U.S. patent application number 10/818757 was filed with the patent office on 2005-02-03 for oxidation resistant treatment for metallic medical devices.
Invention is credited to Chen, Cheng-Han.
Application Number | 20050022627 10/818757 |
Document ID | / |
Family ID | 34107488 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050022627 |
Kind Code |
A1 |
Chen, Cheng-Han |
February 3, 2005 |
Oxidation resistant treatment for metallic medical devices
Abstract
A method of treating a metallic medical device is disclosed and
includes providing a metallic medical device, ionizing the media
surrounding at least one electrode to produce an energized plasma
proximate to the electrode, and exposing the metallic device to the
plasma prior to use of the metallic device. In one embodiment a
vascular stent is the medical device.
Inventors: |
Chen, Cheng-Han; (Santa
Rosa, CA) |
Correspondence
Address: |
STRADLING YOCCA CARLSON & RAUTH
SUITE 1600
660 NEWPORT CENTER DRIVE
P.O. BOX 7680
NEWPORT BEACH
CA
92660
US
|
Family ID: |
34107488 |
Appl. No.: |
10/818757 |
Filed: |
April 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60460365 |
Apr 3, 2003 |
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Current U.S.
Class: |
75/10.19 |
Current CPC
Class: |
A61L 31/088 20130101;
A61L 31/022 20130101; A61L 27/042 20130101; A61L 27/306 20130101;
A61L 2/14 20130101 |
Class at
Publication: |
075/010.19 |
International
Class: |
C22F 003/02 |
Claims
What is claimed is:
1. A method of treating a metallic medical device, comprising:
providing a metallic medical device; ionizing the media surrounding
at least one electrode to produce an energized plasma proximate to
the electrode; and exposing the metallic device to the plasma prior
to use of the metallic device.
2. The method of claim 1 further comprising positioning the
electrode in an atmosphere containing at least one material
selected from the group consisting of Oxygen, Argon, Helium, Neon,
and Xenon.
3. The method of claim 1 further comprising forming an oxidation
layer a surface of the metallic device.
4. The method of claim 1 wherein the metallic device is selected
from the group consisting of vascular stents, replacement joints,
metallic heart valves, screws, pins, bolts, staples, fasteners,
plates, skeletonal fusion devices, spinal fusion devices, bone
anchors, shunts, staples, fasteners, dental implants, orthodontic
braces, dental retainers, retractors, retainers, couplings,
scalpels, needles, forceps, dental tools, surgical tools, bone
cutters, and saws.
5. The method of passivating a medical device, comprising:
providing a metallic medical device; positioning at least one
electrode within an atmosphere containing at least Oxygen; applying
energy to the electrode; forming a plasma by ionizing the
atmosphere proximate to the electrode and exposing the metallic
medical device to the plasma to produce an corrosion resistant
oxidation layer thereon.
6. The method of claim 5 wherein the metallic device is selected
from the group consisting of vascular stents, replacement joints,
metallic heart valves, screws, pins, bolts, staples, fasteners,
plates, skeletonal fusion devices, spinal fusion devices bone
anchors, shunts, staples, fasteners, dental implants, orthodontic
braces, dental retainers, retractors, retainers, couplings,
scalpels, needles, forceps, dental tools, surgical tools, bone
cutters, and saws.
7. An oxidation treatment for a metallic stent, comprising:
providing a metallic stent; forming a plasma within an atmosphere
containing at least Oxygen; and positioning the stent within the
plasma.
8. A corrosion resistant medical device, comprising: a metallic
body; and at least a corrosion resistant oxidation layer formed on
the metallic body.
9. The device of claim 8 wherein the metallic body is manufactured
from stainless steel;
10. The device of claim 8 wherein the medical device is selected
from the group consisting of vascular stents, replacement joints,
metallic heart valves, screws, pins, bolts, staples, fasteners,
plates, skeletonal fusion devices, spinal fusion devices, bone
anchors, shunts, staples, fasteners, dental implants, orthodontic
braces, dental retainers, retractors, retainers, couplings,
scalpels, needles, forceps, dental tools, surgical tools, bone
cutters, and saws.
Description
RELATED APPLICATIONS
[0001] The present application claims priority to U.S. provisional
patent application Ser. No. 60/460,365 filed Apr. 3, 2003 the
entire contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for passivating a
metallic surface. Specifically, an oxidation treatment is described
herein is capable of efficiently passivating a metallic medical
device thereby improving the corrosion resistance of the treated
device. In one embodiment of the present invention the medical
device is a vascular stent.
BACKGROUND OF THE INVENTION
[0003] Devices manufactured from at least one metallic material are
commonly implanted within the body of patient to treat a variety of
conditions. For example, stents, shunts, or other mechanical
scaffoldings may be inserted into an occluded region of a lumen or
luminal structure to provide and maintain patency therethrough. In
an alternate embodiment, metallic screws, braces, or plates may be
positioned within or attached to skeletonal structures throughout
the patient's body to provide support thereto. Recently, total
joint replacement devices such as replacement hip prosthetics and
replacement knee prosthetics have been used to replace incompetent
natural joint systems.
[0004] Presently, implantable metallic devices are manufactured
from a variety of materials, including, stainless steel, tantalum,
titanium, Nickel-Titanium alloys, shape memory alloys, super
elastic alloys, low-modulus Ti--Nb--Zr alloys, and colbalt-nickel
alloy steel (MP-35N). While implantable metallic devices
manufactured these materials have proven useful in treating a
variety of physiological conditions, a number of shortcomings
associated with implantable metallic devices have been identified.
For example, the extended exposure of the implanted metallic
devices to bodily fluids and biological materials may result in
device corrosion. As a result, the performance of the implanted
device may be compromised.
[0005] In response, the materials used in the manufacture of
implantable metallic devices generally undergo a chemical
passivation process during the manufacture of the implantable
device. Typically, the device is coated with, submerged in, or
otherwise exposed to an oxidizing agent or compound. For example,
nitric acid is frequently used as an oxidizing agent when
passivating stainless steel. As a result, free metals on the
surface of the implantable device may be removed and a non-reactive
protective oxide layer capable of reducing or preventing material
corrosion may be formed thereon. While the chemical passivating
process has been effective in passivating implantable metallic
devices, a number of shortcomings have been identified. For
example, the chemical passivating processes tend to be time
intensive procedures typically requiring the implantable device be
exposed to an oxidizing agent for 15 minutes or more. In addition,
oxidizing agents are hazardous materials and pose a health risk to
exposed workers and may result in the unwanted deposition of
chemical residues on the treated device.
[0006] Thus, in light of the foregoing, there is a need oxidation
treatment for metallic medical devices capable of quickly
passivating a metallic device without leaving chemical residues
thereon.
BRIEF SUMMARY OF THE INVENTION
[0007] The oxidation treatment described herein is capable of
efficiently passivating a metallic medical device thereby improving
the corrosion resistance of the treated device. In addition, the
oxidation treatment disclosed herein reduces or eliminates the
possibility of residual chemical impurities remaining on the
treated device as a result of the passivating procedure.
[0008] In one embodiment, a method of treating a metallic medical
device is disclosed and includes providing a metallic medical
device, ionizing the media surrounding at least one electrode to
produce an energized plasma proximate to the electrode, and
exposing the metallic device to the plasma prior to use of the
metallic device.
[0009] In an alternate embodiment, a method of passivating a
medical device is described herein and includes providing a
metallic medical device, positioning at least one electrode within
an atmosphere containing at least oxygen, applying energy to the
electrode, forming a plasma by ionizing the atmosphere proximate to
the electrode, and exposing the metallic medical device to the
plasma to produce an corrosion resistant oxidation layer
thereon.
[0010] In another embodiment, an oxidation treatment for a metallic
stent is disclosed and includes providing a metallic stent, forming
a plasma within an atmosphere containing at least oxygen, and
positioning the stent within the plasma.
[0011] In addition, a corrosion resistant medical device is
described and comprises a metallic body and at least a corrosion
resistant oxidation layer formed on the metallic body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a table detailing the surface composition of
stents subjected to the oxidation treatment of the present
invention as compared with the surface composition of untreated
control stents;
[0013] FIG. 2 shows a table summarizing the test results of a
cyclic potentiodynamic polarization tests performed on untreated
control stents;
[0014] FIG. 3 shows a table summarizing the historical test results
relating to cyclic potentiodynamic polarization tests performed on
the untreated stents;
[0015] FIG. 4 shows a table summarizing the test results of a
cyclic potentiodynamic polarization tests performed on stents
treated with the oxidation treatment of the present invention;
[0016] FIG. 5 shows a graph illustrating the corrosion potential of
the stents treated using an oxidation treatment disclosed herein as
compared to the corrosion potential of untreated control
stents;
[0017] FIG. 6 shows a graph illustrating the cyclic polarization of
the treated stent sample numbers 1, 2, and 3 as compared to the
cyclic polarization of untreated control stent sample numbers 6 and
7; and
[0018] FIG. 7 shows a graph illustrating the cyclic polarization of
the treated stent sample numbers 4 and 5 as compared to the cyclic
polarization of untreated stent sample number 8.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The oxidation treatment disclosed herein may be used to
passivate metallic medical devices to be used within the body of a
patient, thereby improving the ability of the device to resist
corrosion once implanted. Generally, passivation may be described
as the removal of exogenous contaminants or compounds from the
surface of a metallic device. When passivating a stainless steel
item, for example, exogenous iron or iron compounds may be removed
from the surface of the item, thereby altering the surface
chemistry thereof. In addition, the oxidation treatment disclosed
herein results in formation of an oxidation layer on the surface of
the item. In addition to passivating metallic devices, the
oxidation treatment of the present invention provides a metallic
device substantially free of organic residues, unlike conventional
passivating procedures utilizing wet chemical techniques which may
result in the deposition of an organic contaminants on the
implantable device.
[0020] The oxidation treatment of the present invention may be used
to passivate a variety of metallic devices used throughout the body
of a patient. For example, a metallic vascular stent may be
subjected to the oxidation treatment disclosed herein prior to
implantation with the vasculature of a patient. In another
embodiment, the metallic medical device may include components of a
replacement joint such as a replacement ball and socket joint, a
metallic heart valve, implantable screws, pins, bolts, plates,
skeletonal fusion devices, spinal fusion devices, bone anchors,
shunts, staples, fasteners, dental implants or devices including
orthodontic braces and retainers, or other metallic devices capable
of being implanted into the body of a patient. In an alternate
embodiment, the oxidation treatment described herein may be used to
passivate or otherwise treat a variety of medical devices used
prior to, during, or following a surgical or therapeutic procedure.
For example, the disclosed oxidation treatment may be used to
improve the corrosion resistance of retractors, retainers,
couplings, scalpels, needles, forceps, dental tools or devices,
bone cutters, saws, and/or other surgical or dental tools or
devices. In addition, the present oxidation treatment may be used
to passive various metals, including, without limitation, stainless
steel, tantalum, titanium, Nickel-Titanium alloys, shape memory
alloys, super elastic alloys, low-modulus Ti-Nb-Zr alloys, and
colbalt-nickel alloy steel (MP-35N).
[0021] The oxidation treatment of the present invention utilizes a
commercially available corona discharge or corona treatment system
to produce the electrochemical reaction resulting in the
passivation of the metallic device. A voltage sufficient to ionize
the surrounding environment is applied to at least one electrode.
In one embodiment, approximately 18 kV of direct current (DC) may
be applied to the electrode thereby generating a corona discharge
proximate thereto, although any voltage or current capable of
creating a corona discharge may be used. Similarly, any number of
electrodes may be used in the present invention. For example, a
first charged electrode may be positioned proximate to a second
electrode. The first charged electrode may be separated from the
second electrode by a separation gap. The electrodes may positioned
within an air environment, although those skilled in the art will
appreciate that the electrodes may be located within environments
containing other materials or gases. For example, the electrodes
may be positioned within a field containing argon, helium, neon, or
xenon. The application of sufficient voltage to the first charged
electrode ionizes the media surrounding the electrode, for example,
oxygen, thereby forming ozone (O.sub.3) and producing a plasma
between or proximate to the first and second electrodes. Further,
the Applicants theorize the Ozone forming the plasma is capable of
chemically reacting with various metals of the metallic device and
resulting in the oxidation thereof.
[0022] The metallic device may be subjected to or positioned within
the ionized environment formed proximate to the electrode. For
example, a stainless steel device (for example stainless steel
316L) may be subjected to the high energy plasma generated between
or proximate to at least one electrode. As a result, the atoms of
ozone forming the plasma react with atoms of iron, nickel, and
chromium within the stainless steel substrate material thereby
forming or depositing a corrosive resistant oxidation layer
thereon. Those skilled in the art will appreciate that the metallic
device undergoing the oxidation treatment disclosed herein is
maintained at an ambient or near ambient temperature during the
treatment procedure. Unlike wet oxidation procedures which may
result in the deposition of residual materials on the metallic
device and may require additional cleaning processes, the metallic
device treated with the method disclosed herein may be sterilized
and packaged for shipment. In addition, those skilled in the art
will appreciate that the oxidation treatment disclosed herein
results in the deposition of a corrosion resistant layer to the
metallic device in substantially less time than presently required
using a wet oxidation process. In one embodiment, the metallic
device may be passivated by subjecting the metallic device to the
corona discharge for about 3 seconds to several minutes, although
those skilled in the art will appreciate that the metallic device
may be subject to the corona discharge for a considerably less or
more time as desired by the manufacturer. In contrast, the present
wet passivating procedures using nitric acid typically require the
metallic device be exposed to the oxiding agent for a period of 15
minutes or more.
[0023] A further, non-limiting illustration of the oxidation
treatment disclosed herein is illustrated in the following
examples.
EXAMPLE 1
[0024] Seven stainless steel S670 stents manufactured by Medtronic
AVE were washed for three minutes within an ultrasound bath
containing 99% isopropyl alcohol (IPA). Thereafter, the seven
stents were removed from the IPA bath and dried within a gaseous
flow of nitrogen.
[0025] Once dried, the scents were number 1 through 7. Sample
number 1 was left untreated. Sample numbers 2 through 7 underwent
passivation using the oxidation treatment disclosed herein. A
corona discharge device included an electrode was positioned within
an oxygen environment. Approximately 18 kV of direct current
electrical energy was applied to the electrode, thereby ionizing
the oxygen proximate to the electrode and resulting in the creation
of a ionizing plasma. As Table 1 shows, sample numbers 2-7 were
exposed to a plasma created from a corona discharge device for
varying lengths of times.
1TABLE 1 SAMPLE NO. CORONA EXPOSURE TIME 1 0 sec (control) 2 5 sec.
3 10 sec. 4 20 sec. 5 20 sec. (Dwell) 6 60 mm. (Dwell) 7 95 mm.
(Dwell)
[0026] Following the oxidation treatment, sample number 1 (the
untreated control sample) and treated sample numbers 2-7 underwent
Electron Spectroscopy for Chemical Analysis (hereinafter ESCA) to
determine the effects of the oxidation treatment on the surface
composition of the stents. During the ESCA process, a small
diameter x-ray beam is focused across an area of each stent,
thereby causing electrons to be emitted from the of each stent. The
emitted electrons are collected and examined to determine the
surface composition of the device under test. FIG. 1 shows the
results of the ESCA testing on samples 1-7.
[0027] As shown in FIG. 1, the surface composition of sample number
1 (the untreated control sample) included significantly higher
concentrations of carbon when compared with the surface composition
of the treated samples (sample numbers 2-7). In addition, the
treated sample numbers 2-7 exhibited higher surface concentrations
of nitrogen and nickel than the untreated sample 1. Furthermore,
the chromium to iron ratio in the treated samples sample number
2-7) was greatly reduced as a result of the oxidation treatment
when compared with the untreated sample (sample number 1), thereby
producing a more corrosion-resistant device than presently
available.
EXAMPLE 2
[0028] Eight stainless steel S670 stents manufactured by Medtronic
AVE were washed for three minutes within an ultrasound bath
containing 99% isopropyl alcohol (IPA). Thereafter, the eight
stents were removed from the IPA bath and dried within a gaseous
flow of Nitrogen.
[0029] Once dried, the stents were number 1 through 8. Sample
numbers 6-8 were left untreated. Sample numbers 1 through 5
underwent passivation using the oxidation treatment disclosed
within. A corona discharge device included an electrode was
positioned within an oxygen environment. Approximately 18 kV of
direct current electrical energy was applied to the electrode,
thereby ionizing the oxygen proximate to the electrode and
resulting in the creation of a ionizing plasma. As Table 1 shows,
sample numbers 1-5 were exposed to the plasma created from a corona
discharge device for varying lengths of times between 5 seconds and
10 seconds.
2TABLE 3 SAMPLE NO. CORONA EXPOSURE TIME 1 5-10 sec. 2 5-10 sec. 3
5-10 sec. 4 5-10 sec. 5 5-10 sec. 6 0 (control) 7 0 (control) 8 0
(control)
[0030] Thereafter, the stents were subjected to cyclic
potentiodynamic corrosion testing to determine the corrosion
resistance of each sample. FIG. 2 shows a table summarizing the
cyclic potentiodynamic polarization test results for the untreated
samples (sample numbers 6-8). FIG. 3 shows historical data of
potentiodynamic polarization testing of similar S670 stents
manufactured by Medtronic AVE. As illustrated, the corrosion
potential for the untreated samples (sample numbers 6-8) was
comparable with the historical data obtained by previous
potentiodynamic polarization tests performed on untreated S670
stent samples. The corrosion potential of the untreated samples
(sample numbers 6-8) averaged -108 mV, while the breakdown
potential averaged 462 mV.
[0031] FIG. 4 shows a table summarizing the cyclic potentiodynamic
polarization test results for the treated samples (sample numbers
1-5). As shown, the breakdown potential of the treated samples
(sample numbers 1-5) was consistently higher than the untreated
samples (sample number 6-8). In addition, the potential difference
(i.e. the average difference between the corrosion potential and
the breakdown potential (E.sub.b-Ecorr)) was greater in the treated
samples (sample numbers 1-5) than the untreated samples (sample
numbers 6-8), thereby suggesting that the oxidation treatment had
improved the corrosion resistance of the treated samples (sample
numbers 1-5).
[0032] FIGS. 5-7 graphically illustrate the effects of the
oxidation treatment on the treated samples (sample numbers 1-5) as
compared with the untreated samples (sample numbers 6-8). FIG. 5
shows the corrosion potential ((V.sub.pot/E.sub.ref)/t) of the
treated samples (sample number 1-5) and the untreated samples
(sample numbers 6-8). As shown, the corrosion potential of the
treated samples (sample numbers 1-5)is considerably higher then the
untreated samples (sample numbers 6-8). Further, FIGS. 6 and 7 show
the cyclic polarization ((V.sub.pot/E.sub.ref)/(A/cm.sup.2)) of the
treated samples (sample numbers 1-5) and the untreated samples
(sample numbers 6-8), More specifically, FIG. 6 shows the cyclic
polarization of treated sample numbers 1, 2, and 3 and untreated
sample numbers 6 and 7. FIG. 8 shows the cyclic polarization of
treated sample numbers 4 and 5, and untreated sample number 8. As
shown in FIGS. 2 and 3, the treated samples (sample numbers
1-5)exhibited a higher cyclic polarization than the untreated
samples (sample numbers 6-8).
[0033] In light of the foregoing, cyclic potentiodynamic
polarization test revealed a higher breakdown potential and an
increased difference between the rest potential and the breakdown
potential for the treated stents (sample numbers 1-5)than found in
the untreated stents (sample number 6-8). As a result, the
oxidation treatment disclosed herein reduced the treated stent's
susceptibility to localized corrosion thereby improving the treated
stent's resistance to corrosion.
[0034] In closing it is understood that the embodiments of the
invention disclosed herein are illustrative of the principles of
the invention. In addition, those skilled in the art will
appreciate that the oxidation treatment described herein may be
used to provide the user with a variety of corrosion resistant
metallic medical device, including, for example, vascular stents,
replacement joints, metallic heart valves, screws, pins, bolts,
staples, fasteners, plates, skeletonal fusion devices, spinal
fusion devices, bone anchors, shunts, staples, fasteners, dental
implants, orthodontic braces, dental retainers, retractors,
retainers, couplings, scalpels, needles, forceps, dental tools,
surgical tools, bone cutters, and saws. Accordingly, the present
invention is not limited to that precisely as shown and described
in the present invention.
* * * * *