Note: Descriptions are shown in the official language in which they were submitted.
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1
NON-FORESHORTENING INTRALUMINAL PROSTHESIS
BACKGROUND OF THE INVENTION
1. Field of the Invention
5 The present invention relates to an intraluminal
prosthesis~for implantation into a mammalian vessel,
and in particular, to an intraluminal stent that is
delivered in a compressed state to a specific locat~oT,
inside the lumen of a mammalian vessel and then
to deployed to a.n expanded state to support the vesse:L.
The intraluminal stent is provided with a structural
configuration that maintains the prosthesis at
substantially the same length in both the compres~;e~3
and expanded~states. The intraluminal stmt may a7~:,
15 be provided with varying rigidity or flexibility a.l~oc,
its length.
2. Description of the Prior Art
Intraluminal prosthesis, such as stents, are
commonly used in the repair of aneurysms, as liners
20 for vessels, or to provide mechanical support to
prevent the co7_lapse of stenosed or occluded vessels.
These stems are typically delivered in a compressed
state to a specific location inside the lumen of a
vessel or other tubular structures, and then deployeB
25 at that location of the lumen to an expanded state.
The stmt has a diameter in its expanded state which
is several times larger than the diameter of the st=ent
in its compressed state. These stents are also
frequently deployed in the treatment of
30 atherosclerotie stenosis in blood vessels, especial_1~~
after percutaneous transluminal coronary angioplasty
(PTCA) procedures, to improve the results of the
procedure and to reduce the likelihood of restenosi.s.
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2
The positioning of a scent at the desired locati«o
in the lumen of a body vessel is a critical facto
that affects the performance of the stmt and the
success of the medical procedure. Since the regiem it
5 a lumen at which the stent is to be deployed is
usually very difficult for a physician to access, it
is essential that the scent's deployed diameter anB
length be known before the physician can accuratel~-
position a~stent with the correct size at the preci~;e
10 location. Fo:r example, since the diameter and the
length of the diseased or damaged segment or region ~~f
the body vessel can vary for different body vessels,
disease states, and deployment purposes, it is
important that. a scent having the precise diameter pmt
15 length be delivered to this region for deployment.
careful sizing of this region of the lumen of the
body vessel may pose a difficult challenge for many
physicians who know the exact dimensions of the boc~~
vessel at this region, but are not certain about the
20 stem 's deployed diameter and length. This is due t~
a foreshortening effect which is experienced by many
stem s when they are expanded from their compressed
state to their expanded state.
This foreshortening effect is illustrated in FIGS.
25 !A, 1B, 2A and 2B, which illustrate portions 20 of
stmt having a mesh-like pattern made up of V-shapew
struts or legs 22 and 24 connected at their apices ?F~.
Two pairs of these V-shaped struts 22, 24 are
illustrated in this portion 20 of the stem . Each c~f
30 these struts 22 and 24 has a length h. FIG. 1B
illustrates the portion 20 of the stent in a fu115~
compressed state, in which the length h has a
longitudinal or horizontal component 12 (see FIG. 4P!,
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and FIG. 1A illustrates the same portion 20 of the
stem in a fully expanded state, in which the lengrl h
has a longitudinal or horizontal component 11 (see
FIG. 2A). As illustrated by the imaginary lines :2
5 and 30 in FIGS. 1A and 1B, and in FIGS. 2A and 2F3, 1~
is shorter than 12 because the angle which the str-or-
22 assumes with respect to the horizontal axis is
greater when in the expanded state, so the length of
the expanded portion 20 is shorter than the lengtW~f
10 the compressed portion 20 by a length of 2d. This
foreshortening is caused by the shortening of the
longitudinal component 1 of the struts 22 and 24 as
the stmt is expanded from the compressed state to t-.im~
expanded state,
15 This foreshortening effect is troublesome because i.t
is not easy to determine the exact dimension of this:
foreshortened length 2d. The physician must make this-
calculation based on the material of the stmt, the
body vessel being treated, and the expected diameter
20 of the stem when properly deployed in the lumen o.f
the body vessel. For example, the foreshortened
length 2d will vary when the same stem is deployed it,
vessels having different diameters at the region of.
deployment.
25 In addition, there are certain body vessels that.
experience a change in vessel lumen diameter, anatomy
or disease state along their lengths. Stents to be
deployed at such vessels will need to be capable of
addressing or adapting to these changes.
30 An example of-. such a body vessel are the carotid
arteries. Blaad is delivered from the heart to the
head via the common carotid arteries. These arteries
are approximately e-~10 mm in lumen diameter as they
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4
make their way along the neck up to a position j~.~ar
below and behind the ear. At this point, the corrnnnra
carotid artery branches into a 6-8 mm lumen diameter
internal carotid artery, which feeds blood to the
5 brain, and a 6-8 mm lumen diameter external carotid
artery, which supplies blood to the face and scalp.
Atherosclerotic lesions of the carotid artery tend t~->
occur around this bifurcation of the common caroti_cj
artery into the Internal and external carotid
l0 arteries, so stems often need to be deployed at t.hi.~
bifurcation.
Another example are the iliac arteries, which hat..w -r
lumen diameter of about 8-10 mm at the common iliac
artery but which decrease to a lumen diameter of at~~m,r
15 6-7 mm at the external iliac artery. The common ili~~v
arteries experience more localized stenosis or
occlusive lesion which are quite often calcific and
usually require a shorter stent with greater radial
strength or rigidity. More diffused atheroscleroti~_~
20 disease of the iliac system will commonly involve h~th
the common.and external iliac arteries, and
necessitate a longer stent having increased
flexibility that is suitable for deployment in the
tortuous angulation experienced b~~ the iliac system.
25 The femoropopliteal system similarly experiences
localized and diffused stenotic lesions. In addit'tocr,
the flexibility of a stent is important where deplc~yeci
at locations of vessels that are affected by movements
of joints, such as the hip joint or the knee joint.
30 The renal arteries provide yet another useful
example. The initial 1 cm or so at the orifice of a
renal artery is often quite firmly narrowed due to
atheroma and calcification, and is relatively
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straight, while the remainder of the length of the
renal artery is relatively curved. As a result, a
stent intended for implantation at the renal arteries
should be relatively rigid for its first 1.5 cm or s~~,
5 and then become more flexible and compliant.
Thus, there remains a need for an intraluminal
prosthesis that maintains a consistent length in hc~rl~
its fully compressed and fully expanded states, and iu
all states between its folly compressed and fully
10 expanded states. There also remains a need for a
stent which c:an accomodate body vessels having vary l i,q
lumen diameters, different anatomies, and differecut
disease states.
15 SUMMARY OF THE DISCLOSDR~
In order to accomplish the objects bf-the pts~ent
invention, there is provided a stem having a
plurality of annular elements. Each annular ~lemPnt
has a compressed state and an expanded state, and has
20 a longitudinal dimension which is smaller in the
expanded state than in the compressed state. A
pluralit~,~ of connecting members connects adjacent
annular elements, with the connectinc inlembers
operating to compensate for the smaller longitudinal
25 dimension of each annular element xn fhe expanded
state.
In one ecnbodiment of the present invention, each
annular element includes a plurality of struts and
apices connected to form an annular configuration.
30 The connecting members are conn~=~cter to the apices ef
the adjacent annular elements '1'!ue plurality of
struts of the annular elemer's include left and right
struts, with each pair of left and right Struts
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connected to each other at an apex. Each strut 1»s <~
longitudinal. dimension which is smaller when the
annular element is in the expanded state than in the
compressed state .
5 In one embodiment of the present invention, at le~a~t-
one of the annular elements may have a closed
configuration such that the plurality of alternate y
struts aird apices are connected to each other to firm
a closed annular element. In addition, it is also
l0 possible for at least one of the annular elements t-~~
assume an open configuration such that the plurality
of alternating struts and apices are not connected an
at least one location.
In a preferred. embodiment of the present inventic~n,
15 the connecting members have a plurality of alternatiy~
segments.
In one embodiment, the connecting members have a
plurality of alternating curved segments defining
alternating top and bottom curved apices. In anotl~.°t
20 embodiment, the connecting members have a pluralir~~c-f
alternating curved and straight segments. In a
further embodiment, the connecting members have a
plurality of alternating and angled straight segmec~t_~.
The connecting members have a larger longitudinal.
25 dimension when each annular element is in the exf~auda-1
state than in the compressed state to compensate f-c~r-
the smaller longitudinal dimension of the annular
element in the expanded state.
The stmt according to the present invention furt.ln>l.
30 includes a plurality of apertures defined by adjacent
annular elements and connecting members. In one
embodiment, i.t is possible for the apertures of
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7
different segments of the stent to have different
sizes.
The scent according to the present invention furthex
provides a plurality of segments, at least two of
which have a different degree of flexibility. In c~r~A
embodiment, the varying flexibility is accomplishec3t~y
forming a plurality of gaps. These gaps may be fcarme~~
by omitting one or more of the connecting members,
portions of connecting members, between adjacent
annular elements, or by omitting one or more of the
struts, or by omitting connecting members and strut.
Ln another embodiment; the varying flexibility is
accomplished by providing the apertures of different-
stent segments with. different sizes.
The stmt according to the present invention may
further provide segments that assume different
diameters when the stent is in its expanded state.
The differing diameters may be accomplished by
providing the stent in a tapered or a stepped-
configuration.
In a preferred enW odiment according to the present
invention, .the scent is made from a shape memory
alloy, such as Nitinol, although other materials sucU
as stainless steel, tantalum, titanium, elgiloy, go:lc~,
platinum, or any other metal or alloy, or polymers c~T
composites, having sufficient biocompatibility,
rigidity, flexibility, radial strength, radiopacity
and antithrombogenicity can be used for the stent
material.
Thus, the st mt according to the present invention
maintains a consistent length in both its fully
compressed and fully expanded states, and in all
states between its fully compressed and fully expande-?
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states. As a result, thre stmt accoi:dit~g to the p>:esent
i.aventiotl faci.Litates accurate sizing and deployment,
thereby simplifying, and possibly reducing the tune mee<:1 1
for, the rnedical procectune. In addition, tine stern.
according to the present invention provides varyirng
flexibility arnl rigidit~r along its length and/or
e-i. r: cumf_erence, as well as varying di.ametervs along
different segnr=nts c>f the stmt, thereby facilitat=ing tlm
treatment of b~~dy vessels having varying l_urnen diameter ~-,
1_i) different anat~~tnies art.d different disease states.
In a broad aspect, t=hen, the present im:~entior~
re7.ates to a stmt comprising: a plurality of annular
elements, each annular element hawing a compressed start
at»1 an expanded state, wherein each annular element has ,
1'.:~ 1ongituc~linal d:i_mensions snltich is smaller in tine radial 1.~,
expanded state than in the compressed state; and
connecting members connecting adjacent annular e:lemeuts;
mllerein the annual elements and conruecting members are
blade Of L~li.tirrol, with each connectirug member preset whit
?O an elasticity which causes the contlecting member to
elongate longitudinally when the annular elements are in
t heir expanded state to compensate for tale smaller
longitudinal dimension of the annular elements i_n the
expanded state.
In another: broad aspect, then, the present t n~lent_ t ~-~r~
relates to a stmt having a first segment and a second
segment, faith each segment having a diameter auc~l
comprising: a plurality of annular elements, each amnula~
element having a compressed state and an expanded statf~;
3(1 at least one connecting member connecting adjacent anm.tlm
elements; a plurality of apertures defined by adjacent
annular elements and connecting mem~~ers, each aperture
having a size at~d a geometric conf.igurati.on; svit.li tile
t i_1_st_ aad second segments ha~rin~~ su)estanti.a7_12~ tire sa~u4~
r~:, ~l i_am~tez t n tine ce~rnt~ressed state; and v,l-rerw in the
CA 02537990 1998-02-04
8a
apertures of the first and second segments hare diffei:,eW
sizes but substantially the same geometric configi~rati.«o
when the first and second segments are in tte expanded
state.
Ir2 yet another broad aspec:.t, then, the present
irrvent.ion rel_at:es tc a st.ent having a plurality of
segments and comprising: a plurality o.f annular elemeut~~,
each annular e7_ement having a compressed stat=a arid an
expanded state; a plurality of connecting members
COI~neCtlng ad~aC2Ilt annular elements; and a plurality c~f
gaps formed by omitting at least one of tire connecting
members between adjacent annular elements so as to prov_i ~i«
two of the pluralit=~~ of segments of the stmt with
rti fferent degrees of f_le~:ibility.
1S In a furttrer broad aspect, then, the present
°in~~enti.on relates i~c_~ a stmt having a plurality of
segments and comprising: a plurality- of annular elemenl_~,
each annular element having a compressed state and an
expanded state; a plurality of connecting rnembers
'() connecting adjacent annular elements; and wherein each
annular element comprises a plurality of alternating
struts and api<~es connected to each other to form a
s~~bstantially annu.la.r configuration, arid vaherein the
correcting members are connected to the ap.i.ces of l:he
"_~ adjacent. annular elements; and wherein a plurality of c~t
are formed by omitting at. least one of the struts so as
provide tcao of the plurality of segments of the steut wi i f,
different degrees of flexibility.
In a still further broad aspect, then, the present
3!) inverution relates tc> a st=ent comprising: a p.lurali.ty
annular elements, each annular element havTiug a compress « l
state and an expanded state, and each annular elerneot
ioclucji.ng a p.lurali.t.y of alternating struts and apices
~.-~noe~t-e~ to each ~:,t.her to form a s,rf~st,:ant~ ally aonn Lat
~-~rrfi~amratimo; and at least one ~~onnPctina member
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8b
c.vonrrected adjacent annular element; e~tliereitl at least ~~m
of the anrmlar elements is closed such that the p ll.ara.l. i i ,
of alternating st.r~_~ts and apices are connected to each
other to form a closed annular element, and whe.re~.~~ at.
least one of the annular elements are- open such that 1_Im~
plurality of a.lterruating struts and apices are not
c,onnectec~ at at least oae location.
BRIEF DESCRIPTION OF THE DRAWINGS
L() FIG. 1A is a side elevational viec~~ of a portion of !
prior art scent in its e~;panded state;
FIG. 1B is a side el.evational vie« of the porn o0
fIG. 1A in its com~~ressed state;
F'IG. 2A illustrates the longitudinal component o.f ~a
1 ':~ strut o.f the st=mt of F'IC~S . 1A and 1B when the st ent is i n
it:s e~pandecl state;
fIG. 2B illustrates the lonqiti_idina_l. cornpooemt of o
strut of the scent of FIGS. 1A and LB when the stmt i.s ~ n
ices compressed state;
~i1 FIG. 3 is a perspective view c>f a st:eut accordi-ng
the present inventicn;
FIG. 4A is a side el.evational vieca of a portion ~t
the stmt of FI:G. 3 in it.s expanded state;
FIG. 9B is .a side elevational ~~iew of the portion ~n
?'~ F'LG. 9A in its compressed state;
FIG. 5A illustrates the longitudinal. component. of a
si=rut and its connecting mernber of t-he stel~t of FIGS. 9~
and 4B when the stem is in its expanded state;
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9
FIG. 5B illustrates the longitudinal component of w
strut and its connecting member of the stmt of FT'S
41 and 4B when the stent is in its compressed sta g;
FIG. 6A is a side elevational view of the stmt ~.f
5 FIG. 3 in its expanded state;
FIG. 6B is a side elevational view of the stmt ~F
FIG. 6A in its compressed state;
FIGS. 7 arid 8 illustrate alternative embodiment: <:~f
the connecting member according to the present
10 invention;
FIG. 9 is a side elevational view of a portion of
the stmt of FIG. 3 illustrating a modification
thereto;
FIG. 10 is a side elevatiorial view of a portion of
15 the stent of FIG. :3 illustrating another modificatinm
thereto; and
FIGS. 11A-17_C il:Lustrate modifications to the stmt
of FIG. 3.
20 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMEPffS
The following detailed description is of the best
presently contemplated modes of carrying out the
invention. This description is not to be taken in a
limiting sense, but is made merely for the purpose c~f
25 illustrating general principles of embodiments of the
invention. The scope of the invention is best defirrA~~
by the appended claims.
The intraluminal prosthesis according to the present.
invention is a stmt, although the principles of the
30 present invention are also applicable to other
prosthesis such as liners and filters. The stem is
delivered to a desired location in the lumen of a b~c~y
vessel in a compressed state, and is then deplo}~ed 1~~-
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10
expanding it to its expanded state. The stmt
maintains substantially the same length in both it-.~
fully compressed and fully expanded states, and i_n ale
states between these two states. The stent may bn
5 provided with varying flexibility or rigidity along
different segments thereof to allow the stent to bP.
deployed in body vessels having different anatomies
and different disease states. The stent may also 1,
provided in a configuration in which the same stem_
10 has varying diameters along different portions of tlm
stent to facilitate implantation in body vessels that
have varying diameters.
The stent according to the present invention can t,~~
a self-ea:panding stmt, or a stmt that is radially
15 expandable by inflating a balloon or expanded by am
expansion member, or a stent that is expanded by the
use of radio frequency which provides heat to cause
the stent to change its size. The stmt may also t~
coated with coverings of PTFE, dacron, or other
20 biocompatible materials to form a combined stmt-ar~fr
prosthesis. The vessels in which the stent of the
present invention can be deployed include but are m~r
limited to natural body vessels such as ducts,
arteries, trachea, veins, ureters and the esophagu,~
25 and artificial vessels such as grafts.
1. A Preferred Embodiment
A stent 4o a<~cording to the present invention is
illustrated in FIGS. 3-6 in its expanded state.
Referring to F:CG. 3, the stmt 90 has a tubular
30 configuration and is made up of a plurality of pairs
of substantially V-shaped struts connected at their-
apices, and by connecting a plurality of connecting
members to the apices of each pair of V-shaped stru t .
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FIGS . 4A and 4B illustrate a portion of the stmt ~~o
in greater derail. The stent 40 has a plurality of
pairs of alternating left struts 42 and right struts
44. Each pair of :left and right struts 42, 44 is
5 connected at an apex 46 to form a substantially V-
shape for the pair. The left strut 42 is defined as
being to the left of each apex 46, and the right strut
44 is defined as being to the right Of each apex 4E.
The left struts 42 and right struts 44 are alternar.iy
to since the left strut 42 of one pair of V-shaped strut
is also the left strut of the adjacent pair of V-
shaped struts, and the right strut 44 of one pair ~f
V-shaped struts is also the right strut of the
adj scent pair of V-shaped struts . In this manner, ttn~
15 alternating left and right struts 42 and 44 extend ~n
an annular manner around the tubular stent 4o to form
an annular element. Each apex 46 is connected to
another apex 46 by a connecting member 48. Therefoz~,
the stent 40 resembles a tubular lattice formed by
20 pairs of V-shaped struts 42, 44 connected to
themselves and having their apices 46 connected by the
connecting members 4.8. As shown in FIG. 3, both er~d~
of the stent 40 are defined by a plurality of
alternating.left and right struts 42, 44, with the
25 extremity of.both ends defined by the apices 46 of
these alternating left and right struts 42., 44.
The connecting members 48 have a configuration that
includes a plurality or pattern of alternating
segments. A non-limiting first preferred embodiment
30 of the connecting member 48 is illustrated in FIGS. ~h
and 4B. Each connecting member 48 extends
longitudinally along a longitudinal extension 52 from
an apex 46, then slopes upwardly along a curved
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segment 54 to a top curved apex 56, at whlCh poi.re: nl~«
connecting member 48 slopes downwardly along a ri~tv«ci
segment 58 to a bottom curved apex 60 . The corm«ct- i r~c~
member 48 then slopes upwardly along a curved sec~mpot-
5 62 to another top curved apex 64. From the top ca~r;w~-1
apex 64, the connecting member 48 slopes downwardl~~
along a curved segment 66 to a longitudinal extensi~~T,
68 of the opposing apex 46. Thus, the connecting
member 4e has a plurality of alternating curved
10 segments that are defined by the alternating top aW
bottom apices 56, 60 and 64.
The connecting members 48 are provided to perform
two functions. First, the connecting members 48
connect pairs of apices 46. Second, the connecting
15 members 48 function to compensate for the
foreshortening experienced by the longitudinal
component of each strut 42 and 44, thereby maintaiW m,n
the scent 40 at substantially the same length at all
times. This is accomplished by providing the
20 connecting mentber 48 with a natural bias and a spriry~-
nature, which together with its alternating segments,
combine to shorten i_ts length when compressed. Wtzea
allowed to expand, the connecting member 48 is biase~3
to return to its natural or original position, which
25 lengthens the connecting member 48 to compensate fol
the foreshortening experienced by the longitudinal
component of each strut 42 and 44.
This effect is illustrated in FIGS. 4A, 4B, 5A an:~
5B. When the scent 40 is in its compressed state, tl~~
30 connecting member 48 has a length of L2, which is le~~
than the length L1 when the connecting member 48 is in
its expanded state. When the connecting member 48 i.
in the compressed state, its alternating curves haven
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13
higher amplitude and a smaller wavelength than when it
is in the expanded state (compare FIGS. 4A arid 4B?.
Thus, the difference between L2 and L1 compensate: f<,,-
the difference between 11 and 12 of the struts 42, 4-~
5 at both ends of the connecting member 48. The lines
70 and 72 in FIGS. 4A and 4H also show that the
relevant. portion of the stent 40 does not experience
any foreshoztening, and the lines 74 and 76 in Fzcs.
6A and 6B show that the entire stent 40 maintains a
10 consistent length through all its states.
Although the connecting members 48 have been
described in ~':IGS. 4A, 4B, 5A and 5B as assuming a
particular configuration, it will be appreciated b~i°
those skilled in t=he art that the connecting membeo~
15 48 can assume other configurations without departing
from the spirit and scope of the present invention.
For example, the connecting members 48 can be prowi.~~:~
in any curved, partially curved, or other
configuration as long as they function to compensate
20 for the foreshortening experienced by the longitudi.~~al
component of each strut 42 and 44.
FIG. 7 illustrates a non-limiting second preferred
embodiment of the connecting member, in which the
connecting member 48a has alternating curved segment
25 80 and straight segments 82. When the connecting
member 48a is compressed, its curved segments 80 also
have a higher amplitude and a smaller wavelength than
when it is in it:s expanded state. FIG. a illustrate
a non-limiting second preferred embodiment, in which
30 the connecting member 48b has alternating straight
segments 84 and 86 that are angled with respect to
each other.
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When Che scent 40 is in its fully expanded sta g, it-
preferably has an outer diameter that is slightly
larger than the inner diameter of the region of the
body vessel at which it is to be deployed. This
5 allows the scent 40 to be securely anchored at the
desired location and prevents the scent 40 from
migrating away from the deployed location.
The scent 40 can be provided with varying
flexibility or rigidity at different portions or
10 segments along its length to facilitate deployment-_ iu
body vessels that require such varying flexibility ~n
rigidity. The varying flexibility or rigidity cac~l~u
accomplished by omitting connecting members 48 an~~
struts 42, 44, or. by not connecting one or more st~nt:~~
15 32, 44 and/or connecting members 48, thereby creat.i.n:o
"gaps" at one or more locations along the stmt 40.
These locations c:an be anywhere along the length
and/or the circumference of the stent 40. In
addition, varying degrees of flexibility in the st:~tm.
20 40 can be accomplished by varying the patterns of
these gaps. A non-limiting example would be to
provide a substantially spiral pattern of omitted
struts 42, 44 and/or connecting members 48, such a~
illustrated in FIG. 9. The omitted struts 42, 44 an<j
25 connecting members 48 are illustrated in FIG. 9 in
phantom (i'.e., the dotted lines) by the numerals 47
(for the struts 42, 44) and 49 (for the connecting
members). Far example, the omitted struts 47 assume= -a
relatively spiral pattern along the length of the
30 stent 40 from the top left corner of FIG. 9 to the
bottom right corner of FIG. 9, and can extend aroumi
the circumference of the stent 40. Similarly, the
omitted connACting members 49 assume a relatively
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15
spiral pattern along the length of the stent 40 from
the bottom left corner of FIG. 9 to the top right
corner of FIG. 9, and can extend around the
circumference of the scent 40.
5 Other non-limiting alternatives include providing
such gaps 49 at one or both ends of the stem 40 rmly,
or at a central portion of the stmt 40. Further
limiting alternatives would be to increase the numt~e~
of these gaps 4?, 49 from one or both ends of the
l0 stent 40 towards the center of the stent 40, or to
increase the number of these gaps 47, 49 from the
center of the stent 40 towards one or both ends of t:h~~
stmt 40. It is also possible to omit only a porti~~u
of certain connecting members 48 and not the entirA
15 ones of these connecting members 48. A portion of ttiF~
stmt 40 having a larger number of gaps 47, 49 would
have greater f_:Lexibility or reduced rigidity.
As a result of the omitted struts 47, it is possib~P
that some of t_he annular elements that are made up ~f
20 the alternating struts 42, 44 may be closed or
constitute completely connected annular elements,
while some of these annular elements will be open
annular elements.
The varying flexibility or rigidity can also be
25 accomplished by providing a structural configurati.ec~
where the size of the open areas or apertures 78 (fog-
example, see F7:GS. 4A and 10) defined between the
struts 42, 44 and the connecting members 48 is vari_ec~
at different portions or segments of the stent 40,
30 along the length and/or circumference of the stem 40_
In a non-limiting embodiment, all the apertures 78 ~n
one segment of the scent 40 have substantially the
same first. size, and all the apertures 78 in anothe,
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segment of the stent 40 have substantially the sarnp
second size, t:he first and second sizes being
different. Additional segments, each having apert.u~-P~:
78 with substantially the same size as the other
5 apertures 78 in that segment but having a different
size as the apertures 78 in other segments, can alq:~
be provided.
Varying the size of apertures 78 can be accomplisOe-j
by varying the lengths of the struts 42, 44 and the
10 connecting members 48. For example, a smaller
aperture 78 can be provided by shortening the lengths
of the struts 42, 44 and the connecting members 48
that define tree particular open area 78. Portions cwf
the stmt 40- with smaller apertures 78 are more rigid
15 and less flexible than portions of the stmt 40 wilt,
larger apertures '78. This allows the stent 40 to bA
deployed in body vessels that require a stent to be
more rigid at one end, and to be increasingly f le:{it~ 1 <v
from the rigid end. Examples of such body vessels
20 include the renal and iliac arteries discussed abovA.
Varying the sizes of the apertures 78 also serves
other important purposes. For example, providing
smaller apertures 78 at tree opposing ends of the stPnt
40 provides increased or closer coverage of the vessel
25 wall, thereby improving support of the diseased vessA~
wall and preventing fragments of the plaque from bei.r,cn
dislodged as embolic debris. The dislodgement of
debris can be dangerous in certain vessels, such as
the carotid~ar.teries, where dislodged debris can bP
30 carried to the brain, possibly resulting in a strol:~_
As another example, providing larger apertures 78 at.
central portions of the stent 40 provides wider open,
areas that may be important in preventing the
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obstruction of side branches of other body vessels.
These wider open areas also allow the passage of
guidewires, catheters, stents, grafts, and other
deployment devices through the body of the stmt 40
5 into these side branches.
The stent 40 can also be provided in a manner in
which it assumes a constant diameter in its compressed
state, but in which different portions of the stem: 4!?
can assume different diameters when in their fully
l0 expanded states. Providing an expandable stent 40
with the capability of assuming different diameters at-
different portions is important where the stmt 40
used in certain body vessels or branches of body
vessels where the lumen diameters may vary. Example
15 of such body vessels and branches include the carotid
and iliac arteries discussed above, and the esophagl~~_
The var~~ing stent diameter can be provided in a
number of ways. A first non-limiting alternative i~
to provide a gradually tapered configuration of tire
20 stmt 40a, as shown in FIG. 11A. A tapered
configuration :is best-suited for use in body vessels
which experience a gradual narrowing. A second non-
limiting alternative is to provide an abrupt
transition, such as a stepped configuration, betwee~~
25 two stem segments each having a relatively
consistent, but different, diameter. The step can bA
for a step-up 40c, as shown in FIG. 11C, or for a
step-down 40b, as shown in FIG. 11B. In addition, a
stent 40 can be provided with several changes in
30 diameter along its length to match specific anatomical
requirements.
The tapering or transitioning of the stmt
configuration can be accomplished by pre-shaping, ata:~
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can be enhanced by variations in fl) the thickness «f
the stent material, (2) the size of apertures 78, ~m~
(3) the gaps 47, 49.
In addition to the above, it will be appreciated by
those skilled in the art that varying flexibility arid
rigidity can also be accomplished by varying the width
or thickness of the stent material at certain
locations along the length andJor circumference of t_t~a
stent 40.
10 A number of materials can be used for both the stem-
40 and its struts 42, 44 and connecting members 48,
depending on :its method of deployment. If used as ~3
self-e:cpanding stent, the stent 40 (including its
struts 42, 44 and connecting members 48) is preferat~ly
15 made of a shape memory superelastic metal alloy such
as Nitinol,.which has the unusual property of
"mechanical" memory and trainability. This alloy ran
be formed into a first predetermined shape above a
transition temperature range. The alloy may be
20 plastically deformed into a second shape below the
transition temperature range, but the alloy will
completely recover to its original (first
predetermined) shape when raised back above the
transition temperature range. The Nitinol preferably
25 has a composition of about 50o nickel and about 500
titanium. The properties of shape memory alloys su~-h
as Nitinol and their use in stents have been well--
documented in the literature, and reference can be
made to the article by T.W. Duerig, A.R. Pelton anc9 i:~.
30 Stockel entitled "The Use of Superelasticity in
Medicine", a copy of which is attached hereto and
specifically incorporated into this specification by
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specific reference thereto as though fully set for_tl~
herein.
Alternatively, the stent 40 (including its struts
42, 44 and connecting members 48) can be made of
5 stainless steel, tantalum, titanium, elgiloy, golCl,
platinum, or any other metal or alloy, or polymers m.
composites, having sufficient biocompatibility,
rigidity, .flexibility, radial strength, radiopacit~~
and antithrombogenicity.
to Although the connecting members 48 have been
described abo~,re as having the same material as the
struts 42, 44, it is possible to provide the
connecting members 48 with a different material
without departing from the spirit and scope of the
15 present invention. Such a material should be springy
in nature and should allow the connecting members ~4~
to be compressed and expanded in the longitudinal
direction to compensate for the foreshortening
experienced by the struts 42 and 44. Non-limiting
20 examples of such materials can include any of the
materials described above for the stem 40.
2. Methods of Manufacture
The stmt 40 can he made from one of a number of
methods, depending on the material of the stmt 4o aczc~
25 the desired nature of deployment.
In a non-limiting first preferred method, the sten.r
40 is fabricated from a solid Nitinol tube with
dimensions that are identical to the stmt 40 when it
is in the fully compressed state. The pattern of tl~n
30 stent 40 (i.e., its struts 42, 44 and connecting
members 48~ is programmed into a computer-guided laser
cutter or lathe which cuts out the segments between
the struts 42, 44 and the connecting members 48 in a
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manner which closely controls the outside diameter: -ao
wall thickness of the stem 40.
After the cutting step, the stent 40 is
progressively expanded until it reaches its full}-
5 expanded state. The expansion can be performed by ~T~
internal expansion fixture, although other expans~.o~r
apparatus and methods can be used without departing
from the spirit and scope of the present invention.
The overall length of the stmt 40 must be
10 consistently tnaintained throughout the expansion ~f
the stmt 40 from its fully compressed to its full-
expanded stages.
Once the st_e~nt 40 has been expanded to its fully
expanded stage, it is heat-treated to "set" the sha~~~~
15 memory of the Nitinol material to the fully expanr~Pc~
dimensions. The stent 4U is then cleaned and ele<-rr-~
polished.
The next step is to compress the stent 40 again ir~r~,
a dimension which allows for delivery into a vessel,
20 either through percutaneous delivery or through
minimally invasive surgical procedures. Specifically,
the stent 40 must be compressed into a smaller stare
so that it can be delivered by a delivery device to
the desired lacation of the vessel. Any conventional
25' delivery device could be used, such as but not limpt~,t~
to a tube, catheter, or sheath_ This compression is
accomplished by cooling the stmt 40 to a low
temperature, for example, zero degrees Celcius, a.nc~
while maintaining this temperature, compressing the
30 stmt 40 to allow the scent 40 to be inserted inside
the delivery device. Once inserted inside the
delivery device, the stent 40 is held by the delivery
device in the compressed state at room temperatuz-F.
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In a non-limiting second preferred method, a
balloon-expandable stent 40 can be fabricated by
connecting a plurality of wires that have been bent <,t-
formed into the desired shapes-for the struts 42, ~~~t
5 and connecting members 48. The connection can be
accomplished by welding, tying, bonding, or any ot:he,
conventional method. Alternatively, wire electro-
discharge machining can be used. The wires are
capable of experiencing plastic deformation when t;he
10 stmt 40 is compressed, and when the stent 40 is
expanded. Upon plastic deformation of the stent ~yo t-c~
either the compressed or the expanded state, the steer
40 remains in this state until another force is
applied to plastically deform the stmt 40 again.
15 While certain methods of manufacture have been
described above, it will be appreciated by those
skilled in the art that other methods of manufactu~P
can be utilized without departing from the spirit ami
scope of the present invention.
20 3. Deployment Methods
The scent 40 can be deployed by a number of delivery
systems and delivery methods. These delivery systems
and methods will vary depending on whether the scent
40 is expanded by self-expansion, radial expansion
25 forces, or radio frequency.
While the description above refers to particular
embodiments of the present invention, it will be
understood that many modifications may be made witlic~n!
departing from the spirit thereof. The accompanyii~q
30 claims are intended to cover such modifications as
would fall within the true scope and spirit of the
present invention.
