U.S. patent application number 09/780145 was filed with the patent office on 2001-07-12 for intravascular hinge stent.
Invention is credited to Drasler, William J., Thielen, Joseph M..
Application Number | 20010007955 09/780145 |
Document ID | / |
Family ID | 23175960 |
Filed Date | 2001-07-12 |
United States Patent
Application |
20010007955 |
Kind Code |
A1 |
Drasler, William J. ; et
al. |
July 12, 2001 |
Intravascular hinge stent
Abstract
The hinge stent is a balloon-expandable or self-expandable
intravascular endoprosthesis used for treatment of vascular injury.
The hinge stent is formed of a single stent section or of multiple
stent sections joined together. Each stent section has a node and
strut structure extending throughout in order to uncouple expansion
forces of the stent to hold a blood vessel outward from crush
forces that resist the formation of an oval shape during a crush
deformation. Each node includes a hinge which is joined via a
transition region to a strut. The hinge can bend in the direction
of a uniformly curved surface of the stent but not in the radial
direction. The strut can bend in the radial direction but not in
the uniformly curved surface of the stent. The widths, lengths, and
radial dimensions of the hinges and struts provide a
balloon-expandable hinge stent that is non-crushable. For a
self-expandable stent the hinge and strut dimensions provide
expansion forces that are controlled independently from crush
forces. The hinge stent can be formed of a high modulus metal with
expansion properties being determined by the hinge dimensions and
crush properties being determined independently by the design of
the strut dimensions. The node and strut structure of the hinge
stent provides for flexibility in traversing along tortuous
passages.
Inventors: |
Drasler, William J.;
(Minnetonka, MN) ; Thielen, Joseph M.; (Buffalo,
MN) |
Correspondence
Address: |
William J. Drasler
4100 Dynasty Drive
Minnetonka
MN
55345
US
|
Family ID: |
23175960 |
Appl. No.: |
09/780145 |
Filed: |
February 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09780145 |
Feb 9, 2001 |
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09304310 |
May 3, 1999 |
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Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2002/91541
20130101; A61F 2/915 20130101; A61F 2002/91558 20130101; A61F
2220/0016 20130101; A61F 2/88 20130101; A61F 2/91 20130101; A61F
2230/0054 20130101; A61F 2250/0036 20130101; A61F 2002/9155
20130101 |
Class at
Publication: |
623/1.15 |
International
Class: |
A61F 002/06 |
Claims
We claim:
1. An expandable stent deliverable to the site of a lesion within a
tubular vessel of the body in a nondeployed state with a smaller
nondeployed diameter and capable of undergoing an expansion
deformation to a deployed state with a larger deployed diameter and
be implanted within the tubular vessel in order to hold the wall of
the tubular vessel outward, said expandable stent comprising; A. a
first stent section, said first stent section being comprised
entirely of nodes and struts with each of said struts extending
between two of said nodes, said first stent section being formed of
a plurality of repeat units, each of said plurality of repeat units
being joined together to form said stent section, B. each of said
nodes having one or more hinges, said hinges providing for movement
of said struts within a uniform surface of said stent section, C.
each of said hinges having a hinge width, a hinge length, and a
hinge radial dimension which do not allow said hinges to bend in a
radial direction due to a crush deformation and which allow said
hinges to bend in a uniform surface of said expandable stent due to
the expansion deformation and provide said expandable stent in the
deployed state with an expansion force against the tubular vessel
wall, D. each of said struts having a strut width, a strut length,
and a strut radial dimension which do not allow said struts to bend
in the uniform surface of said expandable stent, and which allow
said hinge to bend substantially elastically in the radial
direction due to crush deformation and provide said expandable
stent in a deployed state with a crush elastic bending force,
whereby said expandable stent providing an uncoupling of the
expansion force of said hinge from the elastic bending force of
said strut such that these forces can be varied independently from
one another.
2. An expandable stent deliverable to the site of a lesion within a
tubular vessel of the body in a nondeployed state with a smaller
nondeployed diameter and capable of undergoing an expansion
deformation to a deployed state with a larger deployed diameter and
be implanted within the tubular vessel in order to hold the wall of
the tubular vessel outward, said expandable stent comprising; A. a
first stent section, said first stent section being comprised
entirely of nodes and struts with each of said struts extending
between two of said nodes, each of said nodes having one or more
hinges and at least two transition regions, B. said nodes and
struts forming a continuous configuration extending continuously
throughout said first stent section, said first stent section being
deliverable as said expandable stent, C. each of said hinges having
a hinge width, a hinge length, and a hinge radial dimension which
do not allow said hinges to bend in a radial direction due to a
crush deformation and which allow said hinges to bend in a uniform
surface of said expandable stent due to the expansion deformation,
said hinges providing movement for said struts within the uniform
surface of said expandable stent, and provide said expandable stent
in the deployed state with an expansion force against the tubular
vessel wall, D. each of said struts having a strut width, a strut
length, and a strut radial dimension which do not allow said struts
to bend in the uniform surface of said expandable stent, and which
allow said struts to bend elastically in the radial direction due
to crush deformation and provide said expandable stent in a
deployed state with a crush elastic bending force, whereby said
expandable stent provides an uncoupling of the expansion force of
said hinge from the elastic bending force of said strut such that
these forces can be varied independently from one another.
3. The expandable stent of claim 1 wherein said hinge length, said
hinge width, and said hinge radial dimension provide each of said
hinges with a plastic deformation during the expansion deformation
from a nondeployed state to a deployed state.
4. The expandable stent of claim 3 wherein said hinges undergo
plastic deformation during expansion deformation and said struts
undergo elastic deformation during crush deformation to provide
said stent with being balloon-expandable and non-crushable.
5. The expandable stent of claim 1 wherein said hinge length, said
hinge width, and said hinge radial dimension provide said hinges
with an elastic deformation during the expansion deformation from a
nondeployed state to a deployed state, said stent being
self-expandable, said stent having an expansion deformation force
controlled by said hinges and a crush deformation force controlled
independently by said struts.
6. The expandable stent of claim 1 wherein said first stent section
has a first stent section body having three or more struts per
node.
7. The expandable stent of claim 1 wherein said first stent section
is comprised of a series of struts and nodes forming a helical
structure extending continuously throughout said first stent
section.
8. The expandable stent of claim 7 wherein said helical structure
is comprised of helical repeat units with one or more connecting
nodes, each of said helical repeat units being joined to another of
said helical repeat units located adjacently by one or more hinged
interconnectors joined between connecting nodes of said repeat
units.
9. The expandable stent of claim 1 wherein said hinge width, said
hinge length, and said hinge radial dimension are modified near the
ends of said expandable stent in comparison to the mid-length of
said expandable stent to provide a tapered flexibility to said
expandable stent.
10. The expandable stent of claim 1 further comprising a second
stent section, said first stent section being joined to said second
stent section by one or more hinged interconnectors, said hinged
interconnectors having at least one strut (and two hinges) and
being joined to a connecting node of said first stent section and a
connecting node of said second stent section.
11. The expandable stent of claim 1 further comprising a second
stent section, said first stent section being joined to said second
stent section by one or more connecting elements, said connecting
elements being comprised of a straight or curved element.
12. The expandable stent of claim 1 wherein said strut radial
dimension is less than said hinge radial dimension to provide
elastic bending of said strut in a radial direction during a crush
deformation.
13. The expandable stent of claim 1 wherein said hinge radial
dimension is greater than said strut radial dimension to prohibit
bending of said hinge in a radial direction due to a crush
deformation.
14. The expandable stent of claim 1 wherein said hinge width is
less than said strut width to allow bending of said hinge due to
expansion deformation in a uniform surface of said expandable
stent.
15. The expandable stent of claim 1 wherein said strut width is
greater than said hinge width to prohibit bending of said strut in
a uniform surface of said expandable stent.
16. The expandable stent of claim 1 wherein said strut length can
be increased to increase flexibility of said stent to form an oval
surface of said expandable stent due to crush deformation.
17. The expandable stent of claim 1 wherein said hinge length can
be lengthened to provide less drop-off of expansion force and
shortened to focus the deformation to a smaller hinge length.
18. The expandable stent of claim 17 wherein said hinge length is
shortened to provide more plastic deformation to the hinge during
an expansion deformation.
19. The expandable stent of claim 17 wherein said hinge length is
shortened to provide a greater elastic expansion force outward
against the vessel wall.
20. The expandable stent of claim 17 wherein said strut length,
strut width, and strut radial dimension provide said struts with a
smaller crush elastic force during a crush deformation than the
expansion deformation force provided by said hinge length, hinge
width, and hinge radial dimension, thereby allowing said expandable
stent to undergo a crush deformation without affecting the
expansion deformation of said expandable stent.
21. The expandable stent of claim 1 wherein at least one of said
nodes comprises a barb.
22. The expandable stent of claim 21 wherein said barb is held in a
nonextended conformation during delivery and is allowed to extend
to its fullest extent upon expansion of said expandable stent to a
specific deployment angle.
23. The expandable stent of claim 21 wherein said barb is formed
contiguously with said node.
24. The expandable stent of claim 1 wherein said stent is formed
from an elastic metal with a high elastic modulus.
25. The expandable stent of claim 1 wherein said stent is formed
from a metal that undergoes a plastic deformation during an
expansion deformation.
26. The expandable stent of claim 1 wherein said stent is formed
from a metal taken from the list including: Nitinol, stainless
steel, titanium, tantalum, gold, platinum, and metal alloys.
27. The expandable stent of claim 1 wherein said stent is
attachable to an intravascular graft to hold the intravascular
graft outwards against the blood vessel wall, to reduce leakage of
blood between a native blood lumen and the intravascular graft, or
to prevent migration of the intravascular graft within the blood
vessel.
28. An expandable stent deliverable to the site of a lesion within
a tubular vessel in a nondeployed state with a smaller nondeployed
diameter and capable of undergoing an expansion deformation to a
deployed state with a larger deployed diameter, said expandable
stent comprising; A. a stent section, said stent section being
comprised entirely of hinges and struts with each of said struts
extending between two of said hinges, said hinges providing
movement for said strut within a uniform surface of said stent
section, said stent section being formed of a plurality of repeat
units, each of said plurality of repeat units being joined together
to form said stent section, B. each of said hinges having a hinge
width, a hinge length, and a hinge radial dimension which do not
allow said hinges to bend in a radial direction due to a crush
deformation and which allow said hinges to bend in a uniform
surface of said stent section due to the expansion deformation, C.
each of said struts having a strut width, a strut length, and a
strut radial dimension which do not allow said struts to bend in
the uniform surface of said stent section, and which allow said
struts to bend substantially elastically in the radial direction
due to crush deformation, whereby said expandable stent provides an
uncoupling of the expansion force of said hinges from the elastic
bending force of said struts such that these forces can be varied
independently from one another.
29. An expandable stent deliverable to the site of a lesion within
a tubular vessel in a nondeployed state with a smaller nondeployed
diameter and capable of undergoing an expansion deformation to a
deployed state with a larger deployed diameter and be implanted
within the tubular vessel in order to hold the wall of the tubular
vessel outward, said expandable stent comprising; A. a stent
section, said stent section being comprised entirely of hinges and
struts with each of said struts extending between two of said
hinges, said hinges providing for a movement of said struts within
a uniformly curved surface of said stent section, B. said hinges
and struts forming a continuous configuration extending
continuously throughout the axial length of said stent section,
said stent section being deliverable as said expandable stent, C.
said hinges having a hinge width, a hinge length, and a hinge
radial dimension which do not allow said hinges to bend in a radial
direction due to a crush deformation and which allow said hinges to
bend within in a uniform surface of said stent section due to the
expansion deformation, D. said strut having a strut width, a strut
length, and a strut radial dimension which do not allow said struts
to bend within the uniform surface of said stent section, and which
allow said struts to bend elastically in the radial direction due
to crush deformation.
30. An expandable stent deliverable to the site of a lesion within
a tubular vessel in a nondeployed state with a smaller nondeployed
diameter and capable of undergoing an expansion deformation to a
deployed state with a larger deployed diameter and be implanted
within the tubular vessel, said expandable stent comprising; hinges
and struts with each of said struts extending between two of said
hinges, and said hinges providing for a movement of said struts
within a uniformly curved surface of said stent section, said
hinges and struts forming a continuous configuration extending
continuously throughout the axial length of said expandable stent,
said hinges having a hinge width, a hinge length, and a hinge
radial dimension which do not allow said hinges to bend in a radial
direction due to a crush deformation and which allow said hinges to
bend within in a uniform surface of said expandable stent due to
the expansion deformation, said struts having a strut width, a
strut length, and a strut radial dimension which do not allow said
struts to bend within the uniform surface of said stent section,
and which allow said hinge to bend in the radial direction due to
crush deformation.
31. An expandable stent deliverable to the site of a lesion within
a tubular vessel in a nondeployed state with a smaller nondeployed
diameter and capable of undergoing an expansion deformation to a
deployed state with a larger deployed diameter and be implanted
within the tubular vessel, said expandable stent comprising; hinges
and struts with each of said struts extending between two of said
hinges, and said hinges providing for a movement of said struts
within a uniformly curved surface of said stent section, said
hinges and struts forming a plurality of repeat units being joined
together to form said expandable stent, said hinges having a hinge
width, a hinge length, and a hinge radial dimension which do not
allow said hinges to bend in a radial direction due to a crush
deformation and which allow said hinges to bend within in a uniform
surface of said expandable stent due to the expansion deformation,
said struts having a strut width, a strut length, and a strut
radial dimension which do not allow said struts to bend within the
uniform surface of said stent section, and which allow said hinge
to bend in the radial direction due to crush deformation.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to an expandable
endoprosthesis that is placed within a tubular member of the human
body to treat a region that is pathologically affected by
supporting it or holding the tubular member outwards. More
specifically the invention relates to an intravascular
endoprosthesis placed within a blood vessel of the body generally
at the site of a vessel lesion in order to provide a more widely
open lumen and enhance patency of the vessel. The present invention
further relates to a stent that can be used in blood vessels and
tubular vessels of the body that have become stenotic or blocked by
tissue or other material and require reestablishment of a lumen and
maintenance of the lumen.
[0003] 2. Description of Prior Art
[0004] Stents used to internally support tubular vessels of the
body can generally be categorized into two groups, those that are
mechanically expanded by an external device such as a balloon
dilitation catheter, and those that are self-expandable. Advantages
of the balloon expandable stents lies in part in the ability of
these stents to be delivered accurately to the site of a stenotic
lesion. The location of the stent prior to deployment or expansion
can be visualized under flouroscopy and deployment of the stent is
generally made by inflation of a dilitation balloon which expands
the stent radially into contact with the inner surface of the
vessel wall. After the dilitation balloon has been deflated and the
dilitation catheter removed, the stent is left in place to balance
radial forces applied by the vessel wall and ensure that the vessel
lumen is maintained in a widely patent conformation.
[0005] Some difficulties associated with balloon expandable stents
can be related to their lack of flexibility and their inability to
withstand external forces that can lead to irreversible crushing of
the stent. Several stents exhibit a structure that will not easily
bend around tortuous pathways found in the human vasculature to
reach the site of the lesion in their nondeployed state. Other
stents have a structure that is made more flexible but are not
appropriately capable of supporting or balancing the radial forces
applied by the vessel acting to compress the stent. A stent with a
low radial balancing force characteristics may be expected to
undergo an irreversible crushing action if exposed to an externally
applied force. Arteries of the neck and leg region can sometimes be
exposed to such external forces resulting in permanent deformation
of the stent and loss of vessel patency. This has been the case for
some balloon expandable stents that have been placed in the carotid
artery and exposed to digital or other external forces that have
led to collapse of the stent.
[0006] In the balloon expandable stents currently found in the
prior art one cannot adjust the amount of force required to expand
the stent independently from the force required to crush the stent.
As a result, a stent design that resists crushing action will
generally be too stiff and require too much force to accomplish its
deployment.
[0007] Self-expandable stents overcome some of the problems
associated with the crushability of balloon expanded stents. These
stents are typically made of Nitinol, a stainless steel with high
yield strength, or some other material that can store energy
elastically. Self-expandable stents can be delivered within a
sheath to the site of the lesion. There the sheath can be removed
and the stent can be deployed as it expands out to a larger
diameter associated with its equilibrium diameter.
[0008] Some problems associated with self-expandable stents include
the inability of the physician delivering the stent to define
precisely the location of both ends of the stent. Oftentimes the
stent can undergo significant changes in it axial length in going
from an nondeployed state to a deployed state. Such length changes
can result in inaccuracies in defining a precise placement for the
stent. This disadvantage can be somewhat offset by the ability of
some self-expandable stents to resist crushing deformation
associated with an external force directed toward the side of the
stent. Self-expandable stents also do not generally allow the
radial expansion force to be adjusted independently from the stent
forces that are directed to resist crushing forces. A
self-expandable stent with an appropriate elastic balancing force
to hold the vessel open may have a weak crush balancing force to
resist crushing deformation due to externally applied crushing
forces.
[0009] Palmaz discloses in U.S. Pat. No. 4,733,665 a
balloon-expandable stent that is formed by machining slots into a
metal tube forming a series of elongate members and bars. The stent
is mounted in its nondeployed state onto the balloon portion of a
balloon dilitation catheter and delivered to the site of a lesion
that has been previously dilated to allow passage of the stent
mounted balloon catheter. Dilation of the balloon causes the
balloon-expandable stent to plastically deform at the junction of
the elongate members and bars of the stent. For the stent to
undergo an expansional deformation the balloon must supply an
expansion applied force that exceeds the expansion yield force
associated with the junction of the elongate members and the bars.
Typically a balloon dilitation catheter used to dilate a coronary
lesion found in a three millimeter diameter coronary artery can be
dilated at a balloon pressure ranging from one to fifteen
atmospheres. With the stent mounted on the balloon, the balloon
must be capable of radially expanding the stent and holding the
vessel in a widely patent conformation. Upon removal of the balloon
catheter, the stent must continue to supply a compression balancing
force to balance the compression applied force of the vessel acting
inward on the stent. If an externally placed side force is imposed
onto the side of the stent, the stent can deform into an oval or
flattened shape representative of a crushing deformation. This
deformation can involve an elongate member or it can occur at a
junction of an elongate member with a bar. The elongate member can
be formed such that it resists plastic deformation associated with
crushing deformation. The junction of the elongate member with the
bar cannot be adjusted to resist crushing deformation without also
affecting the force required to expand the stent from its
nondeployed state to its deployed state; additionally, the
compression balancing force would also be affected. The Palmaz
stent disclosed herein therefore can be susceptible to crush
deformation in order to maintain appropriate characteristics for an
expansion yield force during deployment and a compression yield
force to hold the vessel in an open conformation.
[0010] A stent is required to have axial flexibility in order to
negotiate the tortuous turns found in the coronary vasculature.
Palmaz describes in U.S. Pat. No. 5,102,417 connector members that
connect between small cylindrical stent segments. Although the
connector members provide an enhanced axial flexibility, this stent
is still subject to crush deformation. The compression yield force
that is capable of holding the vessel outward with the stent in a
deployed state is coupled to the crush yield force that prevents
the stent from crush deformation.
[0011] Fischell describes in U.S. Pat. No. 5,695,516 a
balloon-expandable stent formed from a metal tube and having
circumferential arcs and diagonal struts. When this stent is
expanded to a deployed state the junctions of the arcs and struts
undergo plastic deformation and the deployed stent takes on a
honeycomb shape. The expansion yield force of this stent describes
the force required to plastically deform an arc with respect to a
strut at a junction during stent expansion. The compression yield
force describes the force required to plastically deform an arc
with respect to a strut when exposed to a compression applied force
by the blood vessel. Deformation due to crushing would also occur
at the junction of the arc with the strut. The crush yield force of
this stent is therefore directly coupled to the expansion yield
force and the compression yield force. If this stent were designed
to expand upon exposure to a dilitation balloon with a nominal
expansion applied force, it would not be able to resist crushing
deformation when exposed to an external side force that can be
encountered in a carotid or femoral artery position.
[0012] Fischell describes in U.S. Pat. No. 5,679,971 a
balloon-expandable stent that has two different types of cells, one
for radial rigidity and one for axial flexibility. Neither one of
these cells addresses the need to provide an anti-crush
characteristic to the stent. One cannot adjust the crush yield
strength of this stent independently of the expansion yield
strength.
[0013] Lam (U.S. Pat. No. 5,649,952), Anderson (U.S. Pat. No.
5,800,526), Frantzen (U.S. Pat. No. 5,843,164), and Orth (U.S. Pat.
No. 5,681,346) each describe balloon-expandable stents formed from
metal cylinders and having serpentine wave patterns connected by
interconnecting members, In each of these stent disclosures the
stent has a crush yield force that is coupled to the expansion and
compression yield force. These stents would be susceptible to
irreversible crush deformation if exposed to an external force to
the side of the stent.
[0014] Gianturco discloses in U.S. Pat. No. 4,800,882 a
balloon-expandable stent constructed from a metal wire and
discloses in U.S. Pat. No. 5,041,126 a method of insertion for a
balloon-expandable stent. The wire stent disclosed by Gianturco has
adjacent curved sections or loops joined by a bend or cusp. During
stent expansion by a balloon the loops diverge as the metal wire
irreversibly and plastically deforms. The deformation of the metal
wire that occurs during expansion has a similar yield force as the
deformation of the metal wire that can occur during compression of
the stent if the compression applied force of the vessel exceeds
the compression yield strength of the stent. If this stent is
exposed to an external side force that could lead to a crush
deformation, this stent can undergo plastic deformation that is
irreversible and can occur with a similar yield force as the
compression yield force. This stent is not well suited to provide
independent adjustment of compression yield force with respect to
crush yield force. As a result, this stent can be subject to
crushing deformation even though the expansion and compression
yield force are appropriate for allowing balloon expansion and
support of the blood vessel.
[0015] Hillstead (U.S. Pat. No. 4,856,516), Wiktor (U.S. Pat. Nos.
5,133,732 and 4,886,062), Globerman (U.S. Pat. No. 5,776,161),
Fontaine (U.S. Pat. No. 5,527,354), Horn (U.S. Pat. No. 5,591,230),
Boyle (U.S. Pat. Nos. 5,613,981 and 5,591,198), and Hillstead (U.S.
Pat. No. 5,116,365) each describe balloon-expandable wire stents
made from loops, zig zags, helical wires, curved rings, sinusoidal
waves, or other similar form of construction. All of the stents
described in these disclosures are expandable by the expansion
applied forces of a balloon of a balloon dilitation catheter or
other similar catheter. During the expansion of the stents, the
wires or each stent undergoes a plastic deformation once the
expansion yield force has been exceeded. A plastic deformation
would also be required for any of these stents to compress under
the compression applied force applied by the vessel wall; this
could occur once the compression yield force of the stent has been
exceeded. Exposure of any of these stents to an external side force
could lead to a crush deformation. It is not possible for any of
these stents to enhance the crush yield force without altering the
expansion or compression yield force of the stent. Cox (U.S. Pat.
No. 5,733,330) and Wall (U.S. Pat. No. 5,192,307) each describe
balloon-expandable stents with ratchet mechanisms. The stents can
be formed out of an elastic metal that will not allow for stent
crushing and the ratchet mechanism can prevent the stents from
collapsing under the force of compression applied by the blood
vessel. Each one of these disclosures describes a separate latching
or ratcheting mechanism that is required to provide the properties
of balloon-expandable and non-crushability. The latching or
ratcheting mechanism adds to the size and the complexity of the
device.
[0016] Wallsten describes in U.S. Pat. Nos. 4,655,771 and 5,061,275
self-expandable stents formed from helically wound braided flexible
thread elements or wires. The metal wires are elastic or resilient
in nature with a high energy storage capacity. The stents can be
delivered to the site of the lesion by an external sheath that
applies a constraining force upon the stent to hold it in an
nondeployed state of a smaller diameter. Upon release of the stent
within the blood vessel, the stent undergoes a radial expansion to
a larger predetermined diameter. The vessel provides a compression
applied force due to vessel elasticity and collagenous scarring and
contraction that can occur during vessel healing; this compression
applied force acts inward on the stent. The stent in its deployed
state provides an expansion elastic balancing force outward against
the vessel wall to balance the compression applied force. If the
stents described by these disclosures are acted upon by an external
crush applied force delivered to the side oI the stent, the stents
can undergo an crush deformation forming an oval or flattened
shape. The stents can provide a crush elastic balancing force to
balance the crush applied force and limit the amount of crush
deformation. The degree of crush deformation that can occur for a
specific crush applied force is directly related to the size and
number of flexible thread elements or wires used in the formation
of the stents. The size and number of wires has a direct bearing on
the expansion elastic balancing force provided by the stents.
Therefore an increase in the crush balancing force will generally
be associated with a corresponding increase in elastic balancing
force. It can be desirable to adjust the crush balancing force
independently of the elastic balancing force. The stents disclosed
by Wallsten are not well suited to independent adjustment of the
crush and the expansion elastic balancing force. Similarly, the
crush balancing force is directly coupled to the expansion elastic
balancing force.
[0017] Gianturco describes in U.S. Pat. Nos. 4,580,568 and
5,035,706 self-expandable stents formed from metal wire in a
zig-zag pattern. These stents are elastically compressed to a
smaller diameter for delivery within a blood vessel and undergo an
elastic expansional deformation during delivery at the lesion site.
The stents provide a deployed expansion elastic balancing force
outward against the vessel wall to maintain the diameter of the
vessel in an open and widely patent conformation. If exposed to an
external crush applied force the stents will deform elastically and
provide a crush elastic balancing force. The expansion and crush
elastic balancing force are directly coupled and are not easily
varied with respect to one another. Such stents with appropriate
expansion characteristics are not easily adjusted to provide
altered crush characteristics independently of one another.
[0018] Lauterjug (U.S. Pat. No. 5,630,829) and An (U.S. Pat. No.
5,545,211) describe self-expandable stents formed from metal wire.
Lauterjung provides a high hoop strength stent due to the angle of
the wire in the expanded state. An describes a zig-zag pattern that
is spiraled into turns and is cross-linked with each other at
adjacent turns. Each of these stents has an expansion and a crush
elastic balancing force that is coupled directly to each other. One
can not appropriately adjust the expansion characteristics with
respect to the crush characteristics.
[0019] Carpenter describes in U.S. Pat. No. 5,643,314 made of a
series of elastic metal bands or loops interconnected along a
backbone. A lock is used to hold the loops in a contracted
configuration around a balloon portion of a delivery catheter
during delivery to the lesion site. Once expanded by the balloon, a
lock is used to hold the loops outward in their expanded
configuration. The strength of the lock provides the balancing
force of the stent to hold the vessel in an open widely patent
configuration. The dimensions of the metal loops determines the
crush balancing force for a specific crush deformation. This stent
is cumbersome to use with sliding required between metal and a
locking mechanism that occupies areal space and volume.
[0020] McIntyre (U.S. Pat. No. 5,833,707) and McDonald (U.S. Pat.
No. 5,728,150) each describe a stent formed from a flexible elastic
metal sheet that has been coiled into a small diameter for delivery
to a blood vessel. Upon release of the coiled stent, it springs out
to form a larger deployed diameter and hold the vessel with an
expansion elastic balancing force. The crush balancing force of
these stents involves a similar defomation of the metal sheet as
the expansion or compression deformation involved with the
expansion delivery of the stents or collapse of the stents due to
vessel compression applied forces. These stents do not provide for
adjustment of the crush balancing force with respect to the
expansion or compression balancing force.
[0021] Dotter (U.S. Pat. No. 4,503,569), Alfidi (U.S. Pat. No.
3,868,956), and Froix (U.S. Pat. No. 5,607,467) describe coiled
stents constructed out of plastic or metal that can change in shape
from a small diameter to a large diameter due to the application of
heat, or application of another external condition. Most plastic
stents are not acceptable due to the inadequate strength per volume
of material in comparison to a metal stent. As a result, plastic
stents require excessive areal space or volume which can be very
undesirable in a small diameter blood vessel. Metal stents with a
coiled shape have a similar mode of deformation in providing an
expansion or compression balancing force in comparison to providing
a crush balancing force. These stents do not allow the crush
balancing force to be adjusted with respect to the expansion or
compression balancing force.
[0022] Roubin discloses in U.S. Pat. No. 5,827,321 a stent that is
radially expandable by balloon or self-expandable and designed to
maintain its axial length upon expansion. The stent has annular
elements connected by connecting members. The connecting members
are formed from Nitinol and have a desire to lengthen upon
deployment of the stent. The expansion or compression balancing
force against the vessel wall is provided by the annular elements
which have a curved or zig-zag structure. Upon exposure to a crush
deformation it is the annular elements that provide the crush
balancing force. The crush balancing force is coupled to the
expansion or compression balancing force; the stent does not
provide for independent adjustment of the balancing forces.
[0023] Williams (U.S. Pat. No. 5,827,322) describes a
balloon-expandable or self-expandable stent formed from Nitinol
flat metal sheet and having a ratchet mechanism to hold the stent
in an expanded state. This stent is not flexible in the axial
direction and the ratchet mechanism requires additional areal space
and volume. This stent does not allow independent adjustment of
crush balancing force without also significantly impacting the
expansion elastic balancing force provided by the stent.
[0024] Hilaire describes in International Application with
International Publication Number WO 98/58600 an expandable stent
with variable thickness. The variable thickness is intended to
allow the balloon expandable stent to expand more evenly along its
perimeter. The stent is formed from a plurality of tubular elements
with a zig zag shape that are joined together by linking members.
This device does not teach or describe a stent that provides
independent adjustment of stent expansion forces with respect to
stent crush forces.
SUMMARY OF THE INVENTION
[0025] The present radially expandable intravascular stent
overcomes the disadvantages described for other prior art
balloon-expandable and self-expandable stents. The stent of the
present invention has nodes that are attached to two or more
struts. Each node has a hinge that focuses the deformation
associated with expansion of the stent from its nondeployed or
insertion state with a smaller diameter to its deployed or
implanted state with a larger diameter. The radially expandable
stent of this invention exerts forces against its environment and
is exposed to applied forces from the environment. These forces
will be described by the element generating the force, the
direction of the force in either expansion or compression, and the
type of force being exerted. For a balloon-expandable stent the
hinge allows an inserted stent compression yield force and an
implanted stent expansion yield force to be decoupled from an
implanted stent crush elastic force thereby providing a stent that
can be balloon expandable but noncrushable based on strut and hinge
dimensions. This can be extremely valuable for applications such as
carotid stenting where exact placement of a balloon-expandable
stent is crtitcal and the ability of the stent to resist crushing
is a necessity. For a self-expandable stent, decoupling an
implanted stent crush elastic force from an implanted stent
expansion elastic force provides a stent that can be soft in crush
deformation but provide adequate expansion elastic force to hold
the vessel open. This type of stent may be advantageous in specific
coronary artery stenting applications. Alternately, a
self-expandable stent can be formed under the present disclosure
that provides a large implanted stent crush elastic force but with
a small or modest implanted stent expansion elastic force. This
type of device may be useful in a situation where sear tissue may
be contracting down on a vessel lumen. The stent of the present
invention can be applied to any tubular vessel or passage found in
the human body. Application of the hinge stent of the present
invention can be made in particular to treatment of arterial blood
vessels of the body. Such arterial blood vessels that can be
treated with the present invention include small arteries such as
coronary arteries and carotid arteries, middle size arteries such
as femoral arteries and other vessels of the leg, and larger
vessels including the aorta.
[0026] For a radially expandable balloon-expandable stent, a
balloon expansion applied force is applied to the inside surface of
the stent by a balloon of a balloon dilitation catheter or a
similar catheter. Dilation of the balloon causes the stent to
undergo a radial expansion that requires a plastic deformation such
that the stent exceeds its elastic limit and exceeds the inserted
stent compression yield force. A typical balloon dilitation
pressure for a three millimeter diameter balloon is about 5-10
atmospheres. Balloon pressures can range from one atmosphere to
dilate a very soft lesion to over 15 atmospheres to dilate a
heavily calcified lesion. The stent will retain its expanded or
deployed diameter and a tissue compression applied force applied by
the blood vessel would have to exceed the implanted stent expansion
yield force for the stent to collapse. The force exerted by the
stent on the vessel wall is an implanted stent expansion holding
force that must be large enough to hold the vessel at the deployed
or implanted diameter of the stent and resist any diameter changes
due to external forces or scarring. The inserted stent compression
yield force cannot be so high that the balloon catheter is unable
to expand the stent to the appropriate diameter. During this radial
expansion of the stent the most significant plastic deformation
occurs as an expansion deformation in an axial or circumferential
direction within the uniformly curved surface of the stent, and
relatively little crush deformation occurs with respect to the
radius of curvature of the stent within a cross section. If a
deployed stent is exposed to an external tissue crush applied force
from one side it tends to form an oval shape representative of a
crush deformation. If the tissue crush applied force exceeds the
implanted stent crush yield force, the oval shape becomes extreme
and can flatten as the stent can exceed its elastic limit in a
crush deformation. During the crush deformation the wall of the
stent is formed into an oval shape that is not the same as the
expansion deformation encountered during the radial expansion.
[0027] The stent of the present invention allows a
balloon-expandable and noncrushable stent to be formed from a metal
that has a relatively high yield strength or high expansion yield
force. The yield strength for the metal of the stent can be high
enough such that when the stent is formed into an oval or flattened
shape such as that found during crush deformation, the struts do
not surpass their elastic limit and hence remain elastic. Each
strut can be connected to two nodes through a hinge. The hinge is
configured to provide plastic expansion deformation to the stent as
it extends from a nondeployed insertion diameter to a deployed
implantation diameter. The expansion deformation is focused in the
hinge region such that localized plastic deformation occurs in the
hinge. The hinge resists bending in the radial direction such as
that deformation produced during a crush deformation. The result is
a stent with appropriate inserted stent compression yield force
that can be properly overcome by the balloon expansion applied
force from the balloon dilitation catheter and strength to support
the blood vessel and resist vessel contraction, and further provide
the stent with non-crush characteristics.
[0028] A balloon-expandable stent of one embodiment of the present
invention can be modified to provide modified stent expansion and
compression yield force characteristics or modified implanted stent
crush yield force characteristics independent of one another. This
is accomplished by altering a radial dimension for the hinge and
changing its width and length perpendicular to the radial
dimension. For example, to increase the implanted stent crush yield
force while maintaining the inserted stent compression yield force
constant, the struts can be first enlarged in their sectional area
to provide the desired crush yield force, or the material of the
stent can be changed to attain a higher yield strength material.
The struts can be formed of appropriate material and thickness to
ensure that they remain elastic for any reasonable crush
deformation encountered during normal use. The radial dimension of
the hinge can be increased to provide an accompanying similar
increase in crush yield force to the node. The width of the hinge
in a direction perpendicular to the radial dimension and lying in
the uniformly curved surface of the stent can be decreased such
that the inserted stent compression yield force will remain
constant. The hinge length can be decreased to further focus the
expansion deformation in the hinge and ensure that plastic
deformation will occur in consideration of the narrowing of the
hinge width. If the hinge length is maintained in a longer
configuration, the hinge can be configured to remain in an elastic
state and not undergo a plastic deformation during expansion
deformation; this node and hinge design of the present stent thus
allows the formation of a self-expandable stent to also be
accommodated.
[0029] A self-expandable stent generally has an equilibrium
diameter wherein it is not applying any radial forces; this
equilibrium diameter is somewhat larger than or approximately equal
to the diameter of the vessel in which it is deployed or its
implantation diameter. For a radially expandable self-expandable
stent, the stent can be held and delivered to the blood vessel in a
nondeployed state of smaller insertion diameter with a sheath
compression applied force applied by some external holding means
such as a sheath. The self-expandable stent exerts an inserted
stent expansion elastic force upon the external holding means. Upon
release from the holding means within a blood vessel, the
self-expandable stent expands, and once fully deployed exerts an
outwardly directed implanted stent expansion elastic force upon the
walls of the blood vessel that is dependent upon the equilibrium
diameter of the stent. If the implanted stent expansion elastic
force is too large when the self-expandable stent comes into
contact with the blood vessel, the blood vessel wall can begin to
dilate and the stent can travel into the vessel wall causing
trauma. If the implanted stent expansion elastic force is too low,
vessel scarring and retraction of the vessel wall can apply a
tissue compression applied force on the stent causing the stent to
reduce in diameter to a value smaller than desired.
[0030] As the self-expandable stent undergoes an expansion from an
nondeployed or insertion diameter to a deployed or implantation
diameter an elastic expansion deformation occurs within the stent.
This elastic expansion deformation occurs in the axial and
circumferential direction of the stent wall and is not the same as
the curvature change which occurs with respect to the radius of
curvature of the stent in a radial direction during stent crushing.
This elastic expansion deformation is very different from the
deformation that would occur if the stent were exposed to a force
along its side that would cause it to form an oval sectional shape
associated with a crush deformation.
[0031] The stent of the present invention allows a self-expandable
stent to be formed out of an elastic metal that will not
plastically deform during normal use involving elastic expansion
deformation or during exposure to a crush deformation. The struts
could be formed with a sectional dimension that provides the
self-expandable stent with an elastic crush deformation when
exposed to an external tissue crush applied force to form an oval
shape due to a crush deformation. The implanted stent crush elastic
force of the stent can be high or low depending upon the desired
properties of the stent. The struts are connected to one or more
nodes through a hinge. The hinge has a greater radial dimension
than the struts to resist the formation of an oval cross section
associated with crush deformation. The hinge has a width that can
be adjusted to provide an implanted stent expansion elastic force
that is appropriate to resist the tissue compression applied force
of the blood vessel. The hinge length can further be adjusted to
alter the implanted stent expansion elastic force. The result is a
self-expandable stent with appropriate expansion elastic force
properties and a soft feel in a crush deformation. Similarly, the
stent can have appropriate or nominal expansion elastic force
properties and a very rigid, difficult to crush characteristic
associated with a large implanted stent crush elastic force.
[0032] A self-expandable stent of the present invention can be
modified to alter the inserted stent and the implanted stent
expansion elastic force or implanted stent crush elastic force
independent of one another. For example, to increase the crush
elastic force while maintaining the inserted or implanted expansion
elastic force, the struts can be enlarged in sectional area to
provide the desired crush elastic force. The radial dimension of
the hinge can be increased to provide an accompanying similar
increase in crush elastic force in the node region. The width of
the hinge in the uniformly curved surface of the stent can be
decreased such that the expansion elastic force will remain
constant. The hinge length can be decreased to provide a more
focused bending of the hinge through a smaller radius of curvature
to generate the appropriate expansion elastic force.
[0033] In an embodiment of the present invention a metal tube
constructed of stainless steel, Nitinol, titanium, tantalum, or
other metal used in constructing stents is machined using laser
machining, mechanical machining, chemical etching or other
machining process to form raised areas in the outside surface of
the metal tube. These raised areas have a greater radial dimension
than the rest of the tube and will later be formed into the hinges
of the stent. It is important to note that the raised areas can be
formed such that their radial dimension is as thin as any normal or
standard balloon-expandable or self-expandable stent. The strut
region can be formed such that the radial dimension is thinner than
the strut region of a standard stent. The design of the present
invention allows a material of greater elastic modulus to be chosen
for stent formation thereby providing appropriate expansion force
characteristics based on the design of nodes and struts utilizing a
thinner strut dimension than could be used with other prior art
stents. Slots are then formed into the metal tube using laser,
mechanical, or chemical machining methods. The slots can be any
combination of straight slots or curved slots at any combination of
parallel, perpendicular, or at an oblique angle with respect to the
axis of the tube. The metal tube is thereby formed into a repeating
array of struts and nodes with each node generally connected to at
least two struts through a hinge. Each strut has a radial
dimension, a width, and a length and it extends between two nodes.
The nodes have a greater radial dimension than the struts. Each
node can include a hub which has a radial dimension that is greater
than the strut radial dimension. The hub is connected to or
contiguous with at least two hinges which have a width that is
narrower than the width of the struts. The node can be a single
long hinge if it is connected to only two struts. Each hinge has a
transition region which serves to join and provide a uniform
transition between a hinge and a strut. Each transition region
expandable is formed of the same metal as the hinge and the strut
and is therefore contiguous with the hinge and the strut.
[0034] In one embodiment of a balloon-expandable stent the node is
connected to four struts. As the slotted tubular stent is expanded
from an nondeployed or insertion diameter to a deployed or
implanted diameter an array of diamond shaped spacings is formed
between the struts and the nodes. Upon exposure of the stent to
expansion deformation, plastic deformation occurs in the hinges
located between the struts and the hubs. The struts move with
respect to the hub during expansion deformation of the stent such
that the stent is capable of supporting a blood vessel in an
expanded or deployed state. Exposure of this expanded stent to a
side force tends to create a crush deformation. The entire stent
and the struts are formed of a metal with a high yield strength and
hence the struts will bend elastically when exposed to such a crush
deformation. The node, including the hub, the hinge, and the
transition region have a greater radial dimension and hence will
not deform significantly under the crush deformation. Thus the
stent undergoes plastic expansion deformation in a localized region
of the hinge but remains elastic in all other areas to resist
irreversible plastic crush deformation.
[0035] In another embodiment a self-expandable stent has each node
connected to four struts and has an equilibrium diameter
approximately equal to its deployed diameter. Diamond shaped
spacings are found between the struts and the nodes in a deployed
state. This stent can either be machined in the deployed diameter
or it can be machined in the nondeployed diameter or in an
intermediate diameter between the deployed diameter and the
nondeployed diameter and work hardened to form an elastic
self-expandable stent with an equilibrium diameter approximately
equal to the deployed diameter. Prior to delivery the stent is
collapsed down to a nondeployed diameter and delivered through a
constraining sheath or other delivery system to the blood vessel.
The nondeployed self-expandable stent exerts an inserted stent
expansion elastic force outward against the sheath. Upon delivery
to the blood vessel and removal of the constraining sheath the
self-expandable stent attempts to assume its equilibrium diameter
and hold the blood vessel in an expanded state with an implanted
stent expansion elastic force. The inserted and implanted stent
elastic force for a particular metal of construction is determined
primarily by the length, width, and radial dimension of the hinge.
Exposure of this stent to a crush deformation causes the struts to
reversibly bend in the shape of the oval cross section. The strut
has been designed to deform elastically when exposed to a crush
deformation. The strut can either provide a large implanted stent
crush elastic force when deformed to a particular degree of
deformation or a small implanted stent crush elastic force
dependent upon the width, length, and radial dimension of the
strut. The magnitude of the implanted stent crush elastic force is
independent of the expansion elastic force which is determined by
the hinge width, length, and radial dimension. The self-expandable
stent of this invention allows the implanted and inserted expansion
elastic force to be altered independently from the implanted stent
crush elastic force. The stent of the present invention can be
formed of a single cylindrical stent segment or section or it can
be formed of two or more stent sections joined together by a
connecting means.
[0036] In further embodiments of the present invention, one or more
cylindrical stent sections of either the self-expandable stent or
the balloon-expandable stent formed with an array of nodes and
struts can be connected together with one or more flexible
connecting means. The connecting means can be a hinged
interconnector formed of nodes and struts similar to those of the
stent section structure or it can be a connecting element formed of
a straight or curved connecting leg without nodes or hinges. Two or
more stent sections can be connected together with hinged
interconnectors or connecting elements to provide the stent with
additional axial flexibility around a bend in a blood vessel. Axial
flexibility is particularly important in allowing a stent to be
deliverable to very tortuous vessels such as are often found in the
heart. The connecting means can attach from a node of one
cylindrical segment of stent to a node of another cylindrical
segment. The hinged interconnctor or the connecting element will
allow the stent wall that is on the inside radius of curvature
through a tortuous or bent path to compress or contract as the
connecting means is deformed to a shorter axial length. The hinge
of the hinged interconnector can undergo a plastic deformation or
an elastic deformation as the stent passes along a tortuous path.
The struts of the hinged interconnector remain elastic during
passage along a tortuous path. The connecting means located on the
outside of the radius of curvature of a bend is able to extend to a
larger length. The connecting means can be formed of the same
material as the struts and nodes of the stent and can be machined
into the stent structure in a manner similar to the forming of the
slots. The radial dimension of the hinged interconnectors can be
equal to or smaller than the radial dimension of the struts and can
have an equal or smaller width than the struts. The hinged
interconnectors and connecting elements are generally designed to
remain elastic during the extensional deformation encountered as
the stent extends and contracts while extending along a bend in a
blood vessel. As the stent in its nondeployed state is bent around
a tortuous path the hinged interconnectors and connecting elements
provide the stent with a flexible characteristic. After the stent
is deployed, the hinged interconnectors also provide the stent with
an ability to conform with a tortuous vessel wall without trying to
exert forces that could undesirably try to straighten the
vessel.
[0037] In still another embodiment the stent is formed in an array
of nodes and struts wherein each node is connected to three struts.
The configuration of nodes and struts can be used for either a
balloon-expandable stent or a self-expandable stent. The presence
of hinges with a greater radial dimension and a smaller width that
the struts provides this embodiment with the advantage of
decoupling the inserted stent compression yield force and the
implanted stent expansion yield force from the implanted stent
crush yield force, and decoupling the implanted and inserted stent
expansion elastic force from the implanted stent crush elastic
force. In addition, axial flexibility can be provided directly from
the array of nodes and struts without the need for connecting
means.
[0038] In one more embodiment of the present invention the metal
tube can be formed into a stent with an array of nodes and struts
that have each node connected to two struts. The node can be a
single hinge that connects two struts. The hinges and struts can be
formed in any combination of straight or curved shape along with
any combination of axial, circumferential, or oblique orientation
for either the hinges or struts. This stent can be formed into a
balloon-expandable stent or a self-expandable stent. In a
balloon-expandable stent the hinge uncouples the inserted stent
compression yield force and the implanted stent expansion yield
force from the implanted stent crush yield force. The strut portion
is constructed such that crush deformation will not result in
plastic deformation; the strut will remain elastic. This allows the
balloon-expandable stent to be balloon-expandable and noncrushable.
In a self-expandable stent the hinge uncouples the inserted and
implanted stent expansion elastic force from the implanted stent
crush elastic force. The strut portion is similarly constructed
such that crush deformation will not result in plastic deformation
of the strut which will remain elastic. This allows the
self-expandable stent to have independent design of inserted and
implanted stent expansion elastic force with respect to implanted
stent crush elastic force.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Other objects of the present invention and many of the
attendant advantages of the present invention will be readily
appreciated as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings, in which like reference numerals
designate like parts throughout the figures thereof and
wherein:
[0040] FIG. 1 A is an isometric view of a hinge stent having a four
strut per node stent body in a nondeployed state;
[0041] FIG. 1 B is a sectional view of the hinge stent of FIG.
1A;
[0042] FIG. 2A is an isometric view of a hinge stent having a four
strut per node stent body in a deployed state;
[0043] FIG. 2B is a sectional view of the hinge stent of FIG.
2A;
[0044] FIG. 3 is a sectional view of the hinge stent of FIG. 2A
exposed to a crush deformation;
[0045] FIG. 4 is an enlarged detail view of a portion of the hinge
stent shown in FIG. 1A;
[0046] FIG. 5 is an enlarged detail view of a portion of the hinge
stent shown in FIG. 2A;
[0047] FIG. 6 is an isometric angled view of a hinge stent having a
four strut per node body in a deployed state;
[0048] FIG. 7 is an isometric view of a hinge stent having a three
strut per node body in a nondeployed state;
[0049] FIG. 8 is an isometric view of a hinge stent having a three
strut per node body in a deployed state;
[0050] FIG. 9 is an enlarged detail view of a portion of the hinge
stent shown in FIG. 7;
[0051] FIG. 10 is an enlarged detail view of a portion of the hinge
stent shown in FIG. 8;
[0052] FIG. 11 is an illustration of a hinge stent having three
struts per node similar to the hinge stent of FIG. 8 in a curved
conformation in a deployed state;
[0053] FIG. 12 is an isometric view of a hinge stent having a three
strut per node body in an intermediate state;
[0054] FIG. 13A is a frontal view of two stent sections joined by a
hinged interconnector;
[0055] FIG. 13B is an enlarged detail view of a hinged
interconnector;
[0056] FIG. 14 is an isometric view of two stent sections joined by
several hinged interconnectors;
[0057] FIG. 15 is a frontal view of two stent sections joined by a
straight leg element;
[0058] FIG. 16 is a frontal view of two stent sections joined by a
curved leg element;
[0059] FIG. 17A is an isometric view of a hinge stent in a
nondeployed state;
[0060] FIG. 17B is an illustration of a repeat unit for a helical
hinge stent;
[0061] FIG. 18 is an isometric view of a hinge stent having in a
deployed state;
[0062] FIG. 19 is a portion of a helical repeat unit having one
hinge per node in a nondeployed state;
[0063] FIG. 20 is a portion of a helical repeat unit having one
hinge per node in a deployed state;
[0064] FIG. 21 is an enlarged detail view of a node having one
hinge;
[0065] FIG. 22 is a portion of a helical repeat unit having two
hinges per node in a nondeployed state;
[0066] FIG. 23 is a portion of a helical repeat unit having two
hinges per node in a deployed state;
[0067] FIG. 24 is an enlarged detail view of a node having two
hinges;
[0068] FIG. 25 is a portion of two helical repeat units joined by a
hinged interconnector;
[0069] FIG. 26 is an enlarged detail view of a hinged
interconnector joining two helical repeat units;
[0070] FIG. 27 is a portion of two helical repeat units joined by
several hinged interconnectors;
[0071] FIG. 28 is an isometric view of a hinge stent having a four
strut per node body in a deployed state with barbs;
[0072] FIG. 29 is an isometric view of a hinge stent having a four
strut per node body in a nondeployed state with barbs;
[0073] FIG. 30 is an enlarged detail view of a portion of a hinge
stent in a nondeployed state with a barb;
[0074] FIG. 31 is an enlarged detail view of a portion of a hinge
stent in a deployed state with a barb.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0075] The present invention is a hinge stent that is formed of a
plurality of nodes and struts that are arranged to provide enhanced
properties over stents identified in the prior art. A
balloon-expandable hinge stent is balloon-expandable and
noncrushable to provide the accurate placement associated with some
balloon-expandable stents and not be susceptible to plastic crush
deformation from externally applied forces. A self-expandable hinge
stent can provide a large outward expansion elastic force and yet
be soft in a crush deformation while remaining elastic in this
crush deformation.
[0076] FIG. 1A shows one embodiment of a hinge stent 5 of the
present invention in a nondeployed state or inserted state with
struts 10 and nodes 15 joined together to form a stent section 20.
A stent section 20 is made up entirely of nodes 15 and struts 10
extending throughout the stent section. Each node 15 of the hinge
stent 5 includes at least one hinge 23 and at least two transition
regions 25; each transition region 25 connects a node with a strut;
and each strut extends between two nodes 15. At each stent end 30
of the hinge stent 5 the pattern of nodes 15 and struts 10 can
differ from the general structure found throughout the stent
section body 35. In this embodiment each node has four struts 10
joined contiguously to it throughout the hinge stent section body
35 and two struts 10 per node at each end of the hinge stent 5. The
metal forming each of the struts 10 flows contiguously, from the
same metal or material of construction, into the node to which it
is joined without an attachment site. The hinge stent 5 has a
generally cylindrical shape wherein the struts 10 are separated by
interstrut openings 40 and nodes 15 are separated by intemodal
openings 45. Intranodal openings 50 are found within the nodes 15
and are connected to the interstrut openings 40. The hinge stent 5
of this embodiment is formed of a stent section 20 that extends
with a single common pattern of nodes 15 and struts 10 throughout
its length. The stent section 20 is made up of more than one repeat
unit 55 of the same type or configuration that are joined
contiguously together and are formed entirely of nodes and struts.
A repeat unit is the smallest repeating portion of the stent
structure which when combined with another repeat unit allows the
stent section to extend in the axial direction 60 and consisting
entirely of nodes and struts. A repeat unit repeats itself at least
twice to form at least two repeat units along the length of a stent
section. The stent section has a substantially continuous structure
throughout its perimeter along the entire length of the stent
section. This continuous structure provides the stent section with
an outer surface that cannot form an abrupt transition in diameter
that can cause a stress riser or stress concentration region to
form in the vessel wall being treated. Such stress risers can lead
to adverse healing of the treated vessel. The hinge stent 5 of this
embodiment has a nondeployed repeat unit length 65 in the axial
direction 60 that repeats more than one time to form the stent
section 20. The repeat unit for this embodiment has a closed
structure with four struts 10 joined to four nodes 15 forming an
enclosed space. The closed structure or closed configuration
provides structural integrity to the stent in an expanded or
deployed state in both the axial and circumferential direction 70.
The closed configuration of the present embodiment provides nodes
and struts that extend in both the circumferential and the axial
direction to form a continuous structure of nodes and struts
extending continuously throughout the stent section. This
continuous configuration of nodes and struts provides the hinge
stent with a coupling or sharing of forces exerted in the axial
direction with those exerted in the circumferential direction. The
circumferential strength to hold the vessel outward is also
supported throughout the entire stent section. A partial expansion
of a portion of the stent section will result in at least a partial
expansion of an axially adjacent portion of the stent section
forming a smooth tapering of the stent section along its axial
length rather than an abrupt change in stent diameter. FIG. 1 B
shows a sectional view with a noninserted diameter, a nonexpanded,
or a nondeployed diameter 75 of the hinge stent 5.
[0077] FIG. 2A is an isometric view of the hinge stent 5 in a
deployed state showing a deployed repeat unit length 80. FIG. 2B is
a sectional view of the hinge stent 5 shown in FIG. 2A showing the
implanted diameter, expanded diameter, or deployed diameter 85. In
the deployed state the hinge stent 5 has a generally cylindrical
uniformly curved hinge stent surface 90. All reference numerals
found in FIGS. 2A and 2B correspond to those elements previously or
otherwise described.
[0078] The hinge stent 5 of the present invention is not required
to have a uniform pattern of nodes 15 and struts 10 throughout its
entire length as shown in this embodiment with a single stent
section. The hinge stent 5 of the present invention can be formed
of a stent section 20 that consists of a length of hinge stent 5
with more than one common pattern of nodes 15 and struts 10, and is
made up entirely of nodes 15 and struts 10. The hinge stent 5 of
the present invention can be formed of a single stent section 20
such as described in the embodiment of FIGS. 1A and 2A or the hinge
stent 5 can be comprised of more than one stent section 20. A hinge
stent 5 with more than one stent section 20 can be formed by
joining one or more nodes 15 located at the end of one stent
section 20 with one or more nodes 15 of another stent section 20
using one or more section connectors as described in more detail
later. The section connectors can be themselves formed of nodes 15
and struts 10 or the section connectors can be a metal bar element.
The nodes 15 on the end of one stent section 20 can be uniformly
joined to the nodes 15 of another stent section 20 along their
perimeters with section connectors formed of nodes 15 and struts
10. It is understood that a single stent section forms the
preferred embodiment of the hinge stent of this embodiment. Section
connectors can be used to allow individual stent sections to be
brought together to form a longer hinge stent.
[0079] The hinge stent 5 of the present invention can be a
balloon-expandable hinge stent 5 or a self-expandable hinge stent
5. As a balloon-expandable stent the hinge stent 5 can be mounted
in its nondeployed state on a balloon of a balloon dilitation
catheter for percutaneous delivery or insertion into the blood
vessel that is to be treated. Upon reaching the site of vessel
injury, the balloon of the balloon dilitation catheter can be
expanded to apply a balloon expansion applied force onto the hinge
stent 5. Once this applied force exceeds the inserted hinge stent
compression yield force the hinge stent 5 will expand to the
deployed diameter 85. In the deployed state the hinge stent 5
exerts an implanted stent expansion holding force outwards to
balance the tissue compression applied force acting inward by the
vessel wall. If the tissue compression applied force exceeds an
implanted stent yield force, the stent will not be able to hold the
native vessel outwards and it will reduce in diameter. The hinge
stent 5 can be formed out of a metal that provides for plastic
deformation of specific portions of the hinge stent 5 during the
expansion from a nondeployed state to a deployed state. Such metals
include titanium, tantalum, stainless steel, and other metals or
alloys suitable for implant.
[0080] As a self-expandable stent the hinge stent 5 can be
delivered or inserted into the vasculature with a delivery sheath
that imparts a sheath compression applied force onto the hinge
stent 5 which is being held elastically in a nondeployed state. The
hinge stent 5 exerts an outward inserted stent expansion elastic
force against the sheath. Once the hinge stent 5 is delivered to
the site of the lesion, it can be removed from the sheath or other
delivery means and allowed to expand outward and exert an implanted
stent expansion elastic force against the vessel wall to hold the
wall outwards with a force that balances the tissue compression
applied force exerted by the vessel wall. The hinge stent 5 can be
formed out of a metal that provides for elastic deformation
including stainless steel, Nitinol, and other metals and metal
alloys.
[0081] A balloon-expandable or self-expandable hinge stent 5 of the
present invention in a deployed state will form an oval hinge stent
surface 93 as shown in FIG. 3 when exposed to a tissue crush
applied force. Such an applied force can occur when the hinge stent
5 is exposed to an externally placed side force or if patient or
tissue movements can cause the hinge stent 5 to undergo a crush
deformation or become oval. When the hinge stent 5 is exposed to a
crush deformation, the struts 10 will bend elastically to a radial
radius of curvature 95 that is smaller in the crushed portion of
the stent perimeter. The hinge stent 5 exerts an outward implanted
stent crush elastic force to resist the crush deformation. All
reference numerals correspond to those elements previously or
otherwise described.
[0082] FIG. 4 is an enlarged detail view of a portion of the hinge
stent 5 shown in FIG. 1A in a nondeployed state and FIG. 5 is an
enlarged detail view of a portion of the hinge stent 5 shown in
FIG. 2A in a deployed state. In this embodiment four struts 10 are
connected to a node which includes a hub 100, four hinges 23, and
four transition regions 25. The hub 100 forms a region of the node
that does not provide significant deformation during an expansion
deformation from a nondeployed state to a deployed state or during
a crush deformation as shown in FIG. 3. Each of the four hinges 23
is contiguously joined on one end to the hub 100. Each hinge has
hinge dimensions which include a hinge width 105, a hinge length
110, a hinge radial dimension 115, and a hinge cross sectional area
120. The hinge is contiguously joined on another end to a
transition region 25 which has a transition region length 125,
transition region width 130, transition region radial dimension
135, and transition region cross sectional area 140. The transition
region 25 is joined contiguously to a strut which has strut
dimensions which include a strut length 145, a strut width 150, a
strut radial dimension 155, and a strut cross sectional area 160.
The hinge dimensions are such that they can provide the hinge stent
5 with a large outward expansion force yet not be subject to
bending due to crush deformation. The strut dimensions are such
that they provide the hinge stent 5 with a strong beam that can
transfer the large outward expansion force of the hinge to the
vessel wall to hold it open, yet allow elastic bending to occur due
to crush deformation. The transition region 25 provides the
appropriate transition between the hinge and the strut to allow the
hinge and strut to perform their respective functions as described
previously in the most efficient manner without allowing for
bending of the transition region 25 due to crush deformation or
bending of the transition region 25 due to expansion deformation
from a nondeployed to a deployed state. The result is a hinge stent
5 that uncouples the expansion forces generated by the hinge from
the bending characteristics generated by the strut in crush
deformation. These characteristics will be further discussed in
general terms and applied to the hinge stent 5 of the present
invention.
[0083] The nodes and struts form a diamond shaped configuration to
the hinge stent in a deployed state. This diamond shaped
configuration is a closed configuration that ties the
circumferential and axial movement within the stent section
together. This closed structure forms a continuous configuration of
struts and hinges that extends throughout the entire stent section.
Forces exerted outward by the stent section are stabilized by the
struts and hinges extending throughout the stent section.
[0084] The stress versus strain relationship for a metal beam such
as a strut or a hinge can in general be estimated by Hooke's law
which states that stress applied to the metal beam is equal to an
elastic modulus times the strain or deformation to which the beam
will deform. This elastic modulus or Young's modulus is a material
property characteristic of the particular metal being used for the
beam. The deformation can be a bending deformation that is
characteristic of the expansion deformation encountered by the
strut or the hinge, or it can be a bending deformation
characteristic of a crush deformation. A beam in an unstressed
state that is exposed to an applied stress below its elastic limit
or yield stress will undergo an elastic flexure or elastic
deformation which is reversible and the bar will return to its
unstressed state upon removal of the applied stress. If the beam is
exposed to an applied stress that is larger than its yield stress
or if it is deformed to an inelastic flexure that is greater than
its elastic limit or proportional limit, or if it is deformed
beyond its yield point, plastic deformation wil occur and the beam
will not return to its original unstressed state with the original
conformation or shape of the beam. The beam will generally return a
fraction of the way back to its initial unstressed state due to the
elastic portion of the deformation.
[0085] Exposing a beam to a torque or moment can result in bending
the beam from a straight shape to a bent conformation with a radius
of curvature. The relationship between the applied moment and the
radius of curvature can be estimated by the equation that states
that moment is equal to Young's modulus times moment of inertia
divided by radius of curvature. The moment of inertia is different
for different cross sectional shapes of the beam that is being
bent. For a beam with a circular cross section and having a
diameter, the moment of inertia is given by Pi time the diameter to
the fourth power divided by 64. For a rectangular beam cross
section with one side of magnitude B and another side of magnitude
H, where B is the magnitude of the side in the radial direction of
the radius of curvature and H is the magnitude of the side
perpendicular to B, the moment of inertia is given by B to the
third power times H divided by 12. Similarly, the beam can be bent
from one radius of curvature to a second radius of curvature with a
similar type of analysis as described above by examining the change
in radius of curvature that is comparable to that of starting with
a flat or straight shape and bending it to a curved shape.
[0086] A beam of a specific length and cross section that is
exposed to a moment will undergo a bending deformation to a
specific radius of curvature and one end of the beam will undergo a
specific displacement with respect to other end. A beam of half the
specific length but of the same cross section exposed to the same
moment will undergo a bending deformation to the same radius of
curvature but the displacement of one end with respect to the other
end will be half of the original specific displacement. Although
the localized deformation within each element of the beam is the
same in both instances, the overall displacement of the longer beam
was twice as great. Expanding upon this concept one finds that for
a similar specific displacement of one end with respect to the
other, a longer beam will have a smaller radius of curvature and
each element of the beam will undergo a smaller localized
deformation. Also expanding upon the concept one finds that a
smaller moment is required to bend the larger beam to the same
displacement of one end with respect to the other as the smaller
beam. These concepts can be applied directly to the hinges 23 and
struts 10 of the present invention. For example, a longer hinge can
provide a greater displacement, corresponding to a greater
deployment angle, without as much localized deformation of the
hinge, than a shorter hinge. A shorter hinge that provides the same
displacement, corresponding to the same deployment angle, will
require a greater moment, than a longer hinge assuming that both
the short and the long hinges 23 are behaving either elastically or
plastically. A similar discussion can be applied to the strut
length 145.
[0087] The hinge cross sectional area 120 is equal to the
multiplication product of the hinge width 105 and the hinge radial
dimension 115. Each hinge has a large hinge radial dimension 115
that does not allow for significant bending deformation along a
radius of curvature with a radius aligned along the hinge radial
dimension 115. The hinge radial dimension 115 is larger than the
strut radial dimension 155. During an expansion deformation of the
hinge stent 5, bending deformation for each hinge occurs to form a
radius of curvature with the radius aligned along the hinge width
105, and this radius of curvature is referred to as the hinge width
radius of curvature 165 (see FIG. 5). The moment of inertia for the
hinge for expansion deformation can be estimated by using the hinge
width 105 to correspond with the magnitude B and the hinge radial
dimension 115 to correspond with the magnitude H. The strut cross
sectional area 160 is equal to the multiplication product of the
strut width 150 and the strut radial dimension 155. The moment of
inertia for each of the struts 10 for bending due to crush
deformation can be estimated using the strut radial dimension 155
to correspond with the magnitude B and the strut width 150 to
correspond with the magnitude H. The radial dimension for the strut
is small in comparison to the hinge radial dimension 115 to allow
the strut to bend elastically to a radius of curvature with the
radius in the direction of the strut radial dimension 155, this
radius of curvature will be referred to as the strut radial radius
of curvature 95 (see FIG. 3). In one preferred embodiment the strut
radial dimensions 155 are preferably less than the radial thickness
of prior art metal wire or uniform metal tubes that are formed into
a prior art stent. The small strut radial dimension 155 allows the
struts 10 to undergo a crush deformation with the strut deforming
elastically and allowing the hinge stent 5 to return to its initial
unstressed state once the tissue crush applied force has been
removed. In the hinge stent 5 of the present invention the hinge
cross sectional area 120 can be varied independently of the strut
cross sectional area 160 to provide the hinged stent with a variety
of expansion force characteristics and other properties. The hinge
width 105 is small in comparison to the strut width 150 such that
the hinge can bend more easily with a hinge width radius of
curvature 165. During expansion deformation, the hinge can bend
within the uniformly curved hinge stent surface 90. If, for
example, the hinge radial dimension 115 were equal to the hinge
width 105 and each were equal to the diameter of a round wire, the
bending moment of the hinge would be approximately 1.67 times
larger than the round wire based on the equation for moment stated
earlier. Thus for a similar magnitude of hinge width 105 in
comparison to the diameter of a round wire, the hinge stent 5 in a
nondeployed state can provide a greater outward extension force by
the hinge to the struts 10 than a circular cross sectional or round
wire. The hinge radial dimension 115 can also be increased in
magnitude to provide an even greater moment of inertia to the hinge
such that even larger moment is generated to produce larger
extensional forces by the hinge stent 5. The larger hinge radial
dimension prevents significant bending of the hinge in the radial
direction during a crush deformation imposed onto the hinge stent
by an external crush force.
[0088] In one preferred embodiment for the design of the
self-expandable hinge stent 5, the hinge radial dimension 115 can
be formed such that it is approximately equal to the radial
thickness of a prior art metal wire or uniform radial thickness
metal tube that is formed into a stent. A larger hinge width 105
will supply a greater implanted hinge stent 5 expansion elastic
force as long as the hinge remains reversibly elastic. For a
self-expandable hinge stent 5 the hinge width 105 can be smaller
than the uniform radial thickness of the prior art stent allowing
the hinge stent 5 to undergo a smaller amount of localized
deformation associated with a bend to a specific radius of
curvature and remain elastic throughout the deformation. A
relatively longer hinge length 110 is preferred to be used in the
self-expandable hinge stent 5 in comparison to the hinge length 110
for a balloon-expandable hinge stent 5 in order to provide the
smaller amount of localized deformation. The self-expandable hinge
stent 5 is preferably formed out of a metal with a higher elastic
modulus than the prior art stents to provide greater outward
expansion force without undergoing plastic deformation. Other prior
art stents cannot be formed out of such high elastic modulus metal
as the present hinge stent without affecting the flexibility of
these stents in a crush deformation. The present hinge stent 5
uncouples the outward expansion force of the hinge stent 5 from the
hinge stent flexibility in a crush deformation by providing a thin
strut radial dimension 155 and other hinge dimensions that can be
varied as discussed earlier. The hinge stent 5 of the present hinge
stent 5 can thus produce an equal or greater expansion moment than
prior art stents that are formed of lower modulus material in order
to balance expansion force with implanted stent crush elastic
force. This embodiment for the hinge stent 5 is particularly useful
for a self-expandable hinge stent 5.
[0089] The hinge length 110 for the self-expandable hinge stent 5
is preferably longer than the hinge length 110 for the
balloon-expandable hinge stent 5. As mentioned earlier, the longer
hinge length 110 allows the deformation in expanding from a
nondeployed state to a deployed state to be spread out over a
longer length and allows the localized deformation within the hinge
to remain less than the yield point necessary for plastic
deformation to occur. The longer hinge length 110 also allows the
implanted stent expansion elastic force to drop off in magnitude
less over the expansion deformation from a nondeployed state to a
deployed state. This allows the outward expansion elastic force to
be more similar over a wide range of deployed or expanded diameters
to which the hinge stent 5 is deployed. Thus the hinge stent 5
exerts a more similar outward expansion force regardless of small
variations in vessel diameter.
[0090] For a balloon-expandable hinge stent 5 the hinge length 110
can be shortened such that the bending deformation of the hinge
associated with expansion from the nondeployed state to the
deployed state exceeds the yield point of the metal used to form
the hinge stent 5. Shortening the hinge length 110 can focus the
deformation of the hinge to a smaller hinge length 110 that
undergoes a greater bending deformation along a hinge width 105
radius of curvature during expansion deformation. Thus a
balloon-expandable hinge stent 5 formed of a high modulus metal can
be required to undergo a plastic deformation in the hinge in an
expansion deformation. This focusing of the deformation with a
short hinge length 110 reduces the amount of rebound or partial
return of the deployed diameter 85 of the hinge stent 5 toward the
nondeployed diameter 75 of the nondeployed state that can occur in
a balloon-expandable stent following the deflation of the balloon.
This partial return or rebound occurs due to elastic deformation
that occurs in part during a predominantly plastic deformation of
the hinge. The hinge length 110 or the hinge stent 5 of the present
invention can range from significantly less than to several times
greater than the radial thickness of prior art stents. For a
bending deformation of the hinge from one hinge width radius of
curvature 165 to another hinge width radius of curvature 165, an
increase in the hinge width 105 will also serve to increase the
amount of hinge material exposed to deformation beyond the yield
point of the metal. A larger hinge width 105 that undergoes plastic
defonnation beyond its yield point will provide the
balloon-expandable hinge stent 5 with a greater implanted stent
expansion holding force to hold the blood vessel outwards. Both
hinge length 110 and hinge width 105 can be adjusted to provide
inelastic flexure of the metal and plastic deformation. The hinge
radial dimension 15 can be further adjusted to control the amount
of force that is required to expand the hinge stent 5 to a
particular amount of deformation during deployment of the hinge
stent 5 and to control the amount of force exerted by the hinge
stent 5 against the vessel wall in its deployed diameter 85. The
balloon-expandable hinge stent 5 is able to uncouple the implanted
stent expansion yield force associated with deformation of the
hinge from the implanted stent crush elastic force associated with
crush deformation of the strut. The balloon-expandable hinge stent
5 is thus able to be balloon expandable and yet be noncrushable due
to characteristics of the strut related to the strut
dimensions.
[0091] The strut cross sectional area 160 can be different than the
hinge cross sectional area 120 and can be varied independently from
it. The strut width 150 is designed to be large enough such that
during expansion of the hinge stent 5 the struts 10 do not bend or
flex significantly within the generally cylindrical uniformly
curved hinge stent surface 90 of the hinge stent 5 with a radius of
curvature having a radius aligned with the strut width 150. The
strut width 150 for the hinge stent 5 of the present invention can
be approximately equal to or up to more than triple the stent
radial thickness of prior art stents. The hinge can therefore
transfer its moment to the strut which then exerts an outward force
upon the vessel wall to hold it outwards. Since the strut width 150
and strut radial dimension 155 provide approximately a rectangular
cross sectional shape for the strut, the strut width 150 can be
similar to the diameter of prior art struts or bars with a circular
cross section and provide a greater moment in resisting bending
deformation to a radius of curvature having a radius in the
direction of the strut width 150 in order to provide support to
hold the blood vessel outwards.
[0092] The strut radial dimension 155 is designed in a preferred
embodiment to be thin in comparison to the hinge radial dimension
115 such that it can flex to form a radius of curvature with a
radius aligned with the strut radial dimension 155; this bending
deformation is similar to a crush deformation that would cause the
hinge stent 5 to form an oval shape (see FIG. 3) for the hinge
stent 5 surface rather than the generally cylindrical hinge stent
surface 90 that it normally has. The struts 10 would remain elastic
due to the small strut radial dimension 155 and due to a choice of
metal such that the struts 10 do not exceed the elastic limit of
the metal. The metal chosen for forming the hinge stent 5 could be
chosen from a high elastic modulus material and still remain
flexible to allow this bending deformation to form an oval shape
due to the thin radial dimension. Prior art stents formed of a
round wire or a bar of high modulus could not provide a combination
of a large outward extension force and a low or soft crushing
force; furthermore they would be prone to plastic deformation in
the crush deformation. The larger radial thickness of prior art
struts or bars which leads to their tendency to plastic deformation
is necessary in the prior art devices in order to provide the
necessary expansion forces provided by the expansion deformation.
With this embodiment of the present invention, a hinge stent 5
could be formed entirely out of a high modulus metal with the hinge
providing a large moment for providing a large implanted
balloon-expandable hinge stent expansion holding force or
self-expandable hinge stent expansion elastic force, and the strut
allowing the hinge stent 5 to be bent elastically to an oval shape
to without plastic deformation and therefore not becoming
permanently crushed. Thus one embodiment of the present invention
is a balloon-expandable hinge stent 5 that is balloon-expandable
and non crushable.
[0093] The strut cross sectional area 160 can be altered
independently of the hinge cross sectional area 120. An increase in
strut radial dimension 155 will provide the strut with a greater
resistance to bending to a strut radial radius of curvature 95.
Thus the hinge stent 5 of the present invention can be designed to
resistant crush deformation that would cause the hinge stent 5 to
form an oval shape. The strut radial dimension 155 required to
provide this additional resistance to crush deformation is smaller
than the hinge radial dimension 115 which does not provide any
significant deformation due to exposure to crush deformation
forces.
[0094] The hinge stent 5 of the present invention has a strut
length 145 that provides a lever arm that is associated with
expansion from a nondeployed state to a deployed state and that is
associated with crush deformation or forming an oval shape. The
hinge stent 5 of the present invention can be formed with any
number of struts 10 and with any strut length 145 that is suited to
a particular application. The hinge of the present invention can
provide a greater moment to hold the vessel open in a deployed
state than the moment provided by prior art circular cross
sectional wire stents of similar width. As stated earlier, the
hinge can be designed with a larger hinge radial dimension 115, a
larger hinge width 105, and with a metal of higher elastic modulus
in order to provide a greater expansion moment. Therefore the hinge
of the present invention can transfer a torque to a strut of larger
strut length 145 than the length of other prior art round wire
stents and provide a greater outward force against the blood vessel
to hold it outward than a round wire stent or other stents. A
longer the strut length 145 will require a stronger hinge moment in
order to hold the blood vessel outwards with a specific expansion
force. This concept was discussed earlier in the discussion of
bending moments. The hinge of the present hinge stent 5 can also be
designed to provide a smaller bending moment during the expansion
deformation by providing a smaller hinge width 105 and a smaller
hinge radial dimension 115. This smaller bending moment can be
better suited to provide the outward expansion force to a smaller
strut in order to hold the vessel outwards. The hinge stent 5 of
the present invention can therefore be used to provide a short or a
long strut length 145 in comparison to other prior art stents. The
strut length 145 for the hinge stent 5 also impacts the flexibility
or ease of the hinge stent 5 to form an oval shape. A long strut
length 145 provides a greater percentage of the perimeter of the
hinge stent 5 in the deployed state to be associated with the
struts 10 in comparison to the hinges 23 or transition regions 25.
Since the struts 10 are more flexible in a crush deformation than
the hinges 23 or transition regions 25, the hinge stent 5 with
longer struts 10 will be more flexible in forming an oval shape.
Crush deformation is therefore tied to strut length in addition to
strut width and strut radial dimension. The strut width 150 and
strut radial dimension 155 are therefore tied to the strut length
145 in order to provide a hinge stent 5 with an ability to flex in
crush deformation. For example, if the strut length 145 were to be
reduced in length while trying to maintain the same crush
flexibility and expansion strength, the strut radial dimension 155
would have to be reduced to compensate for the reduced flexibility
due to the strut length 145, and the strut width 150 would be
altered to provide a bending moment in the direction of the strut
width 150 in order to transfer the same expansion force provided by
the hinge.
[0095] A deployment angle 170 (see FIG. 6) of the present hinge
stent embodiment as shown in FIGS. 1A and 2A is preferred to remain
small in the deployed state such that the deployed repeat unit
length 80 (see FIG. 2A) is not significantly shorter than the
nondeployed repeat unit length 65. A deployment angle 170 of less
than approximately 50 degrees will provide a length reduction of
less than 10 percent in going from a nondeployed state to a
deployed state. A small percentage change in repeat unit length
provides the hinge stent 5 with a capability for more accurate
placement of the hinge stent 5 within the blood vessel under
fluoroscopy.
[0096] The hinge stent 5 of the present invention can be designed
such that the hinge will provide a large deployment angle 170
ranging from zero to over 190 degrees. The hinge of the present
invention can be formed from a metal of large Young's modulus as
stated earlier. The hinge can be formed of a thin hinge width 105
and a long hinge length 110 such that the moment maintained by the
hinge will still be adequate even at a large bending deformation
angle or deployment angle 170. Thus the hinge of the present
invention can supply adequate outward force at a deployment angles
170 ranging from zero to over 190 degrees.
[0097] The transition regions 25 serve to join the hinges 23 to the
struts 10. During the expansion of the hinge stent 5 from a
nondeployed state to a deployed state the transition region 25
transfers the moment of the hinge to the strut without undergoing
any significant transition region 25 bending. If the hinge stent 5
is exposed to a crushing deformation, the struts 10 will bend
elastically to form a new strut radial radius of curvature 95 but
the transition region 25 and the hinge will not bend in crush
deformation. The transition region width 130, transition region
radial dimension 135, and transition region cross sectional area
140 are such that the transition region 25 does not undergo
significant bending deformation in either the direction of the
transition region width 130 or transition region radial dimension
135. The transition region length 125 is preferably short or abrupt
in order to maximize the length of the struts 10 or the hinge. The
transition region width 130 ranges from the hinge width 105 to the
strut width 150 and the transition region radial dimension 135
ranges from the hinge radial dimension 115 to the strut radial
dimension 155. Stepped changes in hinge or strut cross sectional
areas 160 are avoided to eliminate the possibility of metal
fracture at that site. The transition region 25 is designed to
transfer the moment generated by the hinge to the strut without
bending in the direction of the transition region width 130 and to
resist bending in the direction of the transition region radial
dimension 135 when the hinge stent 5 is deformed with a crush
deformation.
[0098] The hinge provides an outward expansion force against the
vessel wall when the hinge stent 5 is in a deployed state. This
outward force is an expansion holding force for a
balloon-expandable hinge stent 5 and an expansion elastic force for
a self-expandable hinge stent 5. As the balloon-expandable or
self-expandable hinge stent 5 is exposed to a crush applied force
that causes a crush deformation, the struts 10 of the hinge stent 5
exert a crush elastic force to resist crush deformation. It is
preferred that the outward expansion force of the hinge is greater
than the crush elastic force of the strut. Thus in a crush
deformation, the deployment angle 170 does not undergo significant
change. Other prior art stents tend to undergo local change in
deployment angle 170 when exposed to crush deformation due to the
high degree of coupling between expansion and crush characteristics
provided by the prior art stents. The present hinge stent 5
uncouples the expansion characteristics from the crush
characteristics. For a self-expandable hinge stent 5 the implanted
hinge stent expansion elastic force provided by the hinge provides
a larger outward force to hold the vessel outwards and maintains a
constant perimeter in contact with the vessel wall without
significant change in deployment angle 170, and allows the struts
10 of the hinge stent 5 to flex in a crush deformation to an oval
shape elastically with a lower implanted stent crush elastic force.
For a balloon-expandable hinge stent 5 the implanted hinge stent
expansion holding force provided by the hinge provides a greater
outward force to hold the vessel outwards with a constant perimeter
without significant change in deployment angle 170, and allows the
struts 10 of the hinge stent 5 to flex in a crush deformation to an
oval shape elastically with a lower implanted stent crush elastic
force.
[0099] The hinge length 110, hinge width 105, and hinge radial
dimension 115 provide an outward expansion force to the hinge 23 as
the hinge undergoes an expansion deformation in the uniformly
curved hinge stent surface 90. The struts 10 transfer the expansion
forces generated by the hinges 23 to the vessel wall. The struts 10
do not deform in the uniformly curved hinge stent surface 90 due in
part to the larger strut width 150 in comparison to the hinge width
105. If the hinge stent 5 is subjected to a crush deformation such
that it forms an oval hinge stent surface 93, the struts 10 have a
strut length 145, strut width 150, and strut radial dimension 155
that will provide for bending of the struts 10 in the radial
direction with an elastic deformation. The hinge 23 will not deform
in the radial direction upon exposure to a crush deformation due in
part to the large hinge radial dimension l15 in comparison to the
strut radial dimension 155. A longer strut length 145 allows the
hinge stent 5 to have a greater percentage of the hinge stent
associated with the struts 10 in comparison to the hinges 23 and
hence provides the hinge stent 5 with a greater flexibility in
bending due to a crush deformation.
[0100] Another primary embodiment of the hinge stent 5 of the
present invention is shown in FIG. 7 in a nondeployed state and in
FIG. 8 in a deployed state. An enlarged detailed view of a portion
of the hinge stent 5 shown in FIG. 7 is shown in FIG. 9 and an
enlarged detailed view of a portion of the hinge stent 5 shown in
FIG. 8 is shown in FIG. 10. Discussion of FIGS. 7-10 will occur
together with reference numerals found collectively in these
figures. In this embodiment three struts are joined to each node
throughout the body of the hinge stent 5. Two different types of
nodes 15 are found in this hinge stent 5, a Y node 175 and a T node
180. The Y node 175 has a small portion termed a Y hub 185 that
does not deform significantly during an expansion deformation from
the nondeployed state to the deployed state or during a crush
deformation. Similarly the T node 180 has a small portion termed a
T hub 190 that does not undergo a significant deformation. A node
is not required to have a hub region and the T nodes 180 and Y
nodes 175 of this embodiment could have been shown without the
small T hub 190 and Y hub 185, respectively, without affecting the
overall function of the hinge stent 5. The Y node 175 is joined via
two Y arm transition regions 195 and via two Y arm hinges 200 to
two arm struts 205, and the Y node 175 is also joined via a Y tail
transition region 210 and via a Y tail hinge 215 to a tail strut
220. The T node 180 is joined via two T arm transition regions 225
and via two T arm hinges 230 to two arm struts 205, and the T node
180 is also joined via a T axial transition region 235 and via a T
axial hinge 240 to an axial strut 245. The struts joined to the Y
nodes 175 and T nodes 180 have strut widths 150, strut lengths 145,
and strut radial dimensions 155; the hinges 215, 200, 240, &
230 associated with the Y nodes 175 and T nodes 180 have hinge
widths 105, hinge lengths 110, and hinge radial dimensions 115 that
bear the same reference numerals as described in FIGS. 1A-6 in the
first embodiment of the hinge stent 5 of the present invention. The
dimensions for the transition regions for the present embodiment
also bear the same reference numerals as described in FIGS. 1A-6.
The arm struts 205, tail struts 220, axial struts 245, Y arm hinges
200, Y tail hinges 215, T arm hinges 230, T axial hinges 240, Y arm
transition regions 195, Y tail transition regions 210, T arm
transition regions 225, and T axial transition regions 235 found in
this embodiment as shown in FIGS. 7-10 behave in the same manner as
the struts 10, hinges 23, and transition regions 25, respectively
described earlier for the first embodiment shown in FIGS. 1A-6.
Specific differences between this embodiment shown in FIGS. 7-10
will be further discussed.
[0101] The hinge stent 5 of the embodiment shown in FIGS. 7-10 has
a generally cylindrical shape with a deployed diameter 85 and a
nondeployed diameter 75. The hinge stent 5 of this embodiment is
made up of a stent section 20 formed of a single common pattern of
struts and hinges throughout the entire length. Repeat units 55 are
joined contiguously together and allow the stent section 20 to
extend in an axial direction upon addition of additional repeat
units. In this embodiment the nodes and struts form a closed
structure to provide integrity to the structure and strength in the
axial direction 60 and circumferential direction 70 of the hinge
stent 5. The continuous structure of struts and hinges extend along
the perimeter and throughout the length of the stent section. This
continuous structure does not allow abrupt changes in stent
diameter to occur as one portion of the stent is expanded to a
deployed diameter, and does not allow stress risers to occur in the
vessel wall.
[0102] This embodiment as shown in FIGS. 7-10 can be a
self-expandable hinge stent 5 or a balloon-expandable hinge stent
5. In a nondeployed state and with a nondeployed diameter 75 the
balloon-expandable hinge stent 5 can be mounted on a balloon of a
balloon dilitation catheter for percutaneous delivery to the site
of a vascular lesion. Once the hinge stent 5 has reached the site
of the lesion the balloon of the balloon dilitation catheter can be
expanded to expand the hinge stent 5 from a nondeployed state to a
deployed state. The hinge stent 5 of this embodiment has
significant axial flexibility in passing along a tortuous pathway
to reach the site of the lesion.
[0103] The self-expandable hinge stent 5 of this embodiment can be
contained in a delivery sheath that applies a compression applied
force to maintain the hinge stent 5 in a nondeployed state for
percutaneous delivery to the site of vessel lesion. The
selfexpandable hinge stent 5 also is very flexible in a nondeployed
state such that it can be easily delivered through tortuous vessels
to reach the lesion site. For a tubular shaped hinge stent 5 such
as that shown in FIGS. 7-10 to pass along a tortuous pathway or
around a curve requires that the portion of the stent on the
outside of the curve be able to extend in length, or that the
portion of the stent on the inside of the curve be able to compress
in length, or that both can occur. Both the balloon-expandable and
self-expandable hinge stent 5 of this embodiment obtain this axial
flexibility by allowing the portion of the stent on the outside of
the curve to extend in length and allow some compression along the
inside of the curve. This extension in length can occur by allowing
two T nodes 180 which are adjacent to each other to move apart from
each other in an axial direction 60. Once the hinge stent 5 of this
embodiment has reached the site of the vascular lesion, it is
important that the hinge stent 5 remain flexible in an axial
direction 60 in a deployed state. Often the vascular lesion can be
located on a curved portion of a blood vessel and requires that the
hinge stent 5 can extend along the outside radius of curvature of
the curved vessel or compress along the inside radius of curvature.
An illustration of a hinge stent with three struts per node,
similar to that shown in FIGS. 7-10 is shown in a bent or curved
configuration in FIG. 11. All reference numerals correspond to
those elements previously or otherwise described.
[0104] The Y arm hinges 200 and T arm hinges 230 each have a hinge
length 110, hinge width 105, and hinge radial dimension 115. The
hinge radial dimension 115 can generally have a magnitude similar
to the radial thickness of a standard prior art stent. In order to
provide a greater flexibility to the hinge stent 5 in traversing
around a tortuous path, the hinge radial dimension 115 for the Y
arm hinges 200 and the T arm hinges 230 can be reduced in order to
provide a greater flexibility to these hinges. For a
balloon-expandable hinge stent 5 the hinge width 105 can be reduced
to reduce the amount of force necessary to generate deformation of
Y arm hinges 200 and T arm hinges 230 and allow the two adjacent T
nodes 180 to move apart easily while traversing around a comer.
This movement of the T nodes 180 away from each other can occur in
a nondeployed state during insertion of the hinge stent 5 or after
implantation of the hinge stent 5 in a curved portion of the blood
vessel. For a self-expandable hinge stent 5 the hinge width 105 can
be reduced and the hinge length 110 can be increased to reduce the
amount of force necessary to generate deformation of the Y arm
hinges 200 and T arm hinges 230 and allow the two adjacent T nodes
180 to move apart as the hinge stent 5 traverses around a comer.
Therefore, this embodiment for a self-expandable or
balloon-expandable hinge stent 5 can be made flexible in traversing
around comers of a tortuous path in both the nondeployed state and
the deployed state. The hinge stent 5 of this embodiment has a Y
tail hinge 215 that is designed to provide a large expansion force
to ensure that the hinge stent 5 is provided with a large hoop
strength in a deployed state to hold the vessel outwards with
adequate force. This Y tail hinge 215 is joined via a Y tail
transition region 210 to a tail strut 220 with a large strut width
150 that transfers the large expansion force of the Y tail hinge
215 to the vessel wall. Increased hinge expansion force can be
generated as discussed earlier in previous embodiments and include
enlarging the hinge width 105 and hinge length 110. The Y arm
hinges 200 and the Y arm struts 205 are connected in a closed loop
247 to ensure that a large hoop strength is maintained. This closed
loop includes a Y node 175 connected to an arm strut, to a T node
180, to an arm strut, to a Y node 175, to an arm strut, to a T node
180, to an arm strut and back to the original Y node 175. The hinge
stent also has a closed configuration 248 that provides integrity
and stability in both the circumferential and axial direction. This
closed configuration 248 consists of struts and hinges joined to
form an enclosed space. Such a closed configuration 248 is formed
by the tail struts 220, Y nodes 120, arm struts 205, T nodes 180,
and axial struts 245. The geometry of the closed loop 247 along
with having a long hinge radial dimension 115 for the hinges 200
& 230 of the closed configuration 248 allows the closed
configuration 248 to maintain a large hoop strength. The
flexibility of the hinges of the closed loop 247 allows the T nodes
180 to move apart easily during bending of the hinge stent 5 around
a curved path. Thus the hinge stent 5 of the present invention can
be flexible around corners and provide a large outward force to
hold the vessel outwards. The closed configuration provides a
structure of nodes and struts that extends both circumferentially
as well as axially and is therefore continuous throughout the stent
section. The closed configuration of this embodiment is a
continuous configuration of nodes and struts with struts connected
via hinges to the nodes forming the stent section of this
embodiment. The continuous configuration of hinges and struts
substantially along the perimeter and throughout the length of the
stent section provide this hinge stent with hoop strength in the
circumferential direction that is supported throughout the stent
section including in the axial direction. The forces supplied by
the hinge stent to hold the vessel outward are distributed through
the nodes and struts throughout the entire stent section. The
continuous structure of struts and hinges does not allow the stent
section to undergo an abrupt change in diameter which could lead to
stress concentration points in the tubular vessel being
treated.
[0105] Stents in general and the hinge stent 5 of this invention
can be exposed to a bending moment applied by the tissue of the
blood vessel and surrounding tissue as they traverse through a
tortuous vessel or are implanted in a curved portion of a blood
vessel. This applied bending moment causes the hinge stent 5 as
shown in FIGS. 7-10 to form a curved shape as shown in an
illustration of a three strut per node hinge stent in FIG. 11. The
hinge stent 5 as well as other prior art stents in general that are
bent into a curved shape by a vessel will exert a bending moment
outward against the blood vessel that is equal and opposite to the
tissue applied bending moment. Boundary conditions imposed upon the
ends of the hinge stent 5 require that the hinge stent radius of
curvature 250 found along the stent axis 255 in the stent
mid-length 260 is very often not the same as the hinge stent radius
of curvature 250 at the ends 30 of the hinge stent 5. As a result,
the stent exerts a lateral force against the side of the blood
vessel as the stent tries to move back to an equilibrium shape that
has a generally straighter stent axis than the curved stent axis
imposed on the stent by the curved blood vessel. This lateral force
imposed onto the vessel wall can generate a hyperplastic tissue
growth at the ends of the stent and can lead to stenosis and
eventual occlusion of the stent. This potential problem can be
addressed with the hinge stent 5 of the present embodiment as shown
in FIGS. 7-10 by providing a greater amount of flexibility to the Y
arm hinges 200 and T arm hinges 230 located near the stent ends 30
in comparison to those located near the stent mid-length 260. Hinge
flexibility can be increased by reducing the hinge width 105 and
hinge radial dimension 115. Hinge flexibility can be gradually
tapered such that those T arm hinges 230 and Y arm hinges 200 near
the stent ends 30 have the greatest flexibility and they become
gradually more stiff as the hinges get nearer to the stent
mid-length 260. In a deployed state a hinge stent 5 of this design
can provide enhanced healing at the ends of the stent. The outward
expansion force exerted by the stent to hold the blood vessel
outwards is independent of its flexibility or ability to bend
around a curve. The outward expansion force exerted outward to hold
the blood vessel outward is generated by the Y tail hinge 215 along
with the geometry of the closed configuration. Thus, this
embodiment of the hinge stent 5 can be very flexible in traversing
around a comer of a blood vessel and have large expansion force to
hold the vessel outwards. The hinges can provide tapered
flexibility such that the stent is more flexible in bending around
a curved passage near the ends of the stent. This tapered
flexibility provided by the dimensions of the hinges can be equally
well applied to the hinge stent embodiments shown in FIGS. 1A-6 as
well as the hinge stent embodiments shown later in FIGS.
17A-27.
[0106] In a crush deformation, the embodiment of the hinge stent 5
shown in FIGS. 7-10 behaves very similarly to the hinge stent 5
shown in FIGS. 1A-6. The tail struts 220, and arm struts 205 have
thin radial dimensions in comparison to the radial dimensions of
the Y tail hinges 215, Y arm hinges 200, and T arm hinges 230. In a
crush deformation, the tail struts 220 and arm struts 205 can bend
elastically to a strut radial radius of curvature 95 (see FIG. 3)
as the hinge stent 5 forms an oval shape. The strut lengths 145 for
the tail struts 220 and the arm struts 205 also affect the ability
of the hinge stent 5 to form an oval shape when subjected to a
crush deformation. A longer strut length 145 will allow a greater
percentage of the perimeter of the hinge stent 5 in a deployed
state to be occupied by the struts 220 & 205 as opposed to
hinges 215, 200 & 230 and transition regions 210, 195 &
225. Since the struts 220 & 205 are more flexible in a crush
deformation than either the hinges 215, 200 & 230 or the
transition regions 210, 195 & 225 longer struts tend to provide
the hinge stent 5 with an increased flexibility to form an oval
shape due to a crush deformation. The hinges will not bend to form
a radius of curvature in the direction of the hinge radial
dimension 115 due to the larger hinge radial dimension 115. During
expansion from a nondeployed state to a deployed state the Y tail
hinges 215, Y arm hinges 200, and T arm hinges 230 undergo a
deformation. For a balloon expandable hinge stent 5 this
deformation involves plastic deformation that was described in the
embodiment shown in FIGS. 1A-6. The hinge width 105, hinge length
110, and hinge radial dimension 115 are all involved in determining
the amount of expansion holding force applied by the stent in
holding the blood vessel outwards. A short hinge length 110 helps
to focus the deformation of the metal hinge to create a greater
amount of plastic deformation. This focusing of the deformation
reduces the amount of rebound effect or partial return of the
deployed diameter 85 of the hinge stent 5 toward the nondeployed
diameter 75 due to elastic deformation that accompanies the plastic
deformation. A larger hinge width 105 serves to increase the amount
of localized plastic deformation within the hinge for a particular
deployment angle 170. A larger hinge radial dimension 115 provides
a greater magnitude of stent expansion holding force for the
balloon-expandable hinge stent 5 to exert against the vessel wall
in a deployed state. For a self-expandable hinge stent 5 the
deformation of the hinges 215 in going from a nondeployed state to
a deployed state is elastic. A longer hinge length 110 provides the
hinge stent 5 with less localized hinge deformation for a
deployment to a particular deployment angle 170. The longer hinge
also allows the drop off of expansion elastic force to be less
during its deployment from a nondeployed state to a deployed state.
The smaller drop off of expansion elastic force allows the hinge
stent 5 to exert a more similar expansion elastic force for a wider
range of vessel diameters. A smaller hinge width 105 and hinge
radial dimension 115 will provide a smaller magnitude of stent
expansion elastic force exerted by the hinge stent 5 against the
vessel wall.
[0107] The tail struts 220 and arm struts 205 have a larger strut
width 150 than any of the hinge widths 105. The strut width 150
allows the expansion force and moments generated by the Y tail
hinges 215, Y arm hinges 200, and T arm hinges 230 to be delivered
to the vessel wall to hold it outwards.
[0108] The T nodes 180 provide a contiguous junction between the
axial struts 245 and the arm struts 205. Each T node 180 includes a
T axial hinge 240 and a T axial transition region 235 that is
joined contiguously to the axial strut 245. The T axial hinge 240
is similar to other hinges described and it has a hinge width 105
that is small in comparison to the axial strut width 150. The T
axial hinge 240 ensures that the hinge stent 5 of this embodiment
maintains a continuous stent axis without shifting due to possible
misalignment of repeat units 55 along the hinge stent axial
direction 60. The axial struts 245 maintain an axial length for the
stent that does not change from its nondeployed state to its
deployed state. Maintaining a constant axial length from the
nondeployed state to the deployed state provides the hinge stent 5
of this invention with the additional advantage of accurate
placement of the hinge stent 5 into the vasculature under
fluoroscopy.
[0109] The balloon-expandable hinge stent 5 of the embodiment shown
in FIGS. 7-10 is a noncrushable hinge stent 5. The advantages of a
balloon-expandable stent provide the hinge stent 5 of this
invention with an ability to position the stent accurately at the
site of the lesion prior to deploying it to its expanded or
deployed diameter 85. The maintenance of a constant axial length
during deployment further enhanced the capability of this stent to
be positioned accurately within the vasculature. This hinge stent 5
is balloon-expandable due to the plastic deformation which occurs
in the Y tail hinges 215, the Y arm hinges 200, and the T arm
hinges 230 during the deployed from a nondeployed diameter 75 to a
deployed diameter 85. The balloon-expandable hinge stent 5 of this
invention will not form a plastic deformation if exposed to a crush
deformation. The tail struts 220 and the arm struts 205 will bend
elastically during a crush deformation due to their thin radial
dimension in comparison to the hinge radial dimensions 115. The
larger hinge radial dimensions 115 for the Y tail hinges 215, the Y
arm hinges 200, and the T arm hinges 230 will not allow these
hinges to deform in a radial direction during exposure to a crush
deformation. Exposure of the hinge stent 5 to crush deformation
will also not cause the hinges to change in deployment angle 170.
The Y tail hinge 215 has enough strength due to its hinge
dimensions and the metal of construction. The Y arm hinges 200 and
T arm hinges 230 are stabilized by the geometry of the closed
construction as described earlier. This hinge stent 5 is ideally
suited for placement in the carotid artery of the body where
placement of a stent is important and the stent cannot be crushed
due to externally applied forces to the neck of the individual.
Then balloon-expandable hinge stent 5 of the present invention is
therefore balloon-expandable and noncrushable.
[0110] The self-expandable hinge stent 5 of the embodiment shown in
FIGS. 7-10 and other embodiments of the present invention provide a
stent with the property that the inserted stent expansion elastic
force with which the hinge stent 5 pushes out against the sheath
during stent insertion and the stent expansion elastic force with
which the hinge stent 5 exerts outwards against the vessel wall are
independent and uncoupled from the implanted stent crush elastic
force with which the hinge stent 5 exerts against crush
deformation. The advantage of this property is that the hinge stent
5 can hold a vessel outward with a very large force and yet be very
soft or easily flexible in a crush deformation. This property can
help reduce hyperplastic growth and stenosis that can occur at or
near the ends of the stent and within the blood vessel near the
ends of the stent. Since the expansion elastic force is uncoupled
from the crush elastic force, it is equally possible to form a
hinge stent 5 with very low expansion elastic force and a very
large crush elastic force. A hinge stent 5 of this character would
be very difficult to crush or form an oval shape and yet the force
that it exerted outwards against the vessel wall could be very low.
A hinge stent 5 of this character would be well suited to a vessel
of the body with a thin wall that did not require a large outward
expansion elastic force to hold it open, but could be exposed to a
large crushing force. Some veins of the body may be suitable
candidates for a hinge stent 5 of this character. The Y tail hinges
215, the Y arm hinges 200, and the T arm hinges 230 with hinge
widths 105 smaller than strut widths 150 and radial dimensions
larger than strut radial dimensions 155 provide the expansion
elastic force for the self-expandable hinge stent 5. These hinges
215, 200, & 230 undergo elastic deformation as the hinge stent
5 expands from the nondeployed diameter 75 to the deployed diameter
85. The hinge lengths 110 can be long enough to provide elastic
deformation of the hinges 215 during the expansion deformation. Due
to the larger hinge radial dimension 115 the hinges 215, 200 &
240 will not undergo deformation in the radial direction associated
with a crush deformation. The hinges 215, 200 & 240 will also
not change in their deployment angle 170 as the hinge stent 5 is
exposed to a crush deformation. The tail struts 220 and arm struts
205 have a thin radial dimension to provide for elastic bending to
a radial radius of curvature 95 when exposed to crush deformation
or forming an oval shape. A longer length for the struts provides
the hinge stent 5 with a greater percentage of the stent perimeter
associated with struts 220 & 205 as opposed to hinges 215, 200
& 230 or transition regions 210, 195 & 225. This can
provide a more flexible hinge stent 5 in a crush deformation in
forming an oval shape due to elastic bending of the struts. The
large strut width 150 provides the hinges 215, 200 &230 with a
beam that will transfer the elastic expansion force outward against
the vessel wall without bending in the direction of the strut width
150. The self-expandable hinge stent 5 therefore has the Y tail
hinges 215, the Y arm hinges 200, and the T arm hinges 230 for
providing expansion elastic force, and has tail struts 220 and arm
struts 205 for providing crush elastic force.
[0111] The embodiment of the hinge stent 5 shown in FIGS. 7-10 can
be machined using machining techniques described for the embodiment
shown in FIGS. 1A-6. For the balloon-expandable hinge stent 5 a
metal tube with an intermediate diameter 265 as shown in FIG. 12
between the nondeployed diameter 75 and the deployed diameter 85
can be used as a starting material. Standard mechanical machining
of the outer surface of the tube can be performed to form the outer
contour of all the hinges, transition regions, and struts of the
hinge stent. Laser machining, chemical etching, electrochemical
machining, mechanical machining, or other machining techniques can
then be used to remove metal material and leave the structure as
shown in FIG. 12. The tubular structure shown in FIG. 12 could then
be compressed down to a smaller nondeployed diameter 75 such as
shown in FIG. 7 forming the hinge stent 5 in a nondeployed state.
Machining the balloon-expandable hinge stent 5 in an intermediate
state with an intermediate diameter 265 allows the outer contour of
the Y nodes 175, T nodes 180, arm struts 205, tail struts 220, and
axial struts to be easily machined in either an axial or
circumferential direction 70. The laser, chemical, electrochemical,
or other machining techniques used to form the strut widths 150,
hinge widths 105, and other dimensions of the Y and T nodes (175
& 180) and the arm, tail, and axial struts (205, 220, &
245) can also be more easily performed with respect to an axial or
circumferential direction 70. The deformation performed on the Y
tail hinges 215 in going from the intermediate state to the
nondeployed state is less than the deformation that the Y tail
hinge 215 encounters during its deployment from the nondeployed
state to the deployed state. As the Y tail hinge 215 is deformed
from the nondeployed state as shown in FIG. 7 during the deployment
of the hinge stent 5 it will pass through the intermediate state as
shown in FIG. 12 and will continue to be deformed until it reaches
the deployed state as shown in FIG. 8. The deformation of the Y
tail hinge 215 in going from the intermediate state to the
nondeployed state is in the opposite direction as the deformation
in going from the nondeployed state to the deployed state.
Alternately, it is understood that the balloon-expandable hinge
stent 5 of this embodiment can be machined in the nondeployed state
as shown in FIG. 7. In this case the hinge stent 5 would not
require significant further compression to a smaller diameter prior
to deployment to the deployed diameter 85. A small amount of
compression of the nondeployed hinge stent 5 can be performed in
order to enhance the attachment of the hinge stent 5 to the balloon
of a balloon dilitation catheter for insertion into the
vasculature. All reference numerals correspond to those elements
previously or otherwise described.
[0112] The self-expandable hinge stent 5 of the present invention
can be machined using the same techniques described for the
balloon-expandable hinge stent 5 using a metal tube with a deployed
diameter 85 as shown in FIG. 8. The hinge stent 5 could then be
machined with a deployed diameter 85 and folded to form a
nondeployed diameter 75 as shown in FIG. 7. The hinge stent 5 is
placed within a sheath which holds the hinge stent 5 in the
nondeployed diameter 75 and allows the hinge stent 5 to be
delivered to the site of the vessel lesion where it is allowed to
expand out to its deployed diameter 85. The self-expandable hinge
stent 5 can also be machined with a smaller diameter than the
deployed diameter 85. Metal hardening techniques, metal elastic
memory techniques such as those known in the art of working with
Nitinol or other alloys, or other techniques can be employed to
provide elastic behavior to all the hinges of the hinge stent 5 of
the present invention.
[0113] Embodiments of the hinge stent 5 of the present invention
have been described which have four struts per node and three
struts per node throughout the stent section body 35. The four
strut per node embodiment and the three strut per node embodiment
each were formed of a stent section 20 having a strut and hinge
conformation with a uniform pattern along the perimeter and
extending throughout the axial length of the stent section body 35.
The hinge stent 5 of the present invention can include a stent
section which includes a varying number of struts per node ranging
from two struts per node to approximately six struts per node. A
hinge stent structure could be formed of a single stent section
with a varying number of nodes and struts that extends throughout
the stent section body 35. Such a hinge stent can be formed, for
example, by joining a portion of a stent section of the embodiment
shown in FIGS. 1A-6 with a portion of a stent section of the
embodiment shown in FIGS. 7-10. The end nodes of each portion, for
example, can be shared or form common nodes between each portion.
The hinge stent 5 of the present invention can also be formed of
stent sections 20 which are joined with uniformly spaced junctions
along the perimeters of each stent section 20, with a first section
having a specific number of struts per node and being joined to a
second section that has another number or a varying number of
struts per node and positioned generally axially from the first
section. A hinge stent 5 of this structure would be comprised of
more than one stent section with struts and hinges extending along
a perimeter and also throughout the stent section body 35. The
hinge stent 5 of the present invention can additionally be formed
of two or more stent sections 20, each stent section 20 being
joined together with an adjacent section by one or more section
connectors, each section being comprised of repeat units. Such
section connectors can be formed of nodes and struts which are
similar to the nodes and struts with hinges connecting the nodes
with the struts described thus far in this disclosure or the
section connectors can be formed of a metal element as will be
described later in this disclosure.
[0114] FIGS. 13A and 13B show an embodiment of the hinge stent 5 of
the present invention with two stent sections 20 being joined
contiguously together by a hinged interconnector 270. The hinged
interconnector 270 is comprised of at least one strut and is joined
to at least one connecting node 275 from each of the sections to
which it is joined, each node having a hinge that is connected and
providing flexure with respect to a strut of the hinged
interconnector. Nodes and struts which form a hinged interconnector
270 have a structure that is similar to the node and strut
structure that has been described in the embodiment of FIGS. 1A-6
and FIGS. 7-10. A hinged interconnector 270 can have several nodes
and struts joined together and joined to connecting nodes 275 of
each section. This hinge stent 5 does not form a single stent
section 20 as described earlier in the embodiment shown in FIGS. 1
A-6 or the embodiment shown in FIGS. 7-10, but instead has more
than one stent section 20. The stent sections 20 being joined in
this embodiment are similar in structure to the stent section 20
shown in the embodiment of FIGS. 1A-6 although stent sections of
the embodiment shown in FIGS. 7-10 could equally have been shown
joined by the hinged interconnector 270. Other end nodes 280 at the
end of the stent section 20 are shown not joined to an hinged
interconnector 270. The hinged interconnector 270 is joined to a
connecting node 275 of each stent section 20. The hinged
interconnector 270 of this embodiment has two connecting struts 285
that are joined together by a flex node 290 that consists of a flex
hinge 295 and two flex transition regions 300. The connecting node
275 of each stent section 20 that is to be joined has a connecting
hinge 305 that is joined to a connecting transition region 310. The
connecting transition region 310 of the connecting node 275 is
joined to one connecting strut of the hinged interconnector 270.
The hinged interconnector 270 of this embodiment of the hinge stent
5 provides an ability of the hinge stent 5 to be more flexible in
traversing around a curved blood vessel during insertion as well as
more flexibility during implant in a curved vessel. The hinged
interconnector 270 also supplies axial length stability and
transfer of expansion and crush forces in the axial direction. The
hinged interconnector 270 allows the portion of the hinge stent 5
located in the outside of the curve to extend in axial length and
the portion of the hinge stent 5 on the inside of the curve to
compress in axial length. The hinged interconnector 270 can
increase or decrease in length along the axial direction of the
hinge stent due to flexure from one or more of its hinges.
[0115] The connecting hinges 305 and the flex hinge 295 have a
small hinge width 105 in comparison to the strut width 150 such
that these hinges can deform easily either plastically or
elastically as the hinge stent 5 is placed into a curved blood
vessel pathway. A longer hinge length 110 for the connecting hinge
305 or the flex hinge 295 allows a greater amount of hinged
interconnector 270 deformation to occur while remaining elastic. A
shorter hinge length 110 can be used to focus the deformation into
a smaller region of the connecting hinge 305 or the flex hinge 295
and generate a greater percentage of localized plastic deformation
within the hinge with less rebound or partial return to the initial
hinge shape or initial hinge conformation. The strut radial
dimension 155 is small in comparison to the hinge radial dimension
115 to allow for ease of elastic deformation of the strut to
undergo a bending deformation in the direction of its radial
dimension in passing around a curved vessel. The large hinge radial
dimension 115 and large strut width 150 provide a torque
characteristic in the circumferential direction 70 that can be
transmitted from one stent section 20 to the adjacently joined
stent section 20. A longer strut length 145 will provide a greater
percentage of the hinged interconnector 270 to be associated with
the connecting struts 285 in comparison to the flex hinges 295,
connecting hinges 305, connecting transition regions 310, or flex
transition regions 300. An increased strut length 145 will allow
the hinged interconnector 270 to provide a greater flexibility to
the hinge stent 5 in passing around curved vessels.
[0116] Each end node 280 (see FIG. 13A) of a stent section 20 can
be formed into a connecting node 275 and connected via an hinged
interconnector 270 to another stent section 20 to form an
embodiment of the hinge stent 5 of the present invention. This
embodiment is shown in FIG. 14 where two sections similar to the
embodiment shown in FIGS. 1A-6 are connected in a contiguous and a
uniform manner along the perimeters of each stent section 20. The
interconnectors 270 comprised of nodes and struts used in this
embodiment are the same as the interconnectors 270 shown and
described in FIGS. 13A and 13B although other types of
interconnectors 270 can be used. The hinge stent 5 of this
embodiment has four strut per node portions 315 that are similar to
the stent section body 35 shown in the embodiment of FIGS. 1A-6.
The hinge stent 5 also has a three strut per node portions 320 and
two strut per node portions 325. This hinge stent 5 embodiment will
be very flexible in an axial direction 60 due to the three strut
per node portions 320 and two strut per node portions 325. As the
hinge stent 5 of this embodiment is placed into a curved portion of
a blood vessel, these portions can extend and compress as described
in the embodiment shown in FIG. 13 providing this hinge stent 5
with great flexibility.
[0117] Another embodiment of the hinge stent 5 of the present
invention can be formed by connecting stent sections 20 together
with a connecting element 328. The connecting element 328 does not
contain struts or nodes as shown in the embodiments of FIGS. 1A-6
or 7-10 or described for the interconnector 270. The connecting
element 328 is not joined to each stent section via a hinge that is
joined or directed toward the connecting element 328. Such an
embodiment is shown in FIG. 15 where a straight leg element 330 is
used to join two stent sections 20 together. The stent sections 20
shown in this embodiment are similar to the stent section 20 shown
in the embodiment of FIGS. 1A-6 although stent sections of another
embodiment of this invention could equally have been shown. The
straight leg element 330 is shown connecting an end node 280 of one
stent section 20 with an end node 280 of another stent section 20.
The connecting element 330 could connect directly to a hinge
portion of end node 280 although this structure would not provide
the flexibility of the hinged interconnector 270 found in FIG. 13B.
The hinged interconnector 270 shown in FIG. 13B has a connecting
hinge 305 that provides for specific movement of the interconnector
270 in the uniform surface of the hinge stent and not bend in the
radial direction of the hinge stent. The connecting element 328
provides the hinge stent 5 with axial flexibility such that the
hinge stent 5 can easily traverse a tortuous path in a nondeployed
or deployed state. The straight leg element 330 is not required to
align with the axial direction 60 of the hinge stent 5 in order to
provide extension or compression properties to the appropriate
outside or inside portions, respectively, of the hinge stent 5 in
traversing a curved vessel. The connecting element 328 can also
have the form of a curved leg element 335 as shown in FIG. 16. A
curved leg element 335 provides the necessary extension along the
outside of a curve or compression along the inside of a curve to
the hinge stent 5 as it traverses along a curved path within a
blood vessel. The curved leg element 335 can be place between end
nodes 280 (FIG. 13A) of individual stent sections 20 that are
aligned in a generally axial direction 60 or can be placed between
end nodes that have been offset as shown in FIG. 16. It is
understood that any embodiment of the hinge stent 5 of the present
invention can be used with interconnectors 270 or connecting
element 328 to join stent sections 20.
[0118] In still another embodiment of the hinge stent 5 of the
present invention, a series of nodes 340, upper struts 345, and
lower struts 350 can be formed into a helical shape that extends
throughout the entire length of the hinge stent 5 forming a
continuous structure as shown in FIGS. 17A and 18. A frontal view
of a portion of a helically shaped hinge stent 5 is shown in a
nondeployed state and with a nondeployed diameter 75 in FIG. 17A
and in a deployed state with a deployed diameter 85 in FIG. 18.
FIG. 17B is an illustration of a repeat unit 355 formed from a
helical stent similar to that shown in FIGS. 17A and 18. The stent
section body 35 of this embodiment has two struts 345 & 350 per
each node 340. A single continuous series of nodes 340, upper
struts 345, and lower struts 350 extends in a helical configuration
throughout the entire length of the hinge stent 5 forming a
cylindrically shaped hinge stent 5. This embodiment of a hinge
stent 5 forms a continuous configuration of nodes and struts that
extend with a helical wind in a circumferential 70 and axial 60
direction as the helix forms a continuous spiral. The
circumferential expansion of this embodiment of hinge stent is
coupled in the axial direction 60 of a stent section since a single
series of nodes and struts extends throughout the length of the
stent section 20. Expansion forces directed in the circumferential
direction are distributed and shared in the axial direction also.
This distribution of forces in both the axial and circumferential
direction serves to prevent abrupt change in the diameter of the
stent section that could otherwise lead to localized high stress
regions in the vessel being treated. The hinge stent 5 of this
embodiment can either be a balloon-expandable hinge stent 5 or a
self-expandable hinge stent 5. As a balloon-expandable hinge stent
5 it can be mounted onto the balloon of a balloon dilitation
catheter in its nondeployed state and delivered percutaneously to
the site of the lesion. Each repeat unit 355 is connected to the
adjacent repeat unit with struts and hinges. As the helical
structure winds continuously throughout the helical length of the
stent section, this continuous structure provides a continuous
uniform surface without abrupt changes in diameter. This embodiment
of the hinge stent 5 as shown in FIGS. 17A and 18 is comprised of
helical repeat units formed entirely of nodes and struts joined to
each other contiguously to form a single stent section 20. In
traversing around a curve in a tortuous vessel one helical repeat
unit 355 can move away in an axial direction 60 from an adjacent
helical repeat unit 355 along the outside portion of the curve in
which the hinge stent is being placed. Once the hinge stent 5 has
reached the site of the lesion the balloon can be expanded to
expand the hinge stent 5 to the larger deployed diameter 85 shown
in FIG. 18. in its expanded or deployed state the hinge stent 5 is
also very flexible axially and can be easily implanted around a
curved vessel as adjacent helical repeat units 355 of the hinge
stent 5 are not connected or joined to each other. The upper struts
345 can be of equal length and shape to the lower struts 350 or the
upper struts 345 can differ from the lower struts 350. If the upper
struts 345 and lower struts 350 are of an equal length, then the
struts 345 & 350 will not align parallel with the axial
direction 60 in the nondeployed state.
[0119] FIGS. 19 and 20 show an enlarged view of a portion of a
helical repeat unit 355 (see FIG. 17B) of the embodiment of the
helical hinge stent 5 shown in FIGS. 17A and 18, respectively. The
upper 345 and lower 350 struts are aligned parallel to each other
and in the axial direction 60 in a nondeployed state shown in FIG.
19. The nodes 340, upper struts 345, and lower struts 350 are
joined contiguously together in series as they form a helical
repeat unit 355 of the hinge stent 5. In this embodiment the upper
345 and lower 350 struts are of two different sizes or lengths, the
upper strut 345 having an upper strut length 360 that is shorter
than the lower strut length 365 of the lower strut 350. Each strut
is aligned parallel to each other and in the axial direction 60 in
a nondeployed state providing the closest packing configuration for
the struts. In a deployed state as shown in FIG. 20 the upper 345
and lower 350 struts of this embodiment form a deployment angle 368
that is symmetrical with respect to the axial direction 60.
Positioning the upper 345 and lower 350 struts parallel to each
other in a nondeployed state provides this embodiment with the
greatest expansion ratio of deployed diameter to nondeployed
diameter. Ease of machining a balloon-expandable hinge stent 5 in a
nondeployed state with the struts parallel to the axis provides an
additional advantage for forming the hinge stent 5 as shown in FIG.
19 although it is understood that the struts are not required to be
parallel in the nondeployed state. For a self-expandable hinge
stent 5 the machining can occur in an expanded or deployed state as
shown in FIG. 19. Following machining the self-expandable hinge
stent 5 can be folded to form the smaller nondeployed state and
held in a sheath at its smaller nondeployed diameter 75 for
percutaneous insertion into the blood vessel. The node of this
embodiment as shown in FIGS. 19 and 20 can consist of a single
hinge that is joined to each of two struts. Hinge and strut
dimensions will affect the stent function in a manner consistent
with the discussion made earlier for the embodiments or FIGS. 1A6
and FIGS. 7-10.
[0120] FIG. 21 shows an enlarged isometric view of a portion of the
helical hinge stent 5 of the embodiment of FIG. 19 in a nondeployed
state. The node 340 of this embodiment includes a hinge 370 joined
contiguously to two transition regions 375. Each transition region
375 is contiguously joined to an upper 345 or lower 350 strut. The
hinge has a hinge width 105, a hinge length 110, and a hinge radial
dimension 115. The transition region 375 has a transition region
width 130, a transition region length 125, and a transition region
radial dimension 135. The upper strut 345 and lower strut 350 each
have a strut width 150, a strut length 145, and a strut radial
dimension 155. The description of the hinges, the struts, the
transition regions 375 of this embodiment along with their
dimensions and functions is similar to the descriptions that have
been presented for the preceding embodiments of the hinge stent 5.
All reference numerals correspond to those elements previously or
otherwise described.
[0121] An abbreviated discussion of the present embodiment will
follow, referring collectively to FIGS. 17A-21. The hinge stent 5
of this embodiment can be a balloonexpandable hinge stent 5 or a
self-expandable hinge stent 5. The hinge width 105 is significantly
smaller than the strut width 150 for either the upper strut 345 or
lower strut 350 to allow the hinge to deform the hinge width radius
of curvature 380 in going from a nondeployed state to a deployed
state. The hinge radial dimension 115 can be lengthened to increase
the amount of expansion holding force for a balloon-expandable
hinge stent 5 or expansion elastic force for a self-expandable
hinge stent 5 is provided by the hinge stent 5 to hold the blood
vessel open in a deployed state. The strut radial dimension 155 is
significantly smaller than the hinge radial dimension 115 to allow
the strut to deform elastically as the hinge stent 5 is exposed to
a crush deformation that causes the hinge stent 5 to form an oval
shape. The strut width 150 is significantly greater than the hinge
width 105 such that the moment provided by the hinge to hold the
blood vessel outward is transferred via the strut to the vessel
wall without bending in the direction of the strut width 150. A
longer strut length 145 will allow the hinge stent 5 to bend easier
when exposed to a crush applied force that tends to form the hinge
stent 5 into an oval shape. A longer hinge will increase the
percentage of the perimeter of the hinge stent 5 that is associated
with the struts in comparison to the nodes. Since the upper struts
345 and lower struts 350 are formed with a thin radial dimension
that will deform elastically in the radial direction and the nodes
are formed with a larger radial dimension that does not provide for
significant deformation in the radial direction, a longer strut
length 145 will allow the hinge stent 5 to deform more easily in
crush deformation.
[0122] For a balloon-expandable hinge stent 5 of this embodiment
the hinge length 110 can be preferably short to focus the
deformation of the hinge into a smaller volume of hinge and require
that the hinge undergo a greater amount of plastic deformation.
Focusing of the plastic deformation will provide a greater
percentage of plastic deformation in comparison to elastic
deformation and provide less rebound following balloon expansion of
the balloon-expandable hinge stent 5. The balloon-expandable hinge
stent 5 of this embodiment provides an advantage of balloon
expandability for accuracy of placement within the vasculature but
non crushability such that the hinge stent 5 deforms elastically in
the crush deformation mode. The upper 345 and lower 350 struts will
deform elastically in a crush deformation and will return to their
original conformation found in the deployed state. The use of
hinges 370 to provide a moment to the upper 345 and lower 350
struts allows the hinge stent 5 to provide an expansion holding
force that is as large or as small as desired and provide a crush
strength that is as large or as small as desired. The expansion
holding force is controlled independently from the crush elastic
force. The expansion holding force is established by the hinge
dimensions and the crush elastic force is established by the strut
dimensions. For example, a large hinge width 105 and a large hinge
radial dimension 115 along with a hinge length 110 that ensures
primarily plastic deformation will provide a large expansion
holding force for the hinge stent 5. A thin strut radial dimension
155 and a long strut length 145 along with the smallest strut width
150 that will still transfer the outward expansion force of the
hinge to the vessel wall will provide the hinge stent 5 with the
most flexible structure in a crush deformation.
[0123] For a self-expandable hinge stent 5 the hinge can have a
longer hinge length 110 in order to better allow for an elastic
deformation of the hinge without plastic deformation by reducing
the amount of localized deformation of the hinge for a specific
deployment angle 368 & 170. A longer hinge length 110 also
provides the self-expandable hinge stent 5 with a reduced drop off
of expansion elastic force in going from a nondeployed state to a
deployed state. This allows the hinge stent 5 of this embodiment to
provide a more uniform outward force regardless of small variations
in the diameter of the vessel in which it is deployed. The
expansion elastic force provided by the self-expandable hinge stent
5 of this embodiment is controlled independently from the crush
elastic force. The expansion elastic force is determined by the
hinge dimensions and the crush elastic force is controlled by the
strut dimensions. Thus the self-expandable hinge stent 5 of this
embodiment can have a large or a small expansion elastic force to
hold the vessel outward, and it can have a large or a small crush
elastic force to resist forming an oval shape when exposed to a
crush deformation. For example, to provide a large expansion
elastic force the hinge width 105 is enlarged to its greatest
extent without allowing for plastic deformation. The hinge length
110 is adjusted in conjunction with the hinge width 105 to ensure
that only elastic deformation will occur. A shorter hinge length
110 will provide a greater expansion elastic force for the same
deployment angle 368 & 170. A longer hinge length 110 will
provide less drop off of expansion elastic force from a nondeployed
state to a deployed state. For a longer hinge length 110 the hinge
width 105 can be increased to provide a large expansion elastic
force without allowing plastic deformation. A longer hinge radial
dimension 115 will further increase the magnitude of the expansion
elastic force provided by the hinge. The strut dimensions can be
adjusted as described for the balloon-expandable hinge stent 5 to
provide for flexibility in crush deformation. This discussion for
adjusting the expansion elastic force for the self-expandable hinge
stent 5, the expansion holding force for the balloon-expandable
hinge stent 5, and the crush elastic force for either the
self-expandable hinge stent 5 or the balloon-expandable hinge stent
5 applies equally well to the embodiments shown in FIGS. 1A-6,
FIGS. 7-10, as well as the embodiments shown in FIGS. 17A-24.
[0124] The metal used in the formation of the embodiments shown in
FIGS. 17A-24 can be the same as described earlier for other
embodiments. The choice of elastic modulus and yield point for the
metal will also influence the choice of hinge length 110 and hinge
width 105 in order to obtain a deformation that provides elastic
deformation for the self-expandable hinge stent 5 or plastic
deformation for the balloon-expandable hinge stent 5. The choice of
elastic modulus will also directly influence the hinge radial
dimension 115 that used to provide the appropriate expansion
elastic force for the self-expandable hinge stent 5 or the
expansion holding force for the balloon-expandable hinge stent 5.
It is preferred that a high elastic modulus material be chosen such
that the radial thickness for the hinge stent is smallest and that
the expansion forces and crush forces be determined by the
dimensions of the hinges and struts.
[0125] An alternate embodiment for the node structure for the
helical hinge stent 5 shown in FIGS. 17A and 18 is shown in FIGS.
22-24. FIG. 22 shows a portion of a repeat unit having a node 340,
upper 345, and lower 350 strut structure in a nondeployed state of
an embodiment of the helical hinge stent 5 of FIG. 17A. FIG. 23
shows a portion of a repeat unit having a node 340 and upper 345
and lower 350 strut structure in a deployed state for an embodiment
of FIG. 18. FIG. 24 shows a close-up isometric view of a node 340
and a portion of the upper 345 and lower 350 struts joined to the
node. Referring collectively to FIGS. 22-24 this embodiment will be
briefly described. This embodiment is very similar to the
embodiment described in FIGS. 1921. The main difference found in
this embodiment is that the node 340 contains a hub 385, two hinges
390, and two transition regions 395 rather than a hinge 370 and two
transition regions 375 as shown in FIGS. 19-21. The upper 345 and
lower 350 struts are the same as those shown in the embodiment of
FIGS. 19-21. The hub 385, as described in earlier embodiments does
not undergo significant deformation during the expansion of the
hinge stent 5 from a nondeployed state to a deployed state or
during exposure to crush deformation. Each hinge 390 as shown in
this embodiment in FIGS. 22-24 is similar to the hinge 370 shown in
FIGS. 19-21 except that the hinge length 110 for each of the two
hinges 390 has a shorter hinge length 110 than the embodiment shown
in FIGS. 19-21. The presence of two smaller hinges 390 can help to
focus the deformation of the hinge for a balloon-expandable hinge
stent 5 and can provide a greater expansion elastic force for a
self-expandable hinge stent 5. This embodiment with two hinges 390
can also provide advantages from an ease of machining standpoint.
The presence of a hub can provide a suitable site for attaching an
interconnecting means or a barb attachment means as will be
discussed later. The function of the hinges 390, upper 345 and
lower 350 struts and transition regions 395 are similar to what has
been described previously for the embodiments of the hinge stent 5
shown in FIGS. 17A-21. All reference numerals correspond to those
elements previously or otherwise described.
[0126] FIGS. 25 and 26 show yet another embodiment of the hinge
stent 5 of the present invention. This embodiment is similar to the
embodiments shown in FIGS. 17A-24. To ensure that the adjacent
helical repeat units 355 of the node and strut structure maintain a
relative approximation with each other in an axial direction during
the insertion of the hinge stent 5 and after implantation of the
hinge stent 5 a hinged interconnector 270 or connecting element 328
(not shown) can be used to axially join to two separate nodes of
adjacent helical repeat units 355. Preferably the hinged
interconnector 270 comprised of nodes and struts is used to join
nodes from adjacent helical repeat units 355 that are axially
displaced as shown in FIG. 25. The resultant stent has advantageous
properties discussed earlier for the hinge stent including
uncoupling of expansion force from crush force and having an
elastic crush deformation associated with strut bending in a radial
direction that provides this hinge stent with being noncrushable.
This embodiment for the helical hinge stent 5 has properties which
are similar to those described for other embodiments of the present
invention formed from nodes and struts. The embodiment shown in
FIGS. 25 and 26 can have approximately one interconnector 270 to
join each helical repeat unit 355 of the hinge stent 5. In this
embodiment the hinged interconnector 270 has one connecting strut
285 joined by two connecting transition regions 410 and two
connecting hinges 405 to connecting nodes 400 from two adjacent
helical repeat units 355. Details of the function of this hinged
interconnector 270 comprised of nodes and struts have been
described previously in FIG. 13. The two connecting hinges 405 have
a thin hinge width 105 that allows for ease of flexing in the
direction of the hinge width 105 as the hinge stent 5 is placed
into a tortuous or curved blood vessel. The connecting strut 285
has a thin radial dimension to allow ease of flexing in the
direction of their radial dimension. The hinged interconnector 270
of this embodiment provides axial flexibility to the hinge stent 5
such that flexibility in traversing tortuous vessels will not be
significantly affected by the hinged interconnector 270. The
connecting hinges 405 will bend to provide this hinge stent 5 with
flexibility in tortuous vessels. Multiple interconnectors 270 can
be placed between connecting nodes 400 of adjacent helical repeat
units 355 (FIG. 17B) of the hinge stent 5. Each node 340 of each
helical repeat unit 355 of the helical hinge stent 5 can be formed
into a connecting node 400 and joined to an adjacent connecting
node 400 on an adjacent helical repeat unit 355 to form a stent
section with three struts per node portion 320 as shown in FIG. 27.
This embodiment has a closed configuration. This closed
configuration provides additional axial and circumferential
stability to the helical hinge stent beyond that found in FIGS. 17A
and 18. the closed configuration is comprised of the nodes and
struts of the hinged interconnector 270, the connecting nodes 400,
the upper struts 345, and the lower struts 350. All reference
numerals correspond to those elements previously or otherwise
described. It is understood that the straight 330 or curved 335 leg
elements as shown in FIGS. 15 and 16 can be used to join adjacent
connecting nodes 400 from adjacent helical repeat units 355 of the
hinge stent 5 to form an alternate embodiment.
[0127] The nodes and struts of the embodiments of the present
invention provide for an expansion deformation of the hinge stent
from a nondeployed diameter to a deployed diameter. The hinges
undergo an elastic or a plastic expansion deformation in the
uniformly curved surface of the stent. The expansion deformation
forces generated by the hinges are independent of the crush deform
forces generated by the struts as they bend in a radial direction
due to a crush deformation. In traversing along curved or tortuous
vessels the nodes and struts of a hinge stent can also provide the
hinge stent with an ability to elongate in an axial direction on
the outside of the curved vessel and compress in an axial direction
along the inside of the curved vessel. The hinges allow for bending
to occur in the uniformly curved hinge stent surface as the stent
is required to elongate or compress axially in passing along a
curved passage. Struts can provide axial alignment for the stent to
ensure that the stent lies flat against the vessel wall without
ridges that can cause stress risers between the stent and the
vessel wall are avoided. Axial alignment of the stent with the
vessel wall can provide enhanced healing of the vessel wall in
contact with the stent. Hinged interconnectors with a similar node
and strut structure as that described for the structure of each
stent section can similarly provide the hinge stent of the present
invention with an ability to elongate or compress axially when
passing along a curved or tortuous vessel. The structure of the
present invention includes hinges and struts extending in both a
generally circumferential and generally axial direction from one
repeat unit to another repeat unit throughout the entire structure
of the stent section. One embodiment has hinged interconnectors
that connect one stent section with another. Axial extension of the
stent along the outside of a curved vessel or axial compression
along the inside of a curved vessel is controlled by extension
deformation of the hinge. An extension deformation force of the
hinge generated by the extension deformation due to passage along a
curved passage is determined by the hinge length, hinge width, and
hinge radial dimension. These hinge dimensions affect the extension
deformation force of the hinge in the same way that they affect the
expansion deformation force of the hinge as described for the
expansion deformation from the nondeployed state to the deployed
state. The hinge does not bend in the radial direction during
extensional deformation in passing along a curved passage due in
part to the large hinge radial dimension. Struts can provide
bending in the radial direction as the stent is bending along a
curved passage. The strut width, strut length, and strut radial
dimension allow the struts to bend elastically in the direction of
the strut radial dimension with a strut elastic bending force that
is independent of the extension deformation force of the hinge.
Expansion forces exerted outward by the hinge stent against the
vessel wall to hold it outwards and extensional forces exerted
axially during bending of the hinge stent along a curved passage
are shared throughout the node and strut structure that extends
continuously throughout the hinge stent of this invention. These
expansion and extension forces are controlled by the hinge
dimensions. The hinge stent of the present invention can be formed
of a metal with an elastic modulus that provides hinges with
appropriate expansion deformation forces to hold the vessel open,
provides struts with appropriate elastic crush deformation forces,
and provides hinges with extensional forces to allow bending in a
curved passage.
[0128] All of the embodiments of the hinge stent 5 can be used as a
stent to help hold the blood vessel open at the site of a vessel
lesion, stenosis, or other vessel injury. The hinge stent 5 of the
present invention can also be used to hold an intravascular graft
or other tubular member outwards against the vessel wall at or near
the site of vessel injury. When used in this manner, the hinge
stent 5 can be placed into the vessel and into at least a portion
of the lumen of the intravascular graft. The hinge stent 5 can then
be allowed to expand either by balloon expansion or by self
expansion such that it holds the intravascular graft outwards
against the vessel wall. Alternately, the hinge stent 5 of the
present invention can be attached to the intravascular graft prior
to implant and both the intravascular graft along with the hinge
stent 5 are delivered to the site of the vessel injury together
where they are deployed to a larger deployed diameter 85. One form
of attaching the hinge stent 5 to the intravascular graft could
involve sutures or other securing means that serve to tie the
elements together. Another form of attaching the hinge stent 5 of
the present invention to the intravascular tubular member could
involve forming a physical encapsulation of the hinge stent 5 with
the material of the intravascular graft. Here the material of the
intravascular graft could surround some or all of the struts or
some or all of the hinges of any of the embodiments of the hinge
stent 5. For example, the hinge stent 5 could be physically
contained within a portion of or all of an expanded
polytetrafluoroethylene tubular member to form a stent graft for
treatment of vessel injury. Attachment of the hinge stent 5 to the
intravascular graft can also include physical or chemical bonding
between the metal of the hinge stent 5 and the material of the
intravascular graft.
[0129] An embodiment of the hinge stent 5 of the present invention
can be formed with a barb attachment means or barbs 415 as a
component of one or more nodes 420 of the hinge stent 5 and
extended as shown in FIG. 28 in a deployed state of the hinge stent
5 with a deployed diameter 85. Each barb is contiguously joined to
the hinge or hub of a node. Each barb 415 can be machined
contiguously with the node of the hinge stent using mechanical,
laser, chemical, electrochemical, or other appropriate machining
methods. This contiguous junction of the barb with the hinge stent
reduces any tendency for fracture of the barb from the hinge stent
to occur. The barbs 415 are shown joined to one stent end 30 of a
hinge stent 5 similar to the embodiment shown in FIGS. 1A-6. The
barbs 415 can just as well be placed on both ends of the hinge
stent 5 or can be a component of any of the nodes 420 located
throughout the stent section body 35. Barbs 415 can similarly be a
component of the nodes of other embodiments of the hinge stent 5 of
the present invention. For example, barbs 415 can be a component of
any of the Y tail nodes of the hinge stent 5 shown in FIGS. 6-10.
Similarly, barbs 415 can be a component of any of the nodes of the
embodiments of the hinge stent 5 found in FIGS. 17A-24. The barbs
415 can serve to hold the hinge stent 5 in place within the blood
vessel without significant possibility for stent migration.
Additionally, the hinge stent 5 can be attached as described
earlier to an intravascular graft to hold the intravascular graft
outward against the vessel wall and ensure that the intravascular
graft does not migrate. FIG. 29 shows the hinge stent 5 of the
present invention with barbs 415 retracted and the hinge stent 5 in
a nondeployed state with a nondeployed diameter 75. As the stent is
expanded to a specific diameter, the struts separate and allow the
barb 415 to deploy fully. Barb deployment is not gradual and is not
proportional to the amount of strut deployment.
[0130] FIGS. 30 and 31 show a close-up view of a portion of a hinge
stent 5 with the barbs 415 retracted and extended, respectively.
The node 420 shown in FIGS. 30 and 31 can be a node 15 from an
embodiment of FIGS. 1A-6, the Y node 175 of an embodiment or FIGS.
7-10, or a node 340 from an embodiment of FIGS. 17A-24. The node
420 has a hinge 423 which can be the hinge from any of the
previously mentioned embodiments. In a retracted state the barbs
415 are folded over and deformed elastically into an intranodal
opening 425 and held by the struts 430 or transition regions 395.
The struts 430 are intended to represent struts 10 found in the
embodiments of FIGS. 1A-6, arm struts 205 and tail struts 220 of
FIGS. 7-10, or upper and lower struts 345 and 350 found in FIGS.
17A-24. The barb 415 can be attached directly to the hinge 423 as
shown in FIGS. 30 and 31 or can be attached to a hub 100 (see FIG.
4) as identified in prior embodiments and shown in FIGS. 28 and 29.
Upon deployment of the hinge stent 5 the struts move apart to form
a deployment angle 435 and allow the barbs 415 to elastically
return to an extended position as shown in FIG. 31. The barb do not
extend in proportion to the amount of deployment angle as with
other barb attachment means of other prior art stents. The present
hinge stent 5 has barbs 415 that extend fully once they have been
released by the movement of the struts to a specific deployment
angle.
REFERENCE NUMERALS IN THE DRAWINGS
[0131] 5. Hinge Stent
[0132] 10. Struts
[0133] 15. Nodes
[0134] 20. Stent Section
[0135] 23. Hinge
[0136] 25. Transition Region
[0137] 30. Stent End
[0138] 35. Stent Body
[0139] 40. Interstrut Openings
[0140] 45. Intemodal Openings
[0141] 50. Intranodal Openings
[0142] 55. Repeat Units
[0143] 60. Axial Direction
[0144] 65. Nondeployed Repeat Unit Length
[0145] 70. Circumferential Direction
[0146] 75. Nondeployed Diameter
[0147] 80. Deployed Repeat Unit Length
[0148] 85. Deployed Diameter
[0149] 90. Uniformly Curved Hinge Stent Surface
[0150] 93. Oval Hinge Stent Surface
[0151] 95. Radial Radius of Curvature
[0152] 100. Hub
[0153] 105. Hinge Width
[0154] 110. Hinge Length
[0155] 115. Hinge Radial Dimension
[0156] 120. Hinge Cross Sectional Area
[0157] 125. Transition Region Length
[0158] 130. Transition Region Width
[0159] 135. Transition Region Radial Dimension
[0160] 140. Transition Region Cross Sectional Area
[0161] 145. Strut Length
[0162] 150. Strut Width
[0163] 155. Strut Radial Dimension
[0164] 160. Strut Cross Sectional Area
[0165] 165. Hinge Width Radius of Curvature
[0166] 170. Deployment Angle
[0167] 175. Y Node
[0168] 180. T Node
[0169] 185. Y Hub
[0170] 190. T Hub
[0171] 195. Y Arm Transition Region
[0172] 200. Y Arm Hinges
[0173] 205. Arm Struts
[0174] 210. Y Tail Transition Region
[0175] 215. Y Tail Hinge
[0176] 220. Tail Strut
[0177] 225. T Arm Transition Regions
[0178] 230. T Arm Hinges
[0179] 235. T Axial Transition Region
[0180] 240. T Axial Hinge
[0181] 245. Axial Strut
[0182] 247. Closed Loop
[0183] 248. Closed Configuration
[0184] 250. Hinge Stent Radius of Curvature
[0185] 255. Stent Axis
[0186] 260. Stent Mid-Length
[0187] 265. Intermediate Diameter
[0188] 270. Hinged Interconnector
[0189] 275. Connecting Node
[0190] 280. End Node
[0191] 285. Connecting Struts
[0192] 290. Flex Node
[0193] 295. Flex Hinge
[0194] 300. Flex Transition Regions
[0195] 305. Connecting Hinge
[0196] 310. Connecting Transition Region
[0197] 315. Four Strut per Node Portions
[0198] 320. Three Strut per Node Portions
[0199] 325. Two Strut per Node Portions
[0200] 328. Connecting Element
[0201] 330. Straight Leg Element
[0202] 335. Curved Leg Element
[0203] 340. Nodes
[0204] 345. Upper Struts
[0205] 350. Lower Struts
[0206] 355. Helical Repeat Unit
[0207] 360. Upper Strut Length
[0208] 365. Lower Strut Length
[0209] 368 Deployment Angle
[0210] 370. Hinge
[0211] 375. Transition Regions
[0212] 380. Hinge Width Radius of Curvature
[0213] 385. Hub
[0214] 390. Hinges
[0215] 395. Transition Regions
[0216] 400. Connecting Node
[0217] 405. Connecting Hinge
[0218] 410. Connecting Transition Region
[0219] 415. Barbs
[0220] 420. Node
[0221] 425. Intranodal Space
[0222] 423. Hinge
[0223] 430. Struts
[0224] 435. Deployment Angle
[0225] Various modifications can be made to the present invention
without departing from the apparent scope hereof.
* * * * *