U.S. patent application number 13/271789 was filed with the patent office on 2013-04-18 for removal of an island from a laser cut article.
This patent application is currently assigned to ABBOTT CARDIOVASCULAR SYSTEMS, INC.. The applicant listed for this patent is Nicholas R. Haluck, Austin M. Leach, Patrick C. Vien. Invention is credited to Nicholas R. Haluck, Austin M. Leach, Patrick C. Vien.
Application Number | 20130092555 13/271789 |
Document ID | / |
Family ID | 48085257 |
Filed Date | 2013-04-18 |
United States Patent
Application |
20130092555 |
Kind Code |
A1 |
Haluck; Nicholas R. ; et
al. |
April 18, 2013 |
REMOVAL OF AN ISLAND FROM A LASER CUT ARTICLE
Abstract
Methods and apparatuses for use in such methods for removing
islands from laser cut articles. Methods include using a chemical
etching solution to remove material in the strut-island gap.
Optionally, heat and/or agitation can be applied during the etching
process to increase the chemical activity of the chemical etching
solution and/or to vibrate the islands out of position.
Inventors: |
Haluck; Nicholas R.; (San
Jose, CA) ; Leach; Austin M.; (San Francisco, CA)
; Vien; Patrick C.; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Haluck; Nicholas R.
Leach; Austin M.
Vien; Patrick C. |
San Jose
San Francisco
San Jose |
CA
CA
CA |
US
US
US |
|
|
Assignee: |
ABBOTT CARDIOVASCULAR SYSTEMS,
INC.
Santa Clara
CA
|
Family ID: |
48085257 |
Appl. No.: |
13/271789 |
Filed: |
October 12, 2011 |
Current U.S.
Class: |
205/661 ;
216/94 |
Current CPC
Class: |
C23F 1/02 20130101; A61L
2400/18 20130101; A61L 31/022 20130101; A61F 2/91 20130101; C23F
1/26 20130101 |
Class at
Publication: |
205/661 ;
216/94 |
International
Class: |
C23F 1/02 20060101
C23F001/02; C25F 3/16 20060101 C25F003/16; C23F 1/26 20060101
C23F001/26 |
Claims
1. A method for removing an island from a laser cut article,
comprising: providing a refractory metal workpiece having an outer
surface and an inner surface; laser cutting the refractory metal
workpiece substantially continuously along a laser cut line that
extends from the outer surface to the inner surface to produce an
article that includes a plurality of laser cuts and one or more
islands remaining between the laser cuts; and chemically treating
the article to remove the one or more islands therefrom so as to
form an implantable device.
2. The method of claim 1, wherein the laser cutting is performed in
a single pass.
3. The method of claim 1, wherein the one or more islands are
affixed to the article by one or more of slag, remelt, laser
ablated material, oxide-oxide bonding, or geometric
constraints.
4. The method of claim 1, wherein the refractory metal workpiece is
made from a material selected from the group consisting of
tantalum, niobium, tungsten, and alloys thereof.
5. The method of claim 1, wherein the implantable device is an
implantable refractory metal stent.
6. The method of claim 1, the chemically treating further
comprising disposing the article in a chemical etching solution
that includes hydrofluoric acid (HF) and nitric acid
(HNO.sub.3).
7. The method of claim 6, further comprising disposing the article
in the chemical etching solution for a period of time in a range
from about 10 minutes to about 60 minutes.
8. The method of claim 6, further comprising: sonicating in the
chemical etching solution using an ultrasonic cleaning apparatus
while the article is disposed in the chemical etching solution; and
heating the article in the chemical etching solution to a
temperature in a range from about 40.degree. C. to about 70.degree.
C. while the article is disposed in the chemical etching
solution.
9. The method of claim 1, the chemically treating further
comprising etching the article in a chemical etching solution
including at least one mineral acid.
10. The method of claim 9, the at least one mineral acid including
hydrofluoric acid (HF).
11. The method of claim 9, the at least one mineral acid including
hydrofluoric acid (HF) and nitric acid (HNO.sub.3).
12. The method claim 11, the chemical etching solution including
about 1% HF by volume to about 10% HF by volume, about 10%
HNO.sub.3 by volume to about 50% HNO.sub.3 by volume, and
water.
13. The method claim 11, the chemical etching solution including
about 1% HF by volume to about 5% HF by volume, about 20% HNO.sub.3
by volume to about 45% HNO.sub.3 by volume, and water.
14. The method claim 11, the chemical etching solution including
about 1% HF by volume to about 3% HF by volume, about 25% HNO.sub.3
by volume to about 35% HNO.sub.3 by volume, and water.
15. The method claim 11, wherein the chemical etching solution
further includes urea.
16. The method claim 11, the chemical etching solution including
about 2% HF by volume to about 4% HF by volume, about 25% HNO.sub.3
by volume to about 35% HNO.sub.3 by volume, about 0.9 weight % ("wt
%") to about 1.3 wt % urea, and water.
17. A method for removing an island from a refractory metal
article, the method comprising: providing a refractory metal
workpiece having an outer surface and an inner surface; laser
cutting the refractory metal workpiece substantially continuously
along a laser cut line that extends from the outer surface to the
inner surface in a single pass to produce a laser cut refractory
metal article that includes a plurality of laser cuts and one or
more islands remaining between the laser cuts; and treating the
laser cut refractory metal article to remove the one or more
islands therefrom, the treating comprising: disposing the laser cut
refractory metal article in a chemical etching solution that
includes hydrofluoric acid (HF) and nitric acid (HNO.sub.3) for a
period of time sufficient to remove the one or more islands
therefrom so as to form an implantable device.
18. The method of claim 17, the treating further comprising:
heating the laser cut refractory metal article in the chemical
etching solution to a temperature in a range from about 40.degree.
C. to about 70.degree. C.; and sonicating the laser cut refractory
metal article in the chemical etching solution using an ultrasonic
apparatus.
19. The method of claim 18, further comprising treating the laser
cut refractory metal article for a period of time in a range from
about 10 minutes to about 60 minutes.
20. The method claim 17, wherein the chemical etching solution
includes about 1% HF by volume to about 10% HF by volume, about 10%
HNO.sub.3 by volume to about 50% HNO.sub.3 by volume, and
water.
21. The method of claim 17, wherein the refractory metal workpiece
is made from a material selected from the group consisting of
tantalum, niobium, tungsten, and alloys thereof.
22. The method of claim 17, wherein the refractory metal workpiece
is made from a tantalum alloy, comprising: about 75 to about 90
weight percent tantalum; about 8 to about 12 weight percent
niobium; about 2 to about 10 weight percent tungsten.
23. The method of claim 22, wherein the refractory metal workpiece
further comprises at least one of zirconium or molybdenum.
24. A method for removing an island from an implantable article,
the method comprising: providing a tubular a tantalum alloy
workpiece having an outer surface and an inner surface; laser
cutting the tubular a tantalum alloy workpiece substantially
continuously along a patterned laser cut line that extends from the
outer surface to the inner surface to produce a laser cut stent
that includes a patterned plurality of laser cut struts and one or
more islands remaining between the laser cut struts, wherein the
laser cut struts have a cross-sectional dimension of about 40 .mu.m
to about 120 .mu.m; and treating the laser cut stent to remove the
one or more islands therefrom, the treating comprising: disposing
the laser cut stent in a chemical etching solution that includes
hydrofluoric acid (HF) and nitric acid (HNO.sub.3); heating the
laser cut stent in the chemical etching solution to a temperature
in a range from about 40.degree. C. to about 70.degree. C.;
sonicating the laser cut stent in the chemical etching solution
using an ultrasonic apparatus; and treating the laser cut stent in
the chemical etching solution under heating and sonication for a
period of time sufficient to remove the one or more islands
therefrom so as to form an implantable stent.
25. The method of claim 24, wherein the laser cutting is performed
in a single pass using a picosecond laser apparatus.
26. The method of claim 24, wherein the tubular tantalum alloy
workpiece includes tantalum and one or more of niobium, tungsten,
zirconium and molybdenum.
27. The method of claim 24, wherein the laser cut struts of the
laser cut stent have a cross-sectional dimension of about 45 .mu.m
to about 80 .mu.m.
28. The method of claim 24, wherein the laser cut struts of the
laser cut stent have a cross-sectional dimension of about 50 .mu.m
to about 80 .mu.m.
29. A method of manufacturing an implantable article, comprising
providing a first refractory metal workpiece having an outer
surface and an inner surface, the first refractory metal workpiece
being made from a material selected from the group consisting of
tantalum, niobium, tungsten, zirconium, molybdenum, and alloys
thereof; laser cutting the first refractory metal workpiece in a
single pass using a picosecond laser apparatus substantially
continuously along a patterned laser cut line that extends from the
outer surface to the inner surface to form a laser cut stent that
includes a patterned plurality of laser cut struts and one or more
islands remaining between the laser cut struts, wherein the laser
cut struts have a cross-sectional dimension of about 40 .mu.m to
about 120 .mu.m; treating the laser cut stent for a period of time
sufficient to remove the one or more islands therefrom, the
treating comprising: disposing the laser cut stent in a chemical
etching solution that includes hydrofluoric acid (HF) and nitric
acid (HNO.sub.3); heating the laser cut stent in the chemical
etching solution to a temperature in a range from about 40.degree.
C. to about 70.degree. C.; sonicating the laser cut stent in the
chemical etching solution using an ultrasonic apparatus; wherein
the treating does not include use of a mask capable of defining a
plurality of struts and a plurality of islands remaining between
the struts; electropolishing the laser cut metal stent in an
electropolishing solution; and heat treating the laser cut
refractory metal stent so as to form an implantable stent.
Description
BACKGROUND
[0001] 1. Technological Field
[0002] The present disclosure relates to laser cut articles and
methods for their manufacture.
[0003] 2. The Relevant Technology
[0004] The human body includes various lumens, such as blood
vessels or other passageways. A lumen may sometimes become at least
partially blocked or weakened. For example, a lumen may be at least
partially blocked by a tumor, by plaque, or both. An at least
partially blocked lumen may be reopened or reinforced with an
implantable stent.
[0005] A stent is typically a tubular body that is placed in a
lumen in the body. A stent may be delivered inside the body by a
catheter that supports the stent in a reduced size configuration as
the stent is delivered to a desired deployment site within the
body. At the deployment site, the stent may be expanded so that,
for example, the stent contacts the walls of the lumen to expand
the lumen.
[0006] Advancement of the stent through the body may be monitored
during deployment. After the stent is delivered to the target site,
the stent can be monitored to determine whether the placement
thereof is correct and/or the stent is functioning properly.
Methods of tracking and monitoring stent after delivery include
X-ray fluoroscopy and magnetic resonance imaging ("MRI").
[0007] Stents made from tantalum alloys have been identified as
being easily detectable using X-ray fluoroscopy and MRI because of
the high density of tantalum. Furthermore, tantalum alloys are
typically compatible with MRI techniques because they do not
produce substantial amounts of magnetic artifacts and/or image
distortions or voids during MRI imaging. Additionally, tantalum
alloys have proven to be biocompatible and corrosion resistant.
SUMMARY
[0008] Articles such as stents are typically fabricated by laser
cutting a selected pattern into a length of metal tubing. Following
laser cutting, islands (i.e., the cut out sections between the
struts and other structural features) may be stuck in between the
struts and other features of the laser cut pattern for a variety of
reasons. The present disclosure includes methods for removing
islands from laser cut articles using a chemical etching solution
to remove material in the strut-island gap. The methods disclosed
herein may optionally include application of heat and/or ultrasonic
agitation to increase the chemical activity of the chemical etching
solution and to vibrate the islands out of position. The etching
methods described here can be used to effectively remove islands
from laser cut articles with no structural damage and no operator
dependency.
[0009] In one embodiment, a method for removing an island from a
laser cut article is disclosed. The method includes steps of (1)
providing a refractory metal workpiece having an outer surface and
an inner surface, (2) laser cutting the refractory metal workpiece
substantially continuously along a laser cut line that extends from
the outer surface to the inner surface to produce an article that
includes a plurality of laser cuts and one or more islands
remaining between the laser cuts, and (3) chemically treating the
article to remove the one or more islands therefrom so as to form
an implantable device. Typically, the islands may be affixed to the
laser cut article with one or more of slag, remelt, laser ablated
material, oxide-oxide bonding; or the islands may be affixed to the
laser cut article by geometric constraints. According to one
embodiment, the refractory metal workpiece is made from a material
selected from the group consisting of tantalum, niobium, tungsten,
and alloys thereof. According to another embodiment, the
implantable device is an implantable refractory metal stent.
[0010] In one embodiment, the chemical treating step further
includes disposing the article in a chemical etching solution that
includes hydrofluoric acid (HF), nitric acid (HNO.sub.3), and,
optionally, urea. Optionally, the chemical treating step can
further include agitating the article in the chemical etching
solution and/or heating the article in the chemical etching
solution to a temperature in a range from about 40.degree. C. to
about 70.degree. C. while the article is disposed in the chemical
etching solution.
[0011] In another embodiment, a method for removing an island from
a refractory metal article is disclosed. The method includes steps
of (1) providing a refractory metal workpiece having an outer
surface and an inner surface, (2) laser cutting the refractory
metal workpiece substantially continuously along a laser cut line
that extends from the outer surface to the inner surface in a
single pass to produce a laser cut refractory metal article that
includes a plurality of laser cuts and one or more islands
remaining between the laser cuts, and (3) treating the laser cut
refractory metal article to remove the one or more islands
therefrom. The treating includes disposing the laser cut refractory
metal article in a chemical etching solution that includes HF,
HNO.sub.3, and, optionally, urea for a period of time sufficient to
remove the one or more islands therefrom so as to form an
implantable device.
[0012] In yet another embodiment, a method for removing an island
from an implantable article is disclosed. The method includes steps
of (1) providing a tubular a tantalum alloy workpiece having an
outer surface and an inner surface, (2) laser cutting the tubular a
tantalum alloy workpiece substantially continuously along a
patterned laser cut line that extends from the outer surface to the
inner surface to produce a laser cut stent that includes a
patterned plurality of laser cut struts and one or more islands
remaining between the laser cut struts, wherein the laser cut
struts have a cross-sectional dimension of about 40 .mu.m to about
120 .mu.m, (3) treating the laser cut refractory metal stent to
remove the one or more islands therefrom, and (4) treating the
laser cut refractory metal stent in the etching solution under
heating and sonication for a period of time sufficient to remove
the one or more islands therefrom so as to form an implantable
stent. The treating includes (i) disposing the laser cut refractory
metal stent in a chemical etching solution that includes HF,
HNO.sub.3, and, optionally, urea, (ii) heating the laser cut
refractory metal stent in the chemical etching solution to a
temperature in a range from about 40.degree. C. to about 70.degree.
C., (iii) sonicating the laser cut refractory metal stent in the
chemical etching solution using an ultrasonic apparatus. The
treating does not include use of a mask capable of defining a
plurality of struts and a plurality of islands remaining between
the struts.
[0013] In still another embodiment, a method of manufacturing an
implantable article includes (1) providing a first refractory metal
workpiece having an outer surface and an inner surface, the first
refractory metal workpiece being made from a material selected from
the group consisting of tantalum, niobium, tungsten, zirconium,
molybdenum, and alloys thereof, (2) laser cutting the refractory
metal workpiece in a single pass using a picosecond laser apparatus
substantially continuously along a patterned laser cut line that
extends from the outer surface to the inner surface to form a laser
cut stent that includes a patterned plurality of laser cut struts
and one or more islands remaining between the laser cut struts,
wherein the laser cut struts have a cross-sectional dimension of
about 40 .mu.m to about 120 .mu.m, (3) treating the laser cut
refractory metal stent to remove the one or more islands therefrom,
(4) treating the laser cut refractory metal stent in the etching
solution under sonication and heating for a period of time
sufficient to remove the one or more islands therefrom so as to
form an implantable stent, (5) electropolishing the laser cut
refractory metal stent in an electropolishing solution, and (6)
heat treating the laser cut refractory metal stent so as to form an
implantable stent. The treating includes (i) disposing the laser
cut refractory metal stent in a chemical etching solution that
includes HF, HNO.sub.3, and, optionally, urea, (ii) heating the
laser cut refractory metal stent in the chemical etching solution
to a temperature in a range from about 40.degree. C. to about
70.degree. C., (iii) sonicating the laser cut refractory metal
stent in the chemical etching solution using an ultrasonic
apparatus.
[0014] These and other objects and features of the present
invention will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of embodiment of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] To further clarify the above and other advantages and
features of the present invention, a more particular description of
the invention will be rendered by reference to specific embodiments
thereof which are illustrated in the appended drawings. It is
appreciated that these drawings depict only illustrated embodiments
of the invention and are therefore not to be considered limiting of
its scope. The invention will be described and explained with
additional specificity and detail through the use of the
accompanying drawings in which:
[0016] FIG. 1A schematically illustrates a laser cut stent having
islands intact;
[0017] FIG. 1B illustrates an enlarged view of the stent of FIG.
1A;
[0018] FIG. 2A schematically illustrates an isometric view of a
laser cut stent similar to the stent depicted in FIG. 1A with the
islands having been removed according to one or more the methods
described herein;
[0019] FIG. 2B illustrates an enlarged view of the stent of FIG.
2A;
[0020] FIG. 3 is a photomicrograph of a laser cut stent showing a
cleaned surface and intact islands;
[0021] FIG. 4 is an electron micrograph of the interior diameter of
a laser cut stent with intact islands;
[0022] FIG. 5 is an electron micrograph of a laser cut stent
showing a cross-section of individual laser cuts;
[0023] FIG. 6 is a flow diagram illustrating a method for removing
an island from a laser cut article;
[0024] FIG. 7 is a flow diagram illustrating a method for removing
an island from a laser cut article;
[0025] FIG. 8 is a flow diagram illustrating a method for removing
an island from a laser cut article;
[0026] FIG. 9 is a flow diagram illustrating a method for
manufacturing a laser cut stent;
[0027] FIG. 10 is a flow diagram illustrating another method for
manufacturing a laser cut stent; and
[0028] FIG. 11 illustrates a device adapted for supporting a
plurality of laser cut articles during a procedure for removing one
or more islands.
DETAILED DESCRIPTION
[0029] Articles such as stents are typically fabricated by laser
cutting a selected pattern into a length of metal tubing. Following
laser cutting, islands (i.e., the cut out sections between the
struts and other structural features) may be stuck in between the
struts and other features of the laser cut pattern for a variety of
reasons. The present disclosure includes methods for removing
islands from laser cut articles using a chemical etching solution
to remove material in the strut-island gap. The methods disclosed
herein may optionally include application of heat and/or ultrasonic
agitation to increase the chemical activity of the chemical etching
solution and to vibrate the islands out of position. The etching
methods described here can be used to effectively remove islands
from laser cut articles with no structural damage and no operator
dependency. And while the description that follows refers to stents
and other implantable articles, one will appreciate that the
methods and apparatuses described herein can be applied to
essentially any metal laser cut article.
I. Stents
[0030] Referring now to FIGS. 1A and 1B, an exemplary laser cut
stent 100 having intact islands 112 is illustrated. Laser cut stent
100 is fabricated by laser cutting a selected stent pattern into a
metal tube. The laser cuts extend all the way from the outer
surface of the tube through the inner surface of the tube. In the
illustrated embodiment, the laser cut stent 100 appears to have a
solid outer wall with a series of patterned cuts in the tube. That
is, the cut-out material tends to stay in the tube even after laser
cutting.
[0031] The stent 100 in the illustrated embodiment includes a
number of structural elements such as struts 104, bends 106, and
connector elements 108. The regions of waste material left in
between the structural elements after the laser cutting process are
referred to as islands 112. The islands 112 need to be removed in
order to convert the laser cut stent 100 into an implantable stent
such as stent 200 shown in FIG. 2. Each island 112 in the
illustrated embodiment further includes a series of circular cuts
114 joined by linear cuts 116 and 118 that are positioned in the
islands 112 to facilitate removal of the islands 112.
[0032] Laser cut stent 100 is made up of a number of ring
structures 102 that are coupled together lengthwise. The ring
structures 102 are in turn made up of a number of strut elements
104 that are joined together by bends 106. Individual rings (e.g.,
rings 102a and 102b) are interconnected longitudinally one to
another by a number of connector elements 108 that connect a subset
of the bends 106 to the illustrated double bend structures 110a and
110b. In the illustrated example, the strut elements 104, bends
106, connector elements 108, and the other structural elements have
a square or slightly rectangular profile with dimensions of about
70 .mu.m to about 150 .mu.m on a side.
[0033] The illustrated stent 100 is fabricated by laser cutting the
desired pattern of struts 104, bends 106, and connectors 108 into a
length of metal tubing. Stents such as stent 100 are typically
laser cut out of metal tubes formed from metals such as, but not
limited to, nickel-titanium, cobalt-chromium, stainless steel, and
refractory metals such as tantalum and tantalum alloys. When the
desired stent pattern is cut, the material between the patterned
cuts (i.e., the islands 112) typically stays attached to the tube.
In many respects, the laser cut stent 100 with attached islands 112
resembles a solid tube having a series of patterned lines cut into
the tube. This is illustrated by the line drawings in FIGS. 1A and
1B and in the photomicrographs shown in FIGS. 3 and 4.
[0034] The islands 112 can stay attached to the laser cut stent 100
by a number of possible mechanisms. For example, the islands 112
can be affixed to the stent 100 by slag, remelt, or oxide-oxide
bonding left by the laser cutting process. The laser cutting
process also results in the re-deposition of laser ablated material
into the gap between the laser cut features (e.g., struts 104,
bends 106, and connectors 108) and the islands 112.
[0035] Even in the absence of slag, remelt, oxide-oxide bonding, or
deposited laser ablated material, the islands 112 may be
geometrically constrained from falling out of the laser cut tube by
the physical dimensions of the tube and the cuts and/or because of
changes that can occur as a result of the laser cutting process. In
the present case, for example, blank tubes for stent fabrication
are only about 1.5 mm to about 5 mm in diameter and the material is
only about 50 .mu.m to about 110 .mu.m thick. In turn, the kerf
from the laser used to cut the stent pattern is only about 10 .mu.m
to about 15 .mu.m on the outer diameter of the tube and about 2
.mu.m to about 4 .mu.m on the inner diameter. This is illustrated
in FIGS. 4 and 5. FIG. 4 is an electron micrograph of a
stent-patterned laser cut tube 400 at approximately 60.times.
magnification. Given that the tube 400 is only about 1.5 mm in
diameter, one can readily appreciate the precision of the laser
cuts 402 that are visible on the interior of a laser cut tube 400.
One can also see that the laser cuts 402 extend all the way through
the tub 400. FIG. 5 is an electron micrograph of a cross-section
502 of a laser cut tube 500 at approximately 600.times.
magnification. FIG. 5 illustrates the size difference of the laser
cut kerf on the outer diameter 504 and the inner diameter 506 of a
laser cut tube 500. As mentioned above, the laser kerf is only
about 10 .mu.m to about 15 .mu.m on the outer diameter 504 of the
tube 500 and about 2 .mu.m to about 4 .mu.m on the inner diameter
506, which leaves relatively little space for the islands to fall
out on their own. In another example, the act of laser cutting the
tube may have the effect of relieving stress in the tube, which can
cause the material to expand slightly or twist slightly,
essentially locking the islands 112 in place.
[0036] The island removal methods disclosed herein are an
alternative to traditional island removal techniques (e.g.,
"flicking"), which can damage delicate laser cut articles. The
refractory metal materials (e.g., tantalum alloys) discussed herein
are durable, biocompatible, and radiopaque. Refractory metal tubes
can be laser cut to produce stents having struts with an as-cut
cross-sectional dimension of about 80 .mu.m and finished dimensions
of about 50 .mu.m to about 65 .mu.m. Nevertheless, the thin struts
and other structural elements like those shown in the illustrated
examples are quite fragile and are therefore easily distorted,
which disfavors the use of flicking and other traditional
techniques for island removal.
[0037] Also, as explained above, the laser cutting process leaves a
very small kerf that leaves very little room for the islands to
fall out on their own. Traditionally, island removal can be
facilitated by using multiples passes with the laser, which widens
the kerf. For example, some stent designs and materials can
tolerate up to 6 or 7 passes through the laser cutting apparatus,
which generally makes the islands fall out on their own or with
minimal flicking. In addition, it is possible to increase the size
of the laser kerf by increasing the laser power or increasing the
gas pressure in the laser. However, these processes can increase
the size of the heat-affected zone and can present dimensional
difficulties in terms of tolerances of the strut widths and crest
radii, since you are depending on the laser's mechanical controls
to ensure the laser is cutting essentially the exact same location
on each laser pass. In addition, the laser cutting process can
cause dimensional changes in the tube that can essentially wedge
the islands in the tube. The effectiveness of traditional island
removal techniques such as flicking also depends to a large extent
on operator skill. For these reasons and others, traditional island
removal techniques are not applicable to the laser cut articles
discussed herein.
[0038] Referring now to FIGS. 2A and 2B, a stent 200 is shown.
Stent 200 is similar to the stent 100 depicted in FIGS. 1A and 1B
except the islands 112 have been removed. Stent 200 is made up of a
number of ring structures 102 that include strut elements 104 that
are joined together by bends 106. Individual rings (e.g., rings
102a and 102b) are interconnected one to another by a number of
connector elements 108 that connect a subset of the bends 106a to
the illustrated double bend structures 110a and 110b. Removal of
the islands 112 according to the methods disclosed herein produces
a stent 200 with an open, expandable structure that is well-suited
to, for example, scaffolding a blood vessel.
Ii. Methods for Island Removal
[0039] The methods described herein relate to methods for removing
an island from a laser cut article (e.g., a stent) using chemical
etching solution to remove material in the strut-island gap. The
methods disclosed herein may optionally include application of heat
and/or ultrasonic agitation to increase the chemical activity of
the chemical etching solution and to vibrate the islands out of
position. The island removal methods disclosed herein are an
alternative to traditional island removal techniques (e.g.,
"flicking"), which can damage delicate laser cut articles and which
are not particularly effective with the laser cut articles
discussed herein
[0040] Referring now to FIG. 6, a flow diagram illustrating an
embodiment of a general method 600 for removing one or more islands
from a laser cut article is shown. The method 600 includes act 610
of disposing a laser cut article in a chemical etching solution and
an act 620 of etching the laser cut article to remove one or more
islands therefrom. In one embodiment, the laser cut article may be
etched in act 620 for about 10 to 60 minutes or about 15 to 30
minutes. In actual practice, however, the etching time necessary to
remove the islands from the laser cut article may be affected by
parameters such as, but not limited to, the concentration of the
etchant, type of acid in the etchant, the size of the kerf, the
temperature of the etchant, presence or absence of
stirring/agitation of the etchant, and combinations thereof.
[0041] In one embodiment, the laser cut article etched in act 610
can be made from essentially any known metal or metal alloy. For
example, the article can be made from steel, a stainless steel such
as, but not limited to, 316L stainless steel, a nickel-titanium
alloy such as, but not limited to, a binary Ni--Ti alloy, a cobalt
chromium alloy such as, but not limited to, L605 cobalt chromium, a
platinum chromium alloy, palladium-containing alloys,
molybdenum-containing alloys, a cobalt super alloy, a refractory
metal, or a refractory metal alloy such as, but not limited to, a
tantalum alloy, and the like.
[0042] Referring now to FIG. 11 a device 1100 that can be used to
dispose an article (e.g., stent 1160) in a chemical etching
solution is illustrated. The device 1100 includes a handle 1110
that can be used to lower or raise the device 1100 into or out of a
chemical etching solution, a plurality of supports 1120 that can be
used to support one or more laser cut articles (e.g., stents 1160),
a support base 1130 that includes cut-outs 1140 for allowing flow
of the chemical etchant around the device 1100, and a plurality of
support legs 1150. Because of the corrosivity of the chemical
etchant, it is preferred that the device 1100 be made from an inert
material. Suitable examples of inert materials include, but are not
limited to, plastics such as polyethylene and
polytetrafluoroethylene (PTFE, Teflon).
[0043] In one embodiment, the etching solution employed in act 610
or any of the other methods disclosed herein includes at least one
mineral acid. A mineral acid is an inorganic acid derived from one
or more inorganic compounds. All mineral acids release hydrogen
ions when dissolved in water. Suitable examples of mineral acids
include, but are not limited to, hydrochloric acid (HCl), nitric
acid (HNO.sub.3), phosphoric acid (H.sub.3PO.sub.4), sulfuric acid
(H.sub.2SO.sub.4), hydrofluoric acid (HF), and hydrobromic acid
(HBr).
[0044] Most mineral acids are classified as "strong acids," meaning
that they dissociate completely when they are dissolved in aqueous
solution. One notable exception is hydrofluoric acid (HF), which is
technically classified as a weak acid. HF is a solution of hydrogen
fluoride gas in water. HF is best known to the public for its
ability to dissolve glass by reacting with SiO.sub.2, the major
component of most glass, to form silicon tetrafluoride gas and
hexafluorosilicic acid. HF is also notable for its ability to
dissolve chemically resistant metal and semimetal oxides and
refractory metals such as, but not limited to, tantalum, niobium,
tungsten, and alloys thereof.
[0045] In spite of the fact that HF is technically a "weak" acid,
working with HF can be extremely dangerous. HF is readily absorbed
through the skin where it can react destructively with the calcium
in bones and/or the calcium in blood serum. As a result, acute
exposure to HF can, for example, require limb amputation in some
cases due to HF's ability to react with and corrode the calcium
compounds that form the structure of bone. In other instances, HF
exposure can even cause cardiac arrest through the depletion of
serum calcium levels due to the formation of insoluble calcium
fluoride.
[0046] In one embodiment, the mineral acid in the chemical etching
solution employed in act 610 includes at least hydrofluoric acid
(HF). In another embodiment, the chemical etching solution employed
in act 610 includes hydrofluoric acid (HF) and nitric acid
(HNO.sub.3). In yet another embodiment, the chemical etching
solution employed in act 610 includes about 1% HF by volume to
about 10% HF by volume, about 10% HNO.sub.3 by volume to about 50%
HNO.sub.3 by volume, and water, or preferably about 1% HF by volume
to about 5% HF by volume, about 20% HNO.sub.3 by volume to about
45% HNO.sub.3 by volume, and water, or more preferably about 2% HF
by volume to about 4% HF by volume, about 25% HNO.sub.3 by volume
to about 35% HNO.sub.3 by volume, and water.
[0047] In still yet another embodiment, the chemical etching
solution employed in act 610 includes about 1% HF by volume to
about 10% HF by volume, about 10% HNO.sub.3 by volume to about 50%
HNO.sub.3 by volume, about 0.5 weight % to about 2 weight % urea,
and water, or preferably about 1% HF by volume to about 5% HF by
volume, about 20% HNO.sub.3 by volume to about 45% HNO.sub.3 by
volume, about 0.8 weight % to about 1.5 weight % urea, and water,
or more preferably about 2% HF by volume to about 4% HF by volume,
about 25% HNO.sub.3 by volume to about 35% HNO.sub.3 by volume,
about 0.9 weight % to about 1.3 weight % urea, and water. Without
being tied to one theory, it is believed that the addition of urea
to the chemical etching solution may help to stabilize the solution
and to increase its longevity (i.e., increase the number of
articles that can be etched before having to change the solution).
Weight and volume percentages for an etching solution containing
about 2% HF by volume to about 4% HF by volume, about 25% HNO.sub.3
by volume to about 35% HNO.sub.3 by volume, about 0.9 weight % to
about 1.3 weight % urea, and water are shown below in Table 1.
TABLE-US-00001 TABLE 1 Compo- Weight % Low Range High Range nent
(w/w) Weight % Volume % Weight % Volume % HNO.sub.3 25-35% 25%
18.9% 35% 27.8 HF 2-4% 2% 1.84% 4% 3.5% H.sub.2O 56-76% 72.1% 79.2%
59.7% 68.7% Urea 0.9-1.3% 0.9% 1.0 1.3% 1.5%
[0048] Referring now to FIG. 7, another flow diagram illustrating a
method 700 for removing an island from a laser cut article is
shown. The method 700 includes an act 710 of providing a first
refractory metal article that includes a plurality of laser cuts
and one or more islands remaining between the laser cuts and an act
720 of chemically treating the article to remove the one or more
islands therefrom so as to form an implantable device.
[0049] In one embodiment, the article provided in act 710 is made
from a material selected from the group consisting of tantalum,
niobium, tungsten, and alloys thereof. Suitable examples of
refractory metals employed in any of the methods discussed herein
can include, but are not limited to, tantalum, niobium, tungsten,
and alloys thereof. It has been found that a tantalum alloy that
includes tantalum, niobium, and at least one additional element
selected from the group consisting of tungsten, zirconium,
molybdenum, and/or at least one of hafnium, rhenium, and cerium can
fulfill the mechanical and biocompatibility requirements needed for
functioning as in a medical device.
[0050] In one embodiment, the refractory metal articles disclosed
herein can be made from an alloy including (a) about 0.1 weight
percent to about 70 weight percent niobium, (b) about 0.1 weight
percent to about 30 weight percent of at least one element selected
from the group consisting of tungsten, zirconium, and molybdenum,
(c) up to 5 weight percent of at least one element selected from
the group consisting of hafnium, rhenium, and cerium, (d) and
tantalum.
[0051] In one embodiment, the refractory metal articles disclosed
herein can be made from a tantalum alloy that includes a tantalum
content of about 78 weight-percent ("wt %") to about 91 wt %, a
niobium content of about 7 wt % to about 12 wt %, and a tungsten
content of about 1 wt % to about 10 wt %. However, the tantalum
alloy may also include other alloying elements, such as one or more
grain-refining elements in an amount up to about 5 wt % of the
tantalum alloy. For example, the one or more grain-refining
elements may include at least one of hafnium, cerium, or rhenium.
Tungsten is provided to solid-solution strengthen tantalum, and
niobium is provided to improve the ability of tantalum to be drawn.
The tantalum alloy is a substantially single-phase, solid-solution
alloy having a body-centered cubic crystal structure. However, some
secondary phases may be present in small amounts (e.g., inclusions)
depending upon the processing employed to fabricate the tantalum
alloy.
[0052] The composition of the tantalum alloy may be selected from a
number of alloy compositions according to various embodiments. In
an embodiment, the niobium content is about 9 wt % to about 10.5 wt
%, the tungsten content is about 6.0 wt % to about 8 wt %, and the
balance may include tantalum (e.g., the tantalum content being
about 80 wt % to about 83 wt %) and, if present, other minor
alloying elements and/or impurities. In a more detailed embodiment,
the niobium content is about 10 wt %, the tungsten content is about
7.5 wt %, and the balance may include tantalum (e.g., the tantalum
content being about 82.5 wt %) and, if present, other minor
alloying elements and/or impurities. In another more detailed
embodiment, the niobium content is about 10 wt %, the tungsten
content is about 2.5 wt %, and the balance may include tantalum
(e.g., the tantalum content being about 87.5 wt %) and, if present,
other minor alloying elements and/or impurities.
[0053] In another embodiment, the niobium content is about 10.5 wt
% to about 13 wt %, the tungsten content is about 5.0 wt % to about
6 wt %, and the balance may include tantalum (e.g., the tantalum
content being about 80 wt % to about 82 wt %) and, if present,
other minor alloying elements and/or impurities. In a more detailed
embodiment, the niobium content is about 12.5 wt %, the tungsten
content is about 5.8 wt %, and the balance may include tantalum
(e.g., the tantalum content being about 81 wt % to about 81.5 wt %)
and, if present, other minor alloying elements and/or
impurities.
[0054] In a specific example, the tantalum-containing refractory
metal article disclosed herein may be made from a tantalum alloy
that includes about 82.5 weight percent tantalum, about 10 weight
percent niobium, and about 7.5 weight percent tungsten.
[0055] In another specific example, the tantalum-containing
refractory metal article disclosed herein may be made from a
tantalum alloy that includes about 87.5 weight percent tantalum,
about 10 weight percent niobium, and about 2.5 weight percent
tungsten.
[0056] In an embodiment, the refractory metal (e.g., a tantalum
alloy) may exhibit a grain microstructure including recrystallized,
generally equiaxed grains characteristic of being formed by heat
treating a precursor product or a stent body itself, both of which
may be severely plastically deformed in a drawing process.
Depending upon the extent of recrystallization process, the grain
microstructure may be only partially recrystallized. In some
embodiments, the recrystallization process may substantially
completely recrystallize the grain microstructure with the new
recrystallized grains having consumed substantially all of the old
deformed grains. Even when the grain microstructure is partially
recrystallized, it will be apparent from microstructural analysis
using optical and/or electron microscopy that the grain
microstructure includes some recrystallized grains having, for
example, a generally equiaxed geometry. An average grain size of
the tantalum alloy may be about 10 .mu.m to about 20 .mu.m and,
more particularly, about 13 .mu.m to about 16 .mu.m depending on
the extent of recrystallization and the amount of the optional one
or more grain-refining alloy elements in the tantalum alloy.
[0057] In other embodiments, the refractory metal alloy may be
stress relieved at a temperature below a recrystallization
temperature of the tantalum alloy so that the grain microstructure
is relatively unchanged from the as-drawn condition. Thus, in the
stress-relieved condition, the grain microstructure may include
essentially only non-equiaxed, deformed, cold-worked grains.
However, the stress-relief heat treatment may at least partially
remove at least one of hydrogen, oxygen, or oxygen from the
tantalum alloy, which can detrimentally embrittle the tantalum
alloy. Thus, the tantalum alloy in the stress-relieved condition
may exhibit an improved ductility relative to the as-drawn
condition, while the tensile yield strength and tensile ultimate
tensile strength are generally unaffected by the stress-relief heat
treatment.
[0058] The heat-treated refractory metal alloy from which the stent
body is made may exhibit combination of strength (e.g., tensile
yield strength and ultimate tensile strength) and ductility (e.g.,
percent elongation) suitable to withstand loading conditions
encountered when implanted and utilized in a lumen of a living
subject. The tensile yield strength may be the 0.2% offset yield
strength determined in a uniaxial tensile test when no yield point
is present, and the yield point if the tantalum alloy exhibits a
yield point. For example, the tantalum alloy may exhibit a tensile
elongation of about 9% to about 40%, a tensile yield strength of
about 400 MPa to about 815 MPa, and an ultimate tensile strength of
about 500 MPa to about 850 MPa as determined by, for example,
tensile testing a tubular body from which the stent body may be cut
from or a drawn wire in a uniaxial tensile test. In an embodiment,
the tantalum alloy (e.g., about 82.5 wt % tantalum, about 10 wt %
niobium, and about 7.5 wt % tungsten) may exhibit a tensile
elongation of about 9% to about 40%, a tensile yield strength of
about 455 MPa to about 810 MPa, and an ultimate tensile strength of
about 515 MPa to about 850 MPa. In another embodiment, the tantalum
alloy may exhibit a tensile elongation of about 10% to about 25%, a
tensile yield strength of about 400 MPa to about 500 MPa, and an
ultimate tensile strength of about 500 MPa to about 550 MPa. In one
embodiment, the tantalum alloy may exhibit a tensile elongation of
about 20% to about 23%, a tensile yield strength of about 450 MPa
to about 500 MPa, and an ultimate tensile strength of about 500 MPa
to about 550 MPa.
[0059] In an embodiment, a heat-treated refractory metal alloy from
which the stent body is made having a tantalum content of about
87.5 wt %, a niobium content of about 10 wt %, and a tungsten
content of about 2.5 wt % and an at least partially recrystallized
grain microstructure may exhibit a tensile elongation of about 9%
to about 40%, a tensile yield strength of about 400 MPa to about
800 MPa, and an ultimate tensile strength of about 500 MPa to about
850 MPa. In one embodiment, the heat-treated tantalum alloy may
exhibit a tensile elongation of about 10% to about 25%, a tensile
yield strength of about 400 MPa to about 500 MPa, and an ultimate
tensile strength of about 500 MPa to about 550 MPa.
[0060] In an embodiment, a stress-relieved refractory metal alloy
from which the stent body is made having a tantalum content of
about 82.5 wt %, a niobium content of about 10 wt %, and a tungsten
content of about 7.5 wt % may exhibit a percent elongation of about
9% to about 15% (e.g., about 10% to about 11%), a tensile yield
strength of about 650 MPa to about 850 MPa, and an ultimate tensile
strength of about 700 MPa to about 850 MPa. In the stress-relieved
condition, the percent elongation of the tantalum alloy may
increase by at least about 100%, at least about 200%, at least
about 300%, or about 200% to about 300% compared to the same
tantalum alloy in the as-drawn (i.e., un-stress-relieved
condition), while the tensile yield strength and ultimate tensile
strength are reduced. As yield strength and ultimate tensile
strength go down, the ductility of the tantalum alloy tends to
increase. The reduction in tensile yield strength and ultimate
tensile strength and the increase in ductility needs to be
balanced, but, in general, increasing ductility tends to yield a
more durable medical device fabricated from the tantalum alloy. For
example, an alloy having increased ductility is less likely to
crack when radially stressed. The grain microstructure may also be
relatively un-changed from the as-drawn condition and may include
deformed, non-equiaxed grains.
[0061] Metals, such as tungsten, molybdenum, tantalum, niobium,
rhenium, and alloys thereof are known to be highly reactive with
and/or have a high solubility for oxygen, hydrogen, and other
atmospheric gases. It is therefore desirable to limit the presence
of such gases during the drawing, laser cutting, or vacuum laser
cutting. As such, in one embodiment, the article provided in act
710 is manufactured using at least one of drawing, laser cutting,
or vacuum laser cutting. Drawing a partial vacuum may provide a
sufficient vacuum level so that the refractory metal article does
not react with and/or dissolve a sufficient amount of hydrogen to
cause hydrogen embrittlement before, during, and/or after the act
of laser cutting. For example, the partial vacuum can be
characterized as a vacuum environment ranging from about 25 torr to
about 10.sup.-12 ton in pressure (i.e., approximately 3000 Pa to
approximately 10.sup.-10 Pa). The pressure may range from about 1
ton to about 10.sup.-7 ton (i.e., approximately 100 Pa to
approximately 10.sup.-5 Pa) or, more specifically, the pressure may
range from about from about 10.sup.-3 ton to about 10.sup.-7 ton
(i.e., approximately 10.sup.-1 Pa to approximately 10.sup.-5
Pa).
[0062] Suitable examples of lasers that can be used to cut the
refractory metal workpiece in a single pass include, but are not
limited to, fiber lasers and ultrashort pulse lasers such as a
picosecond lasers. A fiber laser is a laser in which the active
gain medium is an optical fiber doped with rare-earth elements such
as erbium, ytterbium, neodymium, dysprosium, praseodymium, and
thulium. Typical fiber lasers cut by melting through the material,
which can produce a significant heat affected zone and metallic
slag. Fiber lasers are typically pumped by semiconductor laser
diodes or by other fiber lasers.
[0063] A picosecond (ps) laser is a laser that emits high-energy
pulses of optical radiation that can cut materials, such as
refractory metals, by ablation (i.e., vaporization) of the
material. A typical ps-laser pulse has a duration between about 1
ps and some tens of picoseconds. Ps-pulses are short enough to
avoid thermal diffusion of the energy and reach the peak power
densities necessary for these ablation processes. As a result,
ps-lasers typically do not substantially produce slag or produce a
minimal amount of slag associated with the cut, and the size of the
heat affected zone is minimized.
[0064] A variety of laser types can generate picosecond pulses,
with other performance parameters varying in wide ranges. Suitable
lasers include actively or passively mode-locked solid-state bulk
lasers. These can provide very clean (i.e., transform-limited and
low-noise) ultrashort pulses with pulse repetition rates varying
from a few megahertz to more than 100 GHz. For example, a passively
mode-locked Nd:YAG or vanadate laser can easily generate 10-ps
pulses with several watts of output power, and thin-disk lasers can
generate many tens of watts in shorter pulses.
[0065] In one embodiment, act 720 further includes disposing the
article in a chemical etching solution that includes hydrofluoric
acid (HF) nitric acid (HNO.sub.3), and, optionally, urea.
Optionally, act 720 can further include agitating the article in
the chemical etching solution while the article is disposed in the
chemical etching solution and/or heating the article in the
chemical etching solution to a temperature in a range from about
40.degree. C. to about 70.degree. C. while the article is disposed
in the chemical etching solution.
[0066] Agitation and heating are not required, but they can
increase the chemical activity of the etching solution, which
reduces the time needed to remove the islands from the article(s)
disposed in the solution. For example, agitation can help vibrate
the islands out of the laser cut articles. In another example, it
is believed that approximately every temperature increase of about
10.degree. C. produces an approximate doubling of the chemical
activity of the etching solution.
[0067] Suitable examples of implantable articles fabricated in act
720 include, but are not limited to, medical implants and devices
including minimal-invasive devices, such as, guide wires,
intra-cavernous implants, in particular intra-esophagus,
intra-urethra, intra-tracheal implants and intra-vascular implants,
in particular stents, stent grafts, stent graft connector, heart
valve repair device, or filters.
[0068] Referring now to FIG. 8, yet another flow diagram
illustrating a method 800 for removing an island from a laser cut
stent is shown. The method 800 includes act 810 of providing a
laser cut refractory metal stent that includes a patterned
plurality of laser cut struts and one or more islands remaining
between the laser cut struts and an act 820 of disposing the laser
cut refractory metal stent in a chemical etching solution that
includes hydrofluoric acid (HF) nitric acid (HNO.sub.3), and,
optionally, urea, as described in greater detail above. The method
800 further includes an act 830 of heating the laser cut refractory
metal stent in the chemical etching solution to a temperature in a
range from about 40.degree. C. to about 70.degree. C., an act 840
of sonicating the laser cut refractory metal stent in the chemical
etching solution using an ultrasonic apparatus, and an act 850 of
treating the laser cut refractory metal stent in the etching
solution under heating and sonication for a period of time
sufficient to remove the one or more islands therefrom so as to
form an implantable stent.
[0069] Sonication increases the chemical activity of the etching
solution. Ultrasonic sound is sound transmitted at frequencies
generally beyond the range of human hearing. As the sound waves
produced by the ultrasonic cleaning apparatus radiate through the
solution disposed in the apparatus, they cause alternating high and
low pressure waves in the solution. During the low pressure stage,
millions of microscopic bubbles form and grow. This process is
called cavitation. During the high pressure stage, the bubbles
formed in the low pressure stage collapse or "implode" releasing
enormous amounts of energy. These implosions act like an army of
tiny scrub brushes. The collapsing bubbles work in all directions,
attacking every surface and invading all recesses and openings.
[0070] In one embodiment, the sonication can be conducted in an
ultrasonic cleaning apparatus. One illustrative example of a
suitable ultrasonic cleaning apparatus is the Branson 2510
manufactured by Branson Ultrasonics Corporation of Danbury, Conn.
USA. The Branson 2510 is an ultrasonic cleaning unit that operates
at a frequency of 40 kHz and that includes a temperature controlled
bath. In operation, a beaker or another vessel containing the
etching solution and the laser cut articles can be disposed in the
ultrasonic bath. The beaker containing the laser cut articles can
be left in the ultrasonic bath under heating and sonication for a
period of time sufficient to remove the one or more islands
therefrom so as to form an implantable stent.
[0071] In one embodiment, the period of time in the etching
solution sufficient to remove the islands from the laser cut
article is in a range from about 5 minutes to about 90 minutes, or
about 10 minutes to about 60 minutes, or about 15 minutes to about
30 minutes. One will appreciate, however, that the actual time
needed may be affected by factors such as the size of the laser cut
kerf(s) in the article, the temperature, sonication, concentration
and composition of the acids in the etching solution, and the
like.
[0072] Referring now to FIG. 9, still yet another flow diagram
illustrating an embodiment of a method 900 for manufacturing an
implantable article is illustrated. The method 900 includes an act
910 of providing a first refractory metal workpiece, the first
refractory metal workpiece being made from a material selected from
the group consisting of tantalum, niobium, tungsten, zirconium,
molybdenum, and alloys thereof and an act 920 of laser cutting the
first refractory metal workpiece to form a laser cut refractory
metal stent that includes a patterned plurality of laser cut struts
and one or more islands remaining between the laser cut struts.
[0073] Method 900 further includes an act 930 of disposing the
laser cut refractory metal stent in a chemical etching solution
that includes hydrofluoric acid (HF) nitric acid (HNO.sub.3), and,
optionally, urea, an act 940 of heating the laser cut refractory
metal stent in the chemical etching solution to a temperature in a
range from about 40.degree. C. to about 70.degree. C., an act 950
of sonicating the laser cut refractory metal stent in the chemical
etching solution using an ultrasonic apparatus, and an act 960 of
treating the laser cut refractory metal stent in the etching
solution under heating and sonication for a period of time
sufficient to remove the one or more islands therefrom so as to
form an implantable stent, as described in greater detail
above.
[0074] According to the method 900 illustrated in FIG. 9, the
method of manufacturing a refractory metal stent further includes
an act 970 of chemically treating and/or heat treating the
refractory metal stent to produce a substantially defect-free
surface finish and improve the performance characteristics of the
stent. For example, the heat treating may be used to modify one or
more mechanical properties of the stent, such as, but not limited
to, an increase or a decrease in yield strength, tensile strength,
flexibility, toughness, and the like.
[0075] Referring now to FIG. 10, still yet another flow diagram
illustrating a method 1000 for manufacturing an implantable article
is illustrated. The method 1000 includes an act 1010 of providing a
first refractory metal workpiece, the first refractory metal
workpiece being made from a material selected from the group
consisting of tantalum, niobium, tungsten, zirconium, molybdenum,
and alloys thereof, an act 1020 of laser cutting the first
refractory metal workpiece to form a laser cut refractory metal
stent that includes a patterned plurality of laser cut struts and
one or more islands remaining between the laser cut struts, an act
1030 of disposing the laser cut refractory metal stent in a
chemical etching solution that includes hydrofluoric acid (HF)
nitric acid (HNO.sub.3), and, optionally, urea, an act 1040 of
heating the laser cut refractory metal stent in the chemical
etching solution to a temperature in a range from about 40.degree.
C. to about 70.degree. C., an act 1050 of sonicating the laser cut
refractory metal stent in the chemical etching solution using an
ultrasonic apparatus, and an act 1060 of treating the laser cut
refractory metal stent in the etching solution under heating and
sonication for a period of time sufficient to remove the one or
more islands therefrom so as to form an implantable stent, as
described in greater detail above.
[0076] The method 1000 of manufacturing a refractory metal stent
further includes an act 1070 rinsing, drying, and inspecting the
laser cut and island free stent. For instance, the act 1070
rinsing, drying, and inspecting can include at least three rinses
in deionized water (either with or without sonication), a rinse in
alcohol such as methanol, ethanol, or isopropanol, and drying the
stent with compressed air.
[0077] The method 1000 further includes an act 1080 of
electropolishing the laser cut refractory metal stent in an
electropolishing solution to produce a substantially defect free
finish on the stent, and an act 1090 of heat treating the laser-cut
refractory metal stent so as to form an implantable stent.
[0078] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *