|
Medical Patent Abstract
Various coupling agents are disclosed to form lap joints between
metallic and polymeric surfaces within catheters and other medical
devices. The coupling agents disclosed in the present invention
can be applied directly to a metallic surface, or the coupling agents
may be incorporated within a polymeric material. In certain circumstances,
the mere application of the coupling agent between the two dissimilar
materials provides sufficient adhesive strength to form a fatigue-free
lap joint bond. Alternative methods utilize coupling agents as primers
for later thermal bonding and laser welding procedures that form
lap joint bonds.
Medical Patent Claims
What is claimed is:
1. In a catheter having a lap joint between a metallic tubular
member and a polymeric tubular member, the improvement in the catheter
comprising: a coupling agent, wherein the coupling agent is disposed
between the metallic tubular member and the polymeric tubular member
in the lap joint, the coupling agent having a first functional group
and second functional group, the first functional group providing
bonding adhesion to the metallic tubular member, the second functional
group providing bonding adhesion to the polymeric tubular member,
wherein the coupling agent maintains bonding adhesion between the
metallic tubular member and the polymeric tubular member when in
use, wherein the coupling agent is a functionalized titanate.
2. The improvement of claim 1, wherein the first functional group
of the coupling agent comprises at least one hydrolyzable functional
group.
3. The improvement of claim 2, wherein the second functional group
of the coupling agent comprises at least one (meth)acrylate monomer.
4. The improvement of claim 1, wherein the second functional group
of the coupling agent comprises of at least one amine monomer.
5. The improvement of claim 1, wherein the functionalized titanate
is neopentyl(diallyl)oxy,tri(dioctyl)pyro-phosphato titanate.
6. The improvement of claim 1, wherein the functionalized titanate
is neopentyl(diallyl)oxy,tri(N-ethylenediamino)ethyl titanate.
7. The improvement of claim 1, wherein the functionalized titanate
is neopentyl(diallyl)oxy,tri(m-amino)phenyl titanate.
Medical Patent Description
TECHNICAL FIELD
The present invention relates generally to the field of intravascular
medical devices having a polymeric material disposed directly upon
a metallic surface of the medical device. More specifically, the
present invention relates to the use of a coupling agent to improve
the physical properties, processing and performance of a bond formed
between a metallic surface and a polymeric overlay in a catheter
shaft, as well as other similar medical devices.
BACKGROUND OF THE INVENTION
Intravascular diseases are commonly treated by relatively non-invasive
techniques such as percutaneous transluminal angioplasty (PTA) and
percutaneous transluminal coronary angioplasty (PTCA). These therapeutic
techniques are well known in the art, and typically involve the
use of a balloon catheter with a guidewire, possibly in combination
with other intravascular devices such as stents. A typical balloon
catheter has an elongate shaft with a balloon attached proximate
the distal end and a manifold assembly attached to the proximal
end. In use, the balloon catheter is advanced over the guidewire
such that the balloon is positioned adjacent a restriction in a
diseased vessel. The balloon is then inflated, and the restriction
in the vessel is opened.
There are three basic types of intravascular catheters for use
in such procedures including fixed-wire (FW) catheters, over-the-wire
(OTW) catheters and single-operator-exchange (SOE) catheters. The
general construction and use of FW, OTW and SOE catheters 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 balloon catheter is disclosed in commonly assigned
U.S. Pat. No. 5,156,594 to Keith.
The pushability and the trackability of a catheter are two performance
characteristics essential to the success of intravascular catheters
in medical procedures. Pushability refers to the catheter's ability
to transmit force from the proximal end of the catheter to the distal
end of the catheter. Trackability refers to the catheter's ability
to navigate the tortuous vasculature of a patient. The trackability
of a particular catheter design is analyzed in terms of the trackability
of the distal portion of the catheter. The distal portion is the
section of the catheter that must track the guidewire through the
small tortuous vessels of a patient's vasculature. The size of the
distal tip, the flexibility of the distal tip and the lumen diameter
all influence the trackability of a catheter. Imparting more flexibility
to the distal portion of a catheter, in particular, is found to
improve catheter trackability. Moreover, increasing the flexibility
within the distal tip improves handling and navigation over a guidewire.
Materials particularly suitable for enhancing the pushability of
a catheter also decrease a catheter's trackability, and the converse.
For example, if a catheter is comprised entirely of a flexible polymeric
material, the catheter loses pushability and may be unable to drive
the balloon to its proper position within a patient's vasculature.
Likewise, if a catheter is comprised entirely of a rigid polymeric
material, the catheter may be unable to navigate the tortuous pathways
of a patient's vasculature. As a result, prior art catheter manufacturers
have reached compromises in materials and construction in order
to accommodate these two conflicting performance characteristics.
In efforts to accentuate both pushability and trackability within
a single catheter design, manufacturers have experimented with various
catheter materials. A specific example of such material selection
is the use of hypotube tubing. The term "hypotube," as
used herein, refers generally to a thin-walled, high-strength metallic
tube having a lumen extending the length therein. The hypotube is
preferably a stainless steel hypodermic tube that exhibits superior
pushability characteristics.
Additionally, manufacturers have incorporated these various materials
at particular locations on a catheter. Strategically positioning
these materials along the length of a catheter frees manufacturers
from the performance compromises associated with prior art catheters.
For example, often the hypotube construction is incorporated within
the proximal shaft region of a catheter, either entirely or in part,
due to its superior pushability characteristics. Alternatively,
a flexible polymeric material, such as high-density polyethylene,
is incorporated within the distal shaft region of the same catheter.
An example of a catheter incorporating the enhanced pushability
performance associated with a hypotube with the improved trackability
of a flexible distal region is disclosed in U.S. Pat. No. 5,567,203,to
Euteneuer, et al., the disclosure of which is incorporated herein
by reference. In some embodiments, the Euteneuer et al. patent discloses
an intravascular balloon catheter having a proximal hypotube shaft
segment, a distal polymer shaft segment, a distally-mounted inflatable
balloon segment, and a hollow tubular member having a proximal end
connected to the distal end of the hypotube shaft segment such that
the lumen of the hollow tubular member is in communication with
the exterior of the balloon catheter, and the distal end of the
hollow tubular member is connected to the distal end of the balloon.
The above-described materials that, in combination, accentuate
medical device performance also tend to adhere poorly to one another.
Bonds formed between these dissimilar materials are often exposed
to stresses. Improvement in the bond between metal and polymeric
components of a catheter shaft is desirable.
SUMMARY OF THE INVENTION
The present invention overcomes many of the disadvantages of the
prior art by providing an improved lap joint between metallic and
polymeric surfaces of catheters and other similar intravascular
medical devices. The present invention also provides various coupling
agents to increase the bonding affinity between otherwise dissimilar
materials of a lap joint in an intravascular catheter.
The present invention discloses specific families of coupling agents
that are particularly suitable for bonding polymeric materials to
the metallic components or frameworks of medical devices. In particular,
the present invention discloses specific coupling agents capable
of forming a fatigue-free catheter lap joint at room temperature.
The present invention additionally discloses coupling agents that
are particularly suited for methods of lap joint manufacturing utilizing
thermal bonding and/or laser welding.
In another embodiment of the present invention, a process is disclosed
for improving bonding in lap joints between metallic surfaces and
polymeric surfaces in catheter shafts. In particular, coupling agents
are disclosed for the process that may be applied directly to a
metallic surface, or alternatively, the coupling agents may be incorporated
within a polymeric material that is later extruded over the metallic
surface of the medical device.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 is a partial plan view of a catheter assembly depicting
potential locations for lap joints in accordance with the present
invention;
FIG. 2 is a partial cross-sectional view of a portion of the catheter
assembly of FIG. 1 having a lap joint between a metallic tubular
member and a polymeric tubular overlay;
FIG. 3 is a partial cross-sectional view of a single operator exchange
guidewire port joint of the catheter of FIG. 1 including a metallic
tubular member joined with two polymeric members; and
FIG. 4 is a cross-sectional view at 4-4 of FIG. 3 depicting further
details of the joint.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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.
Referring now to the drawings, FIG. 1 is a schematic plan view
of a single operator exchange (SOE) dilation balloon catheter 10,
which is representative of one type of catheter that can incorporate
bonds of the present invention. Other intravascular catheter embodiments
are additionally suitable without deviating from the spirit and
scope of the present invention. For example, intravascular catheters
suitable for incorporating the present invention include fixed-wire
(FW) catheters and over-the-wire (OTW) catheters.
The balloon catheter 10 includes a shaft assembly 12 and a balloon
assembly 14 connected proximate the distal end of shaft assembly
12. The proximal end of the shaft assembly 12 extends into a manifold
assembly 16 adhesively bonded to the shaft assembly 12. A manifold
port 20 extends from the manifold assembly 16 for attaching and
fluidly connecting ancillary apparatus to a lumen extending through
the balloon catheter 10. Multiple manifold ports can be included
terminating into either a common lumen or a dedicated lumen extending
within the shaft assembly 12 (e.g., a guidewire lumen in an OTW
catheter). Functionally, the manifold assembly 16 additionally provides
a convenient place for a physician to apply longitudinal or rotational
forces in order to manipulate the catheter 10 during a medical procedure.
Referring specifically to FIG. 1, the manifold assembly 16 illustrated
includes a luer type manifold port 20. In alternative embodiments,
the union between the manifold assembly 16 and ancillary medical
devices (not shown) is completed using alternative connectors. Alternative
connecting mechanisms between the manifold assembly 16 and ancillary
medical devices, being known in the art, are also incorporated as
within the spirit and scope of the present invention.
A strain relief 18 is fit to the manifold assembly 16, and the
shaft assembly 12 extends into the manifold assembly 16 through
the strain relief 18. In specific embodiments, a proximal corewire
(not shown) can be securely attached within the manifold assembly
16. The proximal corewire is generally a stainless steel wire member
that provides additional stiffness and kink resistance throughout
the proximal region of the catheter 10. This added proximal support
again aids in the pushability of the catheter 10 to traverse the
intravascular anatomy of a patient.
The shaft assembly 12 depicted in FIG. 1 includes multiple outer
tubular members to illustrate exemplary uses of metal-to-polymer
lap joints of the present invention. It is recognized that in preferred
embodiments, not all illustrated joints are used in a single embodiment.
The outer tubular members include a proximal segment 30, an intermediate
segment 31 and a distal segment 32. In preferred embodiments of
an SOE catheter, an inner tubular member 33 extends coaxially with
a portion of the outer tubular member from a guidewire port 40 to
the distal end 41 of the catheter to define an annular inflation
lumen therebetween. In one embodiment, the outer tubular member
segments 30, 31, 32 surrounding the inner tubular member 33 have
an outer diameter ranging from about 0.040 inches to about 0.045
inches, with a wall thickness ranging from about 0.0028 inches to
about 0.0044 inches. Materials used to form the outer tubular member
segments 30, 31, 32 may vary depending upon the stiffness desired
for the particular portion of shaft assembly 12. When the use of
polymeric materials is desired, nylon and similar polyamides such
as DURETHAN.RTM. (available from Bayer) are particularly suitable
for obtaining rigid outer tubular members. Other suitable polymeric
materials forming a rigid outer tubular segment include, but are
not limited to, polyetheretherketone (PEEK), polyimide (PI), and
polyetherimide (PEI). Additional rigidity within a polymeric material
may be imparted to an outer tubular member segment by incorporating
a braid or other support member on or within the tubular member.
As discussed in detail below, in preferred embodiments, at least
one of the outer tubular member segments 30, 31 may comprise a metallic
tube or hypotube. In these embodiments, the hypotube can be utilized
as the outer tubular member segment 30, 31 in the more proximal
regions of the catheter 10 to provide stiffness and torqueability.
The hypotube segment can then be bonded to a more flexible polymeric
outer tubular member 31, 32 at a distal region of the catheter shaft
12, later discussed in detail with respect to FIG. 2 and FIG. 3.
The inner tubular member 33 defines a guidewire lumen, which provides
a passage for at least one guidewire 22. The inner tubular member
33 is generally made of a polymeric material such as a polyethylene,
for example Marlex HDPE. In alternative embodiments, the inner tubular
member 32 can be made of a lubricious material such as polytetrafluoroethylene
(PTFE) or other suitable polymer. At the proximal end of the inner
tubular member 33, the inner tubular member 33 has an outside diameter
ranging from 0.024 inches to 0.026 inches. The inner diameter of
the inner tubular member 33 measures approximately 0.018 inches
to 0.0195 inches. The outside diameter-to-wall thickness ratio is
preferably sufficiently small to reduce the likelihood that the
shaft assembly 12, and more specifically the inner tubular member
33, will kink.
At the distal end of the shaft assembly 12 is a balloon assembly
14. The balloon assembly 14 includes an expansible balloon 24 having
a proximal balloon waist 26 and a distal balloon waist 28. The proximal
balloon waist 26 adheres the expansible balloon 24 to the distal
tubular segment 32 near its distal end by means of an adhesive,
or alternatively, by thermally bonding, including RF bonding, laser
bonding and other suitable thermal bonding techniques. The distal
balloon waist 28 similarly adheres the expansible balloon 24 to
the inner tubular member 33 near its distal end by means of an adhesive
bond or a thermal bond. This particular balloon assembly 14 arrangement
allows the expansible balloon 24 to be in fluid communication with
the inflation lumen defined by the outer tubular member segments
30, 31, 32.
As discussed in detail above, the proximal region and the distal
region of a catheter 10 are functionally different and, therefore,
preferably possess differing structural attributes to enhance their
particular functionality. The distal region of a catheter 10 is
designed for flexibility. Intravascular procedures often require
a catheter 10 to track through a tortuous pathway to a desired location
within a patient's body. Navigation through the vascular system
requires the distal tip, as well as the remaining sections of the
catheter 10, to bend and twist to complement the tortuous vasculature.
The proximal region of a catheter 10, on the other hand, must provide
sufficient longitudinal and axial strength to advance the entire
distal region of the catheter 10 within a patient's anatomy. A joint
is required at locations where materials of differing properties
are utilized in the catheter shaft. FIG. 1 depicts two exemplary
locations and types of joints which may be utilized. The first depicted
joint is a lap joint 50 between proximal segment 30 and intermediate
segment 31. In this embodiment, proximal segment 30 is preferably
a metallic hypotube and intermediate segment 31 is a polymeric tubular
member having greater flexibility. The lap joint 50 is depicted
in greater detail in FIG. 2 and discussed below. The second exemplary
joint depicted in FIG. 1 is lap joint 60 which is located at the
proximal guidewire port 40 of the SOE catheter design. In this embodiment,
intermediate tubular member 31 is preferably a metallic hypotube
which forms a lap joint with distal outer tubular segment 32 and
inner tubular member 40. This joint is shown in greater detail in
FIGS. 3 and 4 and discussed in detail below. It should be recognized
that the number of tubular segments incorporated into the outer
tubular member can be varied for particular applications. The proximal
member 30 and intermediate member 31 may also be combined to include
a single hypotube member eliminating joint 50 and only including
the port joint 60 discussed below.
Refer now to FIG. 2, where a cross-sectional view of joint 50 between
proximal segment 30 and intermediate segment 31 of the outer tubular
shaft of the catheter assembly 10 of FIG. 1 is shown in detail.
The joint 50 of catheter 10 transitions between the proximal segment
30 and the intermediate segment 31 of the shaft assembly 12. Transitioning
between regions reduces kinking and increases force transference
between the two regions.
The joint 50 of catheter 10 depicted in FIG. 2 shows a proximal
portion of intermediate segment 31 overlying and affixed to a distal
portion of the proximal segment 30 via a coupling agent 51 (depicted
in exaggerated thickness as a separate layer). The coupling agent,
in preferred embodiments, is a very thin monolayer of material.
The length of the joint 50 can be varied from catheter to catheter.
Variances in joint 50 design and length depend upon the desired
application for the catheter 10, materials chosen for the proximal
and distal regions, and overall length of the catheter as a whole.
In a preferred embodiment, the proximal segment 30 within the joint
50 is a tubular member, and more preferably, is a metallic hypotube.
In certain embodiments, the hypotube originates from the catheter's
manifold assembly 16. The hypotube then extends distally to a point
within the intermediate segment 31 where the hypotube then terminates.
In alternative embodiments, the proximal end of the hypotube originates
distally from the catheter manifold assembly 16.
The second component of the joint 50 of FIG. 2 is a polymeric overlay
portion of the intermediate segment 31. In preferred embodiments,
a polymeric material is extruded over a portion of the metallic
tubular member. The polymeric material is then further extruded
to form a tubular member in the distal region of the catheter assembly
10. Polymeric material is extruded in a tubular configuration having
a lumen defined therein. Alternatively, the tubular segment 31 may
be preformed and assembled in overlapping fashion with the proximal
segment 30.
Materials used to form the intermediate outer tubular member may
vary depending on the stiffness or flexibility desired for the shaft
assembly. Nylon and similar polyamides such as DURETHAN.RTM. (available
from Bayer) are particularly suitable for rigid outer tubular members.
Other suitable materials for a rigid outer tubular member include
polyetheretherketone (PEEK), polyimide (PI), and polyetherimide
(PEI). Polyether block amide (PEBA) is a relatively flexible polymeric
material having a durometer of approximately 70 D which can also
be utilized as a shaft material. 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 PEBA material.
The portion of polymeric material extending over the metallic tubular
member is a lap joint. A lap joint forms a continuous connection
between a first segment and a second segment. By definition, however,
the profile of a lap joint is not contiguous between the two segments.
One segment is displaced over the second segment forming a portion
of catheter assembly 10 having properties of both the first and
second segments.
Referring now to FIGS. 3 and 4, a joint 60 depicting a bond between
a metallic shaft segment, namely intermediate shaft segment 31 and
a polymeric distal shaft segment 32 at the guidewire port 40 of
the SOE catheter, is depicted in cross-sectional view. FIG. 4 further
shows the cross section at line 4-4 of FIG. 3. As shown in FIG.
3, a distal portion of the intermediate shaft segment 31 extends
within and is overlapped by the distal outer tubular segment 32.
Further, the inner tubular member 33 overlaps the distal portion
of the intermediate tubular segment 31. Thus, a bond is formed between
the single proximal hypotube member and the two polymeric segments
extending distally therefrom. In the embodiment shown in FIG. 3,
the coupling agent is not shown as it would likely be a very thin
layer or monolayer of material relative to the thicknesses of the
tubular members. Alternatively, as discussed below, the coupling
agents can be incorporated into the polymeric tubular members prior
to extrusion.
Dissimilarities in material compositions of the two components
of the joint generally require sufficient length for adequate strength
in the resulting lap bond. Lap joint failure may result in the separation
of the two component halves of the catheter shaft 10. Achieving
a stronger bond between the two dissimilar materials allows shortening
of the length of the bond. As such, an improved bond is desired
in forming the lap joint.
Success in bonding a lap joint between a polymeric material and
a stainless steel hypotube has been traditionally achieved using
thermal bonding in combination with an adhesive. In these traditional
methods, the adhesive is first applied between the two components.
The two components are then thermally bonded together to form the
completed lap joint. There exist drawbacks, however, to using adhesives
in lap joint formation. Adhesives suitable for lap joints are commonly
associated with long curing times, sensitivity to ambient conditions
(including humidity and temperature), and the need for extensive
surface treatment (generally including expensive plasma treatment
systems). As a result, lap joints formed using adhesives are typically
time and labor intensive. Further, the layer of adhesive fills a
gap between the stainless steel hypotube and polymeric shaft and
increases the profile of the resulting bonded shaft in the joint
area.
Adhesives common in catheter manufacturing often take up to four
hours to cure. In certain circumstances, a backfilling procedure
may also be required. Backfilling over lap joints, on average, may
add at least two additional hours to the overall curing time to
the lap joint formation procedure. Moreover, procedures for lap
joint formation are highly dependent on operator skill. Assemblers
must initially apply the appropriate amount of adhesive between
the lap joint to insure proper adhesion. The assembler must then
sculpt a backfill onto the bond using additional adhesive to provide
a smooth transition. Assembler errors and curing times may result
in substantial delays. Delays in catheter production increase the
manufacturer's costs.
The present invention identifies the use of coupling agents, alone
and in conjunction with thermal bonding processes, to eliminate
needless production delays that may result in increased consumer
costs. Coupling agents are materials that improve the adhesive bonding
characteristics between dissimilar surfaces. With respect to the
present invention, the two dissimilar surfaces of particular concern
are the stainless steel hypotube and the polymeric overlay portion
or the shaft segment at joint 50 of catheter assembly 10.
A bond using a coupling agent as a primer generally requires little
or no curing time. A coupling agent applied to a catheter segment
may be immediately passed down the assembly line for assembly. Under
preferred conditions, the cumulative throughput from priming to
the final heat shrink removal may take less than ten minutes. Additionally,
the use of coupling agents in the lap joint formation processes
is substantially less operator dependent. Current technology provides
machinery capable of streamlining the formation process from the
initial application of the coupling agent to the laser weld that
insures the strength of the final bond.
Coupling agents are compounds containing at least two sets of functional
groups. A first set of functional groups has a bonding affinity
with organic compounds. A second set of functional groups has a
bonding affinity with inorganic compounds. For example, the first
set of functional groups may bind with a polymeric material, whereas
the second set of functional groups may bind with a metal. Preferred
coupling agents possess first functional groups that form covalent
bonds with a polymeric material, whereas the second set of functional
groups of the same preferred coupling agent forms ionic bonds with
a metal such as stainless steel
Preferred coupling agents include functionalized titanates, functionalized
aluminates, functionalized silanes and functionalized zirconates.
In accordance with the general description of coupling agents described
in detail above, these coupling agents have a first functional group
and a second functional group corresponding to a bonding affinity
with a polymer and a metal, respectively. In preferred embodiments,
the functionalized coupling agents include a first functional group
comprising hydrolyzable functional groups. In an alternative embodiment,
the functionalized coupling agents include a second functional group
comprising (meth)acrylate monomers. In yet another embodiment, the
functionalized coupling agents include a second functional group
comprising amine monomers.
A number of coupling agents suitable for medical device lap joint
formation are commercially available. In a presently preferred embodiment,
a series of functionalized titanates are used which are commercially
available from Kenrich Petrochemicals, Inc., of Bayonne, N.J. under
the tradename LICA. Functionalized titanates, neopentyl(diallyl)oxy,tri(diooctyl)pyro-phosphato
titanate (tradename LICA 38), neopentyl(diallyl)oxy,tri(N-ethylenediamino)ethyl
titanate (tradename LICA 44), and neopentyl(diallyl)oxy,tri(m-amino)phenyl
titanate (tradename LICA 97) are particularly suitable for lap joints
between stainless steel and polymeric materials. These coupling
agents possess superior bonding affinities with both polymeric and
stainless steel materials, with and without the use of thermal bonding
and laser welding.
Coupling agents are commercially available in a variety of differing
material states. For example, specific coupling 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 the medical device. Coupling agents in powder form
are particularly suited for incorporation within a polymeric material,
but can also be used separate from the polymer. The powdered coupling
agent is measured, added and dispersed within the polymeric material
to maintain a specified concentration throughout the mixture. The
coupling agent polymer is then fed into an extruder. The extruder
then dispenses the polymeric material so that it may overlay at
least a portion of the hypotube, and furthermore, continue to form
the remaining portions of the polymeric tubular member. Coupling
agents in paste and liquid form are additionally suitable for this
manufacturing method.
In alternative manufacturing techniques, the hypotube or polymeric
tubular member may be primed with a thin layer of coupling agent.
The applied "primer layer" is generally very thin, on
the order of molecules of thickness. The primer layer is generally
applied to the metallic or polymeric material by a dipping or a
spraying process. Alternative methods of primer application, being
known in the art, are also incorporated as within the spirit and
scope of the present invention.
The use of certain coupling agents may require no further processing
beyond application of the primer layer and the subsequent joining
of the two dissimilar materials. In some embodiments, lap joints
formed with these coupling agents can exceed the strength and durability
requirements necessary for intravascular medical devices. Alternatively,
other coupling agents require further processing in order to achieve
the desired strength requirements. Likewise, coupling agents that
do not require further processing can be further aided by such additional
processing. Thermal bonding techniques can aid in lap joint formation
using coupling agents. The following example of a lap joint formation
process for an intravascular catheter is presented by way of illustration,
and not by way of limitation:
The bonding site on a stainless steel hypotube is cleaned and polished
using a very fine sandpaper. The bonding site is then washed using
detergent and water to remove any remaining residual debris from
the hypotube. The cleaned parts are then placed into a 65 degree
Centigrade oven until dried. A 1% solution of neopentyl(diallyl)oxy,
tri(N-ethylenediamino) ethyl titanate (tradename LICA 44 from Kenrich
Petrochemicals, Inc., of Bayonne, N.J.) is then brushed over the
bonding site on the hypotube's surface. The hypotube is then again
placed within the 65 degree Centigrade oven for 30 minutes to dry
the bonding site surface. The dried hypotube is then washed twice
and dried. A portion of a polymeric tubular member is then disposed
over the bonding site. The bonding site is then placed within a
thermal bonding machine that subjects the bonding site, in particular,
to a temperature of 400 degrees Fahrenheit for 30 seconds to form
the lap joint.
Although the use of coupling agents to this point has focused primarily
on improving the adhesion between a stainless steel hypotube and
an overlaid polymeric material of a catheter, coupling agents may
additionally be used to increase adhesion of other medical device
components having a polymeric material overlaying a metallic surface.
More specifically, often the metallic framework of stents is coated
with a polymeric material. Polymeric materials are excellent carrier
mediums for therapeutic substances. Various polymers may be utilized
that are bioresorbable at specific rates. Combining these polymers
with therapeutic substances allows for prolonged treatment of a
localized area deep within the tortuous vasculature of a patient.
As with the formation of lap joints, the polymeric material often
resists attachment to the metallic framework of the stent. Therefore,
it is believed that priming either of the dissimilar surfaces with
a coupling agent may enhance the resulting bond between the metal
framework of the stent and the polymeric overlay.
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. |