular member as the walls move past each other can make removal of the tubular member from the stmt difficult. One means of minimizing this problem is by the application of pressure between the walls of the tubular member to move the walls of the tubular member away from contact with each other. However, this makes the delivery device difficult to operate.
The operator of the delivery device must continuously I~ME.NDEt~ S!' F[T

.., - .,' monitor the pressure to ensure that the pressure is maintained in a certain range. If the pressure is too low, friction forces will not be overcome. If the pressure it too high, the delivery device could rupture.
EP 0 481 365 relates to a device for widening a stenosis in a body vessel, the device made of a shape-memory alloy which radially expands at a temperature above ambient temperature and below body temperature. DE 4 022 956 relates to an intraluminal rail, consisting of a wire enclosed by an electrically insulating sheathing and shaped into a basket which detachably encloses an inflatable balloon, wherein the clearances stretching in the direction of the circumference are kept free. The clearances are formed in the manner of a mesh by a regularly recurring approximation and bonding of the sheathing of neighboring sections of the wire and circumferentially expandable, whereby the sheathing can be softened by heat at least once in order to facilitate dilation by applying an electrical voltage to the wire. DE 3 918 736 relates to metal grid stem s for the permanent dilation of arterial strictures which are coated with a thin layer of polytetrafluoroethylene. 410 88/01924 relates to a grasping means comprising an inner wall section and an outer wall section each comprised of flexible material with an annular region therebetween. GB 2 195 257 relates to a device for implantation by insertion of a substantially tubular, radially expandable prosthesis, comprising in combination such prosthesis and concentric therewith a flexible probe with means for maintaining said prosthesis in a radially contracted state and for releasing same at ~M~.ND~'~ S~'trT

the desired location, said means for maintaining the prosthesis comprising a hose concentrically surrounding said probe and radially surrounding the prosthesis to form a compartment therefor, characterized in that the probe has a central axial channel enabling supply of a liquid flushing medium at its other end and that the probe is provided with at least one radial aperture opening into the prosthesis compartment to enable flushing of the prosthesis compartment to remove gases therefrom before implantation.
Therefore, it would be desirable to provide a stmt that will maintain the patency of a body vessel and reduce the tissue ingrowth through the stmt.
It would also be desirable to provide a stmt that is removably placeable within a body vessel.
It would be further desirable to provide a stmt delivery device that can deploy a stmt at a treatment site with little difficulty.
Summary of the Invention The invention provides a radially expandable stent, comprising: at least one first thread element which extends in a helix configuration along a center line of the stmt and having a first direction of winding; at least one second thread element which extends in a helix configuration along the center line of the stmt and having a second direction of winding so as to cross the at least one first thread element and form a lock between the thread elements thereat and form a plurality of interstices between each of the thread elements; the first thread element and the second thread element defining a stmt inner surface and a stent outer surface; and a flexible matrix of polymeric material surrounding and encircling each of the first thread element and the second thread element and said lock formed therebetween and occluding the interstices between each of the first thread element and the second thread element, the matrix being integral with and radially expandable with and covering the stmt and preventing tissue ingrowth therethrough;
wherein the stmt is adapted to assume a radially contracted state and a radially expanded state, and the first thread element and the second thread element form an axially directed angle greater than 60° when the stmt is in the radially expanded state, the stmt exerting a radial force sufficient to fixedly implant the stmt in a body vessel.
The flexible matrix is preferably applied to the stmt by dip coating the stmt in a bath of silicone rubber and an organic solvent. The thickness of the matrix film can be controlled by the ratio of the silicone rubber and organic solvent in the bath and by the number of dip coatings to which the stmt is subjected.
The stmt delivery device includes an elongate and flexible length of inner tubing with a central lumen for accommodating a guidewire. The stmt is placed on this tubing in a radially contracted state for transport to the treatment site. A flexible hose surrounds the tubing and is folded over itself to form a double-walled section. This double-walled section surrounds and confines the stmt in a radially - 5a - ~ 1 5 87 5 7 contracted state on the tubing. To facilitate the movement of the flexible hose away from the stmt, at least that portion of the hose that contacts itself in the double-walled section is lubricous. This lubricous characteristic can be achieved by placing a lubricous coating on the surface of the hose that contacts itself in the double-walled section of the hose, by injecting a lubricous liquid into the space between the walls of the double-walled section or by forming the flexible hose from a naturally lubricous material. This makes the stmt delivery device of the present invention I

easy to use and makes simple the deployment of a stmt therefrom.
When it is desired to deploy the stmt at a treatment site, the flexible hose is rolled back proximally to first expose the distal end of the stmt. This allows the operator of the stmt delivery device first to align properly the distal portion of the st mt in the body vessel. When proper alignment is obtained, the operator can continue to roll the flexible hose proximally to completely uncover the stmt and allow it to radially self-expand into engagement with the vessel wall.
Brief Description of the Drawings The above and other objects and advantages of this invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout and in which:
FIG. 1 is a perspective view of the covered stent of this invention clearly showing the braided configuration of the thread elements;
FIG. 2 is a perspective view of the covered stmt of this invention in a radially contracted state clearly showing the braided configuration of the thread elements;
FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 9.
FIG. 4 is a detailed view in perspective of a portion of the stent of this invention without the covering to show the braided configuration of the thread elements;
FIG. 5 is a detailed sectional view of a portion of the stmt of this invention without the covering ~,~G~}n~n .. .... ...._. _ ~~...._. .~._w._ ... . ~...~...... . _ _ _. .. _ _.__ _._.._ ._ _.__ _ . .. _____ . ..~.._ I

to show the braided configuration of the thread elements;
FIG. 6 is a diagrammatic sectional view of a portion of the covered stmt of this invention showing the flexible polymeric matrix located along the exterior of the stmt;
FIG. 7 is a view similar to the view of FIG. 6 with the flexible polymeric matrix located along the interior of the stent;
FIG. 8 is a side view of the stmt delivery device of this invention with a covered stmt loaded therein;
FIG. 9 is an enlarged side view of the area encircled at 9 in FIG. 8;
FIG. 10 is an enlarged side view of the area encircled at 10 in FIG. 8; and FIGS. 11-14 are side views of a distal portion of the stmt delivery device and the covered stent of the present invention in various stages of a stmt deployment operation in a body vessel.
Detailed Description of the Invention In FIG. 1 there is shown an example of the covered st mt 10 of the present invention in an unloaded condition. Covered stmt 10 is in the form of a cylindrical tubular body. Stent 10 is formed by a number of individual thread elements 11. Some of these elements extend in helix configuration in one direction axially displaced in relation to each~other having the center longitudinal axis of st mt 10 as a common axis. The other elements extend in helix configuration in the opposite direction and are also axially displaced in relation to each other having the center longitudinal axis as a common axis. Thus thread elements 11 extend in two directions and cross ttJIFN(~~t7 ,~~~j~~

. , 2~1 5 8 7 5 7 _8_ each other in a braided over and under configuration.
Thread elements 11 of stmt 10 are preferably arranged symmetrically so that the same number of thread elements are used in each direction of a winding. The number of thread elements needed is a function of the diameter of stmt 10 in an unloaded condition. For a stent having a diameter of 10 millimeters preferably 24 thread elements are used.
Thread elements 11 are helically wound about a cylindrical mandrel. One set of thread elements is wound in one direction while the other set of thread elements is wound in the opposite direction.
Thread elements 11 should be maintained in tension. Insufficient tensile force may allow the individual thread elements to depart from their configuration causing the braided structure of stmt l0 to unravel. When thread elements 11 are properly tensioned, a slight impression is formed in the overlying thread element at each intersection. See FIGS. 4 and 5. Each thread element is thus deformed such that it is bent over other thread elements and partly circumscribes these other thread elements.
Generally, only the parts of the respective thread elements lying on top of the crossing thread elements as seen in the radial direction have been subject to bending. These impressions, or saddles, tend to lock the thread elements relative to one another at the intersections. This maintains the stent configuration without the need for welding or other bonding of thread elements 11 at their intersections.
In addition, this allows a suitable length of the tubular braid to be cut in order to make a st mt of the desired length. The cut length of the tubular braid essentially maintains its cylindrical shape at h!~.~~.i~(i~~1 a't~'' the end sections.
In order to further improve the radial stability of stmt 10, the axially directed angle between crossing thread elements should be at least 600, preferably greater than about 90' and even more preferably greater than about 100' when stent 10 is in an unloaded condition. The greater the angle, the higher the stability of stmt 10 under external pressure.
Thread elements 11 forming stmt 10 can be made from a biocompatible and flexible yet rigid material such as various polymers, e.g. Kevlar~, and metal such as stainless steel. Other materials include alloys substantially based on cobalt, chromium, nickel and molybdenum, the alloying residue being iron. In addition, thread elements 11 cam be formed from a core and a tubular case surrounding the core.
This configuration can enhance the radiopacity of stmt 10. For example, the core can be constructed of tantalum for radiopacity while the case can be constructed of a cobalt-based alloy such as an alloy available under the brand name Elgiloy°, "Phynox" and "MP35N".
The diameter of stent 10 can be changed by radially compressing stent 10 or by axially displacing the ends of stent 10 relative to each other. In FIG. 2 there is illustrated how stent 10 according to FIG. 1 has been given reduced diameter by moving the ends away from each other in the direction of the arrows. Since stmt 10 must engage against the wall of the body vessel in which stmt 10 is to be placed with certain pressure in order to ' . , ~ '~1 2158'57 remain fixed, the diameter of stmt 10 in the radially contracted state must be smaller than the diameter of stent 10 at free expansion.
Stent 10 is covered by a matrix 15 of a flexible, polymeric material such as silicone rubber, polyurethane or Teflon . Other flexible and biocompatible polymers could also be used.
Preferably silicone rubber is used. Matrix 15 can take the form of a film or a braided or woven covering.
Matrix 15 is preferably applied to stmt 10 by dip coating. Liquid silicone rubber is mixed with an organic solvent, preferably xylene, to make the silicone rubber flowable. For a stent having a diameter of 10 mm, 24 thread elements and a braid angle of 1100 and where the stmt is supported in the silicone rubber and xylene bath only at the ends, a ratio of 27% silicone rubber to xylene is preferably used. Using this arrangement only one dip coating is needed to completely cover stmt 10. For a stmt having a diameter of 20 mm, 36 thread elements and a braid angle of 1100 and where the stent is supported in the silicone rubber and xylene bath by an internal mandrel, a ratio of 18% silicone rubber to xylene is preferably used. Using this arrangement 3 to 5 dip coatings is needed to completely cover stmt 10.
Additional coats could be applied to stmt 10 beyond what is described above. However, if too many coats are used, the flexibility of the resulting stmt will be compromised making it difficult to load the resulting stmt on a delivery device on to deploy the resulting stmt at a treatment site. It has been found that a coating about 0.010 cm (.004 inchesl thick is preferable. Alternatively, if a matrix 15 ~i ~c ~D~D ~~

_. , - ~ , with more flexibility is desired, matrix 15 can take the form of a braided or woven covering.
Stent 10 can be dip coated by supporting the ends of stmt 10, by using an external mandrel or by using an internal mandrel to support stmt 10 when it is dipped in the bath of silicone rubber and xylene.
When stmt 10 is dip coated by supporting the ends of stmt 10, the silicone rubber surrounds thread elements 11 so that the silicone rubber only extends in the interstices between thread elements 11 and there is little excess silicone rubber on the outside or inside of stmt 10. See FIG. 3 and FIG. 14. When stmt 10 is supported by an external mandrel the silicone rubber coating tends to extend toward the outside of thread elements 11 forming stmt 10. See FIG. 6. When stmt 10 is supported by an internal mandrel the silicone rubber tends to extend toward the inside of thread elements 11 forming stmt 10.
See FIG. 7. Preferably, stmt l0 should be supported at the ends or by an external mandrel during the dip coating process. The matrix resulting from this process tends to be stronger and more tear resistant so that it is better able to prevent tissue ingrowth through the interstices between thread elements 11 forming stmt 10.
Although the dip coating process described above is the preferred process for covering the stmt of this invention, matrix 15 can also be applied by other methods such as by injection molding or spray coating stmt 10 with the polymeric material.
Stent 10 is placed on a stmt delivery device 20 in.a radially contracted state for delivery to the treatment site in a body vessel. Stent 10 is carried by the distal portion of delivery device 20. The r,~~~rio~o s~~

proximal portion of delivery device 20 generally remains outside of the body for manipulation by the operator.
Delivery device ~0 comprises an elongated, inner tube 30, preferably having an axially extending lumen 35 therethrough. A distal portion of inner tube 30 is flexible and can be made from nylon or any other suitably flexible biocompatible polymeric material.
At its distal end, inner tube 30 is provided with a head 31, through which lumen 35 continues. Head 31 serves to facilitate the insertion of delivery device through a narrow opening in a body vessel. The proximal portion of inner tube 30 is preferably formed from stainless steel or some other suitably 15 rigid metal alloy. The proximal end of the distal portion of inner tube 30 is bonded to the distal end of the proximal portion of inner tube 30 in any conventional manner such as by using a standard adhesive.
20 A proximal tube 50 surrounds the proximal portion of inner tube 30 in coaxial fashion.
Preferably proximal tube 50 is formed from polyurethane. The proximal end of proximal tube 50 is connected to a valve body 40 having a side port 41. An extension tube 45 extends from side port 41 to an opening 42. This arrangement allows fluid to be injected through extension tube 45 and between proximal tube 50 and inner tube 30. -A moveable hose 55 surrounds the distal portion of inner tube 30. Hose 55 is rolled over itself to form a double-walled section. The proximal end of the inner wall 56 of the double-walled section is connected directly to inner tube 30. The proximal end of the outer wall 57 of the double-walled section AME~~DED S''t r~

._ i is connected to the outer surface of the distal portion of proximal tube 50. These connections can be achieved by any conventional means such as by a standard adhesive. This arrangement allows hose 55 to be rolled off stmt 10 placed on the distal portion of inner tube 30. By moving valve body 40 in the proximal direction, outer wall 57 of hose 55 slides proximally over inner wall 56. This causes inner wall 56 to "roll back" off of stmt 10. To facilitate movement of hose 55 off of stmt 10, at least that portion of inner wall 56 that contacts outer wall 57 in the area where hose 55 is folded over to form the double-walled section should be lubricous.
The lubricous characteristic can be achieved by adding a lubricous substance to this surface of hose 55; injecting a lubricous liquid between inner wall 56 and outer wall 57 or forming hose 55 from a naturally slippery material such as Teflon .
In the preferred embodiment, at least the surfaces of inner wall 56 and outer wall 57 that face each other in the double-walled section are coated with a lubricous hydrophilic coating. Preferably a hydrophilic coating manufactured and sold by The Hydromer Company under the designation 2018-M is used. Other materials include polyethylene oxide and hyaluronic acid. When wet the hydrophilic coating becomes lubricous and thus reduces friction between inner wall 56 and outer wall 57 of the double-walled section of hose 55 as outer wall 57 moves past inner wall 56. This facilitates the removal of the double-walled section of hose 55 from stent 10..
Preferably, hydrophilic material is added to hose 55 during the assembly of delivery device 20.
,~~t~i0~0 SH~'FT

'"' \ . .
i In order for the hydrophilic material to adequately bond to hose 55, the material used to manufacture hose 55 must be matched to the hydrophilic material used. It has been found that polyurethane works well as the material to form hose 55. In particular, a blend of 65D and 75D polyurethane provides sufficient flexibility to allow hose 55 to roll over itself yet still be soft enough and compatible with the hydrophilic material so it can be properly coated.
Preferably the blend is composed of 50% 65D
polyurethane and 50% 75D polyurethane.
During the assembly of delivery device 20, one side of hose 55 is coated with the hydrophilic material after hose 55 (outer wall 57) has been connected to proximal tube 50. Isopropyl alcohol is first applied to one side of hose 55 to clean the surface and remove the waxy film resulting from the plasticizers in the polyurethane. Next that same side of hose 55 is coated with the hydrophilic material. The surface of hose 55 should be flushed with alcohol for about 30 seconds. Similarly, that surface of hose 55 should be flushed with the hydrophilic coating for about 30 seconds. It has been found that this technique deposits sufficient hydrophilic material on inner wall 56 and outer wall 57 to allow hose 55 to be rolled back with minimal friction when the hydrophilic material is wet.
Once delivery device 20 has been assembled and is ready for use, the hydrophilic coating is wetted with physiological saline solution by injecting the solution through extension tube 45, past proximal tube 50 and into the space between inner wall 56 and outer wall 57 of the double-walled section of hose 55. Excess fluid exits from the hole 59 formed A~PFPzO~il ',,'~'r~..,.

' . ~ ._ toward the distal end of the double-walled section of hose 55. In this same manner, a lubricous fluid such as polyethylene glycol can be injected into the space between inner wall 56 and outer wall 57 of the double-walled section to provide the lubricous characteristic of hose 55 in place of adding a lubricous hydrophilic material to hose 55 as described above.
To deliver stmt 10 to a treatment site in a body vessel, stent 10 is placed in a radially compressed state in a surrounding relationship to the outer distal end of inner tube 30. Stmt 10 is constrained on inner tube 30 by the double-walled section of hose 55. It is important that stmt 10 not be confined too tightly on inner tube 30. Hose 55 should apply just enough force to stmt 10 to hold stmt 10 in place. The double-walled section of hose 55 can be removed from surrounding relation to stmt 10 by pulling valve body 40 and proximal tube 50 in a proximal direction. The double-walled section "rolls" off of stmt 10. No sliding movement takes place between stent 10 and inner wall 56 which contacts stmt 10. Along with the movement of the double-walled section in a proximal direction, the distal end of stmt 10 will be exposed in a radial direction to engagement against the wall of the body vessel. See FIG. 13. As the double-walled section of hose 55 continues moving proximally, more of stent 10 expands in a radial direction until the entire length of stmt 10 is exposed and engages the wall of a body vessel. See FIG. 14.
Lumen 35 is used to allow stmt delivery device 20 to follow a guidewire (not shown) previously inserted percutaneously into the body vessel. Lumen _.,.
. ~ n~ F jl, i~~~ ,~r~ .:
f.'~.
ri ;i 35 of inner tube 30 can also be used to introduce a contrast fluid to the area around the distal end of delivery device 20 so that the position of delivery device 20 may be easily detected for example by using X-ray technique.
Thus it is seen that a covered stent is provided that maintains the patency of a body vessel and reduces tissue ingrowth through the stmt. In addition, a stmt delivery device is provided that minimizes friction between moving parts and that can deploy a covered stmt at a treatment site with little difficulty. One skilled in the art will appreciate that the described embodiments are presented for purposes of illustration and not of limitation and that the present invention is only limited by the claims which follow.
r,ntw~f'.F'~ :~~"

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A radially expandable stmt, comprising:
at least one first thread element which extends in a helix configuration along a center line of the stent and having a first direction of winding;
at least one second thread element which extends in a helix configuration along the center line of the stent and having a second direction of winding so as to cross the at least one first thread element and form a lock between the thread elements thereat and form a plurality of interstices between each of the thread elements;
the first thread element and the second thread element defining a stmt inner surface and a stent outer surface; and a flexible matrix of polymeric material surrounding and encircling each of the first thread element and the second thread element and said lock formed therebetween and occluding the interstices between each of the first thread element and the second thread element, the matrix being integral with and radially expandable with and covering the stent and preventing tissue ingrowth therethrough;
wherein the stent is adapted to assume a radially contracted state and a radially expanded state, and the first thread element and the second thread element form an axially directed angle greater than 60° when the stent is in the radially expanded state, the stmt exerting a radial force sufficient to fixedly implant the stent in a body vessel.

2. The stent of claim 1 wherein the polymeric material is silicone rubber.

3. The stent of claim 1 wherein the polymeric material is polyurethane.

4. The stent of claim 1 wherein the polymeric material is Teflon R.

5. The stent of any of claims 1 - 4 wherein the matrix occluding the interstices is about 0.010 cm (.004 inches) thick.

6. The stent of any of claims 1 - 5 wherein the matrix of polymeric material covers the outer surface of the stent.

7. The stent of any of claims 1 - 5 wherein the matrix of polymeric material covers the inner surface of the stent.