U.S. patent application number 17/175319 was filed with the patent office on 2021-06-03 for intrauterine device with controlled copper ion elution.
This patent application is currently assigned to SEBELA VLC LIMITED. The applicant listed for this patent is SEBELA VLC LIMITED. Invention is credited to Bob H. KATZ, Scott M. RUSSELL, Michael TAL.
Application Number | 20210161703 17/175319 |
Document ID | / |
Family ID | 1000005399505 |
Filed Date | 2021-06-03 |
United States Patent
Application |
20210161703 |
Kind Code |
A1 |
TAL; Michael ; et
al. |
June 3, 2021 |
INTRAUTERINE DEVICE WITH CONTROLLED COPPER ION ELUTION
Abstract
A method of manufacturing an intrauterine device (IUD) for
contraception that has a desired copper elution rate is described.
The method may involve selecting an elongate shape memory member
comprising a first metal having a first galvanic potential,
selecting at least one attachment member comprising a second metal
having a second galvanic potential that is different from the first
galvanic potential, attaching the attachment member(s) to the shape
memory member, and shaping the shape memory member to form a frame
of the intrauterine contraceptive device. The first metal and the
second metal are specifically selected as materials for the shape
memory member and the attachment member(s), in order to achieve the
desired copper elution rate.
Inventors: |
TAL; Michael; (Savyon,
IL) ; KATZ; Bob H.; (San Jose, CA) ; RUSSELL;
Scott M.; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEBELA VLC LIMITED |
HAMILTON |
|
BM |
|
|
Assignee: |
SEBELA VLC LIMITED
HAMILTON
BM
|
Family ID: |
1000005399505 |
Appl. No.: |
17/175319 |
Filed: |
February 12, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15441539 |
Feb 24, 2017 |
10918516 |
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17175319 |
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14289530 |
May 28, 2014 |
10188546 |
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15441539 |
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61890714 |
Oct 14, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 6/144 20130101;
A61F 6/18 20130101; Y10T 29/49826 20150115 |
International
Class: |
A61F 6/14 20060101
A61F006/14; A61F 6/18 20060101 A61F006/18 |
Claims
1. A method of manufacturing an intrauterine device (IUD) for
contraception that has a desired copper elution rate, the method
comprising: selecting an elongate shape memory member comprising a
first metal having a first galvanic potential; selecting at least
one attachment member comprising a second metal having a second
galvanic potential that is different from the first galvanic
potential; attaching the at least one attachment member to the
shape memory member; and shaping the shape memory member to form a
frame of the intrauterine contraceptive device, wherein the first
metal and the second metal are specifically selected as materials
for the shape memory member and the at least one attachment member,
in order to achieve the desired copper elution rate.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of U.S. patent
application Ser. No. 15/441,539, entitled, "Intrauterine Device
with Controlled Copper Ion Elution," filed Feb. 24, 2017, which is
a continuation-in-part of U.S. patent application Ser. No.
14/289,530, entitled "Intrauterine Device with Controlled Copper
Ion Elution," filed May 28, 2014, now U.S. Pat. No. 10,188,546,
which claims priority to U.S. Provisional Patent Application No.
61/890,714, entitled "Intrauterine Device with Controlled Copper
Ion Elution," filed on Oct. 14, 2013. The full disclosures of the
above-listed patent applications are hereby incorporated by
reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates to medical devices. More
specifically, the invention relates to intrauterine devices for
contraception.
BACKGROUND
[0003] An intrauterine device (IUD) is a small, often T-shaped
device, containing copper or hormone (e.g., levonorgestrel), which
is inserted into the uterus to provide long-acting, reversible
contraception. As of 2007, IUDs are the most widely used form of
reversible contraception, with more than 180 million users
worldwide. IUDs typically are one of two types--copper or
hormonal.
[0004] Copper IUDs primarily work by disrupting sperm motility and
damaging sperm so that the sperm are prevented from joining with an
egg. Copper acts as a spermicide within the uterus, increasing
levels of copper ions, prostaglandins, and white blood cells within
the uterine and tubal fluids. The increased copper ions in the
cervical mucus inhibit the sperm's motility and viability,
preventing sperm from traveling through a thickened cervical mucus
and/or destroying it as it passes through. Copper IUDs have a
typical first-year contraceptive success rate greater than 98
percent.
[0005] Most copper IUDs have a plastic T-shaped frame that is wound
with pure electrolytic copper wire and/or has copper collars
(sleeves). The arms of the frame hold the IUD in place near the top
of the uterus. The Paragard.RTM. intrauterine copper contraceptive
device (www.paragard.com) and the generic TCU 380A are currently
the most common copper IUDs. Copper IUDs can typically be implanted
for up to 10 years.
[0006] The mechanism of action of a copper IUD is essentially a
predictable electrochemical process of corrosion, driven by the
IUD's immersion in the uterine fluid. Over time, the copper element
(wires, beads, tubes, etc.) corrodes and releases copper ions.
Typically, the release rate is governed by the surface area and
volume of copper, the chemistry (especially pH) of the uterine
fluid, and the specific composition and surface properties of the
copper elements. The frame of the IUD on which the copper is
attached is typically made of a flexible, non-corrosive polymer.
Since typical polymers are not electrochemically active, they do
not influence the ion release rate of the copper elements.
Therefore, the copper ion release characteristics of a typical
plastic-frame IUD are strictly governed by the amount, preparation
and configuration of the copper itself. One challenge with copper
IUDs has been that increased effectiveness typically means
increased amounts of copper on the IUD, and increased amounts of
copper typically lead to increased side effects, primarily
increased menstrual and intermenstrual bleeding, and increased
pelvic pain. Balancing effectiveness with minimization of side
effects has been a continuing challenge for making copper IUDs.
[0007] One advantage of the copper IUD is its ability to provide
emergency contraception up to five days after unprotected sex. It
is generally known as the most effective form of emergency
contraception available. Another advantage is that it contains no
hormones, so it can be used while breast feeding, and fertility
returns quickly after removal. Lastly, copper IUDs have been shown
to be clinically effective for up to 10 years of continuous use.
Disadvantages include the possibility of heavier menstrual periods
and more painful menstrual cramping in some women.
[0008] A hormonal IUD, such as the Mirena.RTM.
Levonorgestrel-releasing intrauterine system (www.mirena-us.com),
uses the controlled release of a hormonal contraceptive such as
Levonorgestrel (a progestin). The hormonal contraceptive released
from a hormonal IUD prevents ovulation from occurring. The hormone
also thickens the cervical mucus so that sperm cannot reach the
fallopian tubes. Hormonal IUDs can typically be implanted for up to
5 years.
[0009] Hormonal IUDs do not increase bleeding as copper-containing
IUDs do. Instead, they can often reduce menstrual bleeding or
prevent menstruation altogether, and thus they are sometimes used
as a treatment for menorrhagia (heavy menstrual bleeding). Hormonal
IUDs have common side effects, however. The most common side
effects with levonorgestrel IUDs are hormone-related effects, such
as headaches, nausea, breast tenderness, depression and cyst
formation.
[0010] Based on effectiveness and the types of side effects, copper
IUDs are preferable for many women. Although currently available
copper IUDs are very effective, it would still be advantageous to
have improved copper IUDs. For example, it would be advantageous to
have copper IUDs that were very effective but had minimal side
effects.
BRIEF SUMMARY
[0011] Disclosed herein are various embodiments of an improved
copper IUD. Generally, the described embodiments provide an IUD
with a desirable (or "controlled") release rate of copper ions.
Different embodiments may be configured with different copper ion
release rates. For example, a particular copper ion release rate
may be identified to provide a desired balance between IUD
effectiveness and reduced side effects, compared to currently
available devices.
[0012] In one aspect of the present application, an intrauterine
contraceptive device may include a frame comprising a first metal
having a first galvanic potential and at least one metallic member
coupled with the frame, the at least one metallic member comprising
a second metal having a second galvanic potential different from
the first galvanic potential. In some embodiments, the first
galvanic potential may be more anodic than the second galvanic
potential. In alternative embodiments, the first galvanic potential
may be more cathodic than the second galvanic potential.
[0013] In some embodiments, the frame may be made entirely of
metal. Alternatively, the frame may be made partially of metal and
partially of a non-metallic substance. For example, the first metal
may in some embodiments be Nitinol. The second metal may be copper.
In some embodiments, for example, the metallic members are multiple
copper sleeves disposed around the frame at various locations. Some
embodiments include the combination of the first metal being
Nitinol and the second metal being copper. In embodiments where the
second metal is copper, the first galvanic potential and the second
galvanic potential may be configured to achieve approximately a
desired copper elution rate of the at least one metallic member. In
all of these embodiments, the non-metallic substance may be a
polymer, a silicone rubber or other engineered polymer plastic, for
example. Optionally, the device may further include a retrieval
string attached to one end of the metal frame.
[0014] In another aspect of this disclosure, a method of preventing
conception may involve advancing an intrauterine contraceptive
device into a uterus, where the intrauterine device includes a
frame comprising a first metal having a first galvanic potential,
and at least one metallic member coupled with the frame, comprising
a second metal having a second galvanic potential different from
the first galvanic potential. In some embodiments, the second metal
may be copper, and the first and second galvanic potentials may be
configured to achieve approximately a desired copper ion elution
rate. In some embodiments, the first metal may be Nitinol, and
advancing the contraceptive device into the uterus may involve
advancing a distal end of an introducer device through a cervix,
into the uterus, and advancing the contraceptive device out of the
distal end, thus allowing the Nitinol of the frame to expand to
contact a wall of the uterus.
[0015] In yet another aspect of the disclosure, a method of
manufacturing an IUD for contraception that has a desired copper
elution rate may involve: selecting an elongate shape memory member
comprising a first metal having a first galvanic potential;
selecting at least one attachment member comprising a second metal
having a second galvanic potential that is different from the first
galvanic potential; attaching the attachment member(s) to the shape
memory member; and shaping the shape memory member to form a frame
of the intrauterine contraceptive device. The first metal and the
second metal may be specifically selected as materials for the
shape memory member and the at least one attachment member, in
order to achieve the desired copper elution rate.
[0016] In some embodiments, the shape memory member may be a wire.
Merely by way of example, the first material may be Nitinol,
stainless steel, titanium, cobalt-based alloys, tantalum, platinum,
gold, silver, or MP35N. In one embodiment, for example, the first
metal is Nitinol, and the second metal is copper. Some embodiments
may include multiple copper sleeves, which may be attached to the
frame, for example, by passing the multiple copper sleeves over the
shape memory member. In such an embodiment, the method may also
include positioning the multiple sleeves along the shape memory
member at different positions before or after shaping the shape
memory member. The attachment member(s) may have any of a number of
different forms, such as but not limited to sleeves, wires,
ribbons, coils, tubes and beads.
[0017] In some embodiments, the first galvanic potential is more
anodic than the second galvanic potential. Alternatively, the first
galvanic potential may be more cathodic than the second galvanic
potential. In some embodiments, the frame is made entirely of the
first metal. In other embodiments, the frame is made partially of
the first metal and partially of a non-metallic substance. For
example, the frame may include a non-rigid material, such as but
not limited to a flexible polymer thread, a polyester thread, a
nylon thread or other biocompatible fabric. Optionally, the method
may also include attaching a retrieval string to a bottom portion
of the frame.
[0018] In one embodiments, shaping the shape memory member may
involve forming the frame to include: a bottom loop; a middle
portion comprising two parts of the elongate shape memory member
extending upward from the bottom loop; multiple twists in the
middle portion, forming a spring portion; two bends in the elongate
shape memory member at a location above the multiple twists, where
the elongate member crosses over itself; a first arm extending from
a first bend of the two bends; a second arm extending from a second
bend of the two bends; a first end loop at an end of the first arm;
and a second end loop at an end of the second arm, where the first
end loop and the second end loop in the elongate shape memory
member comprise tissue contact surfaces.
[0019] In another aspect of this application, a method of
manufacturing an IUD for contraception that has a desired copper
elution rate may involve: selecting a wire comprising a first metal
having a first galvanic potential; selecting at least one
attachment member comprising a second metal having a second
galvanic potential that is different from the first galvanic
potential; attaching the at least one attachment member to the
wire; and shaping the wire to form a frame. The shaping step may
result in a frame that has: a bottom loop; a middle portion;
multiple twists in the middle portion; two bends in the elongate
shape memory member at a location above the multiple twists in the
middle portion, where the elongate member crosses over itself; two
arms extending from the two bends; a first end loop at an end of
one of the two arms; and a second end loop at an end of the other
of the two arms.
[0020] These and other aspects and embodiments will be described in
further detail below, in reference to the attached drawing
figures.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a front view of a prior art, T-shaped, copper IUD
with a plastic support structure;
[0022] FIG. 2 is a bar graph illustrating a galvanic series for a
number of common metals and alloys;
[0023] FIG. 3 is a front view of a copper IUD with a metal frame,
according to one embodiment;
[0024] FIG. 4 illustrates potentiodynamic polarization curves for
copper sleeves tested in simulated uterine fluid at 37.degree. C.,
pH=7.1;
[0025] FIG. 5 illustrates potentiodynamic polarization curves for
bare Nitinol frames tested in simulated uterine fluid at 37.degree.
C., pH=7.1; and
[0026] FIG. 6 illustrates potentiodynamic polarization curves for
finished device assemblies (copper sleeves crimped onto Nitinol
frames) tested in simulated uterine fluid at 37.degree. C.,
pH=7.1.
DETAILED DESCRIPTION
[0027] The mechanism of action of a copper IUD is essentially a
predictable electrochemical process of corrosion, driven by the
IUD's immersion in the uterine fluid. Over time, the copper
elements of the IUD (copper wires, beads, tubes, or the like)
corrode and release copper ions. For a given IUD, the copper ion
release rate can be measured using standard laboratory tests in
simulated uterine fluid (SUF). Typically, the release rate is
governed by the surface area and volume of copper, the chemistry
(especially pH) of the SUF, and the specific composition and
surface properties of the copper elements. In currently available
IUDs, the primary driver influencing the copper release rate is the
amount of exposed copper surface area. In other words, to achieve a
higher copper ion release rate, an IUD would typically have an
increased copper surface area, which generally means the IUD will
contain more copper overall.
[0028] Referring now to FIG. 1, a typical, prior art, T-shaped,
copper IUD 10 is illustrated. The IUD 10 includes a frame 12,
copper sleeves 14 disposed around the frame 12 in three areas, and
a retrieval string 16. The frame 12 is typically made of a flexible
polymer and is often T-shaped for positioning in the uterus. Since
typical polymers are not electrochemically active, they do not
influence the ion release rate of the copper elements 14.
Therefore, the copper ion release characteristics are strictly
governed by the amount of surface area of the copper sleeves 14
themselves.
[0029] Galvanic corrosion is an electrochemical process in which
one metal corrodes preferentially to another when both metals are
in electrical contact and immersed in an electrolyte. The strength
of this electrical potential between two metals or alloys is called
the galvanic potential. The galvanic reaction can be exploited for
positive benefit. For example, a galvanic potential between
dissimilar metals can be used in primary batteries to generate an
electrical voltage. The measured voltage is representative of the
transfer of charged metal ions from one of the metals (the anode)
to the other (the cathode). The stronger the galvanic effect
between the two metals, the higher the transfer rate of ions from
the anode to the cathode.
[0030] To determine the galvanic potential between two metals, we
use a galvanic series, an example of which is illustrated in FIG.
2. In a galvanic series, metals are ranked by the electrical
potential they develop in a given electrolyte against a standard
reference electrode--i.e., their galvanic potential versus the
reference electrode. The relative position of two metals on such a
series determines which metal will be the anode and which will be
the cathode (if they are put in contact in an appropriate
electrolyte). The magnitude of the distance between the two metals
on the galvanic series will determine the strength of the galvanic
potential between them. A specific galvanic series can be
determined for any metals or alloys of interest, tested in a
specific electrolyte (e.g., SUF) at an appropriate pH.
[0031] Referring now to FIG. 3, in one embodiment, an IUD 20 may
include a metal frame 22 (or "shape memory member"), multiple
copper sleeves 24 (or "copper elements"), and a retrieval string
26. This embodiment of the IUD 20, as well as other, alternative
embodiments, is described in further detail in pending U.S. patent
application Ser. No. 13/795,940, entitled "Intrauterine
Contraceptive Device," filed Mar. 12, 2013, which is hereby
incorporated by reference in its entirety. In this embodiment, the
shape memory member 22 is generally made of a wire or wire-like
material, and the copper sleeves 24 are generally tubular or
partially tubular structures. In alternative embodiments, however,
the shape memory member 22 and/or the sleeves 24 may take any of a
number of different forms. For example, in one embodiment, the
shape memory member 22 may be configured more like a flat ribbon
that a cylindrical wire. In other embodiments, the sleeves 24 may
be replaced by any other suitable attachment members, such as
balls, coatings, clamps, tape or the like. Thus, the sleeves 24 are
merely one example of a type of attachment member that might be
used in forming the IUD 20.
[0032] In various embodiments, the elongate shape memory member 22
may have a two-dimensional (i.e., predominantly flat)
configuration, as shown, or may have a more three dimensional
(i.e., slightly bent out of plane) configuration. The elongate
shape memory member 22 may include a loop portion 36 at the bottom
(or "vertex") of the IUD 20, two generally parallel portions 35
extending vertically upward from the loop portion 36, multiple
twists 34, a middle portion, two bends 32 that form the shape
memory member 22 into two, approximately oppositely directed arms
31, and two tissue contact surfaces (or "end points") 28 at the
ends of the two arms 31. The copper sleeves 24 are disposed around
the shape memory member 22 at multiple locations, such as near each
of the tissue contact surfaces 28, along the arms 31 between the
bends 32 and the tissue contact surfaces 28, and at or near the
loop portion 36. Different numbers and positions of the copper
sleeves 24 may be provided in different alternative
embodiments.
[0033] In this embodiment, the bottom loop portion 36 does not form
any turns of a spring structure. Instead, to generate resilience in
the arms 31 of the IUS 20, this embodiment includes twists the 34
between the parallel portions 35 and the middle portion 30. Twists
34 may be formed when the two portions 35 of the elongate member 22
cross each other more than once in a longitudinally extending helix
containing multiple turns that run in series from closer to the
loop portion 36 upward, until the arms diverge again from the
twisted portion 34. FIG. 3 shows three twists 34. However, other
numbers of twists (e.g., 1-5, 6-10, greater than 10) are also
possible. In this embodiment, the twists 34 act as the "spring
portion" to confer laterally directed pressure to tissue contact
surfaces 28.
[0034] It may be desirable to be able to easily modify the
properties of the elongate member 22. For example, the anatomical
dimensions or characteristics of the uterus or medical conditions
of a patient may call for adjustments to the outward force produced
by the IUD 20. In such applications, the location of the twists 34
along the shape memory member 22, the number of the twists 34,
and/or the tightness of the twists 34 may be used to provide
variability in the properties of the device 20. For example,
increasing the number of twists 34 may increase the stiffness of
the elongate member 22, and decreasing the number of twists 34 may
decrease the stiffness of the elongate member 22. For another
example, increasing the tightness of the twists 34 may increase the
stiffness of the elongate member 22. Decreasing the tightness of
the twists 34 may decrease the stiffness of the elongate member 22.
Moving the twists 34 upward along the shape memory member 22 may
increase the stiffness of the elongate member 22, and moving the
twists downward along the shape memory member 22 may decrease the
stiffness of the elongate member 22. With the device of FIG. 3, a
variety of differently configured devices can be made available to
physicians to apply in the appropriate circumstances. The
variability provided by the twists 34 also allows much easier and
more continuous customization of properties by merely modifying the
nature of the twists 34, rather than the thickness or material of
the wire used to for the shape memory member 22 itself to produce
similar variations in properties. Wires come in standard sizes and
materials, and if some intermediate is desired, the expense can
make producing such a modified device impractical. Controlling
properties of the device with the properties of the twists 34
resolves this issue.
[0035] According to various embodiments, the galvanic effect can be
exploited in the copper IUD 20 by coupling the copper elements 24
to the metal frame 22 or other metal structure. The material of the
metal frame 22 or other elongate shape memory structure may be
chosen to achieve a desired galvanic effect between itself and the
copper elements 24. In one embodiment, for example, the frame 22
may be made of Nitinol (see FIG. 3, on which Nitinol and copper are
depicted). In other embodiments, however, any of a number of other
suitable biocompatible metals (or combinations of metals) may be
selected for making the frame 22. In various embodiments, the type
of material selected for the frame 22, the characteristics of the
material (thickness, for example), the overall size of the IUD 20
(and thus the amount of the material used to make the frame 22),
and/or other characteristics of the frame 22 may be specifically
selected to provide a particular copper elution rate. Similarly,
the type of size, number, positioning, and/or other factors
pertaining to the copper sleeves 24 may be specifically selected to
provide a particular embodiment with a particular copper elution
rate. In other words, any of a number of characteristics of the
frame 22 and/or the sleeves 24, such as but not limited to their
materials, may be selected to provide a desired copper elution
rate.
[0036] For the sake of comparison, a "baseline" copper ion elution
rate may be defined as one in which there is no galvanic effect
present (e.g., copper on a polymer frame, as in prior art IUDs). If
the metal frame 22 (or other metallic structure) is selected to
have a galvanic potential more anodic than the galvanic potential
of the copper sleeves 24 (lower on the galvanic series), then the
electrochemical driving force would be toward the copper sleeves
24, thereby reducing the copper ion release rate relative to the
baseline. Alternatively, if the metal frame 22 or structure that
has a galvanic potential more cathodic than the copper sleeves 24
(higher on the galvanic series), then the electrochemical driving
force would be away from the copper sleeve 24, thereby increasing
the copper ion release rate relative to the baseline. The greater
the difference between the materials on the galvanic series, the
more significant the decrease or increase in copper ion release
rate. The galvanic potential is also related to the relative
surface areas of the anode and the cathode, so the surface area
ratio between the frame 22 and the copper sleeves 24 may also be
selected to achieve a desired ion release rate.
[0037] In such a way, the material of the frame 22 and/or other
elements in contact with the copper elements 24 may be selected to
control the galvanic potential between the frame 22 and the copper
24, thereby allowing specificity, control and optimization of the
ion release rate. This may have a number of advantages. In some
embodiments, the IUD 20 may achieve a copper release rate
comparable or identical to that of a currently available (i.e.,
prior art) IUD with a lower amount (i.e., less surface area) of
copper, by coupling the copper 24 with the metal frame 22 that is
more cathodic than the copper 24. The smaller surface area of the
copper 24 may help reduce copper-related side effects, compared to
prior art copper IUDs. Alternatively, in other embodiments, the IUD
20 may be configured to release copper ions at a rate similar or
identical to that of a currently available copper IUD but for a
longer period of time. This may be achieved by giving the copper
sleeves 24 a greater exposed surface area than the copper
element(s) of a currently available device, while coupling the
sleeves 24 with the frame 22 made of a material that is more anodic
than the copper elements 24. In this case, the greater amount of
available copper is balanced by a slower release rate to achieve,
overall, a similar ion release profile. However, in this case, the
slower release rate with a larger copper reservoir allows the
elution to happen over a potentially longer period of time, thereby
extending the effectiveness of the IUD 20 beyond the typical 10
years of device life.
[0038] In still other embodiments, the IUD 20 may achieve a copper
ion release rate whose release curve is more curvilinear or more
linear in comparison to the standard commercial copper IUD release
rate curve. In this manner, a metallic IUD with a controlled
release rate may be chosen to avoid the burst release of copper
ions typically associated with commercial copper IUDs which
implement a plastic core. The burst release of copper ions has been
shown to be directly associated with the onset of clinical side
effects of the standard commercial copper IUDs, including in
particular, side effects experienced in the first 1 to 6 months of
IUD use, including increased menstrual bleeding, intermenstrual
bleeding, cramping and general pelvic pain. Such a reduction in
clinical side effects without with the need for ancillary
medications would be a significant advantage.
[0039] In various embodiments, a method for making the IUD 20 may
first involve selecting the wire material for making the metal
frame 22 and selecting (or perhaps manufacturing) the copper
sleeves 24. The metal frame 22 and/or any other metal structure(s)
on IUD 20 may be made from any material with desired galvanic
properties, including but not limited to Nitinol, stainless steel,
titanium, cobalt-based alloys, tantalum, platinum, gold, silver,
and MP35N. The frame 22 may be made from one material or multiple
materials. In alternative embodiments, the frame 22 may be made
entirely of metal or may have discrete active metallic portions or
elements, some or all of which may be in contact with the copper
elements 24, with non-metallic parts between the metallic portions
or with no parts at all between the metallic portions. The copper
elements 24 may take any suitable shape, size, form and number,
according to various embodiments. In the embodiment illustrated in
FIG. 3, there are ten copper sleeves 24 disposed on the frame 22.
Alternative embodiments may include more or fewer sleeves 24 and/or
smaller or larger sleeves 24. In other alternative embodiments, the
sleeves 24 may be replaced by, or used in combination with, other
copper elements, including but not limited to wire, ribbon, coils,
tubes, beads, and the like. Additionally, surface processing of the
frame 22 and/or other metallic structure may be tailored to achieve
a desired galvanic potential. For example, this may be accomplished
through heat treatment, oxidation, electropolishing, passivation,
and/or other chemical processing.
[0040] In some embodiments, the sleeves 24 may be complete tubes.
In these embodiments, the sleeves 24 may be passed onto the frame
22 before the frame 22 is bent and twisted to assume its final
shape. Alternatively, each sleeve 24 may be a partial tube, and
each may include a slit, for example, so that the sleeves 24 can be
placed over the frame 22 after the frame 22 has been formed. In
some embodiments, some sleeves 24 may be placed over the frame 22
before it is formed into its final shape, and other sleeves 24 may
be placed over the frame 22 after it is shaped.
Description of Corrosion Testing
[0041] To determine the baseline corrosion behavior of a Nitinol
frame and copper sleeves, such as those described above in
reference to FIG. 3 (together referred to below as the "ContraMed
IUD"), and to evaluate the effects of different surface processing
on the Nitinol frame, preliminary potentiodynamic polarization
testing was conducted. Processing of the Nitinol surface was
targeted to achieve a rest potential ("Erest") similar to or higher
than that of the copper sleeves, in order to both optimize the
intentional corrosion (and ion release) of the copper and minimize
any deleterious galvanic corrosion effects on the Nitinol frame. A
review of the literature of electropolished, etched,
chemically-polished, and heat-treated (with oxide) Nitinol revealed
that rest potentials can be of a wide range, from less than -420 mV
to as high as +20 mV vs. SCE.
[0042] Potentiodynamic polarization testing was conducted according
to ASTM F2129 on copper sleeves and Nitinol frames made from
different starting wires and processed in different ways. This
testing was conducted in phosphate buffered saline (PBS) at
37.degree. C. at a pH of 7.1. PBS was chosen for this testing for
simplicity as well as to allow comparison of the Nitinol corrosion
behavior with data from the literature. The testing was conducted
using a Gamry Cyclic Polarization Corrosion Apparatus.
[0043] Testing was also conducted in simulated uterine fluid (SUF)
per the following composition: NaHCO30.25; NaH2PO4.2H20 0/072;
Glucose 0.50; CaCl2 0.167; KCl 0.224; NaCl 4.97. The Simulated
Uterine Fluid solution was purged with nitrogen gas, and pH was
adjusted to 7.1 before testing. The Rest Potential ("Er") was
monitored for one hour before the corrosion test began. Specimens
were subjected to a scan from below the zero current potential to
1.0 V at a rate of 1 mV/s. No reverse scan was conducted, and the
test was stopped after a scan of -1 mV/s to 0.8 V (vs. Er).
Results
[0044] As described previously, the ideal Nitinol surface
processing scheme would achieve a rest potential (Erest) that is
similar to or higher than that of the copper sleeves (-286.1 mV),
in order to both optimize the intentional corrosion (and ion
release) of the copper and minimize any deleterious galvanic
corrosion effects on the Nitinol frame. At the same time, the
Nitinol surface should demonstrate excellent resistance to
breakdown. Based on the work of Rosenbloom and Corbett, a Nitinol
surface with an average breakdown potential in excess of 600 mV (as
tested in PBS at 37.degree. C.) is generally considered to be in an
optimum state for use as a medical implant.
[0045] FIGS. 4-6 illustrate plots of all the curves for a given
sample group on the same axes. FIG. 4 illustrates potentiodynamic
polarization curves for copper sleeves tested in simulated uterine
fluid at 37.degree. C., pH=7.1. FIG. 5 illustrates potentiodynamic
polarization curves for bare Nitinol frames tested in simulated
uterine fluid at 37.degree. C., pH=7.1. FIG. 6 illustrates
potentiodynamic polarization curves for finished device assemblies
(copper sleeves crimped onto Nitinol frames) tested in simulated
uterine fluid at 37.degree. C., pH=7.1. As illustrated in FIGS.
4-6, the copper curves and the Nitinol curves are very different.
Copper corrodes via generalized corrosion, while Nitinol, due to
its formation of a protective surface oxide layer, corrodes via
breakdown (i.e., pitting). As expected, the corrosion of the
assembled devices is dominated by corrosion of the copper sleeves,
and no breakdown behavior is observed in the potentiodynamic
polarization curve.
[0046] Although various embodiments and features are described
herein, the present invention extends beyond the specifically
disclosed embodiments to other alternative embodiments and/or uses
of the invention and obvious modifications and equivalents thereof.
Thus, the scope of the present invention herein disclosed should
not be limited by the particular disclosed embodiments described
above.
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