Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED LEAFLET AND VALVE APPARATUS
FIELD
[0001] The present invention relates generally to valve leaflets and
apparatus and
systems having valve leaflets, such as prosthetic valves and more
specifically,
prosthetic cardiac valves.
BACKGROUND
[0002] 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.
[0003] 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.
[0004] A number of fabrication techniques have been used to couple the
leaflets
to a frame, including sewing individual leaflets to the frame (biological and
synthetic),
and for synthetic leaflets only, injection molding and dip coating a polymer
onto the
frame. In many cases, the resulting leaflet is supported on the frame and
defines a
flap having a mounting edge where the leaflet is coupled to the frame and a
free
edge that allows the flap to move. The flap moves 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
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influence of downstream fluid pressure closing the valve to prevent downstream
blood from flowing retrograde through the valve.
[0005] Valve durability under the repetitive loads of the leaflets opening and
closing is dependent, in part, on the dynamic characteristics of the leaflets.
Thin
leaflets can develop folds that repeatedly form in the central portion of the
leaflet
during the opening and closing action of the valve, often times resulting in
the
formation of a hole within the leaflet at a site of repeated bending stress.
[0006] One contribution to the heretofore insurmountable problem of developing
a
successful synthetic leaflet valve is that synthetic leaf bending appears to
be a
chaotic process. Each leaflet takes a characteristic bending shape that is
repeated
with each cycle, but each leaflet's characteristic bending shape is different
from an
adjacent leaflet. In some cases, the leaflet bending profile is a large-
radius,
continuous, three-dimensional curve. In others, however, particularly in very
thin
materials, tight radius bends appear in the form of out-of-plane buckling
imposing
high strains resulting in leaflet failure.
[0007] Therefore, there exists a need for thin leaflet prosthetic valves that
exhibit
improved longevity while still providing equal, or better yet, improved
hemodynamic
performance when compared with valves that have heretofore been developed.
SUMMARY
[0008] In accordance with embodiments, the present invention comprises
apparatus and systems for valve replacement or augmentation, such as cardiac
valve replacement. The present invention is directed towards leaflet design or
modifications and leaflet-type cardiac valves that not only improve upon
conventional
prosthetic valve hemodynamics, but also reduce the incidence of premature
leaflet
failure. Stated otherwise, the leaflet designs contemplated herein demonstrate
improved performance and improved longevity in valve leaflets that would
otherwise
exhibit tight-radius buckling.
[0009] In accordance with other embodiments, a leaflet comprises a guiding
element that improves both the longevity and the hemodynamic performance by
stabilizing the motion of the leaflet. The guiding element is operable to
control the
bending pattems or shapes assumed by the leaflet as it moves between open and
closed positions. Additionally, the guiding element is operable to minimize or
eliminate tight-radius bending, buckling, wrinkling, and other undesirable
folding in
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the central portion of the leaflet, thus contributing to both its hemodynamic
performance and its longevity.
[0010] In accordance with other embodiments, a leaflet for a prosthetic valve
comprises a plurality of layers of film coupled together and configured in the
form of
the leaflet. One or more guiding elements are coupled between two of the
plurality
of layers of film, wherein the guiding element is relatively more stiff
compared to the
plurality of layers of film.
[0011] In accordance with other embodiments, a prosthetic valve comprises a
frame, at least one leaflet, and a guiding element. Each leaflet comprises a
plurality
of layers of film coupled together. Each leaflet defines a leaflet base, a
leaflet edge
portion opposite the leaflet base, and a central portion between the leaflet
base and
the leaflet edge portion. The leaflet is coupled to the frame along at least a
portion of
the leaflet base. The guiding element is coupled between two of the plurality
of
layers of film that the leaflet is made. The guiding element is located in the
central
portion and spaced apart from the frame. The guiding element is relatively
more stiff
compared to the plurality of layers of film.
[0012] In accordance with other embodiments, a prosthetic valve comprises a
frame, at least one leaflet, and a guiding element. Each leaflet comprises a
plurality
of layers of film coupled together. Each leaflet defines a leaflet base, a
leaflet edge
portion opposite the leaflet base, and a central portion between the leaflet
base and
the leaflet edge portion. Each leaflet is coupled to the frame along at least
a portion
of the leaflet base. Each leaflet is pivotable between an open position and a
closed
position. The central portion has a greater stiffness than at least one of the
leaflet
edge portion and the leaflet base.
[0013] In accordance with other embodiments, a leaflet for a prosthetic valve
comprises a plurality of layers of film coupled together and configured in the
form of
the leaflet and one or more guiding elements coupled between two of the
plurality of
layers of film. The leaflet defines a leaflet edge portion and a leaflet base
opposite
from the leaflet edge portion and a central portion between the leaflet edge
portion
and the leaflet base. The guiding element is located in the central portion.
The
guiding element is relatively more stiff compared to the plurality of layers
of film. The
one or more guiding elements have a length which is aligned radiating away
from but
spaced apart from the leaflet base such that the leaflet pivots substantially
from the
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leaflet base when the leaflet is deployed in the prosthetic valve and the
prosthetic
valve is operated so as to flex the leaflet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Embodiments will be described in conjunction with the accompanying
drawing figures in which like numerals denote like elements and:
[0015] FIG. 1A is a top view of an embodiment of a valve in a closed
configuration, in accordance with an embodiment;
[0016] FIG. 1B is an axial view of an embodiment of the valve of FIG. 1A in an
open configuration, in accordance with an embodiment;
[0017] FIG. 2 is a perspective view of an embodiment of a valve in a closed
configuration, in accordance with an embodiment;
[0018] FIG. 3 is a perspective view of an embodiment of a valve frame, in
accordance with an embodiment;
[0019] FIG. 4A is a perspective view of an embodiment of a valve in a closed
configuration having a leaflet with a guiding element, in accordance with an
embodiment;
[0020] FIG. 4B is an axial view of the embodiment of the valve of FIG. 4A;
[0021] FIG. 4C is an axial view photo of the embodiment of the valve of FIG.
4A;
[0022] FIG. 5 is an axial view of an embodiment of a valve having leaflets
comprising a guiding element, in accordance with an embodiment;
[0023] FIG. 6 is an axial view of an embodiment of a valve having leaflets
comprising a guiding element, in accordance with an embodiment;
[0024] FIG. 7 is an axial view of an embodiment of a valve having leaflets
comprising a guiding element and two guiding elements, in accordance with an
embodiment;
[0025] FIG. 8 is an axial view of an embodiment of a valve having leaflets
comprising five guiding elements, in accordance with an embodiment;
[0026] FIG. 9 is an axial view of an embodiment of a valve having leaflets
comprising a central guiding element and two side guiding elements, in
accordance
with an embodiment;
[0027] FIG. 10 is an axial view of an embodiment of a valve having leaflets
comprising a guiding element;
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[0028] FIG. 11 is a side perspective view of a leaflet frame coupled to a
mandrel
in the process of having a film wound thereon defining layers, with a guiding
element
contained between at least two of the layers of film, in accordance with an
embodiment; and
[0029] FIG. 12 is a cross-sectional view of a guiding element between layers
of
film, in accordance with an embodiment.
DETAILED DESCRIPTION
[0030] Persons skilled in the art will readily appreciate that various aspects
of the
present invention may be realized by any number of methods and apparatus
configured to perform the intended functions. Stated differently, other
methods and
apparatus may be incorporated herein to perform the intended functions. It
should
also be noted that the accompanying drawing figures referred to herein are not
all
drawn to scale, but may be exaggerated to illustrate various aspects of the
present
invention, and in that regard, the drawing figures should not be construed as
limiting.
[0031] 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.
[0032] The term leaflet as used herein in the context of prosthetic valves is
a
flexible 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 the open position the leaflet allows blood to flow through the valve. In
the 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 the inflow side of
the
valve rises above the pressure on the outflow side of the valve, the leaflets
open and
blood flows therethrough. As blood flows through the valve into a neighboring
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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 raises
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.
[0033] The term membrane as used herein refers to a sheet of material
comprising a single composition, such as, but not limited to, expanded
fluoropolymer
and synthetic polymer having a structure defining fibers, such as, but not
limited to,
porous polyethylene.
[0034] 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 can 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.
[0035] The term laminate as used herein refers to multiple layers of membrane,
composite material, or other materials, such as elastomer, and combinations
thereof.
[0036] The term film as used herein generically refers to one or more of the
membrane, composite material, or laminate.
[0037] 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.
[0038] 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
can receive a prosthetic valve include, but are not limited to, veins,
arteries, ducts
and shunts. It is further understood that a valve orifice or implant site may
also refer
to a location in a synthetic or biological conduit that may receive a valve.
[0039] As used herein, "couple" means to join, connect, attach, adhere, affix,
or
bond, whether directly or indirectly, and whether permanently or temporarily.
[0040] Embodiments herein include various apparatus, systems, and methods for
a prosthetic valve suitable for, 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 dose so as to occlude the valve
orifice
and prevent retrograde flow.
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[0041] Embodiments are directed to an apparatus and system for valve
replacement or augmentation, such as cardiac valve replacement. The present
embodiments are directed towards leaflet design or modifications and leaflet-
type
cardiac valves that not only improve upon conventional prosthetic valve
hemodynamics, but also reduce leaflet fatigue and failure. Stated otherwise,
the
leaflet embodiments presented herein provide improved leaflet bending, and
thereby
improved lifetime and improved hemodynamics.
[0042] Embodiments provided herein are related to prosthetic heart valve
leaflets
comprising one or more guiding elements that allow for control of the movement
of
the leaflets, such as, but not limited to, controlling the bending
characteristics of the
leaflet.
[0043] In accordance with embodiments presented herein, a prosthetic valve
comprises a plurality of polymer leaflets. The polymer leaflets comprise a
laminate
of multiple layers of membrane, composite material, or other materials, such
as
elastomer, and combinations thereof. One or more guiding elements are coupled
to
and contained within the laminate lying between two of the multiple layers of
membrane or composite material. The guiding element is operable to provide a
structural influence on the leaflet such as to control the bending
characteristics of the
leaflet.. Since the guiding element is fully contained within the laminate
layers, the
guiding element remains permanently coupled to the leaflet. Further, since the
guiding element is fully contained within the laminate layers, the guiding
element is
not exposed to the blood stream.
[0044] Another embodiment is directed towards a prosthetic valve comprising a
leaflet support member and at least one leaflet as described above wherein the
leaflet is connected to the support member along the base portion of the
leaflet. The
leaflet is movable between a first position and a second position, such that
in the first
position, the valve is a flow occluder and in the second position, the valve
is a flow
orifice. The valve further comprises a guiding element, as described herein,
connected to at least one leaflet. Similarly, in a valve embodiment comprising
multiple leaflets 140, at least one leaflet 140 may not have a guiding element
150,
while at least one leaflet does comprise a guiding element 150.
[0045] In a further embodiment, the valve comprises a compressed configuration
and an expanded configuration. As such, a valve can be compressible or
crushable
under the application of a binding or compression force to obtain a compressed
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configuration. However, once the force is removed, the expanded configuration
of
the valve as it was prior to the compression is substantially retained. To
this end, a
support member may comprise a shape memory material. A compressible valve may
be implanted via endovascular techniques now known or hereinafter derived.
Valve
[0046] FIGS. 1A and 1B are axial views of a valve 100 in the closed and open
condition, respectively, in accordance with an embodiment. FIG. 2 is a
perspective
view of the valve 100 in the closed condition. The valve 100 comprises a frame
130
and a film 160 covering the frame 130 forming the leaflets 140 coupled to the
frame
130, in accordance with an embodiment. FIG. 3 is a perspective view of the
frame
130, in accordance with an embodiment.
Film
[0047] The film 160 that makes up the leaflet 140 can comprise any
biocompatible material sufficiently compliant and flexible, such as a
biocompatible
polymer. The film162 can comprise a membrane that is combined with an
elastomer
to form a composite material. The film160, according to an embodiment,
includes a
composite material comprising an expanded fluoropolyrner 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.
[0048] A film 160 generically refers to one or more of the membrane, composite
material, or laminate as previously defined. The leaflets 140 are comprised of
the
film 160. Details of various types of film 160 are discussed below. In an
embodiment, the film 160 can be formed from a generally tubular material to
couple
the frame 130 and to form the leaflets 140. As will be discussed below, the
laminate
comprises a number of layers of membrane and/or composite material, with the
guiding element 150 being coupled and contained within at least two layers of
membrane and/or composite material.
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[0049] In an embodiment, the film 160 comprises a biocompatible polymer that
is
combined with an elastomer, referred to as a composite. 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 materials, and the like
while
remaining within the scope of the present disclosure.
[0050] 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. Patent No. 7,306,729 to Bacino.
[0051] 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. Patent No. 5,708,044, to Branca, U.S. Patent
No.
6,541,589, to Baillie, U.S. Patent No. 7,531,611, to Sabol et al., U.S. Patent
Application No. 11/906,877, to Ford, and U.S. Patent Application No.
12/410,050, to
Xu et al.
[0052] 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. Patent 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 2, and possibly less than 1.5.
[0053] In another embodiment, the expanded fluoropolymer membrane has a
microstructure of substantially only fibrils, as is generally taught by U.S.
Patent No.
7,306,729, to Bacino. The expanded fluoropolymer membrane having substantially
only fibrils, can possess a high surface area, such as greater than 20m2/g, or
greater
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than 25m2/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 x 105 MPa2, and/or a ratio of matrix tensile strengths in two
orthogonal
directions of less than 4, and possibly less than 1.5.
[0054] 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 pm. The expanded
fluoropolymer membrane can possess a mass per area of about 1.15 g/m2.
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.
[0055] 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 pm and a mass per area of about
4.1
g/m2.
[0056] 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 substantially all of the pores of the
at least
one fluoropolymer layer. Having elastomer filling the pore volume or present
in
substantially all of the pores reduces the space in which foreign materials
can be
undesirably incorporated into the composite. An example of such foreign
material is
calcium that may be drawn into the membrane from contact with the blood. If
calcium
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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.
[0057] 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. Patent 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] After reaching a minimum percent by weight of elastomer, the leaflets
constructed from fluoropolymer materials or ePTFE generally performed better
with
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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. Patent 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.
Frame
[0063] FIG. 3 is a perspective view of the frame 130 in the embodiment of
FIGS.
1A and 1B. The frame 130 is a generally tubular member defining a valve
orifice 102
and providing structural, load-bearing support to the leaflet 140. In
addition, the
frame 130 can be configured to provide positive engagement to the recipient
tissue
at the implantation site.
[0064] The frame 130 can comprise any metallic or polymeric biocompatible
material. For example, the frame 130 can comprise a material, such as, but not
limited to nitinol, cobalt-nickel alloy, stainless steel, and polypropylene,
acetyl
homopolyrner, acetyl copolymer, ePTFE, other alloys or polymers, or any other
biocompatible material having adequate physical and mechanical properties to
function as described herein.
[0065] By way of example, and as illustrated in the embodiments of FIGS. 1A-B,
2 and 3, the frame 130 defines a stent having apertures 122. The open
framework of
the stent can define any number of features, repeatable or otherwise, such as
geometric shapes and/or linear or meandering series of sinusoids. An open
framework can 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. In other
embodiments, the frame 130 can have a solid wall. Alternatively, an elongated
material, such as a wire, bendable strip, or a series thereof, can be bent or
braided
and formed into a substantially cylindrical structure. For example, the frame
130 can
comprise a stent or stent graft type structure known in the art.
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[0066] In accordance with embodiments, the frame 130 can be configured to
provide positive engagement to an implant site. In another embodiment, the
valve
100 further includes a sewing cuff (not shown) coupled about the frame 130,
that is
operable to accept suture so as to be sewn to a tissue orifice as is known in
the art.
It is understood that conventional surgical and transcatheter techniques to
implant
prosthetic valves can be used to implant the valve 100.
[0067] The frame 130 comprises three interconnected U-shaped portions 132.
Each of the U-shaped portions 132 defines a base 134. The U-shaped portions
132
intersect with an adjacent U-shaped portion defining a post 131. The frame 130
as
shown in FIG. 3 comprised three U-shaped portions 132 and three posts 131,
upon
each of which a leaflet 140 is coupled as shown in FIG. 2.
[0068] The frame 130 can comprise, such as, but not limited to, an elastically
deformable metallic or polymeric biocompatible material. The frame 130 can
comprise a shape-memory material, such as nitinol, a nickel-titanium alloy.
Other
materials suitable for the frame 130 include, but not limited to, other
titanium alloys,
stainless steel, cobalt-nickel alloy, polypropylene, acetyl homopolymer,
acetyl
copolymer, other alloys or polymers, or any other biocompatible material
having
adequate physical and mechanical properties to function as a frame 130 as
described herein.
Leaflet
[0069] Each of the U-shaped portions 132 of the frame 130 is provided with a
biocompatible material, such as the film 162 which can be coupled to the frame
outside surface 133a and the frame inside surface 133b of the frame 130;
wherein
the film 162 defines a leaflet 140. Each leaflet 140 defines a leaflet free
edge 142
that is not coupled to the frame 130.
[0070] In accordance with an embodiment, the leaflet 140 can comprise a
biocompatible material that is not of a biological source and that is
sufficiently
compliant and strong for the particular purpose, such as a biocompatible
polymer. In
an embodiment, the leaflet 140 comprises a membrane that is combined with an
elastomer to form a composite material.
[0071] The shape of the leaflets 140 are defined at least in part by the shape
of
the frame 130 and the leaflet free edge 142. The shape of the leaflets 140 can
also
be defined, at least in part, by guiding elements 150 as described below. The
shape
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of the leaflets 140 can also be defined, at least In part, by processes used
to
manufacture the valve 100, such as, but not limited to a molding and trimming
processes to impart a predetermined shape to the leaflet 140.
[0072] Fluid flow is permitted through the valve orifice 102 when the leaflets
140
are in an open position as shown in FIG. 2. The leaflets 140 generally flex
about the
base 134 of the U-shaped portion 132 as the leaflets 140 open and close. In an
embodiment, 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. 2. The three leaflets 140 of the embodiment of FIGs. 1A and 2
meet at a triple point 148. The valve orifice 102 is occluded when the
leaflets 140 are
in the closed position stopping fluid flow.
[0073] 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 dosed. 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.
[0074] It is understood that the frame 130 can comprise any number of U-shaped
portions 132, and thus leaflets 140, suitable for a particular purpose. Frames
130
comprising one, two, three or more U-shaped portions 132 and corresponding
leaflets 140 are appreciated.
[0075] It is appreciated that the film 160 can be coupled to the frame 130 in
many
ways suitable for a particular purpose. By way of example, and not limited
thereto,
the frame 130 can be wrapped with overlapping layers of the film 160. The film
160
can be coupled to the frame outside surface 133a or the frame inside surface
133b
of the frame 130. In another embodiment, the film 160 can be coupled to either
of the
frame outside surface 133a or the frame inside surface 133b.
[0076] The film 160 can be configured to prevent blood from traveling through
or
across the valve 100 other than through the valve orifice 102 when the
leaflets 140
are in an open position. As such, the film 160 creates a barrier to blood flow
in any
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interstitial space(s), such as apertures 122 shown in FIG. 3, of the frame 130
that the
film 160 covers.
[0077] The film 160 is fixedly secured or otherwise coupled at a single or a
plurality of locations of the frame outside surface 133a and the frame inside
surface
133b of the frame 130, for example, using one or more of taping, heat
shrinking,
adhesion and other processes known in the art. In some embodiments, a
plurality of
membrane/composite layers, such as, but not limited to a laminate, are used
and
can be coupled to the frame 130 to form at least a portion of the film 160.
Leaflet Dynamics
[0078] A leaflet 140 in accordance with the present embodiments as used in the
context of cardiac valves is configured to move between an open and closed
position
which allows blood to flow when open and which substantially blocks retrograde
flow
of blood when dosed. In embodiments comprising multiple leaflets 140, a
leaflet 140
cooperates with at least one neighboring leaflet 140 to block retrograde flow
of blood
and each leaflet is coupled to a support member, such as, but not limited to,
pivotally
or rotatably mounted to the frame 130.
[0079] Fluid flow is permitted through the valve orifice 102 when the leaflets
140
are in an open position as shown in FIG. 1B. The leaflets 140 generally flex
about
the base 134 of the U-shaped portion 132 as the leaflets 140 open and close,
as
shown in FIG. 3. In an embodiment, 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. 2. The three leaflets 140 of the
embodiment of FIGs. 1A and 2 meet at a triple point 148. The valve orifice 102
is
occluded when the leaflets 140 are in the closed position stopping fluid flow.
[0080] The leaflet 140 can be configured to actuate at a pressure differential
in
the blood caused, for example, by the contraction of a ventride 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
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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.
[0081] For purposes of cardiac valves, a leaflet thickness may range from
about
pm to about 100 pm but again such thickness may vary from the above stated
ranges depending on the size, material, and desired function of the leaflet.
As
discussed below, improvements in accordance with the present embodiments may
provide for leaflet thicknesses outside of conventional thicknesses.
[0082] FIG. 5 is an axial view of a representation of a valve 101. A leaflet
edge
portion 113 comprises a coaptation region 146 of the leaflet 140. A central
portion
147 comprises an area between a leaflet base 135 and the leaflet edge portion
113.
A coaptation region 146 is the area comprising the junction formed between two
leaflets 140 in the closed position. The leaflet 140 also comprises a vertical
axis X1.
The height of the leaflet 140 is the length of the leaflet 140 along a line
parallel to the
vertical axis X1. The width of the leaflet 140 is the length of the leaflet
140 along a
line perpendicular to the vertical axis X1, which may vary between the leaflet
base
135 and the leaflet free edge 142. The guiding element defines a guiding
element
length and the leaflet defines a leaflet length extending from the leaflet
base and the
edge portion, the guiding element length being less than the leaflet length.
Guiding Elements
[0083] Embodiments of leaflets presented herein comprise one or more guiding
elements that are operable to control the movement of the leaflet in a
predetermined
way.
[0084] The guiding element improves both the longevity, such as, but not
limited
to, durability, and the hemodynamic performance of the valve.
[0085] In accordance with an embodiment, the leaflet further comprises a
guiding
element 150 as shown in FIGS. 4A-4D and 5. A guiding element 150 Is an element
within the leaflet 140 that stabilizes the motion of the leaflet 140 and/or
affects the
bending patterns or shapes assumed by the leaflet 140 as it moves between the
open and closed positions as shown in FIGs. 4B and 4C. Similarly, the guiding
element 150 may be a load distribution element operable for distributing the
load
more evenly through the central portion 147 of the leaflet 140.
[0086] In accordance with embodiments, the guiding element 150 is an element
disposed in the central portion 147 of the leaflet 140, spaced apart from the
leaflet
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base 135 and spaced apart from the frame 130, that is operable to resistant
deformation, such as bending along or proximate to the vertical axis X1 that
contains
the guiding element 150, and as such, shifts a majority of the bending from
the
central portion 147 towards the leaflet edge portion 113 and to the leaflet
base 135
of the leaflet 140. By resisting such deformation, the central portion 147
pivots in a
substantially more predictable manner between a substantially closed to open
position, or vice versa. For example, the guiding elements 150 in accordance
with
the present embodiments may facilitate pivoting of the central portion 147
relative to
the leaflet base 135 in a substantially planar manner, as opposed to "rolling"
open.
By so doing, issues such as tight radius bending, buckling, undesirable
folding or
wrinkling, and the like, as well as other durability and longevity-decreasing
occurrences, are minimized or eliminated. In various embodiments, the motion
of
the central portion 147 of the leaflet 140 between the first position and the
second
position substantially follows the guiding element 150.
[0087] Referring to FIG. 5, the guiding element 150 is located on or within
the
central portion 147 of the leaflet 140, spaced apart from the leaflet base 135
and
spaced apart from the frame 130. The guiding element 150 is operable to
stabilize,
minimize, or prevent leaflet deformation during leaflet movement between the
open
position and the closed position as shown in FIGs. 4B and 4C. In an
embodiment, a
majority of the guiding element 150 is locatable on or within the central
portion 147
and crosses, or is coincident with, the vertical axis X1. In an embodiment,
the
guiding element 150 has a height less than the leaflet height and a width
through a
point along the vertical axis X1 less than the leaflet's width through that
same point.
Stated differently, the guiding element 150 in embodiments does not extend all
the
way to a particular edge of the leaflet 140, such as, but not limited to the
leaflet base
135. In embodiments, the leaflet edge portion 113 and/or the leaflet base 135
are
free from any portion of the guiding element 150. In an embodiment, the
leaflet 140
may comprise the guiding element 150 substantially coincident with the
vertical axis
X1 and ranging up to the line of coaptation on the axis down to at least half
the
distance to the leaflet base 135. In various embodiments, the guiding element
150
may have a vertical dimension longer or shorter than the dimension in the
orthogonal
direction.
[0088] With the addition of the guiding element 150, the amplitude or number
of
sigmoid, or S-shaped, curves formed on the leaflet about the vertical axis X1
during
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the transition may be reduced, and a majority of such curves are formed closer
to the
leaflet edge portion 113 and the leaflet base 135 of the leaflet 140 and in a
more
controlled manner.
[0089] For example, the motion of a point on the guiding element 150, as the
leaflet 140 moves from a first position to a second position, may exist
substantially
on a plane, substantially on an arc, and in an embodiment, substantially on an
elliptical arc. The motion of the guiding element 150 as a whole tracks a
substantially
planar pivoting surface while transitioning between the first position and the
second
position.
[0090] In an embodiment, a guiding element 150 may comprise any shape, any
configuration, or any material configured to resist leaflet deformation
described
above about the vertical axis, and in accordance with an embodiment, over a
majority of the central portion. For example, with reference to FIGs. 4B, 6-
10, a
guiding element 150 may comprise at least one of a wire, or otherwise
comprises an
area of greater stiffness than areas without a guiding element 150.
[0091] It is believed that despite the presence of additional mass added to
the
leaflet 140, the leaflet 140 comprising the guiding element 150 is more
responsive to
changes in fluid pressure because bending occurs primarily at the leaflet edge
portion 113 and the leaflet base 135 of the leaflet 140 rather than occurring
first
through undesirable bending and buckling in the central portion of the
leaflet, as
would be the case without a guiding element. Furthermore, as mentioned above,
by
minimizing planar buckling, the likelihood of leaflet failure is reduced.
[0092] In accordance with embodiments, the stiffness of the central portion
147 is
increased relative to the leaflet base 135 and leaflet edge portion 113 by at
least one
of an extra layer of film, a fiber, and a filament located between two of the
plurality of
layers of film 160 that comprise the leaflet 140, as shown in FIG. 12.
[0093] In an embodiment, the shape of the guiding element 150 comprises a wire
formed into an oval, such as, but not limited to, a parallel-sided oval, as
shown in 4A
as guiding element 150. Altemative configurations are appreciates, such as,
but not
limited to, a polygon, an undulating shape, an S-shape, straight wires, and a
figure-
eight shape also known as a lemniscate.
[0094] FIG. 6 is an axial view of an embodiment of a valve 100b having
leaflets
140 comprising a second guiding element 150b. The guiding element 150b has a
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substantially V shape that is spaced apart from the frame 130 and spans a
significant portion of the leaflet 140.
[0095] Similarly, a leaflet need not be limited to one guiding element per
leaflet.
FIG. 7 is an axial view of an embodiment of a second valve 100c having
leaflets 140
comprising a first guiding element 150a flanked by a third guiding element
150c on
each side of first guiding element 150a. The first guiding element 150a and
the third
guiding element each have a substantially oval shape and are positioned
relative to
each other in the leaflet 140 spaced apart from the frame and so as to span a
significant portion of the leaflet 140.
[0096] FIG. 8 is an axial view of an embodiment of a valve 100d having
leaflets
140 comprising a plurality of fourth guiding elements 150d. Each of the fourth
guiding elements 150d is essentially a straight wire or a small diameter rod.
The
plurality of fourth guiding elements 150d is positioned relative to each other
in the
leaflet 140 spaced apart from the frame and so as to span a significant
portion of the
leaflet 140. The fourth guiding elements 150d extend from adjacent the leaflet
base
toward the leaflet free edge in a fan-like pattern.
[0097] FIG. 9 is an axial view of an embodiment of a valve 100e having
leaflets
140 comprising a sixth guiding element 150f flanked by a fifth guiding element
150e
on each side of sixth guiding element 150f. The sixth guiding element 150f is
essentially a straight wire or a small diameter rod having one end bent into a
rounded shape. The fifth guiding element 150e is essentially a wire or a small
diameter rod bent into a V or U shape having each end bent into a rounded
shape.
The rounded shape of the ends may help to prevent the ends from penetrating
the
leaflet causing failure as compared with a sharp point of an un-bent end. The
plurality of sixth guiding elements 150f and the fifth guiding element 150e
are
positioned relative to each other in the leaflet 140 so as to span a
significant portion
of the leaflet 140. The sixth guiding element 150f and the fifth guiding
elements
150e are spaced apart from the frame 130 and extend from adjacent the leaflet
base
135 in FIG. 5 toward the leaflet free edge 142 in a fan-like pattern.
[0098] FIG. 10 is an axial view of an embodiment of a valve 100g having
leaflets
140 comprising a seventh guiding element 150g. The seventh guiding element
1509
has a substantially triangular shape that spans a portion of the leaflet 140
with one
side of the triangular shape spaced apart from the frame 130 and adjacent to
the
leaflet base 135 as shown in FIG. 5.
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[0099] Any number of guiding elements may be present, and the present
embodiments contemplate any guiding element comprising any leaflet
modification
of any shape or configuration with any material of any combination that
stabilizes
leaflet motion or resists leaflet deformation on or about the vertical axis,
and more
over a majority of the central portion.
[00100] In accordance with embodiments, the one or more guiding elements 150
have a length which is aligned substantially perpendicular to predetermined
stress
lines corresponding to lines of stress in the leaflet when the leaflet is
deployed in the
valve and the valve is operated so as to flex the leaflet. Lines of stress in
the leaflet
140 are substantially perpendicular to the lines representing the fourth
guiding
elements 150d shown in FIG. 8.
[00101] The guiding element 150 may comprise any material, including a
biocompatible material. For example, the guiding element 150 may comprise a
metallic, polymeric, or ceramic material. The guiding element 150 may be of
the
same or different material from that of the leaflet 140. Such material may
comprise a
shape memory material such as nitinol. Other materials contemplated include
PTFE,
such as ePTFE or other fluoropolymers or elastomers, polyurethanes, stainless
steel, and other biocompatible materials. In accordance with the present
embodiments, the guiding elements 150 may be connected to the surface of the
leaflet, embedded therein, such as between layers of leaflet material, or a
constituent
part thereof.
[00102] In an embodiment, the guiding element 150 may comprise a plurality of
materials, and thereby exhibit a variable resistance to deformation along its
length or
width.
[00103] In accordance with embodiments, the guiding element defines a shape of
one of a polygon, a square-sided oval, an undulating shape, a lemniscate, and
an S-
type shape.
Example 1
[00104] Referring again to FIGs. 4A-4C, the guiding element 150, in
embodiments,
adds mass to the leaflet 140. As such, the expected effect would be a slower
movement of the leaflet 140 than a leaflet 140 without a guiding element 150.
Surprisingly, in embodiments, the leaflet 140 comprising the guiding element
150
has better hemodynamics than the substantially same leaflet without a guiding
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element. For example, improvements in various performance parameters used to
measure hemodynamics from 1.5 fold to 3.3 fold have been observed. As noted
previously, such performance parameters may include closing volume,
regurgitation
fraction (%), elapsed time to open and close, and the amount of pressure drop
across the open valve during the positive portion of forward flow. Lower
values are
indicative of better performance. By adding guiding element 150, the closing
volume
and regurgitant fraction may be decreased by at least two fold, and similarly,
the
change in pressure may be decreased nearly two fold. Table 1 below provides an
example of actual improved hemodynamics observed by adding the guiding element
150.
Guiding Leaflet Closing Regurgitant AP
Element Thickness Volume Fraction (%) (mm/Hg)
(14 (ml)
No 25 9.45 11.9 7.6
Yes 25 4.46 3.6 3.9
Table 1
[00105] Improved hemodynamics was visually confirmed in that the valve orifice
area in the open position was greater with the guiding element 150 than
without a
guiding element. It was visually confirmed that a valve with guiding element
150 in
its open position had a substantially more circular shape. More particularly,
the
shape formed along the perimeter of the orifice of a cardiac valve in the open
position is substantially more circular with the addition of the guiding
element 150
than the same valve without a guiding element It was also observed that the
leaflets
140 with the guiding element 150 open and close with less wrinkling and In a
more
planar fashion in the central portion of the leaflets compared to leaflets 140
without
guiding elements.
Example 2
[00106] A valve 100a of FIG. 4A having polymeric leaflets 140 was formed from
a
film in a form of a composite material having an expanded fluoropolymer
membrane
and an elastomeric material and joined to a semi-rigid, non-collapsible frame
130,
and was constructed according to the following process:
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[00107] A valve frame was laser machined from a length of MP35N cobalt
chromium tube hard tempered with an outside diameter of 26.0 mm and a wall
thickness of 0.6 mm in the shape shown in FIG. 3. The frame 130 was electro-
polished resulting in 0.0127 mm material removal from each surface and leaving
the
edges rounded. The frame 130 was exposed to a surface roughening step to
improve adherence of leaflets to the frame 130, without degrading fatigue
durability
performance. The frame was cleaned by submersion in an ultrasonic bath of
acetone
for approximately five minutes. Plasma treatment of the entire frame surface
was
performed as commonly known in the arts for cleaning. This treatment also
served
to improve the wetting of the fluorinated ethylene propylene (FEP) adhesive.
[00108] FEP powder (Daikin America, Orangeburg N.Y.) was applied to the frame
130by first stirring the powder into an airborne "cloud" in a standard kitchen
type
blender and suspending the frame in the cloud until a uniform layer of powder
adhered to the entire surface of the frame 130. The frame 130was then
subjected to
a thermal treatment by placing it in a forced air oven set to 320 C for
approximately
three minutes. This caused the powder to melt and adhere as a thin coating
over the
entire frame 130. The frame 130was removed from the oven and left to cool to
room
temperature.
[00109] A strain relief and sewing ring (not shown) were attached to the frame
130in the following manner: a 23mm diameter cylindrical mandrel was wrapped
with
a single layer of Kapton (DuPont) polyimide film and held in place by an
adhesive
strip of Kapton tape over the length of the overlapping seam. One wrap of a
two
layer laminate consisting of an ePTFE membrane laminated to a 25.4 pm thick
layer
of fluoroelastomer as described below and shown in FIG. 11, was wrapped with
the
high strength direction along the axis of the Kapton -covered mandrel 710 with
no
overlap at the seam. The frame 130 was aligned coaxially over the wrapped
mandrel 710. An additional 1 wrap of the two layer laminate was wrapped onto
the
mandrel encapsulating the entire frame 130 with the seam oriented 180 from
the
seam of the single inner wrap. The four layer laminate was end cut 135 mm from
the
base of the frame 130 encapsulated within. The four layer laminate was hand
rolled
axially in the direction of the base of the frame until the 135 mm length of
material
constituted approximately a 3 mm outer diameter ring adjacent to the base of
the
frame. The four layer laminate was end cut approximately 20 mm from the top of
the
frame and the assembly was compression wrapped helically with two sacrificial
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layers of ePTFE membrane imbibed with a polyimide, four layers of unsintered
ePTFE membrane, and approximately one hundred wraps of an ePTFE flber. The
entire assembly was subjected to a thermal treatment by placing it in a forced
air
oven set to 280 C for five minutes and returned to room temperature by
immediate
water quench upon removal from the oven. The sacrificial layers were removed
and
the four layer laminate at the top end of the frame trimmed to allow a 2 mm
length to
extend beyond the perimeter of the top of the frame. The mandrel and Kapton
were
then removed from the interior of the frame forming a strain relief and sewing
ring
with the frame laminated within.
[00110] A single female mold (not shown) defining the shape of the tri-leaflet
was
made. Three identical male molds that match the shape and contour of the
female
mold are held together with a mechanism that enables radial pivoting of the
male
molds with respect to each other at their base while maintaining both axial
and
rotational spacing. The female and male molds are wrapped with a single layer
of
un-sintered ePTFE membrane to act as a cushioning layer and then a single
layer of
substantially nonporous ePTFE membrane with FEP on one side is used to adhere
the membranes together and onto the mandrels with a soldering iron. The
sacrificial
layers ensure that all the mating surfaces between the male and female molds
have
a cushioning layer when compressed together; an additional function is as a
release
layer to prevent the leaflet material from adhering to the molds. The male and
female molds are initially combined to create a single cylindrical structure
to facilitate
leaflet construction and attachment to the frame with strain relief and sewing
ring
component via a tape wrapping process.
[00111] A leaflet material was then prepared. A membrane of ePTFE was
manufactured according to the general teachings described in US Patent
7,306,729.
The ePTFE membrane had a mass per area of 1.0 g/m2 a matrix tensile strength
of
447 MPa in the longitudinal direction and 421 MPa in the transverse direction.
[00112] The above membrane was imbibed with a copolymer fluoroelastomer. The
copolymer consists essentially of between about 65 and 70 weight percent
perfluoromethyl vinyl ether and complementally about 35 and 30 weight percent
tetrafluoroethylene. Additional fluoroelastomers may be suitable and are
described in
U.S. Publication No. 2004/0024448. The fluoroelastomer was dissolved in Novec
HFE7500 (3M, St Paul, MN) in a 2.5% concentration. The solution was coated
using
a mayer bar onto the ePTFE membrane (while being supported by a polypropylene
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release film) and dried in a convection oven set to 145 C for 30 seconds.
After 2
coating steps, the final ePTFE/fluoroelastomer or composite had a mass per
area of
6.92 g/m2, 14.4% fluoropolymer by weight, and thickness of 3.22 pm.
[00113] Five layers of the composite material were wrapped around the combined
molds with the membrane oriented such that the matrix tensile strength of 447
MPa
is oriented axially and the elastomer rich side of the composite facing away
from the
molds.
[00114] The subassembly containing the frame 130 with strain relief and sewing
ring was aligned both axially and rotationally to match theleatures of the
female
mold over the three inner wraps. Ten additional layers of the composite
material
were wrapped around the combined molds with the membrane oriented such that
the
matrix tensile strength of 410.9 MPa was oriented axially and the elastomer
rich side
of the composite facing toward the molds.
[00115] FIG. 11 is a simplification of the above method showing a mandrel 710
over which a frame 130 is positioned. The film 160, in the form of composite,
is
wrapped around the mandrel 710 over the frame 130 forming multiple layers of
film
160 with the guiding element 150 of FIG. 4A contained between two of the
multiple
layers of film 160, as shown In FIG. 12, with area 137 eventually being formed
into a
leaflet. The leaflet 140 comprises multiple layers of film 160 coupled
together with
elastomeric material 164 therebetween. FIG. 12 is a cross-section of the
leaflet 140
showing the layers of film 160 bound together with elastomeric material 164
therebetween, and the guiding element 150 between two of the multiple layers
of film
160.
[00116] The male molds were then slid out from underneath the 15-layer
composite laminate tube. Each of the male molds was expanded with respect to
each other about the pivot at their base. The male mold assembly was coaxially
aligned to the female mold facilitating the male molds to compress the
cantilevered
15-layer composite laminate tube onto the female tri-leaflet mold surface.
Both
radial and axial compression were applied by placing a hose clamp over the
male
molds while simultaneously applying axial load with the translational end of
the lathe
apparatus.
[00117] The assembly consisting of male and female molds, composite laminate,
strain relief, frame, and sewing ring was compression wrapped helically with
two
sacrificial layers of compliant ePTFE membrane imbibed with a polyimide, four
layers
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of un-sintered ePTFE membrane, and approximately one hundred wraps of an
ePTFE fiber. The entire assembly was removed from the lathe and placed in a c-
clamp fixture to maintain axial compression while subjected to a thermal
treatment
by placing it in a forced air oven set to 280 C for 30 minutes. The assembly
was
removed from the oven and brought back to room temperature via immediate water
quench. The sacrificial layers, male, and female molds were removed leaving a
fully
adhered valve in a closed three dimensional form.
[00118] The excess leaflet material was trimmed with scissors from the top of
the
frame posts to the common triple point of each leaflet to create three
commissures or
coapting surface regions as depicted in FIG. 4A. The leaflets were opened with
an
ePTFE mandrel tapered from 10 mm to 25 mm. The round sewing ring at the base
of the frame was molded into a flange by placing the valve assembly into a
fixture
depicted in FIGs. 28a and 28b and using an Branson ultrasonic compression
welder
(#8400, Branson ultrasonics, Danbury CT) with a weld time of 0.8 seconds, hold
time
of 3.0 seconds, and pneumatic pressure of 0.35 MPa. The ultrasonic welding
process was performed twice to create a sewing ring flange thickness of
approximately 2 mm with an outer diameter of 33 mm.
[00119] The final leaflet was comprised of 14.4 % fluoropolymer by weight with
a
thickness of 58 pm. Each leaflet had 15 layers of the composite and a ratio of
thickness/number of layers of 3.87 pm.
[00120] The resulting valve assembly includes leaflets formed from a composite
material with more than one fluoropolymer layer having a plurality of pores
and an
elastomer present in substantially all of the pores of the more than one
fluoropolymer
layer. Each leaflet is capable of being cycled between a closed position,
shown
illustratively in FIG. 4B, in which blood is prevented from flowing through
the valve
assembly, and an open position, shown illustratively in FIG. 4C, in which
blood is
allowed to flow through the valve assembly. Thus, the leaflets of the valve
assembly
cycle between the closed and open positions generally to regulate blood flow
direction in a human patient.
[00121] The performance of the valve leaflets in each valve assembly was
characterized on a real-time pulse duplicator that measured typical anatomical
pressures and flows across the valve The flow performance was characterized by
the following process:
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1) The valve assembly was potted into a silicone annular ring (support
structure) to allow the valve assembly to be subsequently evaluated in a real-
time
pulse duplicator. The potting process was performed according to the
recommendations of the pulse duplicator manufacturer (ViVitro Laboratories
Inc.,
Victoria BC, Canada)
2) The potted 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 VSI Vivitro Systems Inc., Victoria BC, Canada: a Super
Pump, Servo Power Amplifier Part Number SPA 3891; a Super Pump Head, Part
Number SPH 5891B, 38.320 cm2 cylinder area; a valve station/fixture; a Wave
Form
Generator, 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, Carolina Medical Electronics Inc., East Bend, NC,
USA.
In general, the flow pulse duplicator system uses a fixed displacement, piston
pump to produce a desired fluid flow through the valve under test.
3) The heart flow pulse duplicator system was adjusted to produce the
desired flow, mean pressure, and simulated pulse rate. The valve under test
was
then cycled for about 5 to 20 minutes.
4) Pressure and flow data were measured and collected during the test
period, including ventricular pressures, aortic pressures, flow rates, and
pump piston
position.
5) Parameters used to characterize the valve and to compare to post-fatigue
values are pressure drop across the open valve during the positive pressure
portion
of forward flow, effective orifice area, and regurgitant fraction. The values
recorded
for this valve are displayed in Table x below. All data contained in this
table were
recorded at 5 liters/min cardiac output at 37degrees centigrade.
Example 3
[00122] A second valve 100c was constructed as above, except that a first
guiding
element 150a was flanked by a third guiding element 150c on each side of first
guiding element 150a, as shown in FIG. 7, were incorporated into the laminated
leaflet construction so that they were contained entirely within each of the
three
leaflets 140. The first guiding element 150a and the third guiding elements
150c
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were constructed of 0.151mm Nitinol wire into elliptical elements. The first
guiding
element 150a and the third guiding elements 150c were arranged into a pattern
radiating from but spaced from the leaflet base 135 of the leaflet 140, shown
in FIGS.
and 7, and were not attached to the frame 130. The first guiding element 150a
was
11.66mm in length and each third guiding element 150c were lOmm in length. The
first guiding element 150a and the third guiding elements 150c were formed on
a pin
jig and placed into an oven at 450 degrees centigrade for 10 minutes, removed
and
water quenched. As above, the valve was loaded into a real-time heart valve
tester
and performance characteristics measured (see Table 2).
Example 4
[00123] A third valve was constructed as above in example 3, also with 3
0.151mm
guiding elements 150a, 150c, see FIG. 7, made of Nitinol. The central guiding
element 150a was configured the same as the central guiding element 150a of
example 3 and was11.43mm in length. Each of the two side guiding elements or
third guiding elements 150c was 8.26mm in length. None of the 3 guiding
elements
150a, 150c were attached directly to the frame 130 and were spaced from the
frame
130. These guiding elements 150a, 150c were formed as described in example 3.
As
above, the valve was loaded into a real-time heart valve tester and
performance
characteristics measured (see Table 2).
Valve EOA Regurgitation .AP Leakage volume Closing volume
(cm2) (%) (mm Hg) (m1) (m1)
Example 3 1.9 8.7 8.8 0.4 6.3
Example 4 1.9 5.6 8.1 2.8 1.4
Example 5 1.9 3.7 8.1 0.1 2.7
Table 2
Example 5
[00124] Another valve identical to that of example 1 was constructed and
tested.
Example 6
[00125] This example illustrates the application of non-metallic guiding
elements.
An additional composite membrane was formed from a composite material
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comprising a membrane of ePTFE imbibed with a fluoroelastomer, as shown in
FIG.
12, leaflet 140. A piece of the film 160 in the form of a composite material
approximately 10 cm wide was wrapped onto a circular mandrel to form a tube.
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. Patent No.
7,306,729. The fluoroelastomer was as in example 2.
[00126] The ePTFE membrane had the following properties: thickness = about 15
pm; MTS in the highest strength direction = about 400 MPa; MTS strength in the
orthogonal direction = about 250 MPa; Density = about 0.34 g/cm3; IBP = about
660
KPa.
[00127] The percent weight of the fluoroelastomer relative to the ePTFE was
about
53%.
[00128] The multi-layered composite had the following properties: thickness of
about 40 pm; density of about 1.2 g/cm3; 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),
and mass/area = about 14 g/m2.
[00129] Ten layers of the above composite were heated and compressed together
so as to bond to form a single composite. Side elements in the form of dart
shapes
(not shown) were cut from the 10 layer sheet and were subsequently bonded into
the
leaflet as in examples 3 and 4. Test results are illustrated below in table 3.
Reductions in regurgitation, leakage volume, and closing volume were observed,
along with a modestly elevated degree of pressure drop.
Valve EOA Regurgitation AP Leakage volume Closing volume
(cm2) (%) (mm Hg) (ml) (ml)
Example 4 2.0 11.5 7.9 3.4 5.6
Example 5 1.9 7.3 8.3 0.2 5.3
Table 3
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Example 7
[00130] The purpose of this example is to illustrate that the guiding elements
in an
embodiment can be employed in valves to be delivered via catheter. Another
valve
was constructed as in example 3, except that the valve frame employed was of a
type that can be diametrically crushed to a small diameter (6mm), and then,
using a
balloon, re-expanded to the original diameter of 26mm. In this case, the
material
employed to form the leaflet had a weight/area of 0.3gm/meter2, and each layer
was
30% ePTFE and 70% PMVE/PTFE copolymer. Fifty layers were used to form the
leaflets for a final thickness of about 50 micrometers. The guiding elements
were
formed and laminated into the leaflets as in example 3.
[00131] The results demonstrate that the valve had hemodynamics after
crushing/re-expansion very similar to that of before crushing (within
measurement
error), as shown in Table 4.
Valve #7 EOA AP Leakage Closing
(cm2) Regurgitation (mm volume volume
(%) Hg) (ml) (ml)
Before crushing 2.2 10.1 6.3 4.7 3.1
After re- 2.2 10.6 7.2 4.7 3.7
expansion
Table 4
[00132] The foregoing disclosure is merely illustrative of the present
invention and
is not intended to be construed as limiting the invention. Although one or
more
embodiments of the present invention have been described, persons skilled in
the art
will readily appreciate that numerous modifications could be made without
departing
from the spirit and scope of the present invention. As such, it should be
understood
that all such modifications are intended to be included within the scope of
the
present invention.
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