U.S. patent application number 15/445770 was filed with the patent office on 2017-11-23 for vascular stents and related methods.
This patent application is currently assigned to Brigham Young University. The applicant listed for this patent is Brigham Young University. Invention is credited to Anton E. Bowden, Brian D. Jensen, Darrell J. Skousen.
Application Number | 20170333232 15/445770 |
Document ID | / |
Family ID | 50385908 |
Filed Date | 2017-11-23 |
United States Patent
Application |
20170333232 |
Kind Code |
A1 |
Skousen; Darrell J. ; et
al. |
November 23, 2017 |
Vascular Stents and Related Methods
Abstract
A vascular stent assembly includes at least a first and a second
strut, each including a thickness and a depth. The assembly
includes a pair of end radii, with each of the first and second
struts extending from one of the pair of end radii. A thickness of
at least one of the first and second struts includes a tapering
profile extending from one of the end radii to another of the end
radii, the tapering profile following a continuously increasing or
decreasing function through at least half a length of the at least
one strut.
Inventors: |
Skousen; Darrell J.; (Lehi,
UT) ; Jensen; Brian D.; (Orem, UT) ; Bowden;
Anton E.; (Lindon, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brigham Young University |
Provo |
UT |
US |
|
|
Assignee: |
Brigham Young University
Provo
UT
|
Family ID: |
50385908 |
Appl. No.: |
15/445770 |
Filed: |
February 28, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15057935 |
Mar 1, 2016 |
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15445770 |
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14533979 |
Nov 5, 2014 |
9271853 |
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15057935 |
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61900211 |
Nov 5, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61L 31/146 20130101;
A61F 2/86 20130101; A61L 31/122 20130101; A61L 2400/12 20130101;
A61F 2002/91583 20130101; A61F 2002/91575 20130101; A61F 2/915
20130101; B82Y 40/00 20130101; A61F 2/82 20130101; A61F 2210/0014
20130101; A61F 2002/91558 20130101; A61F 2/844 20130101; A61F
2250/0036 20130101; B29C 59/007 20130101 |
International
Class: |
A61F 2/915 20130101
A61F002/915; A61F 2/844 20130101 A61F002/844 |
Claims
1. A vascular stent assembly, comprising: at least a first and a
second strut, each including a thickness and a depth; and a pair of
end radii, each of the first and second struts extending from one
of the pair of end radii; wherein a thickness of at least one of
the first and second struts includes a tapering profile extending
from one of the end radii to another of the end radii, the tapering
profile following a continuously increasing or decreasing function
through at least half a length of the at least one strut.
2. The assembly of claim 1, wherein the tapering profile
continuously decreases from one of the end radii to a midpoint of
the strut, then continuously increasing from the midpoint of the
strut to the other of the end radii.
3. The assembly of claim 1, wherein the tapering profile is a
curvilinear profile.
4. The assembly of claim 1, wherein the tapering profile is a
sloped line.
5. The assembly of claim 1, wherein the tapering profile is
convex.
6. The assembly of claim 1, wherein the tapering profile is
concave.
7. The assembly of claim 1, wherein one face of the strut is
substantially unsloped, and wherein an opposing face of the strut
includes the tapering profile.
8. The assembly of claim 1, wherein opposing faces of the strut
each include a tapering profile.
9. The assembly of claim 1, wherein the assembly is formed from
carbon-infiltrated carbon nanotubes (CI-CNTs).
10. The assembly of claim 1, wherein a depth of at least one of the
struts can vary along a length of the strut as the thickness of the
strut varies.
11. A vascular stent assembly, comprising: a series of struts, each
including a length, a thickness and a depth; and a series of end
radii, each of the struts extending between one end radius on one
end of the strut and another end radius on another end of the
strut; wherein a thickness of each of the struts includes a
tapering profile extending from one end of the strut to another end
of the strut, the thickness of the tapering profile continuously
increasing or decreasing along the length of the strut through at
least half a length of the strut; and the depth of each of the
struts being substantially constant along the length of the
strut.
12. The assembly of claim 11, wherein each strut includes an upper
face and a lower, opposing face, and wherein each of the upper face
and the lower face include a tapering profile through at least half
a length of the strut.
13. The assembly of claim 11, wherein each strut includes an upper
face and a lower, opposing face, and wherein only one of the upper
face and the lower face includes a tapering profile through at
least half a length of the strut.
14. The assembly of claim 11, wherein the tapering profile is a
curvilinear profile.
15. The assembly of claim 11, wherein the tapering profile is a
sloped line.
16. The assembly of claim 11, wherein the tapering profile is
convex.
17. The assembly of claim 11, wherein the tapering profile is
concave.
18. The assembly of claim 11, wherein the assembly is formed from
carbon-infiltrated carbon nanotubes (CI-CNTs).
19. The assembly of claim 18, wherein the series of struts and end
radii comprise a contiguous unit.
Description
PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/057,935, filed on Mar. 1, 2016, which is a
continuation of U.S. patent application Ser. No. 14/533,979 filed
on Nov. 5, 2014, and now issued as U.S. Pat. No. 9,271,853, which
claims the benefit of U.S. Provisional Patent Application No.
61/900,211, filed Nov. 5, 2013, each of which is incorporated
herein by reference.
BACKGROUND
[0002] The leading cause of death in the United States is heart
disease, claiming approximately 24% of all deaths. Coronary artery
disease is a condition where coronary arteries narrow due to fatty
plaque buildup, reducing the blood flow to the heart which can lead
to heart failure and death. A minimally invasive procedure called
percutaneous coronary intervention (PCI) including balloon and
stent angioplasty has been developed to treat coronary artery
disease. There are two major complications associated with PCI:
restenosis (re-narrowing) and thrombosis (blood clots). Restenosis
is caused by a combination of early elastic recoil, negative
remodeling, and neointimal formation. Early elastic recoil occurs
immediately, and is due to the elastic properties of the arteries.
Late lumen loss in balloon angioplasty is caused by neointima
formation (tissue in-growth) and negative remodeling (arterial
shrinking). In stent angioplasty, a cylindrical scaffold wire mesh
(stent) typically made of stainless steel is implanted in the
artery to prevent restenosis. These stents prevent elastic recoil
and negative remodeling, however, neointimal formation can still
lead to restenosis.
[0003] Stents have proven to reduce the rates of restenosis more
than angioplasty alone. Drug-eluting stents have further reduced
restenosis rates, but there is a concern for their ability to
prevent late-term thrombosis. New stent materials that can improve
these two complications associated with existing coronary stents
will be advantageous in stent development.
SUMMARY OF THE INVENTION
[0004] In accordance with one embodiment, the invention provides a
vascular stent assembly, including at least a first and a second
strut, each including a thickness and a depth. A pair of end radii
can also be provided, with each of the first and second struts
extending from one of the pair of end radii. A thickness of at
least one of the first and second struts can include a tapering
profile extending from one of the end radii to another of the end
radii. The tapering profile can follow a continuously increasing or
decreasing function through at least half a length of the at least
one strut.
[0005] In accordance with another aspect of the invention, a
vascular stent assembly is provided, including a series of struts,
each including a length, a thickness and a depth. A series of end
radii can also be provided, each of the struts extending between
one end radii on one end of the strut and another end radii on
another end of the strut. A thickness of each of the struts
includes a tapering profile extending from one end of the strut to
another end of the strut, the thickness of the tapering profile
continuously increasing or decreasing along the length of the strut
through at least half a length of the strut. The depth of each of
the struts can be substantially constant along the length of the
strut.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Additional features and advantages of the invention will be
apparent from the detailed description which follows, taken in
conjunction with the accompanying drawings, which together
illustrate, by way of example, features of the invention; and,
wherein:
[0007] FIG. 1 is a perspective view of selected segments of a stent
in accordance with an embodiment of the invention;
[0008] FIG. 2 is a side view of two struts and three end radii of a
stent segment in accordance with an embodiment of the
invention;
[0009] FIG. 3 is a perspective view of end radii of a conventional
stent and a stent in accordance with the present technology;
[0010] FIG. 4 is a side, partial view of a stent strut in
accordance with an embodiment of the invention;
[0011] FIG. 5 is a side, partial view of another stent strut in
accordance with an embodiment of the invention;
[0012] FIG. 6 is a side, partial view of another stent strut in
accordance with an embodiment of the invention;
[0013] FIG. 7 is a side, partial view of another stent strut in
accordance with an embodiment of the invention;
[0014] FIG. 8 is a perspective, partial view of a cylindrical stent
assembly in accordance with an embodiment of the invention; and
[0015] FIG. 9 is a perspective, partially sectioned view of a stent
assembly installed within an artery in accordance with an
embodiment of the invention.
[0016] Reference will now be made to the exemplary embodiments
illustrated, and specific language will be used herein to describe
the same. It will nevertheless be understood that no limitation of
the scope of the invention is thereby intended.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0017] The following detailed description of exemplary embodiments
of the invention makes reference to the accompanying drawings,
which form a part hereof and in which are shown, by way of
illustration, exemplary embodiments in which the invention may be
practiced. While these exemplary embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, it should be understood that other embodiments may
be realized and that various changes to the invention may be made
without departing from the spirit and scope of the present
invention.
[0018] In describing and claiming the present invention, the
following terminology will be used.
[0019] As used herein, relative terms, such as "upper," "lower,"
"upwardly," "downwardly," "vertically," etc., are used to refer to
various components, and orientations of components, of the systems
discussed herein, and related structures with which the present
systems can be utilized, as those terms would be readily understood
by one of ordinary skill in the relevant art. It is to be
understood that such terms are not intended to limit the present
invention but are used to aid in describing the components of the
present systems, and related structures generally, in the most
straightforward manner.
[0020] As used herein, the term "substantially" refers to the
complete or nearly complete extent or degree of an action,
characteristic, property, state, structure, item, or result. As an
arbitrary example, when an object or group of objects is/are
referred to as being "substantially" symmetrical, it is to be
understood that the object or objects are either completely
symmetrical or are nearly completely symmetrical. The exact
allowable degree of deviation from absolute completeness may in
some cases depend on the specific context. However, generally
speaking the nearness of completion will be so as to have the same
overall result as if absolute and total completion were
obtained.
[0021] The use of "substantially" is equally applicable when used
in a negative connotation to refer to the complete or near complete
lack of an action, characteristic, property, state, structure,
item, or result. As an arbitrary example, an opening that is
"substantially free of" material would either completely lack
material, or so nearly completely lack material that the effect
would be the same as if it completely lacked material. In other
words, an opening that is "substantially free of" material may
still actually contain some such material as long as there is no
measurable effect as a result thereof.
[0022] As used herein, the term "about" is used to provide
flexibility to a numerical range endpoint by providing that a given
value may be "a little above" or "a little below" the endpoint.
[0023] Directional terms, such as "upper," "lower," "inward,"
"distal," "proximal," etc., are used herein to more accurately
describe the various features of the invention. Unless otherwise
indicated, such terms are not used to in any way limit the
invention, but to provide a disclosure that one of ordinary skill
in the art would readily understand. Thus, while a component may be
referenced as a "lower" component, that component may actually be
above other components when the device or system is installed
within a patient. The "lower" terminology may be used to simplify
the discussion of various figures.
[0024] Distances, forces, weights, amounts, and other numerical
data may be expressed or presented herein in a range format. It is
to be understood that such a range format is used merely for
convenience and brevity and thus should be interpreted flexibly to
include not only the numerical values explicitly recited as the
limits of the range, but also to include all the individual
numerical values or sub-ranges encompassed within that range as if
each numerical value and sub-range is explicitly recited.
[0025] As an illustration, a numerical range of "about 1 inch to
about 5 inches" should be interpreted to include not only the
explicitly recited values of about 1 inch to about 5 inches, but
also include individual values and sub-ranges within the indicated
range. Thus, included in this numerical range are individual values
such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4, and
from 3-5, etc.
[0026] This same principle applies to ranges reciting only one
numerical value and should apply regardless of the breadth of the
range or the characteristics being described.
Example Embodiments
[0027] Many of the issues affecting existing vascular stents
(including restenosis, thrombosis, and the need for anticoagulant
drug therapy (blood thinners)) can be improved or eliminated by
using a more biocompatible material. However, significant
challenges have existed for the design of stents from ceramic
materials. As stents are compliant, expanding and contracting
mechanisms, it can be difficult to design effective stents from
somewhat brittle materials.
[0028] The present technology addresses these limitations by
providing a biocompatible coronary stent that can be formed from a
variety of materials, even relatively brittle materials heretofore
thought unsuitable for such applications. While the invention is
not limited to such a material, the present inventors have found
that stents formed from carbon-infiltrated carbon nanotubes (or
"CI-CNTs") can be used very effectively with existing treatment
regimes. In addition to CI-CNTs, other materials can also be used,
including, without limitation, shape memory alloys, nitinol,
stainless steel, polymers, bioabsorbable polymers, and the
like.
[0029] Nearly all existing coronary stents have the same basic
features, including thin struts that are connected in a zigzag
pattern. The strut connection (referred to below as the end radius)
is rounded to reduce the stress concentration. The struts and
connection form a basic stent segment that is repeated
circumferentially around the stent.
[0030] Vascular stents undergo a large amount of deflection during
insertion. Due to the relatively high strain and elastic properties
of CI-CNTs, the present stents can be formed from this material and
can be fabricated in their "expanded" state and be elastically
compressed for insertion into the body. The present technology
optimizes many compliant geometries for compression to create
usable stent mesh patterns.
[0031] In one particular example, a form of pyrolytic carbon
("PyC") has been developed by the present applicant that allows
high manufacturing tolerances (1-3 micron) and also has excellent
mechanical properties. The CI-CNT stents of the present technology
can be formed from this type of PyC. The PyC can be manufactured by
growing a forest of carbon-nanotubes and then infiltrating the
carbon nanotubes with carbon graphite. Using MEMS manufacturing
processes, a mask can be made with a detailed 2-dimensional
geometry. Carbon-nanotubes are grown vertically extruding the
2-dimensional geometry into a 3-dimensional carbon-nanotube forest.
The forest is then infiltrated with carbon graphite by a vapor
deposition method. The mechanical properties as well as the mass is
dominated by the filler material. The biocompatible properties of
these CI-CNTs can be expected to be similar to other common methods
of manufacturing PyC.
[0032] The current stent designs are optimized to provide the
maximum possible radial force without exceeding the allowable
stress. By reducing the stent strut thickness, as discussed in more
detail below, the stresses can be lowered as needed. However, a
trade-off occurs as radial stiffness/force decreases with decreased
thickness. The stresses and reaction forces for the basic stent
segment can be calculated using mechanics of materials equations as
well as the pseudo-rigid-body model for compliant mechanisms.
[0033] The basic stent segment can be optimized using an exhaustive
search with discrete values for continuous variables. These
constraints allow a tensile stress less than 80 MPa, a compressive
stress less than 120 MPa, and no physical contact (clash) between
the stent segments. The optimal design can have the largest
possible thickness without exceeding the allowable stress. Also,
the optimal strut angle can be the smallest possible angle that can
be achieved without the segments clashing before reaching a 2/3
(67%) compression state is reached. A smaller radius can perform
better, but may be limited by high compressive stresses on the
inner edge of the partial ring.
[0034] A tapered beam can be used in the present implementation
instead of a constant thickness beam. The struts can be modified
from the traditional straight design to a slightly curved design,
in order to avoid clashing. In one exemplary embodiment, the stent
is designed to have a radial depth of about 100 .mu.m with 12
circumferentially repeating segments.
[0035] The improved design results in stresses that are much more
uniformly distributed, and adjacent stent segments that do not
clash together. The present improvements tripled the reaction force
compared to conventional designs while only slightly increasing the
maximum tensile stress. While the invention is not so limited, in
one embodiment the strut includes a length of about 1 mm and a
thickness of about 0.025 mm.
[0036] The performance of the stent design can be analyzed using an
FE arterial model. The stent can be compressed to its crimped
(compressed) condition and then moved into the artery and allowed
to spring back pushing against the artery wall. In one test, the
artery was pressurized at 100 mmHg, and had an initial minimum
lumen diameter of 2.00 mm. After the stent was released, the artery
expanded to have a minimum lumen diameter of 2.05 mm.
[0037] FEA of the stent design shows that the stresses were much
more uniformly distributed across the stent surface (see FIG. 1,
for example). Adjacent strut segments did not clash together.
Although the struts can be initially curved, when they are
compressed they become nearly flat. In this test, the maximum
tensile stress was about 82.1 MPa, with a max compressive stress of
165 MPa. The reaction force was 9.1 mN. Even after accounting for a
change in radial depth and the overall length of the stent
segments, the current stent design showed more than a three-fold
increase in the reaction force over conventional designs while only
slightly increasing the maximum tensile stress.
[0038] Turning now to the figures, FIG. 1 illustrates an exemplary
stent segment or assembly 10a in accordance with an embodiment of
the invention. FEA analysis of this design reveals that the tensile
stresses (1.sup.st principal) are distributed much more uniformly
than with conventional designs. The struts of this design
(discussed in more detail below) do not clash together even under a
65% compression.
[0039] While only a few segments of the stent technology is shown
in FIGS. 1-7 and 9, one of ordinary skill in the art will readily
appreciate that the completed stent assembly 100 will appear
similar to the example shown in FIG. 8. Thus, each of the various
struts, end radii, connecting members, etc., are generally formed
into a contiguous mesh pattern (generally cylindrical in shape), to
allow the stent to perform within an artery or other body.
[0040] FIG. 2 illustrates in more detail the various components of
the overall stent assembly. As shown here, the stent assembly 10b
includes a first 12 and a second 14 strut. Each of the struts
includes a thickness, shown in the figures as the dimension running
from the top to the bottom of the page (see, e.g., thicknesses
T.sub.1 and T.sub.2). The struts also include a depth, which is the
dimension running into the page of FIG. 2. The struts include a
length, indicated by example at "L" in FIG. 2. Each of the struts
extends from, or is coupled to, or joins with one or more end radii
16, 18, 20, etc.
[0041] A thickness of at least one of the struts 12, 14 in each
strut pair can include a tapering profile that extends from one of
the end radii (E1, for example) to another of the end radii (E2,
for example). The tapering profile can follow a substantially
continuously increasing or decreasing function through at least
half a length of the strut. In other words, the tapering profile
varies along the length of the strut, but does not generally
include any sections where the slope of the taper changes
direction. One exception to this condition can occur at the
midpoint of the strut (near the thickness indicated at T.sub.2 in
FIG. 2), where the tapering function can change. Thus, in the
example shown in FIG. 2, the thickness of strut 12 is at a maximum
near end radius 18 (shown by T.sub.1). The thickness of the strut
12 continuously tapers (decreases) along the length of the strut,
until it reaches the midpoint of the strut. As such, thickness
T.sub.2 is smaller than thickness T.sub.1. In this particular
example, the thickness taper changes at the midpoint of the beam
and begins to increase along the length toward end radius 16.
[0042] This tapering design can provide stent segments in which
stresses are much more uniformly distributed across the stent
surface (as illustrated in FIG. 1, for example). In addition,
adjacent stent segments (e.g., struts 12 and 14) are much less
likely to "clash" or contact one another when in a compressed
condition.
[0043] The tapering can follow nearly any substantially
continuously increasing or decreasing function along the length of
the strut. The example shown in FIG. 1 includes a curvilinear
tapering that occurs on both faces of the strut. The example shown
in FIG. 2 includes a linear slope on each end of the strut that
converges at a midpoint of the strut. While the slopes in this
example converge at a midpoint, in some embodiments, the slopes can
converge at differing points along the length of the strut (or not
converge at all, in those cases where only a single taper is
provided).
[0044] Thus, the taper shown in FIG. 2 includes the case where the
upper face or side S.sub.1 of strut 12 exhibits a slope, but the
lower face or side S.sub.2 does not slope. In the example shown in
FIG. 4, side S.sub.1 of strut 12a includes a substantially
constant, linear slope along substantially the entire length of the
strut. In the example shown in FIG. 5, strut 12b includes a single
side or face S.sub.1 that slopes in a curved function. As shown by
strut 12c in FIG. 6, one face or side S.sub.1 can be convex, in
addition to the concave examples provided elsewhere. FIG. 7
illustrates a concave taper in face S.sub.1 of strut 12d that is
continuously curved across the length of the strut, with a
transition occurring at the midpoint of the strut.
[0045] In addition to the tapering profiles explicitly shown in the
figures, the depth of the struts can also vary along the length of
the struts. In other words, the strut can narrow (or broaden) in
either or both a direction of thickness or depth, as any particular
design my dictate.
[0046] The end radii 16, 18, 20, etc. can vary in both size and
design. In the examples shown in FIGS. 1 and 2, the end radii are
relatively simple curvatures that gradually transition from one
strut to another. As shown in FIG. 3, however, the end radii can
include an oversized stress relief pattern that can aid in avoiding
stress concentrations in these areas. The end radius 30 shown on
the left of FIG. 3 is from a conventional stent design, while the
end radius 32 shown on the right of FIG. 3 is from the present
design. As the FEA patterns illustrate in these examples, the
present design is much more effective at evenly distributing stress
along the entire stent assembly, as opposed to the conventional
design, which includes high stress concentration at the end
radii.
[0047] While the forgoing examples are illustrative of the
principles of the present invention in one or more particular
applications, it will be apparent to those of ordinary skill in the
art that numerous modifications in form, usage and details of
implementation can be made without the exercise of inventive
faculty, and without departing from the principles and concepts of
the invention. Accordingly, it is not intended that the invention
be limited, except as by any claims associated with this or related
applications.
* * * * *