Note: Descriptions are shown in the official language in which they were submitted.
CA 02221572 1997-11-19
EXTERNALLY SUPPORTED TAPE REINFORCED VASCULAR. GRAFT
Field of the Invention
The present invention relates generally to
prosthetic vascular grafts, and more particularly to a
tubular, tape-reinforced externally supported vascular
graft formed of a fluoropolymer such as
polytetrafluoroethylene (PTFE), and methods of
manufacture therefore.
Baakgwound of the Invention
Fluoropolymers, such as PTFE have been heretofore
used for the manufacture of various types of prosthetic
vascular grafts. Among these are various vascular grafts
having tubular configurations so that they may be
utilized to replace an excised segment of bland vessel.
The tubular prosthetic vascular grafts have
traditionally been implanted, by open surgical
techniques, whereby a diseased or damaged segment of
blood vessel is surgically excised and removed, and the
tubular bioprosthetic graft is then anastomosed into the
host blood vessel as a replacement for the previously
removed segment thereof. Alternatively, sL~ch tubular
prosthetic vascular grafts have also been used as bypass
grafts wherein opposite ends of the graft are sutured to
a host blood vessel so as to form a bypass conduit around
a diseased, injured or occluded segment of the host
vessel.
More recently, methods have been developed for
endovascular implantation of tubular prosthetic vascular
grafts. Such endovascular implantation initially
involves translumenal delivery of the graft, in a
compacted state, through a catheter or other delivery
apparatus. Thereafter, the graft undergoes in situ
expansion and affixation at its intended site of
implantation within the host blood vessel. An affixation
apparatus is typically utilized to affix the opposite
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expansion and affixation at its intended site of
implantation within the host blood vessel. An affixation
apparatus is typically utilized to affix the opposite
ends of the tubular graft to the surrounding blood vessel
wall. In this regard, the endovascularly implanted
'tubular graft may be utilized to repair an aneurismic
segment of a host blood vessel, without requiring open
surgical dissection of the host blood vessel.
In general, many of the tubular prosthetic vascular
grafts of the prior art have been formed of extruded,
porous PTFE tubes. In some of the tubular grafts of the
prior art a tape, formed of PTFE film is wrapped about
and laminated to the outer surface of a tubular base
graft to provide reinforcement and additional burst
strength. Also, some of the prior tubular prosthetic
vascular grafts have included external support member(s),
such as a PTFE beading, bonded or laminated to the outer
surface of the tubular graft to prevent the graft from
becoming compressed or kinked during implantation. These
externally supported tubular vascular grafts have proven
to be particularly useful for replacing segments of blood
vessel which pass through, or over, joints or other
.regions of the body which undergo frequent articulation
or movement.
one commercially available, externally-supported,
'tubular vascular graft is formed of a regular walled PTFE
'tube having a PTFE filament helically wrapped around, and
bonded to, the outer surface of the PTFE tube. (IMPRA
Flexn Graft, IMPRA, Inc., Tempe, Az)
One other commercially available, externally-
supported, tubular vascular graft comprises a regular
walled, PTFE tube which has PTFE reinforcement tape
helically wrapped around, and bonded to, the outer
surface of the PTFE tube and individual rings of
Fluorinated Ethylene Propylene (FEP) rings disposed
around, and bonded to, the outer surface of the
reinforcement tape. (FEP ringed ePTFE vascular graft,
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W.L. Gore & Associates, Inc., Flagstaff, AZ)
When surgically implanting the externally-supported
'tubular vascular grafts of the prior art, it is typical
for the surgeon to peel the support filament or support
rings) away from the opposite ends of the tubular graft
to facilitate anastomosis of the ends of the graft to the
host blood vessel. However, such peeling away of the
external support filament or rings) .may, in at least
some cases, also result in some peeling or fraying of any
ZO reinforcement tape from the adjacent end portions of the
'tubular graft. Such fraying or peeling of the
.reinforcement tape concurrently with removal of the
external support members) is undesirable.
Accordingly, there remains a need in the art for the
development of new externally-supported, tape-reinforced,
tubular vascular grafts which are constructed to permit
an external support member (e.g., a PTFE filament) to be
peeled away from the end regions of the graft, without
causing concurrent peeling or fraying of the underlying
reinforcement tape from the tubular base graft.
~umzaarv of the Invention
The invention comprises an externally-supported,
tape-reinforced, tubular prosthetic graft which
comprises; a tubular base graft formed of expanded,
sintered fluoropolymer (e.g. PTFE) material; a strip of
reinforcement tape helically wrapped around and bonded to
the outer surface of the tubular base graft, in a first
helical pitch ( i . e. , conf iguration or direction) ; and, an
external support member (e. g., PTFE beading) helically
wrapped around and bonded to the outer surface of the
reinforcement tape, in a second helical pitch (i.e.,
configuration or direction) which is different: from said
first helical pitch. In the preferred embodiment, the
second helical pitch of the external support member is in
a direction which is opposite the direction of the first
helical pitch of the reinforcement tape.
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Further in accordance with the invention, the
external support member may be formed of substantially
non-elastic material which is capable of providing
external configurational support to the tubular graft so as
to prevent substantial indentation or kinking of the tubular
graft when positioned in a region of a host body which
undergoes bending or other movement which would be likely to
indent or kink the tubular graft.
Still further in accordance with the invention,
there is provided a method of manufacturing the
externally-supported, tape-reinforced, tubular prosthetic
grafts of the present invention, said method comprising the
steps of (a) providing a tubular base graft formed of
expanded, sintered fluoropolymer material; (b) providing at
least one strip of reinforcement tape formed of expanded
sintered fluoropolymer film; (c) wrapping said reinforcement
tape helically around the outer surface of the tubular base
graft in a first helical disposition (i.e., configuration
or direction); (d) causing the helically wrapped
reinforcement tape to become fused to the tubular base graft;
(e) providing an external support member formed of
substantially non-elastic beading; (f) helically wrapping the
external support member around the outer surface of the
helically-wrapped reinforcement tape, in a second
h a 1 i c a 1 d i s p o s i t i o n ( i . a . , configuration or direction)
which differs from the first helical disposition of the
reinforcement tape; and, (g) causing the helically wrapped
external support member to become attached to the helically
wrapped reinforcement tape.
Further objects and aspects of the invention will
become apparent to those skilled in the art upon reading and
understanding of the following detailed description and the
accompanying drawings.
Further in accordance with the invention, there is
provided an externally supported, tape-reinforced, tubular
prosthetic graft comprising: a tubular base graft formed of
expanded, sintered fluoropolymer, said tubular base graft
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having an inner luminal surface and an outer surface;
a strip of reinforcement tape helically wrapped around
the outer surface of the tubular base graft in a first
helical pitch, said strip of reinforcement tape having an
inner surface which is in abutment with the outer surface of
the tubular base graft, and an outer surface;
an external support member helically wrapped around the
outer surface of the reinforcement tape in a second helical
pitch which is different from the first helical pitch of said
reinforcement tape.
Still further in accordance with the invention, there
is provided a method of manufacturing an externally
supported, tape-reinforced, tubular prosthetic graft, said
method comprising the steps of:
a) providing a tubular base graft formed of expanded,
sintered fluoropolymer material, said tubular base graft
having an inner luminal surface and an outer surface;
b) providing at least one strip of reinforcement tape
formed of expanded, sintered fluoropolymer film;
c) wrapping said reinforcement tape helically around
the outer surface of the tubular base graft in a first
helical pitch;
d) causing the helically wrapped reinforcement tape to
become attached to the tubular base graft;
e) providing an external support member formed of
substantially non-elastic beading;
f) helically wrapping the external support member
around the helically wrapped reinforcement tape in a second
helical pitch which differs from said first helical pitch;
and,
g) causing the helically wrapped external support
member to become attached to the helically wrapped
reinforcement tape.
Brief Description of the Drawings
Figure 1 is an elevational view of a first step in
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the manufacturing method of the present invention wherein
a tubular base graft is positioned on a rigid mandrel.
Figure 2 is an elevational view showing of a second
step of the manufacturing method of the present invention
wherein a fluoropolymer film reinforcement tape is
helically wrapped about, and heat laminated to, the outer
surface of a tubular base graft.
Figure 3 is an elevational view of a third step in
the manufacturing method of the present invention wherein
a fluoropolymer filament is helically positioned on, and
heat-laminated to, a tape-reinforced tubular graft, the
helical disposition of the support filament being in
opposite disposition to the helical disposition of the
reinforcement tape.
Figure 4 is an elevational view of a segment of
externally supported tape-reinforced tubular vascular
graft material manufactured in accordance with the
present invention.
detailed Description ~f the Preferred Emb~diment
The following detailed description and the
accompanying drawings to which it refers are provided for
purposes of describing and illustrating the presently
preferred embodiments of the invention only, and are not
intended to limit the scope of the invention in any way.
Figure 1 shows a f first step in the method of the
present invention wherein an extruded tubular
fluoropolymer base graft 10 is disposed on a rod or
mandrel 12.
The tubular base graft 10 will typically be
manufactured of expanded, sintered PTFE in accordance
with the following general methodologyo
Preparation of the Tubular Base Graft
i.) Preparation of Paste
The manufacture of the tubular base graft begins
with the step of preparing a PTFE paste dispersion for
subsequent extrusion. This PTFE paste dispersion may be
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prepared by known methodology whereby a tine, virgin PTFE
powder (e. g., F-104 or F°103 Virgin PTFE Fine Powder,
Dakin America, 20 Olympic Drive, Orangebury, NY 10962) is
blended with a liquid lubricant, such as odorless mineral
spirits (e. g., Isopar~, Exxon Chemical Company, Houston,
TX 77253-3272), to form a PTFE paste of the desired
consistency.
ii.) Extrusion of Tube
The PTFE-lubricant blend dispersion is subsequently
gassed through a tubular extrusion dye to form a tubular
extrudate.
iii.) Drying
The wet tubular extrudate is then subjected to a
drying step whereby the liquid lubricant is removed.
'this drying step may be accomplished at room temperature
or by placing the wet tubular extrudate in an oven
maintained at an elevated temperature at or near the
7_ubricant's dry point for a sufficient period of time to
result in evaporation of substantially all of the liquid
lubricant.
iv.) Expansion
Thereafter, the dried tubular extrudate is
longitudinally expanded or longitudinally drawn at a
temperature less than 327°C and typically in the range of
250-326°C. This longitudinal expansion of the extrudate
may be accomplished through the use of known methodology,
and may be implemented by the use of a device known as a
batch expander. Typically, the tubular extrudate is
longitudinally expanded by an expansion ratio of more
than two to one (2:1) (i.e., at least two (2) times its
original length).
v.) Sintering
After the longitudinal expansion step has been
completed, the tubular extrudate is subjecaed to a
sintering step whereby the extrudate is heated to a
temperature above the sintering temperature of PTFE
(i.e. , 350-37o°C) to effect amorphous-locking of the PTFE
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polymer. The methodology used to effect the sintering
step, and the devices used to implement such methodology,
are known in the art.
Completion of the sintering step marks the
completion of the preparation of the expanded, sintered
PTFE base graft 10.
Figure 2 shows a second step in the method wherein
a reinforcement tape 14 formed of material such as
expanded sintered PTFE film is helically wrapped about
the outer surface of the tubular base graft 10, and heat
laminated thereto.
The reinforcement tape 14 may be manufactured by any
suitable method, including the general method for
manufacturing expanded PTFE reinforcement tape, as
follows: B. Preparation of Reinforcement TaQa
i.) Preparation of Paste Dispersion
The preparation of the expanded sintered PTFE
reinforcement tape 14 includes the initial preparation of
a PTFE paste dispersion. The PTFE paste dispersion
prepared in this step may be prepared in the same manner
as described hereabove for preparation of the PTFE paste
dispersion used to form the tubular base graft.
ii.) Extrusion of Film
The PTFE paste dispersion is subsequently passed
through the film extrusion dye to form a wet film
extrudate. The wet film extrudate is taken up or wound
upon a rotating core so as to form a roll of the wet film
extrudate.
iii.) Calendarina
The wet film extrudate is subsequently unrolled and
subjected to an initial cold (i.e., <100°c) calendaring
step by passing the film through at least tine set of
opposing stainless steel calendaring rollers having an
adjustable gap thickness therebetween. The calendaring
rollers are preferably maintained at a temperature
between room temperature and 60°c. The width of the wet
extrudate is held constant as it passes through these
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calendaring rollers. The thickness of the wet film
extrudate is reduced to its desired final thickness
(e.g., 0.004-0.005 inches) while the width of the film is
maintained constant. It will be appreciated that, since
the width of the film is maintained constant, the passage
of the film through the calendaring machine will result
in a longitudinal lengthening of the film. The amount of
longitudinal lengthening will be a function of the
decrease in film thickness which occurs as the film
passes between the calendaring rollers.
One example of a commercially available calendaring
machine useable for this purpose is the small Killion 2
Roll Stack, (Killion Extruders, Inc., Cedar Grove, NJ
07009.)
iv) Drying
Thereafter, the wet film is subjected to a drying
step. This drying step may be accomplished by permitting
or causing the liquid lubricant to evaporate from the
matrix of the film. Such evaporation of the liquid
lubricant may be facilitated by passing the film over a
drum or roller which is maintained in an elevated
temperature sufficient to cause the liquid lubricant to
fully evaporate from the film matrix.
v) ExQansion
Separately, or concurrently with the drying step the
f-_ilm is subjected to an expansion step. Such expansion
step comprises expanding the PTFE film in at least one
direction (e.g., longitudinally). Such expansion of the
film serves to a) increase the porosity of the film, b)
increase the strength of the film, and c) orient the PTFE
fibrils in the direction of the axis of expansion.
This expansion step is typically carried out with
some heating of the film during such expansion, but such
heating does not exceed the crystalline melting point of
the PTFE polymer.
vi) sintering
After the drying step and expansion step have been
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completed, the film is subjected to a sintering step
wherein the film is heated to a temperature above the
melting point of PTFE to accomplish sintering or
amorphous locking of the PTFE polymer. This sintering
step may be carried out by passing the film over a drum
or roller which is maintained at a high surface
'temperature (e. g., 350-420°c) to cause the desired
heating of the PTFE film above the melting point of the
PTFE polymer for a sufficient period of time to effect
l0 'the desired sintering of the film.
vii) Cutting the Film Into Strips
After the film has been dried, the film is cut into
strips, each strip typically having a width of 0.25-0.50
inches, thereby creating strips of expanded, sintered
PTFE reinforcement tape 14.
Thereafter, the strips of expanded sintered PTFE
reinforcement tape 14 are helically wrapped about and
:Laminated to the outer surface of the tubular base graft
:LO, in accordance with the following methodology:
r. Wrappincx and Lamination of the ReinforcEament Tape
c7nto the Tubular Base Grnft
The expanded sintered PTFE reinforcement tape 14 is
helically wrapped onto the outer surface of the tubular
base graft 10 by laying the reinforcement tape 14 onto
the outer surface of the tubular base graft 10, at a
desired angle A~, relative to the longitudinal axis LA of
t:he base graft, while the mandrel 12 and base graft 10
are rotated about such longitudinal axis hA. This
results in helical wrapping of the reinforcement tape 14
onto the outer surface of the base graft 10, :Ln a first
helical configuration or pitch. The helical
configuration or pitch is determined by the longitudinal
spacing between the individual convolutions of the helix
and is a function of the size and direction of angle A~
which is the angle at which the tape 14 is wrapped
relative to the longitudinal axis LA of the base graft.
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The number of layers of tape 14 applied to the base
graft 10 is variable for each size of graft. The number
of layers of tape 14 depends on the desired mechanical
and physical properties of the graft (e. g., burst
pressure, water entry pressure, suture retention
strength). In the preferred manufacturing methodology,
the width of the tape 14 is approximately 0.5 inches,
irrespective of the number of layers of tape which are to
be applied to the base graft 10. Therefore, the pitch
(i.e., the distance from leading edge to leading edge of
the adjacent convolutions of tape) varies depending on
the size of the graft and the numbers of layers of tape
desired. For example, when tape having a width of 0.5
inches is used, and a total of five tape layers are
desired, the pitch of the tape is 0.1 inches, but if ten
layers of tape are desired, the pitch will be 0.05
inches .
Thereafter, a heating apparatus 16, such as an oven,
is used to heat the sintered PTFE reinforcement tape 14
and sintered PTFE base graft 10 to a temperature of
approximately 355-375°C for a period of approximately 10
60 minutes to cause the reinforcement tape 14 to become
laminated to the outer surface of the tubular base graft
10. This results in the formation of a tape-reinforced
tubular graft.
D. Wrapping And Lamination of the External Sun ort
Member Onto the Tane-Reinforced Graft
Thereafter, while the tape-reinforced tubular graft
remains disposed on the rigid mandrel 12, an external
reinforcement member 18, preferably a sintered PTFE
filament, is helically wound onto the outer surface of
the reinforcement tape 14 at a helical disposition which
is opposite or substantially different from the helical
disposition of the reinforcement tape 14. This may be
accomplished by laying the reinforcement member 18 onto
the outer surface of the reinforcement tape at a desired
angle A2 relative to the longitudinal axis LA of 'the base
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graft 10, while concurrently rotating the mandrel in a
direction opposite to that used to wrap the reinforcement
tape onto the graft 12 and tape-reinforced graft about
the longitudinal axis LA. This results in helical
wrapping of the external support member 18 onto the outer
surface of the reinforcement tape 14 in a helical
configuration or pitch which is different from the
helical configuration or pitch of the reinforcement tape.
The external support member 18 functions to increase
the kink resistance and crush resistance of the graft,
without affecting the handling characteristics of the
graft. Typically, the helical configuration or pitch of
the external support member 18 will remain constant for
each size of the graft.
In accordance with the present invention, the
helical configuration or pitch of the external support
member 18 is different from that of the reinforcement
tape 14. In some embodiments, such as the embodiment
shown in Figures 3-4, the size of the angles A~ and AZ at
which the tape 14 and reinforcement member 18 are applied
to the base graft 12 may be of differing or equivalent
size, but the direction of the angles will be opposite
one another, thereby resulting in differing helical
configurations or pitch of the tape 14 and external
support member 18. In other embodiments the directions
of the angles A~ and AZ may be the same, but the angular
size of such angles A~ and AZ will differ, thereby
resulting in directionally similar but different helical
configurations or pitches of the reinforcement tape 14
and external support member 18.
After the external support member 18 has been
wrapped about the outer surface of the reinforcement tape
14 at its desired helical configuration or pitch, a
heating apparatus 16, such as an oven, is used to heat-
laminate the external support member 18 to the outer
surface of the reinforcement tape 14.
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The external reinforcement member 18 may comprise a
sintered PTFE monofilament bead, such as the PTFE beading
commercially available from Zeus Industrial Products,
Inc., Orangeburg, South Carolina.
The above-described manufacturing method results in
the formation of an externally supported tape-reinforced
tubular prosthetic graft 20 which comprises a sintered
PTFE tubular base graft 10 having a sintered PTFE
reinforcement tape 14 helically wrapped thereon in a
first helical disposition, and a sintered PTFE
reinforcement member 18 helically wrapped on the outer
surface of the reinforcement tape 14 in a second helical
disposition which is different from the helical
disposition of the reinforcement tape 14. It will be
appreciated that the present invention has been described
herein with reference to certain preferred or exemplary
embodiments and manufacturing methods. The preferred or
exemplary embodiments and manufacturing methods described
herein may be modified, changed, added to or deviated
from without departing from the intended spirit and scope
of the present invention, and it is intended that all
such additions, modifications, amendments and/or
deviations be included within the scope of the following
claims.
