U.S. patent application number 16/454928 was filed with the patent office on 2019-10-17 for asymmetric opening and closing prosthetic valve leaflet.
The applicant listed for this patent is W. L. Gore & Associates, Inc.. Invention is credited to Joseph R. Armstrong.
Application Number | 20190314154 16/454928 |
Document ID | / |
Family ID | 53269999 |
Filed Date | 2019-10-17 |
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United States Patent
Application |
20190314154 |
Kind Code |
A1 |
Armstrong; Joseph R. |
October 17, 2019 |
ASYMMETRIC OPENING AND CLOSING PROSTHETIC VALVE LEAFLET
Abstract
Described embodiments are directed toward prosthetic valves
having leaflets that move asymmetrically in that a leaflet second
side region of the leaflet initially moves toward the open position
before a leaflet first side region and the leaflet first side
region initially moves toward the closed position before the
leaflet second side region. In the fully open position, the leaflet
first side region opens less than the leaflet second side region.
Asymmetric opening and final open position, in synchrony with the
other leaflets having the same motion and final open position
creates spiral flow exiting the open valve that increases blood
flow on the downstream side of the leaflet and thus reduces
stagnation of the blood that might lead to thrombus formation.
Controlled asymmetric movement of the leaflet reduces closing
volume by initiating closure on the leaflet first side region and
finishing closures on the leaflet second side region.
Inventors: |
Armstrong; Joseph R.;
(Flagstaff, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
W. L. Gore & Associates, Inc. |
Newark |
DE |
US |
|
|
Family ID: |
53269999 |
Appl. No.: |
16/454928 |
Filed: |
June 27, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15333749 |
Oct 25, 2016 |
10368984 |
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16454928 |
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14561148 |
Dec 4, 2014 |
9504565 |
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15333749 |
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61974653 |
Apr 3, 2014 |
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61913235 |
Dec 6, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2/2418 20130101;
A61F 2210/0076 20130101; A61F 2230/0006 20130101; A61F 2250/0014
20130101; A61F 2250/0029 20130101; A61F 2230/0071 20130101; A61F
2/24 20130101; A61F 2/2412 20130101; Y10T 29/49901 20150115; A61F
2250/0036 20130101; A61F 2/2415 20130101; A61F 2250/0018
20130101 |
International
Class: |
A61F 2/24 20060101
A61F002/24 |
Claims
1. A prosthetic valve comprising: a plurality of leaflets, each
leaflet including a leaflet first side region and a leaflet second
side region opposite from the leaflet first side region, at least a
first portion of the leaflet first side region having a first
thickness and the second side region having a second thickness, the
first thickness is greater than the second thickness.
2. The prosthetic valve of claim 1, wherein when in an open
position, the leaflet first side region contributes to a smaller
geometric orifice area as compared with the leaflet second side
region.
3. The prosthetic valve of claim 2, wherein the leaflet second side
region opens further than the leaflet first side region during
forward flow of up to 350 ml/sec.
4. The prosthetic valve of claim 2 wherein when in the open
position, the leaflet first side region contributes up to a 70
percent smaller geometric orifice area as compared with the leaflet
second side region.
5. The prosthetic valve of claim 1, wherein the leaflet first side
region has a first bending stiffness and the leaflet second side
region has a second bending stiffness, the first bending stiffness
being greater than the second bending stiffness.
6. The prosthetic valve of claim 1, wherein the leaflet comprises
at least one layer of a composite material, at least the first
portion of the first side region comprises more layers of composite
material than the second side region.
7. The prosthetic valve of claim 6, wherein the first thickness is
up to ten times greater than the second thickness of the leaflet
second side region.
8. The prosthetic valve of claim 7, wherein the first thickness is
at least 280 micrometer and the second thickness is 25 micrometer
or greater.
9. The prosthetic valve of claim 1, wherein the first thickness is
greater than 110% of a second thickness.
10. The prosthetic valve of claim 6 wherein at least the first
portion of the leaflet first side region further comprises a
leaflet reinforcing member, the leaflet reinforcing member being
operable to provide the first portion of the leaflet first side
region with a first bending stiffness that is greater than a second
bending stiffness of the leaflet second side region.
11. The prosthetic valve of claim 10, wherein the leaflet
reinforcing member comprises at least one layer of composite
material coupled to at least the first portion of the leaflet first
side region.
12. The prosthetic valve of claim 1, wherein the leaflet comprises
a polymeric material.
13. The prosthetic valve of claim 1, further comprising: a leaflet
frame having a generally tubular shape, the leaflet frame defining
a plurality of leaflet windows wherein each of the leaflet windows
includes a leaflet window first side, a leaflet window second side
opposite the leaflet window first side, a leaflet window base
therebetween, wherein a leaflet window side of one leaflet window
is interconnected with a leaflet window side of an adjacent leaflet
window, wherein the plurality of leaflets being coupled to the
leaflet frame, each leaflet including a free edge, a base opposite
from the free edge and coupled to the leaflet window base, and a
leaflet central region between the leaflet first side region and
the leaflet second side region, the leaflet first side region being
coupled to the leaflet window first side and the leaflet second
side region being coupled to the leaflet window second side.
14. The prosthetic valve of claim 13, wherein two adjacent leaflet
window first side and leaflet window second side terminates at a
commissure post, the leaflet first side region being coupled to the
leaflet window first side, the leaflet second side region being
coupled to the leaflet window second side and the leaflet central
region being coupled to the leaflet window base.
15. The prosthetic valve of claim 13, each leaflet including a free
edge, a base opposite from the free edge and coupled to the leaflet
window base, wherein the leaflet reinforcing member extends to the
free edge of the leaflet.
16. The prosthetic valve of claim 1, further comprising: a leaflet
frame having a generally tubular shape, the leaflet frame defining
a plurality of leaflet windows wherein each of the leaflet windows
includes a leaflet window first side and a leaflet window second
side opposite the leaflet window first side and coupled thereto,
wherein a leaflet window side of one leaflet window is
interconnected with a leaflet window side of an adjacent leaflet
window; and a leaflet reinforcing member coupled to the leaflet
window first side, wherein the plurality of leaflets are coupled to
the leaflet frame, each leaflet including a free edge extending
across the leaflet window first side and a leaflet window second
side, wherein the leaflet first side region is coupled to the
leaflet reinforcing member making the leaflet first side region
stiffer than the leaflet second side region.
17. The prosthetic valve of claim 16, wherein two adjacent leaflet
window first side and leaflet window second side terminates at a
commissure post, the leaflet first side region being coupled to the
leaflet window first side, the leaflet second side region being
coupled to the leaflet window second side.
18. The prosthetic valve of claim 17, further comprising a vertical
element extending from each of the commissure posts.
19. The prosthetic valve of claim 16, wherein the leaflet frame
defines three interconnected leaflet windows having a substantially
trapezoidal shape.
20. The prosthetic valve of claim 1, wherein the leaflet comprises
a polymeric material.
21. The prosthetic valve of claim 20, wherein the leaflet comprises
a laminate.
22. The prosthetic valve of claim 21, wherein the laminate has more
than one layer of a fluoropolymer membrane.
23. The prosthetic valve of claim 20, wherein the leaflet comprises
a film having at least one fluoropolymer membrane having a
plurality of pores and an elastomer present in substantially all of
the pores of the at least one fluoropolymer membrane.
24. The prosthetic valve of claim 23, wherein the film comprises
less than about 80% fluoropolymer membrane by weight.
25. The prosthetic valve of claim 23, wherein the elastomer
comprises (per)fluoroalkylvinylethers (PAVE).
26. The prosthetic valve of claim 23, wherein the elastomer
comprises a copolymer of tetrafluoroethylene and perfluoromethyl
vinyl ether.
27. The prosthetic valve of claim 23, wherein the fluoropolymer
membrane comprises ePTFE.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Divisional of U.S. application Ser.
No. 15/333,749, filed Oct. 25, 2016, which is a Division of U.S.
application Ser. No. 14/561,148, filed Dec. 4, 2014, now U.S. Pat.
No. 9,504,565, issued Nov. 29, 2016, which claims priority to U.S.
Provisional Application Ser. No. 61/974,653, filed Apr. 3, 2014,
and 61/913,235, filed Dec. 6, 2013, all of which are herein
incorporated by reference in their entireties.
FIELD
[0002] The present disclosure relates generally to prosthetic
valves and more specifically, synthetic flexible leaflet-type
prosthetic valve devices and methods.
BACKGROUND
[0003] Bioprosthetic valves have been developed that attempt to
mimic the function and performance of a native valve. Flexible
leaflets are fabricated from biological tissue such as bovine
pericardium. In some valve designs the biological tissue is sewn
onto a relatively rigid frame that supports the leaflets and
provides dimensional stability when implanted. Although
bioprosthetic valves can provide excellent hemodynamic and
biomechanical performance in the short term, they are prone to
calcification and cusp tears, among other failure modes, requiring
reoperation and replacement.
[0004] Attempts have been made to use synthetic materials, such as
polyurethane, among others, as a substitute for the biological
tissue, to provide a more durable flexible leaflet prosthetic
valve, herein referred to as a synthetic leaflet valve (SLV).
However, synthetic leaflet valves have not become a valid valve
replacement option since they suffer premature failure, due to,
among other things, suboptimal design and lack of a durable
synthetic material.
[0005] The leaflets move under the influence of fluid pressure. In
operation, the leaflets open when the upstream fluid pressure
exceeds the downstream fluid pressure and close when the downstream
fluid pressure exceeds the upstream fluid pressure. The free edges
of the leaflets coapt under the influence of downstream fluid
pressure closing the valve to prevent downstream blood from flowing
retrograde through the valve.
[0006] It has been found that in some very flexible leaflet
prosthetic valves, the leaflets do not open and close in a
controlled manner. The durability of the leaflets is largely
controlled by the character of bending exhibited by the leaflet
during the opening-closing cycle. Small radius bends, creases and
particularly intersecting creases, can produce high stress zones in
the leaflet. These high stress zones can cause the formation of
holes and tears under repetitive loading. If the leaflet bending is
unrestricted, not only do creases form, but crease intersections
lead to formation of large three dimensional structures (e.g.,
surface disruptions) that oppose bending and slow down the leaflet
motion, both in opening and closing. This slow down of leaflet
motion leads to an increase in closing volume; that is, the volume
of blood that travels back through the valve during the closing
phase in order to close the valve. It is advantageous to minimize
closing volume.
[0007] Further, the flexible nature of the very flexible leaflet
can create regions of blood pooling behind the leaflet when in the
open position potentially causing blood clots to form at the
leaflet base and near the attachment of the leaflet to the
frame.
[0008] What is needed in the art is a flexible leaflet prosthetic
valve that provides a more controlled leaflet movement that reduces
closing volume and potential for blood pooling behind the leaflet
and near any attachment of the leaflet to a support structure.
SUMMARY
[0009] Described embodiments are directed to flexible leaflet
prosthetic heart valves in which the leaflets move into the open
and closed position in a more controlled manner. Each leaflet moves
asymmetrically in that a leaflet second side region of the leaflet
initially moves toward the open position before a leaflet first
side region and the leaflet first side region initially moves
toward the closed position before the leaflet second side region.
Further, in the fully open position, the leaflet first side region
opens less than the leaflet second side region. Such asymmetric
opening and final open position, in synchrony with the other
leaflets having the same motion and final open position creates
spiral flow exiting the open valve that assists in creating an
axial vortex flow that increases blood flow on the downstream side
of the leaflet and thus reduces stagnation of the blood that might
lead to thrombus formation. Further, controlled asymmetric movement
of the leaflet reduces closing volume by initiating closure on the
leaflet first side region and finishing closures on the leaflet
second side region, reducing leaflet buckling resistance to closure
by, in part, allowing one region of the leaflet to close before
another region. Further, the leaflet open position is controlled
such that fluid flow across the leaflet first side region extends
further into the valve orifice of the valve relative to the leaflet
second side region to further expose the leaflet downstream side to
the retrograde blood flow which increases washout of the blood from
the leaflet downstream side and exposes the leaflet downstream side
to improved reverse blood flow and to assist closing during the
closing phase.
[0010] Described embodiments are directed to flexible leaflet
prosthetic valves in which the leaflets have regions of increased
stiffness relative to other regions of the leaflet, so as to
provide asymmetric opening and closing of the leaflet. The region
of increased stiffness provides that the leaflet moves into the
open and closed position in a more controlled manner. Further, the
region of increased stiffness positions the open leaflet so as to
provide an increased blood flow behind the leaflet and where the
leaflet attaches to the leaflet frame.
[0011] In accordance with an embodiment, a prosthetic valve
comprises a leaflet frame and a plurality of leaflets coupled to
the leaflet frame. Each leaflet has a free edge, a leaflet first
side, a leaflet second side, and a leaflet base therebetween. The
leaflet first side, leaflet second side, and leaflet base are
coupled to the leaflet frame. Each leaflet has a leaflet first side
region adjacent the leaflet first side, a leaflet second side
region adjacent the leaflet second side, and a leaflet central
region therebetween and adjacent the leaflet base. At least a
portion of the leaflet first side region has a stiffness that is
greater than the stiffness of the leaflet second side region and
leaflet central region.
[0012] In accordance with another embodiment, a prosthetic valve
comprises a frame having a generally tubular shape with attached
film. The frame defines a plurality of leaflet windows. Each
leaflet window defines a leaflet window first side, a leaflet
window second side, and a leaflet window base. The leaflet window
first side and the leaflet window second side diverge from the
leaflet window base. The film defines at least one leaflet
extending from each of the leaflet windows. Each leaflet has a free
edge, a leaflet first side that is coupled to the leaflet window
first side, a leaflet second side that is coupled to the leaflet
window second side, and a leaflet base therebetween that is coupled
to the leaflet window base. Each leaflet has a leaflet first side
region adjacent the leaflet first side and extending to a
substantially axial line from the leaflet free edge to the
intersection between the leaflet window first side and the leaflet
window base, a leaflet second region adjacent the leaflet second
side and extending to a substantially axial line from the leaflet
free edge to the intersection between the leaflet window second
side and the leaflet window base, and a leaflet central region
therebetween and adjacent the leaflet free edge to the leaflet
base. At least a portion of the leaflet first side region has a
stiffness that is greater than the stiffness of the leaflet second
region and leaflet central region.
[0013] In accordance with another embodiment, a prosthetic valve
comprises a plurality of leaflets where each leaflet includes a
leaflet first side region and a leaflet second side region opposite
from the leaflet first side region. The leaflet first side region
has a thickness that is thicker than a thickness of the second side
region.
[0014] In accordance with another embodiment, a prosthetic valve
comprises a plurality of leaflets where each leaflet includes a
leaflet first side and a leaflet second side opposite from the
leaflet first side. Each leaflet first side is coupled with the
leaflet second side of an adjacent leaflet at a commissure. The
plurality of leaflets defines an orifice when the leaflets are in
an open position. Each of the leaflet first sides extends further
into the orifice than each of the leaflet second sides when the
leaflets are in the open position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings are included to provide a further
understanding of the present disclosure and are incorporated in and
constitute a part of this specification, illustrate embodiments
described herein, and together with the description serve to
explain the principles discussed in this disclosure.
[0016] FIG. 1A is a side view of a prosthetic valve in accordance
with an embodiment;
[0017] FIG. 1B is a perspective view of the embodiment of the valve
of FIG. 1A;
[0018] FIG. 1C is an axial view of the embodiment of the valve of
FIG. 1A in an open configuration;
[0019] FIG. 1D is an axial view of the embodiment of the prosthetic
valve of FIG. 2A in a partially open or partially closed
configuration;
[0020] FIG. 1E is an axial view of the embodiment of the prosthetic
valve of FIG. 2A in a closed configuration;
[0021] FIG. 2A is a representation of an embodiment of a leaflet
frame unrolled to a flat orientation with a strain relief frame
covering and leaflet reinforcing member;
[0022] FIG. 2B is a representation of an embodiment of a leaflet
frame unrolled to a flat orientation of FIG. 2A with a strain
relief frame covering and leaflet reinforcing member, also with a
leaflet;
[0023] FIG. 3A is a perspective view of another embodiment of a
valve frame;
[0024] FIG. 3B is an axial view of the embodiment of the valve of
FIG. 3A in an open configuration;
[0025] FIG. 4A is a representation of an embodiment of a leaflet
frame of the embodiment of FIG. 3A unrolled to a flat orientation
with a strain relief frame covering and leaflet reinforcing
member;
[0026] FIG. 4B is a representation of an embodiment of a leaflet
frame unrolled to a flat orientation of FIG. 3A with a strain
relief frame covering and leaflet reinforcing member, also with a
leaflet;
[0027] FIG. 5A is a side view of the leaflet frame on an assembly
mandrel, in accordance with an embodiment;
[0028] FIG. 5B is a side view of the leaflet frame on an assembly
mandrel, in accordance with an embodiment;
[0029] FIG. 5C is a side view of the leaflet frame construct
showing the strain relief frame covering and leaflet reinforcing
member, in accordance with an embodiment;
[0030] FIG. 5D is a side view of the leaflet frame construct on an
assembly mandrel overlaid with leaflet material, in accordance with
an embodiment;
[0031] FIG. 6A is a side view of the leaflet frame on a mandrel, in
accordance with an embodiment; and
[0032] FIG. 6B is a perspective view of the leaflet frame on the
mandrel of FIG. 6A.
DETAILED DESCRIPTION
[0033] Persons skilled in the art will readily appreciate that
various aspects of the present disclosure can be realized by any
number of methods and apparatus configured to perform the intended
functions. Stated differently, other methods and apparatuses can be
incorporated herein to perform the intended functions. It should
also be noted that the accompanying drawing figures referred to
herein are not necessarily drawn to scale, but may be exaggerated
to illustrate various aspects of the present disclosure, and in
that regard, the drawing figures should not be construed as
limiting.
[0034] Although the embodiments herein may be described in
connection with various principles and beliefs, the described
embodiments should not be bound by theory. For example, embodiments
are described herein in connection with prosthetic valves, more
specifically cardiac prosthetic valves. However, embodiments within
the scope of this disclosure can be applied toward any valve or
mechanism of similar structure and/or function. Furthermore,
embodiments within the scope of this disclosure can be applied in
non-cardiac applications.
[0035] The term leaflet as used herein in the context of prosthetic
valves is a component of a one-way valve wherein the leaflet is
operable to move between an open and closed position under the
influence of a pressure differential. In an open position, the
leaflet allows blood to flow through the valve. In a closed
position, the leaflet substantially blocks retrograde flow through
the valve. In embodiments comprising multiple leaflets, each
leaflet cooperates with at least one neighboring leaflet to block
the retrograde flow of blood. The pressure differential in the
blood is caused, for example, by the contraction of a ventricle or
atrium of the heart, such pressure differential typically resulting
from a fluid pressure building up on one side of the leaflets when
closed. As the pressure on an inflow side of the valve rises above
the pressure on the outflow side of the valve, the leaflets opens
and blood flows therethrough. As blood flows through the valve into
a neighboring chamber or blood vessel, the pressure on the inflow
side equalizes with the pressure on the outflow side. As the
pressure on the outflow side of the valve rises above the blood
pressure on the inflow side of the valve, the leaflet returns to
the closed position generally preventing retrograde flow of blood
through the valve.
[0036] The term membrane as used herein refers to a sheet of
material comprising a single composition, such as, but not limited
to, expanded fluoropolymer.
[0037] The term composite material as used herein refers to a
combination of a membrane, such as, but not limited to, expanded
fluoropolymer, and an elastomer, such as, but not limited to, a
fluoroelastomer. The elastomer may be imbibed within a porous
structure of the membrane, coated on one or both sides of the
membrane, or a combination of coated on and imbibed within the
membrane.
[0038] The term laminate as used herein refers to multiple layers
of membrane, composite material, or other materials, such as
elastomer, and combinations thereof.
[0039] The term film as used herein generically refers to one or
more of the membrane, composite material, or laminate.
[0040] The term biocompatible material as used herein generically
refers to a film or a biological material, such as, but not limited
to, bovine pericardium.
[0041] The term leaflet window is defined as that space that a
frame defines from which a leaflet extends. The leaflet may extend
from frame elements or adjacent to frame elements and spaced apart
therefrom.
[0042] The terms native valve orifice and tissue orifice refer to
an anatomical structure into which a prosthetic valve may be
placed. Such anatomical structure includes, but is not limited to,
a location wherein a cardiac valve may or may not have been
surgically removed. It is understood that other anatomical
structures that may receive a prosthetic valve include, but are not
limited to, veins, arteries, ducts and shunts. Although reference
is made herein to replacing a native valve with a prosthetic valve,
it is understood and appreciated that a valve orifice or implant
site may also refer to a location in a synthetic or biological
conduit that may receive a valve for a particular purpose, and
therefore the scope of the embodiments provided herein is not
limited to valve replacement.
[0043] As used herein, "couple" means to join, connect, attach,
adhere, affix, or bond, whether directly or indirectly, and whether
permanently or temporarily.
[0044] Embodiments herein include various apparatus, systems, and
methods for a prosthetic valve suitable for surgical and
transcatheter placement, such as, but not limited to, cardiac valve
replacement. The valve is operable as a one-way valve wherein the
valve defines a valve orifice into which leaflets open to permit
flow and close so as to occlude the valve orifice and prevent flow
in response to differential fluid pressure.
[0045] Described embodiments are directed to flexible leaflet
prosthetic valves in which the leaflets move into the open and
closed position in a more controlled manner. The leaflets move in
synchrony with each other. Each leaflet moves asymmetrically in
that a leaflet second side region of the leaflet initially moves
toward the open position before a leaflet first side region and the
leaflet first side region initially moves toward the closed
position before the leaflet second side region. Further, in the
fully open position, the leaflet first side opens less than the
leaflet second side. The leaflet first side region of one leaflet
is adjacent to the leaflet second side region of an adjacent
leaflet. Such asymmetric opening and final open position, in
synchrony with the other leaflets having the same motion and final
open position, creates spiral flow exiting the open valve that
assists in creating an axial vortex flow that increases blood flow
on the downstream side of the leaflet and thus reduces stagnation
of the blood that might lead to thrombus formation. Further,
controlled asymmetric movement of the leaflet reduces closing
volume by initiating closure on the leaflet first side region and
finishing closures on the leaflet second side region, reducing
leaflet buckling resistance to closure by, in part, allowing one
side region of the leaflet to close before another side region.
Further, the leaflet open position is controlled such that the
leaflet first side region extends further into the valve orifice of
the valve relative to the leaflet second side region to further
expose the leaflet downstream side to the retrograde blood flow
which increases washout of the blood from the leaflet downstream
side and exposes the leaflet downstream side to improved reverse
blood flow and to assist closing during the closing phase.
[0046] In accordance with embodiments provided herein, at least a
portion of the leaflet first side region is configured to be more
resistant to motion as compared with the leaflet second side
region. The resistant to motion may be affected in a number of
ways, including, but not limited to, configuring the bending
modulus of the leaflet material to have a higher bending modulus in
the leaflet first side region as compared with the leaflet second
side region. The resistant to motion may be affected in a number of
ways, including, but not limited to, adding a reinforcing member
that is separate from but coupled to the leaflet first side region.
The resistant to motion may be affected in a number of ways,
including, but not limited to, increasing the number of layers of a
laminated composite that makes up the leaflet, and thus the
thickness in the leaflet first side region as compared with the
leaflet second side region.
[0047] Embodiments provided herein address controlled leaflet
opening and closing. Embodiments provided herein provide a feature
of differing leaflet stiffness from one side region of the leaflet
to the other side region. The less stiff side region of the leaflet
will initiate opening before the stiffer side of the leaflet.
Therefore, the leaflet will open asymmetrically with respect to the
leaflet free edge rather than symmetrically as with a leaflet
having a uniform or symmetric stiffness property. This asymmetric
movement minimizes crease formation, which is of particular
importance in thin, high-modulus leaflets. If the leaflet bending
is unrestricted, not only may creases form, but crease
intersections lead to formation of large three dimensional
structures (e.g., surface disruptions) that oppose bending and slow
down the leaflet motion, both in opening and closing. Embodiments
provided herein control leaflet opening and to minimize crease
formation provided by the controlled asymmetric opening and closing
of the leaflet.
[0048] Embodiments provided herein address blood pooling or
stagnation that can lead to clot formation behind the leaflet and
along the intersection of the leaflet and the frame when the
leaflet is open. Embodiments provided herein provide a feature of
differing leaflet stiffness from one side region of the leaflet to
the other side region. The stiffer side region of the leaflet will
open to a lesser extent than the less stiff side region. Since the
stiffer side region of the leaflet does not open fully and
therefore protrudes into the flow more so than the less stiff side
region, retrograde blood flow may better extend behind the leaflet,
the downstream side, producing a washing effect along the
attachment of the leaflet to the frame and, in particular, at the
base of the leaflet on the downstream side of the leaflet. Since
the stiffer side region of the leaflet protrudes into the
retrograde flow more so than the less stiff side region, when the
flow reverses, the stiffer leaflet side region protruding into the
flow will actuate the closing of the valve much sooner and in a
more controlled manner. Therefore, the leaflet will close
asymmetrically from the more stiff side region to the less stiff
side region with respect to the leaflet free edge rather than
randomly and chaotically as with a very thin and flexible leaflet
having a uniform or symmetric stiffness property. This asymmetric
movement minimizes crease formation and provides a faster closing
response, which is of particular importance in thin, high-modulus
leaflets. Embodiments provided herein control leaflet closing that
provides minimization of crease formation and a faster closing
response provided by the controlled asymmetric closing of the
leaflet.
[0049] Valve
[0050] FIG. 1A is a side view of a valve 100, in accordance with an
embodiment. FIG. 1B is a perspective view of the valve 100 of FIG.
1A. FIGS. 1C, 1D and 1E are axial views of the valve 100 of FIG. 1A
in an open, partially open, and closed configuration, respectively.
The valve 100 comprises a leaflet frame 130 and film 160 that
defines leaflets 140. In FIGS. 1A, 1B and 1E, the leaflets 140 are
shown slightly open to better show the features but it is
understood that a valve 100 that is fully closed will have the
leaflet free edges 142 of the leaflets 140 coming together to coapt
under the influence of downstream fluid pressure which results in
closing the valve 100 to prevent downstream blood from flowing
retrograde through the valve 100.
[0051] Frame
[0052] Referring to FIGS. 1A-1E, the leaflet frame 130 is a
generally tubular member, in accordance with an embodiment. The
leaflet frame 130 comprises a leaflet frame first end 121a and a
frame second end 121b opposite the leaflet frame first end 121a.
The leaflet frame 130 comprises a leaflet frame outer surface 126a
and a leaflet frame inner surface 126b opposite the leaflet frame
outer surface 126a, as shown in FIG. 1A. The leaflet frame 130
defines commissure posts 136 that couple to the leaflet free edges
142. The commissure posts 136 are defined by a vertical element
122.
[0053] FIGS. 2A and 2B are side views of a leaflet frame 130 of a
valve 100 wherein the leaflet frame 130 has been longitudinally cut
and laid open to better illustrate the elements of the generally
tubular-shaped leaflet frame 130, in accordance with an embodiment.
In FIG. 2A, a leaflet reinforcing member 149 is shown in dashed
line to represent where the leaflet reinforcing member 149 is
located within the leaflet window 137, the leaflet window 137 being
defined by the leaflet window first side 133a and the leaflet
window second side 133b, and the leaflet window base 134. The
leaflet reinforcing member 149 is coupled to the leaflet window
first side 133a and extends into what will be the leaflet first
side region 184a, as shown in FIG. 2B. Also in FIG. 2A, an optional
strain relief frame covering 152 is shown in dashed line following
the contour of the leaflet window 137. The strain relief frame
covering 152 is a covering of film 160 that covers the leaflet
frame 130 and extends about 0.5 mm to 1.0 mm into the leaflet
window 137. The strain relief frame covering 152 provides a
transition region that provides strain relief between the leaflet
frame 130 and the leaflet 140.
[0054] In FIG. 2B, a leaflet 140 is shown in solid line to
represent where the leaflet 140 is located within the leaflet
window 137 and the leaflet reinforcing member 149, shown in dashed
line, being within the leaflet first side region 184a.
[0055] The leaflet frame 130 may comprise a cut tube, or any other
element suitable for the particular purpose. The leaflet frame 130
may be etched, cut, laser cut, or stamped into a tube or a sheet of
material, with the sheet then formed into a substantially
cylindrical structure.
[0056] The leaflet frame 130 can comprise any metallic or polymeric
material that is biocompatible. For example, the leaflet frame 130
can comprise a material, such as, but not limited to nitinol,
cobalt-nickel alloy, stainless steel, or polypropylene, acetyl
homopolymer, acetyl copolymer, ePTFE, other alloys or polymers, or
any other biocompatible material having adequate physical and
mechanical properties to function as described herein.
[0057] Referring to FIGS. 2A and 2B, the leaflet frame comprises a
plurality of spaced apart leaflet frame elements defining
substantially an isosceles trapezoid interconnected by a base
element 138 defining leaflet windows 137. Each of the leaflet
window first side 133a and leaflet window second side 133b is
defined by a side of one trapezoid and a side of an adjacent
trapezoid defining a trapezoidal shape, and wherein each leaflet
window base 134 is defined by the base element 138 between the
leaflet window first side 133a and leaflet window second side 133b.
In the embodiment of FIG. 1B there are three interconnected leaflet
windows 137, where a leaflet window first side 133a of one leaflet
window 137 is interconnected with an adjacent leaflet window second
side 133b of an adjacent leaflet window 137.
[0058] Referring again to FIGS. 1A, 2A and 2B, the leaflet frame
first end 121a further comprises commissure posts 136 extending
from an apex of the leaflet frame elements defining substantially
an isosceles trapezoid. The commissure post 136 may affect the
leaflet free edge 142 so as to create a larger or wider coaptation
region 146 between adjacent leaflet free edges 142.
[0059] In accordance with an embodiment, the leaflet frame 130
comprises a frame having a shape determined, at least in part, by
wrapping a two dimensional isosceles trapezoid every 120 degrees
onto the tubular shape of the leaflet frame 130, the isosceles
trapezoid having a leaflet window base 134, a leaflet window first
side 133a, and a leaflet window second side 133b that diverge from
the leaflet window base 134, and wherein a leaflet window first
side 133a and leaflet window second side 133b from adjacent
isosceles trapezoids meet at the leaflet frame first end 121a and
frame second end 121b, as shown in FIG. 2A. A leaflet 140 is shown
located within the leaflet window 137, the leaflet window 137 being
defined by the leaflet window first side 133a, the leaflet window
second side 133b, and the leaflet window base 134.
[0060] In accordance with an embodiment of a valve 100, each
leaflet 140 has substantially the shape of an isosceles trapezoid
having a leaflet first side 141a and a leaflet second side 141b, a
leaflet base 143 and a leaflet free edge 142 opposite the leaflet
base 143, wherein the leaflet first side 141a and a leaflet second
side 141b diverge from the leaflet base 143, wherein the leaflet
base 143 is substantially flat, as shown in dashed lines in FIG.
2B.
[0061] FIG. 3 is a perspective view of a leaflet frame 230 that is
a generally tubular member, in accordance with another embodiment.
The leaflet frame 230 comprises a frame first end 221a and a frame
second end 221b opposite the frame first end 221a. The leaflet
frame 230 comprises a leaflet frame outer surface 226a and a
leaflet frame inner surface 226b opposite the leaflet frame outer
surface 226a, as shown in FIG. 3A. The leaflet frame 230 defines
commissure posts 236 that couple to the leaflet free edges 242.
[0062] FIGS. 4A and 4B are side views of a leaflet frame 230 of a
valve 200 wherein the leaflet frame 230 has been longitudinally cut
and laid open to better illustrate the elements of the generally
tubular-shaped leaflet frame 230, in accordance with an embodiment.
The leaflet frame comprises a plurality of interconnected parabolic
leaflet frame elements 235 terminating at commissure posts 236
defining leaflet windows 237. Each parabolic leaflet frame elements
235 may be defined by a leaflet window first side 233a and leaflet
window second side 233b on either side of a plane P symmetrically
bisecting the parabolic leaflet frame elements 235 aligned with the
axial axis X, shown in FIG. 3B.
[0063] The commissure posts 236 extend from an apex of intersecting
parabolic leaflet frame elements 235. The length of the commissure
post 236 may define the length of the coaptation region 146 between
adjacent leaflet free edges 142. Where the commissure post 236 is
made longer and the leaflet is attached thereto, a larger or wider
coaptation region 146 may be defined between adjacent leaflet free
edges 142.
[0064] In accordance with an embodiment of a valve 200, each
leaflet 240 has substantially the shape of a parabola having a
leaflet first side 241a including a leaflet first side region 284a
and a leaflet second side 241b including a leaflet second side
region 284b defined by a plane P symmetrically aligned with the
axial axis X bisecting the parabola, and a leaflet free edge 142
between the leaflet first side 241a and a leaflet second side
241b.
[0065] In FIG. 4B, a leaflet reinforcing member 249 is shown in
dashed line to represent where the leaflet reinforcing member 249
is located within the leaflet window 237. The leaflet reinforcing
member 249 is coupled to the leaflet window first side 233a and
extends into what will be at least a portion of the leaflet first
side region 284a. Also in FIG. 4B, an optional strain relief frame
covering 252 is shown in dashed line following the contour of the
leaflet window 237. The strain relief frame covering 252 is a
covering of film 160 that covers the leaflet frame 130 and extends
about 0.5 mm to 1.0 mm into the leaflet window 237. The strain
relief frame covering 252 provides a transition region that
provides strain relief between the leaflet frame 130 and the
leaflet 240. In FIG. 14B, a leaflet 240 is shown located within the
leaflet window 237 and the leaflet reinforcing member 249 being
within the leaflet first side region 284a.
[0066] Film
[0067] The film 160, as shown in FIG. 1A, is generally any
sheet-like material that is biologically compatible and configured
to couple to the leaflet frame 130, in accordance with embodiments.
It is understood that the term "film" is used generically for one
or more biocompatible materials suitable for a particular purpose.
The leaflets 140 are also comprised of the film 160.
[0068] In accordance with an embodiment, the biocompatible material
is a film 160 that is not of a biological source and that is
sufficiently flexible and strong for the particular purpose, such
as a biocompatible polymer. In an embodiment, the film 160
comprises a biocompatible polymer that is combined with an
elastomer, referred to as a composite.
[0069] Details of various types of film 160 are discussed below. In
an embodiment, the film 160 may be formed from a generally tubular
material to at least partially cover the leaflet frame 130. The
film 160 can comprise one or more of a membrane, composite
material, or laminate. Details of various types of film 160 are
discussed below.
[0070] In an embodiment, the film 160 comprises a biocompatible
polymer that is combined with an elastomer, referred to as a
composite material. A material according to one embodiment includes
a composite material comprising an expanded fluoropolymer membrane,
which comprises a plurality of spaces within a matrix of fibrils,
and an elastomeric material. It should be appreciated that multiple
types of fluoropolymer membranes and multiple types of elastomeric
materials can be combined to form a laminate while remaining within
the scope of the present disclosure. It should also be appreciated
that the elastomeric material can include multiple elastomers,
multiple types of non-elastomeric components, such as inorganic
fillers, therapeutic agents, radiopaque markers, and the like while
remaining within the scope of the present disclosure.
[0071] In accordance with an embodiment, the composite material
includes an expanded fluoropolymer material made from porous ePTFE
membrane, for instance as generally described in U.S. Pat. No.
7,306,729 to Bacino.
[0072] The expandable fluoropolymer, used to form the expanded
fluoropolymer material described, may comprise PTFE homopolymer. In
alternative embodiments, blends of PTFE, expandable modified PTFE
and/or expanded copolymers of PTFE may be used. Non-limiting
examples of suitable fluoropolymer materials are described in, for
example, U.S. Pat. No. 5,708,044, to Branca, U.S. Pat. No.
6,541,589, to Baillie, U.S. Pat. No. 7,531,611, to Sabol et al.,
U.S. patent application Ser. No. 11/906,877, to Ford, and U.S.
patent application Ser. No. 12/410,050, to Xu et al.
[0073] The expanded fluoropolymer membrane can comprise any
suitable microstructure for achieving the desired leaflet
performance. In accordance with an embodiment, the expanded
fluoropolymer comprises a microstructure of nodes interconnected by
fibrils, such as described in U.S. Pat. No. 3,953,566 to Gore. The
fibrils radially extend from the nodes in a plurality of
directions, and the membrane has a generally homogeneous structure.
Membranes having this microstructure may typically exhibit a ratio
of matrix tensile strength in two orthogonal directions of less
than or equal to 2, and possibly less than 1.5.
[0074] In another embodiment, the expanded fluoropolymer membrane
has a microstructure of substantially only fibrils, as is generally
taught by U.S. Pat. No. 7,306,729, to Bacino. The expanded
fluoropolymer membrane having substantially only fibrils, can
possess a high surface area, such as greater than 20 m.sup.2/g, or
greater than 25 m.sup.2/g, and in some embodiments can provide a
highly balanced strength material having a product of matrix
tensile strengths in two orthogonal directions of at least
1.5.times.10.sup.5 MPa.sup.2, and/or a ratio of matrix tensile
strengths in two orthogonal directions of less than 4, and possibly
less than 1.5.
[0075] The expanded fluoropolymer membrane can be tailored to have
any suitable thickness and mass to achieve the desired leaflet
performance. By way of example, but not limited thereto, the
leaflet 140 comprises an expanded fluoropolymer membrane having a
thickness of about 0.1 .mu.m. The expanded fluoropolymer membrane
can possess a mass per area of about 1.15 g/m.sup.2. Membranes
according to an embodiment of the invention can have matrix tensile
strengths of about 411 MPa in the longitudinal direction and 315
MPa in the transverse direction.
[0076] Additional materials may be incorporated into the pores or
within the material of the membranes or in between layers of
membranes to enhance desired properties of the leaflet. Composite
materials described herein can be tailored to have any suitable
thickness and mass to achieve the desired leaflet performance.
Composite materials according to embodiments can include
fluoropolymer membranes and have a thickness of about 1.9 .mu.m and
a mass per area of about 4.1 g/m.sup.2. In other embodiments, the
fluoropolymer membranes have a thickness of about 100 .mu.m and a
mass per area of about 100 g/m.sup.2.
[0077] The expanded fluoropolymer membrane combined with elastomer
to form a composite material provides the elements of the present
disclosure with the performance attributes required for use in
high-cycle flexural implant applications, such as heart valve
leaflets, in various ways. For example, the addition of the
elastomer can improve the fatigue performance of the leaflet by
eliminating or reducing the stiffening observed with ePTFE-only
materials. In addition, it may reduce the likelihood that the
material will undergo permanent set deformation, such as wrinkling
or creasing, that could result in compromised performance. In one
embodiment, the elastomer occupies substantially all of the pore
volume or space within the porous structure of the expanded
fluoropolymer membrane. In another embodiment the elastomer is
present in a portion of the pores of the at least one fluoropolymer
layer. Having elastomer filling the pore volume or present in a
portion of the pores reduces the space in which foreign materials
can be undesirably incorporated into the composite material. An
example of such foreign material is calcium that may be drawn into
the membrane from contact with the blood. If calcium becomes
incorporated into the composite material, as used in a heart valve
leaflet, for example, mechanical damage can occur during cycling
open and closed, thus leading to the formation of holes in the
leaflet and degradation in hemodynamics.
[0078] In an embodiment, the elastomer that is combined with the
ePTFE is a thermoplastic copolymer of tetrafluoroethylene (TFE) and
perfluoromethyl vinyl ether (PMVE), such as described in U.S. Pat.
No. 7,462,675 to Chang et al. As discussed above, the elastomer is
combined with the expanded fluoropolymer membrane such that the
elastomer occupies substantially all of the void space or pores
within the expanded fluoropolymer membrane to form a composite
material. This filling of the pores of the expanded fluoropolymer
membrane with elastomer can be performed by a variety of methods.
In one embodiment, a method of filling the pores of the expanded
fluoropolymer membrane includes the steps of dissolving the
elastomer in a solvent suitable to create a solution with a
viscosity and surface tension that is appropriate to partially or
fully flow into the pores of the expanded fluoropolymer membrane
and allow the solvent to evaporate, leaving the filler behind.
[0079] In one embodiment, the composite material comprises three
layers: two outer layers of ePTFE and an inner layer of a
fluoroelastomer disposed therebetween. Additional fluoroelastomers
can be suitable and are described in U.S. Publication No.
2004/0024448 to Chang et al.
[0080] In another embodiment, a method of filling the pores of the
expanded fluoropolymer membrane includes the steps of delivering
the filler via a dispersion to partially or fully fill the pores of
the expanded fluoropolymer membrane.
[0081] In another embodiment, a method of filling the pores of the
expanded fluoropolymer membrane includes the steps of bringing the
porous expanded fluoropolymer membrane into contact with a sheet of
the elastomer under conditions of heat and/or pressure that allow
elastomer to flow into the pores of the expanded fluoropolymer
membrane.
[0082] In another embodiment, a method of filling the pores of the
expanded fluoropolymer membrane includes the steps of polymerizing
the elastomer within the pores of the expanded fluoropolymer
membrane by first filling the pores with a prepolymer of the
elastomer and then at least partially curing the elastomer.
[0083] After reaching a minimum percent by weight of elastomer, the
leaflets constructed from fluoropolymer materials or ePTFE
generally performed better with increasing percentages of elastomer
resulting in significantly increased cycle lives. In one
embodiment, the elastomer combined with the ePTFE is a
thermoplastic copolymer of tetrafluoroethylene and perfluoromethyl
vinyl ether, such as described in U.S. Pat. No. 7,462,675 to Chang
et al., and other references that would be known to those of skill
in the art. Other biocompatible polymers which can be suitable for
use in leaflet 140 include but are not limited to the groups of
urethanes, silicones(organopolysiloxanes), copolymers of
silicon-urethane, styrene/isobutylene copolymers, polyisobutylene,
polyethylene-co-poly(vinyl acetate), polyester copolymers, nylon
copolymers, fluorinated hydrocarbon polymers and copolymers or
mixtures of each of the foregoing.
[0084] Leaflet
[0085] Each leaflet window 137 is provided with a biocompatible
material, such as a film 160, which is coupled to a portion of the
leaflet window sides 133 with the film 160 defining a leaflet 140,
as shown in FIGS. 1A-1D and 2B. Each leaflet 140 defines a leaflet
free edge 142 and a leaflet base 143, in accordance with an
embodiment. As will be described below, it is anticipated that a
plurality of embodiments of leaflet shapes, including with and
without a defined leaflet base 143, may be provided. In accordance
with an embodiment, the film 160 is coupled to at least a portion
of the leaflet window first side 133a and leaflet window second
side 133b and to the leaflet window base 134 where the leaflet 140
is defined by the portion of the leaflet window first side 133a,
the leaflet window second side 133b and to the leaflet window base
134. The leaflet 140 has a leaflet upstream side 193 and a leaflet
downstream side 191 opposite the leaflet upstream side 193. The
leaflet upstream side 193 is that side of the leaflet 140 that is
facing away from the leaflet frame 130 when in the open position
and the leaflet downstream side 191 is that side of the leaflet 140
that is facing toward the leaflet frame 130 when in the open
position.
[0086] When the leaflets 140 are in a fully open position, the
valve 100 presents a substantially circular valve orifice 102 as
shown in FIG. 1C. Fluid flow is permitted through the valve orifice
102 when the leaflets 140 are in the open position. Since the
leaflet first side region 184a is stiffer than the leaflet second
side region 184b, the leaflet first side region 184a does not open
fully leaving a pocket 194 defined in part by the leaflet
downstream side 191 adjacent the leaflet first side region 184a. As
the blood exits the valve 100, retrograde flow may enter the pocket
194 so as to wash out the area defined by the leaflet downstream
side 191.
[0087] A geometric orifice area (GOA), as is known in the art, is
an area measurement of an axial projection of an open area defined
by the valve when in the fully open position. As explained below, a
first portion of a leaflet will extend further into the valve
orifice defined by the valve frame, that is, not open as much, than
a second portion of the same leaflet, which opens further. From an
axial viewpoint, the first portion of the leaflet will create a
smaller GOA than the second portion of the leaflet
[0088] FIG. 1C is an axial view of the valve 100 in the fully open
position. As shown in FIG. 1C, the leaflets 140 do not completely
open to conform to the leaflet frame inner surface 126b, therefore
projecting a smaller geometric orifice area compared with an
orifice area of a frame without leaflets. The leaflet frame inner
surface 126b in cross-section transverse to the X axis defines a
frame orifice 139 having a frame orifice area that is circular in
shape.
[0089] The axial view shown in FIG. 1C is bisected into six
segments by three planes P1, P2, P3 where each plane passes through
one commissure post 136, the axis X and bisects a leaflet 140 in
half, defining a first segment 172 and a second segment 174. The
leaflet first side region 184a of the leaflet 140 in the first
segment 172 is defined between the leaflet first edge 185a and the
plane (e.g., P1, P2, P3) bisecting the leaflet 140 in half, and
extends more into the frame orifice 139 defined by the leaflet
frame inner surface 126b defining a smaller GOA, for example, up to
70 percent smaller, than the leaflet second side region 184b in the
second segment 174, where the leaflet second side region 184b is
defined between the leaflet second edge 185b and the plane (e.g.,
P1, P2, P3) bisecting the leaflet 140 in half. The benefit of this
relationship of the leaflet first side region 184a extending into
the valve orifice as compared to the leaflet second side region
184b will be detailed below.
[0090] FIG. 1D is an axial view of the valve 100 in the partially
open position or a partially closed position. The leaflet first
side region 184a of one leaflet 140 is adjacent to the leaflet
second side region 184b of an adjacent leaflet 140. The leaflet
first side region 184a is stiffer compared to the leaflet second
side region 184b. The leaflet second side region 184b will
initially open first and will close last compared to the leaflet
first side region 184a. This controlled motion provides a
consistent leaflet motion from cycle to cycle imparting the
benefits previously described.
[0091] As the leaflets 140 cycle between the open and closed
positions, the leaflets 140 generally flex about the leaflet base
143 and the portion of the leaflet window first side 133a and the
leaflet window second side 133b to which the leaflets 140 are
coupled. Since the leaflet first side region 184a is more stiff
than the leaflet second side region 184b, the leaflet first side
141a does not flex as much about the leaflet window first side 133a
as compared with the leaflet second side 141b defining a channel
145 between the leaflet first side 141a of one leaflet 140 and the
leaflet second side 141b of an adjacent leaflet 140 when the
leaflet is not in the closed position. The channel 145 is defined
when the leaflet 140 moves from the closed position. The channel
145 allows for blood flow therethrough throughout the opening phase
of the leaflet 140 and thus reduces the potential for blood
pooling, stagnation and clot formation between the leaflet first
side 141a and the leaflet window first side 133a, and the leaflet
second side 141b and the leaflet window second side 133b, and
therebetween.
[0092] When the valve 100 is closed, generally about half of each
leaflet free edge 142 abuts an adjacent half of a leaflet free edge
142 of an adjacent leaflet 140, as shown in FIG. 1E. The three
leaflets 140 of the embodiment of FIG. 1E meet at a triple point
148. The valve orifice 102 is occluded when the leaflets 140 are in
the closed position stopping fluid flow. Although the leaflet first
side region 184a is stiffer than the leaflet central region 182 and
the leaflet second side region 184b, the flexibility of the leaflet
central region 182 and the leaflet second side region 184b of an
adjacent leaflet 140 allows for coaptation with the leaflet first
side region 184a allowing for proper closing of the valve 100.
[0093] Referring to FIG. 1E, in accordance with an embodiment, each
leaflet 140 includes a leaflet central region 182, a leaflet first
side region 184a, and a leaflet second side region 184b on opposite
sides of the leaflet central region 182. The leaflet central region
182 is defined by a shape substantially that of a rectangle defined
by two leaflet central region sides 183, the leaflet base 143 and
the leaflet free edge 142. The two leaflet central region sides 183
extend from the leaflet base 143 to the leaflet free edge 142.
[0094] In accordance with an embodiment, the leaflet first side
region 184a is stiffer than the leaflet central region 182 and the
leaflet second side region 184b. The stiffness characteristics of
the leaflet first side region 184a, leaflet second side region 184b
and the leaflet central region 182 may be affected by any suitable
means. In accordance with an embodiment, the leaflet 140 comprises
a film that is a laminate of multiple layers of composite material.
Additional layers of composite material are provided in the leaflet
first side region 184a which imparts additional stiffness to the
leaflet first side region 184a as compared with the leaflet central
region 182 and the leaflet second side region 184b. Example 1
provides additional details as to the embodiment just
described.
[0095] Referring to the embodiment of FIGS. 3A, 3B and 4A, 4B, in
contrast to the embodiment of FIGS. 1B, 2A and 2B, the parabolic
shaped leaflet window 237 does not define a distinct base but only
a leaflet window first side 233a and leaflet window second side
233b on either side of a plane P symmetrically bisecting the
parabolic leaflet frame elements 235 aligned with the axial axis X,
shown in FIGS. 4A and 4B. Therefore, the film 160 is coupled to at
least a portion of the leaflet window first side 233a and leaflet
window second side 233b where the leaflet 240 is defined by the
portion of the leaflet window first side 233a and the leaflet
window second side 133b. The leaflet 240 has a leaflet upstream
side 193 and a leaflet downstream side 191 opposite the leaflet
upstream side 193. The leaflet upstream side 193 is that side of
the leaflet 140 that is facing away from the leaflet frame 230 when
in the open position and the leaflet downstream side 191 is that
side of the leaflet 240 that is facing toward the leaflet frame 130
when in the open position.
[0096] The embodiments of FIGS. 1A-E and 3, 4A and 4B are examples
of two different leaflet and leaflet window geometries that are
suitable for the particular purpose. It is understood that other
leaflet and leaflet window geometries may also be suitable for the
particular purpose and are not limited thereto.
[0097] The axial view of the valve 200 shown in FIG. 3B is bisected
into six segments by three planes P1, P2, P3 where each plane
passes through one commissure post 236, the axis X and bisects a
leaflet 240 in half, defining a first segment 172 and a second
segment 174. The portion of the leaflet in the first segment 172
defined between the leaflet first edge 285a and the plane (e.g.,
P1, P2, P3) bisecting the leaflet 240 in half corresponds to the
leaflet first side region 284a of the leaflet 240, which defines a
smaller GOA than the portion of the leaflet in the second segment
174 defined between the leaflet second edge 285b and the plane
(e.g., P1, P2, P3) bisecting the leaflet 240 in half, which
corresponds to the leaflet second side region 284b of the leaflet
240, by virtue of the leaflet first side region 284a extending
further into the frame orifice 139 defined by the leaflet frame
inner surface 126b as compared to the leaflet second side region
284b.
[0098] FIG. 3B is an axial view of the valve 200 in the partially
open position or a partially closed position. The leaflet first
side region 284a of one leaflet 240 is adjacent to the leaflet
second side region 284b of an adjacent leaflet 240. The leaflet
first side region 284a is stiffer compared to the leaflet second
side region 284b. The leaflet second side region 284b will
initially open first and will close last compared to the leaflet
first side region 284a. This controlled motion provides a
consistent leaflet motion from cycle to cycle imparting the
benefits previously described.
[0099] The leaflet 140 can be configured to actuate at a pressure
differential in the blood caused, for example, by the contraction
of a ventricle or atrium of the heart, such pressure differential
typically resulting from a fluid pressure building up on one side
of the valve 100 when closed. As the pressure on an inflow side of
the valve 100 rises above the pressure on the outflow side of the
valve 100, the leaflet 140 opens and blood flows therethrough. As
blood flows through the valve 100 into a neighboring chamber or
blood vessel, the pressure equalizes. As the pressure on the
outflow side of the valve 100 rises above the blood pressure on the
inflow side of the valve 100, the leaflet 140 returns to the closed
position generally preventing the retrograde flow of blood through
the inflow side of the valve 100.
[0100] It is understood that the leaflet frame 130 may comprise any
number of leaflet windows 137, and thus leaflets 140, suitable for
a particular purpose, in accordance with embodiments. Leaflet
frames 130 comprising one, two, three or more leaflet windows 137
and corresponding leaflets 140 are anticipated.
[0101] Although embodiments provided above comprise a leaflet frame
that supports the leaflets, it is understood and appreciated that
the leaflets may not necessarily be supported by a frame. In
accordance with an embodiment, the leaflets may be supported by the
inner wall within a solid-walled conduit without a frame that
defines leaflet windows and commissure posts. In other embodiments,
the leaflets may be constructed as in the tissue valve art that are
formed into the desired shape without a frame.
[0102] In another embodiment of a valve including a plurality of
leaflets, each leaflet includes a leaflet first side and a leaflet
second side opposite from the leaflet first side. Each leaflet
first side is coupled with the leaflet second side of an adjacent
leaflet at a commissure. The plurality of leaflets defines an
orifice, also referred to as a lumen, when the leaflets are in an
open position. Each of the leaflet first sides extend further into
the orifice than each of the leaflet second sides.
[0103] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. Each leaflet defines a leaflet base and a
leaflet free edge opposite from the leaflet base. Each leaflet
first side region is coupled with the leaflet second side region of
an adjacent leaflet at a commissure. The leaflet base of the
plurality of leaflets defines an orifice. The leaflet second side
regions extend further into the orifice than the leaflet first side
region when the leaflets are in the fully open position.
[0104] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. At least a first portion of the leaflet first
side region has a first thickness and the leaflet second side
region has a second thickness wherein the first thickness is
greater than the second thickness. In operation, each leaflet opens
asymmetrically. In one embodiment, the first thickness may be ten
times greater than the second thickness.
[0105] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. The leaflet first side region has a first
bending stiffness and the leaflet second side region has a second
bending stiffness. The first bending stiffness is greater than the
second bending stiffness. In operation, each leaflet opens
asymmetrically.
[0106] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. The leaflet first side region being more
resistant to moving compared with the leaflet second side region.
In operation, each leaflet opens asymmetrically.
[0107] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. The leaflet first side region being slower to
open compared with the leaflet second side region. In operation,
each leaflet opens asymmetrically.
[0108] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. Each leaflet defines a leaflet base and a
leaflet free edge opposite from the leaflet base. Each leaflet
first side region is coupled with the leaflet second side region of
an adjacent leaflet at a commissure. The leaflet base of the
plurality of leaflets defines an orifice. At least one of the
leaflet second side regions extends further into the orifice than
the leaflet first side region when the leaflets are in the fully
open position.
[0109] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. At least one leaflet includes a leaflet
first side region and a leaflet second side region opposite from
the leaflet first side region. The leaflet first side region has a
first thickness and the leaflet second side region has a second
thickness. The first thickness is greater than the second
thickness.
[0110] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. At least one of the leaflets has a leaflet first
side region having a first bending stiffness and the leaflet second
side region having a second bending stiffness, wherein the first
bending stiffness is greater than the second bending stiffness.
[0111] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. At least one of the leaflets presents with the
leaflet first side region being more resistant to moving compared
with the leaflet second side region.
[0112] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. At least one of the leaflets presenting the
leaflet first side region being slower to open compared with the
leaflet second side region.
[0113] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. At least one leaflet has a thickness that tapers
from the leaflet first side region to the leaflet second side
region.
[0114] In another embodiment, a prosthetic valve comprises a
plurality of leaflets. Each leaflet includes a leaflet first side
region and a leaflet second side region opposite from the leaflet
first side region. At least one leaflet has a thickness that varies
from the leaflet first side region to the leaflet second side
region.
[0115] One skilled in the art will appreciate that the leaflet
embodiments provided herein may be applied to any prosthetic valve
design regardless as to how the leaflets are supported to function
as described.
[0116] Other Considerations
[0117] In accordance with an embodiment, the valve 100 can be
configured to prevent interference with a heart conduction system
by not covering a bundle branch in the left ventricle when
implanted, such as might be encountered with an aortic valve
replacement procedure. For example, the valve 100 can comprise a
length of less than about 25 mm or less than about 18 mm. The valve
100 can also comprise an aspect ratio of less than one, wherein the
ratio describes the relationship between the length of the valve
100 to the expanded, functional diameter. However, the valve 100
can be constructed at any length and, more generally, any desirable
dimension.
[0118] Sewing Cuff
[0119] In accordance with a valve 100 suitable for surgical
implantation, the valve 100 further comprises a sewing cuff about a
leaflet frame 130 in accordance with an embodiment. The sewing cuff
is operable to provide structure that receives suture for coupling
to the implant site. The sewing cuff may comprise any suitable
material, such as, but not limited to, double velour polyester. The
sewing cuff may be located circumferentially around a perimeter of
the base of the leaflet frame 130. Sewing cuffs are known in the
art.
[0120] The valve 100 can further comprise a bio-active agent.
Bio-active agents can be coated onto a portion or the entirety of
the film 160 for controlled release of the agents once the valve
100 is implanted. The bio-active agents can include, but are not
limited to, vasodilator, anti-coagulants, anti-platelet,
anti-thrombogenic agents such as, but not limited to, heparin.
Other bio-active agents can also include, but are not limited to
agents such as, for example, anti-proliferative/antimitotic agents
including natural products such as vinca alkaloids (i.e.
vinblastine, vincristine, and vinorelbine), paclitaxel,
epidipodophyllotoxins (i.e. etoposide, teniposide), antibiotics
(dactinomycin (actinomycin D) daunorubicin, doxorubicin and
idarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin
(mithramycin) and mitomycin, enzymes (L-asparaginase which
systemically metabolizes L-asparagine and deprives cells which do
not have the capacity to synthesize their own asparagine);
antiplatelet agents such as G(GP) IIb/IIIa inhibitors and
vitronectin receptor antagonists; anti-proliferative/antimitotic
alkylating agents such as nitrogen mustards (mechlorethamine,
cyclophosphamide and analogs, melphalan, chlorambucil),
ethylenimines and methylmelamines (hexamethylmelamine and
thiotepa), alkyl sulfonates-busulfan, nitrosoureas (carmustine
(BCNU) and analogs, streptozocin), trazenes-dacarbazinine (DTIC);
anti-proliferative/antimitotic antimetabolites such as folic acid
analogs (methotrexate), pyrimidine analogs (fluorouracil,
floxuridine, and cytarabine), purine analogs and related inhibitors
(mercaptopurine, thioguanine, pentostatin and
2-chlorodeoxyadenosine {cladribine}); platinum coordination
complexes (cisplatin, carboplatin), procarbazine, hydroxyurea,
mitotane, aminoglutethimide; hormones (i.e. estrogen);
anti-coagulants (heparin, synthetic heparin salts and other
inhibitors of thrombin); fibrinolytic agents (such as tissue
plasminogen activator, streptokinase and urokinase), aspirin,
dipyridamole, ticlopidine, clopidogrel, abciximab; antimigratory;
antisecretory (breveldin); anti-inflammatory: such as
adrenocortical steroids (cortisol, cortisone, fludrocortisone,
prednisone, prednisolone, 6.alpha.-methylprednisolone,
triamcinolone, betamethasone, and dexamethasone), non-steroidal
agents (salicylic acid derivatives i.e. aspirin; para-aminophenol
derivatives i.e. acetominophen; indole and indene acetic acids
(indomethacin, sulindac, and etodalac), heteroaryl acetic acids
(tolmetin, diclofenac, and ketorolac), arylpropionic acids
(ibuprofen and derivatives), anthranilic acids (mefenamic acid, and
meclofenamic acid), enolic acids (piroxicam, tenoxicam,
phenylbutazone, and oxyphenthatrazone), nabumetone, gold compounds
(auranofin, aurothioglucose, gold sodium thiomalate);
immunosuppressives: (cyclosporine, tacrolimus (FK-506), sirolimus
(rapamycin), azathioprine, mycophenolate mofetil); angiogenic
agents: vascular endothelial growth factor (VEGF), fibroblast
growth factor (FGF); angiotensin receptor blockers; nitric oxide
donors; anti-sense oligionucleotides and combinations thereof; cell
cycle inhibitors, mTOR inhibitors, and growth factor receptor
signal transduction kinase inhibitors; retenoids; cyclin/CDK
inhibitors; HMG co-enzyme reductase inhibitors (statins); and
protease inhibitors.
[0121] Method of Making
[0122] Embodiments described herein also pertain to a method of
making the valve 100 embodiments as described herein. In order to
make the various embodiments, a mandrel 710 that is cylindrical can
be used. With reference to FIGS. 3A-3C, the mandrel 710 comprises a
structural form operable to receive the leaflet frame 130
thereon.
[0123] An embodiment of a method of making a valve 100 comprises
the steps of wrapping a first film layer 160a, e.g., a composite as
described herein, into a tubular form about the mandrel 710;
placing the leaflet frame 130 over the first film layer 160a, as
shown in FIG. 5A; thermally setting the assembly; trimming the
first film layer 160a to define a leaflet reinforcing member 149
that is at least a portion of the leaflet first side region
adjacent to and depending from the leaflet window first side 133a
and removing the first film layer 160a from the leaflet window that
substantially defines the leaflet central region 182 and the
leaflet second side region 184b; trimming the first film layer 160a
to within about 0.5 to 1.0 mm of the leaflet window second side
133b and the leaflet window base 134 within the leaflet window 137,
as shown in FIG. 5B; define at least a portion of the leaflet first
side region and removing the first film layer 160a from the leaflet
window that substantially defines the leaflet central region 182
and the leaflet second side region 184b, as shown in FIG. 5B;
forming a second film layer 160b over the leaflet frame 130, as
shown in FIG. 5C; thermally setting the assembly; receiving the
assembly over a mandrel 712 as shown in FIGS. 6A and 6B; cutting
the film 160 across the leaflet window top within the leaflet
window 137.
[0124] The resulting valve 100 comprises a leaflet 140 having a
leaflet first side region 184a that includes a leaflet reinforcing
member 149 that is the first film layer 160a coupled to the second
film layer 160b, and the leaflet central region 182 and leaflet
second side region that only includes the second film layer 160b. A
small border of the first film layer 160a that depends from the
leaflet window second side 133b and the leaflet window base 134
within the leaflet window 137 provides a strain relief that reduces
the strain in the leaflet 140 at the interface between the leaflet
140 and the leaflet window 137 of the leaflet frame 130.
EXAMPLE
[0125] In an embodiment, a heart valve having polymeric leaflets
formed from a composite material having an expanded fluoropolymer
membrane and an elastomeric material and joined to a metallic
frame, and further a having a strain relief frame covering and a
leaflet reinforcing member was constructed according to the
following process:
[0126] A leaflet frame 130 was laser machined from a length of
MP35N cobalt chromium tube hard tempered with an outside diameter
of 23.0 mm and a wall thickness of 0.6 mm. The leaflet frame was
electro-polished resulting in 0.01 mm material removal from each
surface and leaving the edges rounded. The leaflet frame was
cleaned by submersion in an ultrasonic bath of acetone for
approximately five minutes.
[0127] A strain relief was attached to the leaflet frame in the
following manner. A steel metal mandrel having tapered diameter of
21.5 mm to 22.0 mm outer diameter (taper angle of 0.1 degrees) was
obtained. A thin-walled (122 .mu.m) sintered 15 mm diameter ePTFE
tube was disposed on the metal mandrel by stretching radially over
another tapered mandrel and transferring to the 21.5 mm to 22.0 mm
mandrel. One layer of a substantially nonporous ePTFE membrane with
an FEP coating was circumferentially wrapped on the mandrel with
the FEP side towards the mandrel. This membrane was adhered by
tacking using a soldering iron (Weller) set to 400.degree. C.,
thereby creating a covered mandrel. The ePTFE and substantially
nonporous ePTFE membrane combined to serve as an inner release
liner. This entire release liner was removed in a later step.
[0128] A composite material comprising a membrane of ePTFE imbibed
with a fluoroelastomer was obtained. The composite material was
comprised of three layers: two outer layers of ePTFE and an inner
layer of a fluoroelastomer disposed therebetween. The ePTFE
membrane was manufactured according to the general teachings
described in U.S. Pat. No. 7,306,729. The fluoroelastomer was
formulated according to the general teachings described in U.S.
Pat. No. 7,462,675.
[0129] The ePTFE membrane had the following properties:
thickness=about 15 .mu.m; MTS in the highest strength
direction=about 400 MPa; MTS strength in the orthogonal
direction=about 250 MPa; Density=about 0.34 g/cm.sup.3; IBP=about
660 KPa.
[0130] The fluoroelastomer consists essentially of between about 65
and 70 weight percent perfluoromethyl vinyl ether and
complementally about 35 and 30 weight percent
tetrafluoroethylene.
[0131] The percent weight of the fluoroelastomer relative to the
ePTFE was about 53%.
[0132] The multi-layered composite had the following properties:
thickness of about 40 .mu.m; density of about 1.2 g/cm.sup.3; force
to break/width in the highest strength direction=about 0.953 kg/cm;
tensile strength in the highest strength direction=about 23.5 MPa
(3,400 psi); force to break/width in the orthogonal direction=about
0.87 kg/cm; tensile strength in the orthogonal direction=about 21.4
MPa (3100 psi), IPA bubble point greater than about 12.3 MPa,
Gurley Number greater than about 1,800 seconds, and mass/area=about
14 g/m.sup.2.
[0133] Ten layers of this composite material was circumferentially
wrapped on top of the covered mandrel, and tacked with a soldering
iron. One layer of film consisting of only the above described
fluoroelastomer (0.04 mm) was then wrapped on top of the previously
applied film and tacked with a soldering iron, thereby creating a
leaflet frame covering. For this tacking operation, a 0.03 mm thick
polyimide film (Kapton polyimide, 2271K1, McMaster-Carr, Santa Fe
Springs Calif.) was temporarily placed between the fluoroelastomer
film and the iron to prevent the fluoroelastomer film from adhering
to the iron.
[0134] The clean leaflet frame was then placed over the leaflet
frame covering on the mandrel from the small diameter side of the
taper until it fit snugly, with the base of the frame toward the
small diameter portion of the taper, as shown in FIG. 5A.
[0135] The leaflet frame covering that extended beyond the base of
the frame toward the small taper was then everted over the frame
until the entire frame was encapsulated and the folded edge of the
everted material was flush with the base of the frame to create an
outer leaflet frame covering, as shown in FIG. 5B.
[0136] Approximately ten layers of a sacrificial longitudinally
expanded PTFE film having a thickness of about 0.1 mm were tightly
wrapped around the covered frame. The resulting assembly was then
placed in a convection oven set at 320.degree. C. for 20 minutes.
This assembly was removed from the oven and allowed to cool, and
the outer sacrificial layers were removed. This assembly was then
removed from the mandrel, ensuring that it was released from the
inner sacrificial layer.
[0137] Using a surgical blade, the leaflet frame cover was trimmed,
as shown in FIG. 2B, to create a construct 154 consisting of a
leaflet frame 130, a leaflet reinforcing member 149 adjacent to one
side of each post and a strain relief frame covering 152. The
remainder of the frame covering was trimmed at 1 mm from the edge
of the frame, leaving 6 mm leaflet reinforcing member 149 on one
side of each post, as shown in FIG. 5C, the leaflet window first
side 133a, as shown in FIG. 2A.
[0138] A leaflet material was then prepared having a membrane layer
of ePTFE imbibed with a fluoroelastomer. More specifically, the
membrane layer of ePTFE was manufactured according to the general
teachings described in U.S. Pat. No. 7,306,729. The ePTFE membrane
was tested in accordance with the methods described below. The
ePTFE membrane had a mass per area of about 0.6 g/m.sup.2, a
porosity of about 90%, a thickness of about 3 .mu.m, a bubble point
of about 450 KPa, a matrix tensile strength of about 350 MPa in the
longitudinal direction and about 250 MPa in the transverse
direction. This membrane was imbibed with the same fluoroelastomer
as described above. The fluoroelastomer was dissolved in Novec
HFE7500 (3M, St Paul, Minn., USA) in an about 2.5% concentration.
The solution was coated using a mayer bar onto the ePTFE membrane
(while being supported by a polypropylene release film) and dried
in a convection oven set to about 145.degree. C. for about 30
seconds. After two coating steps, the resulting composite material
of ePTFE/fluoroelastomer had a mass per area of about 4
g/m.sup.2.
[0139] The final leaflet was comprised of about 30% fluoropolymer
by weight with a thickness of 25 .mu.m. Each leaflet had 31 layers
of the composite.
[0140] The encapsulated frame with frame covering defining a strain
relief and a reinforcing member was then attached to the leaflet
material in a cylindrical or tubular shape in the following manner.
The encapsulated frame with strain relief covering and reinforcing
member was placed on the release liner-covered tapered mandrel
described above, as shown in FIG. 5D.
[0141] Thirty-one layers of the above described leaflet material
were circumferentially wrapped over the encapsulated frame, as
shown in FIG. 5D.
[0142] Approximately ten layers of a sacrificial longitudinally
expanded PTFE film having a thickness of about 0.1 mm were tightly
wrapped around the covered frame. The resulting assembly was then
placed in a convection oven set at 280.degree. C. for 60 minutes.
This assembly was removed from the oven and allowed to cool, and
the outer sacrificial layers were removed. This assembly was then
removed from the mandrel, ensuring that it was released from the
inner sacrificial layer.
[0143] The leaflet material was trimmed approximately 5 mm above
the leaflet frame first end 121a, also referred to as the frame
top. The resulting assembly was placed in a convection oven set at
150.degree. C. for 15 min while closing the valve with 5 cm of Hg
vacuum to close the leaflets. The assembly was removed from the
oven and allowed to cool. Leaflets were trimmed using scissors to a
height of approximately 1-2 mm above the coaptation line.
[0144] The average maximum leaflet thickness in the leaflet first
side region was 281 micrometers and the average maximum leaflet
thickness in the leaflet second side region was 27 micrometers.
These measurements were an average of three measurements obtained
on a Mitutoyo Litematic VL-50A (Aurora, Ill.) digimatic measuring
unit.
[0145] The performance of the valve leaflets was characterized on a
real-time pulse duplicator. The following results were obtained:
EOA=1.9 cm.sup.2 and regurgitant fraction=2.5%.
[0146] A geometric orifice area (GOA) test was performed. With a
flow of 450 ml/s of 37.degree. C. saline flowing through the 22 mm
ID valve, a picture was taken of the leaflets in the fully open
position. This image was analyzed by pasting the image in CAD
software (SOLIDWORKS 2012). A circle was drawn connecting the inner
surface of the centers of each of the three posts. From the middle
of each of these three posts, a diameter line was drawn. These
diameter lines split the image into six (6) slices, or two slices
per leaflet, similar to FIG. 1C. A spline line 156 was then drawn
around the full circumference of the edge of the open leaflets. The
geometric orifice area (GOA) for each of the three leaflets was
then calculated by calculating the luminal area within the spline
for the 1/3 of the total valve area encompassed by each leaflet.
This resulted in a calculation of GOA for each leaflet (the sum of
these three GOAs equals the GOA of the entire valve). Subsequently,
the GOA of each side of the leaflet was calculated by using the
diameter line drawn previously which bisects the leaflet. The GOA
from the reinforced section of the leaflet is always less than the
GOA of the unreinforced section. For the example presented above,
the ratio of the GOA on the reinforced side of the leaflet to the
total leaflet GOA was 34%, 37%, and 33%, while the other side of
the leaflet had a ratio of 66%, 63%, and 67%, respectively.
[0147] Test Methods
[0148] Pulsatile Flow Testing
[0149] The flow performance was characterized by the following
process:
[0150] The valve assembly was placed within a silicone annular ring
(support structure), supporting its outer diameter without changing
its diameter, to allow the valve assembly to be subsequently
evaluated in a real-time pulse duplicator. The process was
performed according to the recommendations of the pulse duplicator
manufacturer (ViVitro Laboratories Inc., Victoria BC, Canada).
[0151] The valve assembly was then placed into a real-time left
heart flow pulse duplicator system. The flow pulse duplicator
system included the following components supplied by ViVitro
Laboratories Inc., Victoria BC, Canada: a Super Pump, Servo Power
Amplifier Part Number SPA 3891; a Super Pump Head, Part Number SPH
5891B, 38 cm.sup.2 cylinder area; a valve station/fixture; Vivitro
software capable of waveform control and data collection; I/O
module Part Number XXXX, TriPack Part Number TP 2001; a Sensor
Interface, Part Number VB 2004; a Sensor Amplifier Component, Part
Number AM 9991; and a Square Wave Electro Magnetic Flow Meter
(positioned approximately 2 cm upstream of the valve), Carolina
Medical Electronics Inc., East Bend, N.C., USA. The outflow chamber
used to evaluate the performance of the pulmonary valve was chosen
such that the internal diameter of the outflow chamber was matched
to that of the valve diameter. A 40 ml source compliance, a large
peripheral compliance was added to the tester to simulate
physiological pulmonary conditions. Additionally, as a straight
outflow chamber was used, the root compliance was not used in the
test set-up.
[0152] In general, the flow pulse duplicator system uses a fixed
displacement, piston pump to produce a desired fluid flow through
the valve under test. Testing and definitions are consistent with
ISO 5840-3, 2013 except where otherwise noted for testing to
pulmonary conditions. While this testing is conducted to pulmonary
conditions, testing and use (e.g. aortic, mitral, tricuspid,
venous, etc.) in other conditions is not excluded.
[0153] The heart flow pulse duplicator system was adjusted to
produce the desired flow (5.0.+-.0.5 L/min), mean pressure (20.+-.2
mmHg), simulated pulse rate (70 bpm), a 35% systolic duration
sinusoidal waveform, and a stroke volume (i.e., the amount of fluid
pushed by the driving pump) of 84.+-.1 ml. The operating
temperature was 37.+-.1.degree. C. using 0.9% saline as test
solution. The valve under test was then cycled for between 5 to 15
minutes.
[0154] Pressure and flow data were measured and collected during
the test period for ten (10) continuous cardiac cycles, including
right ventricular pressures, pulmonary pressures, flow rates, and
pump piston position. Parameters used to characterize the valve are
effective orifice area and regurgitant fraction. The effective
orifice area (EOA), which can be calculated as follows:
EOA(cm.sup.2)=Q.sub.rms/(51.6*(.DELTA.P).sup.1/2) where Q.sub.rms
is the root mean square of the flow rate (cm.sup.3/s) during the
positive pressure interval of systolic period and .DELTA.P is the
mean differential pressure during the positive pressure interval of
the systolic period (mmHg) (note that density of saline is taken to
be 1 g/cm.sup.3, therefore this equation eliminates the density as
compared to the equation presented in ISO 5840).
[0155] During this test, during the period when the maximum flow is
flowing through the valve, a digital picture was taken. This
picture was taken from the outflow region with the lens normal to
the direction of flow with a field of view to encompass the full
outflow side of the valve. The flow rate was recorded from the
Pulse Duplicator at this time and the image used for GOA (Geometric
Orifice Area) calculations.
[0156] Another measure of the hydrodynamic performance of a valve
is the regurgitant fraction, which is the amount of fluid or blood
regurgitated through the valve divided by the Forward Volume (i.e.,
amount of flow passing through the valve during the forward phase
of the valve).
[0157] Steady Flow Testing
[0158] To demonstrate the asymmetrical opening of the leaflets in a
steady flow apparatus, saline heated to 37.degree. C. was pumped at
a steady rate though the valve to open it. Saline was pumped using
a pump (WEG Electric, Duluth, Ga., part number 10086261) with
voltage regulator (Staco Energy Products, Miamisburg, Ohio, part
number 3PN2210B) though the valve at 5 L/min (as measured by a
large graduated cylinder and stopwatch). The valve was placed
within a silicone holder in the recirculating loop that started and
finished within an open 37.+-.1.degree. C. heated reservoir. An
image of the valve was taken using a digital camera (Vision
Research, Wayne, N.J., Model Miro EX4), and the GOA measured using
the same technique as noted previously. For all three leaflets, the
geometric open area on one half of each leaflet was 39% of each
leaflets total GOA (i.e. other half of leaflet geometric open area
was 61% of each leaflets total GOA).
[0159] Material Characterization Testing
[0160] As used in this application, the surface area per unit mass,
expressed in units of m.sup.2/g, was measured using the
Brunauer-Emmett-Teller (BET) method on a Coulter SA3100Gas
Adsorption Analyzer, Beckman Coulter Inc. Fullerton Calif., USA. To
perform the measurement, a sample was cut from the center of the
expanded fluoropolymer membrane and placed into a small sample
tube. The mass of the sample was approximately 0.1 to 0.2 g. The
tube was placed into the Coulter SA-Prep Surface Area Outgasser
(Model SA-Prep, P/n 5102014) from Beckman Coulter, Fullerton
Calif., USA and purged at about 110.degree. C. for about two hours
with helium. The sample tube was then removed from the SA-Prep
Outgasser and weighed. The sample tube was then placed into the
SA3100 Gas adsorption Analyzer and the BET surface area analysis
was run in accordance with the instrument instructions using helium
to calculate the free space and nitrogen as the adsorbate gas.
[0161] Bubble point and mean flow pore size were measured according
to the general teachings of ASTM F31 6-03 using a capillary flow
Porometer, Model CFP 1500AEXL from Porous Materials, Inc., Ithaca
N.Y., USA. The sample membrane was placed into the sample chamber
and wet with SilWick Silicone Fluid (available from Porous
Materials Inc.) having a surface tension of about 20.1 dynes/cm.
The bottom clamp of the sample chamber had an about 2.54 cm
diameter hole. Isopropyl alcohol was used as the test fluid. Using
the Capwin software version 7.73.012 the following parameters were
set as specified in the table below. As used herein, mean flow pore
size and pore size are used interchangeably.
TABLE-US-00001 Parameter Set Point Maxflow (cm.sup.3/m) 200000
Bublflow (cm.sup.3/m) 100 F/PT (old bubltime) 50 Minbpress (PSI) 0
Zerotime (sec) 1 V2incr (cts) 10 Preginc (cts) 1 Pulse delay(sec) 2
Maxpre (PSI) 500 Pulse width (sec) 0.2 Mineqtime (sec) 30 Presslew
(cts) 10 Flowslew (cts) 50 Eqiter 3 Aveiter 20 Maxpdif (PSI) 0.1
Maxfdif (PSI) 50 Sartp (PSI) 1 Sartf (cm.sup.3/m) 500
[0162] Membrane thickness was measured by placing the membrane
between the two plates of a Kafer FZ1000/30 thickness snap gauge
Kafer Messuhrenfabrik GmbH, Villingen-Schwenningen, Germany. The
average of the three measurements was reported.
[0163] The presence of elastomer within the pores can be determined
by several methods known to those having ordinary skill in the art,
such as surface and/or cross section visual, or other analyses.
These analyses can be performed prior to and after the removal of
elastomer from the leaflet.
[0164] Membrane samples were die cut to form rectangular sections
about 2.54 cm by about 15.24 cm to measure the weight (using a
Mettler-Toledo analytical balance model AG204) and thickness (using
a Kafer Fz1000/30 snap gauge). Using these data, density was
calculated with the following formula: .rho.=m/w*l*t, in which:
.rho.=density (g/cm.sup.3): m=mass (g), w=width (cm), l=length
(cm), and t=thickness (cm. The average of three measurements was
reported.
[0165] Tensile break load was measured using an INSTRON 122 tensile
test machine equipped with flat-faced grips and a 0.445 kN load
cell. The gauge length was about 5.08 cm and the cross-head speed
was about 50.8 cm/min. The sample dimensions were about 2.54 cm by
about 15.24 cm. For longitudinal measurements, the longer dimension
of the sample was oriented in the highest strength direction. For
the orthogonal MTS measurements, the larger dimension of the sample
was oriented perpendicular to the highest strength direction. Each
sample was weighed using a Mettler Toledo Scale Model AG204, then
the thickness measured using the Kafer FZ1000/30 snap gauge. The
samples were then tested individually on the tensile tester. Three
different sections of each sample were measured. The average of the
three maximum loads (i.e., peak force) measurements was reported.
The longitudinal and transverse matrix tensile strengths (MTS) were
calculated using the following equation: MTS=(maximum
load/cross-section area)*(bulk density of PTFE)/(density of the
porous membrane), wherein the bulk density of the PTFE was taken to
be about 2.2 g/cm.sup.3. Bending stiffness was measured by
following the general procedures set forth in ASTM D790. Unless
large test specimens are available, the test specimen must be
scaled down. The test conditions were as follows. The leaflet
specimens were measured on a three-point bending test apparatus
employing sharp posts placed horizontally about 5.08 mm from one
another. An about 1.34 mm diameter steel bar weighing about 80 mg
was used to cause deflection in the y (downward) direction, and the
specimens were not restrained in the x direction. The steel bar was
slowly placed on the center point of the membrane specimen. After
waiting about 5 minutes, the y deflection was measured. Deflection
of elastic beams supported as above can be represented by:
d=F*L.sup.3/48*EI, where F (in Newtons) is the load applied at the
center of the beam length, L (meters), so L=1/2 distance between
suspending posts, and EI is the bending stiffness (Nm). From this
relationship the value of EI can be calculated. For a rectangular
cross-section: I=t.sup.3*w/12, where I=cross-sectional moment of
inertia, t=specimen thickness (meters), w=specimen width (meters).
With this relationship, the average modulus of elasticity over the
measured range of bending deflection can be calculated.
[0166] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present embodiments
without departing from the spirit or scope of the embodiments.
Thus, it is intended that the present embodiments cover the
modifications and variations of this invention provided they come
within the scope of the appended claims and their equivalents.
* * * * *