U.S. patent application number 11/342182 was filed with the patent office on 2007-08-02 for metal injection molded article with a radiopaque dispersion and methods of making same.
This patent application is currently assigned to Accellent, Inc.. Invention is credited to Mark W. Broadley, John Eckert, Jeffrey M. Farina.
Application Number | 20070178005 11/342182 |
Document ID | / |
Family ID | 38069210 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070178005 |
Kind Code |
A1 |
Broadley; Mark W. ; et
al. |
August 2, 2007 |
Metal injection molded article with a radiopaque dispersion and
methods of making same
Abstract
The present invention includes a method of making a metal
injection molded article and the metal injection molded article.
The method includes mixing metal powders and a binder to form a
mixture. The metal powders include a bulk material and at least one
radiopaque material. The mixture is injected into a mold and
processed into a green part. The green part is debound to form a
brown part. The brown part is sintered to create a completed
article. The completed article includes a metal alloy that includes
the bulk material and a dispersion of the at least one radiopaque
material substantially independent of the metal alloy.
Inventors: |
Broadley; Mark W.;
(Downingtown, PA) ; Eckert; John; (Boyertown,
PA) ; Farina; Jeffrey M.; (Zionsville, PA) |
Correspondence
Address: |
DRINKER BIDDLE & REATH;ATTN: INTELLECTUAL PROPERTY GROUP
ONE LOGAN SQUARE
18TH AND CHERRY STREETS
PHILADELPHIA
PA
19103-6996
US
|
Assignee: |
Accellent, Inc.
Collegeville
PA
|
Family ID: |
38069210 |
Appl. No.: |
11/342182 |
Filed: |
January 27, 2006 |
Current U.S.
Class: |
419/37 |
Current CPC
Class: |
B22F 3/225 20130101;
A61F 2/82 20130101 |
Class at
Publication: |
419/037 |
International
Class: |
B22F 3/12 20060101
B22F003/12 |
Claims
1. A metal injection molded article comprising: a metal alloy; and
a dispersion of at least one radiopaque material substantially
independent of the metal alloy.
2. A metal injection molded article according to claim 1, wherein
the article comprises a medical device.
3. A metal injection molded article according to claim 1, wherein
the metal alloy comprises one or more of commercially pure
Titanium, Ti 6Al 4V, Ti 6Al 4V ELI, Nitinol, Cobalt Chrome Moly,
316L stainless steel, 304 stainless steel, and 17-4PH stainless
steel.
4. A metal injection molded article according to claim 1, wherein
the at least one radiopaque material comprises at least one
radiopaque element.
5. A metal injection molded article according to claim 4, wherein
the at least one radiopaque element is selected from the group
consisting of iridium, platinum, gold, rhenium, tungsten,
palladium, rhodium, tantalum, silver, ruthenium, and hafnium.
6. A metal injection molded article according to claim 1, wherein
the at least one radiopaque material comprises at least one
radiopaque alloy.
7. A metal injection molded article according to claim 6, wherein
the at least one radiopaque alloy comprises one or more of the
iridium, platinum, gold, rhenium, tungsten, palladium, rhodium,
tantalum, silver, ruthenium, and hafnium.
8. A metal injection molded article according to claim 1, wherein
the article has a density of at least 95%.
9. A metal injection molded article according to claim 8, wherein
the article has a density of at least 97%.
10. A method for making a metal injection molded article, the
method comprising: mixing metal powders and a binder to form a
mixture, the metal powders comprising a bulk material and at least
one radiopaque material; injecting the mixture into a mold;
processing the mixture in the mold to form a green part; debinding
the green part to form a brown part; and sintering the brown part
to create a completed article.
11. A method according to claim 10, wherein the binder comprises a
polymer binder.
12. A method according to claim 11, wherein the debinding step
comprises heating the green part.
13. A method according to claim 11, wherein the debinding step
comprises dissolving the binder in at least one solvent or
water.
14. A method according to claim 10, wherein the completed article
has a density of at least 95%.
15. A method according to claim 14, wherein the completed article
has a density of at least 97%.
16. A method according to claim 10, wherein the radiopaque material
is selected to have limited solubility in the matrix material
during sintering.
17. A method according to claim 16, wherein the completed article
comprising a metal alloy comprising the bulk material and a
dispersion of the at least one radiopaque material substantially
independent of the metal alloy.
18. A method according to claim 10, wherein the sintering step is
performed at a temperature at or above the alloying temperature of
the at least one radiopaque material.
19. A method according to claim 18, wherein the completed article
comprising a metal alloy comprising the bulk material alloyed with
a dispersion of the at least one radiopaque material.
20. A method according to claim 10, wherein the at least one
radiopaque material comprises at least one radiopaque element.
21. A method according to claim 20, wherein the at least one
radiopaque element is selected from the group consisting of
iridium, platinum, gold, rhenium, tungsten, palladium, rhodium,
tantalum, silver, ruthenium, and hafnium.
22. A method according to claim 10, wherein the at least one
radiopaque material comprises at least one radiopaque alloy.
23. A method according to claim 22, wherein the at least one
radiopaque alloy comprises one or more of the iridium, platinum,
gold, rhenium, tungsten, palladium, rhodium, tantalum, silver,
ruthenium, and hafnium.
24. A method according to claim 10, further comprising machining
the completed article.
25. A method according to claim 10, further comprising coating the
completed article.
26. A method according to claim 10, further comprising annealing
the completed article.
27. A method according to claim 10, where the article is a medical
device.
Description
FIELD OF INVENTION
[0001] The material and methods disclosed herein relate to a metal
injection molded article, and a metal injection molded article with
a radiopaque dispersion.
BACKGROUND OF INVENTION
[0002] Metal Injection Molding ("MIM") has been practiced for years
in industries such as agricultural, automotive, business machine,
food & beverage, hardware, medical, small appliance, and
sporting good. MIM provides articles for those industries, as well
as others, that have strengths that are comparable to articles
produced by forging, stamping, casting, and machining processes,
while, at the same time, providing the ability to produce high
volumes of the articles in a cost effective manner. Additional
advantages of MIM include the ability to produce articles with
intricate shapes, the ability to produce articles with close
tolerances, and the ability to produce articles with multiple
components in one mold, thereby reducing assembly costs.
[0003] Because of the materials typically used in metal injection
molding, MIM articles generally have low radiopacity, which raises
concerns in many applications. Low radiopacity is of particular
concern where the article is a medical device, and more
particularly where the article is a medical device that is intended
to be implanted or used in a patient. When a medical device with
low radiopacity is placed in a patient, it is difficult to view the
device with imaging technologies such as x-ray fluoroscopy. As a
result, proper placement and/or alignment of the medical device
cannot be readily verified.
[0004] Attempts have been made to overcome this problem. For
example, it is common practice to attach radiopaque markers to a
medical device. The markers are generally made from materials such
as iridium, platinum, gold, and tantalum. The markers, because of
their size and composition, may cause galvanic corrosion. Another
disadvantage of the markers is that they are generally not integral
with the medical device. Therefore, the markers can inadvertently
dislodge from the medical device or otherwise interfere with the
performance and/or deployment of the medical device. Yet another
disadvantage of the markers is that they are generally not
co-extensive with the entire surface of the medical device.
Consequently, imaging technology, such as x-ray fluoroscopy, will
show only a portion of the medical device.
[0005] It is also common practice to coat or plate medical devices
with radiopaque materials. The resulting radiopaque coated or
plated medical devices suffer from similar disadvantages as medical
devices with radiopaque markers, i.e., galvanic corrosion,
interference with performance of the medical device, interference
with deployment of the medical device, and inadvertent separation
of the coating or plating.
[0006] What is needed is an article that combines the benefits of
metal injection molded articles with the benefits of high
radiopacity, while, at the same time, overcoming the problems
associated with the prior art.
SUMMARY OF INVENTION
[0007] One embodiment of the invention encompasses a metal
injection molded article that includes a metal alloy and a
dispersion of at least one radiopaque material substantially
independent of the metal alloy.
[0008] Another embodiment of the invention includes a method of
making a metal injection molded article. The method includes mixing
metal powders and a binder to form a mixture. The metal powders
include a bulk material and at least one radiopaque material. The
mixture is injected into a mold and processed into a green part.
The green part is debound to form a brown part. The brown part is
sintered to create a completed article. The completed article
includes a metal alloy that includes the bulk material and a
dispersion of the at least one radiopaque material substantially
independent of the metal alloy.
[0009] In a further embodiment of the invention, the completed
article comprises a metal alloy that includes both the bulk
material and at least one radiopaque material dissolved in the
alloy.
BRIEF DESCRIPTION OF DRAWINGS
[0010] For the purpose of illustrating the invention there is shown
in the drawings various forms which are presently preferred; it
being understood, however, that this invention is not limited to
the precise arrangements and instrumentalities particularly
shown.
[0011] FIG. 1 is a perspective view of an article according to one
embodiment of the invention.
[0012] FIG. 1A is an exaggerated view of a portion of the article
of FIG. 1.
[0013] FIG. 2 is a perspective view of an article according to a
second embodiment of the invention.
[0014] FIG. 3 is a perspective view of an article according to a
third embodiment of the invention.
[0015] FIG. 4 is a perspective view of an article according to a
fourth embodiment of the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0016] The present invention includes a method of making a metal
injection molded article. The method includes mixing metal powders
and a binder to form a mixture. The metal powders include a bulk
material and at least one radiopaque material. The mixture is
injected into a mold and processed into a green part. The green
part is debound to form a brown part. The debinding includes
removing a substantial portion of the binder from the mold. The
brown part is sintered to create a completed article. The completed
article includes a metal alloy comprising the bulk material. The
completed article also includes a dispersion of the at least one
radiopaque material, which is substantially independent of the
metal alloy.
[0017] The bulk material can be powders of any metal suitable for
metal injection molding. Preferably, the bulk material includes
fine metal powders. More preferably, the bulk material includes
fine metal powders having a diameter of less than 50 microns. Most
preferably, the bulk material includes fine metal powders having a
diameter of less than 25 microns.
[0018] The bulk material preferably includes powders capable of
forming various metals and alloys. More particularly, the bulk
material can include powders capable of forming any metals and
alloys suitable for the medical industry. For example, the bulk
material can include powders capable of forming the following
medical metals and alloys: 304 stainless steel per ASTM F899, 316L
stainless steel per ASTM F899 and ASTM F138, commercially pure Ti
per ASTM F67, Ti 6Al 4V per ASTM F1472, Ti 6Al 4V ELI per ASTM
F136, Nitinol per ASTM F2063, Cobalt Chrome Moly per ASTM F75,
and/or combinations thereof.
[0019] The bulk material can include powders capable of forming an
implantable austenitic stainless steel alloy (e.g., 316L stainless
steel per ASTM F138). An austenitic alloy formed from the bulk
material generally has excellent corrosion resistance, excellent
elongation and is easily weldable. Generally such an alloy is used
where corrosion resistance is more important than strength or wear
resistance.
[0020] The bulk material can include powders capable of forming a
precipitation hardened stainless steel alloy (e.g., 17-4PH
stainless steel per ASTM F899). This material exhibits a good
balance between corrosion resistance and strength. The strength and
hardness can be modified by adjusting the temperature at which the
material is heat treated after sintering. The precipitation
hardened alloy generally provides for better corrosion resistance
than 400 series stainless steels and better strength than 300
series stainless steels.
[0021] The bulk material can include powders capable of forming a
martensitic stainless steel (e.g. 440C per ASTM F899). This
material exhibits the highest hardness and strength among the
stainless steels with some tradeoff in corrosion resistance.
[0022] The bulk material can include a combination of low alloy
steel, carbon, nickel, and molybdenum. The combination provides for
a multi-purpose, economical material for non medical applications
that provides flexibility in various properties such as strength,
hardness, and wear resistance. The material can be plated or coated
for additional corrosion resistance.
[0023] The radiopaque material can be any material that precludes
x-rays or other types of radiation commonly used in diagnostic
imaging from penetrating it. When the radiopaque material is
present in the completed article, it essentially blocks radiation
from penetrating the completed article where it is present. The
blocking of radiation is advantageous in many fields, but
particularly in the medical device field. A medical device having a
radiopaque material integral with the structural component of the
device allows the device to be visible when viewed by imaging
technology such as x-ray fluoroscopy.
[0024] The radiopaque material preferably comprises at least one
element and/or at least one alloy. If the radiopaque material
comprises at least one element, preferably the one or more
element(s) is selected from the group consisting of iridium,
platinum, gold, rhenium, tungsten, palladium, rhodium, tantalum,
silver, ruthenium, and hafnium. If the radiopaque material
comprises at least one alloy, preferably the one or more alloy(s)
includes one or more of iridium, platinum, gold, rhenium, tungsten,
palladium, rhodium, tantalum, silver, ruthenium, and hafnium.
[0025] The binder can include any material commonly used as a
binder in metal injection molding. Preferably, the binder is a
polymer binder. The binder may also be a combination of two or more
polymeric materials.
[0026] The bulk material, radiopaque material, and the binder are
mixed together to form a mixture. Preferably, the mixture is
flowable at relatively low temperature and pressure. A flowable
mixture allows the mixture to fill all of the crevices and small
dimensional features of a mold.
[0027] The binder, the bulk material, and the at least one
radiopaque material are mixed using a conventional mixing
apparatus. The temperature at which the materials are mixed can
vary.
[0028] The mixture is injected into a mold. Generally, the mixture
is injected with an injection molding machine. Injection molding
machines are known in the art and are typically capable of applying
from less than one hundred to several hundred tons of force to a
mold. The mold is typically constructed with internal cooling
passages to solidify the flowable mixture prior to removal from the
mold. The mold cavity typically is larger than that of the desired
finished part to account for the shrinkage that occurs after binder
removal. The mold structure can be a rigid or a flexible material.
The mold typically includes vents or bleeder lines to allow air to
escape from the mold during the molding process. Alternatively, the
mold can include a porous metal or ceramic insert to allow air to
escape from the mold.
[0029] After the mixture is injected into the mold, the mixture is
processed. Processing of the mixture includes applying pressure to
the mold/mixture to form a green part. The applied pressure is
typically about 10-12 ksi.
[0030] After molding, the green part is removed from the mold and
an initial debinding step may be performed. During initial
debinding, some portion of the binder is removed from the green
part to create a brown part. The binder can be removed by heating
the green part, generally with a low-temperature thermal treatment.
When the green part is heated, a portion of the binder will melt,
decompose, and/or evaporate. The binder can also be removed by
solvent or water extraction or by a combination of heating and
solvent extraction.
[0031] After initial debinding, the brown part is thermally debound
and sintered to create a completed article. Sintering is the
process of heating metal powders until the powders adhere to each
other, thereby forming a substantially solid form having the same
or nearly the same mechanical properties as the metal in its cast
or wrought form. Sintering can include heating the brown part to a
temperature close to, but not exceeding, the melting point of the
part. Where it is desirable for the radiopaque material to remain
generally independent of the alloy formed by the bulk material, the
radiopaque material is selected to have limited solubility in the
bulk material.
[0032] Preferably, the sintering temperature is about 20.degree. C.
to about 100.degree. C. less than the melting point of the bulk
material. That temperature is then maintained for a set period of
time. Under those conditions, interparticulate melting and
substantial diffusion can occur, thereby eliminating interstitial
void spaces and causing the material densities to become
substantially solid. Where it is desirable for the radiopaque
material to remain generally independent of the alloy formed by the
bulk material, the sintering temperature and the length of time of
sintering should be limited so as to limit diffusion of the
radiopaque material. Specific times and temperatures are dependent
on the characteristics of the bulk material, the radiopaque
material, and so on.
[0033] Complete solidification (i.e., 100% density) is desired but
generally does not occur. Preferably, the density of the completed
article is at least 95% of theoretical. More preferably, the
density of the completed article is at least 97% of theoretical.
These density measurement percentages are based on the theoretical
density of the article.
[0034] During the sintering steps, the brown parts typically shrink
due to the decrease in the size of the interstitial void spaces.
The shrinkage typically causes the completed article to be about
10% to about 30% smaller than the green part from which it is made.
More particularly, the completed article is about 20% smaller than
the green part. The amount of shrinkage should be considered when
designing/selecting a mold for a particular part.
[0035] In another embodiment of the present invention, the at least
one radiopaque material forms an alloy with the bulk material. The
alloying of the radiopaque material can be achieved during the
sintering process by exposing the brown part to a sufficient time
and temperature to insure long range diffusion of the radiopaque
material.
[0036] As shown in FIG. 1, the article made by a method of the
present invention is an implantable medical device 10. The device
10 includes a metal alloy 12 and a dispersion of at least one
radiopaque material 14 substantially independent of the metal
alloy. The dispersion of the radiopaque material 14 is interspersed
homogenously throughout the metal alloy 12. FIG. 1A shows a portion
of the device 10 at an exaggerated scale so as to illustrate the
homogenous dispersion. This exaggerated scale is presented merely
for illustrative purposes. Preferably, the dispersion of the
radiopaque material 14 is not visible to the naked eye.
[0037] Alternatively, the dispersion 14 can be positioned at
specific locations on the article. For example, the dispersion 14
can be homogenously mixed with the metal alloy at the ends 16, 18
of the article only (as shown in FIG. 2). It can be homogeneously
mixed with the metal alloy along only longitudinal lines traversing
the length of the article (as shown in FIG. 3). It can be
homogeneously mixed with the metal alloy along only latitudinal
lines traversing the circumference of the article (as shown in FIG.
4). The alternative orientations for the dispersion 14 can be
accomplished by configuring the mold such that the radiopaque
material mixes with the metal alloy in only discrete locations
(e.g., at the end of the article). Although FIGS. 2-4 illustrate
the dispersion of the radiopaque material 14 as being visible with
the naked eye, this is done merely for illustrative purposes.
Preferably, the dispersion of the radiopaque material 14 is not
visible to the naked eye.
[0038] While the article is shown as an implantable medical device,
the article is not so limited. The article can be all or just a
portion of any structure having the elements described herein. The
article can be all or a part of a product including, but not
limited to, actuators, automotive components, cellular telephones,
dental instruments, electrical connectors, electronic heat sinks
and hermetic packages, fiber optic connectors, hard disk drives,
hydraulic line couplings, pharmaceutical devices, power hand tools,
and sporting equipment. The article is particularly advantageous in
the medical field where it can be, for example, in the form of
laparoscopic parts such as graspers, dissectors, and surgical
instrument end effectors. Preferably, the article is used in the
medical field as a medical device including, but not limited to,
stents, grafts (e.g., aortic grafts), artificial heart valves,
cerebro-spinal fluid shunts, pacemaker components, axius coronary
shunts, catheters, biopsy sectioning and retrieval equipment, vena
cava filters, reconstructive implants such as intramedullary nails
and screws, fixation plates and anchors, orthopedic implants such
as knee, hip and shoulder components, spinal prostheses, and dental
implants.
[0039] Where device 10 is a stent, it can be placed into a patient
to treat a variety of medical conditions. The most common use of
stents is to hold open clogged blood vessels after angioplasty.
When used for this purpose a catheter is moved through the body to
the site where the blood vessel is blocked. A balloon is then
inflated to open the vessel. In some cases, the stent is then
placed to decrease chances that the blood vessel will close up
again.
[0040] Stents also are used to hold open blood vessels, bile ducts,
or other pathways in the body that have been narrowed or blocked by
tumors or other obstructions. Areas where stents are most often
used for this reason include: the esophagus, to treat blockages or
narrowing of the esophagus that make it difficult to swallow; the
bile ducts in the pancreas or liver, when an obstruction prevents
bile from draining into the digestive tract; and the airways of the
lungs, to treat obstructions that interfere with normal
breathing.
[0041] To place the stent, a medical personnel makes a very small
incision in the skin, about the size of a pencil tip. The stent,
which is placed on the end of a catheter, is threaded under
guidance of imaging technology such as x-rays to the area of
treatment. Because imaging technology is generally used to guide
the placement of the stent, it is advantageous to have a catheter
and a stent with high radiopacity so that they can be more easily
viewed by the medical personnel performing the placement. High
radiopacity is similarly advantageous on other types of medical
devices that rely on imaging technology to guide the placement.
Once in place, the high radiopacity allows medical personnel to
view the device to ensure proper alignment, potential damage to
adjacent tissue, and so on.
[0042] Completed articles produced by the MIM process can be
further processed. For example, the completed articles can be
machined to provide a smooth surface or other similar
characteristics. The completed article can be coated to enhance
functionality. The completed article can be annealed to relieve
internal stresses or soften the metal.
[0043] An article made by metal injection molding provides the
design flexibility of plastic injection molding (e.g., the ability
to produce articles with intricate shapes, the ability to produce
articles with close tolerances, and the ability to produce articles
with multiple components in one mold) with the material properties
at or near that of wrought metals.
[0044] Although the disclosure describes the metal injection molded
article as a medical device, the present invention is not so
limited. The article can be all or part of any product where a
metal injection molded article having high radiopacity is
desired.
[0045] It will be appreciated by those skilled in the art that the
present invention may be practiced in various alternate forms and
configurations. The previously detailed description of the
disclosed methods is presented for clarity of understanding only,
and no unnecessary limitations should be implied therefrom.
* * * * *