U.S. patent application number 09/837353 was filed with the patent office on 2002-04-25 for single-piece endoprosthesis with high expansion ratios.
Invention is credited to Escano, Arnold M., Pollock, David T..
Application Number | 20020049490 09/837353 |
Document ID | / |
Family ID | 34915588 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020049490 |
Kind Code |
A1 |
Pollock, David T. ; et
al. |
April 25, 2002 |
Single-piece endoprosthesis with high expansion ratios
Abstract
A new endoluminal prosthesis provides for a compressible and
expansible single-piece thick walled cylindrical structure. The
cylindrical structure is comprised of curved elongated beams which
intermittently merge with adjacent curved elongated beams. Each
beam has a radial thickness greater than the circumferential width.
The configuration of the curved beams reduces stress concentrations
in the expanded and compressed condition of the prosthesis.
Features are provided for high expansion ratios allowing the
prosthesis to collapse into a very small diameter and expand into a
very large diameter.
Inventors: |
Pollock, David T.; (Redwood
City, CA) ; Escano, Arnold M.; (Santa Clara,
CA) |
Correspondence
Address: |
FULWIDER PATTON LEE & UTECHT, LLP
HOWARD HUGHES CENTER
6060 CENTER DRIVE
TENTH FLOOR
LOS ANGELES
CA
90045
US
|
Family ID: |
34915588 |
Appl. No.: |
09/837353 |
Filed: |
April 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09837353 |
Apr 17, 2001 |
|
|
|
09546966 |
Apr 11, 2000 |
|
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Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2002/075 20130101;
A61F 2002/91558 20130101; A61F 2/915 20130101; A61F 2002/91575
20130101; A61F 2002/91516 20130101; A61F 2002/91533 20130101; A61F
2230/0013 20130101; A61F 2/91 20130101; A61F 2002/91508 20130101;
A61F 2002/91541 20130101 |
Class at
Publication: |
623/1.15 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. A collapsible cylindrical endoprosthesis comprising: a plurality
of longitudinal members in a cylindrical arrangement, each having
at least one end; a plurality of circumferential members connecting
the ends of adjacent longitudinal members; and a plurality of
opposed contact surfaces on adjacent longitudinal members near the
circumferential members, with the opposed surfaces being oriented
relative to each other, wherein, as the endoprosthesis is
collapsed, the circumferential members bend until the opposed
contact surfaces come together and then continued deflection of the
longitudinal members produces stress at the contact surfaces.
2. The collapsible cylindrical endoprosthesis of claim 1, wherein
the manner of bending distributes the stresses throughout the
longitudinal members and circumferential members.
3. The collapsible cylindrical endoprosthesis of claim 1, wherein
the circumferential members comprise a loop.
4. The collapsible cylindrical endoprosthesis of claim 1, wherein
the circumferential members comprise an eyelet configuration.
5. The collapsible cylindrical endoprosthesis of claim 1, wherein
the circumferential members comprise a merge section of the ends of
adjacent longitudinal members.
6. The collapsible cylindrical endoprosthesis of claim 1, wherein
the longitudinal members further comprise a width measured
circumferentially and a thickness measured radially wherein the
thickness is greater than the width.
7. A collapsible cylindrical endoprosthesis comprising: a plurality
of longitudinal members arranged adjacently into a cylindrical
configuration each having a first end section, a middle section and
a second end section; a first a plurality of eyelets connecting
adjacent longitudinal members at the first end sections; a second
plurality of eyelets connecting adjacent longitudinal members at
the second end sections; and a plurality of merge sections
connecting adjacent longitudinal members at the middle section.
8. The collapsible cylindrical endoprosthesis of claim 7, wherein
the first plurality of eyelets and the second plurality of eyelets
connect the same longitudinal members forming pairs of longitudinal
members connected at both the first ends and second ends.
9. The collapsible cylindrical endoprosthesis of claim 7, further
comprising: opposed contact surfaces on the longitudinal members
near the first plurality of eyelets and the second plurality of
eyelets wherein the contact surfaces come together when the
prosthesis is collapsed.
10. The collapsible cylindrical endoprosthesis of claim 9, wherein
the first plurality of eyelets and the second plurality of eyelets
bend while the endoprosthesis is collapsed until the contact
surfaces come together and the longitudinal members bend
thereafter.
11. The collapsible cylindrical endoprosthesis of claim 7, wherein
the stresses due to collapsing the endoprosthesis are distributed
between the longitudinal members, the first plurality of eyelets
and the second plurality of eyelets.
12. The collapsible cylindrical endoprosthesis of claim 8, wherein
alternating pairs of longitudinal members define a first longer
length between the first end section and the middle section and a
second shorter length between the first end section and the middle
section.
13. The collapsible cylindrical endoprosthesis of claim 12, wherein
alternating pairs of longitudinal members define a first longer
length between the second end section and middle section, and a
second shorter length between the second end section and the middle
section.
14. The collapsible cylindrical endoprosthesis of claim 12, wherein
upon collapsing the endoprosthesis the eyelets connecting
alternating pairs of longitudinal members defining the second
shorter length nestle below the eyelets connecting alternating
pairs of longitudinal members defining the first longer length.
15. The collapsible cylindrical endoprosthesis of claim7, wherein
each longitudinal member defines a width measured circumferentially
and a thickness measured radially, wherein the thickness is greater
than the width.
16. A compressible endoprosthesis configured to secure an
endoluminal graft within a body lumen, comprising: a plurality of
curved beams arranged longitudinally in a cylindrical structure,
each beam having at least one end; a plurality of merge sections
formed by adjacent curved beams merging together; at least one
eyelet formed in a merge section at the ends of adjacent curved
beams; and wherein at least one eyelet provides an anchor for
stitching the endoprosthesis to the endoluminal graft.
17. The endoprosthesis of claim 16, further comprising: opposed
contact surfaces on the curved beams near the at least one eyelet,
wherein the contact surfaces come together when the endoprosthesis
is compressed.
18. The endoprosthesis of claim 16, wherein the at least one eyelet
is configured to distribute stress throughout the curved beams
while the endoprosthesis is compressed.
19. An expandable endoprosthesis comprising: a plurality of curved
beams arranged longitudinally in a cylindrical structure, each beam
having at least one end; a plurality of merge sections formed by
adjacent curved beams merging together; and at least one bulbous
extension formed in a merge section at the ends of adjacent curved
beams.
20. The endoprosthesis of claim 19, wherein the endoprosthesis is
formed from a single integral structure.
21. A collapsible cylindrical endoprosthesis comprising: a
plurality of curved longitudinal members in a cylindrical
arrangement, each having a proximal end and a distal end; a
plurality of proximal connections integrally formed by the proximal
ends of adjacent longitudinal members; a plurality of distal
connections integrally formed by the distal ends of adjacent
longitudinal members; and the cylindrical endoprosthesis has a
first diameter sized to compress against the interior of a
corporeal lumen and a second smaller diameter sized to fit within a
delivery catheter; wherein the cylindrical endoprosthesis
withstands stresses induced by collapsing through bending of the
curved longitudinal members.
22. The collapsible cylindrical endoprosthesis of claim 21, wherein
the proximal connections further comprise a looped
configuration.
23. The collapsible cylindrical endoprosthesis of claim 21, wherein
the distal connections further comprise a looped configuration.
24. The collapsible cylindrical endoprosthesis of claim 21, wherein
the plurality of curved longitudinal members further comprise pairs
of opposed contact surfaces on adjacent members.
25. The collapsible cylindrical endoprosthesis of claim 21, further
comprising: a plurality of bulbous extensions attached at the ends
of the connections.
Description
RELATED APPLICATIONS
[0001] This Application is a continuation-in-part of application
Ser. No. 09/546,966 filed Apr. 11, 2000 entitled "Single Piece
Thick-Walled Endoprosthesis."
BACKGROUND OF THE INVENTION
[0002] This invention relates to medical devices for the treatment
of vascular diseases generally referred to as endoluminal
prostheses. A variety of such devices are available for a broad
range of treatment modalities. Examples of such devices are
"vascular grafts" and "stents." Vascular grafts are typically used
to treat weakened areas of vessels known as aneurysms. Stents are
typically used to prop open a narrowed or stenosed vessel.
[0003] Stents and grafts may be delivered intraluminally through a
narrow incision or a puncture in the patient's skin. The device may
be mounted on a delivery catheter and inserted into a corporeal
lumen through the skin. The device and catheter are then advanced
through the various lumens to the site to be treated. To accomplish
this, stents and grafts are generally collapsible for delivery and
expansible for treatment.
[0004] Vascular grafts are primarily composed of an artificial
lumen which isolates the natural lumen from the flow of bodily
fluids, such as blood. Grafts may incorporate attachment devices to
secure the graft into the natural lumen and keep the graft
expanded. Stents are typically formed of metallic wire or bars
configured in a cylinder. Prior art stents have generally taught
that the resulting thickness of the cylinder should be kept small
to provide as large of an open lumen as possible. They have also
taught the use of wide bar elements to compress plaque or tissue
and hold it against the lumen wall. These stents expand by
configuring the elements of the cylindrical structure such that
they bend from a generally longitudinal orientation while
compressed to a more circumferential orientation while expanded.
These bending elements are then connected by elements which
typically lie and remain in a circumferential orientation. This
configuration limits the compressibility of the prior art stents
because elements in a circumferential orientation cannot be tightly
packed and thin elements in a longitudinal orientation tend to
overlap while compressed.
[0005] The configuration of prior art stents causes stress
concentrations by limiting the portions of the structure that bend
during expansion and compression. These stents have taught the use
of configurations which limit bending either to circumferential
members or to the areas immediately about such members. Such
configurations limit the ability of the prior art stents to expand
through very high expansion ratios.
[0006] At least one prior art device has incorporated the benefits
of a cylindrical structure composed of flat wires. This device is
described in U.S. Pat. No. 5,993,482 (Chuter) as a Flat-Wire Stent.
The teachings of that patent are hereby incorporated by
reference.
[0007] The Chuter flat-wire stent teaches a stent comprised of
flat-wires which results in a relatively thick-walled structure.
This approach has proven to have many advantages. The Chuter
flat-wire stent exhibits a greater expansion ratio than other
prosthesis. This is due in part to superior packability when
compressed. Other advantages include a reduction in stress
concentrations while expanded and the minimizing of foreshortening
during expansion.
SUMMARY OF THE INVENTION
[0008] Briefly and in general terms, the present invention relates
to an improved endoluminal prosthesis. This prosthesis may function
as a stent or as a means to secure an endoluminal graft in a
corporeal lumen such as an artery. Stents typically are used to
ensure the patency of diseased corporeal lumens by resisting
collapse and occlusion. Endoluminal grafts typically are used to
isolate diseased corporeal lumens from the flow of bodily
fluids.
[0009] The prosthesis incorporating the present invention is
configured as a series of intermittently merging curved beams (e.g.
leaf springs) formed into a cylinder. This cylindrical structure is
capable of being compressed into a small diameter and expanded into
a large diameter. To facilitate both compression and expansion the
beams have a cross-section which is greater in the radial direction
(thickness) than in the circumferential direction (width). The
beams of the present invention are also generally continuously
curved to reduce or minimize stress concentrations in the
structure. The beams straighten during compression until they are
nearly straight.
[0010] While compressed the thickness of the beams prevents
overlap. In a tightly packed configuration, the curved beams
straighten out, come together and generally lie flat in close
proximity to each other. The beams resist overlap because the
thickness of each beam requires substantial radial displacement to
move over or under the adjacent beam. The compression of the
prosthesis may be maximized by configuring the beams to fit
together tightly in a collapsed condition.
[0011] While expanded and during expansion, the thickness of the
beams and the configuration of the beams increase the strength of
the prosthesis and reduce or minimize stress concentrations.
Thicker beams provide for more material in the radial direction to
prevent radial collapse. The curved configuration of the beams
spreads the bending due to expansion throughout the entire length
of the beam. This prevents one area of the beam from generating
most of the bending and withstanding resultant stress
concentrations.
[0012] In various preferred embodiments of the present invention,
further improvements distribute stresses throughout the beams more
evenly. For example, the extreme ends of adjacent beams may be
connected by a loop or eyelet connector. In such an embodiment the
stresses from bending due to compression of the prosthesis
concentrate in the loop portion of the connector until the lower
portion of the connector just adjacent to the loop portion closes
on itself, bringing the adjacent beams into contact. Further
compression after that point concentrates stresses in the beam
below the loop. A similar result can be achieved by configuring the
beams to form a significant area of contact adjacent other types of
connectors prior to full compression of the prosthesis.
[0013] The present invention is a single integrated structure
without welds or fasteners. This may be accomplished by removing
almond-shaped cells from a thick-walled cylinder. This eliminates
the need to construct the prosthesis from individual pieces and
possible weak points created by fasteners or joining.
[0014] In a first embodiment, the prosthesis may have curved beams
which are only merged to adjacent beams at their end points. This
creates a single repetitive pattern around the circumference of the
cylinder, with each beam merged to opposite adjacent beams at
opposite end points. This embodiment may be viewed as the simplest
structure to include the invention described herein. It includes
alternating half-cells divided by curved beams. This embodiment is
not necessarily short, as the beams may be of any length. However,
it may be viewed as the shortest configuration for any given cell
size.
[0015] In a second embodiment, the prosthesis may have curved beams
like leaf springs which are repeatedly merged to alternating
adjacent beams throughout their length. This second embodiment may
also be viewed as the single repetitive pattern of the first
embodiment repeated throughout the length of the prosthesis. For
example, a prosthesis may be comprised of two or more of the single
pattern prosthesis connected end to end. Instead of actually
connecting the prosthesis, they may be formed as a single
structure. Thereby, the beams could be viewed as continuous
throughout the length of the prosthesis. The beams would then have
many curved portions which bring them in connection with
alternating adjacent beams at merge sections.
[0016] The prosthesis may also embody these curved beams forming
individual cylindrical elements and connected together by separate
elements. Thus, a variety of prosthesis may be formed by connecting
different cylindrical elements together with different connecting
elements. One configuration includes cylindrical elements having
curved beams which are only merged to adjacent beams at their end
points connected to cylindrical elements having curved beams which
are repeatedly merged to alternating adjacent beams throughout
their length. This provides a prosthesis having varying strength
and flexibility throughout its length.
[0017] In the compressed condition the prosthesis may be
intraluminally inserted and delivered within a corporeal lumen.
Once delivered to the site to be treated, the prosthesis may be
expanded and imbedded into the interior of the lumen. Various
methods for intraluminally expanding prostheses are well-known in
the art. Expansion due to spring forces is particularly suited for
this invention. The super-elastic properties of Nickel-Titanium
alloys (for example Nitinol) allow a great amount of expansion and
compression of structures without permanent deformation. Thus a
prosthesis made of such material may be compressed into a very
small configuration, and will spring back into a preset form when
released. Other known methods of expansion include balloon
expansion, and expansion due to the highly elastic properties of
certain alloys.
[0018] The present invention may also be balloon expandable. To
expand the prosthesis by balloon an angioplasty-type dilation
catheter is inserted through a compressed or not-fully expanded
prosthesis until the balloon portion of the catheter is
longitudinally aligned within the prosthesis. The balloon is then
expanded forcing the prosthesis radially outwardly.
[0019] Once expanded the prosthesis remains in the expanded
condition, and the strength of the prosthesis resists radial
collapse. When used alone the prosthesis can expand and resist
re-collapse of a previously collapsed or stenosed corporeal lumen.
When used in combination with a graft, the prosthesis can maintain
the graft open and secure the graft to the vessel.
[0020] Additional preferred embodiments of the present invention
may provide benefits for high-expansion ratios. That is, the
prosthesis may be configured to readily withstand high degrees of
expansion and compression. Prostheses having loop or eyelet
connectors according to this invention may also include beams of
different lengths. Alternating pairs of beams having longer lengths
and shorter lengths provide a more controlled expansion. This
configuration also permits the eyelets of the shorter length beams
to nestle below the eyelets of the longer length beams upon
compression. A further feature aiding the expansion of the
prosthesis includes varying the widths of the individual beams. For
example, configuring beams having longer lengths with greater
widths will improve the prosthesis ability to accomplish high
expansion. Furthermore, varying the width along the length of the
beam may also improve the expansion and compression abilities of
prosthesis.
[0021] Other configurations of the prosthesis may be beneficial
when the prosthesis is used in combination with a graft. The ends
of prosthesis which are to be configured within a graft may include
a flattened bulbous tail. Such an extension of the prosthesis
prevents wear on the fabric of the graft. Eyelets on the ends of
the prosthesis may also be used for stitching the prosthesis
together with the graft. Eyelets provide a good anchoring point for
such stitching. Various combinations of connected prosthesis
according to the present invention may be used within grafts.
[0022] These and other advantages of the invention will become more
apparent from the following detailed description of the preferred
embodiments. When taken in conjunction with the accompanying
exemplary drawings the person of skill in the art will appreciate
that various embodiments incorporate the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a perspective view of a first embodiment of the
prosthesis in an expanded condition.
[0024] FIG. 2 is a perspective view of the first embodiment of the
prosthesis in a compressed condition.
[0025] FIG. 3 is a cross-sectional view of the first embodiment of
the prosthesis in an expanded condition.
[0026] FIG. 4 is a cross-sectional view of the first embodiment of
the prosthesis in a compressed condition.
[0027] FIG. 5 is a perspective view of a second embodiment of the
prosthesis.
[0028] FIG. 6 is a side view of a third embodiment of the
prosthesis.
[0029] FIG. 7 is a top view of a portion of a flat pattern for the
prosthesis.
[0030] FIG. 8 is a side view of a fourth embodiment of the
prosthesis.
[0031] FIG. 9 is a side view of a vascular graft secured in a
corporeal lumen by a prosthesis.
[0032] FIG. 10 is a side view of a prosthesis embedded in a
corporeal lumen.
[0033] FIG. 11 is a perspective view of a thick-walled cylindrical
tube with cells designed therein.
[0034] FIG. 12 is a flat pattern view of a portion of a prosthesis
embodying variable thickness beams.
[0035] FIG. 13 is a flat pattern view of a portion of a prosthesis
including alternative embodiments of variable thickness beams.
[0036] FIG. 14 is a flat pattern view of a portion of a prosthesis
including additional alternative embodiments of variable thickness
beams.
[0037] FIG. 15 is a flat pattern view of a portion of a prosthesis
including additional alternative embodiments having varying
flexibility.
[0038] FIGS. 16a and 16b are side views of a first alternative
embodiment of the beam ends and connector.
[0039] FIGS. 17a and 17b are side views of a second alternative
embodiment of the beam ends and connector.
[0040] FIG. 18 is a flat pattern view of a first embodiment of a
prosthesis having the alternative beam end connectors shown in
FIGS. 16a and 16b.
[0041] FIG. 19 is a flat pattern view of a second embodiment of a
prosthesis having the alternative beam end connectors shown in
FIGS. 16a and 16b.
[0042] FIG. 20 is a flat pattern view of the prosthesis of FIG. 19
in a collapsed state.
[0043] FIG. 21 is a flat pattern view of a prosthesis from within a
vascular graft.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] The following description, as well as the Figures, describe
embodiments of the invention. These embodiments are exemplary of
the inventors known uses of the invention, and are not intended to
limit the scope of the claimed invention. Those skilled in the art
of endoluminal devices will appreciate that the invention described
herein may encompass many embodiments.
[0045] As shown in the Figures, the present invention relates to an
endoluminal prosthesis. More particularly, the invention is an
expandable and compressible prosthesis for repairing corporeal
lumens. The prosthesis may be formed from a metallic cylinder by
removal of cells.
[0046] As depicted in FIGS. 1 and 2, the result of removing cells
20 from the metallic cylinder 22 is a prosthesis 24 having a series
of curved beams 26 and merge sections 28. It is to be recognized
that the prosthesis 24 shown in FIG. 2 can be compressed, where
desired, to a smaller diameter such that the cells 20 are
essentially defined by slits (not shown).
[0047] The beams 26 are generally longitudinal members
circumferentially spaced about the prosthesis 24. In one
embodiment, as depicted in FIG. 5, the ends of these beams 26 merge
with the ends of circumferentially adjacent beams to form the merge
sections 28 only at the ends of the prosthesis. The ends of each
beam 26 merge with one adjacent beam on the forward end 30 and the
opposite adjacent beam on the rear end 32. This creates a single
circumferential pattern of staggered half-cells 21 divided by beams
26. (For comparison, a full cell 25 is identified in FIG. 1).
Preferably, the beams 26 each include at least two curved segments
34 of opposite orientations and an inflection point 36 near the
mid-point of the beams.
[0048] In the embodiment depicted in FIG. 5, the merge sections 28
include either the forward ends 30 or rear ends 32 of two such
beams 26 as well as the ends of the prosthesis. These merge
sections 28 are also circumferentially spaced about the prosthesis
24, preferably equidistantly.
[0049] The single pattern as depicted in FIG. 5 may be extended to
build longer prostheses 24. This may be done by extending the
length of each beam 26 with additional curved segments 34 and
forming additional merge sections 28. This forms the prosthesis 24
as depicted in FIGS. 1 and 2. Alternatively, multiple single
patterns may be connected with a separate connector element 58. The
connector elements 58 may have various configurations and be
distributed throughout the prosthesis 24 in a variety of
arrangements. Such a prosthesis 24, having "S"-shaped connector
elements at each merge section is depicted in FIG. 6. Other
embodiments (not shown) may have connectors with other shapes only
at every second or third merge section. Such embodiments may have
advantages in providing longitudinal flexibility to the prosthesis
24.
[0050] In the embodiments depicted in FIGS. 1 and 2 the beams 26
may extend beyond the first merge sections 28 to form additional
merge sections 28. This configuration may also be viewed as the
merge sections 28 connected end-to-end with opposite facing merge
sections 28. This may provide for a prosthesis 24 of greater
lengths. The continuous beams 26 of this embodiment merge with
adjacent beams 26 repeatedly and alternately throughout their
length. The continuous beams are comprised of multiple curved
segments 34. The merge sections 28 may also contain flat segments
(not shown).
[0051] As depicted in FIGS. 3 and 4 the prosthesis 24 is preferably
formed from a thick-walled cylinder 22. The difference between the
external radius of the cylinder and the internal radius of the
cylinder defines a radial thickness 40. Preferably, the cells 20 of
the prosthesis 24 are removed such that the remaining beams 26 have
a width (measured circumferentially) 42 that is less than the
radial thickness 40. A typical design might have dimensions of
0.007" circumferential width 42 and 0.014" radial thickness 40.
This defines a deep cross-section for the beams 26. To take
advantage of the benefits of this invention, the radial thickness
40 of the beams 26 needs to be substantially greater than the
circumferential width 42. Preferably, the radial thickness 40 will
be at least one and one-third (11/3) times the circumferential
width 42.
[0052] A theoretical flat pattern of the beams 26 and merge
sections 28, as depicted in FIG. 7 reveals the novel configuration
of the beams. Preferably, each beam 26 is continuously curved,
alternating between curves 56 of opposite orientations throughout
its length. In this ideal configuration, the beams 26 form
inflection points 36 between the opposite facing curves 56.
[0053] Each curve 56 in each beam 26 is defined by two radii, an
internal radius 64 and an external radius 66. The difference
between these radii define the circumferential width 42 of the beam
26.
[0054] The continuously curved configuration of beams 26 disposed
longitudinally along a cylinder, provides some of the unique
properties of this invention. As the cylinder is expanded from a
partially compressed configuration 50, the radii of each curve 56
within each beam 26 becomes smaller as the beams spread apart.
Since the beams 26 are ideally continuously curved, the bending is
spread throughout the entire length of the beam 26. This spreads
the resultant stresses throughout the beam 26 and reduced or
minimizes stress concentrations.
[0055] As depicted in FIGS. 2 and 4 the use of deep cross-sections
has significant advantages for collapsing the prosthesis 24 in
preparation of intraluminal delivery. The deep cross-section allows
for significant compression without incidental overlapping of the
beams 26. The large radial thickness 40 of the beams 26 prevents
one beam from extending over the top of another.
[0056] As depicted in FIGS. 1 and 3 there are also advantages to
the use of deep cross-sections in expansion of the prosthesis 24.
In general, as cylindrical, expandable prosthesis are expanded,
longitudinally-oriented members of the collapsed prosthesis tend to
bend circumferentially. The relatively narrow width of the beams 26
of the present prosthesis 24 permits circumferential bending
without inducing high stress concentrations. The large overall
cross-sectional area of the beams 26 prevents recompression of the
prosthesis 24. The configuration of the curved segments 34 spreads
the stresses induced by expansion across the entire length of the
beams 26, also reducing stress concentrations. In a preferred
embodiment, the prosthesis is self-expandable. Alternatively, the
prosthesis may be expanded by balloon.
[0057] FIGS. 1 and 3 and FIGS. 2 and 4 depict two separate
configurations of the prosthesis 24. The prosthesis 24 of the
present invention has an expanded configuration 44 while deployed
in the lumen as depicted in FIGS. 1 and 3. This configuration has a
large inner diameter which allows maximum patency of the lumen 46
to be treated. The prosthesis 24 of the present invention also has
a second partial compressed configuration 50 as depicted in FIGS. 2
and 4. This configuration is beneficial to the intraluminal
delivery of the device which is facilitated by a smaller external
diameter.
[0058] In a typical procedure the prosthesis 24 will be constrained
in the compressed configuration 50 within a catheter. This catheter
may then be inserted into a small diameter lumen 46 such as the
femoral artery. To prevent damage to such an artery the entire
system of catheter and prosthesis 24 must have as small a diameter
as possible. Small diameters also facilitate the navigation of the
prosthesis 24 and catheter through arduous vasculature. Once
inserted into such an artery, the catheter and prosthesis 24 may be
advanced through the corporeal lumens, possibly to larger arteries
for treatment. The prosthesis 24 may then be released from the
catheter. Spring forces within the compressed prosthesis of a
self-expanding version will force the prosthesis from the partially
compressed configuration 50 into the expanded configuration 44. The
spring forces may be great enough to expand the lumen of the
diseased vessel as the prosthesis 24 expands. These forces will
also be great enough to impinge the beams 26 into the tissues of
the vessel. This impinging secures the prosthesis 24 and possibly
an associated graft 52 into place.
[0059] Another embodiment of the prosthesis 24, depicted in FIG. 8,
has a conical rather than cylindrical shape while in the expanded
configuration 44. In this embodiment, the prosthesis 24 has a
cylindrical shape in the compressed configuration 50. Upon
expansion, however, a broader end 60 of the prosthesis 24 expands
more than a narrower end 62. This conical embodiment of the
prosthesis 24 is useful in similarly shaped lumens and various
configurations of grafts. The broader end 60 may include cells 20
that are longer and wider in the expanded configuration 44, than
those at the narrower end 62.
[0060] The prosthesis 24 of the current invention may be used in a
variety of procedures, two of which are depicted in FIGS. 9 and 10.
As depicted in FIG. 9 one or more prostheses embodying the present
invention may be used in the treatment of aneurysms. An aneurysm is
a weakening of the vessel wall of a vein or artery, causing a sack
to form in the lumen 46 or possibly rupture. When an aneurysm forms
in the abdominal aorta, the condition can be life-threatening. A
known treatment for aneurysms is the intraluminal delivery and
implantation of a vascular graft 52. Such a graft 52 bypasses the
sack formed by the aneurysm and isolates the weakened tissues from
the blood flow. To operate properly, the graft 52 must have
leak-proof fixation to the healthy vascular tissue on either side
of the aneurysm. The prosthesis 24 described herein may provide
that fixation at one or more ends of the graft 52. The prosthesis
24 may also extend throughout the length of the graft 52. When
expanded the prosthesis 24 may compress the flexible graft material
52 against the arterial wall. Preferably, the prosthesis 24 extends
further from the aneurysm than the graft 52 so that parts of the
prosthesis 24 are imbedded in healthy tissue. This configuration
maintains the patency of the artificial lumen of the graft 52 as
well as securing the graft in place by forcing the end of the graft
against the wall of the lumen 46. The prosthesis 24 also ensures a
leak-proof seal.
[0061] As depicted in FIG. 10, a prosthesis 24 embodying the
present invention may be used to treat a stenosis or collapse of
the lumen 46. Stenosis is often caused by the gradual occlusion of
veins or arteries through the build-up of plaque. Preferably a
single prosthesis 24 is inserted into the diseased vessel while
mounted within a catheter. When the prosthesis 24 is at the
location of the narrowing, the prosthesis 24 may be expanded. As
depicted in FIG. 10 the spring forces of the prosthesis are
preferably sufficient to expand the narrowed vessel. The prosthesis
24 is thereby forced into the tissues of the lumen 46 to secure the
prosthesis 24 in place. The structure of the prosthesis 24 resists
collapse after expansion.
[0062] The prosthesis 24 may be manufactured in the compressed
configuration 50 as in FIG. 2, or in the expanded configuration 44
as in FIG. 1 or in any configuration in between. The manufacturing
procedure requires the removal of cells 20 from a thick-walled
cylinder 22. This may be accomplished with several known
manufacturing methods such as laser cutting, chemical etching,
photo-etching, electrical discharge machining (EDM) and mechanical
means. Two materials found to be particularly suited to this
application are implantable stainless steel, and Nickel-Titanium
alloys such as Nitinol.
[0063] As depicted in FIG. 11, each cell 20 of the endoprosthesis
24 may consist of two sides 54 having three curves 56, and two
inflection points 36. Such a configuration produces almond-shaped
cells. There may also be flat portions (not shown) designed into
the cell 20. These cells 20 are then designed on the thick walled
cylinder 22 in a pattern which repeats along the length of the
cylinder 22. This pattern is then repeated with a longitudinal
stagger of half a cell 20 around the circumference of the cylinder
22. The pattern also includes half cells at each end of the tube.
Upon removal of the cells 20 the remaining material constitutes the
prosthesis 24 described herein.
[0064] The prosthesis 24 may be formed from a thick walled cylinder
22 approximately the size of the compressed configuration 50. This
thick walled cylinder 22 may be a Nickel Titanium alloy. Cells 20
are laser cut into the thick walled cylinder 22 while the thick
walled cylinder 22 is mounted over a wire. The cells 20 are formed
in a long narrow configuration, with each of the curves 56 having
large radii.
[0065] After the cells 20 are cut into the thick walled cylinder
22, the prosthesis 24 is cleaned and deburred to eliminate
manufacturing irregularities. This may include blasting techniques,
acid etching, ultrasonic cleaning and/or other well known methods
of cleaning.
[0066] The prosthesis may then be stretched into more expanded
configurations. One method of expanding this prosthesis is by
mechanically stretching it over a mandrel. The mandrel may be
specifically designed with pins to maintain the desired curvature
of the beams. Once stretched the prosthesis is annealed to set the
new expanded shape of the prosthesis. Annealing can be accomplished
by heating the prosthesis within a variety of media such as air,
molten salt, inert gas or vacuum. Annealing at 500-550.degree. C.
is appropriate for Nickel-Titanium alloys. After stretching the
prosthesis 24 is cleaned again. This process of stretching,
annealing and cleaning can be repeated until the desired
configuration is obtained. Once the desired configuration has been
obtained, the prosthesis is electropolished by any of the
well-known methods.
[0067] Alternatively, a prosthesis 24 may be formed from a Nickel
Titanium thick walled cylinder 22 approximately the size of
expanded configuration. In this process cells 20 are cut into the
thick walled cylinder in a shorter and wider configuration. This
method would eliminate the need to stretch and anneal the
prosthesis 24 to achieve the expanded configuration 94.
[0068] As best seen in FIGS. 12-14, it is also contemplated that
the beams of a prosthesis may embody variable widths beams or
struts 70 and generally uniform width beams or struts 71. The
incorporation of variable width struts 70 into a prosthesis
facilitates uniform expansion. For example, to achieve uniform
expansion, it is desirable to have struts 70 of the same width
meeting at connecting junctions 72. Asymmetric prosthesis portions
74, 76 as shown in FIGS. 12 and 13 may further require the strut 70
to embody a width that gradually varies along the length of the
strut 70. Moreover, as shown in FIG. 14, where a prosthesis portion
78 embodies a plurality of adjacent oriented cells 80, the point of
connection 82, 83 between adjacent cells 80 may be varied in
length, for example to accommodate a hole 84. To facilitate uniform
expansion of such a prosthesis portion 78, the struts 70 extending
from a relatively shorter point of connection 82 between adjacent
cells 80 can embody a tapering thickness.
[0069] The novel features of the present invention may be applied
to configure a prosthesis having variable properties throughout the
length of the prosthesis. As an example, and as depicted in FIG.
15, the flexibility of the prosthesis 24 may vary along the length
of the prosthesis. To accomplish this, connector elements 58 may be
used to combine segments 90 of the prosthesis 24. Each segment 90
may be composed of curved beams 26 in the various configurations
described above. In a preferred embodiment, a segment 90 composed
of full cells 20 may be combined with multiple segments 90 composed
of half-cells 21. The portion of the prosthesis 24 composed of
half-cell 21 segments 90 will tend to be significantly more
flexible longitudinally and slightly more flexible radially. The
invention includes any combination of full cells and half-cells in
a prosthesis including, but not limited to, full cells between
half-cells.
[0070] One application of a prosthesis 24 having variable
flexibility throughout its length is for the support of a vascular
graft 52. In such an application, the more flexible segments 90 of
the prosthesis 24 may be configured to support the artificial lumen
46 of the graft 52. The less flexible segment 90 of the prosthesis
24 may be configured to extend beyond the artificial lumen 46 and
into the patients natural lumen. In this manner, the less flexible
segments 90 help secure the graft 52 into place, while the more
flexible segments 90 support the material of the graft 52.
[0071] The invention described herein may also embody features to
facilitate the high ratios of expansion possible with this
prosthesis 24. As depicted in FIGS. 16a and 16b, as well as FIGS.
17a and 17b, the ends 92 of the beams 26 may be connected in a
manner which evenly distributes the stresses incurred by expansion
and compression.
[0072] An eyelet or loop connector 94 (shown in FIGS. 16a and 16b)
may connect the ends of the beams 26. These eyelet connectors 94
distribute stresses from compression of the prosthesis 94. As the
prosthesis 24 is initially compressed and adjacent beams 26 are
brought together, the bending and resultant stresses are initially
concentrated in the eyelet or loop portion of the connector 94.
Eventually, a contact area 96 is formed at the edge of the eyelet
connector 24. As the prosthesis 24 is further compressed and
adjacent beams 26 are brought even closer together, the bending and
resulting stresses are now concentrated at the ends of the beams 26
near the contact area 96. Even further compression may relieve the
stresses in the eyelet connector 24 by creating a fulcrum at the
contact area 96.
[0073] A prosthesis 24 composed entirely of eyelet connectors 94,
as depicted in FIG. 18, may facilitate the distribution of stresses
induced by high expansion ratios. Thus, the prosthesis 24 of the
present invention may be used in particularly large corporeal
lumens, such as the abdominal aorta. This same prosthesis 24 may
also be introduced into relatively small corporeal lumens, such as
the femoral artery. Such an application requires the prosthesis to
transition between a highly compressed state for insertion into the
femoral artery, to a highly expanded state for implantation into
the abdominal aorta. This application, as well as others, induce
high stresses on the prosthesis 24 through bending of the beams 26
in expansion and compression.
[0074] A similar distribution of the stresses may be accomplished
by configuring the ends 92 of the beams 26 into increased contact
end connectors 98 (FIGS. 17a and 17b). In such a configuration
(depicted in FIGS. 17a and 17b), the ends 92 of the beam 26 connect
together with a substantial area of contact 96 near the actual
connection. As the prosthesis 24 is compressed, and the beams 26
are brought closer together, the stresses due to bending are
concentrated in the beams 26 near the contact area 96. The contact
area 96 expands as the beams 26 are brought closer together and the
stress concentrations are thereby distributed along the length of
the beams 26.
[0075] To further support high expansion ratios, the prosthesis 24
of the present invention may be configured to pack tightly for
compression into a collapsed state. One example, as depicted in
FIGS. 19 and 20 may utilize eyelet connectors 94 aligned to
differing heights. That is, every other eyelet connector 94 may be
configured upon beams 26 of a first, greater length 100, while each
other eyelet connector 94 may be configured upon beams 26 of a
second lesser length 102. Thus the eyelet connectors 94 configured
upon beams at the second length would have their greatest width at
the same location that the eyelet connectors 94 configured upon
beams at the first length have their least width. In this manner
the beams 26 and eyelet connectors 94 fit together in the most
compact condition while compressed. Similar results may be
accomplished by varying the thickness of the beams 26 and
connectors 94.
[0076] Varying the circumferential width 42 of the beams 26 may
also provide benefits in high expansion ratios. For example, using
larger widths on beams 26 of a first, greater length 100 may help
control the expansion of the prosthesis 24 and reduce stress
concentrations. Varying the circumferential width 42 along the
length of individual beams 26 may provide superior nesting when the
prosthesis is provided with eyelet connectors 94.
[0077] Further configurations, as depicted in FIG. 21, may be
advantageous when the prosthesis 24 is configured for use in a
vascular graft 52. Eyelet connectors 94 may be used to provide an
anchor for the stitching 104 between the graft 52 and the
prosthesis 24. The merge sections 28 at the end of the prosthesis
may include a flattened bulbous tail 106. These tails 106 reduce
the wearing on the fabric of the graft 52. Tails 106 may also help
control the expansion of the prosthesis 24. Instead of springing
open when the ends of the prosthesis 24 are released, the tails 106
may remain constrained within a delivery catheter and provide the
prosthesis 24 with a slower more controlled expansion.
[0078] While the present invention has been described herein in
terms of a prosthesis for the repair of blood vessels, those of
skill in the art will readily recognize that prostheses embodying
the described invention can be used to treat a variety of corporeal
lumens, for example the bronchial tree and intestines. The
invention described herein is intended to be limited only by the
claims that follow and not by any particular embodiment.
* * * * *