U.S. patent application number 10/379156 was filed with the patent office on 2004-02-12 for method and apparatus for etching-manufacture of cylindrical elements.
Invention is credited to Dufresne, Michael J., Lundblad, LeRoy J..
Application Number | 20040026359 10/379156 |
Document ID | / |
Family ID | 22180139 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040026359 |
Kind Code |
A1 |
Dufresne, Michael J. ; et
al. |
February 12, 2004 |
Method and apparatus for etching-manufacture of cylindrical
elements
Abstract
A process is described for the manufacture of flexible tubular
elements, particularly stents for the medical field, the process
comprising the steps of: a) providing a hollow metal tube (or metal
coated tube) with an open pattern of a chemical-etch-resistant
coating layer; b) supporting the hollow metal tube with a coating
thereon onto a chemical etch resistant support element; c)
contacting the open pattern with a solution capable of etching the
metal of the hollow metal tube so that said metal is etched away
from physically exposed surfaces of the metal tube and openings in
the metal tube corresponding to the open pattern of the coating
layer are created in the metal tube element without etching the
chemical etch resistant support element; and d) removing the metal
tube from the chemical etch resistant support element.
Inventors: |
Dufresne, Michael J.; (Inver
Grove Heights, MN) ; Lundblad, LeRoy J.; (St. Paul,
MN) |
Correspondence
Address: |
INSKEEP INTELLECTUAL PROPERTY GROUP, INC
1225 W. 190TH STREET
SUITE 205
GARDENA
CA
90248
US
|
Family ID: |
22180139 |
Appl. No.: |
10/379156 |
Filed: |
March 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10379156 |
Mar 3, 2003 |
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09553069 |
Apr 20, 2000 |
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6537459 |
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09553069 |
Apr 20, 2000 |
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09083703 |
May 22, 1998 |
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6086773 |
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Current U.S.
Class: |
216/8 |
Current CPC
Class: |
A61F 2/915 20130101;
A61F 2230/0013 20130101; A61F 2002/91533 20130101; C23F 1/04
20130101; A61F 2/91 20130101 |
Class at
Publication: |
216/8 |
International
Class: |
B44C 001/22; B32B
001/08 |
Claims
What is claimed:
1. A process for the manufacture of a stent comprising: coating a
hollow metal tube with a photosensitive resist coating layer;
supporting the metal tube on a rotatable support; radiating said
photosensitive resist coating layer as to alter its relative
solubility in a desired pattern; performing said radiating while
rotating said support; washing said photoresist from said metal
tube; substantially sealing an internal surface of said hollow
metal tube; and, contacting said hollow metal tube with etchant
material which etches away metal from said hollow metal tube
according to said desired pattern.
2. A method according to claim 1, wherein sealing the internal
surface of said hollow metal tube is performed by mounting said
hollow metal tube on a support element.
3. A method according to claim 2, wherein an external diameter of
said support element substantially seals against an internal
diameter of said hollow metal tube.
4. A method according to claim 3, wherein said support element is
substantially etch resistant.
5. A process for the manufacture of a stent comprising: coating a
hollow metal tube with a photosensitive resist coating layer;
supporting the metal tube on a rotatable support; radiating said
photosensitive resist coating layer as to alter its relative
solubility in a desired pattern; performing said radiating while
rotating said support; washing said photoresist from said metal
tube; contacting said hollow metal tube with etchant material that
etches away metal from said hollow metal tube according to said
desired pattern; and, preventing said etchant material from
contacting internal surfaces of said hollow metal tube.
6. A process according to claim 5, wherein preventing said etchant
material from contacting internal surfaces of said hollow metal
tube is performed by mounting said hollow metal tube on a support
tube prior to contacting said hollow metal tube with etchant
material.
7. A process according to claim 6, wherein an external diameter of
said support tube is only slightly less than an internal diameter
of said hollow metal tube.
8. A process according to claim 7, wherein said support tube is
substantially etch resistant.
9. A process according to claim 8, wherein said support tube is
longer than said hollow metal tube.
10. A process for the manufacture of a stent comprising: coating a
hollow metal tube with a photosensitive resist coating layer;
supporting the metal tube on a rotatable support; radiating said
photosensitive resist coating layer as to alter its relative
solubility in a desired pattern; washing said photoresist from said
metal tube; and, contacting only an external surface of said hollow
metal tube with etchant material that etches away metal from said
hollow metal tube according to said desired pattern.
11. A process according to claim 10, wherein contacting only an
external surface of said hollow metal tube is performed by
substantially sealing an internal surface of said hollow metal tube
from said etchant material.
12. A process according to claim 11, wherein sealing of said
internal surface is performed by introducing a support tube into
said hollow metal tube.
13. A process according to claim 12, wherein said support tube has
an external diameter only slightly less than an internal diameter
of said hollow metal tube.
14. A process according to claim 12, wherein said support tube is
greater in length than said hollow metal tube.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an etched tubular device,
particularly cylindrical, biocompatible medical devices for
insertion into a body during medical procedures and to a method for
manufacturing these devices. More particularly, the invention
relates to flexible tubular devices for use as stents, catheters
(including, for example, guide catheters and balloon catheters,
guidewires, catheter sheaths, microcircuitry containing catheters,
catheter introducers and drug infusion catheters/guidewires) and
methods for making these devices.
[0003] Catheters and Guidewires
[0004] Catheters are relatively thin and flexible tubes used in the
medical field for numerous applications. Catheters are made by any
number of different methods and designs. However, in most catheter
designs it is desirable to obtain a maximum torsional rigidity
while retaining a satisfactory longitudinal flexibility and
stiffness without kinking. These features allow the catheter to be
manipulated so that the catheter can be guided through small body
vessels and cavities. These features will also prevent any kinking
from occurring, and provide the catheter with sufficient stiffness
to prevent the catheter from wrinkling or folding back on itself
during this process. The specific nature of these characteristics
vary depending on the specific application for which the catheter
is being used. Another consideration is that a relatively small
outside diameter must be maintained while providing a lumen or an
inside diameter as large as possible.
[0005] Guidewires require the same general type of physical
characteristics. However, with guidewires it is important to
minimize the outside diameter of the guidewire so that they will
readily fit inside of the lumen of the catheter.
[0006] Catheters and guidewires are used both as diagnostic tools
and therapeutic tools in the treatment of diseases. One such
diagnostic procedure is cardiac catheterization which is a widely
performed procedure, being used for assessment of coronary artery
disease. Other uses are neurologic uses, radiologic uses,
electrophysiologic uses, peripheral vascular uses, etc. Example of
therapeutic uses are balloon catheterization in dilation procedures
to treat coronary disease and retroperfusion delivery of drugs at
targeted sites within the human body. Dilation procedures rely upon
the use of a catheter for injection of contrast and delivery of
guidewires and dilation catheters to the coronary artery or other
arteries. An example of the use of guidewires is for Percutaneous
Transluminal Coronary Angioplasty (PTCA) balloons and for guiding
diagnostic catheters through the arteries and to body organs.
Retroperfusion drug delivery requires the use of the catheter to
guide a tube carrying the drug to be delivered, and in some cases
to have the catheter determine part of the rate of perfusion by the
size, number and distribution of openings in the catheter through
which the drug will pass.
[0007] The catheters and guidewires used in these and other
procedures must have excellent torque characteristics, and must
have the requisite flexibility. In addition, it is important that
catheters and guidewires provide sufficient longitudinal support
for "pushing" of items through the arteries and other vessels such
as when feeding the balloon portion of an angioplasty catheter
through the arteries. Unless there is sufficient stiffness, the
catheter or guidewire will wrinkle or fold back on itself.
[0008] Typically, in the case of a catheter, the larger the ratio
of inside to outside diameter, the better, even while striving for
minimum outside diameters for the catheters. Smaller catheter and
guidewire outside diameter sizes result in less chance of arterial
damage.
[0009] Catheters and guidewires must have sufficient torque to
reduce buckling when being manipulated. Additionally, flexibility
is important so that the catheter or guidewire can be manipulated
into the varying arterial branches encountered by the catheter. The
guidewire must resist being inadvertently kinked, as this can
result in loss of torque control.
[0010] Prior art catheters are typically made of flexible materials
which are reinforced such that the resulting composite catheter
approximates the desired characteristics. In alternative
approaches, guidewires are used in conjunction with catheters to
assist in manipulating and moving the catheters through the
arterial system in the body.
[0011] Stents are small, expandable tubes, usually used for
insertion into a blocked vessel (vein or artery or duct) or other
bodily part. Their physical characteristics must often be the same
as those for catheters, except for the fact that they also must be
expandable. This expansiveness is effected, not by elastic
expansion under pressure, as is the case with balloons or
parachutes in surgical procedures, but by more spring-like, metal
memory characteristics in the material. Stents are often formed of
a metal tube which is compressed (without exceeding the elastic
flexibility or stress of the metal), inserted, and then released to
allow the stent to expand to its original size and shape.
[0012] U.S. Pat. No. 4,020,829 discloses a spring guidewire for use
in catheterization of blood vessels. The guidewire is axially
slidable within a thin-walled, flexible plastic catheter. The
distal portion of the guidewire is of a relatively short length and
is connected to a relatively long, manipulative section capable of
transmitting rotational torque along its length. In this invention
the catheter tube might be advanced over the guidewire after the
guidewire has been properly positioned or the catheter might be
advanced together with the guidewire, the guidewire providing a
reinforcement for the thin wall of the catheter.
[0013] U.S. Pat. No. 4,764,324 discloses a method for making a
catheter. A reinforcing member is heated and applied to a
thermoplastic catheter body so as to become embedded in the wall of
the catheter. The wall of the catheter is then smoothed and sized
so as to produce a composite, reinforced catheter.
[0014] Current catheters often suffer from either problems of
torque, size, flexibility, kinking, and poor support during PTCA in
the case of guide catheters. Moreover, catheters cannot be readily
made with variable stiffness along the length of the catheter.
[0015] Catheter Sheaths and Introducers
[0016] Catheter sheaths and introducers are used to provide a
conduit for introducing catheters, fluids or other medical devices
into blood vessels. A catheter introducer typically comprises a
tubular catheter sheath, a hub attached to the proximal end of the
sheath having hemostasis valve means to control bleeding and to
prevent air embolisms, and a removable hollow dilator that is
inserted through the hub, valve means and the lumen of the catheter
sheath. Many catheter introducers also contain a feed tube that is
connected to the hub to facilitate the introduction of fluids into
the blood vessel.
[0017] Positioning an introducer into a blood vessel begins by
inserting a hollow needle through the skin and into the lumen of
the desired blood vessel. A guidewire is then passed through the
needle and into the blood vessel. The needle is then removed
leaving the guidewire in the vessel. Next, the sheath and dilator
are advanced together over the guidewire until the distal ends of
the dilator and sheath are positioned within the lumen of the
vessel. The guidewire and dilator are then removed, leaving the
distal end of the sheath within the vessel. Catheters or other
medical devices can then be passed through the introducer and
sheath into the desired vessel.
[0018] Conventional sheaths are made of plastic and are subject to
kinking if bent without internal support. This kinking can occur
during the insertion of the device or if the patient moves while
the sheath is in the vessel. Unfortunately, this kinking can create
sharp edges or irregularities in the sheath that can damage blood
vessel linings. This kinking can also make the introduction of
devices or fluids more difficult and can cause patient bleeding
problems around the sheath tubing. Therefore, there arises a need
for a catheter introducer with a catheter sheath that is flexible
and resistant to kinking.
[0019] Drug Infusion Catheters/Guidewires
[0020] Drug infusion catheters/guidewires are devices that act like
both catheters and guidewires and are capable of delivering drugs
or other fluids to a specific location within a patient's blood
vessel such as an occluded blood vessel. The guidewire type devices
are typically comprised of a coil spring with a heat-shrunk
TEFLON.RTM. coating and a core wire that can be inserted and
removed from the lumen in the coil spring. The coated coil also
contains either side holes or an end hole or a combination thereof
in its distal end to enable the drugs or other fluids to be sprayed
into the blood vessel.
[0021] During use, the coated coil spring and its core wire are
advanced together through the patient's circulatory system much
like conventional guidewires. Upon reaching the desired location,
the core wire is removed creating a small catheter-like device.
Drugs or other fluids are pumped through the lumen in the coated
coiled spring, out of the holes and into the blood vessel at the
desired location.
[0022] Because these devices act like guidewires, the outside
diameter of the devices, and therefore the lumen, are limited in
size. Therefore, a second type of drug infusion catheter/guidewire
device utilizes a catheter-like member with side holes and a
tapered distal end having an end hole generally equal to the
outside diameter of a guidewire. These catheter-type drug infusion
catheter/guidewire devices are advanced over a guidewire to the
desired location and then drugs are then pumped through and out of
the holes in the catheter-like member. These devices can also be
used in combination with the guidewire-type drug infusion
devices.
[0023] As described above, drug infusion catheter/guidewire devices
act like both catheters and guidewires. Therefore, these devices
must have the same characteristics as catheters and guidewires.
These devices must obtain a maximum torsional rigidity while
retaining a satisfactory longitudinal flexibility and stiffness
without kinking. They must also maintain a small outside diameter
while providing a lumen as large as possible.
[0024] Stents
[0025] Stents are devices that are placed into and/or implanted in
the body, and in particular in body structures including vessels,
tracts or ducts. For example, stents are commonly used in blood
vessels, the urinary tract and in the bile duct, to treat these
body structures when they have weakened. With blood vessels, stents
are typically implanted therein to treat narrowings or occlusions
caused by disease, to reinforce the vessel from collapse or to
prevent the vessel from abnormally dilating, as with an aneurysm or
the like.
[0026] Stents are typically produced at a first smaller diameter
for deployment and then expanded to a larger diameter, upon
placement into the body vessel, tract, duct or the like. Deployment
of stents it typically achieved by mounting the stents on balloon
catheters and then once at the requisite position in the body
vessel, tract, or duct, expanding the stent to the larger diameter,
for permanent placement therein. U.S. Pat. No. 4,856,516 to
Hillstead discloses a typical stent and describes a method for its
deployment and placement with a balloon catheter.
[0027] U.S. Pat. Nos. 5,649,952 and 5,603,721 describes an
expandable stent, a method for implanting a stent in a patient and
a method for making that type of stent. The stent comprises a
cylindrical frame which has patterns of materials removed from the
cylindrical mass formed of interconnected elements designed to
expand evenly under radial stress. In a preferred structure, a
serpentine pattern is formed aligned on a common longitudinal stent
axis to form elements that expand evenly under radial stress and
maximize the overall radial expansion ratio. Although no methods
are claimed in the patent for manufacturing the elements, various
methods of manufacture are described such as coating a thin walled
tubular element with a material which is resistant to chemical
etchant, removing patterns of the resist material to expose
portions of the underlying tubular element, and subsequently
etching to remove a pattern of the tubular material which will
leave the designed pattern in the tubular element so that it has a
pattern which provides the desired expandability. It is stated that
it is preferred to apply the etchant resistant coating by
electrophoretic deposition and to remove the etchant-resistant
material by means of a machine-controlled laser.
[0028] U.S. Pat. No. 5,437,288 describes an apparatus for use as a
catheter guidewire and a method for manufacturing a catheter
guidewire. The apparatus for use as a guidewire comprises an
elongate, non-coiled wire having a flexible portion located between
a distal and a proximal end, the distal end (and distal portion) of
the apparatus having spaced grooves cut therein. The claimed method
of making the guidewire comprises providing a metal wire, cutting a
plurality of axially spaced grooves in the metal wire, and
increasing the depth of the grooves toward the distal tip to create
a flexible portion. The grooves are suggested to be formed in the
wire by any suitable machining method, such as grinding,
electrostatic discharge machining (EDM), lasers or the like.
[0029] WO 97/42910 relates to a novel apertured flexible tubular
member with an encasing for insertion into vessels of the body as
part of a medical device. For example, the invention can be used as
catheters, including guide catheters and balloon catheters,
guidewires, catheter sheaths for use with catheter introducers, or
drug infusion catheter/guidewires. These catheters also relate to
novel apertured flexible tubular stents which may be coated, for
insertion into vessels, tracts or ducts. One embodiment is coated
with a low friction material such as a low friction polymer so as
to provide for lubricity. Samples of materials that might be used
are polyurethane, hydrogels, polyethylene, polytetrafluoroethylene
(PTFE) and, in particular, one such material which might be used is
TEFLON.RTM..
[0030] In some embodiments, such as catheters or sheaths, the
inside of the flexible tubular member is also preferably coated
with a low friction material such as hydrogel and/or with an
anticoagulant such as heparin. Another embodiment uses slots of a
predetermined configuration cut into a single, hollow, thin-walled
metal tube at predetermined spacings, depth and pattern so as to
provide the tube with a desired flexibility. The tube is then
encased in a suitable low-friction material as noted above or some
other suitable coating material. The method of forming the tubular
member includes:
[0031] a) providing a tubular element including an outer
surface;
[0032] b) providing a light source (including columnated
light);
[0033] c) creating a pattern on the tubular element by:
[0034] 1. applying a photoresistive material to at least a portion
of the outer surface of said tubular element,
[0035] 2. providing a mask intermediate the tubular element and the
light source, at least a portion of the mask including a
predetermined pattern formed of predetermined locations translucent
to light from the light source,
[0036] 3. activating the light source to expose a first area of the
photoresistive material on the outer surface of the tubular
element,
[0037] 4. moving the tubular element such that at least a second
area on the outer surface of said tubular element is substantially
aligned with said at least a portion of the mask including
predetermined locations translucent to light from the light
source,
[0038] 5. activating the light source to expose the second area of
the photoresistive material on the outer surface of the tubular
element, and
[0039] 6. developing the photoresistive material on the tubular
element, to create first portions and second portions of the
photoresistive material, the first portions and the second portions
corresponding to their respective exposure from the light source
(including columnated light); and
[0040] d) removing segments of the tubular element corresponding to
the first portions of the photoresistive material.
[0041] The mask is shown to include typical stencil-type masks, ink
patterns (e.g., applied by a laser printer), and film masks, and
either negative-acting or positive-acting resists can be used.
Chemical etching of the tube is shown.
SUMMARY OF THE INVENTION
[0042] The present invention describes a method for providing a
flexible cylindrical element, such as a medical stent, comprising
the steps of providing a cylindrical body (e.g., a hollow
cylindrical body), coating the cylindrical body with a
photosensitive resist material (either positive or negative
acting), exposing the photosensitive resist material to focused or
coherent radiation to which the photoresist composition is
sensitive, developing the exposed photosensitive resist material to
a fluid developing environment which will selectively remove areas
of the photoresist which are more soluble in the fluid developing
environment, and then chemically etching exposed surfaces of the
cylindrical element which has been exposed by the development of
the photoresist coating. The residual photoresist material may be
stripped, the patterned cylindrical element cleaned, inspected,
packaged and sent to the end user.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 shows a side view of a typical stent within a
catheter within a vein.
[0044] FIG. 2 shows an aperture mask for use with the present
invention.
[0045] FIGS. 3(a) and (b) shows front and back views of a flat for
supporting multiple cylindrical elements for etching of stents.
[0046] FIG. 4 of the present invention shows a flow diagram of the
process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0047] As compared to prior art processes, the present invention
process is believed to provide some specific technical advantages.
For example, direct machining grooving of patterns is complex and
less exact than the combined photolithographic imaging and etching
process of the present invention. Even when direct laser etching of
a surface is to be done with a laser (as suggested in U.S. Pat. No.
5,437,288), the laser energy has to be sufficiently high to etch
through the metal. This creates a potential for etching of the
inside opposed surface of the tubular element and localized
redeposition of ablated metal material within or on the cylindrical
element. Removal the etchant-resistant material by means of a
machine-controlled laser as suggested in U.S. Pat. Nos. 5,649,952
and 5,603,721 requires actual etching of the resist coating with a
laser and subsequent chemical etching of the exposed portions of
the underlying cylinder provides similar problems with redeposition
of the ablated material. Because heat is generated in the ablative
removal of the photoresist coating or explosive ablation of
material may occur from rapid volatilization of the coating, and
because the underlying metal can conduct heat laterally, there are
many control considerations which must be made in such a laser
ablation step to effect high resolution and smooth patterns in the
resist.
[0048] A process according to the invention for the manufacture of
hollow tubular metal elements, such as flexible stents, comprises
the steps of:
[0049] a) providing a hollow metal tube with an open pattern of a
chemical-etch-resistant coating layer;
[0050] b) supporting the hollow metal tube with a coating thereon
onto a chemical etch resistant support element;
[0051] c) contacting the open pattern with a solution capable of
etching the metal of the hollow metal tube so that the metal is
etched away from physically exposed surfaces of the metal tube and
openings in the metal tube corresponding to the open pattern of the
coating layer are created in the metal tube element; and
[0052] d) removing the metal tube from the chemical etch resistant
support element.
[0053] Contacting of the open pattern is preferably effected by
having the metal tube both rotate and revolve, and by having spray
which repeatedly alters its angle of spray towards said metal tube.
The spray may, for example be provided by banks of nozzles within a
spray chamber, and the nozzles or banks of nozzles may shift their
positions to change the angle at which the spray is directed
towards the exposed metal surface during the etch process.
Preferably more than one metal tube is supported within a movable
support, and said movable support is passed through an area where
chemical etch solution is applied by spraying. The movable support
may be a tray carrying the hollow tube elements with the pattern of
resist already developed on their surfaces or a bank of supported
hollow tube elements, with the supports not covering the surface of
the openings in the resist pattern.
[0054] The process preferably uses etch solution capable of etching
the metal of the metal of the metal tube which are heated above
40.degree. C. Preferred solutions comprise ferric chloride
solution, particularly those with a Baume' above 47.5.degree.. The
supported cylindrical element (the hollow metal tube) preferably
both rotates on a longitudinal axis and is revolved with at least
some movement in a direction perpendicular to said longitudinal
axis, while the etchant solution capable of etching the metal of
the metal tubular element is sprayed onto said at a temperature
between 40 and 150.degree. F. Preferably the etchant comprises a
ferric chloride solution (with HCl) with a Baume' between 48 and 55
degrees and preferably between 48.5 and 54 degrees at a temperature
above 100.degree. F. and between 110 and 140.degree. F.
[0055] A laser or focused radiation initiated photoresist imaging
process with chemical etching or development of the resist pattern
is very controllable and sensitive. Few special treatment, manual
or intermediate finishing steps are required to provide the product
in a highly automated system. Photoresist development is gentle and
non-destructive to the underlying cylindrical surface and
collateral damage to the interior backside (inside) of the
cylindrical element can be readily avoided. However, even the
columnated radiation exposed process of WO 97/42910 is general in
description of the process and fails to consider the engineering
and physics of the process, and merely discloses a literal use of
conventional photolithographic imaging and resist development in a
cylindrical exposure method, which occurs on drum supports in
photoimaging technology in many different fields. The description
of chemical etching also fails to provide any specific advances
over standard etch procedures used on flat surfaces and
three-dimensional surfaces.
[0056] Amongst the steps used in the practice of the present
invention (without every step being required in combination with
all of the other steps) are those within a process whereby:
[0057] 1) a tubular, hollow, cylindrical metal element is
provided:
[0058] The tubular element is preferably a metal element, and most
preferably a biologically compatible metal or metal alloy (e.g.,
Nitinol, titanium, surgical grade stainless steel,
cobalt-nickel-chrome alloy, platinum, or the like). It dimensions
are chosen on the basis of particular application needs and are not
solely dependent upon the process itself. Generally the element may
be within the range of 0.02 inches (0.5 mm) to 1 inch (25.4 mm) in
cross-section thickness (outside diameter), with a wall thickness
of from about 2 or 3 to 40% (per wall) of the cross-section
thickness (or about 0.01 mm to 10.2 mm, preferably from 0.01 to 2.0
mm, more preferably from 0.015 to 1.0 mm), the hollow interior
thereby being generally allowed to comprise from 20 to 94% of the
linear cross-section thickness, preferably from 40 to 94% of the
linear cross-section thickness.
[0059] 2) the metal element is cleaned to remove oils, especially
hydrocarbon or other organic oils. Typically, cleaning may include
such steps as:
[0060] i) detergent rinse (any detergent which is capable of
removing oils, especially hydrocarbon and other organic oils,
including skin oil, from metal surfaces without damaging the metal
surface,
[0061] ii) deionized water rinse,
[0062] iii) acid rinse to make the surface acidic and neutralize
the detergent residue, (which improves adhesion of later applied
layers), using such preferably non-oxidizing acids such as HCI or
solutions of acid salts, and
[0063] iv) drying.
[0064] More abrasive treatments may be used, as well as solvent
treatments to remove materials which have collected on the surface
during manufacture or transportation.
[0065] 3) possible coating (undercoating) of the metal element with
a photosensitive or non-photosensitive layer to assist in the
control of resolution in the photoresistive imaging of the
subsequent photoresist imageable layer.
[0066] As shown in U.S. Pat. No. 4,672,020, the use of an
undercoating or coadhered layer with a photoresist layer can adjust
or improve the operation of a photoresist layer, especially where
fine details are required and where such factors as undercutting
are to be avoided or controlled.
[0067] 4) application of a photoresist layer (e.g., by dipping,
spray coating, electrophoretic coating, etc. with drying).
[0068] The photoresist layer may be applied by any of the many
known film coating application techniques. Dipping and spray
coating are the most common, but electrophoretic deposition is the
preferred method at present in the practice of this step of the
preparation of the materials in the practice of this invention. The
thickness of the coating needs to be only sufficient to have the
remaining relatively non-soluble pattern resist the chemical etch.
The photoresist layer is preferably kept as thin as possible so
that the flow of resist developer (and after resist development,
the flow of etchant solution through the pattern in the resist) is
not restricted. This thickness may range, for example from 10 to
200 micrometers, preferably from 10 to 150 micrometers, and most
preferably between 15 or 20 to 100 micrometers). This dimension is
therefore dependent upon the solvent resistance of the coating (to
both the developer solvent solution and the etchant solvent
solution), the strength of the developing and etching solvent.
Certain resist materials tend to respond better to electrophoretic
deposition than others, and manufacturers provide recommendations
for their specific resists according to process applications. In
the practice of the present invention, an acrylic, negative-acting
photoresist, e.g., Eagle Resist from Shipley, Corp. (Alternatively
a positive resist such as Shipley, Negative Resist SP2029) is the
most preferred.
[0069] It may at times also be desirable to apply an aqueous
removable (soluble or dispersible) coating over the surface of the
photoresist, especially where the resist is an acrylic composition.
Acrylic resins tend to be moisture and oxygen sensitive, preventing
them from curing to their highest potential molecular weights. A
water removable, temporary oxygen barrier coating (e.g., polyvinyl
alcohol, polyvinyl pyrollidone, polysaccharide film, gelatin, etc.)
Should be applied to the surface of the photoresist element. The
thickness should be chosen mainly as a function of optical
properties of the protective film, to assure that it does not
absorb too much radiation which will be used during exposure, nor
disrupt the laser beam sufficiently to disperse the radiation and
reduce the resolution of the exposure.
[0070] Photoresist materials may be selected from amongst the broad
classes of photoresists which are known in the art and are
commercially available. The systems may be positive-acting
(becoming more soluble where irradiated or heated) or
negative-acting (becoming less soluble where irradiated or heated).
The systems may be based upon polymerization or polymer cleavage or
upon generation of more or less soluble species within a carrier
medium (as with diazo oxides or naphthoquinones in epoxy or other
polymer systems). The polymer systems useful may include a very
wide variety of classes, including, but not limited to
polyacrylates (including poly(meth)acrylates), polyvinyl resins,
polyurethanes, epoxy resins, silane chemistry (polysilanes,
polysiloxanes, etc.), phenol/formaldehyde resins (both novolaks and
resols), and the like. Polymerizable systems having multiple
classes of functionalities (epoxy-silanes, (meth)acrylate silanes,
aminosilanes, etc.) are also generally useful. Initiator systems of
many various types may also be used, such as radiation-sensitive
iodonium, sulfonium, diazonium and phosphonium salts, triazine,
s-triazines, biimidazoles, benzophenones, radiation-sensitive free
radical photoinitiators generally, radiation-sensitive cationic
initiators generally, radiation-sensitive acid generators, and the
like. It is especially desirable that the substantive photoresist
remaining on the cylindrical metal element after imaging and
development exhibits some strong resistance to the metal etchant
solution used later in the process. If the photoresist does not
exhibit such strength, it may be too rapidly removed during the
etching and expose metal to the etchant in undesired areas.
[0071] 5) supporting the photoresist coated metal element on a
rotating workpiece holder;
[0072] This is highly desirable during the process to keep the work
piece (the tubular or cylindrical element) from flexing and for
maintaining its position on the element. It may be desirable to
have a pinning or latch element which would keep the tubular
element from shifting (longitudinally or rotationally) during any
rotational operation. Although the speed and forces generated by
the rotation are small, any slippage would be disastrous. For
example, the tubular element could have a notch or protrusion on at
least one position (e.g., an end), and a post or guide could slip
or fit into the notch or hole to reduce the tendency for movement
of the element out of alignment. Rotation of the work piece holder
should be effected by a smooth drive device (e.g., electrical,
hydraulic, air pressure drive, or the like) so that wobble in the
rotation is minimized or eliminated. Mechanical drives (gearing and
belts drives) are useful, but can operate to more significantly
limit the resolution and precision of the exposure as compared to
other drive mechanisms. The support may also serve a function of
protecting the interior distal backside surface from etching
solutions, the support acting like a plug within the hollow
interior of the cylindrical material. The tolerance between the
outside diameter of the support rod and the inside diameter of the
tubular metal element should be sufficient to allow the metal
element to rotate and slide along the developer resistant support
rod.
[0073] 6) positioning the photoresist coated metal element in the
light path of a laser imaging device, the laser imaging device
having a laser source and an optical aperture mask, with the
optical aperture mask being located between the laser source and
the metal element;
[0074] The gross positioning of this step may be effected by
placing the tubular element on the work piece holder, placing the
work piece on a support rod within a rotation effecting system and
the like on the distal side of the aperture mask from the laser
source. The actual positioning must be more precisely effected
during the processing or at least during the initial set-up for the
process. For example, placement and alignment of the work piece may
be automatically evaluated by sensing devices such as infrared
sensors, reflecting/detection systems, interferometric detectors or
position detectors. Once the workpiece is found to be in proper
alignment, the process may then proceed on a basis of essentially
only rotational position awareness and detection. That is, once the
axis of the workpiece (and/or the support) have been assured to be
accurate, and the radiation beam is focused on the correct spatial
position, rotation (and longitudinal movement) of the cylinder and
longitudinal movement of the cylinder that needs to be accurately
changed to position the surface of the longitudinal element at the
appropriate focal plane for the laser beam after is has passed
through the aperture openings.
[0075] The rotational position of the surface of the metal element
with the photoresistive coating thereon must be coordinated with
the laser emissions from the laser source. A computer preferably
should be programmed to indicate the proper pulse or emission time,
or the proper shutter operation time and sequence (if a physical
shutter is used) to have the laser imaging system (creating a
latent image on the photosensitive resist material) coordinate its
activity with the proper positioning of the photoresist material
coated metal element. Because the laser radiation moves so quickly,
especially relative to the dimensions of the system, the
photosensitive coated metal element may effectively move
continuously and be exposed whenever the appropriate spot is to be
irradiated, although it may be stopped at particular positions if
desired. The laser may be pulsed accordingly, the shutter may be
opened and closed accordingly, or any other measure taken to time
the passage of the radiation through the aperture openings and time
the impact of the radiation on the appropriate surface
position.
[0076] The software operating the system should operate on a basis
of establishing an initial position on the cylinder (which may be
determined as an angular orientation of the cylinder, such as
artificially designating a position on the rotation of the cylinder
[or its support] as zero or some other value). As the cylinder is
rotated (either continuously or in a step-wise fashion, e.g., with
increments of between 5 and 90 degree rotations of the cylinder,
preferably between 20 and 80 degrees, the pulses of the laser are
timed to pass through the apertures in the aperture mask so that
the position of the stenciled light (the radiation or light from
the laser which has been shaped by the aperture) is appropriately
targeted on the surface of the photoresist. As the speed and
duration of the laser pulse (e.g., the speed of light with pulse
times of for example 3 to 100 nanoseconds, preferably 3 to 20 ns)
make the distances and the rotational speeds which can be used
(e.g., 1 to 1,000 revolutions per minute, or even more)
insignificant with respect to the resolution of the image exposure
on the surface.
[0077] More significant than the speed of revolution of the
cylindrical element is the percentage of the arcuate surface of the
cylindrical substrate which is covered by the exposure. As the
radiation of the exposure strikes further up the latitude of the
cross-section with respect to the surface of the cylinder closest
to the laser source (e.g., where the laser would strike the
cylinder surface at a ninety degree angle of incidence), the angle
of incidence increases, there is a greater tendency for reflection
of the radiation off the surface, a greater tendency for refraction
of the radiation passing through the photoresist (or any protective
cover layer), which would weaken or vary the exposure levels of the
radiation on the photoresist. Even though exposure levels tend to
be used which are at least five times higher, preferably at least
10 times higher, and more preferably at least 20 times higher than
the radiation levels needed to fully initiate or cure the
photoresist composition, the angle of incidence can still be
important from a sensitometric position. In addition, as the
angularity of the exposure changes, the angularity of the exposed
resist material changes. Rather than having a latent image which
has wall which are perpendicular to the surface of the cylinder
(e.g., radially emanating), the walls will tend to be more angular.
This affects the shape and even location of the bottom of developed
openings in the resist, and therefore would affect the shape of the
etched pattern in the cylindrical element and the orientation of
the walls of the etched pattern.
[0078] 7) exposing through different sections of the aperture mask,
each section having a different image or portion of an image
aperture thereon (and optionally, but preferably, the aperture
holes or patterns having shapes and sizes which compensate for
spread of the image on the surface or which do not have a 1:1
correspondence for radiation spread on the surface (with the
aperture size being >1:1 with respect to the actual intended
image size). The aperture is usually moved only vertically, with
the individual patterns through which exposure is to be made being
oriented in a preferably linear arrangement within the aperture
mask. In this way, the aperture mask may be moved in only one
direction as it is coordinated with the rotation of the tube
element and the emissions of the laser. The arrangement may be
other than linear with motion control in at least two dimensions
(vertically and horizontally) then being necessary. That
arrangement would tend to allow for a larger number of available
patterns on the aperture mask.
[0079] The spot size of the laser (e.g., the diameter of a circular
spot or the longest axis of an elliptical spot) should be greater
than the longest dimension of the apertures in the mask. The
longest dimension of the aperture should also correspond with the
greatest size dimension of the spot. That is, correspond with the
One specifically unique aspect of the present invention in this
particular step is the use of segments of patterns, rather than
complete patterns of exposure in the aperture mask. It is typical,
as shown in FIG. 21b of WO 97/42910, to have a single type of
aperture hole (or a complete pattern in contact with the surface as
with a conventional stencil or exposure mask) through which the
exposure of the radiation is projected. As shown in FIG. 2, an
aperture mask 20 is shown with a pattern of aperture holes 22, 24,
26, and 28 of which at least two are significantly different in
size and shape (usually most or all may be different). Laser
radiation (e.g., ultraviolet, visible or infrared) 30 passes
through one of the openings 22 in the aperture mask 20 and exposes
a latent image 32 corresponding to the shape of the opening 22 on
the surface of the photosensitive (photoresist) coated tubular
element 40. The position of the latent image 32 is formed at a
desired relationship to an existing latent image 34. It is to be
noted that the respective latent image (e.g., 32 with respect to
22) is not necessarily the same size as the aperture hole through
which the latent image was exposed. As compared to the use of a
mask in contact with a surface, this type of exposure is believed
to provide resolution advantages even with the added distance
between the mask and the surface to be imaged. Considerations of
spreading, edge effects from the aperture mask, and the like can be
readily predicted in this system and accommodated for in the
process.
[0080] FIG. 1 of the present invention shows a vein 1 having a
catheter 2 therein. The catheter 2 has within its lumen 3, a
pushwire 11 and a stent 10. The stent 10 has open areas 12 which
are defined by a sinusoidal pattern of etched metal 13. The stent
10 is typically pushed out of the opening 6 in the catheter 2 and
then allowed or forced to expand against the inner surface 5 of the
vein. The dimensions of a stent will be dependent upon the
particular use to which it is put and the particular vasculature or
body part in which it is used. Intracranial stents would be quite
small, both in gross diameter and metal thickness, while catheters
for ducts and the like from the liver or gall bladder or pancreas
would be relatively large. For example, the gaps within a stent
(the space between the metal structural material) may be from 0.5
to 7 mils, depending on the area of use, with typical vascular
stents having gaps between 2 to 5 mils and preferably from 2.5 to
4.5 mils. The thickness of the structural metal may be from 3 to 10
mils. The practice of the present invention provides a unique
capability of accurately providing relatively thin metal stents,
e.g., those having metal thicknesses of less than 6 mils,
preferably less than 5 mils, and even from 2 to 4.5 mils, with high
resolution and clean edges. This is extremely difficult to effect,
and only with the practice of the present invention is this
capability known to be provided. One of the difficulties with the
prior art techniques is the fact that the chemical etch tends to
leave rough surfaces. The thin metal walls of the stent do not
allow any significant mechanical smoothing after the etch because
of the fragile nature of the porous and open nature of the stent.
The width of the metal in the stent (which describes the gaps or
openings in the stent) are again determined by the design and use
of the final stent product. These gaps are limited only by the
resolution of the imaging technology, the strength of the metal,
and the quality of the chemical etch. The present invention
optimizes these qualities so that metal widths of less than 2 mils,
even less than 1.5 mils, can be produced. It is preferred that the
metal width be between 0.5 to 10 mils, preferably between 1 and 8
mils, and more preferably between 1.5 and 4, 5 or 6 mils.
[0081] FIG. 4 of the present invention shows a flow diagram of the
process with an optical lens 48 present between the aperture mask
50 and the cylindrical object 52.
[0082] One feature that is desirable in the practice of laser
imaging exposure is the fact that the original laser beam may be
split or reflected off a rotating mirror at different targets in
sequence or contemporaneously. That is, a single beam 42 may be
split to image two distinct cylindrical objects (either on the same
support at different longitudinal locations or on a separate,
preferably parallel support). As shown in FIG. 4, a beam splitter
54 provides a second beam 56 which is then reflected off a second
optical mirror 58 as an independent, but similarly pulsed light
beam 60 which may then be used in an independent imaging process.
The split beam 60 may pass through different aperture masks (not
shown) or may pass through different openings in the same aperture
mask. To effect the latter, it would be desirable to provide
multiple sets of aperture holes on the mask, each set being capable
of providing the necessary individual segments for the completed
pattern on a cylindrical element.
[0083] The spot size, as mentioned earlier should be of somewhat
greater maximum dimension than the greatest dimension of the
largest aperture to be used in the imaging process. This means, in
the practice of the present invention that the spot size may be
greater than 1 or 1.5 cm with correspondingly smaller individual
apertures. Each of the apertures provides an individual field of
exposure on the photoresist surface which adds up to the final
composite. The individual fields should be exposed so as to have
portions which slightly overlap at zones where the fields overlap.
It is preferred that the individual fields overlap along a linear
dimension where the fields abut by at least 0.03 mm, preferably at
least 0.01 to 0.03 m.m., and most preferably by at least 0.005-0.03
mm. This overlap allows for the photoresist to be assured of having
the abutting areas sufficiently exposed (in a negative-acting
imaging resist system) to assure complete hardening or (in the case
of positive-acting resist systems) to assure complete reduction in
solubility.
[0084] FIG. 3 shows an example of an aperture mask 100 which can
provide this function. The mask 100 comprises two distinct sets of
apertures 102 and 104. The two sets of apertures 102 and 104 have
the same pattern of individual apertures 106, 108, 110 and 112. By
having two supported cylinders (not shown) synchronized in their
rotation, a split beam may image essentially identical patterns in
the two different cylinders by passing the beam through the two
sees of apertures 102 and 104. Extended feet 114 are shown, these
feet 114 extending from one imaged area into another imaged area to
assure complete exposure at the interfaces of the exposed
images.
[0085] The latent image is imposed upon the photosensitive coating
by incrementally piecing segment of images together according to
the openings in the aperture mask. Rather than having to alter spot
sizes at the source of the laser, using the same laser spot shape
and size for a variety of patterns (which means a greater number of
exposures and greater likelihood of spillover imaging), or some
other standard mask variation, the provision and exposure through a
variety of aperture openings of different shapes which have been
specifically designed and selected to provide the individual shapes
and areas which can be used to generate the precise pattern needed
in the etched article. The computer program controls the passage of
the radiation through the openings in the aperture mask both with
respect to time and position (of the appropriate mask opening). The
program would operate by:
[0086] a) assigning one point as a starting point or reference
point on a surface of the cylindrical photoresist coated metal
element,
[0087] b) identifying a specific pattern of exposure desired on the
surface of a target (the cylindrical, photoresist coated metal
element),
[0088] c) identifying a series of patterns of aperture openings
available to expose the surface of the target,
[0089] d) while said surface of the target, signaling a laser
imaging system to provide exposing radiation to the surface of the
target (e.g., either by pulsing the laser according to a timed
distribution, or by operating an associated device (e.g., a shutter
or lens) at selected times,
[0090] e) directing radiation through one of a series of openings
in an aperture mask, and imaging a pattern on the surface of the
target by using more than one opening (at least two openings, up to
as many openings as desired, such as twenty or more) in the
aperture mask to shape the exposure pattern on the surface of the
target, at least two different openings of different shapes and/or
size being used in this exposure step, and
[0091] f) while said cylindrical element is moving horizontally
(parallel to its longitudinal axis) as well as rotationally,
identifying the appropriate exposure signals to be sent to the
laser imaging system to cause the pattern to form over both
circumferential and longitudinal surfaces on the cylindrical metal
element.
[0092] 8) rotating the photoresist to present different regions of
the photoresist coated surface of the metal element towards the
aperture mask, with the different sections of the photoresist
coated surface being exposed as desired;
[0093] As noted in the previous step, the cylindrical metal element
is rotated to present its surface to the exposing laser beam. This
rotation must be smoothly performed coordinated with the timing of
the laser. Additionally, the trajectory of the laser beam or the
position of the aperture mask must be adjusted to impact the
surface appropriately. The beam may be directed towards the surface
by altering the position of guiding mirrors which typically direct
the beam from the laser emitter to the aperture. By controllably
altering the angle and/or position of the mirror, the radiation may
be directed through the appropriate opening in the aperture to the
proper position on the surface of the photosensitive coating. The
mask itself may also be reoriented appropriately while the beam
remains steady. Exposing radiation may often intentionally impact
solid portions of the aperture mask, as the metal is generally
impervious to the energy level of this exposing (as opposed to
ablating) laser radiation. The rotation should be effected in a
manner which minimizes chatter, stutter, wobble or other irregular
variations in the uniformity of the movement of the surface of the
cylindrical element and resist. Non-belt driven or non-gear driven
assemblies, such as hydraulic or electromagnetic direct or torque
drives are preferred for this purpose.
[0094] 9) preferably rotating the element continuously, with the
exposure timed through the apertures by one or more of a computer
program identifying the position of the metal element, pulsing of
the laser, shutter control of the laser beam, and laser spot
location/overlap as exposure compensation for the angularity of the
surface being exposed, and forming a pattern of material from the
photoresist material which is differentially soluble in a solvent
as between exposed and unexposed areas. As noted earlier, the
rotation of the element may be done episodically rather than
continuously (in a step-by-step manner). It is preferred, however,
that the cylindrical element be rotated continuously during imaging
for processing speed.
[0095] Again, as noted earlier, one of the advantages of the system
is to keep the metal element rotating continually so that a nearly
continuous process can be performed on each metal element. The
metal element may comprise a long section of metal tubing so that a
number of stents may be imaged on the single tube and then the tube
cut into appropriate segments, each of which is a stent.
[0096] 10) baking or burning of the resist to make the solubility
differences between exposed and unexposed areas more pronounced,
toughening the less soluble component, increasing surface adherence
of the less soluble component of the pattern to the metal surface,
etc.;
[0097] This is a step often done in the positive printing plate
art, which is a type of resist or differential surface tension
imaging system. It is not known to be used in the photolithographic
imaging and etching of stents as practiced in the present
invention. The burn-in may be affected by the application of heat,
the application of UV, visible, or infrared radiation to which the
photosensitive media was sensitive, or to infrared radiation as an
alternative source of heat. The energy additions for the burn-in
may also be combined. The burning step may be performed after the
development step (which is listed herein as step 11).
[0098] 11) developing, removing the more soluble areas of materials
by contact with a developing solution which is more active towards
exposed or unexposed areas than to unexposed versus exposed areas,
respectively;
[0099] It is preferred that this contact be an active contact, that
is a contact with some kinetic activity as by stirring a solution
in which the element has been placed, swishing the element through
a solution, spraying the solution against the surface, or the
like); an optional scumming (scum removal) treatment with optical
powder, pumice scrub, or the like to mildly remove or abrade away
scumming to make the surface to be chemically etched more uniform
in properties can be performed about here in the sequence of steps.
It is to be noted that the removal of residual resist material
within the finely developed image areas by the use of particulate
materials in a slurry (e.g., particles having an average particle
diameter of less than 25 microns or less than 20 microns,
preferably an average particle diameter of less than 10 microns
with a particle size variation of less than 25 number percent of
the particles having a deviation above the average particle size of
more than 30% (and preferably no more than 25%). It is also
preferred to use a very fine slurry of particulates with average
particles sizes less than 5, preferably less than 3 and even less
than 2 microns in average particle size diameter. The particulate
slurries are applied to the developed resist image with mild
agitation or pressure and then followed with a rinsing step (e.g.,
step 12, following). This has been found to provide a sharper
image, which is not believed to have been disclosed within the
photoresist imaging art for non-flat (e.g., three dimensional or
especially cylindrical) resist imaging.
[0100] There are also additional particle properties desirable in
the materials used for the slurries of the present invention. For
example, it is preferred that the particles have a hardness of at
least 8 Mohs (preferably >8.5, >9 or more), a Knoop hardness
of at least 1900, preferably at least 2000, and more preferably
2100 or more, insolubility in water or organic solvents, and being
non-polymerizable under working conditions. A bulk density of
greater than 1.4 g/m.sup.3, preferably grater than 1.5 g/m.sup.3,
and most preferably greater than 1.6 g/m.sup.3, is desirable. Such
abrasive are typically prepared from inorganic oxides, inorganic
sulfides, inorganic nitrides, inorganic sulfides and the like.
Typical examples of these are aluminum oxides, aluminum sulfide,
titanium oxide, titanium sulfide, and silicon oxide or silicon
sulfide, alone or in mixtures. Minor amount of other oxides or
sulfides (e.g., Na.sub.2O, MgO and CaO) may be present in minor
amounts in the composition, these latter materials being generally
too soft or tending to undesirable solubility.
[0101] 12) rinsing and drying the developer solution off the metal
element with a patterned resist coating on it. Rinsing is done with
aqueous solutions, including deionized water or water with mild
detergents or surface active agents to assist in material removal
from the developed surface.
[0102] As an independent step in this removal of resist from the
developed region, the present invention has found that further
stress can be placed on the side walls and features of the
developed areas by the use of fine abrasive powder in slurries or
dispersions, as opposed to merely liquid washing materials. The
slurry or powder (such as the use of optical polishing powders and
ultrafine abrasive grit) improves the removal of resist material
from the edges of the developed areas adjacent the metal cylinder
surface and the remaining side walls of the resist layer. This has
not been disclosed before and has shown particular advantages in
the cleaning of developed areas in three-dimensional resist images
and particularly in cylindrical etched elements.
[0103] 13) chemically etching the exposed surface of the metal
element through the open pattern exposed and developed in the
photoresist coating on the metal element.
[0104] The metal tube may be rotated in the etch solution with mild
stirring or agitation of the solution to get a uniform etch on all
sides of the element (e.g., by placing the metal element on a
preferably non-etchable support element or rod which is rotated);
again, a spray of the chemical etch, rather than immersion, appears
to be uniquely beneficial to the formation of the cylindrical
patterned elements of the present invention. Rather strong etch
solution may have to be used, depending most particularly upon the
nature of the metal, as with nickel containing metals requiring
stronger and more frequently replenished etchant solutions. For
example, a typical etch will contain ferric chloride solution.
Additional materials may include hydrofluoric acid, nitric acid,
ammonium difluoride, hydrochloric acid (as a trace from the ferric
chloride or as an additive material). It has been found to be
desirable to operate with a Baume of 47.degree. .+-.8 degrees. At
the higher Baume levels, especially with ferric chloride, it is
necessary to elevate the temperature of the etch to between 110 and
150.degree. F., preferably between 115 and 135.degree. F. This
elevated temperature in combination with Baume levels above
47.5.degree., usually above 47.5 and below 56.degree. Baume and
especially between 48 and 53.degree. Baume, is itself novel in
three dimensional etching;
[0105] Even the provision of the high Baume' etchant solutions is
not a trivial task and its provision is not reported in the
literature. Because the solutions are of such a high concentration
of etchant and adjuvant materials, it is very difficult to merely
mix the high concentrations into a solution at room temperature or
even at elevated temperature. It has been found to be most
advantageous and convenient in the practice of the present
invention to provide a typical etch solution with a Baume' of 47 or
less and then to controllably evaporate liquid (water) out of the
solution at room temperature or at an elevated temperature (e.g.,
25-90.degree. C., 72 to 186.degree. F.) to provide the proper
concentration of materials. It is particularly preferred to perform
this at elevated temperatures (e.g., 35-90.degree. C., preferably
40-75 or 80.degree. C.) to assure that the materials in the etchant
solution do not crystallize out. It is desirable during the
practice of the invention, both in the formation of the
compositions and the in the etching step itself to minimize any
crystallization, so that less than 2% by weight of solids in the
solution crystallize out of the solution during that specific step
(either during the compounding or particularly during the
etching).
[0106] The high specific gravity of the etchant solution which is
measured on the Baume' scale is surprising in its ability to
perform a higher quality, more smooth surface etch than traditional
low Baume' etching solutions. Even though the concentration of
active agents is higher in the higher Baume' solutions tends to be
higher than in the traditional solutions with a Baume' of less than
47.5 (e.g., 47 and lower), the etch is slower (a lower rate or
material dissolution or etching), but the quality of the etch (as
visually and statistically determined in the roughness of the
surface left after etching) is much higher. This is particularly
beneficial, if not critical in the manufacture of small medical
devices such as catheters and stents. Because these devices must
often be small and have thin walls, reduced quality in the etch
itself can cause increased waste of materials (which are quite
expensive), require attempts at salvaging rough items (which is
expensive and difficult, again due to the small and thin nature of
the material), and can lead to defects in the device which are not
readily found in ordinary inspection (e.g., structural defects in
the orientation, structure or crystallinity of the metal
materials). The fact that the use of higher Baume' etchant
solutions, irrespective of the chemical nature of the etchant
solution, can provide this effect, is a significant advance in the
manufacture of small metallic articles. This is particularly true
where the surface of the article being etched is three dimensional,
as opposed to etching on a flat surface. Even though the higher
Baume' (specific gravity of greater than 47 degrees Baume')
increases the quality of etching on such flat surfaces, the use of
these solutions and the degree of benefit on the etching of
surfaces, especially where all the exterior surfaces of an element
is being developed, which surfaces are not all within a single
plane, has been found in the practice of the present invention to
be uniquely beneficial. As noted earlier, the etch over the
cylindrical surface is not necessarily always radial (from the
center of the cylinder) or not always perpendicular to the
underlying surface (because of the angle of exposure and
development of the resist). These unavoidable characteristics in
the object or the resist provide an innate limitation on the
quality of the resist image and the need for increased quality in
the physics and control of the etch itself becomes more critical.
This is even more critical in medical devices of small dimensions
where etch failure is potentially fatal, injurious and
expensive.
[0107] To define and distinguish a three-dimensional surface from a
two dimensional surface, the following should be considered. A
two-dimensional surface lies essentially within a single plane or
occupies a complete rectangular volume (considering the length,
width and depth, for example, of a layer coated on a flat surface).
The extension of the paths of the etch through the substrate will
consist essentially of parallel paths of extension. A
three-dimensional etch surface will have etch paths which are not
parallel to each other. As when etching a cylinder with either a
square, triangular or rectangular cross-section, many of the paths
of the etch in the substrate will radiate away from each other in a
non-parallel orientation. It would be common with three-dimensional
articles that do not have predominantly flat faces (as with the
triangular or rectangular cross-sections) that the paths of the
openings in the resist layer may have parallel sides on the walls
of the developed resist, but do not have all walls perpendicular to
the underlying surface to be subsequently etched.
[0108] 14) rinse away the chemical etch and/or neutralize the
etching solution;
[0109] 15) strip the remaining photoresist (relatively insoluble
photoresist as compared to the relatively soluble photoresist that
was removed) from the etched element (e.g., with an organic solvent
such as isopropanol). With a positive-acting photoresist, the
residue may be removed by exposing the remaining coating and
developing the exposed (and solubility-increased) material.
[0110] 16) remove the etched element from the support and pack it
for transportation.
[0111] The process and materials of the present invention also
encompasses techniques for the photolithographic and chemical
etching of circuitry onto or into medical inserts such as catheters
or stents. The process for this embodiment of the invention would
encompass the formation of a partial or complete metal (conductive)
coating on the surface of a catheter or stent. It would be
preferred if the catheter or stent had a sacrificial layer
(preferably non-conductive) under the metal layer. The catheter or
stent material should be resistant to an etch useful on the metal
coating. The tubular element (the catheter or stent) with the metal
coating on it, is coated, imaged and resist developed according to
the process described above. That imaging, however, would be in the
form of providing negative images (exposed areas for development)
of desired electrical patterns (e.g., resistive heating elements,
conducting leads, etc.), circuitry, Magnetic Resonance Imaging
coils, or the like. After development of the resist layer, the
exposed metal can then be etched to provide the positive structure
of the desired conductive (metallic) pattern on the catheter or
stent. All of the steps and features of the present invention can
be used as desired in the practice of such electronic or circuitry
preparation on catheters and stents.
[0112] The following information describes and circumscribes the
best mode of practicing the invention.
[0113] I. In the selection of raw materials for stents, the metal
tubing is preferably a high quality, uniform composition and
uniform thickness metal tube. An example of the preferred metals
are Nitinol or 316LSS fully annealed stainless steel. The preferred
range of dimensions for tubing used in the present invention
comprises:
[0114] ID (Inside Diameter)=0.01 to 0.5 cm, preferably about 0.051
inch (0.13 cm)
[0115] Wall thickness=0.002-0.3 cm, preferably 0.0025-0.004 inches
(0.0066-0.11 cm)
[0116] OD (Outside Diameter)=0.1 cm to 0.2 cm, preferably 0.056
in.-0.059 in. (0.14-0.15 cm)
[0117] Length=0.1 to 1.5 m, preferably about 2 ft (0.61 m)
[0118] Photoresist
[0119] 1. Electrodeposited Resist, Shipley Co. Negative-acting
photoresist, aqueous-based.
[0120] 2. The process is equally amendable to the use of positive
resist, such as Shipley SP2029.
[0121] II. Tube Cutting Prior to Etching
[0122] A. Tubing may be cut into shorter (e.g., 6.25 inch, 15.9 cm)
lengths using a rotating blade cutter
[0123] III. Pre-Cleaning:
[0124] A. Handling Devices Used
[0125] 1. Hand held screened basket to support elements without
compressive damage
[0126] B. Sprex.TM. Cleaner Dip Tank
[0127] 1. Bath Composition: -1.5 wt % Sprex.TM. A.C. powder
[0128] Balance: city water; Sprex is Du Boise Sprex.TM. A.C.
Cleaner, a caustic-based detergent
[0129] 2. Process settings:
[0130] Temp=145 to 180 degrees F., preferably about 166.degree.
F.
[0131] Time=2-5 minutes
[0132] 3. Parts are placed in a screened basket and dipped in the
tank for 2-5 minutes, then removed.
[0133] C. DI Water Rinse
[0134] 1. De-ionized water spray, room temperature, spray pressure
of 5-8 psi, time=5-30 seconds, preferably about 20 seconds
[0135] 2. Tubes are hand-held in spray at various angles; some
spray is directed into the interior of the tubes such that visible
flow can be seen exiting the opposite end of the tube.
[0136] D. HCI Acid Dip Tank
[0137] 1. Bath Composition: 25% HCl acid reagent, 36% HCl
[0138] Balance city water
[0139] 2. Process Settings:
[0140] Temp=60-80 degrees F., preferably about 70.degree. F.
[0141] Time=5-30 seconds, preferably about 20 seconds
[0142] 3. Parts are hand-held in tank
[0143] E. DI water rinse as per step C
[0144] F. Dry Box
[0145] 1. Process Settings:
[0146] Temp=115 to 145.degree. F., preferably 130.degree. F.
[0147] Time=until dry, generally 10-15 minutes
[0148] 2. Parts are laid on absorbent sheets such as Kimwipes.TM.,
often air is blown through the interior hallway through the drying.
Pressurized air nozzle, hand-held
[0149] IV. Resist Coating--currently performed by electrophoretic
deposition of resist polymer composition,
[0150] A. Electro-deposited negative photoresist
[0151] B. Performed in a tank
[0152] C. Resist thickness at the end of the element is about 10 to
150 micrometers.
[0153] VI. Resist Drying
[0154] VII. Resist Imaging--This is described thoroughly above.
[0155] A. Equipment
[0156] 1. Laser source--pulsed laser, e.g., excimer laser
[0157] 2. Optical focusing and focussing mirrors
[0158] 3. Optical Aperture Mask--made by Buckbee-Mears St. Paul
[0159] 4. Tube positioning fixture
[0160] a. Silicon supporting element with a hole drilled into a
face thereof which matches the OD of metal tube closely, and also
has a piece taken out of the side where the laser is directed.
[0161] 5. Motion Control Systems
[0162] a. For tube: A motivating system, e.g., rotational assembly,
attaches to one end of the support for the tube. The assembly
directs the tube rotationally (turning about its longitudinal axis)
and longitudinally, moving the supporting element parallel to the
longitudinal axis. The system is preferably operated continuously
(rotated and translated longitudinally) throughout imaging.
[0163] b. For aperture mask: currently connects to S5 aperture mask
(thickness=0.001 to 0.005 inches [0.025 to 0.076 mm], preferably
about 0.002 in. [0.051 mm]) moves vertically on a screw system, but
hydraulic, or electrically driven pulley, torque, or magnetic
system may also be used. A wheel aperture mask which would rotate
has also been investigated. It is to be noted that in its preferred
operation, the aperture mask only moves periodically.
[0164] c. A computer controls both motion systems (that for the
tube and that for the aperture); and could also control the laser
shutter as well.
[0165] VII. Resist Developing
[0166] A. Spray developing, with the resist developer being sprayed
against all cylinder surfaces of the tube. The spray may be
directed from all areas around the supporting tube as it is carried
through a spray chamber and/or the tube may be turned in a chamber
with fixed spray heads. The resist developer may also be applied by
pad wiping application, dip application with some agitation within
or after removal from the dip tank, and the like.
[0167] VIII. Post-developing Burn-In/Re-Exposure of Resist
[0168] A. A variety of burn-in methods were experimented with;
including no burn-in.
[0169] B. Conditions Tried
[0170] 1. Pizza oven:
[0171] temp setting=610.degree. F., time=25-30 seconds, tube placed
in the oven=38
[0172] 2. Lower Temperature, IR heating: temp setting=450.degree.
F., speed setting tube taped to a clip and hung on conveyor through
vertical Ir banks
[0173] 3. Higher Temperature IR oven: temp setting=1150.degree. F.,
speed setting=25-35 Tubes ran as above; note this is a different
machine than the lower T IR
[0174] 4. None (no burn-in)
[0175] 5. Dry box; temp=150.degree. F., time=90 minutes, tubing
hung in dry box taped to clips
[0176] IX. Resist Repair and spotting
[0177] A. This process is manually performed and is intended to be
eliminated in the future. It is done to improve the quality of some
of the developed prints. Not all samples were spotted.
[0178] B. Spotting material is hydrocarbon based; applied with a
paintbrush with tube under magnification, to repair and fill in any
handling scratches, pin holes, or other defects.
[0179] X. Etching
[0180] A. Equipment
[0181] 1. Rotary Spray Etches
[0182] a. constructed of etch resistant materials (Titanium,
PVC)
[0183] b. oscillating spray nozzles
[0184] c. rotating flat
[0185] d. further rotation of tube
[0186] e. city water hose rinse
[0187] f. light table for visual inspection
[0188] 2. Tube Handling Fixture
[0189] a. PVC round flat-modified
[0190] b. Titanium support rod supporting the metal tube to be
etched fits on both ends of the tube and must penetrate into the
opening into the tube sufficiently to maintain support of the tube,
e.g., -0.02 to 0.90 inches, preferably about 0.045" into holes
drilled in 2 PVC support bars. The fit is loose enough to allow for
turning of the tubular metal about the support rod, but without
sufficient clearance to allow unrestricted flow of etchant between
the rod and the supported metal tube.
[0191] c. An etch resistant gear-like (PVC pinwheel) is attached
(permanently) to the Titanium rod so that the natural motion of the
etchant spray will cause the Ti rod to rotate as the pinwheel is
turned. The metal tubes (e.g., the stainless steel tubes) fit
somewhat snugly onto the Ti rod; but some clearance exists, which
allows for slipping the tubes on and the etched pieces off with
minimal damage.
[0192] 3. Rough Inspection Equipment (for Etch Time determined)
[0193] a. Light Table
[0194] b. 40.times. microscope
[0195] c. PVC piece, 3/4" thick, with channel drilled in the
middle. This provides a support for the microscope so that when the
flat is laid on the light the Ti rod and sample lie deep in a
channel near the top surface of the PVC piece. Then one can hold
the microscope steady, adjust it easier, and even rotate the tube
more easily.
[0196] B. Etch Process Set Points--these are the most commonly used
parameters for this application
[0197] 1. Temperature=115-130.degree. F.
[0198] 2. Baume=48.degree.B, .+-.7% (preferably for difficult to
etch metals, between 47.5 and 55 Baume', more preferably between 48
and 55 Baume'.
[0199] 3. Spray Pressure=10-25 psi; front & back nozzles
[0200] 4. Spray oscillation speed=60 (setting on dial),
approximately 8 to 40 sweeps or cycles (up and down) of the nozzle
per minute.
[0201] 5. Flat rotation speed setting=60 (e.g., the approximately 1
meter flat moves at a top edge speed between 0.1 or 1 and 30 cm/sec
through the spray area, more preferably between 1 and 5
cm/sec.)
[0202] 6. HCL Acid level=<1%
[0203] 7. Etch time=10-14 minutes, dependent upon tube wall
thickness, etch composition and parameters, and other issues.
[0204] C. Pre-Etch Scumming
[0205] 1. This optimizes the uniformity of the exposed metal
surface on the developed prints. Performed with the tubes already
placed on the titanium rods, hand-done at present.
[0206] 2. Scumming with Optical Powder--rubbed w/ cotton
[0207] 3. Scumming with Lan-O-Sheen.TM.--rubbed w/ cotton
[0208] 4. Electrocleaning of metal surface
[0209] XII. Stripping and Cleaning
[0210] A. Handling Fixtures
[0211] 1. Thin Stainless steel rods
[0212] a. Individual etched pieces are removed from the carrier and
handled using a very small stainless steel (often referred to
herein as "SS") rod, which fits loosely enough inside the cylinders
that fluid can flow freely on the inside surface. The tubes are
stripped, cleaned, and dried while on this rod, then placed back
into the carrier.
[0213] b. Thus far the rods have been hand-held, 1 rod at-a-time,
and hung in the tanks with bulldog clips individually as well.
Fixtures containing multiple thin SS rods are easily produced.
[0214] B. Both compositions: Stripper=RD68 and
[0215] 30% RD68 (ChemClean CULX.TM. Cleaner) (15% by KOH by volume)
balance city water
[0216] C. Process Settings:
[0217] Temp=160-180 .degree. F., preferably about 175.degree.
F.
[0218] Time=3-10 minutes, preferably about 5 minutes
[0219] D. DI Water Rinse
[0220] 1. Similar to Process C; DI Spray is directed such that the
resist is blown off of the tube.
[0221] E. Isopropyl Alcohol Rinse Room temperature IPA bath used as
a final clean, also to aid in the drying
[0222] XIII. Inspection, Packaging
[0223] A. Inspection has been performed using hand-held microscopes
and stereoscopes.
[0224] B. Packaging thus far has been in clear plastic tubes with
caps on both ends.
[0225] The process of the invention, including the photoresist
imaging aspects may include, for example, the steps of:
[0226] a) coating a hollow metal tube with a photosensitive resist
coating layer;
[0227] b) supporting the metal tube on a (preferably rotatable)
support;
[0228] c) providing radiation comprising wavelengths of radiation
to which the photosensitive resist coating layer is sensitive (the
radiation being a laser, flash exposure, focussed beam, lamp
exposure, continuous exposure or the like);
[0229] d) directing the radiation onto the surface of the resist
layer in a pattern (negative or positive, depending upon the nature
of the resist) which defines the shape of the resist which is to be
left on the hollow tube surface. This patterned distribution of
radiation may be effected by positioning of small laser spots in
the desired pattern (as is typically done with the exposure of
printing plates, especially gravure plates, a form of photoresist
coating), passing said radiation (either as a laser beam, focussed
beam or open illumnation from a lamp) through at least a first
opening in an aperture mask which is not in contact with the coated
hollow tube to expose an area on the surface of the photoresist
coating on the metal tube and alter its relative solubility. A
focussing lens may be present after of before the aperture mask or
other radiation which is directed at the surface of the resist.
[0230] The rotatable support is rotated to rotate the surface of
the photoresist layer, and then additional radiation (usually from
the same source, although a separate source, e.g., second light
emitting diode or laser may be used) comprising wavelengths of
radiation to which the photosensitive resist coating layer is
sensitive is similarly or additionally directed to the surface of
the photoresist coating to be exposed. This radiation, when used
with an aperture mask, may pass through the first opening (if the
pattern can be used a second time in the exposure of the
photoresist coating on the surface to be an additive part of the
final image desired) or through a second opening in said aperture
mask. The shape of the second opening preferably being different
than the shape of the first opening in said aperture mask. The
exposure and timing of the position of the openings in the aperture
mask and the passage of said focussed beams through said openings
so that a desired pattern of exposure of the surface of said
photoresist coating layer is formed, said desired pattern
comprising combinations of areas exposed through at least said
first opening and said second opening;
[0231] h) washing said photoresist coating layer having the desired
pattern of exposure thereon with a developer which will develop
either the exposed desired pattern of photoresist coating layer
more readily than unexposed areas of the photoresist coating layer
or developed the unexposed areas of the photoresist coating layer
more readily than the desired pattern of irradiated photoresist
coating layer to assist in removing areas of the photoresist
coating layer while leaving other areas of the photoresist coating
layer on a surface of the hollow metal tube in a negative image of
said desired pattern or in said desired pattern, thereby forming a
cylindrical element with a physically exposed pattern of metal
underneath the photoresist coating layer;
[0232] I) transferring said metal tube with a physically exposed
pattern of metal onto a chemical etch resistant support
element;
[0233] j) contacting the physically exposed pattern of metal with a
solution capable of etching the metal of the metal of the metal
tube so that said metal is etched away from physically exposed
surfaces of the metal tube and openings in the metal tube
corresponding to the pattern of physically exposed metal are
created in the metal tube element;
[0234] k) removing said metal tube from said chemical etch
resistant support element.
[0235] The process may include contacting the physically exposed
surface of the metal tubular element with a solution capable of
etching the metal of the metal tubular element comprises spraying
said solution onto said tubular element. The process may be
performed where the pattern of physically exposed metal comprises a
pattern resulting from the combination of overlapping individual
shape patterns in openings in said aperture mask and wherein each
of the individual shape patterns which are used to form a
developable image in said photoresist coating layer which is
developed into said pattern of physically exposed metal are
radiation exposed by said focussed beam of radiation through one
individual shape pattern at a time.
[0236] The rotating flat referred to above provides a means for
supporting the cylindrical elements and for assuring their exposure
to the etchant (e.g., generically a developing solution),
particularly while providing a number of cylindrical elements for
etching at one time. A Flat is shown in FIGS. 2(a) and (b).
[0237] The flat 100 comprises a supporting element 102 of etchant
resistant material (e.g., a polymeric or composite substrate, such
as polyvinyl chloride or polyolefin polymer). The supporting
element 102 is a flat sheet of the polymer, cut in a generally
round shape with a diameter of from 0.3 to 2.0 meters, preferably
from 0.5 to 1.5 meters. There is an opening 104 in the central area
of the sheet, the opening preferably having parallel sides (e.g.,
106 and/or 108b) within the opening. L-bars 110 are aligned along
the opposed parallel sides 106. The L-bars 110 have supports (not
shown) for the support elements 112 for the cylindrical elements
114 (which may be as simple as holes (not shown) into which the
ends 116 of the flexible support elements 112 may be inserted). The
L-bars 110 may contain a sufficient number of opposed holes (not
shown) to support the desired number (e.g., 2-30) of supported
cylindrical elements 114 which have already had the photoresist
coatings imaged, developed and otherwise prepared for the etch
process. The individual support elements 112 should not overlap or
be so close to each other as to prevent the ready flow of etchant
between them (or be so positioned that one element might intercept
sprayed etchant before its straight-line path would cause it to
contact another cylindrical element.
[0238] In a preferred embodiment of the present invention, the
supports for the cylindrical elements are provided in such a manner
as to allow them or cause them to rotate around their longitudinal
axis. In this way, the entire 360.degree. of the surface of the
cylindrical element is exposed to the spray of the etchant. The
support element should therefore have a diameter of its cross
section which is less than the diameter of any supporting hole (if
that is the mechanism by which it is supported) on the L-bar. The
support element might also be supported in a hole with bearings or
other means which enables or facilitates rotation of the element. A
fan-like or gear-like element or member 118 may be present on the
support element (or area of the cylindrical element which is not to
be etched) which will assist the etchant spray in rotating the
support element (and hence rotating the cylindrical element).
[0239] The flat is preferably provided in a circular or ovoid shape
so that it can revolve as it is rolled along its outside edge.
[0240] The Baume' of the solution is preferably higher because of
the increased concentration of active etchant ingredients or
standard adjuvants to etchant solutions. However, the Baume' may be
increased by the addition of inert, high specific gravity or
soluble materials and still provide benefits according to the
present invention. There need only be at least an etchant effective
amount of etchant chemistry in the solution, e.g., at least 1% by
weight active etchant, preferably at least 2, 5 or 10% by weight
active etchant material (e.g., at least one of active halides,
oxidizing acids, oxidizing agents, chelating agents, solubilizing
ingredients, etc.). The etchant solutions may comprise typical
ingredients used in etch solutions such as the main chemical
etching materials (e.g., metal chlorides, particularly the higher
valence state metal chlorides, acids, oxidizing acids particularly,
chelating agents [to maintain metal ions in solution], buffering
agents, surfactants, and the like). The preferred materials are
selected from aqueous solutions of ferric chloride, hydrochloric
acid, hydrofluoric acid, nitric acid, sulfuric acid, organic acids
(including carboxylic acids which can act as chelating agents
also), metal salts (some of which are naturally formed during the
etch process and remain in the solution, such as ferrous salts,
nitrous salts, nitric salts, aluminum salts), phosphates, alkali
metal hydroxides (to control the pH), thickening agents (e.g.,
silica or acrylates), and the like.
* * * * *