WO2002015821A1

WO2002015821A1 - Expandable stent having a plurality of expansion cell modules

Info

Publication number: WO2002015821A1
Application number: PCT/US2000/023227
Authority: WO
Original assignee: Stenttech, Inc. Dba Stenttech
Priority date: 2000-08-24
Filing date: 2000-08-24
Publication date: 2002-02-28
Also published as: AU2000269326A1

Abstract

An expandable stent (30) is disclosed temporarly fitted upon a balloon catheter (40), having a distal end (42), an expandable balloon (44), and a catheter shaft (46). One particular embodiment has five cells (66) in each ring (60) and two interconnecting bridges (65) between non-consecutive opposing cell interconnection bridges (62) of each ring (60). Each successive pair of intermodular connecting bridges (65) joining each successive ring (60) rotates around the stent (30) as the successive pair of intermodular connecting bridges (65) extend to the last ring at the distal end (42) of the stent (30).

Description

EXPANDABLE STENT HAVING A PLURALITY OF EXPANSION CELL

MODULES

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation-In-Part Application of U.S. Patent Application

Serial No. 08/810,819, filed March 5,1997, entitled EXPANDABLE AND SELF-EXPANDING STENTS AND METHODS OF MAKING AND USING THE SAME.

BACKGROUND OF THE INVENTION The present invention relates to stents and, most preferably, to stents which can be expanded, for example, by expanding an internally positioned balloon.

Under normal circumstances, the heart functions as a pump to perfuse blood throughout the body through arteries. The arteries of some patients are subject to stenosis, a localized partial blockage which narrows the passageway and interferes with normal blood flow. This condition is termed atherosclerotic coronary artery disease. It is a leading cause of morbidity in adults in

the western world. One corrective procedure used to treat this disease is coronary bypass surgery, which is a highly invasive operation, h recent years a corrective procedure, percutaneous

fransluminal coronary angioplasty, and devices known as balloon angioplasty catheters have been

widely used to correct stenotic conditions within arteries, particularly coronary arteries, in a

relatively efficient manner.

An angioplasty procedure generally includes inserting a deflated balloon, mounted on a

catheter, within the affected vessel or artery at the point of a stenosis. The balloon is then

inflated to physically force the dilation of the partially occluded vessel. Roughly 300,000

patients per year in the United States are presently undergoing coronary angioplasty procedures. However, a substantial percentage of patients who have had balloon angioplasty redevelop the stenosis in a relative short period of time. The reoccurrence typically becomes evident within

less than about 6 months after angioplasty and. may affect 30 to 40 percent of patients. The

percentage of patients who have reoccurring stenoses is generally reduced by installing a

"scaffolding" device, known as a stent, at the site of the stenosis. The underlying mechanism for

the benefit of stenting may be as simple as preventing immediate elastic recoil and maintaining

a large luminal cross-section for a few days after angioplasty. The drawbacks of stenting are

thought to relate to an increased potential for thrombus formation and hyperplasia induced by metallic or other stent materials.

One of the complications of balloon angioplasty is the occurrence of tears in the wall of

the artery leading to intimal dissections which is a principle cause of closure of the artery due to the procedure and may require emergency surgery. Endovascular stents offer the potential of tacking these intimal flaps to keep the lumen patent. These tears are of variable length and often

spiral in shape, hi addition, following balloon angioplasty patients may have a suboptimal result due to a markedly irregular lumen. In these situations stenting with stents offers the advantage of attaining excellent results.

While coronary and other arterial stenosis are common applications for stenting, stents

can be used to treat narrowings in any hollow or tubular organs such as the Esophagus, urethra, Biliary Tract and the like.

A number of challenges are present in the preparation, deployment and use of stents. One

challenge is to efficiently prepare a stent without compromising the present medical

effectiveness of the stent. Another challenge is to improve the medical effectiveness of stents.

For example, large metal stent surface areas are thought to have a positive correlation with

increased platelet deposition and potentially increase the risk of thrombosis formation and intimal hypoplasmia. Yet another challenge is to improve techniques for delivery and deployment of stents.

For example, jagged edges associated with stents can result in snagging in the arteries and can, therefore, cause complications during movement of the stent to the location of a stenosis to be

treated. A tear in an artery wall resulting either from a snag or expansion mishap may require

emergency corrective surgery or may lead to a new closure site in the artery. Inadequate

radiopacity is also an issue with stents made of materials which are not radiopaque. It will be

appreciated that measures for making the stents radiopaque, and therefore, viewable within the

body during procedures using real-time x-ray viewing techniques, will provide improvements to the art.

The current medical prior art contains a number of insights into stent technology. Some examples are noted here to provide background. Schepp-Pesch et al. (U.S. Patent No. 5,354,309) disclose a spiral shaped sheet metal part which widens to a cylindrical jacket-shaped outer contour device at a transition temperature. The device is formed from a memory alloy metal with

parallel elongated slots and web regions between the slots. The slots deform into diamond- shaped gaps or operation between webs upon expansion of web associated with an increase in temperature. Another example is Burton et al., WO 92/11824. Burton discloses a self-expanding intraluminal prosthesis or stent which is tubular and has opposed ends and fenestrated walls. The

Burton stent is taught to be prepared by molding, or alternatively, laser or water-jet cutting of a

solid tube to form a pattern of apertures and leaving intersecting thread-like strips therebetween.

A third example is Wolff (U.S. Patent No. 5,104,404), which discloses a number of stent

segments formed by welding wire strands in a zig-zag arrangement. The segments are connected

by hinges to allow them to articulate. The Wolff hinges can be welded straight wire or coiled

wire. One particularly well accepted stent is the stent disclosed by Palmaz (U.S. Patent Nos.

4,733,665 and 4,739,762, each of which are hereby incorporated herein by reference). The Palmaz stent is in fairly wide use in the U.S. and elsewhere. However, this stent is particularly

rigid and difficult to deliver in through "meandering" coronary arteries due to this rigidity.

Furthermore, the ends at least one of the stents disclosed by Palmaz come together in a series of

points which can catch on the inner walls of the vessels through which the stent is passed

occasionally tearing the tissue along the inner walls. It would be a desirable and a significant

advance in the field of Cardiology to provide a stent which can be articulated to facilitate the delivery of a stent through the often tortuous pathway provided by coronary arteries to a desired

final location within the patient, h particular, the stent should have the ability to "snake" around complex curves and tight curves encountered in the circulatory system, especially those associated with the coronary system which supplies critical blood flow to the heart. The avoidance of any stent structure which tend to snag or catch on the interior of the various blood vessels is also desirable.

Wiktor (U.S. Patent Nos. 4,969,458; 4,886,062; and 5, 133,732) also discloses articulating expandable stents. These stents generally coexist of one or more low memory metal wires which are wound in such a way to provide an articulating metal scaffolding structure which is balloon

expandable once it is placed within the stenotic region of the diseased vessel.

The control of end-to-end length changes upon expansion is a desirable feature in stents.

It would also be a significant advance if the stent could be manufactured economically. It will

also be appreciated that inexpensive quality control would also be desirable.

Accordingly, it will be appreciated that there is a need for stents which address these and

other needs and generally improve upon the stents now available in the public domain. The present invention provides advantages over the prior devices and solves other problems associated therewith.

SUMMARY OF THE INVENTION

In preferred embodiments, the expandable stent of the present invention is expandable

by enlarging an expandable balloon positioned within the stent. The preferred stent including a

plurality of modules, each of the modules having a plurality of individual expansion cells

radially interconnected to form a ring of individual expansion cells interconnected to each other

in series by one of a plurality of cell interconnection bridges. Each of the preferred expansion cells including a continuous strand of a material, the continuous strand of material in each cell

being interconnected with itself so as to generally encompass a radially space within the respective cell. Each expansion cell having an upper half and a lower half, the upper and lower halves being joined together and the lower half of each of the respective expansion cells being interconnected to the upper half of an adjacent expansion cell within that respective ring of

expansion cells by one of the plurality of cell interconnection bridges. Each cell interconnection bridge having a center and each expansion cell having a radial length which is a radial distance consistent with an existing circumference of the respective ring as measured from the center of the cell interconnection bridge interconnected with the upper half of that expansion cell to the

center of the cell interconnection bridge interconnected with the lower half of that expansion cell.

The material being deformable such that the ring can be deformed from a first configuration

wherein each ring has a first circumference and each expansion cell has a first radial length, to

a second configuration wherein each ring has a second circumference greater than the first

circumference and each expansion cell has a second radial length greater than the first radial

length. Each expansion cell preferably having a pair of sides which are mirror images of one another, each side being expandable when the ring of which the cell is a part is in the first configuration such that the second radial length can be at least twice as great as the first radial

length. In preferred embodiments, each side will have an accordion shape which is expandable.

Preferred stents will have a plurality of intermodular connecting bridges; each intermodular

connecting bridge interconnecting a cell interconnection bridge connecting expansion cells of one

module with a cell interconnection bridge connecting expansion cells of an adjacent module.

Preferably, each pair of adjacent modules will be interconnected with one another by at least two intermodular connecting bridges.

The preferred stents of the present invention are expandable, typically, for example, by

enlarging an expandable balloon positioned within the stent, preferably having a plurality of

expandable ring structures. The ring structures are joined end-to-end and feature an absence of potential tissue snagging structures. The stents and ring structures of the preferred stents are characterized by relatively low surface area compared to the surface area of a simple cylinder of similar dimensions and connecting structures which allow the various ring structures to articulate with respect to one another. The stents of the present invention are efficiently and easily

produced using laser etching or chemical etching techniques and amenable to good quality control at a relatively low cost. Moreover, the stents of the present invention, in certain embodiments which may be especially desirable during certain procedures, as they provide little

or no end-to-end shortening upon expansion. These various attributes, advantages, and features will become apparent from the following disclosure.

The expandable stent of the present invention includes a plurality of modules. Each of

the modules have a plurality of individual cells radially interconnected to form a ring of

individual cells interconnected to each other in series. Each of the individual cells include a continuous strand of a material, the continuous strand of material in each cell being

interconnected with itself so as to surround a space central to the interconnected strand and define a plurality of sides. The material employed is deformable, such that the ring can be deformed from a first configuration, wherein the ring has a first circumference, to a second configuration

wherein the ring has a second circumference greater than the first circumference. Each cell of

the rings has an upper half and a lower half. The upper and lower halves are joined together at

respective first and second ends. The plurality of modules includes at least first and second rings

or modules, where the individual expansion cells of the first module are defined as first module expansion cells and the individual expansion cells of the second module are defined as second

module expansion cells. The modules are oriented side by side such that the second ends of the first module are located proximate the first ends of the second module. The respective expansion cells of each of the respective rings or modules are interconnected by a series of cell

interconnection bridges. Each module is interconnected with adjacent modules by at least one intermodular connecting bridge which is interconnected with a cell interconnecting bridge in each of the respective adjacent rings or modules. Further, the modules can articulate relative to one another such that the modules of the expandable stent can pass through otherwise tortuous passageways with many "sharp" turns or twists. Preferably, in this embodiment, the expandable

stent is such that each module is interconnected with adjacent modules by at least two

intermodular connecting bridges. In preferred embodiments, these connecting bridges will connect with cell interconnection bridges which are separated in series by cell interconnection

bridges which are unconnected with intermodular connecting bridges connected with the same

module, but may very well be so interconnected with the next module in series.. In preferred

embodiments, the intermodular connecting bridges will rotate radially around the cylindrical stent

in a generally helical manner.

The preferred expansion cells will have an upper half and a lower half which are mirror images of one another. The material of the continuous strand of the preferred expandable stents of the present invention will be selected from amongst low memory metals such as tantalum,

palladium, silver, gold, stainless steel and the like.

In another embodiment, the present invention is an expandable stent. The stent again

being expandable by enlarging an expandable balloon positioned within the stent. The stent

includes a plurality of individual cells radially interconnected to form a ring of individual cells

interconnected to each other in series, each of the individual cells including a continuous strand of a material. The continuous strand of material in each cell is interconnected with itself so as

to surround a space central to the interconnected strand and define a plurality of segments. The

ring can be deformed from a first configuration, wherein the ring has a first circumference, to a second configuration wherein the ring has a second circumference greater than the first circumference. Each cell has an upper half and a lower half, the upper half being a mirror image

of the lower half, the upper and lower halves being joined together at respective first and second ends which are preferably drawn inward to create an accordion type structure which permits the cell to expand significantly when expanded. These and other various other advantages and features of novelty which characterize the present invention are pointed out with particularity in the claims annexed hereto and forming a

part hereof. However, for a better understanding of the present invention, its advantages and

other objects obtained by its use, reference should be made to the drawings, which form a further

part hereof, and to the accompanying descriptive matter, in which there is illustrated and

described preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, in which like reference numbers indicate corresponding parts throughout

the several views; FIG. 1 is a side view of a first embodiment of the present invention as temporarily mounted upon a balloon catheter (shown in hidden line) and shown in close association with a

longitudinal section of a stenosis in an artery about to be treated;

FIG. 2 is a side view of the embodiment depicted in Figure 1 following inflation of the

balloon catheter (shown in Mdden line) inflated to deform and expand the expandable stent and

treat the stenotic condition shown in longitudinal section;

FIG. 3 is a schematic representation cross-sectional view of the stent and artery shown

in Figure 1 as seen from the line 3-3 of Figure 1;

FIG. 4 is a schematic representation cross-sectional view of the stent and artery shown

in Figure 2 as seen from the line 4-4 of Figure 2;

FIG. 5 is a partial plan view of an enlarged and flattened portion of the embodiment of Figure 1 as seen from the line 5-5 of Figure 3, assuming the circumferential surface is flattened, showing the unexpanded individual expansion cells of portion of respective rings or modules and the respective interconnecting or interconnection bridges;

FIG. 6A is a partial plan view of an enlarged and flattened portion of the expanded embodiment shown in Figure 2 as seen from the line 6-6 of Figure 4, assuming the circumferential surface is flattened, showing the expanded individual expansion cells of portions

adjacent rings or modules of the preferred stent;

FIG. 6B is a partial plan view of an enlarged and flattened portion of an expanded

embodiment similar to that shown in Figure 2, assuming the circumferential surface is flattened,

but showing only a single expanded expansion cell which is expanded more so than the cells

shown if Figure 6A;

FIG. 6C is a partial plan view of an enlarged and flattened portion and flattened of the expanded embodiment similar to that shown in Figure 2, assuming the circumferential surface is flattened, but showing only a single expanded expansion cell which is expanded more so than

the cells shown if Figure 6 A and more so than the cell shown if Figure 6B; and

FIG. 7 is a plan view of the expandable stent of the present invention similar to that

shown in Figure 1, except that the stent is shown in an articulated orientation which enables the

stent to more easily pass through bends and turns in arteries or other vessels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to Figures 1-4, an expandable stent 30 of the present invention is

schematically presented in Figure 1. The stent 30 has a proximal end 32 and a distal end 34 and is depicted in Figure 1 as being temporarily fitted upon or generally coaxial with a balloon

catheter 40 (shown in hidden line), having a distal end 42, an expandable balloon 44 and a catheter shaft 46 . The stent 30 is also shown closely associated within a portion of an artery 50 which is partially occluded by a stenosis 52.

As shown schematically in Figure 2, once the stent 30 is appropriately located in the lumen of the artery 50, preferably spanning the stenosis 52, the stent 30 can be expanded outward

radially by inflating the balloon 44 of the balloon catheter 40. Inflation of balloon 44 is accomplished by application of fluid pressure to its interior by the cardiologist, acting at the proximal end (not shown) of catheter 40 in a manner which is well known in the art. As balloon

44 expands, stent 30 is also expanded outward radially. As the expansion continues, the stent

30 and balloon 44 contact and begin to alter the shape of the stenosis 52. Such expansion is

continued until the stenosis 52 is reformed to a more desirable shape and size, i.e. more nearly

cylindrical, such that patency is restored in the artery 50. The preferred stent 30, shown in

Figures 1, 2 and 7 is especially flexible longitudinally. This flexibility makes it considerably

easier to introduce into coronary arteries having many turns and sharp bends. Furthermore, tissue prolapse is minimized with the present stent 30.

The relatively narrow, initial radius of the stent 30 positioned coaxially, about axis 45 of

the balloon 44 and not yet expanded to contact the stenosis 52 of artery 50 is also schematically

shown in cross section in Figure 3. As schematically shown in Figure 4, the balloon 44 can be

inflated to expand the stent 30 and force the stenosis 52 back against the wall of artery 50. Next,

the fluid pressure on the balloon 44 can be relieved and reduced. The balloon 44 will contract

radially toward axis 45 so that it can be easily withdrawn. The expandable stent 30, however,

generally retains the expanded radius and does not contract, because it is preferably made of a

low memory material such as stainless steel, hi turn, the retained expanded condition of the stent 30 serves to hold the stenosis 52 out of the channel of the artery 50 and restore patency to the artery 50. Because the stent 30 remains expanded but the balloon 44 contracts, withdrawal of the balloon 44 and the balloon catheter 40 is generally straightforward. Even after the balloon

catheter 40 is withdrawn from the patient, patency remains in the artery 50 and more appropriate circulation is possible for the tissues served by the treated artery 50. The stent 30 remains as a support or scaffolding for the artery 50 and may also inhibit tissue prolapse and reformation of the stenosis 52.

The following definitions are provided to facilitate understanding of the invention and disclosure. As used herein, the term "interconnected" means a physical connection, particularly

as it relates to an interconnection or interconnections between a first structure and a second

structure in which a generally constant radial thickness is maintained and no change in material

occurs. As used herein, the term "radial thickness" means the difference in the distance between

the radius from the axis to an inside facing surface and the distance between the radius from the

axis to outside facing surface. As used herein, the term "cells" means the structure defining an

irregular aperture or a frame about an irregular aperture. The cells under discussion in this disclosure have frames with a constant radial thickness and deform in response to radial force. The frames may have curved sides, straight sides or combinations of curved and straight sides,

hi this particular regard, "straight" means appearing to take the shortest path between two points

when shown in a flattened plan view as shown in Figures 5-6C. As these cells deform, the

apertures defined within each respective cell may increase or decrease in size as the shape of the

aperture changes. As used herein, the terms "helical" and "counter helical" mean paths having

many points, each of which is spaced an equal distance apart from a common axis, such that the path curves in an arc as it traverses an incomplete external surface residing around the stents of

the present invention in any configuration. As used herein, the terms "ring" and "module" mean

a plurality of cells interconnected around the axis, preferably in series, such that paths generally created by the interconnected cells are generally spaced an equal distance apart from and proceed around the axis. As used herein, the terms "independent rings" or "independent modules" means rings which can deform, for example by expanding on the order of, for example, but without limit, a 10% increase in radius, without an adjacent ring or module being expanded. As used

herein, the term "articulating" means that two adjacent rings or modules can "articulate" so as to shift their respective axes from an orientation where the respective axes have a coincident orientation to an orientation where the respective axes have a non-coincident orientation thereby

establishing an angle between the respective axes of the respective rings.

As shown schematically in Figures 5 and 6 A, the stent 30 is made up of a plurality of

modules or rings 60 which are closed loops and circumferentially extend about a central axis 45.

Each of the rings 60 have proximal ends 61 and distal ends 64. Each of the rings 60 has at least

one deformation component or expansion cell 66. An expansion cell 66 is a frame defining an

aperture within the frame. Each cell 66 in the expandable stent 30 deforms when radial force is applied outwardly to each of the rings or modules 60 of the stent 30. Preferably, each ring 60 has a plurality of expansion cells 66 and, most preferably, each ring consists of a plurality of generally identical or nearly identical expansion cells lined up in

series in the preferred embodiments. In an unexpanded orientation or condition, as shown in

Figures 1, 3, and 5, each expansion cell 66 is characterized by a greater longitudinal extent "L"

(71) than "circumferential" extent "C" (73). In the present embodiment, the longitudinal extent

"L" of the cell 66 generally corresponds to the distance between the proximal and distal ends 61

and 64 of the cell 66.

In preferred embodiments, each of the expansion cells 66 have an upper half or first portion 67a and a lower half or second portion 67b. The second portion 67b of each cell 66,

which is preferably a mirror image of the first portion 67a and is joined to first portion 67a at inner ends 68 of accordion-like expansion joints 69. Each of the preferred cells 66 have a plurality of outwardly or inwardly extending segments 80a, 80b, 80c, 80d having the effect of allowing the expansion cell to expand circumferentially. These segments are the upper indirect segments 80a and the upper direct segments 80b of the upper half 67a of each expansion cell 66,

and the lower direct segments 80c and the lower indirect segments 80d of the lower half 67b of the expansion cell 66. The indirect segments 80a, 80d pass through a series of oppositely extending curvilinear arcs, while the direct segments 80b, 80c are generally straight, hi alternate

embodiments these segments are exchangeable such that any of the segments of any alternate cell

of any alternate embodiment may, in this sense, be "indirect" or "direct". In the preferred

embodiment shown in the drawings, the respective sides, e.g. left and right sides, of each

expansion cell 66 have an accordion shape because of the accordion-like expansion joint 69,

including the direct segments 80b and 80c which joint the upper half 67a and the lower half 67b,

and the fact that this structure is roughly mirrored by the "hair-pin" joint 70 between the indirect segments 80a, 80d and the respective direct segments 80b, 80c to which the indirect segments are interconnected. It is the combination of the two "hair-pin" joints 70 separated by the

accordion-type joint 69 on each side of each expansion cell 66 which provide the. accordion shape

to each expansion cell 66. As used herein, therefore, an expansion cell which has an accordion

shape is an expansion cell which has a series of direct and/or indirect segments, preferably 4 in

total, on each side of each cell 66, which are joined together at alternating ends generally in a

manner similar to that illustrated in Figures 5 and 6A. It is this accordion shape, which allows

the expansion cells 66 to expand or stretch radially when the radially expanding balloon 44

expands in the manner discussed above and illustrated in Figures 1-4.

Each expansion cell 66 is joined in series with other expansion cells in each ring or module 60 by a series of cell interconnection bridges 62, each of which has a center 63 midway between the respective expansion cells 66 to which the respective interconnection bridge 62 is

interconnected, hi preferred embodiments of the present stent 30, each ring or module 60 will be joined together by one or more intermodular connecting bridge 65 which will connect cell interconnection bridges 62 of the respective rings 60. In the preferred embodiment shown in Figures 1-6 A, the stent 30 has a series of eight rings 60, each ring 60 being connected to each adjacent ring by two intermodular connecting bridges 65.

hi alternate embodiments, the number of intermodular connecting bridges 65 between each ring 60 can equal the number of cells 66 in each ring. This number will characteristically

be the same for each ring 69 of any particular stent. Alternate stents may have a series of rings

having as few as 2 expansion cells or as many as 10 or more, preferably from 3 to 8, more

preferably from 4 to 6. In the embodiment shown in Figures 1-6 A, each ring 60 has 5 cells 66,

and each ring is joined to each adjacent ring by the intermodular connecting bridges 65. In this

embodiment, the intermodular bridges 65 join non-consecutive opposing cell interconnection

bridges of respective rings and the cell bridge 62 between the two non-consecutive cell bridges which are joined to one adjacent ring will be joined to an opposing cell bridge 62 in the next

adjacent ring along with opposing cell bridges connecting the next opposing pair of cells in series

with the following opposing pair. In alternate embodiments, where the respective rings or

modules (not shown) are interconnected once, twice, three, four or more times, the respective

rings can articulate with respect to one another, such that respective axes of each adjacent module

do not coincide with one another when the rings are so articulated. It will be appreciate that the

number and the placement of intermodular connecting bridges can vary and can take any possible

form so long as there is at least one bridge connecting each ring of any alternate stents. the preferred embodiment shown in Figure 7, having five cells 66 in each ring 60 and

two intermodular connecting bridges 65 between non-consecutive opposing cell interconnection bridges 62 of each adjacent ring, each successive pair of intermodular connecting bridges 65 joining each successive ring rotates around the stent 30 as the successive pair of intermodular bridges extend to the last ring at the distal end of the stent 30. This extension has a generally helical orientation

As shown in Figures 6 A, 6B and 6C when the stent 30 is expanded radially and outwardly from axis 45, the expansion cells 66 of each ring 60 expand and increase along the

"circumferential" extent "C" of the stent 30. Simultaneously, the cells 66 generally decrease

somewhat in their longitudinal extent "L" and the proximal and distal ends 61 and 64 of each cell move longitudinally toward each other and the indirect segment 80a of the upper half 67a moves

radially further away from the indirect segment 80d of the lower half 67b.

h the embodiment shown in Figures 1-4, the expansion cells 66 can expand as much as

about 2 times of its original unexpanded radial length as shown in Figure 6 A, preferably as much

as about 2.5 times as much as its original unexpanded radial length as shown in Figure 6B, and

more preferably as much as about 3 times as much as its original radial length as shown in Figure 6C. In this regard, radial length is the radial distance along the circumference of the stent 30 between the centers 63 of the respective cell interconnection bridges 62 on either side of an

expansion cells 66. As cells 66 expanded due to the radial force of an expanding balloon 44, the

cells expand along the circumference, increasing this radial length. As the radial length

increases, the circumference of the ring increases, h preferred stents, such as those shown the

drawings, the radial length can preferably increase from Rj to R₂ as it does when it increases

about 2 fold from Figures 5 to Figure 6A, or more preferably about 2.5 fold as it does when it increases from R_j to R₃ as shown by comparison between Figures 5 and 6B, or more preferably

about 3 fold as it does when it increases from R_j to B^ as shown by comparison between Figures 5 and 6C. While the increase in radial length is usually 3 fold, by increasing the axial length of

each expansion cell and the depth of the loops of the curvilinear arcs in the indirect segments 80a and 80d, greater increases in radial length are possible with balloon expansion. The curvilinear arcs open up or are straightened with greater degrees of expansion. hi other alternative embodiments (not shown), it should be appreciated that stents of the present invention may include as few as one module or ring and as many as 2, 3, 4, 5, 6, 7, 8, 9,

10 or even more rings if practical to provide greater length to the stent. Furthermore, each ring

or module may include any practical number of cells, preferably from 2 to 10, more preferably

from 3 to 8, and more preferably from 4 to 6.

In alternate embodiments, the present invention includes a method of making a stent. The

preferred method includes providing a segment of cylindral walled material from which the stent

will be made. Depending upon the type of stent to be made, any of the materials herein discussed

or other well known materials may be used depending upon the particular characteristics desired

in the stent to be made. The stent is prepared by removal of material from the cylindrical wall

which will not be part of the stent to be formed. This may occur by mechanically cutting away material. Preferably, however, the cutting or material removal is more automated. A computer aided laser cutting device is one option. A computer aided water-jet cutting device is another

option, h each case, software which guides the cutting tool will assure that only the material

which is intended to be removed, will be removed. A removal technique is chemical etching of

the cylinder wall. The portion of the cylinder to be retained as a part of the stent is protected

from exposure to the chemical etching process. For example, in the case of a metallic stent, an etching agent might be one of a number of acids which are well known in the art. A chemically

protective agent, for example, a hydrophobic coating, such as a wax, may be applied over the

entire exterior surface of the cylinder. Next the protective coating is removed mechanically

using a computer aided water jet cutting device, or the like, where etching is desired. If greater surface thickness is desired, wider areas need to be protected, if thinner, then narrower areas are protected. Alternatively, other means of selectively applying protective coatings, for example photographically based methods, which are well known in the etching arts, may be used. Finally, the partially protected cylinder is immersed in an acid bath. Etching occurs throughout the interior cylinder surface but only at selected portions of the exterior. When the etching has

proceeded to the extent that the etching from exterior and interior have fully removed appropriate portions of the cylinder, the piece is removed from the acid. Next, the protective coating is

removed. If the coating is wax, the wax may be removed by heating or by a wax solvent which does not further affect the metal. Chemical etching is a suitable production method for low

volume production. Higher volume production is thought to be more suitably achieved through

the use of computer aided laser etching. The availability of using wider or narrower surface

thickness, as well as different tubing wall thickness is considered an important means of

obtaining stiffness or easier deformability in the desired devices of the present invention.

Generally, thin wall tubing is believed to be preferable, but not absolutely required. A preferred material from which expandable stents of this invention may be prepared is, without limit, stainless steel, particularly type 316 stainless steel, more preferably type 316 L or

316 Lvm stainless steel but gold, platinum, tantalum, silver and the like are also believed to be

suitable. Desirable features of the material selected are deformability and the ability to hold the

shape once deformed. It is also desirable that the stent 30 be made from radiopaque materials.

Stents made of stainless steel which have a thickness of 0.0005 inch are generally radiopaque,

however, stents having lesser thicknesses, such as stents made specifically for use in coronary arteries which often requires thicknesses less than 0.0005 inch (often for example about 0.003

inch) need to be coated with a radiopaque material such as 24 carat gold to a thickness of about 0.0002 inch. In addition, other coatings including specific functional agents may also be

employed to address issues such as blood clotting (e.g. Heparin and the like) or reduction in the amount of intimal hyperplasia and resulting restenosis (e.g. cytotoxic drugs, gene therapy agents and the like). Methods to coat metal prostheses to make them radiopaque or to minimize the risks due to blood clotting are well known in the art and any of these methods and the devices resulting from the use of these methods are all envisioned within he scope of the present invention.

It is understood that even though numerous characteristics and advantages of various

embodiments of the present invention have been set forth in the foregoing description, together

with details of the structure and function of various embodiments of the invention, this disclosure

is illustrative only and changes may be made in detail, especially in matters of shape, size and

arrangement of parts, within the principles of the present invention, to the full extent indicated

by the broad general meaning of the terms in which the appended claims are expressed.

Claims

WHAT IS CLAIMED IS:

1. An expandable stent, the stent being expandable by enlarging an expandable balloon

positioned within the stent, the expandable stent comprising:

a plurality of modules, each of the modules having a plurality of individual expansion

cells radially interconnected to form a ring of individual expansion cells interconnected to each

other in series by one of a plurality of cell interconnection bridges; each of the individual

expansion cells including a continuous strand of a material, the continuous strand of material in each cell being interconnected with itself so as to generally encompass a radially space within

the respective cell; each expansion cell having an upper half and a lower half, the upper and lower halves of each of the respective expansion cells being joined together and the lower half of each of the respective expansion cells being interconnected to the upper half of an adj acent expansion cell within that respective ring of expansion cells by one of the plurality of cell interconnection bridges; each cell interconnection bridge having a center; each expansion cell

having a radial length which is a radial distance consistent with an existing circumference of the respective ring as measured from the center of the cell interconnection bridge interconnected with

the upper half of that expansion cell to the center of the cell interconnection bridge interconnected with the lower half of that expansion cell; the material being deformable such that

the ring can be defoπned from a first configuration wherein each ring has a first circumference

and each expansion cell has a first radial length, to a second configuration wherein each ring has

a second circumference greater than the first circumference and each expansion cell has a second

radial length greater than the first radial length; each expansion cell having a pair of sides which

are mirror images of one another, each side being expandable when the ring of which the cell is

a part is in the first configuration such that the second radial length can be about twice as great as the first radial length.

2. The expandable stent of claim 1 , each side having an accordion shape which is radially

expandable.

3. The expandable stent of claim 1 , the stent having a plurality of intermodular connecting

bridges; each intermodular connecting bridge interconnecting a cell interconnection bridge connecting expansion cells of one module with a cell interconnection bridge

connecting expansion cells of an adjacent module.

4. The expandable stent of claim 3, each pair of adjacent modules being interconnected with one another by at least two intermodular connecting bridges.

5. An expandable stent, the stent being expandable by enlarging an expandable balloon positioned within the stent, the expandable stent comprising:

a plurality of modules, each of the modules having a plurality of individual expansion cells radially interconnected to form a ring of individual expansion cells interconnected to each

expansion cells including a continuous strand of a material, the continuous strand of material in

each cell being interconnected with itself so as to generally encompass a radially space within

the respective cell; each expansion cell having an upper half and a lower half, the upper and

lower halves of each of the respective expansion cells being joined together and the lower half of each of the respective expansion cells being interconnected to the upper half of an adj acent expansion cell within that respective ring of expansion cells by one of the plurality of cell interconnection bridges; each cell interconnection bridge having a center; each expansion cell

having a radial length which is a radial distance consistent with an existing circumference of the

respective ring as measured from the center of the cell interconnection bridge interconnected with

the upper half of that expansion cell to the center of the cell interconnection bridge

interconnected with the lower half of that expansion cell; the material being deformable such that

the ring can be deformed from a first configuration wherein each ring has a first circumference

and each expansion cell has a first radial length, to a second configuration wherein each ring has a second circumference greater than the first circumference and each expansion cell has a second

radial length greater than the first radial length; each expansion cell having a pair of sides which are mirror images of one another, each side being expandable when the ring of which the cell is a part is in the first configuration such that the second radial length can be at least twice as great as the first radial length; the stent having a plurality of intermodular connecting bridges; each intermodular connecting bridge interconnecting a cell interconnection bridge connecting expansion cells of one module with a cell interconnection bridge connecting expansion cells of

an adjacent module.

6. The expandable stent of claim 5, each pair of adjacent modules being interconnected with

one another by at least two intermodular connecting bridges.

7. The expandable stent of claim 6, the stent having at least four modules, each module

being interconnected with each adjacent module by at least two intermodular connecting bridges.

8. The expandable stent of claim 5, each expansion cell having a pair of sides which are mirror images of one another, each side having an accordion shape which is radially

expandable when the ring of which the cell is a part is in the first configuration such that

the second radial length can be about twice as great as the first radial length.

9. An expandable stent, the stent being expandable by enlarging an expandable balloon

positioned within the stent, the expandable stent comprising:

a plurality of modules, each of the modules having a plurality of individual expansion cells radially interconnected to fonn a ring of individual expansion cells interconnected to each

other in series by one of a plurality of cell interconnection bridges; each of the individual expansion cells including a continuous strand of a material, the continuous strand of material in each cell being interconnected with itself so as to generally encompass a radially space within the respective cell; each expansion cell having an upper half and a lower half, the upper and lower halves of each of the respective expansion cells being joined together and the lower half of each of the respective expansion cells being interconnected to the upper half of an adjacent

expansion cell within that respective ring of expansion cells by one of the plurality of cell interconnection bridges; each cell interconnection bridge having a center; each expansion cell

a second circumference greater than the first circumference and each expansion cell has a second radial length greater than the first radial length; each expansion cell having a pair of sides which are mirror images of one another, each side having an accordion shape which is radially

expandable when the ring of which the cell is a part is in the first configuration such that the

second radial length can be about twice as great as the first radial length.

10. The expandable stent of claim 9, the stent having a plurality of intermodular connecting

connecting expansion cells of an adjacent module.

11. The expandable stent of claim 10, each pair of adj acent modules being interconnected with one another by at least two intermodular connecting bridges.

12. The expandable stent of claim 11, the stent having at least four modules, each module being interconnected with each adjacent module by at least two intermodular connecting

bridges.