USO0542 1955A
`9 5,421,955
`[11] Patent Number:
`[19]
`United States Patent
`
`Lau et al.
`[45] Date of Patent:
`Jun. 6, 1995
`
`[54] EXPANDABLE STENTS AND METHOD FOR
`MAKING SAME
`'
`
`[75]
`
`Inventors: Lilip Lau, Cupertino; William M.
`Hartigan Fremont; John J. Frantzen
`San Jose: an of calm
`.
`[73] Assignee: Advanced Cardiovascular Systems,
`Inc” Santa Clara, cam;
`
`’
`
`[21] Appl. No.: 214,402
`22
`F1
`:
`.
`[
`‘ed
`M” 191994
`
`1
`
`FOREIGN PATENT DOCUMENTS
`
`.
`0338816 10/1989 European Pat. Off.
`-
`E“.1'°P¢3n 11:31
`'
`'
`“’°P"‘“‘
`at‘
`.
`0407951 A1/1991 European Pat. Off.
`.
`0423916 4/1991 European Pat. Off.
`0423471A1 5/1991 EU{0P€3n_ Pat 05- -
`2135585
`9/1984 United Kingdom .
`9107139 S/1991 WIPO .
`9209246 6/1992 WIPO .
`
`OTHER PUBLICATIONS
`
`[60]
`
`[51]
`
`Related U.S. Application Data
`Division of Ser. No. 164,986, Dec. 9, 1993, abandoned,
`which is a continuation of Ser. No. 783,558, Oct. 28,
`1991’ aba“d°"ed-
`Int. Cl.6 ........................... B44C 1/22; c231= 1/02
`US. Cl. ......................................
`156/654; 156/659.1; 604/95; 606/198
`[58] Field of Search
`11
`'
`’
`’
`[56]
`References Cited
`
`Duprat et al.: Flexible Balloon—Expanded Stent for
`Small Vessels: PP- 276-278, 1987: Radiology Journal-
`C. R. Bard: PE Plus Peripheral Balloon Dilatation
`Catheter, Aug. 1985, CR Bard, Inc.
`Dotter, Charles T.= Transluminally Placed Coilspring
`continued on next page_)
`
`Primary Examiner-—-William Powell
`Attorney, Agent, or Firm——Fulwider Patton Lee &
`Utecht
`
`’
`
`’
`
`U.S. PATENT DOCUMENTS
`
`[57]
`
`ABSTRACT
`
`-
`
`3,105,492 10/1963 Jeckel .
`3»557»744 4/1972 Efsfik -
`:ve1:§l°“’Z °‘ 31‘
`4:14o:126 2/1979 Chou‘:;}‘m'ry _
`4,159,719 7/1979 Haen__
`4,503,569 3/1985 Done, .
`4,512,333 4/1935 Ban“, et a1_ _
`4,531,933
`7/1935 Norton eg ;,1_ _
`4,553,545 11/1985 Maass et al.
`.
`<
`4,580,568 4/1986 Gianturco .
`4519345 10/1935 M°18331'd'Nl¢15€n 61
`47949322 3/1937 wik‘°" ~
`4’650’466 3/1987 Luther '
`4,655,771
`4/1987 Wallsten .
`4,681,110 7/1987 Wiktor;
`4,706,671 “/1987 weimib _
`4,733,555
`3/1933 paknaz .
`4,739,752 4/1933 Palmaz _
`4,740,207 4/1988 Kreamer .
`4,762,128
`8/1988 Rosenbluth .
`
`.
`
`The invention is directed to an expandable stent for
`implantation in a body lumen, such as an artery, and a
`method for making it from a single length of tubing.
`Tire sitent 1COI11SlStS of a plurzzlilllity radlially expandable
`cy.1n ric_a cements gener y
`igne ‘on a common
`axis and interconnected by one or more interconnective
`elements. The individual radially expandable cylindri-
`cal elements consist of ribbon-like material disposed in
`an undulating pattern. The stents are made by coating a
`length of tubing with an etchant-resistive material and
`then selectively removing portions of the coating to
`form a pattern for the stent on the tubing and to expose
`the portions of the tubing to be removed This may
`done b
`h.
`t H d
`t.
`t.
`' d
`I t.
`..
`3.’ mac "‘°'°°".’° ° .39 ‘Ya 1°“. 3“ “”“"°
`positiomng of a laser in ‘conjunction vvith the coated
`tubing. After the patterning of the tubing, the stent is
`formed by removing exposed portions of the tubing by
`an etching process.
`
`‘
`
`'
`
`(List continued on next page.) '
`
`15 Claims, 3 Drawing Sheets
`
`
`
`001
`
`
`
`ENDOLOGIX, INC
`
`EX. 1012
`
`001
`
`

`
`
`Page 2
`
`5,421,955
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`U.S. PATENT DOCUMENTS
`3/1988
`4,767,418
`Deininger .
`Palmaz .
`10/1988
`4,776,337
`1/1989
`4,795,458
`Regan .
`Gianturco .
`1/1989
`4,800,882
`.
`Wolff et al.
`5/1989
`4,830,003
`Wallsten et al.
`7/1989
`4,848,343
`Hillstead .
`8/1989
`4,856,516
`Dellon et al.
`10/1989
`4,870,966
`Beck et al.
`.
`10/1989
`4,877,030
`Lindemann et al.
`11/1989
`4,878,906
`Wiktor .
`12/1989
`4,886,062
`Koch .
`1/1990
`4,892,539
`Rosenbluth .
`1/1990
`4,893,623
`Gianturco .
`3/1990
`4,907,336
`Hillstead .
`4/1990
`4,913,141
`Strecker .
`5/1990
`4,922,905
`Savin et al.
`8/1990
`4,950,227
`Wiktor .
`11/1990
`4,969,458
`11/1990
`4,969,890
`Sugita et al.
`1/1991
`4,986,831
`King et a1.
`Wilkoff .
`2/1991
`4,990,155
`2/1991
`4,994,071
`MacGregor .
`Delsanti .
`3/1991
`4,998,539
`Machold et al.
`3/1991
`5,002,560
`4/1991
`5,007,926
`Derbyshire .
`5/1991
`5,015,253
`MacGregor .
`Hillstead .
`5/1991
`5,019,085
`Pinchuk .
`5/1991
`5,019,090
`.
`Burton et al.
`6/1991
`5,026,377
`Garrison et al.
`7/1991
`5,034,001
`Gianturco et al.
`7/1991
`5,035,706
`Alonso .
`8/1991
`5,037,377
`Hillstead .
`8/1991
`5,037,392
`Harada et a1.
`8/1991
`5,037,427
`8/1991
`5,041,126
`Gianturco .
`.
`Stack et al.
`10/1991
`5,059,21 1
`Wallsten et a1.
`10/1991
`5,061,275
`11/1991
`5,062,829
`Pryor et al.
`.
`Porter .
`11/1991
`5,064,435
`Terrnin et al.
`12/1991
`5,071,407
`
`.
`
`.
`
`.
`
`.
`
`.
`
`_
`
`.
`
`.
`
`1/1992 Burton et al.
`5,078,720
`1/ 1992 Kreamer .
`5,078,726
`1/1992 Behl.
`5,078,736
`5,084,065 1/1992 Weldon et al.
`5,089,005 2/1992 Harada .
`5,089,006 2/1992 Stiles.
`5,092,877
`3/1992 Pinchuk .
`5,100,429 3/ 1992 Sinofsky et al.
`5,102,417 4/1992 Palmaz.
`5,104,404 4/1992 Wolff .
`5,108,416 4/1992 Ryan et a1.
`5,108,417 4/1992 Sawyer.
`5,116,318
`5/1992 Hillstead.
`5,116,360 5/1992 Pinchuk et a1.
`5,116,365
`5/1992 Hillstead .
`5,122,154 6/1992 Rhodes.
`5,123,917 6/1992 Lee.
`5,133,732 7/1992 Wiktor.
`5,135,536 8/1992 Hillstead .
`
`.
`
`.
`
`.
`
`.
`
`OTHER PUBLICATIONS
`
`Endarterial Tube Grafts, pp. 329-332, Sep. 10, 1969,
`Investigative Radiology.
`Wright et al.: Percutaneous Endovascular Stents: An
`Experimental Evaluation, 69-72, 1985, Radiology Jour-
`nal.
`
`Dotter: Transluminal Expandable Nitinol Coil Stent
`Grafting: Preliminary Report, pp. 259-260, Apr. 1983,
`Radiology Journal.
`Cragg et al.: Non-Surgical Placement of Arterial Endo-
`prostheses:. A New Technique Using Nitinol Wire, pp.
`261-263, Apr. 1983, Radiology Journal.
`Maass et al.: Radiological Follow-up ofTrans1uminal1y
`Inserted Vascular Endoprostheses: An Experimental
`Study Using Expanding Spirals, pp. 659-663, 1984,
`Radiology Journal.
`Palmaz et al.: Expandable Intraluminal Graft: A Prelim-
`inary Study, pp. 73-77, 1985, Radiologv Journal.
`
`002
`
`002
`
`

`
`U.S. Patent
`
`June 6, 1995
`
`Sheet 1 of 3
`
`5,421,955
`
`5
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`xxv\.
`N6?...
`
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`
`
`
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`
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`
`003
`
`
`
`
`

`
`June 6, 1995
`
`Sheet 2 of 3
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`‘
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`5,421,955
`
`004
`
`

`
`U.S. Patent
`
`June 6, 1995 '
`
`Sheet 3 of 3
`
`5,421,955
`
`005
`
`005
`
`

`
`1
`
`5,421,955
`
`EXPANDABLE STENTS AND METHOD FOR
`MAKING SAME
`
`This application is a divisional application of Ser. No.
`08/164,986, filed Dec. 9, 1993, now abandoned, which
`is a continuation of U.S. Ser. No. 07/783,558, filed Oct.
`28, 1991, (now abandoned).
`A
`
`BACKGROUND OF THE INVENTION
`
`5
`
`10
`
`This invention relates to expandable endoprosthesis
`devices, generally called stents, which are adapted to be
`implanted into a patient’s body lumen, such as blood
`vessel, to maintain the patency thereof. These devices
`are very useful in the treatment of atherosclerotic steno- 15
`sis in blood vessels.
`
`Stents are generally tubular shaped devices which
`function to hold open a segment of a blood vessel or
`other anatomical lumen. They are particularly suitable
`for use to support and hold back a dissected arterial
`lining which can occlude the fluid passageway there-
`through.
`Further details of prior art stents can be found in U.S.
`Pat. No. 3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,338
`(Balko et al.); U.S. Pat. No. 4,553,545 (Maass et al.);
`U.S. Pat, No. 4,73_3,665 (Palmaz); U.S. Pat. No.
`4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882 (Gian-
`turco); U.S. Pat. No. 4,856,516 (Hi1lstead); and U.S. Pat.
`No. 4,886,062 (Wiktor), which are hereby incorporated
`herein in their entirety by reference thereto.
`Various means have been described to deliver and
`implant stents. One method frequently described for
`delivering a stent to a desired intralumenal location
`includes mounting the expandable stent on an expand-
`able member, such as a balloon, provided on the distal
`end of an intravascular catheter, advancing the catheter
`to the desired location within the patient’s body lumen,
`inflating the balloon on the catheter to expand the stent
`into a permanent expanded condition and then deflating
`the balloon and removing the catheter. One of the diffi-
`culties encountered using prior stents involved main-
`taining the radial rigidity needed to hold open a body
`lumen while at the same time maintaining the longitudi-
`nal flexibility of the stent to facilitate its delivery.
`What has been needed and heretofore unavailable is a
`stent which has a high degree of flexibility so that it can
`be advanced through tortuous passageways and can be
`readily expanded and yet have the mechanical strength
`to hold open the body lumen into which it expanded.
`The present invention satisfies this need.
`SUMMARY OF THE INVENTION
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`The present invention is directed to an expandable
`stent which is relatively flexible along its longitudinal
`axis to facilitate delivery through tortuous body lumens,
`but which is stiff and stable enough radially in an ex-
`panded condition to maintain the patency of a body
`lumen such as an artery when implanted therein.
`The stent of the invention generally includes a plural-
`ity of radially expandable cylindrical elements which 60
`are relatively independent in their ability to expand and
`to flex relative to one another. The individual radially
`expandable cylindrical elements of the stent are dimen-
`sioned so as to be longitudinally shorter than their own
`diameters. Interconnecting elements or struts extending
`between adjacent cylindrical elements provide in-
`creased stability and are preferably positioned to pre-
`vent warping of the stent upon the expansion thereof.
`
`65
`
`2
`The resulting stent structure is a series of radially ex-
`pandable cylindrical elements which are spaced longitu-
`dinally close enough so that small dissections in the wall
`of a body lumen may be pressed back into position
`against the lumenal wall, but not so close as to compro-
`mise the longitudinal flexibility of the stent. The indi-
`vidual cylindrical elements may rotate slightly relative
`to adjacent cylindrical elements without significant
`deformation, cumulatively giving a stent which is flexi-
`ble along its length and about its longitudinal axis but
`which is still very stiff in the radial direction in order to
`resist collapse.
`The stent embodying features of the invention can be
`readily delivered to the desired lumenal location by
`mounting it on an expandable member of a delivery
`catheter, for example a balloon, and passing the cathet-
`er-stent assembly through the body lumen to the im-
`plantation site. A variety of means for securing the stent
`to the expandable member on the catheter for delivery
`to the desired location are available. It is presently pre-
`ferred to compress the stent onto the balloon. Other
`means to secure the stent to the balloon include provid-
`ing ridges or collars on the inflatable member to restrain
`lateral movement, or using bioresorbable temporary
`adhesives.
`
`The presently preferred structure for the expandable
`cylindrical elements which form the stents of the pres-
`ent invention generally have a circumferential undulat-
`ing pattern, e.g. serpentine. The transverse cross-section
`of the undulating component of the cylindrical element
`is relatively small and preferably has an apect ratio of
`about two to one to about 0.5 to one (e.g., the ratio of
`the-height to the width of an undulation). A one to one
`apect ratio has been found particularly suitable. The
`open reticulated structure of the stent allows for the
`perfusion of blood over a large portion of the arterial
`wall which can improve the healing and repair of a
`damaged arterial lining.
`The radial expansion of the expandable cylinder de-
`forms the undulating pattern thereof similar to changes
`in a waveform which result from decreasing the wave-
`forrn’s amplitude and the frequency. Preferably, the
`undulating patterns of the individual cylindrical struc-
`tures are in phase with each other in order to prevent
`the contraction of the stent along its length when it is
`expanded. The cylindrical structures of the stent are
`plastically deformed when expanded (except with NiTi
`alloys) so that the stent will remain in the expanded
`condition and, therefore, they must be sufficiently rigid
`when expanded to prevent the collapse thereof in use.
`With superelastic NiTi alloys,
`the expansion occurs
`when the stress of compression is removed so as to
`allow the phase transformation from austenite back to
`martensite and as a result the expansion of the stent.
`The elongated elements or members which intercon-
`nect adjacent cylindrical elements should have a trans-
`verse cross-section similar to the transverse dimensions
`of the undulating components of the expandable cylin-
`drical elements. The interconnecting elements may be
`formed in a unitary structure with the expandable cylin-
`drical elements from the same intermediate product,
`such as a tubular element, or they may be formed inde-
`pendently and connected by suitable means, such as by
`welding or by mechanically securing the ends of the
`interconnecting elements to the ends of the expandable
`cylindrical elements. Preferably, all of the interconnect-
`ing elements of a stent are joined at either the peaks or
`the valleys of the undulating structure of the cylindrical
`
`006
`
`006
`
`

`
`3
`elements which form the stent. In this manner there is
`no shortening of the stent upon expansion, when mea-
`sured from the outermost ends of the interconnecting
`members connected to the cylindrical elements at oppo-
`site ends of the stent.
`
`The number and location of elements interconnecting
`adjacent cylindrical elements can be varied in order to
`develop the desired longitudinal flexibility in the stent
`structure both in the unexpanded as well as the ex-
`panded condition. These properties are important to
`minimize alteration of the natural physiology of the
`body lumen into which the stent is implanted and to
`maintain the compliance of the body lumen which is
`internally supported by the stent. Generally, the greater
`the longitudinal flexibility of the stent, the easier and the
`more safely it can be delivered to the implantation site.
`In a presently preferred embodiment of the invention
`the stent is conveniently and easily formed by coating
`stainless steel hypotubing with a material resistant to
`chemical etching, and then removing portions of the
`coating to expose portions of underlying tubing which
`are to be removed to develop the desired stent struc-
`ture. The exposed portions of the tubing are removed
`by chemically etching from the tubing exterior leaving
`the coated portion of the tubing material in the desired
`pattern of the stent structure. The etching process de-
`velops smooth openings in the tubing wall without
`burrs or other artifacts which are characteristic of me-
`chanical or laser machining processes in the small sized
`products contemplated. Moreover, a computer con-
`trolled laser patterning process to remove the chemical
`resistive coating makes photolithography technology
`adaptable to the manufacture of these small products.
`The forming of a mask in the extremely small sizes
`needed to make the small stents of the invention would
`be a most difficult -task. A plurality of stents can be
`formed from one length of hypotubing by repeating the
`stent pattern and providing small webs or tabs to inter-
`connect the stents. After the etching process, the stents
`can be separated by severing the small webs or tabs
`which connect them.
`'
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Other features and advantages of the present inven-
`tion will become more apparent from the following
`detailed description of the invention, when taken in
`conjunction with the accompanying exemplary draw-
`ings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a elevational view, partially in section, of a
`stent embodying features of the invention which is
`mounted on a delivery catheter and disposed within a
`damaged artery.
`FIG. 2 is an elevational view, partially in section,
`similar to that shown in FIG. 1 wherein the stent is
`expanded within an damaged artery, pressing the dam-
`aged lining against the arterial wall.
`FIG. 3 is an elevational view, partially in section
`showing the expanded stent within the artery after
`withdrawal of the delivery catheter.
`FIG. 4 is a perspective view of a stent embodying
`features of the invention in an unexpanded state, with
`one end of the stent being shown in an exploded view
`illustrate the details thereof.
`FIG. 5 is a plan view of a flattened section of a stent
`of the invention which illustrates the undulating pattern
`of the stent shown in FIG. 4.
`
`45
`
`50
`
`55
`
`65
`
`007
`
`5,421,955
`
`4
`FIG. 6 is a schematic representation of equipment for
`selectively removing coating applied to tubing in the
`manufacturing of the stents of the present invention.
`FIGS. 7 through 10 are perspective views schemati-
`cally illustrating various configurations of interconnec-
`tive element placement between the radially expandable
`cylindrical elements of the stent.
`FIG. 11 is a plan view of a flattened section of a stent
`illustrating an alternate undulating pattern in the ex-
`pandable cylindrical elements of the stent which are out
`of phase.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`FIG. 1 illustrates a stent 10 incorporating features of
`the invention which is mounted onto a delivery catheter
`11. The stent generally comprises a plurality of radially
`expandable cylindrical elements 12 disposed generally
`coaxially and interconnected by elements 13 disposed
`between adjacent cylindrical elements. The delivery
`catheter 11 has an expandable portion or balloon 14 for
`expanding of the stent 10 within an artery 15. The artery
`15, as shown in FIG. 1, has a dissected lining 16 which
`has occluded a portion of the arterial passageway.
`The delivery catheter 11 onto which the stent 10 is
`mounted, is essentially the same as a conventional bal-
`loon dilatation catheter used for angioplasty proce-
`dures. The balloon 14 may be formed of suitable materi-
`als such as polyethylene, polyethylene terephthalate,
`polyvinyl chloride, nylon and ionomers such as Sur-
`lyn ® manufactured by the Polymer Products Division
`of the Du Pont Company. Other polymers may also be
`used. In order for the stent 10 to remain in place on the
`balloon 14 during delivery to the site of the damage
`within the artery 15, the stent 10 is compressed onto the
`balloon. A retractable protective delivery sleeve 20 as
`described
`in
`co-pending
`application
`Ser. No.
`07/647,464, filed on Apr. 25, 1990 and entitled STENT
`DELIVERY SYSTEM may be provided to further
`ensure that the stent stays in place on the expandable
`portion of the delivery catheter 11 and prevent abrasion
`of the body lumen by the open surface of the stent 10
`during delivery to the desired arterial location. Other
`means for securing the stent 10 onto the balloon 14 may
`also be used, such as providing collars or ridges on the
`ends of the working portion, i.e. the cylindrical portion,
`of the balloon.
`
`Each radially expandable cylindrical element 12 of
`the stent 10 may be independently expanded. Therefore,
`the balloon 14 may be provided with an inflated shape
`other than cylindrical, e.g. tapered, to facilitate implan-
`tation of the stent 10in a variety of body lumen shapes.
`In a preferred embodiment, the delivery of the stent
`10 is accomplished in the following manner. The stent
`10 is first mounted onto the inflatable balloon 14 on the
`distal extremity of the delivery catheter 11. The balloon
`14 is slightly inflated to secure the stent 10 onto the
`exterior of the balloon. The catheter-stent assembly is
`introduced within the patient’s vasculature in a conven-
`tional Seldinger technique through a guiding catheter
`(not shown). A guidewire 18 is disposed across the
`damaged arterial section with the detached or dissected
`lining 16 and then the catheter-stent assembly is ad-
`vanced over a guidewire 18 within the artery 15 until
`the stent 10 is directly under the detached lining 16. The
`balloon 14 of the catheter is expanded, expanding the
`stent 10 against the a.rtery 15, which is illustrated in
`FIG. 2. While not shown in the drawing, the artery 15
`
`007
`
`

`
`5
`
`5,421,955
`
`6
`undulations, are chosen to fill particular mechanical
`requirements for the stent such as radial stiffness.
`The number of undulations may also be varied to
`accommodate placement of interconnecting elements
`13, e.g. at the peaks of the undulations or along the sides
`of the undulations as shown in FIGS.'5 and 11.
`The stent 10 of the present invention can be made in
`many ways. However, the preferred method of making
`the stent is to coat a thin-walled tubular member, such
`as stainless steel hypotubing, with a material which is
`resistive to chemical etchants, and then to remove por-
`tions of the coating to expose the underlying hypotub-
`ing which is to be removed but to leave coated portions
`of the hypotubing in the desired pattern for the stent so
`that subsequent etching will remove the exposed por-
`tions of the metallic tubing, but will leave relatively
`untouched the portions of the metallic tubing which are
`to form the stent. The coated portion of the metallic
`tube is in the desired shape for the stent. An etching
`process avoids the necessity of removing burrs or slag
`inherent in conventional or laser machining processes.
`It is preferred to remove the etchant-resistive material
`by means of a machine-controlled laser as illustrated
`schematically in FIG. 6.
`A coating is applied to a length of tubing which,
`when cured,
`is resistive to chemical etchants. “Blue
`Photoresis ” made by the Shipley Company in San Jose,
`Calif., is an example of suitable commercially available
`photolithographic coatings. The coating is preferably
`applied by electrophoretic deposition.
`To ensure that the surface finish is reasonably uni-
`form, one of the electrodes used for the electrochemical
`polishing is a doughnut-shaped electrode which is
`placed about the central portion of the tubular member.
`The tubing may be made of suitable biocompatible
`material such as stainless steel, titanium, tantalum, su-
`perelastic NiTi alloys and even high strength thermo-
`plastic polymers. The stent diameter is very small, so
`the tubing from which it is made must necessarily also
`have a small diameter. Typically the stent has an outer
`diameter on the order of about 0.06 inch in the unex-
`panded condition, the same outer diameter of the hypo-
`tubing from which it is made, and can be expanded to an
`outer diameter of 0.1 inch or more. The wall thickness
`of the hypotubing is about 0.003 inch. In the instance
`when the stent was plastic, it would have to be heated
`within the arterial site where the stent is expanded to
`facilitate the expansion of the stent. Once expanded, it is
`cooled to retain its expanded state. The stent may be
`conveniently heated by heating the fluid within the
`balloon or by heating the balloon directly by a suitable
`system such as disclosed in application Ser. No.
`07/521,337, filed Jan. 26, 1990, now U.S. Pat. No.
`5,114,423, entitled “DILATATION CATHETER AS-
`SEMBLY WITH HEATED BALLOON” which is
`incorporated herein in its entirety by reference. The
`stent may also be made of materials such as superelastic
`NiTi alloys such as described in application Ser. No.
`07/629,381, filed Dec. 18, 1990, now abandoned, enti-
`tled SUPERELASTIC GUIDING MEMBER which
`is incorporated herein in its entirety by reference. In this
`case the stent would be formed full size but deformed
`(e.g. compressed) into a smaller diameter onto the bal-
`loon of the delivery catheter to facilitate transfer to a
`desired intralumenal site. The stress induced by the
`deformation transforms the stent from a martensite
`phase to a austenite phase and upon release of the force,
`when the stent reaches the desired intralumenal loca-
`
`is preferably expanded slightly by the expansion of the
`stent 10 to seat or otherwise fix the stent 10 to prevent
`movement. In some circumstances during the treatment
`of stenotic portions of an artery, the artery may have to
`be expanded considerably in order to facilitate passage
`of blood or other fluid therethrough.
`The stent 10 serves to hold open the artery 15 after
`the catheter 11 is withdrawn, as illustrated by FIG. 3.
`Due to the formation of the stent 10 from an elongated
`tubular member, the undulating component of the cylin-
`drical elements of the stent 10 is relatively flat in trans-
`verse cross—section, so that when the stent is expanded,
`the cylindrical elements are pressed into the wall of the
`artery 15 and as a result do not interfere with the blood
`flow through the artery 15. The cylindrical elements 12
`of stent 10 which are pressed into the wall of the artery
`15 will eventually be covered with endothelial cell
`growth which further minimizes blood flow interfer-
`ence. The undulating portion of the cylindrical sections
`12 provide good tacking characteristics to prevent stent
`movement within the artery. Furthermore, the closely
`spaced cylindrical elements 12 at regular intervals pro-
`vide uniform support for the wall of the artery 15, and
`consequently are well adapted to tack up and hold in
`place small flaps or dissections in the wall of the artery
`15 as illustrated in FIGS. 2 and 3.
`FIG. 4 is an enlarged perspective view of the stent 10
`shown in FIG. 1 with one end of the stent shown in an
`exploded view to illustrate in greater detail the place-
`ment of interconnecting elements 13 between adjacent
`radially expandable cylindrical elements 12. Each pair
`of the interconnecting elements 13 on one side of a
`cylindrical element 12 are preferably placed to achieve
`maximum flexibility for a stent. In the embodiment
`shown in FIG. 4 the stent 10 has three interconnecting
`elements 13 between adjacent radially expandable cylin-
`drical elements 12 which are 120 degrees apart. Each
`pair of interconnecting elements 13 on one end of a
`cylindrical element 12 are offset radially 60 degrees
`from the pair on the other side of the cylindrical ele-
`ment. The alternation of the interconnecting elements
`results in a stent which is longitudinally flexible in es-
`sentially all directions. Various configurations for the
`placement of interconnecting elements are possible, and
`several examples are illustrated schematically in FIGS.
`7-10. However, as previously mentioned, all of the
`interconnecting elements of an individual stent should
`be secured to either the peaks or valleys of the undulat-
`ing structural elements in order to prevent shortening of
`the stent during the expansion thereof.
`FIG. 10 illustrates a stent of the present invention
`wherein three interconnecting elements 13 are disposed
`between radially expandable cylindrical elements 11.
`The interconnecting elements 12 are distributed radially
`around the circumference of the stent at a 120 degree
`spacing. Disposing four or more interconnecting ele-
`ments 13 between adjacent cylindrical elements 12 will
`generally give rise to the same considerations discussed
`above for two and three interconnecting elements.
`The properties of the stent 10 may also be varied by
`alteration of the undulating pattern of the cylindrical
`elements 13. FIG. 11 illustrates an alternative stent
`structure in which the cylindrical elements are in ser-
`pentine patterns but out of phase with adjacent cylindri-
`cal elements. The particular pattern and how many
`undulations per unit of length around the circumference
`of the cylindrical element 12, or the amplitude of the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`008
`
`008
`
`

`
`5,421,955
`
`7
`tion, allows the stent to expand due to the transforma-
`tion back to the martensite phase.
`Referring to FIG. 6, the coated tubing 21 is put in a
`rotatable collet fixture 22 of a machine controlled appa-
`ratus 23 for positioning the tubing 21 relative to a laser
`24. According to machine-encoded instructions,
`the
`tubing 21 is rotated and moved longitudinally relative
`to the laser 24 which is also machine controlled. The
`laser selectively removes the etchant-resistive coating
`on the tubing by ablation and a pattern is formed such
`that the surface of the tube that is to be removed by a
`subsequent chemical etching process is exposed. The
`surface of the tube is therefore left coated in the discrete
`pattern of the finished stent.
`A presently preferred system for removing the coat-
`ing on the tubing includes the use of an 80 watt CO2
`laser, such as a Coherent Model 4-4, in pulse mode (0.3
`mS pulse length); 48 mA key current and 48 W key
`power with 0.75 W average power, at 100 Hz; Anorad
`FR=20; 12.5 Torr; with no assist gas. Low pressure air
`is directed through the fine focus head to ensure that no
`vapor contacts the lens. The assist gas jet assembly on
`the laser unit may be removed to allow a closer proxim-
`ity of the fine focus head and the collet fixture. Opti-
`mum focus is set at the surface of the tubing. Cured
`photoresist coating readily absorbs the energy of the
`CO2 wavelength, so that it can be readily removed by
`the laser. A coated 4 inch length of 0.06 inch stainless
`steel tubing is preferred and four stents can be patterned
`on the length of tubing. Three tabs or webs between
`stents provide good handling characteristics for the
`tubing after the etching process.
`The process of patterning the resistive coating on the
`stent is automated except for loading and unloading the
`length of tubing. Referring again to FIG. 6 it may be
`done, for example, using a CNC opposing collect fix-
`ture 22 for axial rotation of the length of tubing, in
`conjunction with a CNC X/Y table 25 to move the
`length of tubing axially relative to a machine controlled
`laser as described. The entire space between collets can
`be patterned using the CO2 laser set—up of the foregoing
`example. The program for control of the apparatus is
`dependent on the particular configuration used and the
`pattern to be ablated in the coating, but is otherwise
`conventional.
`
`This process makes possible the application of present
`photolithography technology in manufacturing the
`stents. While there is presently no practical way to mask
`and expose a tubular photoresist-coated part of the
`small size required for making intravascular stents, the
`foregoing steps eliminate the need for conventional
`masking techniques.
`After the coating is thus selectively ablated, the tub-
`ing is removed from the collet fixture 22. Next, wax
`such as ThermoCote N-4 is heated to preferably just
`above its melting point, and inserted into the tubing
`under vacuum or pressure. After the wax has solidified
`upon cooling, it is reheated below its melting point to
`allow softening, and a smaller diameter stainless steel
`shaft is inserted into the softened wax to provide sup-
`port. The tubing is then etched chemically in a conven-
`tional manner. After cutting the tabs connecting the
`stents any surface roughness or debris from the tabs is
`removed. The stents are preferably electrochemically
`polished in an acidic aqueous solution such as a solution
`of ELECTRO-GLO #300, sold by the ELECTRO-
`GLO CO., Inc. In Chicago, Ill., which is a mixture of
`sulfuric acid, carboxylic acids, phosphates, corrosion
`
`8
`inhibitors and a biodegradable surface active agent. The
`bath temperature is maintained at about 110-135 de-
`grees F. and the current density is about 0.4 to about 1.5
`amps per in.-"- Cathode to anode area should be at least
`about two to one. The stents may be further treated if
`desired, for example by applying a biocompatible coat-
`mg.
`While the invention has been illustrated and de-
`scribed herein in terms of its use as an intravascular
`stent, it will be apparent to those skilled in the art that
`the stent can be used in other instances such as to ex-
`pand prostatic urethras in cases of prostate hyperplasia.
`Other modifications and improvements can be made
`without departing from the scope of the invention.
`What is claimed is:
`1. The process of making a stent which includes the
`steps of:
`a) applying a coating resistive to chemical etching to
`a length of tubing;
`b) selectively removing portions of the resistive coat-
`ing to expose sections of the tubing; and
`c) removing exposed portions of the tubing.
`2. The process of claim 1, wherein a plurality of stents
`are made from a single piece of tubing.
`3. The process of claim 1, wherein the stent is made
`from a biocompatible material selected from the group
`consisting of polymers, stainless steel,
`titanium, su-
`perelastic NiTi alloys and tantalum.
`4. The process of claim 1, wherein the coating is
`applied by electrophoretic deposition.
`5. A method for making an open reticulated tubular
`structure, comprising the steps of:
`a) providing a discrete'length of thin walled tubing;
`b) forming a resistive coating onto the exterior of the
`tubing;
`c) selectively removing portions of the resistive coat-
`ing on the exterior of the tubing to leave the de-
`sired pattern of the complete open reticulated tubu-
`lar structure coated with resistive coating and to
`expose portion of the tubing to. be removed; and
`d) removing the