U.S. patent application number 12/181639 was filed with the patent office on 2010-02-04 for medical device including corrugated braid and associated method.
This patent application is currently assigned to AGA Medical Corporation. Invention is credited to Ryan Mach.
Application Number | 20100030321 12/181639 |
Document ID | / |
Family ID | 41609147 |
Filed Date | 2010-02-04 |
United States Patent
Application |
20100030321 |
Kind Code |
A1 |
Mach; Ryan |
February 4, 2010 |
MEDICAL DEVICE INCLUDING CORRUGATED BRAID AND ASSOCIATED METHOD
Abstract
Embodiments of the present invention provide medical devices for
treating a target site within the body and associated methods for
fabricating and delivering medical devices. According to one
embodiment, a medical device includes a tubular structure having
proximal and distal ends and a side wall extending therebetween. At
least a portion of the side wall can have a corrugated surface. The
side wall further includes at least one layer of a metallic fabric
configured to be compressed and heat set to define the corrugated
surface. The tubular structure may comprise an expanded shape, and
may be configured to be constrained to a smaller diameter than the
expanded shape for delivery within a catheter to a target site and
to assume the expanded shape upon release from the catheter.
Inventors: |
Mach; Ryan; (Durham,
NC) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA, 101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
AGA Medical Corporation
|
Family ID: |
41609147 |
Appl. No.: |
12/181639 |
Filed: |
July 29, 2008 |
Current U.S.
Class: |
623/1.18 |
Current CPC
Class: |
D04C 1/06 20130101; A61F
2/07 20130101; A61F 2230/0078 20130101; D06C 21/00 20130101; D04C
1/02 20130101; D06C 7/00 20130101; A61F 2/90 20130101 |
Class at
Publication: |
623/1.18 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. A medical device for treating a target site within the body, the
medical device comprising: a tubular structure having proximal and
distal ends and a side wall extending therebetween, at least a
portion of the side wall having a corrugated surface, the tubular
side wall comprising at least one layer of a metallic fabric
configured to be compressed and heat set to define the corrugated
surface.
2. The medical device of claim 1, wherein the at least one layer of
metallic fabric comprises a shape memory alloy.
3. The medical device of claim 1, wherein the side wall comprises a
plurality of layers of metallic fabric.
4. The medical device of claim 1, wherein the at least one layer of
metallic fabric is configured to facilitate thrombosis.
5. The medical device of claim 1, wherein the tubular structure is
configured to be moved between an expanded and an unexpanded shape,
and wherein the tubular structure is configured to be constrained
to an unexpanded shape for delivery within a catheter to a target
site and to assume the expanded shape upon release from the
catheter.
6. The medical device of claim 1, wherein the side wall comprises a
plurality of corrugated portions each comprising a corrugated
surface, and wherein at least two corrugated portions of the
plurality of corrugated portions are separated from one another by
a non-corrugated portion.
7. The medical device of claim 6, wherein one corrugated portion of
the plurality of corrugated portions is located adjacent to at
least one of the proximal end or the distal end.
8. The medical device of claim 1, wherein the corrugated surface
comprises a plurality of annular ridges each extending about an
entire circumference of the tubular structure.
9. The medical device of claim 1, wherein the medical device is one
of a stent graft, an occluder, a shunt, or a flow restrictor.
10. The medical device of claim 1, wherein the side wall is
configured to be elongated such that at least a portion of the
corrugated surface has a generally sinusoidal profile along a
direction generally aligned with a central axis of the tubular
structure.
11. The medical device of claim 1, wherein the corrugated surface
comprises a spiral ridge each extending about a circumference of
the tubular structure.
12. A method for increasing the radial strength of a medical device
comprising: providing a tubular structure comprised of at least one
layer of metallic material and having proximal and distal ends and
a side wall extending therebetween; compressing the tubular
structure such that the side wall defines at least one corrugated
surface extending at least partially between the proximal and
distal ends; and heat setting the compressed tubular structure.
13. A method according to claim 12, wherein compressing comprises
axially compressing the tubular structure.
14. A method according to claim 12, further comprising forming the
tubular structure from a plurality of metallic strands.
15. A method according to claim 14, wherein compressing comprises
compressing the tubular structure until a plurality of the strands
buckle to define the corrugated surface.
16. A method of delivering a medical device to a target site within
the body, the method comprising: constraining to a smaller diameter
a tubular structure having proximal and distal ends and a side wall
extending therebetween, at least one portion of the side wall
having a corrugated surface, the side wall comprising at least one
layer of metallic material configured to be heat set to define an
expanded shape, wherein the expanded shape is constrainable to a
smaller diameter; positioning the constrained tubular structure in
a catheter; delivering the tubular structure proximate to the
target site; and deploying the tubular structure from the catheter
such that the tubular structure assumes the expanded shape.
17. The method of claim 16, wherein constraining comprises axially
elongating the tubular structure.
18. The method of claim 16, wherein constraining comprises
constraining the tubular structure to an outer diameter of less
than about 15 French.
19. The method of claim 16, wherein delivering comprises delivering
the tubular structure over a guidewire.
20. The method of claim 16, wherein delivering comprises delivering
the tubular structure such that the tubular structure self-expands
and generally assumes the expanded shape.
21. The method of claim 16, wherein delivering comprises
compressing the tubular structure so as to urge the tubular
structure back to the expanded shape.
22. A medical device for treating a target site within the body,
the medical device comprising: a tubular structure having proximal
and distal ends and a side wall extending therebetween, at least a
portion of the side wall having a corrugated portion that extends
partially between the proximal and distal ends, has a first
diameter, and has a corrugated surface, the side wall further
comprising at least one non-corrugated portion adjacent the
corrugated portion, extending partially between the proximal and
distal ends, and having a second diameter not equal to the first
diameter.
23. The medical device of claim 22, wherein the side wall comprises
at least one layer of a metallic material configured to be
compressed and heat set to define the at least one corrugated
portion.
24. The medical device of claim 23, wherein the at least one layer
of metallic material is configured to facilitate thrombosis.
25. The medical device of claim 22, wherein the at least one
corrugated portion is located adjacent to at least one of the
proximal end or the distal end.
26. The medical device of claim 22, wherein the side wall comprises
a plurality of corrugated portions, and wherein a pair of the
corrugated portions are separated by the at least one
non-corrugated portion.
27. The medical device of claim 22, wherein the tubular structure
is one of a stent graft, a shunt, a flow restrictor, or an
occluder.
28. The medical device of claim 22, wherein the second diameter is
less than the first diameter.
Description
BACKGROUND OF THE INVENTION
[0001] 1) Field of the Invention
[0002] The present invention relates to medical devices and
associated methods for treating various target sites within the
body and, in particular, to medical devices and associated methods
for fabricating and delivering medical devices that respectively
include corrugated surfaces.
[0003] 2) Description of Related Art
[0004] Vascular disease is common in the arterial system of humans.
This disease often results in a build up of plaque or deposits on
the vessel wall, which narrow the vessel carrying oxygenated blood
and nutrients throughout the body. If narrowing should occur, for
example, in an artery within the heart, blood flow may be
restricted to the point of causing pain or ischemia upon body
exertion due to the lack of oxygen delivery to the heart muscle.
The flow disruption from a severe narrowing of the vessel or a
plaque rupture may result in a blood clot formation and flow
stoppage which, if occurring in the heart, would result in a heart
attack.
[0005] Vascular disease may be anywhere in the body, and treating
the disease is important to one's health. One method of treatment
that is widely adopted is expanding the diseased narrowed sections
of a vessel with an angioplasty balloon that is sized to the
vessel's healthy diameter. The balloon is inflated to a high
pressure to crack and expand the plaque outward, restoring the
vessel diameter.
[0006] Another technique that may be used to treat the narrowing of
a vessel is with a stent. A stent is a thin wall metal tubular
member that can be expanded in diameter within the vessel to hold
the ballooned segment open after the balloon is removed. Some
stents (so-called "balloon-expandable" stents) are placed over a
deflated angioplasty balloon and expanded by inflating the balloon,
while other types of stents are self-expanding. Both types may be
delivered to the treatment site by a catheter in a
radially-collapsed configuration and then expanded within the
diseased segment of the artery. Both types of stents may be
fabricated by laser machining of thin wall metal tubes or may be
fabricated from wires formed to a particular shape or by braiding
wires into a tubular shape. Balloon-expandable stents are generally
made from stainless steel or cobalt-containing alloys, where
self-expanding stents tend to be made from highly elastic or
pseudo-elastic metals, such as a shape memory nickel-titanium alloy
commonly referred to as "Nitinol."
[0007] Of particular interest in the design of stents is the amount
of radial force that can be achieved for arterial support while
minimizing the collapsed deliverable diameter. Stents must also be
conformable, when expanded, to the curvature of the target artery
segment, and should be flexible in bending in the collapsed
deliverable diameter so that the stents can be passed through
narrow tortuous arteries to the treatment site. In vessels that are
close to the surface of the body, such as in carotid arteries, only
self-expanding stents are considered suitable since the stent must
spring back from an impact to the body and not close off the
artery. Flexibility and good fatigue resistance are important
properties for stents placed in arterial segments subject to
flexure such as in joints.
[0008] Self-expanding tubular stents made of braided filaments of
Nitinol wire are very useful due to their high flexibility and
ability to be greatly reduced in diameter, by elongation of the
braid, for delivery. The braided stents are even more flexible in
their reduced diameter state. One limiting aspect of conventional
braided Nitinol stents, however, is the ability to achieve high
radial support compared to self-expanding stents cut from Nitinol
tubing. To achieve greater radial support the braided tube may be
fabricated from filaments having a greater diameter, but this
increases the collapsed diameter profile and increases deliverable
stiffness. An alternative to improve radial support is to heat set
the braided stent at the desired expanded diameter with the helix
angle of the filaments at a high angle relative to the longitudinal
axis of the stent. This increases the length of the collapsed stent
and increases the delivery force needed to push the stent through
the delivery catheter since the filaments are under greater stress
at a given collapsed diameter.
[0009] Another application of stents is in stent graft
applications. One important application is the treatment of
vascular aneurysms, a weakening and thinning of the vessel wall
whereby the weakened area causes the vessel diameter to expand
outward much like a balloon. The weakened wall is of greater risk
of rupture due to pulsing blood pressure. Stent grafts are used to
percutaneously reline the aneurysm, sealing against the proximal
and distal healthy vessel wall and thus reducing risk of rupture by
shielding the weakened wall from carrying the blood pressure. It is
important that a seal be achieved on both ends of the graft against
the arterial wall and that no leak occurs along the length of the
graft. Such leaks would subject the weakened aneurysm wall to blood
pressure. To achieve a seal, stent grafts have employed various
design means to increase the pressure against the arterial wall at
each end, such as incorporating end stents that have greater radial
force, using thicker materials near the end, enlarging the expanded
diameter of the stent graft at the ends, or adding sealing
substances such as filler material. Most of these solutions
increase the collapsed profile of the stent graft and increase the
stiffness during delivery to the artery.
[0010] Another approach to the treatment of aneurysms is the use of
a porous tubular stent graft comprised of one or more layers of
braided metal. In this approach, the tubular braid is placed
directly against the aneurysm before the aneurysm has become
dangerous in size. The braid has a maximum expansion diameter
matched to the aneurysm maximum diameter and the stent graft
incorporates into the wall of the aneurysm by tissue ingrowth,
thereby strengthening the wall and inhibiting any further growth of
the aneurysm.
[0011] Another application of stents or stent grafts is for
treating a dissection of a vessel such as, for example, the
thoracic aorta, whereby a tear in the vessel lining threatens to
cause an aneurysm if not treated. In such cases, the tear may allow
blood flow against the adventitial layer of the vessel and must be
sealed. A good seal must be achieved between the vessel wall and
the stent or stent graft to ensure that blood cannot enter the
origin of the dissection. On either side of the origin of the
dissection, the stent graft may be more porous as vascular support
is the primary attribute for the remainder of the stent graft. A
stent graft may achieve the seal by addition of a polymer or
textile fabric but this adds to the device delivery profile.
[0012] Metallic, "super-elastic," braided, tubular members are
known to make excellent vascular occlusion, restrictor, and shunt
devices, for implant within the body. These devices are typically
braided from filaments of Nitinol and subsequently heat set to
"memorize" a final device shape. Such devices may be elongated for
delivery through a catheter to a treatment site, and upon removal
from the delivery catheter, may self-expand to approximate the
"memorized" device heat set shape. The devices have various shapes
designed to occlude, restrict flow, or shunt flow to various parts
of the vascular anatomy by restricting or diverting blood flow
through all or a portion of the device. Since the devices are
subjected to blood pressure, there must be sufficient retention
force between the device and the vascular wall to prevent device
dislodgement.
[0013] Therefore, it would be advantageous to provide a medical
device having increased radial strength while retaining a small
profile and flexibility for delivery to a target site. It would
also be advantageous to provide a medical device capable of being
sufficiently anchored at a target site and effectively treating the
target site.
BRIEF SUMMARY OF THE INVENTION
[0014] Embodiments of the present invention provide a medical
device, such as, for example, a stent graft, an occluder, a shunt,
or a flow restrictor, for treating a target site within the body.
For example, one embodiment provides a medical device including a
tubular structure having proximal and distal ends and a side wall
extending therebetween. At least a portion of the side wall can
have a corrugated surface, for example, comprising a plurality of
ridges each extending about an entire circumference of the tubular
structure. The side wall further includes at least one layer of a
metallic fabric, and in some cases a plurality of layers,
configured to be compressed and heat set to define the corrugated
surface. For example, the metallic fabric can include a shape
memory alloy. The ridges of the corrugated surface may extend
annularly or helically about the tubular structure. The metallic
fabric can additionally be configured to facilitate thrombosis. The
tubular structure may comprise an expanded shape, and may be
configured to be constrained to a smaller diameter than the
expanded shape for delivery within a catheter to a target site and
to assume the expanded shape upon release from the catheter. In
some cases, the side wall is configured to be elongated such that
at least a portion of the corrugated surface has a generally
sinusoidal profile along a direction generally aligned with a
central axis of the tubular structure.
[0015] In some embodiments, the side wall may comprise a plurality
of corrugated portions, with each portion having a corrugated
surface. At least two corrugated portions may be separated from one
another by a non-corrugated portion. One of the corrugated portions
can be located adjacent to the proximal end or the distal end.
[0016] According to another embodiment, a method for increasing the
radial strength or resistance to radial compression of a medical
device is provided. The method includes providing a tubular
structure comprised of at least one layer of metallic material and
having proximal and distal ends and a side wall extending
therebetween. In some cases, the side wall can be formed at least
partially from a plurality of metallic strands. The tubular
structure can be compressed (for example, axially compressed) such
that the side wall defines a corrugated surface extending at least
partially between the proximal and distal ends. For example, where
the side wall includes a plurality of metallic strands, the tubular
structure may be compressed until some of the strands buckle to
define the corrugated surface. Alternatively, an external or
internal mold or both may be used to facilitate formation of the
corrugated surface or to induce a thread-like pitch to the
corrugation. The compressed tubular structure is then heat set.
[0017] In yet another aspect, a method of delivering a medical
device, such as that described above, to a target site within the
body is provided. The method includes constraining the tubular
structure to a smaller diameter (e.g., less than 15 French), for
example, by axially elongating the tubular structure. The
constrained tubular structure can be positioned in a catheter and
delivered, such as, over a guidewire, proximate to the target site.
The tubular structure can then be deployed from the catheter such
that the tubular structure assumes the expanded shape, either by
self-expanding into the expanded shape or by being compressed and
thereby urged back towards the expanded shape.
[0018] According to one embodiment, a medical device for treating a
target site within the body is provided. The medical device
includes a tubular structure, such as, for example, a stent graft,
a shunt, a flow restrictor, or an occluder, having proximal and
distal ends and a side wall extending therebetween. At least a
portion of the side wall can be a corrugated portion that extends
partially between the proximal and distal ends. The corrugated
portion has a first diameter and has a corrugated surface. The side
wall further includes at least one non-corrugated portion adjacent
the corrugated portion. The non-corrugated portion may extend
partially between the proximal and distal ends, and has a second
diameter not equal to (e.g., less than) the first diameter. The
side wall may include at least one layer of a metallic material
configured to be compressed and heat set to define the corrugated
portion. The at least one corrugated portion can be located
adjacent to the proximal end or the distal end. In some
embodiments, the side wall may include a plurality of corrugated
portions, with a pair of the corrugated portions separated by the
at least one non-corrugated portion.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0020] FIG. 1 is a perspective view of a stent graft configured in
accordance with an exemplary embodiment;
[0021] FIG. 2 is a magnified side elevational view of the area
labeled 2 in FIG. 1;
[0022] FIGS. 3 and 4 are schematic side views of stent grafts
configured in accordance with exemplary embodiments, the stent
grafts respectively demonstrating differing arrangements of the
corrugations of the corrugated surface;
[0023] FIG. 5 is a perspective view of the stent graft of FIG. 1
showing the stent graft in an axially compressed configuration
relative to the configuration of FIG. 1;
[0024] FIG. 6 is a magnified side elevational view of the area
labeled 6 in FIG. 5;
[0025] FIG. 7 is a perspective view of the stent graft of FIG. 1
showing the stent graft in an axially elongated configuration
relative to the configuration of FIG. 1;
[0026] FIG. 8 is a magnified side elevational view of the area
labeled 8 in FIG. 7;
[0027] FIGS. 9-13 are perspective views of a stent graft at various
stages of a process for producing a stent graft configured in
accordance with an exemplary embodiment;
[0028] FIGS. 14 and 15 are sketches of an aortic coarctation (14)
and a stent graft placed in the coarctation (15) according to one
embodiment of the present invention;
[0029] FIGS. 16 and 17 are side elevational views of a system for
delivering a stent graft to a target site in a body according to
one embodiment of the present invention;
[0030] FIG. 18 is a perspective view of a stent graft having both
corrugated and non-corrugated portions according to one embodiment
of the present invention;
[0031] FIGS. 19 and 20 are side elevational views demonstrating the
use of a stent graft configured in accordance with an exemplary
embodiment in treating an aortic dissection;
[0032] FIGS. 21 and 22 are side elevational views of stents having
multiple corrugated portions separated by non-corrugated portions
according to exemplary embodiments of the present invention;
[0033] FIG. 23 is a side elevational view of a stent graft
configured in accordance with another exemplary embodiment;
[0034] FIG. 24 is a side elevational view of an occlusion device
configured in accordance with an exemplary embodiment;
[0035] FIG. 25 is a perspective view of a stent graft according to
another embodiment of the present invention; and
[0036] FIGS. 26 and 27 illustrate graphical representations of
experimental data for various stent grafts according to embodiments
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
some, but not all embodiments of the invention are shown. Indeed,
this invention may be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein;
rather, these embodiments are provided so that this disclosure will
satisfy applicable legal requirements. Like numbers refer to like
elements throughout.
[0038] Embodiments of the present invention provide a medical
device for use in treating a target site within the body, such as
excluding or occluding various vascular abnormalities, which may
include, for example, excluding an aneurysm, or occluding an
Arterial Venous Malformation (AVM), an Atrial Septal Defect (ASD),
a Ventricular Septal Defect (VSD), a Patent Ductus Arteriosus
(PDA), a Patent Foramen Ovale (PFO), a Left Atrial Appendage (LAA),
conditions that result from previous medical procedures such as
Para-Valvular Leaks (PVL) following surgical valve repair or
replacement, and the like. The device may also be used as a flow
restrictor or a shunt, filter or other type of device for placement
in the vascular system, as well as a graft for lining a lumen of a
vessel. It is understood that the use of the term "target site" is
not meant to be limiting, as the device may be configured to treat
any target site, such as an abnormality, a vessel, an organ, an
opening, a chamber, a channel, a hole, a cavity, or the like,
located anywhere in the body. For example, the abnormality could be
any abnormality that affects the shape or the function of the
native lumen, such as an aneurysm, a lesion, a vessel dissection,
flow abnormality or a tumor. Furthermore, the term "lumen" is also
not meant to be limiting, as the abnormality may reside in a
variety of locations within the vasculature, such as a vessel, an
artery, a vein, a passageway, an organ, a cavity, or the like.
[0039] As used herein the term "proximal" shall mean closest to the
operator (less into the body) and "distal" shall mean furthest from
the operator (further into the body). In positioning of the medical
device from a downstream access point, distal is more upstream and
proximal is more downstream.
[0040] As explained in further detail below, embodiments of the
present invention provide medical devices for treating various
target sites. The medical devices may include one or more
corrugated surfaces that may increase the radial strength of the
devices such as by having an increased density. Thus, the
corrugated surfaces may improve the fixation of the medical devices
at a target site. Moreover, the corrugated surfaces may facilitate
occlusion at the target site for treating various abnormalities,
while remaining conformable and flexible for delivery to various
target sites.
[0041] With reference to FIG. 1, therein is shown a perspective
view of a medical device 100 for treating a target site within a
body. The medical device 100 of FIG. 1 could be used in a variety
of ways, including as a stent, a stent graft, an occluder, a shunt,
or a flow restrictor, depending on the application. As a matter of
convenience, the medical device 100 will simply be referred to as a
stent graft. The stent graft 100 includes a structure, such as a
tube 102, having proximal and distal ends 104, 106 and a side wall
108 extending therebetween. The side wall 108 may be cylindrical in
shape or any other suitable shape for being positioned within a
vessel or the like. The side wall 108 has a corrugated surface 110
that includes a plurality of corrugations 111.
[0042] Referring to FIG. 2, therein is shown a magnified view of
the stent graft 100 that more clearly illustrates the tube 102 and
corrugated surface 110. The tube 102 can include at least one layer
(and in some cases multiple layers) of an occlusive material, such
as a metallic fabric 112. The fabric 112 can be composed of
multiple metallic strands 114. Although the term "strand" is
discussed herein, "strand" is not meant to be limiting, as it is
understood the fabric may comprise one or more wires, cords,
fibers, yarns, filaments, cables, threads, or the like, such that
such terms may be used interchangeably. The stent graft 100 may be
a variety of occlusive materials capable of at least partially
inhibiting blood flow therethrough in order to facilitate the
formation of thrombus and epithelialization around the device.
[0043] According to one embodiment, the metallic fabric may include
two sets of essentially parallel generally helical strands, with
the strands of one set having a "hand", i.e., a direction of
rotation, opposite that of the other set. The strands may be
braided, interwoven, or otherwise combined to define a generally
tubular fabric. The pitch of the strands (i.e., the angle defined
between the turns of the strands and the axis of the braid) and the
pick of the fabric (i.e., the number of wire strand crossovers per
unit length) may be adjusted as desired for a particular
application. The wire strands of the metal fabric used in one
embodiment of the present method may be formed of a material that
is both resilient and can be heat treated to substantially set a
desired shape. One factor in choosing a suitable material for the
wire strands is that the wires retain a suitable amount of the
deformation induced by the molding surface (as described below)
when subjected to a predetermined heat treatment and elastically
return to said molded shape after substantial deformation.
[0044] For example, in one embodiment, the fabric 112 may form a
braided tubular member by wrapping a number of filaments in a left
helix about a mandrel (e.g., a 15 mm diameter mandrel), while other
filaments are wrapped in a right helix. The filaments of one
helical direction alternately pass over and then under the
filaments of the other helical direction (e.g., two at a time) to
form the braided tubular member. The filaments can be, say, wire
filaments with diameters of about 0.0035 inches, and can be spaced
apart in parallel fashion with 36 filaments in each helical
direction and a pick count of 50. Commercial braiding machines,
such as those offered by Wilhelm STEEGER GmbH & Co. (Wuppertal,
Germany) can be utilized to perform such a braiding process.
Following braiding, the braided tubular member may be placed in an
oven until reaching a temperature of about 425.degree. C. for about
15-20 seconds in order to stabilize the diameter of the braided
tubular member and to improve handling by minimizing
unraveling.
[0045] The metallic fabric 112 can be configured to be compressed
and heat set to define the corrugated surface 110. That is, the
fabric 112 can be composed of materials and/or structurally
arranged such that compression causes the fabric to assume a
corrugated configuration at a surface of the fabric. The
constituent materials can further be configured such that heat can
then be applied to the fabric 112 in order to allow the fabric to
maintain the corrugated configuration, under at least some
conditions, without the application of external force. The process
by which a medical device incorporating a corrugated metal fabric
can be produced is discussed in more detail below. In one
embodiment, metallic fabric 112 can include a shape memory alloy,
such as Nitinol (e.g., 72 strands of Nitinol wire). It is also
understood that the stent graft 100 may comprise various materials
other than Nitinol that have elastic properties, such as spring
stainless steel, trade named alloys such as Elgiloy, Hastalloy,
Phynox, MP35N, or CoCrMo alloys.
[0046] The metallic fabric 112 can also be configured to facilitate
thrombosis, for example, by at least partially inhibiting blood
flow therethrough in order to facilitate the formation of thrombus
and epithelialization around the stent graft 100. In particular,
the braid of the metallic fabric 112 may be chosen to have a
predetermined pick and pitch to define openings or fenestrations so
as to vary the impedance of blood flow therethrough. For instance,
the formation of thrombus may result from substantially precluding
or impeding flow, or functionally, that blood flow may occur for a
short time, e.g., about 3-60 minutes through the metallic fabric
112, but that the body's clotting mechanism or protein or other
body deposits on the braided wire strands results in occlusion or
flow stoppage after this initial time period. For instance,
occlusion may be clinically represented by injecting a contrast
media into the upstream lumen of the stent graft 100 and if no
contrast media flows through the wall of the stent graft after a
predetermined period of time as viewed by fluoroscopy, then the
position and occlusion of the stent graft is adequate. Moreover,
occlusion of the target site could be assessed using various
ultrasound echo doppler modalities.
[0047] Referring to FIGS. 2-4, the corrugated surface 110 may
include a plurality of corrugations 111. The corrugations 111 may
include a plurality of annular ridges 115a that each extend about
an entire circumference of the tube 102 and that are separated from
one another by grooves 117 (e.g., peaks and valleys).
Alternatively, or in some cases additionally, the tube 102 may
include adjacent staggered portions 115b that are transversely
offset from one another along the length of the tube 102, with
respect to a central axis a defined by the tube, such that the
staggered structure of the tube collectively define the
corrugations 111. In either case, the corrugated surface 110 may
have a somewhat sinusoidal profile along a direction aligned with
the central axis a. Note that the portions constituting peaks on
one surface become valleys when traveling circumferentially around
to the other side. The ridges of the corrugated surface extend
circumferentially about the tube at various angles.
[0048] Referring to FIGS. 1, 2, and 5-8, the tube 102 may have an
"expanded" shape (e.g., as depicted in FIG. 3), and the tube may be
configured to be constrained so as to have a smaller diameter than
in the expanded shape. The shape of the tube 102, when constrained,
can be referred to as the "reduced" shape, and an example of a
reduced shape is depicted in FIG. 7. In some embodiments, the tube
102 can be forced into the reduced shape, and will assume the
expanded shape upon the removal of any constraining forces. As will
be discussed further below, the reduced shape may facilitate
delivery of the medical device 100 within a catheter to a target
site, at which point the medical device can be released from the
catheter in order to allow the tube 102 to assume the expanded
shape.
[0049] In embodiments in which the tube 102 includes metal fabric
112 that is braided, the braided structure may allow for the tube
to be forced into the reduced shape by axially elongating the tube.
For example, the tube 102 could be axially elongated by applying
axially-directed tension to the tube, or by radially compressing
the tube. As the tube 102 is elongated, at least a portion of the
corrugated surface 110 may have a generally sinusoidal profile
along a direction generally aligned with a central axis a.
Considering the embodiment described above in which a braided
tubular member is formed by wrapping 72 Nitinol strands with
diameters of about 0.0035 inches in left and right helices about a
15 mm mandrel, the filaments being spaced apart in parallel fashion
with 36 filaments in each helical direction and having a pick count
of 50, axial elongation of a braided member having a length of
about 4 cm in the corrugated configuration (resulting in an inside
diameter of about 16 mm and an outside diameter of about 17-18 mm)
results in a reduced shape in which the braided member is about 70
cm long (or an elongation ratio of about 17.5:1) and a collapsed
diameter of less than about 3 mm (9 French) or even 2 mm (6
French). As such, a ratio of the inner diameters of the tube 102
for the expanded configuration and the reduced configuration may be
about 8:1.
[0050] Referring to FIGS. 9-13, therein are schematically depicted
various aspects of a process for producing a medical device as
discussed above, or, relatedly, for increasing the radial strength
of a medical device by effecting a structure as discussed above. As
shown in FIG. 9, the process includes forming a structure in a
non-compressed configuration, such as a tube 202, that includes at
least one layer 212 (and in some cases multiple layers) of metallic
material, the tube having proximal and distal ends 204, 206 and a
side wall 208 extending therebetween. In the illustrated
embodiment, the side wall 208 is formed by the layer 212 of
metallic material and is entirely cylindrical. In other
embodiments, the side wall need not be entirely cylindrical,
although at least a portion of the side wall would usually be
cylindrical in shape in order to conform to a vessel lumen.
[0051] It is noted that, in some embodiments, a traditional
stent/stent graft structure can be used as the tube 202. For
further details regarding the structure, exemplary dimensions, and
methods of making a stent/stent graft, Applicants hereby
incorporate by reference U.S. Patent Appl. Publ. No. 2007/0168018,
filed on Jan. 13, 2006, and U.S. Patent Appl. Publ. No.
2007/0168019, filed on Jan. 17, 2007, herein in their entirety.
[0052] Referring to FIGS. 10 and 11, the cylindrical portion of the
side wall 208 (which in the illustrated case is the entire side
wall) can be compressed such that the sidewall defines a corrugated
surface 210 extending at least partially (or, in the illustrated
case, completely) between the proximal and distal ends 204, 206.
For example, the side wall 208 can be axially compressed, as
depicted in FIG. 11. In some embodiments, the tube 202 can be at
least partially formed from a plurality of metallic strands 214.
The tube 202 may be compressed in order to cause the strands 214 to
be condensed into a somewhat closely-packed (or even abutting)
configuration, as shown in FIG. 10 (the "compressed, non-corrugated
configuration"). The tube 202 may then be further compressed in
order to cause some of the strands 214 to buckle, usually
repeatedly, as shown in FIG. 11 (the "corrugated configuration").
The repeatedly buckled configuration of the strands 214 may then
define the corrugated surface 210.
[0053] In some embodiments, the tube 202 may be formed from 72
Nitinol wires of about 0.002 inches in diameter and have a braid
pick count of about 48 ppi prior to compression. The tube 202 may
have an outer diameter of about 15.621 mm and an inner diameter of
about 15.392 mm (i.e., a nominal diameter of about 15.5 mm). Thus,
each corrugation 211 may have a wall thickness of about 0.20-0.23
mm (0.008 to 0.009 inches). In addition, the corrugated surface 210
may have corrugations 211 spaced apart from one another by about
0.25 mm (0.010 inches).
[0054] As mentioned above and shown in FIG. 11, the heights h of
the corrugations 211 may be small relative to the diameter d of the
tube 202. However, for some embodiments, the length of the tube 202
in the corrugated configuration can be as little as 25% of the
length of the tube when in the compressed, non-corrugated
configuration. As such, in cases where the embodiments include
metal fabric composed of a plurality of strands, the strand density
in the corrugated configuration is significantly increased with
respect to the non-compressed or compressed, non-corrugated
configuration. Also, some embodiments may exhibit a circumferential
stiffness or "hoop strength" per unit length of the tube 202 when
in the corrugated configuration that is markedly increased relative
to the hoop strength per unit length of the tube when in the
non-compressed or compressed, non-corrugated configuration. This
increase in strength in the corrugated configuration may be
especially pronounced for embodiments incorporating braided metal
fabric, as the corrugated configuration may result in a higher
helix angle and a higher density of the constituent metal strands.
Thus, the corrugated surface may provide an increase in radial
strength or resistance to radial compression.
[0055] Once the side wall 208 has been compressed, heat can be
applied to the tube 202 in order to heat set the side wall 208. In
some cases, compressive forces may continue to be applied to the
side wall 208 simultaneously with heat, for example, by placing the
medical device 200 into a mold 230 (see FIG. 12). The device 200
and mold 230 can then be together placed into an oven and heated.
In other cases, the side wall 202 may be compressed and then all
compressive forces may be removed before heat is applied. In either
case, following heat setting of the side wall 208, the side wall
will exhibit a persistent corrugated surface 210 without the
application of a compressive or restrictive force (see FIG. 13). As
mentioned previously, the corrugated surface may have helical
ridges that provide a lead or thread-like pitch. The corrugated
surface may be formed, for example, using an external or internal
mold or both to facilitate formation of the corrugated surface or
to induce a thread-like pitch to the corrugation.
[0056] The device 200 can be heated until the side wall 208 reaches
the desired temperature, which temperature is dictated by the
materials used to form the side wall and is the temperature at
which the side wall will become heat set. For example, for side
walls composed of a shape memory alloy, the "desired" temperature
would be the temperature at which formation of the material's
austenitic phase is complete. In some embodiments, side walls
formed of 72 Nitinol strands may be sufficiently heat set by
heating the device 200 from room temperature to about 520.degree.
C. over a span of about 18 minutes.
[0057] The particular configuration of the corrugated surface may
depend on the wire diameter, number of wires, type of corrugations,
and braided tube diameter. For example, the corrugated surface may
include a plurality of annular ridges, or according to one
exemplary embodiment shown in FIG. 25, the corrugated surface 910
of the braided tube 902 may include one or more spiral or helical
ridges 911 that extend both circumferentially and longitudinally
along the tube. The corrugations 911 may have a lead or thread-like
pitch. For instance, the corrugated surface 910 may match that of a
5-10.times.11 threads/inch bolt. Thus, the corrugated surface 910
may have 11 corrugations per inch. The tube 902 may be formed using
144 Nitinol wires of about 0.003 inches in diameter that are formed
on a 22 mm diameter mandrel and heat set at about 530.degree. C.
over 10 minutes. The tube 902 may have a braid pick count of about
75 ppi. In its relaxed and expanded configuration, the inner
diameter of each corrugation 911 may be about 16 mm, while the
outer diameter may be about 19.2 mm.
[0058] FIGS. 26 and 27 illustrate exemplary data showing the
increased radial strength or resistance to radial compression that
may be experienced with embodiments of the present invention. In
particular, FIG. 26 shows compressive extension (mm) plotted
against compressive load (lbf) for a medical device having a
corrugated surface, such as that shown in FIG. 25, and for a
medical device not having corrugations. The medical device without
corrugations was braided in the same manner as the corrugated
medical device. The test involved radially compressing each medical
device between 1 inch square plates 2 mm and then releasing the
force. FIG. 26 shows that the medical device having the threaded
corrugations has larger radial strength than the medical device
without corrugations. For instance, at the maximum extension of 2
mm, the threaded device has a resistive compressive load of about
0.033 lbf, while the medical device without corrugations exhibits a
resistive compressive load of about 0.01 lbf. Therefore, the
medical device with threaded corrugations may provide at least a
three-fold increase in resistance to radial compression.
[0059] FIG. 27 depicts a similar graph for the corrugated medical
device, such as a medical device shown in FIG. 6 that includes a
corrugated surface formed by axial compression, and for a
non-corrugated medical device, wherein the non-corrugated medical
device has been braided in a similar manner. The corrugated medical
device again exhibits a greater radial strength than the
non-corrugated medical device. In particular, at 2 mm of
compressive extension, the corrugated medical device provides a
resistive compressive load of 0.051 lbf while the non-corrugated
medical device has a resistive compressive load of about 0.025 lbf.
Thus, in this particular example, the corrugated medical device
provides about 2 times the resistance to radial compression.
[0060] As mentioned earlier, medical devices configured in
accordance with exemplary embodiments can be useful in a variety of
medicinal purposes. Referring to FIGS. 14 and 15, therein are
depicted the use of a stent graft 300 configured in accordance with
an exemplary embodiment for treating a vascular abnormality, an
aortic coarctation ac, at a target site within a body, e.g., the
lumen of an aorta ao. Aortic coarctation is a narrowing of the
aorta in the area where the ductus arteriosus inserts. In the
illustrated embodiment, the stent graft 300 has a corrugated
surface along its entire length. By delivering the stent graft 300
to the location of the aortic coarctation ac, the stent graft tends
to urge wider the affected portion of the aorta ao. The corrugated
configuration of the stent 300 increases the circumferential
stiffness of the stent graft, thereby enhancing the ability of the
stent graft to urge open the affected vessel and to maintain the
patency of the vessel.
[0061] Referring to FIGS. 1, 7, 16, and 17, in order to deliver the
stent graft 100 to a target site within the body, the tube 102 may
be first constrained from an expanded shape (see FIG. 1) to a
smaller diameter (see FIG. 7). For example, where the metallic
material 112 of the tube 102 is a braided metallic fabric that
forms a braided tubular member, the tube may have a first diameter
and may be capable of being collapsed to a second, smaller diameter
by axially elongating the ends of the tube. In some embodiments,
the tube 102 may be constrained to an outer diameter of less than
15 French for delivery within a catheter.
[0062] The constrained tube 102 can then be positioned in a
delivery catheter 440 (see FIG. 16), which is a catheter that
defines an axial bore 441 (FIG. 17) for receiving the tube therein.
The tube 102 may be coupled to a delivery device 444. According to
one embodiment, the delivery device 444 includes an elongated
tubular member 445 having an inside diameter sized to receive a
guidewire 442 or, alternatively, the delivery device may employ a
solid wire or cable in place of the tubular member (discussed
further below). The tubular member 445 may, for example, be
fabricated from a high density polyethylene, Pebax nylon,
polyimide, hollow cable, composite braided polymer, or even a
hypotube of stainless steel or Nitinol. The tubular member 445 may
pass within the delivery catheter 440 (i.e., through the bore 441)
and, in one embodiment, includes a molded distal end 446 that has
an outside profile matching the interior contour of the constrained
tube 102.
[0063] The delivery device 444 may extend through the bore 441 of
the delivery catheter 440 such that the molded distal end 446 of
the delivery device extends beyond the distal end 443 of the
catheter. The tube 102 can be coupled to the molded distal end 446
of the delivery device 444, and thereafter, pulling the delivery
device 444 proximally relative to the delivery catheter 440 moves
the tube into the delivery catheter 440. The tube 102 is then
trapped between the delivery catheter 440 and the molded distal end
446 of the delivery device 444 in order to maintain the tube in the
constrained configuration during delivery.
[0064] The catheter 440 and stent graft 100 can be advanced over
the guidewire 442 until disposed at the target site, where the tube
102 can be deployed from the catheter by advancing the delivery
device 444 distally relative to the catheter. Alternatively, the
catheter may be retracted proximally relative to the delivery
device a small distance followed by advancement of the delivery
device relative to the catheter. Once the tube 102 has been
advanced completely out of the catheter 440, the tube may assume
the expanded shape (to the extent permitted by the surrounding
vasculature). In some embodiments, the tube 102 may self-expand
upon being deployed from the catheter 440 as the constraining
forces of the catheter are removed. In other embodiments, the tube
102 may be physically urged into or toward the expanded shape, say,
by inflating a balloon located within the tube (post dilatation),
or by axially compressing the tube using the delivery device 444
during deployment from the catheter 440 but prior to release of the
proximal end of the tube. In any event, until such time as the tube
102 has been advanced entirely beyond the catheter 440, the stent
graft 100 may be fully retrievable by the catheter for removal or
repositioning.
[0065] In some embodiments, medical devices configured in
accordance with exemplary embodiments may include multiple
corrugated portions. For example, referring to FIG. 18, a medical
device, such as a stent graft 500, a shunt, a flow restrictor, or
an occluder, may have a structure, such as a tube 502, having
proximal and distal ends 504, 506 and a side wall 508 extending
therebetween. The side wall 508 has at least a portion that is
cylindrical in shape and includes at least one corrugated portion
509a that extends partially between the proximal and distal ends
504, 506. The corrugated portion 509a has a first diameter d1 and
has a corrugated surface 510 including a series of corrugations
511. The side wall 508 can further include at least one
non-corrugated portion 509b adjacent the corrugated portion 509a.
The non-corrugated portion 509b also extends partially between the
proximal and distal ends 504, 506, and has a second diameter d2
that is not equal to (e.g., less than) the first diameter d1.
[0066] The tube 502 may include at least one layer 512 (and in some
cases multiple layers) of a metallic material that is configured to
be compressed and heat set to define the corrugated portion 509a.
The metallic material may be configured to facilitate thrombosis.
The corrugated portion 509a and non-corrugated potion 509b can be
arranged such that the corrugated portion is adjacent to the
proximal end 504 (as shown in FIG. 18) or to the distal end 506, or
such that the non-corrugated portion is located centrally in the
tube 502 and adjacent to neither end.
[0067] In order to fabricate a medical device such as the stent
graft 500, one can start with a stent graft including an
uncompressed tube as discussed above (see the stent graft of FIG.
9, which could be used to produce the stent graft 500 above).
However, when forming the tube 502 of the stent graft 500 in order
to define the corrugated portion 509(a), it may not be necessary to
compress the tube along its entire length but, instead, only a
section corresponding to the corrugated portion 509a is axially
compressed. This allows, for example, for a stent graft 500 to have
one or more compressed corrugated portions 509a while the remaining
portion(s) of the stent graft has non-corrugated portion(s). Such
targeted axial compression can be applied to any region(s) of the
tube 502. Thus, a wide array of medical devices may be fabricated
with one or more corrugated portions that may have increased
material density or improved hoop strength relative to the
non-corrugated portions.
[0068] Referring to FIGS. 18-20, the stent graft 500 may prove
useful in the treatment of a dissection di of the aorta ao. It is
desirable to seal the origin o of the dissection as well as add
support to the vessel for healing, thereby keeping the vessel fully
open. With these objectives in mind, the stent graft 500 is
deployed in the aorta ao so as to support the vessel wall in the
area of the dissection di and further such that the corrugated
portion 509a is adjacent to the area of the vessel wall
corresponding to the origin o of the dissection. In this way, the
stent graft 500 provides general support for the vessel while
providing added pressure to the area of the vessel wall
corresponding to the origin o of the dissection, wherein the
additional pressure is due to the increased circumferential
stiffness of the stent graft in the corrugated portion 509a.
[0069] Referring to FIGS. 21 and 22 and according to additional
embodiments, each medical device 600 may include a tube 602 with a
plurality of corrugated portions 609a that each has a corrugated
surface 610. Some or all of the corrugated portions 609a can be
respectively separated from one another by non-corrugated portions
609b. In some embodiments, corrugated portions 609a may be located
adjacent to the proximal end 604 of the tube 602, the distal end
606, or both. Overall, the methods described herein can be used to
create medical devices with a wide range of geometries that may be
tailored for target applications. For example, referring further to
FIG. 23, in still another embodiment, a stent graft 700 can be
developed with a corrugated portion 709a and a non-corrugated
portion 709b that increases in diameter when moving away from the
corrugated portion. This stent graft 700 may be well suited for
treating of abdominal aortic aneurysms, such as by providing
opposed ends configured to anchor the stent graft on either side of
the aneurysm.
[0070] An exemplary procedure for delivering a stent graft
configured in accordance with an exemplary embodiment, including
the above discussed embodiments, to a target location within the
thoracic aorta is now described. First, access to the femoral
artery is gained, for example, by use of the Seldinger technique,
and an introducer sheath is placed through the skin into the
femoral artery. A guidewire is advanced through the femoral and
iliac arteries and along the upper aorta until the point at which
it crosses the target location. The stent graft is then loaded into
the bore of a delivery catheter using a delivery device. The
delivery device includes a distal tubular member with a bead at the
distal end attached to an axial manipulation wire, cable or tube
that engages the proximal end of the stent graft between the
tubular member and bead, such as disclosed in patent application
U.S. Patent Appl. Publ. No. 2007/0118207, which is incorporated in
its entirety herein. The delivery device is then retracted
proximally through the delivery catheter until the stent graft just
extends out of the distal end of the delivery catheter. It is noted
that an introducer tool may prove helpful in accomplishing this
step.
[0071] The proximal end of the guidewire may be inserted into the
distal end of the stent graft, delivery device, and the delivery
catheter, and the delivery catheter may be advanced partially over
the guidewire. While the distal end of the delivery catheter is
still outside the body, the delivery device is pulled proximally to
draw the distal end of the stent graft fully into the delivery
catheter. The delivery catheter can then be introduced through the
access sheath and over the guidewire to the target site within the
body.
[0072] When the delivery catheter reaches the target site in the
body, the delivery device can be advanced to expel the distal end
of the stent graft from the delivery catheter or alternatively the
delivery catheter can be pulled proximally relative to the delivery
device. Prior to extending the contoured portion of the delivery
device out the distal end of the delivery catheter, the position of
the stent graft may be assessed. The location of contact between
the stent graft and the vessel wall can be observed with various
imaging techniques, such as angiography in order to assure
appropriate placement of the stent graft. If the stent graft is not
placed correctly, it can be drawn back into the catheter by pulling
proximally on the delivery device while holding the delivery
catheter stationary. If the placement is as intended, the distal
portion of the delivery device may be extended out of the distal
end of the delivery catheter and the beaded portion advanced
distally relative to the tubular member to release the stent graft.
The delivery catheter, delivery device, and guidewire can then be
removed from the body.
[0073] In an alternative procedure for delivering a stent graft to
a target location in accordance with an exemplary embodiment, the
delivery catheter, without a stent graft loaded, may be advanced
over the guidewire to the treatment site. The stent graft proximal
end may be connected to the distal end of the delivery device as
previously described. The stent graft may be elongated to reduce
the diameter for insertion into the proximal end of introducer
tool. The introducer tool may have a distal tapered end to engage
the lumen of the delivery catheter and a longitudinal slit for
removal. The stent graft may be compressed and advanced into the
introducer tool until the proximal end of the stent graft is
adjacent the proximal end of the introducer. The insertion tool,
stent graft and delivery device distal end can then be placed and
advanced over the guidewire until the insertion tool distal end is
engaged into the delivery catheter lumen at the proximal end.
Advancement of the delivery device moves the stent graft into the
bore of the delivery catheter. The stent graft may then be advanced
as previously described in order to deploy the stent graft at the
treatment site.
[0074] In still another alternative procedure for delivering to a
target location a stent graft configured in accordance with an
exemplary embodiment, a delivery device that replaces the tubular
member with an eccentric wire shaft may be utilized. This design
for the delivery device, when used for over-the-guidewire delivery,
allows the guidewire to run along side the wire shaft (rather than
through a tubular shaft as in the above-described procedure). This
can allow for the use of shorter rapid exchange length guidewires
and facilitate easier device exchange if needed.
[0075] Referring to FIG. 24, therein is shown a side elevational
view of an occlusion device 800 utilizing a compressed braid 802
configured in accordance with an exemplary embodiment. The
compressed braid 802 is constructed and configured as discussed
previously. The device 800 has a disk flange member 850 at one end
and a cylindrical member 852 adjacent thereto, connected by an
articulation member 854. The compressed braid 802 is positioned on
the cylindrical member 852 to provide high radial support for
anchoring the device 800 in a vessel. The free ends of the metallic
fabric may be secured by clamps 856, 858, as known to those of
ordinary skill in the art. For example, the clamp 858 may be
configured to engage a delivery device. For example, the delivery
device may include a threaded distal end for engagement with a
threaded bore formed in the clamp 858 of the occlusion device 800.
Further discussion and examples of the procedures by which an
occlusion device configured in accordance with exemplary
embodiments can be delivered are provided in U.S. patent
application Ser. No. 11/966,397 filed Dec. 28, 2007, which is
hereby incorporated by reference in its entirety.
[0076] Many modifications and other embodiments of the invention
set forth herein will come to mind to one skilled in the art to
which this invention pertains having the benefit of the teachings
presented in the foregoing descriptions and the associated
drawings. For example, the side wall need not be entirely
cylindrical. Rather, only a portion of the side wall may be
cylindrical, with other portions, for example, having irregular or
planar surfaces. Further, while some procedures for delivering a
medical device configured in accordance with an exemplary
embodiment have been described above, other delivery procedures are
also possible. For example, certain embodiments are compatible with
the graft delivery systems previously disclosed as described in
U.S. Pat. Appl. Publ. No. 2007/0118207A1. Considering delivery
devices and delivery catheters for medical devices such as
occlusion, flow restrictor, and shunt devices, these can generally
involve a threaded delivery cable that is threaded to the medical
device. The medical device can be collapsed for delivery through
the bore of a delivery catheter. The threaded delivery device is
used to advance the device through the catheter and artery to the
treatment site, at which point the medical device self-expands upon
exiting the distal end of the delivery catheter in order to lodge
within the vasculature. The delivery device is unthreaded from the
device once the proper deployment has been achieved. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *