U.S. patent application number 14/023763 was filed with the patent office on 2014-04-10 for polymeric marker with high radiopacity for use in medical devices.
This patent application is currently assigned to Abbott Cardiovascular Systems, Inc.. The applicant listed for this patent is Abbott Cardiovascular Systems, Inc.. Invention is credited to Aaron Baldwin, Vincent Peter Bavaro, Peter D'Aquanni, John Arthur Simpson.
Application Number | 20140100447 14/023763 |
Document ID | / |
Family ID | 34313360 |
Filed Date | 2014-04-10 |
United States Patent
Application |
20140100447 |
Kind Code |
A1 |
Bavaro; Vincent Peter ; et
al. |
April 10, 2014 |
POLYMERIC MARKER WITH HIGH RADIOPACITY FOR USE IN MEDICAL
DEVICES
Abstract
High radiopacity is achieved in a polymeric marker by combining
a polymeric resin, a powdered radiopaque agent having uniformly
shaped particles of a specific particle size distribution and a
wetting agent. The method to produce the marker calls for the
blending and pelletization of these materials followed by extrusion
onto support beading. The resulting supported tubing is
subsequently cut to length with the beading still in place. After
ejection of the beading remnant the marker is slipped into place on
the device to be marked and attached by melt bonding. Marking of a
guidewire allows lesions to be measured while the marking of
balloon catheters allow the balloon to be properly positioned
relative to a lesion.
Inventors: |
Bavaro; Vincent Peter;
(Temecula, CA) ; Simpson; John Arthur; (Carlsbad,
CA) ; D'Aquanni; Peter; (Murrieta, CA) ;
Baldwin; Aaron; (Temecula, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Abbott Cardiovascular Systems, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
Abbott Cardiovascular Systems,
Inc.
Santa Clara
CA
|
Family ID: |
34313360 |
Appl. No.: |
14/023763 |
Filed: |
September 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12945566 |
Nov 12, 2010 |
8637132 |
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14023763 |
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11877905 |
Oct 24, 2007 |
7833597 |
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12945566 |
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10945637 |
Sep 21, 2004 |
7303798 |
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11877905 |
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10667710 |
Sep 22, 2003 |
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10945637 |
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Current U.S.
Class: |
600/424 ;
156/297; 156/86; 428/36.4; 523/105; 600/585; 606/130 |
Current CPC
Class: |
A61F 2250/0098 20130101;
A61B 90/39 20160201; A61L 31/125 20130101; Y10T 428/139 20150115;
A61M 25/0012 20130101; A61L 31/18 20130101; A61B 6/485 20130101;
A61L 29/18 20130101; Y10T 156/1089 20150115; A61M 25/1027 20130101;
A61B 5/1076 20130101; A61F 2/958 20130101; A61M 25/0108 20130101;
Y10T 428/12493 20150115; A61B 5/6851 20130101; A61B 2562/17
20170801; A61M 25/09 20130101; A61B 5/6853 20130101; Y10T 428/1372
20150115; A61B 6/12 20130101 |
Class at
Publication: |
600/424 ;
600/585; 606/130; 428/36.4; 156/297; 156/86; 523/105 |
International
Class: |
A61L 31/12 20060101
A61L031/12; A61B 5/107 20060101 A61B005/107; A61B 19/00 20060101
A61B019/00; A61B 6/12 20060101 A61B006/12; A61L 31/18 20060101
A61L031/18; A61M 25/00 20060101 A61M025/00; A61M 25/09 20060101
A61M025/09; A61M 25/10 20060101 A61M025/10; A61M 25/01 20060101
A61M025/01; A61B 5/00 20060101 A61B005/00; A61B 6/00 20060101
A61B006/00 |
Claims
1-17. (canceled)
18. A method of radiopaquely marking a medical device, comprising:
providing a flexible polymeric radiopaque marker containing greater
than 30 volume percent radiopaque particles, wherein such particles
have an average diameter of at least 2 microns and a maximum
diameter of about 20 microns; accurately positioning said marker on
said medical device; and melt bonding said marker in place.
19. The method of claim 18, further comprising disposing a length
of heat shrink tubing about said accurately positioned marker and
heating said tubing.
20. The method of claim 18, wherein said radiopaque particles
comprise tungsten.
21. The method of claim 18, wherein said medical device comprises a
balloon catheter and said marker is positioned on an inner member
disposed within an expandable balloon.
22. The method of claim 18, wherein said medical device comprises a
guidewire.
23. The method of claim 22, wherein a plurality of said markers are
bonded to said guidewire.
24. The method of claim 23, wherein said markers are equally spaced
relative to one another so as to function as a ruler under
fluoroscopic inspection.
25. The method of claim 23, wherein said guidewire includes a
radiopaque feature and wherein said markers are each spaced a
preselected distance from said feature.
26. The method of claim 23, wherein said markers each have a
different length so as to function as gauges under fluoroscopic
inspection.
27. A device for measuring lesion sizes, comprising: a guidewire;
and at least one flexible polymeric radiopaque marker is melt
bonded to a distal end of said guidewire, wherein said marker
contains radiopaque particles comprising at least 30 percent of its
volume.
28. The device of claim 27, wherein two or more of said markers are
melt bonded to said guidewire at preselected spacing relative to
one another so as to function as a ruler under fluoroscopic
inspection.
29. The device of claim 27, wherein said guidewire includes a
radiopaque feature and said marker is melt bonded a preselected
distance therefrom.
30. The device of claim 27, wherein said marker has a preselected
length so as to function as a gauge under fluoroscopic
inspection.
31. The device of claim 27, wherein a plurality of said markers are
bonded to said guidewire, each of a different length so as to
function as gauges under fluoroscopic inspection.
32. The device of claim 27, wherein said radiopaque particles
comprise tungsten.
33. The device of claim 32, wherein a wetting agent facilitates
encapsulation of said radiopaque particles by polyether block
amide.
34. The device of claim 33, wherein said wetting agent comprises
maleic anhydride.
35. A radiopaque, elastomeric composition, comprising: a polymer;
radiopaque particles disposed within said polymer having an average
diameter of at least 2 microns and a maximum diameter of about 20
microns; and a wetting agent for facilitating encapsulation of said
particles by said polymer.
36. The composition of claim 35, wherein said radiopaque particles
comprise greater than 18 volume percent of said marker.
37. The composition of claim 36, wherein said radiopaque particles
comprise approximately 36 volume percent of said marker.
38. The composition of claim 35, wherein said polymer comprises
Pebax and said radiopaque particles comprise tungsten powder.
39. The composition of claim 38, wherein said multi-functional
polymeric additive comprises maleic anhydride graft polyolefin.
40. The composition of claim 35, wherein said radiopaque particles
are substantially equiaxed.
41. The composition of claim 40, wherein said particles are
produced by a pusher process.
42. The composition of claim 41, wherein said particles are
produced by an atomization process, resulting in a substantially
spherical particle.
43. The composition of claim 35, further comprising an
antioxidant.
44. The composition of claim 35, wherein said polymer is
thermoplastic.
45. The composition of claim 35 formed so as to define a tubular
structure.
46. An intraluminal medical device, comprising an elongated shaft
or core member having a radiopaque marker secured to a surface of
the shaft or core member, and the radiopaque marker is formed of a
compounded polymer mixture comprising: a polymer; radiopaque
particles having an average diameter of at least about 2 microns
and a maximum diameter of about 20 microns, the radiopaque
particles comprising at least 30 volume percent of the marker; and
a wetting agent for facilitating encapsulation of said particles by
said polymer.
47-53. (canceled)
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a division of co-pending U.S. Ser. No.
12/945,566 filed Nov. 12, 2010 which is a division of U.S. Ser. No.
11/877,905 filed Oct. 24, 2007, now U.S. Pat. No. 7,833,597, which
is a division of U.S. Ser. No. 10/945,637 filed Sep. 21, 2004, now
U.S. Pat. No. 7,303,798, which is a continuation-in-part of U.S.
Ser. No. 10/667,710, filed Sep. 22, 2003, now abandoned, the entire
contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention is directed to elongated
intracorporeal devices, and more particularly intraluminal devices
for stent deployment, percutaneous transluminal coronary
angioplasty (PTCA), and the similar procedures. PTCA is a widely
used procedure for the treatment of coronary heart disease. In this
procedure, a balloon dilatation catheter is advanced into the
patient's coronary artery and the balloon on the catheter is
inflated within the stenotic region of the patient's artery to open
up the arterial passageway and increase the blood flow through the
artery. To facilitate the advancement of the dilatation catheter
into the patient's coronary artery, a guiding catheter having a
preshaped distal tip is first percutaneously introduced into the
cardiovascular system of a patient by the Seldinger technique
through the brachial or femoral arteries. The catheter is advanced
therein until the preshaped distal tip of the guiding catheter is
disposed within the aorta adjacent the ostium of the desired
coronary artery. A balloon dilatation catheter may then be advanced
through the guiding catheter into the patient's coronary artery
until the balloon on the catheter is disposed within the stenotic
region of the patient's artery.
[0003] Once properly positioned across the stenosis, the balloon is
inflated one or more times to a predetermined size with radiopaque
liquid at relatively high pressures (e.g., generally 4-12
atmospheres) to dilate the stenosed region of a diseased artery.
After the inflations, the balloon is finally deflated so that the
dilatation catheter can be removed from the dilatated stenosis to
resume blood flow.
[0004] Similarly, balloon catheters may be used to deploy
endoprosthetic devices such as stents. Stents are generally
cylindrical shaped intravascular devices that are placed within a
damaged artery to hold it open. The device can be used to prevent
restenosis and to maintain the patency of blood vessel immediately
after intravascular treatments. Typically, a compressed or
otherwise reduced diameter stent is disposed about an expandable
member such as a balloon on the distal end of the catheter, and the
catheter and stent thereon are advanced through the patient's
vascular system. Inflation of the balloon expands the stent within
the blood vessel. Subsequent deflation of the balloon allows the
catheter to be withdrawn, leaving the expanded stent within the
blood vessel.
[0005] Typically, the distal section of a balloon catheter or other
percutaneous device will have one or more radiopaque markers in
order for the operator of the device to ascertain its position and
orientation under X-ray or fluoroscopy imaging. Generally, a band
or ring of solid radiopaque metal is secured about an inner or
outer shaft of a balloon catheter to serve as a radiopaque marker.
Such configuration, however, locally stiffens the catheter shaft
and thereby imparts an undesirable discontinuity thereto as the
solid metal bands are relatively inflexible compared to a polymer
balloon catheter shaft. Additionally, the metallic markers are
relatively expensive to manufacture and relatively difficult to
positively affix to an underlying device.
[0006] As is described in U.S. Pat. No. 6,540,721, which is
incorporated herein by reference, many of the problems associated
with the use of conventional markers may be overcome by replacing
the rigid precious metal tubing with a polymer that is filled or
doped with a suitable radiopaque agent. Such marker may be formed
by blending a polymer resin with a powdered, radiographically dense
material such as elemental tungsten and then extruding the
composition to form a tubular structure with an appropriate inner
diameter and wall thickness. The extrusion may then be cut to
discrete lengths and installed onto the intended component via a
melt bonding process.
[0007] A shortcoming of such an approach has been found to be the
apparent limit to which a suitable polymer can be filled with a
radiographically dense material to yield a composition that can be
successfully compounded, economically shaped into suitable
dimensions for markers and easily assembled onto a component
without unduly compromising the desirable properties of the polymer
matrix. The fill ratio that is achievable will determine how thick
a marker must be in order to achieve a particular degree of
radiopacity. In the case of tungsten in a polymer such as Pebax
(polyether block amide), the fill ratio limit has heretofore been
found to be about 80 weight percent. Such weight percentage equates
to about 18 volume percent which requires the marker to be
excessively thick in order to achieve adequate radiopacity.
[0008] A polymeric marker is therefore needed having a
substantially higher fill ratio than has heretofore been possible.
Such marker would allow devices to be rendered highly visible
without an inordinate increase in overall profile nor a compromise
of the flexibility of the underlying component.
SUMMARY OF THE INVENTION
[0009] The invention is directed to a polymeric radiopaque marker
for a medical device.
[0010] The present invention overcomes the shortcomings of
previously described polymeric radiopaque markers by enabling a
polymer to be filled or doped with a considerably greater quantity
of a radiopaque agent than has heretofore been achievable. The
increased fill ratio nonetheless allows uniform pellets to be
compounded and an extrusion with the appropriate wall thickness to
be formed. The resulting marker provides an unprecedented
combination of radiopacity and flexibility. Such marker would allow
any of various intraluminal devices to be radiopaquely marked
including, but not limited to, coronary and peripheral balloon
catheters, stent delivery catheters, and guiding catheters as well
as guidewires.
[0011] The marker of the present invention relies on the use of
radiopaque materials with a preselected particle shape and a
preselected particle size distribution as well as the inclusion of
one or more additives in the polymer/radiopaque agent blend. A
multifunctional polymeric additive is added to the composition in
order to enhance the wetting, adhesive and flow properties of the
individual radiopaque particles by the polymer so as to cause each
particle to be encapsulated by the polymer and thereby allow the
polymer to form a continuous binder. An antioxidant may optionally
be added in order to preserve the high molecular weight of the
polymer matrix as it is exposed to the high temperatures and shear
stresses associated with the compounding and extrusion
processes.
[0012] While previous attempts to increase fill ratios have
involved tungsten powder of relatively fine particle size, the
present invention relies on the use of particles of increased size
in order to achieve such end. An increase in particle size has been
found to allow the polymer to more effectively function as a
continuous binder and thereby increase ductility at a given fill
ratio or maintain ductility at increased fill ratios. It has been
found that in constraining the average particle size to at least 2
microns and limiting maximum particle size to about 20 microns
provides the desired results. In the case of tungsten in Pebax, a
fill ratio of about 91.3 weight percent (equivalent to 36.4 volume
percent) or more is readily attainable for a polymeric marker
formed in accordance with the invention. In one embodiment, the
fill ratio is about 90.8 weight percent (34.9 volume percent) to
about 93.2 weight percent (42.7 volume percent). Additionally, it
has been found that the process by which the tungsten powder is
produced has a considerable effect on both particle size
distribution as well as the shape of the individual particles.
Tungsten powder produced by either a "pusher" process or
"atomization" process, then milled and classified has been found to
provide discrete particles having a more equiaxed shape and size
respectively and are therefore more ideally suited for the purposes
of the present invention than powders produced employing a "rotary"
process.
[0013] The marker of the present invention is manufactured by first
tumble mixing the polymer resin with a pelletized wetting agent,
such as maleic anhydride graft polyolefin resin (MA-g-PO), and an
antioxidant and then introducing the mixture into the primary
feeder of a twin screw extruder. The mixture is fed in at a
controlled mass flow rate and conveyed down the barrel length as it
is heated above its melting temperature and blended. At a point
downstream, tungsten powder is introduced into the mix at a
controlled mass flow rate via a secondary feeder. The tungsten
powder and the molten ingredients become intimately intermixed as
they are conveyed downstream and discharged through a die as molten
strands which are cooled in water and subsequently pelletized. The
markers are subsequently formed by extruding the tungsten filled
polymer onto a continuous beading of PTFE, and drawn down to yield
the desired wall thickness. The extrusion tolerances are such that
the outer diameter of the extrusion can vary by as much as 0.001
inch, which is large enough to significantly affect the radiopacity
and profile of the finished marker. Consequently, in a presently
preferred embodiment, the extrusion is hot die necked (i.e., the
extruded tube on a support mandrel, such as the PTFE beading, is
pulled through a heated die to take on the die size), to resize the
outer diameter and provide the desired wall thickness. The
extrusion is then cut to the desired lengths, preferably with the
beading still in place so as to provide support. Removal of the
beading remnant then allows the marker to be slipped onto the
medical device or component thereof to be marked and melt bonded in
place. The polymeric marker is typically a closed, solid-walled
band with a tubular or annular shape. However, the polymeric marker
can have a variety of suitable shapes. Reliance on melt bonding
obviates the need for the marker to completely surround the
underlying device. Markers can for example be longitudinally split
in half to form two markers of C-shaped cross-section. Or, solid
strands of extruded marker material may be melt bonded to one side
to form one or more longitudinal stripes or helical patterns.
[0014] During melt bonding, the polymeric marker is heated to an
elevated temperature sufficient to melt the polymeric material to
produce the melt bond. However, in one presently preferred
embodiment, the elevated temperature is low enough to minimize or
prevent flowing of the polymeric material of the marker.
Consequently, the double wall thickness (inner diameter minus outer
diameter) of the polymeric marker after melt bonding is equal to or
not substantially less than (i.e., not more than about 5 to about
25% less than) the double wall thickness prior to melt bonding.
Although some rounding of the edges of the polymeric marker may
occur during melt bonding, the maximum wall thickness of the
polymeric marker is preferably not reduced during the melt bonding.
The marker radiopacity is strongly affected by both the percent
loading of radiopaque material and the final wall thickness of the
marker. Consequently, the percent loading of radiopaque material
and the wall thickness of the finished marker are carefully
controlled to provide the desired radiopacity. If the wall
thickness of the polymeric marker is less than the required minimum
wall thickness, the radiopacity of the marker will be too low. On
the other hand, if the outer diameter/wall thickness of the
polymeric marker is greater than the required maximum outer
diameter/wall thickness, the large profile and added stiffness of
the marker will disadvantageously affect catheter performance.
Thus, the hot die necked extrusion has an outer diameter and wall
thickness which is within the minimum and maximum desired values,
so that little or no thinning of the marker is required during melt
bonding of the marker to provide the desired outer diameter. As a
result, a decrease in wall thickness which can reduce the
radiopacity of the finished marker is prevented or minimized during
bonding. In one embodiment, the polymeric marker is adhesively
bonded to the medical device or component, and as a result, the
wall thickness of the marker is not affected by the bonding
process.
[0015] Due to its high radiopacity, flexibility and melt
bondability, the marker of the present invention is readily
attached to for example the inner member of a balloon catheter, a
guidewire, and even a guide catheter tip. The attachment of
radiopaque markers of known dimensions to a guidewire or the
attachment to a guidewire of multiple radiopaque markers with known
separation distances impart a measurement capability to the
catheter that allows a physician to quickly and easily measure
lesions and decide on appropriate stent lengths.
[0016] These and other features of the present invention will
become apparent from the following detailed description of
preferred embodiments which, taken in conjunction with the
accompanying drawings, illustrate by way of example the principles
of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an enlarged side view of the radiopaque markers of
the present invention attached to a balloon catheter;
[0018] FIG. 2 is an enlarged side view of radiopaque markers of the
present invention attached to a guidewire in a preferred
configuration; and
[0019] FIG. 3 is an enlarged side view of the radiopaque markers of
the present invention attached to a guidewire in an alternatively
preferred configuration.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The present invention provides a radiopaque marker for use
on a variety of devices that is flexible, highly radiopaque and is
easily attachable to such devices by melt bonding. These properties
allow markers to be of minimal thickness and thereby minimize the
effect the marker has on the overall profile and stiffness of the
device to which it is to be attached.
[0021] In order to achieve the high fill ratios that are necessary
to attain the desired radiopacity and in order to do so without
compromising the compoundability and workability of the polymeric
material nor its ultimate strength and flexibility, a number of
different parameters have been found to be of importance. More
specifically, both the particle shape and particle size of the
radiopaque agent must be carefully controlled while the inclusion
of a wetting agent such as MA-g-PO in the polymer blend is
critical. An antioxidant may additionally be included in an effort
to reduce the adverse effect the high processing temperatures and
shear stresses may have on polymer properties.
[0022] A number of polymeric materials are well suited for use in
the manufacture of the markers of the present invention. The
material preferably comprises a low durometer polymer in order to
render the marker sufficiently flexible so as not to impair the
flexibility of the underlying medical device component to which the
finished marker is to be attached. Additionally, in one embodiment,
the polymer is preferably compatible with the polymeric material of
which the component is constructed so as to allow the marker to be
melt bonded in place. For example, in one embodiment, the polymeric
marker and at least an outer layer of the catheter shaft are formed
of the same class of the polymers (e.g., polyamides) so that they
are melt bondable together. In another embodiment, the polymeric
markers are installed on a dissimilar class of polymeric substrate,
and are retained in position by adhesion or dimensional
interference. The polymer must also impart sufficient strength and
ductility to the marker compound so as to facilitate its extrusion
and forming into a marker, its subsequent handling and attachment
to a medical device and preservation of the marker's integrity as
the medical device is flexed and manipulated during use. Examples
of such polymers include but are not limited to polyamide
copolymers like polyether block amide (PEBAX), polyetherurethanes
like PELLETHANE, polyester copolymers like HYTREL, olefin derived
copolymers, natural and synthetic rubbers like silicone and
SANTOPRENE, thermoplastic elastomers like KRATON and specialty
polymers like EVA and ionomers, etc. as well as alloys thereof. A
Shore durometer of not greater than about 63 D to about 25 D is
preferred. The preferred polymer for use in the manufacture of a
marker in accordance with the present invention is polyether block
polyamide copolymer (PEBAX), with a Shore durometer of about 40 D.
However, other classes of polymers allowing for lower durometers
may be used in the radiopaque markers, such as polyurethanes, which
may provide greater flexibility.
[0023] A number of different metals are well known to be
radiographically dense and can be used in a pure or alloyed form to
mark medical devices so as to render them visible under
fluoroscopic inspection. Commonly used metals include but are not
limited to platinum, gold, iridium, palladium, rhenium and rhodium.
Less expensive radiopaque agents include tungsten, tantalum, silver
and tin, of which tungsten is most preferred for use in the markers
of the present invention.
[0024] The control of particle size has been found to be of
critical importance for achieving the desired ultra high fill
ratios. While efforts to increase fill ratios have previously
utilized small average particle sizes (1 micron or less) so as to
minimize the ratio of particle size to as-extruded wall thickness,
it has been found that higher fill percentages can be realized with
the use of somewhat larger average particles sizes. It is desirable
in the formulation of high fill ratio compounds to have the
following attribute: 1) uniform distribution of the filler
particles, and 2) continuity of the surrounding polymer matrix, and
3) sufficient spacing between filler particles so that the polymer
matrix provides ductility to the bulk mixture to impart
processability in both the solid and molten state.
[0025] The use of larger average particle sizes results in greater
spacing between filler particles at a given percentage, thus
maintaining processability during compounding and especially
subsequent extrusion coating. The upper limit of average particle
size is determined by the wall thickness of the coating and the
degree of non-uniformity tolerable (i.e., surface defects). It has
been found that a particle size distribution having an average
particle size range of at least 2 microns to 10 microns and a
maximum particle size of about 20 microns yields the desired fill
ratio and provides for a smooth surface in the marker made
therefrom.
[0026] The control of particle shape has also been found to be of
critical importance for achieving the desired ultra high fill
ratios. Discrete particles of equiaxed shape have been found to be
especially effective, as individual particles of irregular shape,
including agglomerations of multiple particles, have been found to
adversely impact the surface, and thus, the maximum fill ratio that
is attainable.
[0027] It has also been found that the process by which certain
metal powders are produced has a profound effect on the shape of
the individual particles. In the case of metallic tungsten, the
powders may be formed by the reduction of powdered oxides through
either "rotary," "pusher" or "atomization" processing. Of these
processes, "rotary" processing has been found to yield the least
desirable shape and size distribution as partial sintering causes
coarse agglomerates to be formed which do not break up during
compounding or extrusion and thus adversely effect the marker
manufactured therefrom. Atomized powders have been reprocessed by
melting and resolidifying "rotary" or "pusher" processed powders
and result in generally equiaxed, discrete particles which are
suitable for use in the present invention. "Pusher" processed
powders are preferred due to their low cost and discrete, uniformly
shaped particles.
[0028] In order for the polymer to most effectively encapsulate
individual radiopaque particles, it is necessary for a low-energy
interface to exist between such particles and the polymer so as to
enable the polymer to "wet" the surface of the particles. The
materials should have similar surface energies to be compatible.
For materials which do not naturally have similar surface energies,
compatibility can be promoted by generating a similar surface
energy interface, i.e., a surface energy interface which is
intermediate between the natural surface energies of the materials.
Certain additives such as surfactants and coupling agents may serve
as wetting agents and adhesion promoters for polymer/metal
combinations that are not naturally compatible. It has been found
that additives containing maleic anhydride grafted to a polyolefin
backbone provide a significant benefit in this regard wherein
materials commercially available as Lotader 8200 (having LLDPE
Backbone) and Licomont AR504 (having PP backbone) were found to be
particularly effective for use with tungsten/Pebax combinations.
Emerging extrusions were found to be less susceptible to breakage,
and the melt viscosity during compounding was lower as was
manifested by a reduction in torque exerted during the extrusion
process. The use of such additives allowed compounds with higher
fill ratios to be successfully produced.
[0029] The inclusion of an antioxidant in the marker composition
has also been found to be of benefit. Commercially available
antioxidants such as Irganox B225 or Irganox 1010, have been found
to minimize degradation (i.e., reduction in molecular weight) of
the polymer matrix as it is exposed to the multiple heat and shear
histories associated with the compounding, extrusion, and bonding
processes.
[0030] The compound used for the manufacture of the marker of the
present invention is preferably made by first blending the polymer
resin and wetting agent, and optionally, an antioxidant such as by
tumble mixing after which such blend is introduced into a
twin-screw extruder via a primary feeder. The feed rate is
carefully controlled in terms of mass flow rate to ensure that a
precise fill ratio is achieved upon subsequent combination with the
radiopaque agent. The heat that the materials are subjected as they
are conveyed through the extruder causes the polymer to melt to
thereby facilitate thorough homogenization of all of the
ingredients. The radiopaque agent powder, selected for its uniform
particle shape and controlled particle size distribution as
described above is subsequently introduced into the melt stream via
a secondary feeder, again at a carefully controlled mass flow rate
so as to achieve the target fill ratio. The solid powder, molten
polymer and additives are homogenized as they are conveyed
downstream and discharged through a die as molten strands which are
cooled in water and subsequently pelletized. The preferred
extrusion equipment employs two independent feeders as introduction
of all components through a single primary feeder would require
significantly higher machine torques and result in excessive screw
and barrel wear. The powder feeder is preferentially operated in
tandem with a sidefeeder device, which in turn conveys the powder
through a sealed main barrel port directly into the melt stream. A
preferred composition comprises a fill ratio of at least 90.8
weight percent of tungsten (H.C. Starck's Kulite HC600s, HC180s and
KMP-103JP) to Pebax 40 D. A maleic anhydride source in the form of
Licomont AR504 is initially added to the polymer resin at the rate
of approximately 3 pphr while an antioxidant in the form of Ciba
Geigy Irganox B225 at the rate of approximately 2 pphr (parts per
hundred relative to the resin). The temperature to which materials
are subjected to in the extruder is about 221.degree. C.
[0031] Once the marker material has been compounded, the marker can
be fabricated in suitable dimensions by an extrusion coating
process. While free extrusion is possible, this method is
problematic due to the high fill ratios of the polymeric materials.
Extrusion onto a continuous length of beading has been found to
lend the necessary support for the molten extrudate to prevent
breakage. The support beading may take the form of a disposable,
round mandrel made of PTFE (Teflon) coated stainless steel wire or
other heat resistant material that does not readily bond to the
extrudate. By additionally limiting the area draw down ratio (ADDR)
to below 10:1 the tungsten-laden melt can successfully be drawn to
size by an extrusion puller. The beading provides the added benefit
of fixing the inner diameter and improving overall dimensional
stability of the final tungsten/polymer coating. Extrusions of a
91.3 weight percent fill ratio tungsten/Pebax composition described
above over 0.0215'' diameter PTFE beading were successfully drawn
down to a wall thickness of 0.0025'' to yield a marker properly
sized for attachment to for example a 0.022'' diameter inner member
of balloon catheter. Also, extrusion coatings of 91% compound over
0.007'' teflon coated stainless steel wire were successfully drawn
down to single wall thicknesses of 0.002'' to make guidewire
coatings.
[0032] In one embodiment, once the extrudate has cooled, the
extrusion is simply cut to the desired lengths (e.g., 1 to 1.5 mm)
of the individual markers, such as with the use of a razor blade
and reticle, preferably with the beading still in place to provide
support during cutting. The beading remnant is subsequently ejected
and the marker is slipped onto a medical device or a particular
component thereof. In one embodiment, a segment of the extrudate is
hot die necked with the beading inside to resize the outer diameter
and wall thickness of the extrudate prior to cutting into
individual markers. For example, an extrudate, having an inner
diameter of about 0.0215.+-.0.0005 inch and an outer diameter of
about 0.0275.+-.0.001 inch, is hot die necked to an outer diameter
of about 0.0265 inch to produce a double wall thickness of about
0.005.+-.0.0005 inch. To minimize part to part variability in
double wall thickness, the actual hot die size may be selected
based upon the actual beading diameter prior to hot die
necking.
[0033] Finally, the marker is attached to the underlying substrate,
preferably with the use of heat shrink tubing and a heat source
(hot air, laser, etc.) wherein the heat (171-210.degree. C.)
simultaneously causes the marker to melt and the heat shrink tubing
to exert a compressive force on the underlying molten material. To
prevent extensive dimensional changes (e.g., thinning) of the
polymeric marker, the temperatures used are below the melting
temperature, thereby relying on heat and pressure to soften the
marker and generate an adhesive bond with the underlying substrate.
For markers formed of PEBAX 40D, the temperature used is about
120-135.degree. C. Heat bonding a marker onto an underlying
component provides the added benefit of slightly tapering the edges
of the marker to reduce the likelihood of catching an edge and
either damaging the marker or the medical device during assembly or
handling of the medical device.
[0034] A marker formed as per the above described compounding,
fabricating and assembling processes, having a fill ratio of 91.3
weight percent (36.4 volume percent) with a wall thickness of
0.0025'' has been shown to have dramatically more radiopacity than
commercially available 80 weight percent compounds and comparable
to the radiopacity of 0.00125'' thick conventional Platinum/10%
Iridium markers. The radiopacity is a function of the total volume
of radiopaque material present in the marker (i.e., the product of
the volume % and the volume of the marker). In a presently
preferred embodiment, the marker is about 1.5 mm long and has a
double wall thickness of about 0.0045 to about 0.0055 inch and a
fill ratio of about 90.8 to about 93.2 weight percent of tungsten,
which provides a volume of radiopaque material substantially equal
to the volume of Platinum/10% Iridium in a 1.0 mm long, 0.0025 inch
thick (double wall) conventional Platinum/Iridium marker band.
Preferably, the volume of radiopaque material is not less than
about 30%, and the double wall thickness of the marker is at least
about 0.004 inch, to provide sufficient radiopacity. However, as
discussed above, the ability to increase the volume of the marker
by increasing the wall thickness of the marker is limited by the
resulting increase in profile and stiffness. In a presently
preferred embodiment, the double wall thickness of the marker is
not greater than about 0.006 inch.
[0035] FIG. 1 illustrates two radiopaque markers 12 attached to the
inner member 14 of a balloon catheter 16. During assembly of the
catheter 16, the markers are attached to the inner member prior to
the positioning of the inner member within the balloon 18 and
attachment thereto at 20. Fluoroscopic illumination of the device
allows the nonradiopaque balloon to be positioned relative to a
lesion by virtue of the visibility of the radiopaque markers under
fluoroscopy and their known positions relative to the balloon. The
balloon catheter 16 generally comprises an elongated shaft having
an inflation lumen and a guidewire lumen, and balloon 18 with a
proximal end and distal end sealingly secured to a distal section
of the shaft and an interior in fluid communication with the
inflation lumen. The shaft typically comprises an outer tubular
member defining the inflation lumen, and the inner tubular member
14 extending within at least a portion of the inflation lumen and
defining the guidewire lumen.
[0036] FIG. 2 illustrates a preferred embodiment of a guidewire
with a measurement feature 22 wherein a series of radiopaque
markers 24 are attached to the core member of the guidewire 24 at
preselected separation distances 26 to allow the device to be used
as a type of ruler to measure the size of a lesion. The separation
between adjacent markers may be controlled by the use of
radiotransparent tubular spacers 28 that are similarly adhered to
the underlying guidewire. Upon assembly of the radiopaque markers
and the radiotransparent spacers onto at least a distal section of
the guidewire core member, heat shrink tubing of sufficient length
is slipped over the entire section of guidewire and heated to the
appropriate temperature to cause both the markers as well as the
spacers to become adhered to the guidewire core member.
[0037] FIG. 3 illustrates an alternatively preferred embodiment of
a guidewire with a measurement feature 30 wherein an equally spaced
series of differently sized radiopaque markers 32a-e are attached
to the core member of guidewire 34 to allow the device to be used
to gauge the size of a lesion. The separation between adjacent
markers may be controlled by the use of radiotransparent tubular
spacers 36 that are similarly adhered to the underlying guidewire.
Upon assembly of the radiopaque markers and the radiotransparent
spacers onto the guidewire core member, heat shrink tubing of
sufficient length is slipped over the entire section of guidewire
and heated to the appropriate temperature to cause both the markers
as well as the spacers to become adhered to the guidewire core
member.
[0038] While a particular form of the invention has been described,
it will be apparent to those skilled in the art that various
modifications can be made without departing from the spirit and
scope of the invention. More specifically, a variety of different
polymers and radiopaque agents can be compounded using the
appropriate wetting agent, markers of different shape and
dimensions can be formed and the markers can be attached to any of
a variety of medical devices that can benefit from being
radiopaquely marked. Accordingly, it is not intended that the
invention be limited except by the appended claims.
* * * * *