U.S. patent application number 13/010496 was filed with the patent office on 2011-05-12 for conductive composite electrode material.
Invention is credited to L. Liliana Atanasoska, Chandru Chandrasekaran, Tracee E.J. Eidenschink, J. Lee Shippy, III.
Application Number | 20110112617 13/010496 |
Document ID | / |
Family ID | 40089915 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110112617 |
Kind Code |
A1 |
Atanasoska; L. Liliana ; et
al. |
May 12, 2011 |
CONDUCTIVE COMPOSITE ELECTRODE MATERIAL
Abstract
A medical electrical lead and body implantable electrode
suitable for a variety of medical applications are disclosed. In
general, the electrode includes a composite material having
particles of pseudo-capacitive material, such as iridium oxide,
dispersed within a polymer matrix including a polyelectrolyte. The
polymer matrix can also include a conductive polymer doped with an
excess of the polyelectrolyte. The composite may used to form the
electrode itself or an electrode coating. The presence of a
pseudo-capacitive material within the composite may increase the
charge-storage capacity of the electrode and may allow for safe
deliveries of charge densities within an electrochemical window
suitable for pacing a patient's heart.
Inventors: |
Atanasoska; L. Liliana;
(Edina, MN) ; Shippy, III; J. Lee; (Wilmington,
NC) ; Eidenschink; Tracee E.J.; (Wayzata, MN)
; Chandrasekaran; Chandru; (Mercer Island, WA) |
Family ID: |
40089915 |
Appl. No.: |
13/010496 |
Filed: |
January 20, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
12237099 |
Sep 24, 2008 |
7899552 |
|
|
13010496 |
|
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60979906 |
Oct 15, 2007 |
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Current U.S.
Class: |
607/119 |
Current CPC
Class: |
A61N 1/05 20130101; A61N
1/0565 20130101; A61N 1/0568 20130101 |
Class at
Publication: |
607/119 |
International
Class: |
A61N 1/05 20060101
A61N001/05 |
Claims
1. An implantable medical device comprising: an electrode
comprising a polymer matrix including a conductive polymer doped
with an excess of a negatively-charged polyelectrolyte and
pseudo-capacitive, transition metal oxide particles dispersed
throughout the polymer matrix.
2. The implantable medical device of claim 1, wherein the electrode
includes a conductive base material and wherein a coating including
the polymer matrix is disposed over at least a portion of the
conductive base material.
3. The implantable medical device of claim 1, wherein the
conductive polymer is selected from the group consisting of
polypyrrole, polyaniline, polyacetylene, polythiophene,
polyethylenedioxythiophene, poly (p-phenyl vinylene), and mixtures
thereof.
4. The implantable medical device of claim 1, wherein the
conductive polymer comprises polyethylenedioxythiophene.
5. The implantable medical device of claim 1, wherein the
negatively-charged polyelectrolyte is selected from the group
consisting of polystyrene sulfonate, polyglutamic acid,
NAFION.RTM., and mixtures thereof.
6. The implantable medical device of claim 1, wherein the
negatively-charged polyelectrolyte comprises polystyrene
sulfonate.
7. The implantable medical device of claim 1, wherein the
pseudo-capacitive, transition metal oxide particles are selected
from the group consisting of iridium oxide particles, ruthenium
oxide particles, rhodium oxide particles, osmium oxide particles,
titanium oxide particles, and combinations thereof.
8. The implantable medical device of claim 1, wherein the
pseudo-capacitive, transition metal oxide particles comprise
iridium oxide particles.
9. The implantable medical device of claim 1, wherein the
pseudo-capacitive particles, transition metal oxide particles are
present in a sufficient amount such that an electrode potential of
the electrode is maintained within an electrochemical window
suitable for pacing a heart.
10. The implantable medical device of claim 1, wherein the
conductive polymer comprises polypyrrole and the negatively-charged
polyelectrolyte comprises polyglutamic acid.
11. The implantable medical device of claim 1, wherein the
conductive polymer comprises polyethylenedioxythiophene and the
negatively-charged polyelectrolyte comprises polystyrene sulfonate.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of application Ser. No.
12/237,099, filed Sep. 24, 2008, entitled "CONDUCTIVE COMPOSITE
ELECTRODE MATERIAL," which claims the benefit of Provisional
Application Ser. No. 60/979,906, filed Oct. 15, 2007, entitled
"CONDUCTIVE COMPOSITE ELECTRODE MATERIAL," both of which are herein
incorporated by reference in their entireties for all purposes.
TECHNICAL FIELD
[0002] This invention relates to body implantable medical devices,
and more particularly, to implantable electrodes for sensing
electrical impulses in body tissue or for delivering electrical
stimulation pulses to an organ or a nerve.
BACKGROUND
[0003] Cardiac pacing leads are well known and widely employed for
carrying pulse stimulation signals to the heart from a battery
operated pacemaker, or other pulse generating means, as well as for
monitoring electrical activity of the heart from a location outside
of the body. Electrical energy is applied to the heart via an
electrode to return the heart to normal rhythm. Some factors that
affect electrode performance include polarization at the
electrode/tissue interface, electrode capacitance, sensing
impedance, and voltage threshold. In all of these applications, it
is highly desirable to optimize electrical performance
characteristics at the electrode/tissue interface.
[0004] Electrode materials intended for low threshold cardiac
pacing or neuro-stimulation are required to have high electrical
efficiency and minimal polarization loss during charge injection.
The electrode used for electrical stimulation also needs to have
high impedance, meaning a small geometrical surface area, in order
to prevent premature battery depletion. The small geometric surface
area translates into a high current density that can cause the
electrode potential to exceed the limits of a safe electrochemical
window, where no gas evolution or corrosion of the electrode takes
place.
[0005] Charge injection efficiency is directly related to
electrochemically active area and capacitance of the implantable
electrode. Electrode capacitance is directly proportional to charge
storage capacity (mC/cm.sup.2). The presence of a pseudo-capacitive
material increases the electrode charge storage capacity and allows
for safe delivery of charge densities.
SUMMARY
[0006] According to one embodiment, the present invention is a
medical electrical lead. The medical electrical lead includes a
lead body including a conductor extending from a proximal end
adapted to be connected to a pulse generator to a distal end. The
medical electrical lead also includes at least one electrode. The
electrode is operatively connected to the conductor. According to
one embodiment, the electrode includes a composite material
including a negatively-charged polyelectrolyte and a
pseudo-capacitive material. In still further embodiments, the
electrode includes a conductive polymer doped with an excess of the
negatively charged polyelectrolyte or ionomer.
[0007] According to yet another embodiment, the electrode includes
a base material operatively connected to the conductor and a
coating disposed over at least a portion of the base material. The
coating includes the negatively charged polyelectrolyte material
and the pseudo-capacitive material.
[0008] According to yet another embodiment, the present invention
is a body implantable electrode. The body implantable electrode
includes a conductive base. The conductive base includes a
conductive polymer, a negatively charged polyelectrolyte and a
pseudo-capacitive material.
[0009] According to another embodiment, the implantable electrode
also includes a conductive metal base and a coating disposed over
at least a portion of the conductive base. According to this
embodiment, the coating includes the conductive polymer, the
negatively charged polyelectrolyte and a pseudo-capacitive
material.
[0010] According to yet another embodiment, the body implantable
electrode includes a conductive base material and a coating
including a first layer and a second layer disposed over a least a
portion of the conductive base material. The first layer includes a
pseudo-capacitive material. The second layer includes a conductive
polymer and a negatively charged electrolyte.
[0011] While multiple embodiments are disclosed, still other
embodiments of the present invention will become apparent to those
skilled in the art from the following detailed description, which
shows and describes illustrative embodiments of the invention.
Accordingly, the drawings and detailed description are to be
regarded as illustrative in nature and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic view of a lead and a pulse generator
according to an embodiment of the present invention.
[0013] FIG. 2 is a partial, cross-sectional view of a lead shown in
FIG. 1 according to an embodiment of the present invention.
[0014] FIG. 3A is a cross-sectional view of a distal portion of a
lead according to an embodiment of the present invention.
[0015] FIG. 3B is a cross-sectional view of a distal portion of a
lead according to another embodiment of the present invention.
[0016] FIG. 4 is a side, cross-sectional view of an electrode
according to an embodiment of the present invention.
[0017] FIG. 5 is a side, cross-sectional view of an electrode
according to another embodiment of the present invention.
[0018] While the invention is amenable to various modifications and
alternative forms, specific embodiments have been shown by way of
example in the drawings and are described in detail below. The
intention, however, is not to limit the invention to the particular
embodiments described. On the contrary, the invention is intended
to cover all modifications, equivalents, and alternatives falling
within the scope of the invention as defined by the appended
claims.
DETAILED DESCRIPTION
[0019] In the following detailed description, reference is made to
the accompanying drawings which form a part hereof, and in which is
shown by way of illustration specific embodiments in which the
invention may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, and it is to be understood that other embodiments
may be utilized and that structural changes may be made without
departing from the scope of the present invention. Therefore, the
following detailed description is not to be taken in a limiting
sense, and the scope of the present invention is defined by the
appended claims and their equivalents.
[0020] FIG. 1 is a schematic view of a medical electrical lead 10
coupled to a pulse generator 14. In one embodiment, the lead 10 can
be adapted to deliver pacing energy to a patient's heart.
Alternatively, the lead 10 can be a adapted for sensing and
receiving electrical signals from a patient's heart. In still
further embodiments of the present invention, the lead 10 can be
adapted for neuro-stimulation applications.
[0021] The pulse generator 14 can be implanted in a
surgically-formed pocket in a patient's chest or other desired
location. The pulse generator 14 generally includes a power supply
such as a battery, a capacitor, and other components. Additionally,
the pulse generator 14 generally includes electronic components to
perform signal analysis, processing, and control. For example, the
pulse generator 14 can include microprocessors to provide
processing and evaluation to determine and deliver electrical
shocks and pulses of different energy levels and timing for
ventricular defibrillation, cardioversion, and pacing to a heart in
response to cardiac arrhythmia including fibrillation, tachycardia,
and bradycardia.
[0022] FIG. 2 is a partial, cross-sectional view of the lead 10
shown in FIG. 1. As shown in FIG. 2, the lead 10 includes an
elongated, flexible lead body 20 having a proximal portion 24 and a
distal portion 28. In one embodiment of the present invention, the
lead body 20 includes a lumen for receiving a guiding element such
as a guidewire or a stylet.
[0023] Cardiac lead 10 also includes one or more conductors 30,
such as a coiled conductor, extending from a proximal end 32 to a
distal end 36 of the lead body 20. The proximal end 32 is
configured to be operatively connected to a pulse generator 14 via
a connector 40. Conductor 30 is generally helical in configuration
and includes one or more conductive wires or filaments. The
conductor 30 is operatively connected to at least one electrode 50
located on the lead body 20. The lead 10 may include a plurality of
electrodes as necessary or desired.
[0024] FIGS. 3A and 3B are partial, cross-sectional views of the
distal end 36 of the lead body 20 according to various embodiments
of the present invention. As shown in FIG. 3A, the electrode 50 is
a distal tip electrode 50 located at the distal end 36 of the lead
body 20. According to another exemplary embodiment of the present
invention, as shown in FIG. 3B, lead body 20 can include a proximal
electrode 50a and/or a distal tip electrode 50b, making the lead 10
a bipolar lead.
[0025] In various embodiments, as shown in FIGS. 3A and 3B, the
electrode 50 includes a conductive composite material. According to
one exemplary embodiment of the present invention, the electrode 50
is formed from a composite including a conductive polymer, a
polyelectrolyte, and a pseudo-capacitive material.
[0026] According to one embodiment of the present invention, the
conductive polymer is an intrinsically conductive polymer.
Intrinsically conductive polymers include conjugated polymers and
electronically conductive polymers. Intrinsically conductive
polymers are conductive without requiring a non-polymeric
conductive filler or coating, such as a metallic compound or
carbon. Intrinsically conductive polymers include alternating
single and double bonds forming a conjugated backbone that displays
electronic properties. Charge in intrinsically conductive polymers
is transported along and between polymer molecules via charge
carriers generated along the conjugated backbone.
[0027] Intrinsically conductive polymers may include dopants to
enhance their conductivity. Dopants may also help to control the
conductivity characteristics of the polymer. The conductivity of
intrinsically conductive polymers can generally range from
semi-conducting to super conducting, depending upon the doping
levels. Some intrinsically conductive polymers may also exhibit a
quasi-redox behavior that is highly reversible giving them
pseudo-capacitive properties. Examples of intrinsically conductive
polymers include, but are not limited to, the following:
polypyrrole, polyacetylene, polythiophene,
polyethylenedioxythiophene, poly(p-phenyl vinylene), polyaniline,
polynapthalene, other suitable conductive polymers, and mixtures
thereof.
[0028] The inclusion of a conductive polymer into the electrode
composite may increase its biocompatibility, reduce pacing
thresholds, and improve sensing performance. Additionally, the
inclusion of a conductive polymer may present an organic interface
to biological tissue instead of a metallic interface (e.g. metallic
electrode), which may facilitate a favorable biological response to
the implant. The inflammatory and healing response of the tissue at
the local site may be controlled and/or altered to reduce necrosis
in the area next the to the lead, and may reduce the thickness of
any resultant fibrotic capsule.
[0029] Polyelectrolytes (also referred to as a polymer electrolyte
or ionomer) are polymers whose units bear an electrolyte group.
These groups will dissociate in aqueous solutions, making the
polymers charged. Polyelectrolytes can be positively (cationic) or
negatively (anionic) charged. Some polyelectrolytes include both
cationic and anionic repeating groups. Exemplary negatively charged
polyelectrolytes (polyanions) include, but are not limited to, the
following: polystyrene sulfonate (PSS), polyglutamic acid,
NAFION.RTM., and mixtures thereof. Polyelectrolytes can also
include polymer-drug conjugates. Exemplary polymer drug conjugates
include conjugates of polyglutamate or polyethylene glycol with
paclitaxel. Incorporating a polymer drug conjugate into the
electrode composite may be a useful way of locally delivering a
therapeutic agent to a targeted site within a patient's heart.
[0030] A polyelectrolyte can be used to dope a conductive polymer
to form a polymer matrix that is both a good ion and electron
conductor. Doping a conductive polymer with anions induces an
electron conductive path along the conjugated bonds that makes
these polymers "metal-like". One such example of a conductive
polymer doped with a negatively charged polyelectrolyte includes
poly (3,4-ethylenedioxythiophene) doped with an excess of
polystyrene sulfonate (PSS), designated as PEDOT-PSS. PEDOT-PSS is
a non-stochiometric polyelectrolyte complex of PEDOT having an
excess of PSS. Another example of a conductive polymer doped with a
negatively-charged polyelectrolyte includes polypyrrole doped with
polyglutamic acid. The incorporation of a polyelectrolyte in the
electrode composite that allows every volume of the electrode
composite to be generally permeable to small molecules, resulting
in an extremely high effective electrode surface area.
Additionally, the bulk type matrix eliminates the abrupt
electrode-tissue interface. The high electrode surface area
combined with the elimination of the abrupt electrode-tissue
interface allows for a more efficient charge transfer process.
[0031] According to one embodiment of the present invention, the
electrode composite also includes a pseudo-capacitive material. A
pseudo-capacitive material is a material that is capable of
undergoing a reversible faradaic process, such as an
oxidation/reduction (redox) reaction. Pseudo-capacitors are capable
of storing large amounts of charge, and can serve as high or
ultra-high capacitors. When the capacitance of a material is
measured using cyclic voltammetry, the capacitance is directly
proportional to the measured current. Some conductive polymers such
as polyaniline and polythiophenes can also behave as
pseudo-capacitors. According to one embodiment of the present
invention, the pseudo-capacitive material is dispersed throughout
the conductive polymer/polymer electrolyte matrix. Exemplary
pseudo-capacitive materials include, but are not limited to,
transition metal oxides such as iridium oxide, ruthenium oxide,
rhodium oxide, osmium oxide, titanium oxide, and combinations
thereof. The incorporation of one or more of these materials into a
conductive polymer or a conductive polymer doped with a
polyelectrolyte may further boost the capacitive properties of the
pseudo-capacitive materials. The pseudo-capacitive material is
dispersed throughout the polymer matrix in the form or
microparticles or nanoparticles. In some embodiments, the
dispersion of pseudo-capacitive particles can be a uniform
dispersion of particles.
[0032] The amount of pseudo-capacitive material present in the
conductive composite material is important for maintaining the
electrode potential within a safe electrochemical window for
pacing. The amount of pseudo-capacitive material present in the
electrode composite should be sufficient to maintain the electrode
potential within a safe electrochemical window for pacing. A safe
electrochemical window for pacing can be defined as the potential
range within which only reversible reactions occur. This can also
be referred to as the charge injection limit. In general, the
potential limits of the electrochemical window for pacing are the
hydrolysis of water to oxygen and protons (anodic limit) and that
of hydrogen to hydroxide ions (cathodic limit), which is
approximately 2V. Within this potential range a number of
additional reactions may also occur.
TABLE-US-00001 reduction E.sup.o/volts 1 O2 + 4H+ + 4e- .RTM. 2H2O
+1.229 2 Ag+ + e- .RTM. Ag +0.7996 3 Cu2+ + 2 e- .RTM. Cu +0.3419 4
Fe2+ + 2 e- .RTM. Fe -0.447 5 Zn2+ + 2 e- .RTM. Zn -0.7628 6 2H2O +
2e- .RTM. H2 + 2OH- -0.83
[0033] The voltage drop values at the electrode tissue interface
remain within the cathodic and anodic potential limits of the
hydrolysis of water resulting in a high capacitance of the
electrode.
[0034] According to an embodiment of the present invention, the
amount of pseudo-capacitive material present in the conductive
electrode composite material should be sufficient to maintain the
electrode potential within an electrochemical window of about 2V.
According to a further embodiment of the present invention, the
conductive electrode composite material includes a
pseudo-capacitive material present in an amount no greater than
about 35 wt % of the total weight of the fibrous matrix.
[0035] According to one embodiment of the present invention, the
electrode is formed from a composite including
poly(3,4-ethylenedioxythiophene) (PEDOT) doped with an excess of
polystyrene sulfonate (PSS) and iridium oxide. The iridium oxide is
dispersed throughout the polymer matrix in the form of
microparticles or nanoparticles. In a further embodiment of the
present invention the iridium oxide is uniformly dispersed
throughout the polymer matrix.
[0036] According to another further embodiment of the present
invention, the electrode is formed from a composite including
polypyrrole doped with an excess of polyglutamic acid and iridium
oxide.
[0037] FIG. 4 is a side, cross-sectional view of an electrode 50
according to another embodiment of the present invention. As shown
in FIG. 4, the electrode 50 includes a conductive base material 60
and a coating 65 comprising a conductive composite material
disposed on the base material. The base material can be formed from
platinum, stainless steel, MP35N, a platinum-iridium alloy or
another similar conductive material. The coating 65 is disposed on
at least a portion of the conductive base material 60. According to
another embodiment of the present invention, the coating 65 covers
substantially all an outer surface of the base material.
[0038] FIG. 5 is cross-sectional schematic view of an electrode 50
according to yet another embodiment of the present invention.
According to this embodiment, the electrode 50 includes a
conductive base material 60, a composite coating 70 disposed on at
least a portion of the conductive base material 60. The conductive
base material 60 can be formed from platinum, stainless steel,
MP35N, a platinum-iridium alloy or another similar conductive
material.
[0039] As shown in FIG. 5, the composite coating 70 includes a
first layer 72 and a second layer 75. The first layer 72 is a
pseudo-capacitive coating such as those now employed in current
lead technology. According to one embodiment, the first layer 72
may have a micro-porous or nano-porous structure. Exemplary
materials for forming the first pseudo-capacitive layer on the
conductive base material 60 include the transition metal oxides and
other capacitive materials some examples of which include, but are
not limited to, the following: iridium oxide, ruthenium oxide,
rhodium oxide, osmium oxide, titanium oxide, platinum iridium,
platinized platinum, titanium nitride, titanium oxynitride,
titanium carbide, tantalum oxide, tantalum nitride, tantalum
oxynitride, and combinations thereof.
[0040] A polymer matrix including conductive polymer doped with an
excess of a negatively-charged polyelectrolyte forms the second
layer 75. The second layer 75 of the composite coating 70 is
disposed on at least a portion of the first layer 72. According to
another embodiment, the second layer 75 is disposed over
substantially all of the first layer 72. The presence of the
conductive polymer/polyelectrolyte matrix may increase the
capacitive properties of the first layer 72. According to one
embodiment, the conductive polymer/polyelectrolyte matrix includes
poly (3,4-ethylenedioxythiophene) (PEDOT) doped with an excess of
polystyrene sulfonate (PSS). According to another embodiment of the
present invention, the conductive polymer/polyelectrolyte matrix
includes polypyrrole doped with an excess of polyglutamic acid.
Still other combinations of a conductive polymer doped with an
excess of a negatively charged polyelectrolyte are possible. In yet
other embodiments of the present invention, the second layer 75
includes a conductive polymer doped with an excess of a
negatively-charged polyelectrolyte and a pseudo-capacitive material
such as described above.
[0041] According to various embodiments of the present invention,
the electrode 50 and/or coatings 65 and 70 may be formed by
dip-coating, brush-coating, drop coating, electrospray coating,
electrochemical deposition, electrospinning, sputtering, or by
electrodeposition. In further embodiments, the coatings 65 and 70
may be coated on the surface of the electrode 50 by chemical
deposition, plasma coating, or bipolar electrode position. These
and other methods are well known to those of skill in the art.
[0042] In one embodiment of the present invention, conductive
polymers such as polypyrrole or PEDOT can be formed by passing a
current through a conductive substrate while the substrate is
immersed in an aqueous solution of the monomer. The conductive
polymer may incorporate other molecules or dopants that are present
in the solution during its formation (e.g., therapeutic agents or
biomolecules promoting attachment to tissue).
[0043] According to another embodiment, the electrode and or
electrode coating may be formed by spray coating. Spray coating may
allow for greater control of coating placement, which may allow for
selectively coating one area of the lead and/or electrode without
contaminating other areas of the lead and/or electrode with the
spray solution/mixture. Other benefits of spray coating may include
decreased waste of coating solution/mixture and uniform coating on
the device (e.g., along a lead body or on an electrode).
[0044] According to yet another embodiment of the present
invention, the electrode composite and/or electrode coating can be
formed by spin coating the conductive polymer/polyelectrolyte
matrix onto a conductive substrate. Then, cathodic
electro-deposition can be used to incorporate or embed particles of
the pseudo-capacitive material into the conductive
polymer/polyelectrolyte matrix.
[0045] Various modifications and additions can be made to the
exemplary embodiments discussed without departing from the scope of
the present invention. For example, while the embodiments described
above refer to particular features, the scope of this invention
also includes embodiments having different combinations of features
and embodiments that do not include all of the described features.
Accordingly, the scope of the present invention is intended to
embrace all such alternatives, modifications, and variations as
fall within the scope of the claims, together with all equivalents
thereof.
* * * * *