U.S. patent application number 10/020521 was filed with the patent office on 2003-06-19 for catheter having improved curve retention and method of manufacture.
This patent application is currently assigned to SciMed Life Systems, Inc.. Invention is credited to Chen, John, Wang, (Bruce) Yiqun, Wang, Lixiao.
Application Number | 20030114831 10/020521 |
Document ID | / |
Family ID | 21799064 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030114831 |
Kind Code |
A1 |
Wang, (Bruce) Yiqun ; et
al. |
June 19, 2003 |
Catheter having improved curve retention and method of
manufacture
Abstract
The present invention provides a polymeric treatment for curved
regions in shaft assemblies that increases curve retention without
affecting the flexibility within these regions. More specifically,
the present invention modifies the underlying crystalline
morphology of a polymer in order to decrease crystal fracturing. In
particular, the present invention treats polymeric materials
suitable for catheter construction with a nucleating agent.
Inventors: |
Wang, (Bruce) Yiqun; (Maple
Grove, MN) ; Chen, John; (Plymouth, MN) ;
Wang, Lixiao; (Maple Grove, MN) |
Correspondence
Address: |
CROMPTON, SEAGER & TUFTE, LLC
1221 NICOLLET AVENUE
SUITE 800
MINNEAPOLIS
MN
55403-2420
US
|
Assignee: |
SciMed Life Systems, Inc.
|
Family ID: |
21799064 |
Appl. No.: |
10/020521 |
Filed: |
December 14, 2001 |
Current U.S.
Class: |
604/525 ;
264/634 |
Current CPC
Class: |
Y10T 428/1393 20150115;
A61L 29/06 20130101; A61L 29/049 20130101; Y10T 428/1352 20150115;
Y10T 428/139 20150115; A61L 29/06 20130101; A61L 29/126 20130101;
A61L 29/06 20130101; Y10S 138/08 20130101; A61L 29/06 20130101;
A61L 29/06 20130101; C08L 67/02 20130101; C08L 77/12 20130101; C08L
71/00 20130101; C08L 79/08 20130101 |
Class at
Publication: |
604/525 ;
264/634 |
International
Class: |
A61M 025/00 |
Claims
What is claimed is:
1. A catheter shaft comprising: a polymeric tubular member having a
lumen extending the length therein, wherein the tubular member
includes a pre-formed bend along a portion of the length of the
tubular member, wherein the polymeric material forming at least a
portion of the pre-formed bend includes a sufficient quantity of a
nucleating agent dispersed therein.
2. The catheter shaft of claim 1, wherein the polymeric material is
selected from the group consisting of polyamide, polyethylene
terephthalate, polyetheretherketone, polyimide, polyetherimide and
polyether block amide and mixtures thereof.
3. The catheter shaft of claim 1, wherein the nucleating agent is
selected from the group consisting of talc, silica, kaolin,
molybdenum disulfide, iron sulfide, titanium dioxide, sodium
phenylphosphanate and mixtures thereof.
4. The catheter shaft of claim 1, wherein the nucleating agent is
selected from the group consisting of sodium p-tert-butylbenzoate,
monton wax, montanic ester salts, salts of monocarboxylic acids and
polycarboxylic acids and mixtures thereof.
5. The catheter shaft of claim 1, wherein the nucleating agent is
selected from the group consisting of an ethylene and an acrylic
ester copolymer, a fumeric acid polymer, ethylene, propylene,
1,4-hexadiene, norbornadiene and mixtures thereof.
6. The catheter shaft of claim 1, wherein the nucleating agent is
present in a concentration of about 0.01% to 1.0% by weight.
7. The catheter shaft of claim 1, wherein the catheter shaft is a
portion of a guide catheter.
8. The catheter shaft of claim 1, wherein the catheter shaft is a
portion of a vascular catheter.
9. The catheter shaft of claim 1, wherein the catheter shaft is a
portion of a biliary catheter.
10. A catheter shaft comprising: a tubular member having a lumen
extending the length therein, wherein the tubular member further
comprises at least two segments having differing rigidities,
wherein at least one of the segments of the tubular member has a
pre-formed bend extending over at least a portion of the length
thereof which includes a polymer in a portion of said pre-formed
bend having a sufficient quantity of a nucleating agent dispersed
therein.
11. The catheter shaft of claim 10, wherein the polymeric material
is selected from the group consisting of polyamide, polyethylene
terephthalate, polyetheretherketone, polyimide, polyetherimide and
polyether block amide and mixtures thereof.
12. The catheter shaft of claim 10, wherein the nucleating agent is
selected from the group consisting of talc, silica, kaolin,
molybdenum disulfide, iron sulfide, titanium dioxide, sodium phenyl
phosphanate and mixtures thereof.
13. The catheter shaft of claim 10, wherein the nucleating agent is
selected form the group consisting of sodium p-tert-butyl benzoate,
monton wax, montanic ester salts, salts of monocarboxylic acids and
polycarboxylic acids and mixtures thereof.
14. The catheter shaft of claim 10, wherein the nucleating agent is
selected from the group consisting of an ethylene and an acrylic
ester copolymer, a fumeric acid polymer, ethylene, propylene,
1,4-hexadiene, norbornadiene and mixtures thereof.
15. The catheter shaft of claim 10, wherein the nucleating agent is
present in a concentration of about 0.01% to about 1.0% by
weight.
16. The catheter shaft of claim 10, wherein the catheter shaft is a
portion of a guide catheter.
17. The catheter shaft of claim 10, wherein the catheter shaft is a
portion of a vascular catheter.
18. The catheter shaft of claim 10, wherein the catheter shaft is a
portion of a biliary catheter.
19. A process for improving curve retention in catheters having a
pre-formed curve, the process comprising: providing a polymeric
material; providing a nucleating agent; admixing the nucleating
agent with the polymeric material; and extruding the admixed
polymeric material and forming a catheter shaft having a pre-formed
curve along a portion of the catheter shaft's length.
20. The process of claim 19, wherein the pre-formed curve is formed
prior to cooling the extruded polymeric material, followed by
cooling the pre-formed curve.
21. The process of claim 19, wherein the pre-formed curve is formed
subsequent to cooling the extruded polymeric material in a further
step comprising heating a portion of the catheter shaft and forming
the pre-formed curve, followed by cooling.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to the field of
catheter devices having a pre-formed flexible curve along the
length of the catheter body. More specifically, the present
invention relates to the use of certain polymeric materials, and
the treatment of those polymeric materials, to manufacture
pre-formed curves that are more flexible and have a greater curve
retention.
BACKGROUND OF THE INVENTION
[0002] This invention resides in the construction and use of
catheters for interventional procedures in such fields as
cardiology, neurology, urology and gastroenterology. Design
features are incorporated in these catheters to facilitate their
use in: (1) the advancement of the catheter through a patient's
bodily passages to reach specific sites in vessels or chambers of
interest; (2) correct placement of the catheter's distal tip at a
targeted site within the patient, and finally (3) holding the
catheter at a targeted site while procedures with other devices are
completed including while the site moves in response to normal
bodily functions such as breathing or a heart beat.
[0003] Guide catheters are one type of catheter utilized in these
procedures. Guide catheters are relatively large lumen catheters
used to guide smaller diameter catheters such as therapeutic,
diagnostic or imaging catheters into bodily passages that are
curved or branched. More specifically, guide catheters provide a
conduit for at least a portion of the path followed by these
additional catheters to desired target sites within a patient's
vasculature or other body lumen or organ. In order for the catheter
to be effective, however, the catheter must be able to traverse the
tortuous pathways of a patient's vasculature or other anatomy in a
manner as atraumatic as possible.
[0004] In order to function efficiently, guide catheters generally
have a relatively stiff main body portion and a relatively soft
distal portion. The stiff main body portion gives the guide
catheter sufficient pushability and torqueability to allow the
guide catheter to be inserted percutaneously into an artery, moved
and rotated in the vasculature to position the distal end of the
catheter at the desired site. However, the distal portion should
have sufficient flexibility so that it can track over a guide wire
and be maneuvered through a tortuous path to the treatment site. In
addition, a soft distal tip at the very end of the catheter should
be used to minimize the risk of causing trauma to a blood vessel
while the guide catheter is being moved through the vasculature to
the proper position.
[0005] Thus, to limit insertion time and discomfort to a patient, a
catheter must be stiff enough to resist the formation of kinks,
while at the same time, the catheter must possess flexibility to be
responsive to maneuvering forces when guiding the catheter through
the vascular system. In addition to these features, catheters must
be designed to reach a targeted site and maintain the position at
that site throughout the procedure. Guide catheters typically have
pre-formed bends formed along their distal portion to facilitate
both the placement of the distal end of the guide catheter and to
the ostium of a particular coronary artery of a patient and to
remain stable once in position. Likewise, angiographic catheters,
which are used in evaluating the progress of coronary artery
disease in patients, generally have a desired distal end curvature
configuration to facilitate both the steering of the catheter to a
particular artery to be examined and to provide a stable
positioning of the catheter's distal portion.
[0006] As stated above, improved stabilization of a catheter's
position is often achieved through curves or bends imparted to the
catheter by the manufacturer. Some of these pre-formed curves
function by anchoring the catheter against an opposing wall within
a patient's vasculature or other anatomy. Proper anchoring is often
achieved by matching the predisposed shape of the catheter with the
general shape of the targeted site. Often a curve is imparted to
the distal end of a catheter with the intention of placing the
catheter's distal opening at a desired location in the vessel, or
alternatively, on the vessel wall. A guide catheter especially
designed for a procedure in a coronary artery, for example, is
shaped such that when the guide catheter is inserted into the
femoral artery and through the aorta of a patient, the curvature of
the catheter will place its distal tip inside one of the coronary
ostia. Thus, a guide catheter for the right coronary artery is
shaped differently than one for the left coronary artery. A guide
catheter designed to provide access to a carotid artery is again
shaped differently. Likewise, guide catheters of still other shapes
are designed for other bodily passages and regions of interest.
Further, there are differences between patients' body structures
which require varying sizes of each curve type.
[0007] Guide catheters currently available from manufacturers are
designed in a variety of shapes specific for different bodily
passages and procedures. Those of skill in the art recognize these
different shapes by names such as Judkins Right, Judkins Left,
Amplatz Right, Amplatz Left, Bentson, Shepherd Hook, Cobra,
Headhunter, Sidewinder, Newton, Sones and others, each formed in a
different shape. Most of these different shapes are manufactured in
gradations of size and/or curvature to accommodate differences
among individual patients.
[0008] When a guide catheter is inserted and advanced within a
patient, its pre-formed curved shape is often distorted by the
tortuous vasculature and connecting passages of a patient's
vasculature. The bends must essentially become straight as the
catheter is slowly advanced within the anatomy, usually over a
guidewire. In order for the pre-formed manufactured curves or bends
to be effective in properly seating the guide catheter, however,
the imparted curves must be capable of returning their pre-formed
shape or at least a predictable variant of the original shape. This
is referred to herein as curve retention. Similarly, after the
guide catheter is properly seated, the curves of the catheter must
retain the catheter's positioning despite the constant movements in
response to normal bodily functions such as breathing or a
heartbeat or when other devices are passed through the lumen of the
positioned catheter.
[0009] Manufacturers, therefore, often add filler material, or
alternatively, use stiffer materials in curved regions to increase
curve retention. Although adding materials achieves better curve
retention upon placement, decreasing the catheter's flexibility in
curved regions causes significant alterations in the catheter's
overall performance. Specifically, the catheter's trackability is
often affected. For guide catheters having curves imparted within
the distal regions of the catheter, the effect in trackability
performance can be quite significant. Thus, it is a goal of the
present invention to create a catheter design having exceptional
curve retention without diminishing the catheter's flexibility and
overall trackability performance.
SUMMARY OF THE INVENTION
[0010] The present invention provides a polymeric treatment for
curved regions in shaft assemblies that increases curve retention
without significantly affecting the flexibility within these
regions. More specifically, the method of the present invention
modifies the underlying crystalline morphology of a polymer in
order to decrease crystal fracturing. In particular, the present
invention treats polymeric materials suitable for catheter
construction with a nucleating agent. A nucleating agent is a
material that affects the number and size of crystals formed during
the nucleation process. Nucleating agents introduce more nuclei
into a polymer's nucleation process. Therefore, under similar
cooling procedures, a polymer treated with a nucleating agent
results in a rise in the number of crystals formed and a reduction
in the overall size of each crystal when compared with an untreated
polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The appended claims particularly point out and distinctly
claim the subject matter of this invention. The various objects,
advantages and novel features of this invention will be more fully
apparent from a reading of the following detailed description in
conjunction with the accompanying drawings in which like reference
numerals refer to like parts, and in which:
[0012] FIG. 1 is a partial plan view of a catheter assembly in
accordance with the present invention;
[0013] FIG. 2A is an illustration of the crystal morphology of a
polymeric material lacking nucleating agent treatment;
[0014] FIG. 2B is an illustration of the crystal morphology of the
same polymeric material as shown in FIG. 2A, having been treated
with a nucleating agent; and
[0015] FIG. 3 is partial plan view of a diagnostic catheter
assembly in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The following detailed description should be read with
reference to the drawings, in which like elements in different
drawings are numbered identically. The drawings, which are not
necessarily to scale, depict selected embodiments and are not
intended to limit the scope of the invention. Examples of
construction, materials, dimensions, and manufacturing processes
are provided for selected elements. All other elements employ that
which is known to those skilled in the field of the invention.
Those skilled in the art will recognize that many of the examples
provided have suitable alternatives that may be utilized.
[0017] Referring now to the drawings, FIG. 1 is a partial plan view
of a catheter in accordance with the present invention. The
catheter of the present invention may be used in conjunction with
most catheter devices suited for placement within the human
anatomy. As such, the catheter assembly may be utilized in
cardiology, neurology, urology and gastroenterology, among others.
In gastroenterological devices, the catheter of the present
invention may be incorporated into the shaft design of an
endoscope, or alternatively, into a biliary catheter. Likewise, in
vascular devices, the catheter assembly 10 of the present invention
may be incorporated into the shaft design of a guide or diagnostic
catheter, or in the alternative, into the vascular catheters used
to ultimately treat the maladies requiring the medical
procedure.
[0018] For illustrative purposes, the catheter 10 is shown as a
guide or diagnostic catheter, which is representative of a catheter
that can incorporate the present invention. Other intravascular
catheter embodiments are additionally suitable without deviating
from the spirit and scope of the present invention.
[0019] The guide catheter 10 includes a shaft assembly 12. A
conventional manifold assembly 14 is connected to the proximal end
of the shaft assembly 12. The proximal end of the shaft assembly 12
attaches to a strain relief 16 that further extends into the
manifold assembly 14. The strain relief 16 is generally made of a
polyurethane material that snap-fits into the manifold assembly 14
at one end. The other end of the strain relief 16 is generally
adhesively bonded to the shaft assembly 12, forming a continuous
and sealed fluid connection from the proximal end of the manifold
assembly 14 to the distal end of the shaft assembly 12.
[0020] A single manifold portion 18 or multiple manifold ports 18
as shown in FIG. 1 extend from the manifold assembly 14 for
attaching and fluidly connecting ancillary apparatus to a lumen
extending through the guide catheter. Each manifold port 18
includes a lumen terminating into either a common lumen or a
dedicated lumen extending within the shaft assembly 12 (e.g., a
guidewire lumen). Functionally, the manifold assembly 14
additionally provides a convenient place for a physician to apply
longitudinal or rotational forces in order to manipulate the guide
catheter during a medical procedure.
[0021] The dimensions and materials used in making the shaft
assembly 12 are selected based upon the desired catheter
application. For instance, a guide catheter 10 is generally
characterized as having a multi-layer tubular member construction.
This tubular member includes at least a single lumen extending the
length of the shaft assembly 12. The lumen within the guide
catheter 10 possesses an inner diameter capable of receiving
another catheter, preferably a diagnostic catheter. Since many
diagnostic catheters have outer diameters in the range of 5F-10F, a
guide catheter must either accommodate the largest diagnostic
catheter, or identify those catheter sizes the guide catheter 10
may receive. The dimensions of guide catheters are well known in
the art.
[0022] Materials used to form the guide catheter 10 vary depending
upon the stiffness desired for the shaft assembly 12. Nylon and
similar polyamides such as DURETHAN.RTM. (available from Bayer) are
particularly suitable for rigid tubular members. Other suitable
materials for a rigid tubular member include polyetheretherketone
(PEEK), polyimide (PI), and polyetherimide (PEI). Rigidity may
additionally be imparted to the tubular member by incorporating a
braid on or within the tubular member. Polyether block amide
(PEBA), in contrast to the rigid polyamides, is a relatively
flexible polymeric material having a durometer of approximately
70D. Finally, the use of a polyamide such as CRISTAMID.RTM.
(available from Elf Atochem) imparts a slightly less rigid
durometer than the rigid polyamides and slightly greater than the
flexible PEBA material.
[0023] Disposed upon the distal end of the guide catheter 10 is a
distal tip 20. The distal tip 20 generally comprises a soft
polymeric material that allows the guide catheter 10 to navigate
and traverse the tortuous pathways of a patient's vasculature in a
manner as atraumatic as possible. Materials suitable for the distal
tip 20 include a polyethylene, polyamide, or block copolymer such
as PEBAX.RTM. having a lower durometer than the proximal shaft
materials. In preferred embodiments, a distal tip 20 comprising a
polymeric material having a durometer of about 28D is heat welded
or bonded to the distal end of the tubular member. In an
alternative embodiment, the last 1/2 to 1 mm of the tip at its
distal end is made of a different material from the tip material to
form a tip extension. In particular, the last 1/2 to 1 mm is made
from a material that is more durable relative to the softer tip
material. In particular, the more durable material will resist
deforming or tearing when in use, such as in tracking the patient's
tortuous anatomy. For example, this last 1/2 mm to 1 mm may be
manufactured from Marlex high-density polyethylene having
approximately a 63D durometer. This distal tip 20 material
selection often improves the integrity of the tip region at its
distal-most end.
[0024] In yet other embodiments, the distal tip 20 is molded to aid
in catheter navigation, or alternatively, in a manner that more
securely engages the distal tip 20 with a targeted site within the
patient's anatomy. Distally tapering a distal tip 20 from a larger
outer diameter to a smaller outer diameter enhances navigation of
guide catheter 10. A smaller distal tip 20 allows the guide
catheter 10 to more readily follow passages that are curved or
branched.
[0025] As described in detail above, the stabilization of a guide
catheter's position within a patient's anatomy is often achieved
through curves or bends 22 imparted into the shaft assembly by the
manufacturer. These pre-formed curves 22 act by anchoring a
selected portion of the shaft assembly 12 against an opposing wall
within a patient's vasculature or other body portion. Proper
anchoring is often achieved by matching the predisposed shape of
the curved shaft assembly 12 with the general curved anatomical
shape around a targeted site. In vascular procedures involving
treatment to one of the coronary arteries, often a curve 22 is
imparted to the distal end of a shaft assembly 12 with the
intention of placing the catheter's distal tip 20 at a desired
angle. A guide catheter 10 especially designed for a procedure in a
coronary artery, for example, has a shaft assembly 12 shaped so
that when the guide catheter 10 is inserted through the aorta of
the patient, the curvature of the catheter's shaft assembly 12 will
place its distal tip 20 at an angle that engages one of the
coronary ostia.
[0026] Guide catheters currently include a variety of shapes
specific for different bodily passages and procedures. Those of
skill in the art recognize these different shapes by names such as
Judkins Right, Judkins Left, Amplatz Right, Amplatz Left, Bentson,
Shepherd Hook, Cobra, Headhunter, Sidewinder, Newton, Sones and
others, each formed in a different shape. The guide catheter 10 of
FIG. 1 generally depicts a curve. Although one selected curve is
shown in detail, additional pre-formed curves and bends, being
known in the art, and including those listed above, are also
incorporated as within the scope of the present invention. In order
to understand how pre-formed curves and bends 22 are imparted to a
guide catheter 10, and more specifically, how those bends 22 retain
their shape, it is important to understand the physical
characteristics of the polymers forming the curves 22.
[0027] Certain polymeric materials possess a crystalline
microstructure. A polymer's flexibility, tensile strength and
hardness are all directly related to the makeup of that polymer's
crystalline microstructure. In particular, these physical
attributes are greatly influenced by how the crystalline
microstructure was initially developed, under the nucleation
process. Nucleation is the process by which crystals 28 are formed.
The nucleation process starts through the introduction of a foreign
substance that acts as a nucleus 30 for the developing crystal 28.
Under normal reaction conditions, nuclei 30 used for the nucleation
process are generally naturally occurring impurities in the
polymeric material itself. The first beginnings of a crystal 28
form on these nuclei 30. Once started, these crystals 28 quickly
propagate into larger crystals by accretion. FIG. 2A illustrates
the crystal 28 morphology of a typical polymeric material suitable
for the present invention. The Figure depicts numerous individual
crystals 28 each having a nucleus 30, and an array of fine grain
structures 32 radiating from the nucleus 30.
[0028] The crystalline morphology of a polymeric catheter tubular
member is developed after the tubular member is extruded. The
molten polymeric material is shaped into a desired form and then
cooled to retain that desired shape. During the cooling process,
and more generally during the nucleation process, the crystals 28
propagate to support the desired shapen framework. The completion
of the nucleation and cooling process results in a crystalline
microstructure not unlike that depicted in FIG. 2A.
[0029] For some polymers, the nucleation process is very fast, and
for other polymers, the process is so slow that the polymer
generally retains an amorphous morphology. Thus, a key to
understanding a polymer's crystalline microstructure, and later in
manipulating that microstructure, is through quantifying the
polymer's crystal growth rate. The crystal growth rate for any
particular polymer is influenced by the polymer's nucleus density,
the growth rate of crystals 28 in the polymer and the degree of
cooling of the polymer melt. Materials suitable for forming the
shaft assembly 12 of the present invention (PEEK, PI, PEI, PEBA and
certain polyamides) all possess crystal growth rates that support a
crystalline morphology. Moreover, these materials are quantified as
having crystal growth rates that permit their crystalline
microstructure to be modified during the nucleation process.
[0030] Modification of the crystalline microstructure is desirable
in order to overcome some shortcomings in traditional manufacturing
processes. Specifically, it is desirable to modify the crystalline
microstructure in guide catheters 10 having pre-formed bends and
curves 22. Under typical manufacturing processes, crystals 28
develop large elongated fine grain structures 32 that radiate from
the crystal's nucleus 30. The relative size of crystals 28 makes
them prone to fracturing along their elongated fine grain
structures 32. Consequently, fracturing of the elongated fine grain
structures 32 cause the polymeric material, as a whole, to lose
retention in its imparted shape. Crystal fracturing is a particular
problem in curved areas 22 of a guide catheter 10 where curve
retention is paramount to stabilizing the guide catheter's position
within a patient's anatomy.
[0031] When a guide catheter 10 is inserted and advanced within a
patient, its pre-formed curved shape is distorted (essentially
straightened) by the tortuous vasculature and connecting passages
of a patient's vasculature. The bends 22 straighten as the guide
catheter 10 is slowly advanced within the anatomy. Such unavoidable
manipulations to the curved regions 22 of the guide catheter 10
cause the underlying crystalline microstructure to fracture. Once
fractured, the guide catheter 10 is unable to retain its exact
pre-formed shape or a predictable final shape. In order for the
pre-formed manufactured curves 22 to be most effective in properly
seating the guide catheter 10, however, the imparted curves 22 must
be capable of retaining their pre-formed shape or a predictable
final shape.
[0032] Current manufacturing processes compensate for the loss of
curve retention by adding filler material, or alternatively, by
using stiffer materials within the curved regions 22. Although
these modifications increase curve retention, their addition also
decreases the flexibility of guide catheter 10 within these curved
regions 32. Moreover, a loss in flexibility within the curved
regions 32 of the guide catheter 10 may also significantly alter
the overall performance of guide catheter 10. Specifically, the
guide catheter's trackability is often affected. For guide
catheters 10 having curves 22 imparted within the distal regions of
the guide catheter 10, the effect on trackability performance can
be quite significant. The present invention provides a polymeric
treatment for curved regions 20 in shaft assemblies that increases
curve retention without affecting the flexibility within these
regions.
[0033] The present invention modifies the underlying crystalline
morphology of a polymer in order to decrease crystal fracturing. In
particular, the present invention treats polymeric materials
suitable for guide catheter 10 construction with a nucleating
agent. A nucleating agent is a material that affects the number and
size of crystals formed during the nucleation process.
[0034] FIG. 2B depicts the same polymeric material shown in FIG.
2A. However, the material in FIG. 2B has been treated with a
nucleating agent. Nucleating agents introduce more nuclei into a
polymer's nucleation process. Therefore, under similar cooling
procedures, a polymer treated with a nucleating agent results in an
increase in the number of crystals 28 formed and a reduction in the
overall size of each crystal 28, when compared with an untreated
polymer under the same conditions. The discrepancy in crystal 28
number and size is best illustrated by comparing FIG. 2A
(untreated) with FIG. 2B (treated with nucleating agents).
[0035] As described above, crystal fracturing occurs along the
elongated fine grain structures 32 of the crystal 28. With
nucleating agent treated polymers, however, the fine grain
structures 32 are not highly elongated. Individual crystals 28 are
highly crowded in nucleating agent treated polymers. As a result,
crystal growth accretion is extremely short before a crystal 28
abuts a neighboring crystal 28. Thus, the elongated fine grain
structures 32 are also very short. It is these shorter fine grain
structures 32 that resist fracturing as a result of stresses
applied to the crystalline framework.
[0036] Longer elongated fine grain structures 32 (seen in FIG. 2A)
are more susceptible to fracturing because individual crystals 28
become weaker with increased size. Shorter elongated fine grain
structures 32 (which cannot be fully illustrated due to the compact
size of each crystal in FIG. 2B) are unlikely to fracture because
of their compact size. This resistance to fracturing makes
nucleated polymers particularly useful in the bends and curves of a
catheter. In particular, such treated curves and bends fail to
deform from their originally imparted configuration when advanced
through a patient's anatomy. Moreover, these bends and curves are
also more likely to retain their positioning within a patient's
anatomy despite constant movements in response to normal bodily
functions such as breathing and heartbeat. These attributes instill
physician and patient confidence, alike, when using highly
predictable guide catheters. The physician may feel comfortable
that the angle imparted outside of a patient will be reproduced and
be retained when the guide catheter 10 is inserted within the
patient at the targeted site.
[0037] A number of nucleating agents suitable for shaft assembly 12
construction are commercially available. In a presently preferred
embodiment, inorganic additives, organic additives and polymers are
preferred nucleating agents. Examples of inorganic additives
include, but are not limited to, talc, silica, kaolin, molybdenum
disulfide, iron sulfide, titanium dioxide and sodium
phenylphosphonate. Examples of organic additives include, but are
not limited, to sodium p-tert-butylbenzoate, monton wax, montanic
ester salts, salts of monocarboxylic acids and polycarboxylic
acids. Examples of polymers include, but are not limited to,
ethylene and acrylic ester copolymers, fumeric acid polymers,
ethylene, propylene 1,4-hexadiene and norbornadiene. These
nucleating agents possess superior nucleation rates for materials
suitable for forming the guide catheter 10. More specifically,
these nucleating agents are particularly suitable for polymeric
materials used to form the pre-formed bends and curves 22 of
particular catheter assembly embodiments. Utilization of additional
nucleating agents suitable for the preferred polymeric materials
listed above, being known in the art, is also incorporated as
within the scope of the present invention.
[0038] Nucleating agents are commercially available in a variety of
differing material states. For example, specific nucleating agents
are commercially available as powders, pastes and liquids. The use
of one material state may be more appropriate than another
depending upon the manner of manufacturing of the resulting
catheter device. Nucleating agents in powder form are particularly
suited for incorporation within a polymeric material. The powdered
nucleating agent is measured, added and dispersed within the
polymeric material to maintain a specified concentration throughout
the mixture. The required ratio of nucleating agent to polymer that
initiates the desired change in crystalline morphology may vary
depending upon the specific polymeric material used. In certain
polymeric materials, any further increases in the required
concentration ratio fail to further improve the crystalline
microstructure of the polymer. In some embodiments, the ratio of
nucleating agent to polymer is about 0.5% to about 99.5% by weight.
In preferred embodiments, the nucleating agent is present in a
concentration of about 0.01% to about 1.0% by weight.
[0039] Once the nucleating agent containing polymer is properly
admixed, the polymeric mixture is then fed into an extruder. The
extruder then dispenses the admixed polymeric material to form a
tubular member, and this member is configured to a desired shape.
Nucleating agents in paste and liquid form are additionally
suitable for this manufacturing method. Alternatively, the desired
shape can be formed in a subsequent heat treatment process wherein
a select portion including a curve is melted and recrystallized in
a desired configuration.
[0040] As discussed above, the catheter assembly of the present
invention may also be incorporated into other catheters.
Specifically, the multi-lumen shaft assemblies of balloon
dilatation catheters 40 are suited for the catheter assembly
improvement of the present invention. The basic construction and
use of multi-lumen balloon dilatation catheters 40 are all well
known in the art. An example of an OTW catheter may be found in
commonly assigned U.S. Pat. No. 5,047,045 to Arney et al. An
example of an SOE catheter is disclosed in commonly assigned U.S.
Pat. No. 5,156,594 to Keith.
[0041] Multi-lumen catheter 40 construction generally includes the
use of an inner tubular member 42 and an outer tubular member 44.
In one embodiment, the spatial orientation of the two tubular
members is such that the outer tubular member 44 is coaxially
displaced over the inner tubular member 42 defining an annular
inflation lumen therebetween. This spatial relationship is best
illustrated with reference to FIG. 3.
[0042] Materials used to form the outer tubular member may vary
upon the stiffness desired for the shaft assembly 12. Nylon and
similar polyamides such as DURETHAN.RTM. (available from Bayer) are
particularly suitable for rigid outer tubular member 44. Other
suitable materials for a rigid outer tubular member 44 include
polyetheretherketone (PEEK), polyimide (PI), and polyetherimide
(PEI). Polyether block amide (PEBA), in contrast to the rigid
polyamides, is a relatively flexible polymeric material having a
durometer of approximately 70D. Finally, the use of a polyamide
such as CRISTAMID.RTM. (available from Elf Atochem) imparts a
slightly less rigid durometer than the rigid polyamides and
slightly greater than the flexible PEBA material. All of these
materials possess crystal growth rates that support a crystalline
morphology. Moreover, these materials are quantified as having
crystal growth rates that permit their crystalline microstructure
to be modified during the nucleation process.
[0043] The inner tubular member 42 defines a guidewire lumen, which
provides a passage for a guidewire 46. The inner tubular member 42
is generally made of polyethylene such as Marlex HDPE. In
alternative embodiments, the inner tubular member is made of, or
lined with, a lubricious material such as polytetrafluoroethylene
(PTFE). Materials suitable for forming the inner tubular member 42
are generally classified as having a rapid crystallization growth
rate. In contrast to materials forming the outer tubular member 44,
materials forming the inner tubular member 42 generally possess
such rapid crystal growth rates that they fail to support a
crystalline morphology that may be modified using nucleating
agents.
[0044] The benefits of modifying the outer tubular member 44 may be
transferred to the inner tubular member 42, and thereby, to the
balloon dilatation catheter 40 as a whole. Because of the spatial
relationship within the multi-lumen catheter assembly, the outer
tubular member 44 restrains the inner tubular member 42. Therefore,
modifying the outer polymeric structure of tubular member 44, in
effect, also modifies the performance characteristics experienced
by the inner tubular member 42. Nucleating agent modifications to
the outer tubular member 42 are similar to those with reference to
the guide catheter assembly 16 of FIG. 1.
[0045] Numerous characteristics and advantages of the invention
covered by this document have been set forth in the foregoing
description. It will be understood, however, that this disclosure
is, in many respects, only illustrative. Changes may be made in
details, particularly in matters of shape, size and ordering of
steps without exceeding the scope of the invention. The invention's
scope is of course defined in the language in which the appended
claims are expressed.
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