U.S. patent application number 17/697480 was filed with the patent office on 2022-09-29 for methods of making and bioelectronic applications of metalized graphene fibers.
The applicant listed for this patent is Board of Regents, The University of Texas System, University of Wollongong. Invention is credited to Maria Gonzalez-Gonzalez, Rouhollah Ali Jalili, Mario I. Romero-Ortega, Gordon G. Wallace.
Application Number | 20220305253 17/697480 |
Document ID | / |
Family ID | 1000006402540 |
Filed Date | 2022-09-29 |
United States Patent
Application |
20220305253 |
Kind Code |
A1 |
Romero-Ortega; Mario I. ; et
al. |
September 29, 2022 |
METHODS OF MAKING AND BIOELECTRONIC APPLICATIONS OF METALIZED
GRAPHENE FIBERS
Abstract
The present disclosure provides methods of making and applying
metalized graphene fibers in bioelectronics applications. For
example, platinized graphene fibers may be used as an implantable
conductive suture for neural and neuro-muscular interfaces in
chronic applications. In some embodiments, an implantable electrode
includes a multi-layer graphene-fiber core, an insulative coating
surrounding the multi-layer graphene-fiber core, and a metal layer
disposed between the multi-layer graphene-fiber core and the
insulative coating.
Inventors: |
Romero-Ortega; Mario I.;
(Coppell, TX) ; Wallace; Gordon G.; (Wollongong,
AU) ; Gonzalez-Gonzalez; Maria; (Dallas, TX) ;
Jalili; Rouhollah Ali; (Melbourne, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Board of Regents, The University of Texas System
University of Wollongong |
Austin
Wollongong NSW |
TX |
US
AU |
|
|
Family ID: |
1000006402540 |
Appl. No.: |
17/697480 |
Filed: |
March 17, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16691309 |
Nov 21, 2019 |
11311720 |
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17697480 |
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62770540 |
Nov 21, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 14/34 20130101;
H01M 4/96 20130101; C23C 14/185 20130101; A61N 1/0556 20130101 |
International
Class: |
A61N 1/05 20060101
A61N001/05; C23C 14/34 20060101 C23C014/34; C23C 14/18 20060101
C23C014/18; H01M 4/96 20060101 H01M004/96 |
Claims
1. An implantable electrode comprising: a multi-layer
graphene-fiber core; a separating layer; and an electrically
conductive layer disposed at least in part between the multi-layer
graphene-fiber core and the separating layer.
2. The implantable electrode of claim 1 wherein the separating
layer is conductive.
3. The implantable electrode of claim 1 wherein the separating
layer is non-conductive.
4. The implantable electrode of claim 1 wherein the separating
layer is at least partially around the multi-layer graphene-fiber
core.
5. The implantable electrode of claim 1 wherein the multi-layer
graphene-fiber core has an exposed portion.
6. The implantable electrode of claim 3, wherein the separating
layer comprises Parylene-C.
7. The implantable electrode of claim 1, wherein the electrically
conductive layer is adjacent the multi-layer graphene-fiber core
and the electrically conductive layer covers a surface portion of
the graphene-fiber core with partial encapsulation of the
multi-layer graphene-fiber core.
8. The implantable electrode of claim 1, wherein the electrically
conductive layer comprises at least one of platinum, iridium,
iridium oxide, platinum-iridium, and titanium nitride.
9. The implantable electrode of claim 1, wherein the multi-layer
graphene-fiber core has a diameter about 10 .mu.m to about 200
.mu.m.
10. A method for making an implantable electrode, the method
comprising: forming a multi-layered graphene-fiber core using
ordered graphene oxide sheets; adding an electrically conductive
layer to at least a portion of the multi-layered graphene-fiber
core; and applying a separation layer to the multi-layered
graphene-fiber core and electrically conductive layer.
11. The method of claim 10 wherein forming comprises forming the
multi-layered graphene-fiber core by performing an in-situ
reduction of ordered graphene sheets.
12. The method of claim 11 wherein forming comprises forming the
multi-layered graphene-fiber core by performing an in-situ
reduction of ordered graphene sheets in a liquid crystalline.
13. The method of claim 10, wherein the electrically conductive
layer comprises at least one of platinum, iridium, iridium oxide,
platinum-iridium, and titanium nitride.
14. The method of claim 10, wherein the electrically conductive
layer has thickness in the range between about 10 nm to about 500
nm.
15. The method of claim 10, wherein the separation layer comprises
Parylene-C.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/691,309 entitled "Methods of Making and
Bioelectronic Applications of Metalized Graphene Fibers" filed on
Nov. 21, 2019, which claims priority to and the benefit of U.S.
Provisional Application No. 62/770,540 entitled "Methods of Making
and Bioelectronic Applications of Metalized Graphene Fibers" filed
on Nov. 21, 2018. The disclosures of the above referenced patent
applications are incorporated herein, in their entireties, by
reference.
TECHNICAL FIELD
[0002] The present disclosure is related to the making biosensors
and bioelectronics applications of microelectrode arrays including
metalized graphene fibers.
BACKGROUND
[0003] Chronically implantable microelectrodes enable communication
between man-made devices and the nervous system. Neural prostheses
and therapies based on electrical stimulation or action potential
recording, involve electrodes interfaced to central and peripheral
nervous systems. A functional microelectrode is required to
communicate with an individual neuron to record bio-signals, while
delivering sufficient amount of electrical charge to depolarize the
neural tissue and initiate a response. Existing microelectrode
technologies have met significant challenges and limitations.
[0004] For example, while effective bidirectional communication
between a machine and the nervous system requires access to a low
impedance soft microelectrode with a tip size comparable to
individual neurons (D <50 .mu.m and geometric surface area
<2000 .mu.m.sup.2), the performance of conventional
microelectrodes comprised of noble metals (i.e., gold, platinum
(Pt) and platinum/iridium) and crystalline silicon is limited due
to their high impedance, low charge injection capacity (0.05-0.26
mC/cm.sup.2), low surface area and mechanical mismatch between the
electrode and surrounding tissue causing scarring and failure of
the device.
[0005] Accordingly, the selection of material for electrodes at the
interfaces for neural stimulation and recording influences the
efficacy, reliability and lifetime of neural interfaces.
Furthermore, during the stimulation and recording, the electrode
must deliver and record sufficient amount of charge, but not exceed
the threshold for triggering electrolysis of the surrounding media.
The low surface area of conventional metal-based electrodes
intrinsically limits their ability to deliver a high charge density
and adversely affects the sensitivity of individual neuron signal
recording.
[0006] These limitations have motivated the evaluation of other
materials such as nanostructured carbon, nanostructured fibers,
metal oxides, metal nitrides and organic conductors, to provide
enhanced electrochemical characteristics with biocompatibility.
However, such materials provide additional challenges. For example,
coating with titanium nitride (TiN) improves the charge injection
capacity of Pt electrodes from 0.05-0.26 mC/cm.sup.2 to 0.87
mC/cm.sup.2 over a capacitive mechanism, which is favorable for
in-vivo studies. Activated Iridium oxide (IrOx) further enhances
the charge injection capacity of Pt electrodes to 1-5 mC/cm.sup.2
through a faradaic mechanism, however, it has limited stability and
safety margin for neural stimulation. Deposition of conducting
polymers such as PEDOT:PSS, PEDOT:pTS, PEDOT:C104, PEDOT:CNT
further increase the charge injection capacity to 2.92, 2.01, 2.09,
and 1.25 mC/cm , respectively, compared with Pt (0.05-0.26
mC/cm.sup.2). These polymers also reduce the electrode impedance to
8, 26.5, 203 and 42 M.OMEGA. .mu.m.sup.2, respectively, compared
with Pt (.about.390 M.OMEGA. .mu.m.sup.2). However, the
heterogeneous nature of the coated microelectrode is prone to
galvanic coupling that can result in side reactions, corrosion,
delamination and consequently early failure. The selected materials
and fabrication process must also minimize electrode delamination
to ensure robust and reliable operation.
[0007] In addition, conventional low impedance microelectrodes are
not stiff enough to penetrate the soft nerve tissue, yet flexible
or stretchable to minimize mechanical mismatch with the tissue and
accommodate for micromovements once implanted.
[0008] Nanostructured carbonaceous materials including graphene can
provide outstanding electrochemical characteristics while enabling
flexibility and strength. Nanotubes and graphene microfibers
provide excellent electrochemical properties, high surface area,
mechanical strength, high flexibility, and biocompatibility, and
thus ideal for electrode fabrication. Indeed, carbon nanotube
fibers demonstrated significant electrochemical activity,
sensitivity, and resistance to biofouling when implanted, compared
with metal electrodes and conventional carbon fibers. However,
while the neat carbon nanotube based fiber microelectrodes are
stable and able to record neural activity for relatively long
periods of time, the spinning process used to manufacture nanotubes
is challenging. Additionally, the high cost for producing super
aligned carbon nanotube arrays (dry spinning), as well as the
extremely rigorous conditions needed for their manufacturing
including high temperature (>1000.degree. C.), and the use of
corrosive solvents (e.g. fuming sulfuric acid and chlorosulphonic
acid), drastically limits the production of carbon nanotube-based
microfibers.
[0009] Furthermore, an additional major drawback of conventional
free-standing carbon nanotubes and graphene microfibers lies in the
high resistivity compared with their metallic counterparts. When a
microelectrode is longer than a few millimeters, the resistivity
increases significantly, which poses a significant challenge to low
noise recording.
SUMMARY
[0010] The present disclosure is related to the making biosensors
and bioelectronics applications of microelectrode arrays including
metalized graphene fibers. In some embodiments, the fabrication of
flexible and free-standing graphene-fiber based microelectrode
arrays with a thin platinum coating, as a current collector,
results in a structure with low impedance, high surface area and
excellent electrochemical properties. The graphene-fibers may be
manufactured using liquid crystalline dispersions of graphene oxide
(LCGO). The graphene fibers have unique mechanical and
electrochemical properties in addition to its natural
biocompatibility. The resulting microelectrode arrays provide
better performance when compared to conventional graphene or Pt
electrodes. In particular, in some embodiments, the low impedance
and porous structure of graphene fiber results in an unrivalled
charge injection capacity and the improved ability to record and
detect neuronal activity, while the thin Pt layer transfers the
collected electrons along the microelectrode efficiently. Further,
the resulting microelectrode arrays can also detect neuronal
activity with improved signal to noise ratios when compared to
conventional microelectrode arrays.
[0011] In some embodiments, an implantable electrode includes a
multi-layer graphene-fiber core, an insulative coating surrounding
the multi-layer graphene-fiber core, and a metal layer disposed
between the multi-layer graphene-fiber core and the insulative
coating. In some embodiments, the multi-layer graphene-fiber core
does not include a binder material. Optionally, the insulative
coating may be polymer-based coating such as Parylene-C or
silicone. In some embodiments, the insulative coating has a
thickness of about 2 .mu.m. In some embodiments the metal layer may
be adjacent to the multi-layer graphene-fiber core and the metal
layer covers completely or aa surface portion of the graphene-fiber
core with total or partial encapsulation of the multi-layer
graphene-fiber core. In some embodiments, the metal layer covers
about half of the surface of the multi-layer graphene-fiber core.
In some embodiments, the metal layer is adjacent the multi-layer
graphene-fiber core and the metal layer covers a surface portion of
the graphene-fiber core with complete encapsulation of the
multi-layer graphene-fiber core. In some embodiments, the metal
layer comprises at least one of platinum, iridium, iridium oxide,
platinum-iridium, and titanium nitride. In some embodiments, the
metal layer has thickness in the range between about 10 nm to about
500 nm. In some embodiments, the multi-layer graphene-fiber core
has a diameter in the range of between about 10 .mu.m to about 200
.mu.m.
[0012] In some embodiments, a method for making an implantable
electrode includes the steps of forming a multi-layered
graphene-fiber core by performing an in-situ reduction of fully
ordered graphene oxide sheets in a liquid crystalline, coating at
least a portion of the multi-layered graphene-fiber core with a
metal layer, and coating the multi-layered graphene-fiber core and
metal layer with an insulative coating. Forming a multi-layered
graphene-fiber core by performing an in-situ reduction may include
the step of wet-spinning liquid crystalline dispersions of graphene
oxide using a coagulation bath containing an acid. Optionally, the
acid includes hyporphosphorous acid. Optionally, the metal layer
includes at least one of platinum, iridium, iridium oxide,
platinum-iridium, and titanium nitride. Optionally, the metal layer
has thickness in the range between about 10 nm to about 500 nm.
Optionally the insulative coating includes Parylene-C.
[0013] In some embodiments, a method of recording and stimulating a
peripheral includes implanting an implantable electrode by engaging
the peripheral nerve, where the implantable electrode further
comprises a multi-layer graphene-fiber core, an insulative coating
surrounding the multi-layer graphene fiber core, and a metal layer
disposed between the multi-layer graphene-fiber core and the
insulative coating, and at least one of recording and stimulating
from the peripheral nerve. Optionally, engaging a peripheral nerve
may include implanting the implantable electrode inside the
peripheral nerve, sutured through the peripheral nerve, or over the
peripheral nerve. Optionally, the peripheral nerve may innervate
one or more organs including heart, lungs, stomach, liver,
pancreas, kidney and those in the pelvic and perineal areas, among
others. In some embodiments, a system may be used to record and/or
stimulate from autonomic or sematosensory ganglia, including, but
not limited to, the nodose, mesentheric and carotid. Additionally,
in some embodiments, systems and methods built in accordance with
the present disclosure may be used to record from and/or stimulate
neurovascular plexi, where nerve branches travel between arteries
and vein complexes, such as those in the spleenic nerve or the
renal nerve among others.
[0014] In some embodiments, a method of recording and stimulating a
peripheral nerve may include exposing and isolating a target nerve
from the surrounding tissue, engaging an implantable electrode to
the target nerve by at least one of passing the implantable
electrode about the exposed target nerve and forming a knot with
implantable electrode, and inserting the implantable electrode
through the epineurium of the exposed target nerve, wherein the
implantable electrode further comprises a multi-layer
graphene-fiber core, an insulative coating surrounding the
multi-layer graphene fiber core, and a metal layer disposed between
the multi-layer graphene-fiber core and the insulative coating; and
at least one of recording and stimulating from the peripheral
nerve. Optionally, engaging a peripheral nerve may include
implanting the implantable electrode inside the peripheral nerve,
sutured through the peripheral nerve, or over the peripheral nerve.
Optionally, the peripheral nerve may be peripheral to at least one
of the heart, lungs, stomach, liver, spleen, pancreas and pelvic
organs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0016] It is believed that the disclosure will be more fully
understood from the following description taken in conjunction with
the accompanying drawings. Some of the figures may have been
simplified by the omission of selected elements for the purpose of
more clearly showing other elements. Such omissions of elements in
some figures are not necessarily indicative of the presence or
absence of particular elements in any of the exemplary embodiments,
except as may be explicitly delineated in the corresponding written
description. None of the drawings are necessarily to scale.
[0017] FIG. 1A provides a schematic diagram for making and applying
a metalized graphene fiber in accordance with some embodiments of
the present disclosure.
[0018] FIG. 1B provides a flowchart for a process of making a
metalized graphene fiber in accordance with some embodiments of the
present disclosure.
[0019] FIG. 2 provides a scanning electrode characterization of a
metalized graphene fiber electrode built in accordance with some
embodiments of the present disclosure.
[0020] FIG. 3 provides a electrochemical characterization of a
metalized graphene fiber electrode built in accordance with some
embodiments of the present disclosure.
[0021] FIG. 4 provides a mechanical and accelerating aging
characterization of a metalized graphene fiber electrode built in
accordance with some embodiments of the present disclosure.
[0022] FIG. 5 provides neural activity recorded from the rat brain
by a metalized graphene fiber electrode built in accordance with
some embodiments of the present disclosure.
[0023] FIG. 6 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0024] FIG. 7 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0025] FIG. 8 provides a characterization of a metalized thickness
coating on the graphene fiber electrode built in accordance with
some embodiments of the present disclosure.
[0026] FIG. 9 provides a schematic diagram for making and applying
a metalized graphene fiber in accordance with some embodiments of
the present disclosure
[0027] FIG. 10 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0028] FIG. 11 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0029] FIG. 12 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0030] FIG. 13 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0031] FIG. 14 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0032] FIG. 15 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0033] FIG. 16 provides implantation characteristics for a
metalized graphene fiber electrode built in accordance with some
embodiments of the present disclosure.
[0034] FIG. 17 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0035] FIG. 18 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0036] FIG. 19 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0037] FIG. 20 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0038] FIG. 21 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0039] FIG. 22 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0040] FIG. 23 provides implantation characteristics for a
metalized graphene fiber electrode built in accordance with some
embodiments of the present disclosure.
[0041] FIG. 24 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0042] FIG. 25 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0043] FIG. 26 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0044] FIG. 27 provides implantation characteristics for a
metalized graphene fiber electrode built in accordance with some
embodiments of the present disclosure.
[0045] FIG. 28 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0046] FIG. 29 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0047] FIG. 30 provides neural activity recorded by a metalized
graphene fiber electrode built in accordance with some embodiments
of the present disclosure.
[0048] FIG. 31 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0049] FIG. 32 provides a characterization of a metalized graphene
fiber electrode built in accordance with some embodiments of the
present disclosure.
[0050] FIG. 33 provides implantation characteristics for a
metalized graphene fiber electrode built in accordance with some
embodiments of the present disclosure.
[0051] FIG. 34 provides implantation characteristics and neural
recordings for a metalized graphene fiber electrode built in
accordance with some embodiments of the present disclosure.
[0052] FIG. 35 provides implantation characteristics and neural
recordings for a metalized graphene fiber electrode built in
accordance with some embodiments of the present disclosure.
[0053] FIG. 36 provides implantation characteristics for a
metalized graphene fiber electrode built in accordance with some
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0054] The present disclosure relates to the making and
bioelectronics applications of metalized graphene fibers. In some
embodiments, the graphene fibers may be coated with platinum, and
used to record and stimulate from one or more tissues and organs.
In some embodiments, the fabrication of flexible and free-standing
graphene-fiber based microelectrode arrays with a thin metal (i.e.,
platinum) coating, as a charge collector, results in a structure
with low impedance, high surface area and excellent electrochemical
properties. In comparison with conventional graphene electrodes or
platinum (Pt) electrodes, the hybrid platinized graphene fibers
discussed herein may be robust and provide better performance. In
particular, embodiments of microelectrode arrays built in
accordance with the disclosure herein may include low impedance and
porous structure of graphene fiber with a thin platinum layer
thereupon. The graphene fiber may provide for an unrivalled charge
injection capacity and the ability to record and detect neuronal
activity, while the thin Pt layer transfers the collected electrons
along the microelectrode efficiently. Accordingly, the
microelectrodes may be capable of detecting neuronal activity with
a high signal to noise ratio.
[0055] A major drawback of conventional free-standing carbon
nanotubes and graphene microfibers lies in the high resistivity
compared with their metallic counterparts. When a microelectrode is
longer than a few millimeters, the resistivity increases
significantly, which poses a significant challenge to low noise
recording. By contrast, a system built in accordance with the
present disclosure may overcome this limitation by applying a thin
coating of metal (e.g., platinum in the range of 200 nm) as the
current collector on the wet-spun graphene microfibers. This
modification integrates the electrochemical characteristics of
graphene and electronic properties of the metal to the
microelectrodes, without limiting its mechanical flexibility and
high surface area. The low impedance and porous structure of
graphene fiber result in an unrivalled charge injection capacity
with the ability to record and detect neuronal activity, while the
thin metal layer transfers the recorded electrons along the
microelectrode efficiently.
[0056] FIG. 1A provides a schematic diagram of a process for
manufacturing a metalized graphene fiber microelectrode and
implanting the microelectrode in the brain. In particular, at 101,
liquid crystal graphene oxide (LCGO) process is used to generate
graphene oxide fibers 103 which are deposited within an acid bath
105. The bath may be rotated 109 and results in production of
graphene fibers (GF) 111. The GF may be cut into smaller pieces 113
and coated by a metal to form a metal-coated graphene fiber 115.
The metal-coated graphene fiber 117 may then be covered by an
insulating material. The insulating material may then be cut such
that one conducting surface and/or a sharp tip is exposed for
recording and/or stimulation. One or more insulated metal-coated
graphene fibers may be assembled 119 and implanted into a brain
121. A cross-sectional view 123 illustrates the movement of
electrons 125 through the metal layer of the insulated metal-coated
graphene fiber.
[0057] FIG. 1B provides a flowchart illustrating the method for
manufacturing a metalized graphene fiber microelectrode. In a first
step 1125, graphene fibers (GF) are fabricated using wet-spun
liquid crystal graphene oxide (LCGO) process. Description of the
process for fabricating GF using LCGO, and further Solid State
Exfoliation of Graphite is described in Esrafilzadeh, D., Jalili,
R., Stewart, E. M., Aboutalebi, S. H., Razal, J. M., Moulton, S. E.
& Wallace, G. G. (2016). High-performance multifunctional
graphene-PLGA fibers: toward biomimetic and conducting 3D
scaffolds. Advanced Functional Materials, 26 (18), 3105-3117, which
is hereby incorporated by reference in its entirety. In a second
step 1127, the fabricated GF are reduced in an acid bath. In a
third step 1129, a metallic layer is deposited over at least a
portion of the individual GF filaments. In a fourth step 1131, the
GF filaments (with the deposited metallic layer) is cut into
individual pieces and attached to conductive wires. In a fifth step
1133, the individual pieces are coated with an insulative material.
In a sixth step 1135, active sites of the microelectrode including
the GF filaments are exposed 1135.
[0058] In some embodiments, the GF fibers do not include a binder
material. In some embodiments, the GF core may have a diameter in
the range of between about 10 .mu.m to about 200 .mu.m. Embodiments
where the GF fiber does not include a binder may be manufactured at
less cost and provide better performance, as conventional binders
may be detrimental to the electronic and electrochemical properties
of the structure, as they aid the processing of mechanically
support the structure.
[0059] In some embodiments, the insulative coating may be a
polymer-based coating, such as Parylene-C. The insulative coating
may have a thickness of about 2 .mu.m.
[0060] In some embodiments, the metal layer may be sputtered onto
the surface of the graphene fiber core. In such an embodiment, the
metal layer may cover all or a portion of the graphene fiber core.
In some embodiments, the metal layer may cover half the surface
area of the graphene-fiber core. The metal layer may include one or
more of platinum, iridium, iridium oxide, platinum-iridium, and
titanium nitride. In some embodiments, the metal layer has a
thickness in the range between about 10 nm to about 500 nm. In some
embodiments, the metal layer may cover between about 50% to 75% of
the surface area of the graphene fiber core. The percentage of the
surface area covered by the metal layer may be adjusted for
manufacturing processes.
[0061] Further, as illustrated in FIG. 1B, the multi-layered
graphene fiber core may be formed by performing an in-situ
reduction of highly-ordered graphene oxide sheets in a liquid
crystalline. Optionally, this may include the step of wet-spinning
liquid crystalline dispersions of graphene oxide using a
coagulation bath containing an acid. In some embodiments, the acid
may be hypophosphorous acid and/or calcium chloride.
[0062] In some embodiments, graphene fibers may be generated by
producing single sheets of graphene oxide comprising 2 micrometers
having superior flexibility. A less conductive metal, such as
platinum, may then be used to metalize the graphene fibers.
However, the metal layer may be used to improve overall
conductivity by collecting the charges.
[0063] In some embodiments, the graphene fibers built in accordance
with the systems and methods described herein may form a multitude
of shapes, including but not limited to a mesh structure, an array,
thread, yarns, sharpened needle, and the like. Alternatively, the
graphene structures may be bioprinted into any suitable shape for
recording and/or stimulating.
[0064] Fabrication, characterization, and bioelectronic application
of metalized graphene fibers built in accordance with the
disclosure above, are provided in the examples below.
EXAMPLES
Example 1: High-Performance Graphene-Fiber-Based Neural Recording
Microelectrodes
[0065] The foregoing example demonstrates the fabrication,
characterization, and acute in-vivo performance of a flexible and
free-standing microelectrode made from graphene fibers coated with
Pt for neural stimulation and recording applications in accordance
with the disclosure above. Taking advantage of the unique
combination of high mechanical strength and high bending
flexibility of GO, robust, flexible fibers and highly conductive
electrodes were fabricated. The resulting graphene fiber-platinum
coated (GF-Pt) microelectrodes have superior electrochemical
properties and are characterized by remarkably lower impedance and
higher charge storage capacity. Voltage transient analysis
confirmed that these microelectrodes have high charge injection
capacity of over 10 mC/cm.sup.2. For in-vivo applications, a high
signal to noise ratio (SNR) of 7.10 dB for the microelectrode array
and 9.2 dB for a single microelectrode was achieved during neural
recording. Pt-coated graphene fibers seem to be an advantageous
material for developing the next generation neural stimulation and
recording microelectrodes with neural-scale size, low impedance,
high charge injection capacity, and high flexibility, thus
affording closed-loop, bi-directional implantable devices.
[0066] Electrode Fabrication
[0067] In accordance with the methods and techniques described
above, the high mechanical strength and super flexibility of
graphene oxide sheets allowed for the direct processing of
three-dimensional (3D) structures without the need of any binder to
aid the processing. To achieve self-assembled, multi-layer,
binder-free, aligned microfibers with reduced graphene sheets,
wet-spinning of liquid crystalline dispersions of graphene oxide
(LCGO) was conducted using a coagulation bath containing
hypophosphorous acid. This coagulation bath reduced the GO during
the spinning process without compromising the flexibility and
mechanical strength. Flexibility of a microfiber is an important
characteristic for fabricating implantable microelectrode, as it
minimizes foreign body reaction and maximizes greater proximal
neuron survival in comparison with traditional metal
electrodes.
[0068] More particularly, GFs were fabricated via a wet-spinning
process from home-made LCGO. The fabricated wet LCGO fibers were
reduced with hypophosphorous acid solution (50% in water,
Sigma-Aldrich) at 80.degree. C. for 24 h. The dried individual GF
filaments (40 p.m diameter) were deposited with a 200 nm Pt layer
by using a sputter coater to make GF-Pts. The prepared GF-Pts were
cut into 8-12 mm pieces and attached to silver wires using
conductive silver paint (SPI supplies, Z05002-AB). Then the GF-Pts
along with silver wires were coated with Parylene C using a
Parylene deposition system coater (Specialty Coating System, PDS
2010 Labcoater). The assembled GF-Pt-PCs were dipped into liquid
nitrogen for about 10 min and the active sites of a microelectrode
were exposed by cutting its tip with a sharp scissors. The Parlyene
C on the tail of the silver wire was removed before test to make it
conductive. Electrical conductivity of fibers was measured using a
home-made four-point probe conductivity set-up with 240 um probe
spacing using a galvanostat current source (Princeton Applied
Research 363) and a digital multimeter (Agilent 34401A).
As-prepared fibers and electrodes were directly examined by
scanning electron microscopy (JEOL JSM-7500FA) and video microscope
(Leica M2056A).
[0069] FIG. 2 illustrates the flexibility of these graphene
microfibers. As illustrated in Panel A of FIG. 2, the graphene
microfibers are flexible enough to tie an overhand knot 201. Panels
B and C of FIG. 2 illustrate scanning electron microscope (SEM)
imagery of graphene microfibers having a diameter of 20.+-.3 .mu.m
to 40.+-.5 .mu.m, respectively, by using 19-23 gauge nozzles,
respectively. Comparison between the cross-sections of these fibers
suggests that those with larger diameters tend to form more
irregular shapes with intersheet spaces after drying (as
illustrated by the void in a typical fiber of larger diameter
indicated by arrow in Panel B of FIG. 2). This may be indicative of
severe shrinkage during the drying process, which in turn, could
explain the higher conductivity of the 20.+-.3 .mu.m fibers
(205.+-.16 S/cm) compared with 52.+-.0.3 S/cm for the 40.+-.5
.mu.m.
[0070] Panel D of FIG. 2 illustrates an enlarged SEM cross-section
from Panel C of FIG. 2, and shows aligned and highly organized
characteristic features of graphene microfibers. Hundreds of
individual graphene sheets are collapsed together during the
coagulation bath creating a multi-layer core in the graphene fiber
assembly. Higher magnification SEM image of the cross-section of a
typical fiber presented in Panel D of FIG. 2 shows a particularly
aligned feature of the graphene sheet layers. Here, the in-situ
reduction of fully ordered multi-layered GO sheets in liquid
crystalline state inhibited the randomization of the morphology by
preventing the relaxation phase. In fact, the inherent LC order was
maintained allowing the highly organized assembly of GO
microfibers. Furthermore, the in-situ reduction constrained any
uncontrolled re-stacking of the sheets. Consequently, a fully
ordered and porous architecture was obtained. Such reduced graphene
fibers provided an extremely high surface area of up to .about.2210
m.sup.2 g.sup.1 that facilitated the accessibility of electrolyte
and ionic diffusion into the resultant electrode.
[0071] Panel E of FIG. 2 illustrates the electrical resistivity of
graphene microfibers as a function of platinum coating and length.
As illustrated, the resistance increases with fiber length.
Further, GF-Pt electrodes illustrate lower resistance than GF
electrodes. The electric resistance of these microfibers was
affected by their length, which increased from .about.2 to 20
k.OMEGA. as the length increased from .about.0.5 to 5 cm. To
minimize the effect of the fiber length on the resistivity and
facilitate the recording of fine nerve's signals, one side of the
microfibers was sputter coated with up to .about.200 nm thick layer
of Pt (GF-Pt). The Pt coating resulted in a significant increase in
the conductivity from 205.+-.16 S/cm to 460.+-.30.3 S/cm. Moreover,
as Pt acts as current collector, the increase in the resistivity
due to the length of microfibers became considerably less
detrimental. Minimization of the resistivity is particularly
desirable to achieve noise reduction, stability of recordings and
effective electrical stimulation.
[0072] Microelectrodes were fabricated by insulating each
individual platinized microfiber with an insulating polymer coating
of .about.2 .sub.1.tm (Parylene-C, GF-Pt-PC), before a sharp cut of
the tip in a liquid nitrogen bath; leaving only the tip exposed as
an electrochemically active site. Parylene-C was selected due to
its high dielectric property, biocompatibility, pin-hole free and
uniform coatings, and its common use for neural prostheses.
Microelectrodes made from bare graphene fiber (i.e., no Pt coating)
were fabricated for comparison. Moreover, while the polymer coating
process increased the robustness of the graphene microfibers, the
flexibility was also improved as demonstrated by tying an overhand
knot.
[0073] Panels F, G, and H of FIG. 2 show SEM images of a typical
microfiber after each coating step. In particular, Panel F is an
SEM image of the outer surface of a GF electrode. Panel G is an SEM
image of the outer surface of a GF electrode coated with Pt. Panel
H is an SEM image of the outer surface of a GF electrode coated
with Pt and insulated with Parlyene-C. Both Pt and Parylene-C
coatings formed thin layers around the microfibers, retaining the
porous structure and high surface area at the tip, as evidenced by
high-resolution SEM microscopy images (see Panels I, J, K, and L of
FIG. 2). The high surface area results in high recording
sensitivity, and a large charge injection capacity with low
impedance at 1 Hz to 10 kHz. In particular, Panels I and J
illustrate a cross-sectional SEM image of GF-Pt electrodes, and
Panels K and L illustrate SEM images of the tip of the final
microelectrode.
[0074] Electrochemical Characterization
[0075] During the stimulation and recording of bioelectric actions,
the electrode carries out the function of transduction from the
ionic currents in the electrolyte into an electric current in the
measurement system. High electrical impedance of the interface
between electrode and living tissue can negatively impact the
signal-to-noise ratio and increase signal distortion. This
particularly becomes very important for microelectrodes due to the
reduced dimensions. FIG. 3 illustrates the electrochemical
performance of the graphene microelectrodes as evaluated by
electrochemical impedance spectroscopy (EIS), cyclic voltammetry
(CV), and calculations of charge storage capacity and charge
injection limit.
[0076] Electrochemical impedance spectroscopy (EIS) and Cyclic
voltammetry (CV) were performed with a CHI 660E electrochemical
workstation (CH Instruments) in phosphate buffered saline (PBS, pH
7.4, Sigma-Aldrich) at room temperature. A three-electrode cell
system was employed with the test sample as working electrode, a
platinum sheet as counter electrode, and Ag|AgCl as reference
electrode. CVs were recorded between the voltages of -0.2 and 0.8 V
at scan rates of 10-50000 mV/s. Each sample was tested for 3-5
cycles, and the cathodic charge storage capacity was calculated
from the integration of current over time recorded in the last
cycle at scan rate of 100 mV/s. Sweeps from -1.6 to 1.6 V were
performed to determine the water window (e.g., threshold to
electrolysis) of GF-Pt-PC electrodes, and the water oxidation and
reduction potentials were determined when the sharp current peaks
were detected. EIS was performed between frequencies of 1-10.sup.4
Hz, and the specific impedance was calculated at 10.sup.3 Hz.
[0077] Panel A of FIG. 3 illustrates the modulus of impedence of
microelectrodes. An electrode made from Pt wire of similar diameter
with microfibers was also fabricated and tested as the control. EIS
analysis showed that the impedance of graphene microelectrodes was
.about.2 orders of magnitude lower than the Pt electrode in the
range of frequencies tested (1 Hz to 10 kHz, Panel A).
Particularly, the impedance at 1 kHz was over 50 times lower than
the Pt electrode (.about.50k.OMEGA. vs .about.300k.OMEGA.)). This
large reduction in the impedance of the graphene microelectrodes
was as a result of the increased available surface area of fully
ordered and separated graphene sheets. Furthermore, the impedance
of the Pt modified microelectrodes (at 1 kHz) was .about.5 and
.about.300 times lower than neat graphene and Pt microelectrodes,
respectively. Adding a thin layer of Pt on the graphene microfiber
(as current collector) resulted in a strong synergistic effect
leading to a robust and superior hybrid microelectrode with lower
impedance.
[0078] Panel B of FIG. 3 illustrates the phase angle of impedance
of microelectrodes. At an ideally polarisable electrode during the
stimulation, the charge passed would be completely attributed to
the capacitance rather than any Faradic reaction. The phase lag of
microelectrodes, as illustrated in Panel B of FIG. 3, indicates
that the electrochemical interaction at the exposed tip is
controlled by a capacitive charging-discharging process over the
double layer of the microelectrode tip (an adsorption controlled
process).
[0079] Panel C of FIG. 3 illustrates CVs of the microelectrodes at
10 mV/s in PBS solution. CV is a simple and fast technique for
measuring the capacitance and Faradaic components at an
electrode-solution interface. Panel C of FIG. 3 compares cyclic
voltammetry (CV) of different electrodes prepared in this example.
Although, both graphene-based microelectrodes showed
near-rectangular CV curves, the current of the Pt modified
microelectrode was significantly higher than other electrodes. This
improvement was due to integration of high conductivity of Pt
coating coupled with the high surface area of the GO electrode that
allows effective diffusion of electrolyte ions, followed by a
facile electron transfer via the Pt layer. Furthermore, the
cathodic charge storage capacity of the Pt modified GO
microelectrode, calculated from the CV, was 946.+-.140 mC/cm.sup.2,
a value of .about.3 orders of magnitudes higher than Pt electrode
and .about.2 times higher than the unmodified graphene
microfibers.
[0080] Panel D of FIG. 3 illustrates the water window of
microelectrodes, and Panel E of FIG. 3 illustrates the voltage
transient test of microelectodes. And Panel F of FIG. 3 illustrates
a comparison of the charge injection capacity, specific impedance,
and geometrical area of a microelectrode built in accordance with
the methods described herein in comparison with neural interface
electrodes reported in literature.
[0081] In particular, the voltage transient measurement was
performed on a two-electrodes set-up in PBS solution (pH 7.4,
Sigma-Aldrich) at room temperature. A symmetric charge-balanced,
cathodic first, biphasic current pulse with 100 .mu.s is width, 20
.mu.s is interphase open circuit potential and 2.78 ms short
circuit at 250 Hz was generated by a digital stimulator DS800 and
A365 Isolator units (World Precision Instruments). The voltage
waveform across the active microelectrode in response to the
applied current pulse was recorded with an e-corder system (eDAQ).
The maximum negative polarization potential (E.sub.mc) was
calculated by subtracting the initial access voltage (V.sub.a) from
the total voltage transient. The charge injection capacity was
determined when E.sub.mc reached the water reduction limit from the
following equation:
Q.sub.inj=I.sub.c.t.sub.c/GSA'
where Q.sub.inj is the charge injection limit capacity, I.sub.c is
the current pulse applied, t.sub.c is the pulse width, and GSA is
the geometric surface area.
[0082] Electrical stimulation initiates a functional response by
depolarizing the membranes of excitable cells, which is achieved by
the flow of ionic current between the electrodes. Voltage transient
measurements were made to determine the maximum positive and
negative polarization values across the electrode-electrolyte
interface, and estimate the maximum charge that can be injected in
a stimulation pulse without exceeding the water electrolysis limit.
The potential is swept over a wide window to obtain the voltage
range where the electrode, electrolyte and water are neither
oxidised nor reduced. To ensure the safe polarization of the
microelectrode during stimulation, a CV of the microelectrode was
recorded by sweeping the potential between the voltage limits of
-1.6 V to 1.6 V (vs. Ag/AgCl electrode). In biological systems,
this potential range is largely determined by the oxidation and
reduction of water (water window). The water window was limited by
the water oxidation and reduction voltages, indicated by a steep
increase in the current. In this example, the water window of GF
based microelectrodes was found between -1.0 V to 0.9 V (Panel D of
FIG. 3). The upper portion of
[0083] Panel E of FIG. 3 shows a typical input biphasic current
pulse (300 .mu.A and 20 .mu.s delay). The potential excursion
response (see lower portion of Panel E of FIG. 3) to the current
pulse shows an initial, rapid change in potential, known as the
access voltage (Va=-1.35 V), due to the ohmic resistance of the
electrolyte, followed by a slowly rising polarization voltage
(V.sub.p=-0.90 v), which is due to the charging of the
electrode/electrolyte interface. The Vp was calculated by
subtracting the Va from the maximum negative voltage in the
transient (Vt=-2.25 V).
[0084] The polarization voltage of phase one of the biphasic pulse
was used to determine the charge injection limit and obtained by
continuously increasing the current amplitude until the
polarization voltage reached 1.0 V. The charge injection capacity
was calculated at V.sub.p=0.90 V, before the water reduction
potential (Panel E of FIG. 3), to be 10.34.+-.1.5 mC/cm.sup.2 in
the GF-Pt electrode, a value .about.3 orders of magnitudes higher
than Pt and .about.2 times larger than the unmodified graphene
microfibers.
[0085] The charge injection capacity of the GF-Pt microelectrode
was significantly higher than all of the best reported electrode
materials; including but not limited to Pt, carbon nanotube fibers,
conducting polymer coatings, metal nitride and oxides, as presented
in Panel F of FIG. 3. The synergistic effect of ordered graphene
sheets with low electrical resistivity of Pt layer resulted in this
remarkable charge injection capacity along with significantly
enhanced electrochemical performance.
[0086] Durability Characterizations
[0087] FIG. 4 illustrates the durability of electrodes built in
accordance with the methods described herein. Over time,
chronically implanted electrodes are adversely affected by material
degradation, and delamination of the insulator coatings such as
Parylene, which contribute to device failure. The longevity of the
GF-Pt microelectrodes was tested using cyclic voltammetry in PBS
solution. Panel A of FIG. 4 shows a representative SEM image of a
microelectrode after 1000 electrochemical cycles at a scan rate of
50 mV/s. As illustrated, the electrode tip did not show any
noticeable graphene degradation or Parylene delamination. Parylene
coating often peels off from rigid underlying electrodes such as Pt
and silicon. However, here, the strong interfacial adhesion between
the Parylene and graphene microfibers, along with the flexibility
and softness of the underlying fiber, resulted in a remarkable
stability of the Parylene coating.
[0088] Panel B of FIG. 4 confirms that there was no noticeable
change in the electrochemical performance over the prolonged
stability test.
[0089] Furthermore, the stability of graphene microfibers and the
microelectrodes were evaluated against repeated bending and
prolonged soaking in PBS solution (as illustrated in Panels C, D,
E, and F of FIG. 4). In particular, Panel C of FIG. 4 demonstrates
that the graphene microfibers show outstanding stability over the
bending cycle test, as there was neither obvious difference in
conductance between straight and bended GF-Pt fiber electrodes
(105.2.+-.2.7 vs 104.4.+-.3.7 S/cm), nor after 200 times bending
(105.2.+-.2.7 vs 102.7.+-.2.5 S/cm). Further, Panel D of FIG. 4
illustrates that even after soaking in PBS for 2 weeks, only
.about.8% conductivity loss was observed. The microelectrodes also
could maintain 77.6% and 52.2% charge storage capacity after very
tough durability and fatigue tests involving consecutive 200 times
360.degree. folding (Panel E of FIGS. 4) and 2 weeks soaking in PBS
(Panel F of FIG. 4), respectively.
[0090] The electrochemical performance of neural interfacing
electrodes of Example 1, which include a microelectrode built in
accordance with embodiments of the present disclosure, may be
summarized as follows:
TABLE-US-00001 Charge Charge Geometrical Impedance Specific storage
injection surface area (k.OMEGA. at impedance capacity capacity
Material (.mu.m.sup.2) 1 kHz) (M.OMEGA. .mu.m.sup.2) (mC/cm.sup.2)
(mC/cm.sup.2) Graphene 169 .+-. 25 50 .+-. 7.5 19.5 .+-. 2.9 798
.+-. 110 8.7 .+-. 1.3 fiber (GF) Pt coated 10 .+-. 1.3 11 .+-. 1.5
946 .+-. 140 10.5 .+-. 1.5 fiber (GF-Pt)
[0091] Surgical (In-Vivo) Implantation and Neural Activity
Recording
[0092] In connection with Example 1, electrodes built in accordance
with the present disclosure were surgically implanted into
rats.
[0093] All procedures were performed in accordance to an animal use
protocol 15-19 approved by the Institutional Animal Care and Use
Committee at the University of Texas at Dallas on the 6, of Jan.,
2017. A Long-Evans rat was selected for this study, and the target
was within the motor cortex in the region associated with the
control of the left forepaw. The animal was anesthetized using 2%
isoflurane mixed in oxygen, which was followed by intraperitoneal
administration of a cohort consisting of ketamine (65 mg/kg),
xylazine (13.33 mg/kg), and acepromazine (1.5 mg/kg). The animal
was mounted into a Kopf Model 900 small animal stereotaxic
instrument (David Kopf Instruments, CA, United States).
Dexamethasone (2 mg/kg) was administered subcutaneously over the
shoulders to reduce the inflammatory response and was followed by
the subcutaneous administration of 0.5% lidocaine (0.16 cc)
directly under the scalp incision site. After exposing the skull, a
2.0 mm by 2.0 mm craniotomy was created with a center at our
initial coordinates of implantation of 2.5 mm rostral and 2.5 mm
lateral from bregma. The dura in the area was reflected using a
dura pick followed by micro scissors to expose the surface of the
cortex. The entire area was kept under liquid with frequent
application of 7.4 pH sterile physiological phosphate buffered
solution.
[0094] Five implants were selected for this proof-of-concept study.
The first implant consisted of a bundle of four, 40 .mu.m diameter
microelectrodes composed of graphitic fibers coated with a thin
layer of platinum and encapsulated with Parylene-C insulation
(GF-Pt-PC). The second microelectrode consisted of a single, 40
.mu.m diameter graphitic fiber conductor encapsulated with
Parylene-C insulator (GF-PC). The third microelectrode was a
single, 40 .mu.m diameter GF-Pt-PC microelectrode. The final two
microelectrodes consisted one GF-PC and one GF-Pt-PC with 20 .mu.m
diameters.
[0095] The bundle of four microelectrodes was loaded into a Model
2650 hydraulic micropositioner (David Kopf Instruments, CA, United
States) into the microelectrode holder. The tips of the microfiber
wire bundle were lowered until they came into contact with the
cortical surface at the implantation coordinates, the distance
counter on the micropositioner was reset and the device was lowered
into the motor cortex at a speed of 1000 .mu.m/s. If buckling of
the wire began, the implantation was immediately stopped and the
speed was reduced to 100 .mu.m/s. A sterile stainless steel
hypodermic needle was inserted into the rat tail to serve as the
counter electrode. The optimal implantation depth was 1500
.mu.m.
[0096] Each acute recording was performed for at least 10 minutes
using an OmniPlex D Neural Data Acquisition System (Plexon Inc.,
TX, United States). If no single neural units were acquired, we
increased the depth of implantation by 200 .mu.m and performed
another recording. We continued to increase the depth of
implantation until a successful recording with single units was
acquired, or the wire implant reached a maximum depth of 2000
.mu.m. After the recording, the microfiber wire/bundle was
explanted completely from the brain, the micropositioner was
disinfected with isopropanol, and another wire was loaded in the
micromanipulator. Each additional microfiber microelectrode was
implanted at separate locations, with the second implant position
located 200 .mu.m rostral from the initial implant location. The
third microelectrode was implanted 200 .mu.m lateral from the
second location, with the next at 200 .mu.m caudal from the third
location, and the last 100 .mu.m from the third. Identical
recording procedures were followed for all subsequent
microelectrodes. After the investigation, the rat was euthanized
using an overdose of 5% isoflurane vapor which was applied until
breathing cessation occurred.
[0097] The wideband recordings obtained from OmniPlex D were
further processed using Plexon's Offline Sorter software. The
wideband signals were filtered using a 4.sup.th order Butterworth
filter with a cutoff located at 550 Hz and common-mode referencing
was used to eliminate noise. The threshold to select single units
was set to 36 from peak height with the waveform duration of 1500
.mu.s. Waveforms sorted from the threshold crossing were further
evaluated using the software's built-in Valley-Seeking algorithm.
The noise envelope was obtained setting the threshold to
.+-.3.sigma. of the original signal and removing the waveform
segments 250 ms before and 750 ms after the threshold crossing. The
average amplitude of the single unit waveforms was determined by
the largest negative deflection from zero crossing. The
reported
SNR = 10 .times. log 1 .times. 0 ( A s .times. i .times. g .times.
n .times. a .times. l A n .times. o .times. i .times. s .times. e )
2 . ##EQU00001##
[0098] signal-to-noise (SNR) ratio was calculated in decibels using
the following formula.
[0099] To demonstrate proof-of-concept neural recordings in-vivo,
first a single microelectrode was implanted in the cerebral cortex
of adult rats. Cellular-scale microelectrodes (20 .mu.m to 40
.mu.m) containing fully ordered graphene sheets, provided us with a
sufficient mechanical robustness and sharpness to be inserted and
precisely positioned to record neural signals for a total of ten
minutes. Panel A of FIG. 5 shows an image of the implanted
microelectrode. Additionally, the in-vivo test used an array of
four tip-exposed microelectrodes, aligned and glued together at
approximately 1 mm between the wire tips (as illustrated in Panel B
of FIG. 5). Before the in-vivo tests, CV of each individual
microelectrode was recorded (as illustrated in Panel C of FIG. 5)
to confirm a suitable electrochemical performance. While inserting
the bundled microelectrodes, only 3 of the 4 single microelectrodes
penetrated into the motor cortex. The fourth microelectrode buckled
and subsequently did not enter the brain, so it was eliminated from
the recording. Of the three penetrating microelectrodes, two showed
single unit activity at a bundle depth of 1500 .mu.m measured from
the surface of the cortex. Panel D of FIG. 5 shows 10 seconds of
550 Hx high-pass filtered electrical signals obtained from two of
the GF-Pt-PC bundled microelectrodes inserted 1.5 mm into the motor
cortex of a Long Evans rat at the location of 2.5 mm rostral and
2.5 mm lateral from bregma. Panel E of FIG. 5 shows 1543 single
unit signals obtained over 10 minutes of recording time from one of
the GF-Pt-PC implanted microelectrodes. The dark line in the center
of the waveforms represents the average single unit signal which
has an amplitude of -70.2 .mu.V, and a peak to peak value of 130.5
.mu.V. The units of the second active electrode (not shown), have a
similar shape with a slightly lower mean amplitude of -54.3 .mu.V
with a peak to peak value of 89.7 .mu.V. The SNR for the two
microelectrodes are 7.10 dB and 4.43 dB.
[0100] As illustrated in FIG. 6, an additional, single GF-Pt
microelectrode was implanted to a depth of 1500 .mu.m from the
cortical surface, and compared with a GF-only microelectrode
implanted to a depth of 2000 .mu.m. Signals obtained from the
single microelectrodes produced single unit waveforms which were
similar in both shape and duration as compared to the bundled
microelectrodes shown in FIG. 5. The GF-Pt microelectrode displayed
two single units of -75.2 .mu.V and -69.3 .mu.V amplitudes,
peak-to-peak voltages of 183.4 .mu.V and 123.6 .mu.V, and
signal-to-noise ratio (SNR) of 9.2 dB and 8.4 dB respectively. All
of our GF-Pt microelectrode signals have demonstrated recording
signals which are larger than previously reported. On the other
hand, the GF-only microelectrode showed a weaker performance.
Although it possessed a signal amplitude of -93.9 .mu.V and a
peak-to-peak voltage of 146.4 .mu.V, the noise was considerably
larger which lead to a reduced SNR of 3.0 dB.
[0101] Accordingly, the robust, flexible and free-standing
graphene-fiber based microelectrode arrays with an extremely thin
platinum coating demonstrate high performance neural recording
microelectrode with low impedance, high surface area and a high
charge injection capacity. In-vivo studies show that
microelectrodes implanted in the rat cerebral cortex can detect
neuronal activity with remarkably high signal-to-noise ratio
(SNR).
[0102] Carbon nanotubes and graphene have been successfully
demonstrated as an alternative platform to other conductive
materials used as neural implant devices, such as platinum,
iridium, titanium nitride, and iridium oxide, for effectively
capturing neural signals. The example experiments have demonstrated
the ability of the platinum modified graphene microfibers for
single unit recording capability with high signal-to-noise ratio.
Additionally, the recorded units captured by these electrodes were
not dissimilar to those reported with other small microelectrode
platforms.
[0103] FIG. 7 provides SEM imagery of cross-sections of various
fibers and illustrates that fibers with larger diameters tend to
form larger voids during the trying, due to a larger shrinkage than
the smaller fibers.
[0104] FIG. 8 provides a bar chart illustrating the conductivity of
thin graphene fiber with different Pt coating thicknesses.
[0105] FIG. 9 illustrates a process for fabricating microelectrodes
with Pt coating (GF-Pt-PC) and without Pt coating (GF-PC). As
illustrated in FIG. 9, optionally, a graphene fiber (GF) 901 may be
coated with platinum thus forming a microelectrode with Pt Coating
(GF-Pt) 909. The GF or GF-Pt may be attached to a silver wire as
illustrated at steps 903 and 911, respectively. Additionally,
Parylene coating may be applied at steps 905, and 913 respectively.
Further, as illustrated at steps 907, and 915, the tips of each
microelectrode are exposed and the Parylene C on the silver wire
tails are removed for connection.
[0106] FIG. 10 provides optical microscope images of GF-Pt. As
illustrated GF-Pt is very flexible and can be easily knotted 1001
and twined 1003.
[0107] FIG. 11 provides additional electrochemical characterization
of an electrode built in accordance with the disclosure herein. In
particular, Panel A of FIG. 11 provides CV measurement of GF-Pt-PC
to determine the dynamic behavior over the double layer of
graphene. Additionally, Panel B of FIG. 11, illustrates that the
peak current is linearly dependent on scan rate at low scan rate
with linear regression equation as
y=3.2659*10-8+3.0127.times.(R2=0.980), suggesting a surface
adsorption-controlled process of GF-Pt-PC. Further, Panel C of FIG.
11 illustrates that the peak current is linearly dependent on
square root of scan rate at high scan rate with linear regression
equation as y=-1.6698*10-8+5.4659.times.(R2=0.999), suggesting a
diffusion-controlled process.
[0108] FIG. 12 provides a snapshot of the recording process when a
single unit was implanted in the cerebral cortex of adult rats. As
illustrated, a user may use a graphical user interface 1201 to
select recordings from a particular electrode 1203. Further, the
graphical user interface 1201 may allow a user to view a waveform
1205, clusters of waveform data 1207, electrode channel information
1209, a timeline 1211, and the waveform 1213.
[0109] FIG. 13 illustrates in-vivo Cortical Neural Recording using
four array electrodes. As illustrated, electrodes may be inserted
into layers 3-6 of the brain. Four waveforms, one for each
electrode, may be recorded 1303, 1305, 1307, and 1309. A composite
waveform 1301 may be determined.
[0110] FIG. 14 illustrates a recording of endogenous activity from
the splenic nerve evoked by the administration of nitroprusside
(NPS), a molecule that reduces blood pressure. As illustrated, the
graphene fiber electrode, made in accordance with the disclosure
described herein, is able to record spontaneous neural activity
from one of the terminal branches of the spleenic nerve. As
illustrated in the panel 1401, the test involves the recording of
baseline activity for 2 min. After that an intravenous injection of
nitroprusside (NPS) a vasodilator drug that reduces the blood
pressure is administered (green arrow shows the time of injection).
Approximately 1 min after the injection, a high amplitude neural
activity is recorded from the graphene electrode (white vertical
traces). Off-line analysis shows two specific waveforms in that
evoked activity. One waveform is illustrated at 1403 that appeared
367 times after the NPS, with high incidence prior to 1000 seconds
and relatively low frequencies, and the other waveform illustrated
in 1409 observed 52 times that appeared at lower frequencies. Also
illustrated is the power spectrum signal 14-7 and 1413, and
frequency 1405 and 1411, respectively. FIG. 14 demonstrates the
ability to record physiological relevant neural signals in the
spleen using the graphene fiber electrode wrapped around this small
(60-80 micrometer) size nerve.
[0111] FIG. 15 illustrates the recording of nerve activity, evoked
with a hook electrode at increasing voltage, using the graphene
fiber electrode. In particular the recording is of compound action
potentials from the spleenic nerve evoked by electrical stimulation
at increasing voltages (1.2, 1.4, 1.6, 1.8 and 2 V) 1501 applied to
the vagus nerve using a commercial hook electrode (arrows). Two
distinct waveforms were identified in the splenic nerve using the
graphene fiber electrodes, one shown in the top panel 1505 and the
other in the bottom panel 1507; that appeared at increasing numbers
in response to the higher voltage stimulations 1503. This data
confirms the ability of the graphene fiber electrodes built in
accordance with the present disclosure to record neural signals in
small nerves.
[0112] FIG. 16 illustrates engagement of a graphene-Pt electrode to
a small terminal branch of the spleenic nerve by tying over the
Graphene-Pt fiber electrode to splenic plexi to record or stimulate
nerve activity. 1601 is a photograph of a rat spleen slightly
lifted 1605 to visualize the small terminal branches (insert 1603).
A higher magnification of the branch is shown in the right 1603,
where a blood vessel is seen with some fat cells at the bottom. It
is known that a mesh (i.e., plexi) of nerves wrap the blood vessel
and brings neural control to the spleen. The photograph in FIG. 16
also shows a graphene fiber electrode 1607 (made in accordance with
the present disclsoure described herein) that is wrapped around the
blood vessel/plexi to record neural activity.
[0113] FIG. 17 illustrates different waveforms that represent
various types of neural activity recorded from the terminal splenic
plexi using a Graphene-Pt electrode per the present disclosure.
Nine different waveforms recorded with the graphene fiber electrode
are illustrated.
[0114] FIG. 18 illustrates the electrical stimulation capabilities
for graphene fiber electrodes as made per the description herein.
Two graphene fiber electrodes were inserted into the sciatic nerve
in the rat, one serve as cathode and the other as anode. A train of
electrical pulses were applied through the graphene fiber
electrodes and the evoked activity recorded from a more proximal
segment using a hook electrode. The figure shows that with
increased electrical pulses 1801 (yellow arrows) we were able to
recruit three different types of neural signals, each from
different neuronal populations, shown in 1803, 1805, corresponding
to three different waveforms 1807. This data confirms that the
graphene fiber electrodes of the present disclosure are able to
evoke specific neural activity through electrical stimulation.
Example 2
[0115] Electrode Fabrication
[0116] In accordance with the techniques described herein graphene
fiber electrodes with a 20 micrometer diameter, graphene fiber
electrodes coated with platinum with a 20 micrometer diameter,
graphene fiber electrodes with a 40 micrometer diameter, and
graphene fiber electrodes coated with platinum and having a 40
micrometer diameter were fabricated.
[0117] FIG. 19 illustrates the resistance for the four types of
graphene fiber electrodes at various fiber lengths. As illustrated
the resistivity increases with increased fiber length.
[0118] Electrochemical Characterization
[0119] FIG. 20 provides electrochemical characterization of various
microelectrodes made from Pt, graphene microfibers, and Pt coated
graphene microfibers (D=20 and 40 .mu.m). Panel A of FIG. 20
provides modulus impedance of microelectrodes. Panel B of FIG. 20
provides phase angle of impedance of microelectrodes. Panel C of
FIG. 20 provides CVs of the microelectrodes at 10 mV s.sup.-1 in
PBS solution. Panel D of FIG. 20 provides water window of the
microelectrodes. Panel E of FIG. 20 provides voltage transient test
of microelectrodes. Panel F of FIG. 20 provides a comparison of the
charge injection capacity, specific impedance at 1 kHz, and
geometrical area of the modified microelectrodes with conventional
neural interfacing electrodes.
[0120] Electrochemical characterizations were performed in
accordance with the techniques discussed above in relation to
Example 1.
[0121] Durability Characterization
[0122] FIG. 21 illustrates the electrochemical durability
characterization of the modified microelectrodes (GF-Pt-PC-40). In
particular, Panels A and B of FIG. 21 illustrate cross-section SEM
images of a typical modified microelectrode before (Panel A) and
after (Panel B) 1000 CV cycles at scan rate of 50 mV s.sup.1,
showing high stability of the microelectrodes. Panel C of FIG. 21
shows prolonged CV of the modified microelectrodes, 1000 cycles at
scan rate of 50 mV s.sup.1. Panel D of FIG. 21 shows prolonged
pulse stability of the modified microelectrodes. Panel E of FIG. 21
shows electrical conductivity of the modified graphene microfibers
after successive bending cycles, 0 refers to the straight fiber,
while 1 refers to the fiber that was 360.degree. bent. Panel F of
FIG. 21 shows electrical conductivity of the modified graphene
microfibers after prolonged PBS soaking. Panels G and H of FIG. 21
show the CV of the modified microelectrodes after successive
bending and prolonged PBS soaking, respectively. Number of repeats
is four independent tests.
[0123] Durability characterizations were performed in accordance
with the techniques discussed above in relation to Example 1.
Example 3: Single Unit Recordings of Central and Peripheral Nervous
System Neurons Using Graphene Electrodes
[0124] Interfacing the nervous system to decode functional activity
or to electrically stimulate to modulate this function, has a
number of scientific and medical applications. Materials used in
the design of neural interfaces are desired to have low impedance
with high signal-to-noise ratio (SNR) to allow for sensitive
recording of single unit activity, and high charge storage capacity
(CSC) for effectively and safe neural stimulation. Microelectrodes
are commonly fabricated in silicon with platinum (Pt), Pt/Iridium
and Iridium oxide electrodes. However, the micromotion of the
silicone shafts implanted into the soft nervous tissue exacerbates
the foreign body response and contributes to the eventual failure
of these devices. The alternative use of carbon nanotube coated
microelectrodes has been promising due to their biocompatibility
and high CSC (.about.372 mC/cm.sup.2) and low impedance (.about.20
M.OMEGA.), however the stiffness of the metal shafts and
delamination of the carbon nanotube coating limits the chronic use
of these electrodes. The production of graphene fibers from liquid
crystalline dispersions of graphene oxide (LCGO) demonstrated
excellent electrochemical and mechanical characteristics.
Electrodes built in accordance with the present disclosure are used
to record brain and peripheral nerve activity. Single fibers and
multi-electrode arrays were implanted in the motor cortex and
sciatic nerve of adult rats (n=5). The electrodes effectively
recorded single neuronal units, with excellent SNR. Together, the
data supports the use of graphene fibers as intraneural electrodes
for the neural interfacing of brain and peripheral nerve
activity.
[0125] Electrode Fabrication
[0126] FIG. 22 illustrates graphene electrodes built in accordance
with the present disclosure. Panels A and B illustrate 20-40
micrometer graphene fibers obtained by the extrusion of LCGO in an
acidic coagulation bath, which were subsequently coated with
Parylene C. Panels C and D illustrate scanning electron microscopy
images of the graphene fibers.
[0127] Surgical (In-Vivo) Implantation and Neural Activity
Recording
[0128] As illustrated in FIG. 23, graphene electrodes were
implanted into the motor cortex or sciatic nerve of adult female
rats 2300. In particular, metalized graphene electrode multi-array
2303 was implanted in the motor cortex 2301. Additionally, a single
metalized graphene electrode 2307 was implanted in the sciatic
nerve 2309. Signals from the graphene electrodes were transmitted
to a recording system 2305.
[0129] As illustrated in FIG. 24, single unit recordings 2400 were
recorded from the motor cortex. Multi-electrodes were implanted in
different depths of the motor cortex and as such single unit
recordings were obtained from different cortical layers.
[0130] As illustrated in FIG. 25, recordings from the motor cortex
and sciatic nerve were plotted using a raster plot 2501, 2503 and
illustrated the activity of three independent axons (as shown in
the PCA plot of Panel B of FIG. 25). Further, the inter spike
interval 2507 was plotted.
[0131] FIGS. 22-25 illustrate that graphene micro-electrodes may be
used as high performance interfaces for central and peripheral
nervous system. Further, the application of a metallic coating on
the graphene fibers conveys excellent electrochemical
characteristics to the material. Additionally, the design of multi
electrode arrays of graphene fibers represents an alternative for
recording multiple single neuronal units a high sensitive
performance.
Example 4: Intra and Extraneural Activity in the Vagus Nerve
Recorded by Platinized Graphene Fiber Electrodes
[0132] Interfacing the vagus nerve (VN) allows researchers to
decode and modulate its activity. FDA approved clinical therapies
based on VN stimulation include drug resistant epilepsy and
depression, and the vagus nerve is currently being investigated for
morbid obesity, tinnitus and stroke. The VN has a heterogeneous
anatomical composition (.about.80% afferents and .about.20%
efferent fibers) resulting in complex functional electrophysiology
that responds in a unique way to different physiological stimulus.
Conventional electrodes to interface the VN are fabricated with
platinum or platinum iridium and have limited sensitivity and low
charge injection capacity (Qinj, .about.0.05-0.26 mC/cm2), whereas
intraneural electrodes fabricated with carbon nanotubes have shown
promise (CSC .about.372 mC/cm2, 12.5 k.OMEGA.).
[0133] In Example 4, high performance platinized graphene fibers
obtained from liquid crystalline dispersions of graphene oxide,
with excellent electrochemical characteristics (CSC and Qinj
.about.947 and .about.46 mC/cm2 respectively) are implanted in the
VN and in order to use them to record evoked electrophysiological
activity in both, extraneural and intraneural configurations
during: i) systemic reduction in Oxygen tension, ii) decreased mean
arterial pressure induced by intravenous nitroprusside treatment,
and iii) evoked activity in response to proximal VN stimulation
using a platinum hook electrode. Specific activity waveforms and
activity patterns were correlated to the treatments over baseline
conditions with high signal to noise ratios (SNR .about.4.3). The
data supports the use of platinized graphene fibers as extraneural
and intraneural electrodes for interfacing the VN.
[0134] Electrode Fabrication
[0135] Panel A of FIG. 26 illustrates the electrode fabrication
steps. In particular, using LCGO 2601 followed by an extrusion in a
coagulation bath 2603, graphene fibers 2605 are developed, cut
2607, coated with metal (i.e., platinum) 2609, coated with an
insulating material (i.e., Parylene-C) to form a GF-Pt
microelectrode 2611. A SEM image of the microelectrode is provided
2613.
[0136] Electrochemical Characterization
[0137] Panels B, C, and D of FIG. 26 illustrate the impedance
spectroscopy 2615, phase angle 2617 and cyclic voltammetry of
graphene fibers coated with PC (GF-Pt-PC) at 20 and 40 .mu.m OD,
compared to Pt-PC wires 2619.
[0138] Surgical (In-Vivo) Implantation and Neural Activity
Recording
[0139] FIG. 27 illustrates a surgical implantation of electrodes
built in accordance with embodiments of the present disclosure. In
particular, as illustrated, electrodes are implanted into an adult
female rat 2701. The graphene electrodes were either implanted
extraneurally 2703 (see panel B of FIG. 27) or intraneurally 2705
(see panel C in FIG. 27) in the cervical vagus nerve (VN) 2709. The
rat 2701 was oxygenated during the surgery and
neurostimulation/neurorecording procedure. Three techniques were
used to evoke neural activity: vagus nerve stimulation (VNS),
application of nitroprusside, and oxygen reduction. Electrical
activity from the vagus nerve 2709 was recorded and provided to
researchers 2711. Nitroprusside was administered 2713 via the
femoral vein of the rat 2701. Oxygenation measurements and/or blood
pressure measurements were recorded 2715 at the femoral artery.
[0140] FIG. 28 provides a summary of the results of the in vivo
testing setup described in FIG. 27 and more particularly, vagus
nerve activity evoked by hypotension due to systemic nitroprusside.
In particular, panel A illustrates baseline blood pressure
measurements from the femoral artery and recordings of neural
activity from graphene electrodes implanted in the vagus nerve.
Panel B of FIG. 28 illustrates blood pressure measurements and
recordings of neural activity from graphene electrodes implanted in
the vagus nerve as evoked by induced hypotension. Panel C
illustrates the neural activity response to administration of
nitroprusside and lidocaine in a raster plot. As illustrated in
Panel D, two separate wave forms were identified.
[0141] FIG. 29 illustrates evoked activity by electrical
stimulation. As shown in the top plots of FIG. 29, the frequency
and amplitude of compound action potentials increased as a function
of intensity. As illustrated in the bottom panel, one wave form and
its corresponding raster plot was identified.
[0142] FIG. 30 illustrates neural activity detected by intraneural
graphene fibers implanted in the cervical VN in accordance with the
disclosure herein. Oxygen restriction increased the amplitude of
neural electrical activity. A corresponding increase in frequency
was noted in the raster plot of the selected wave form (bottom
right panel of FIG. 30), which is represented in the rate histogram
(top right panel of FIG. 30). The bottom trace provides a schematic
indication time of Oxygen reduction from 2 to 0 L/min.
[0143] Example 4 as illustrated by FIGS. 26-30, demonstrates that
platinized graphene fiber electrodes may be used as a high
performance neural interface, to record neuronal activity in the
cervical VN, both extra- or intraneurally. The electrochemical
properties of these electrodes (low resistance and high
conductivity) allowed to effectively identify single and compound
nerve units with a SNR .about.4.3. The effective detection of
electrical activity evoked by electrical stimulation, decrease in
blood pressure and during oxygen reduction support the use of these
electrodes as autonomic neural interfaces to decode nerve
electrical activity pertinent to bioelectronic medicine.
Example 5: Methods and Bioelectronic Applications of Platinized
Graphene Fibers to Peripheral Nerves
[0144] Electrode Fabrication
[0145] As illustrated in Panel A of FIG. 31, graphene fiber
microelectrodes coated with a .about.200 nm layer Pt and insulated
with 2 .mu.m layer of Parylene-C (GF-Pt-PC) were fabricated in
accordance with the system and methods described herein. The
graphene fiber microelectrodes were connected to a silver wire as
illustrated in Panel B of FIG. 31 and Panel C of FIG. 31. SEM
imagery of the graphene fiber microelectrodes is presented in
Panels D and E of FIG. 31, illustrating greater flexibility than
conventional microelectrodes. Electrodes built in accordance with
the present disclosure can be used as an array of different fibers,
as a yarn, or strand multi-electrode arrays.
[0146] Electrochemical Characterization
[0147] As illustrated in FIG. 32, coating the graphene microfibers
with a thin layer of Pt resulted in a strong synergistic effect
leading to a robust and superior hybrid microelectrode with
.about.1 and .about.3 orders of magnitude lower impedance than the
original GF microfiber and Pt microelectrodes, respectively. The Pt
coating increases significantly the conductivity to from 200 to 460
S/cm of a 40 .mu.m GF fiber. Moreover, the cathodic charge storage
capacity of the microelectrode, calculated from the CV, was 946
mC/cm.sup.2, a value .about.3 orders of magnitudes higher than Pt
electrode and .about.2 times higher than the original GF
microfibers.
[0148] Surgical (In-Vivo) Implantation and Neural Activity
Recording
[0149] Conventional peripheral nerve interfaces (PNIs) may be
categorized based on their fabrication, sensitivity and
invasiveness. Cuff electrodes are PNIs implanted circumferentially
on the peripheral nerves, and made of flexible materials with
helical, spiral, split-cylinder or folding designs to conform to
their cylindrical shape, and metals contacts such as gold, platinum
or platinum/iridium. Traditional cuff electrodes fabricated in
silicone are commonly used due to their softness (i.e., Young's
modulus in MPa range) and chronic stability, although their
fabrication is mostly limited to molding and lamination techniques.
Unfortunately, these conventional cuff devices have relative thick
walls (e.g., 280-600 .mu.m) needed to generate sufficient bending
forces to keep them closed, which causes a significant foreign body
response and epineurial fibrosis, negatively affecting the
sensitivity of the interface. In addition, new clinical
applications for the regulation of organ physiology involved in
cardiac, respiratory, digestive and urinary conditions, focus on
neuromodulation of autonomic peripheral nerves that are smaller and
composed of fewer axons (i.e., approximately 600 axons averaging
2.5 .mu.m in the 60-80 .mu.m rat carotid sinus nerve). The nerve
targets in these conditions also have a thinner epineurium, are
formed mostly of unmyelinated axons and thus, likely more
susceptible of damage by neurointerface devices. The small nerve
size of these targets, their fragile nature, and restricted areas
for implantation, are driving the development of new implantable
electrodes that are small, flexible and with sufficient charge
injection capacity for efficient and safe nerve stimulation.
[0150] As illustrated in Panel A of FIG. 33, the disclosed GP-Pt
fibers can be used as "cuffless" PNIs since they can be simply tied
around 3301 the nerve 3305 and serve as a monopolar or multipolar
electrodes for both recording and stimulation of nerves of any
size, since the fiber can be used use to tie a knot and thus closes
completely. This allows it to be placed in tightly over any nerve,
nerve fascicle or nerve plexi and neuro-vascular plexi. The
sensitivity of the electrodes is such that allows it to wrap it
around small nerves sense their activity.
[0151] Alternatively, as illustrated in Panel B of FIG. 33, if the
tips are sharpened, they can be used individually or as an array
3303, to record or stimulate intravascularly. When used as cuffless
electrodes the segment around the nerve is deinsulated before
placing it around the nerve.
[0152] FIG. 34 illustrates the placement of a unipolar electrode
3401 around the vagus nerve 3403 and shows the sensitive recording
of increase nerve activity evoked by mild hypoxia at 560uV peak to
peak (Panel B of FIG. 34), that is 9-18 fold increased sensitivity
compared to that reported with carbon nanotube fibers in the same
nerve.
[0153] In other configurations the Pt-Gph fiber may be attached to
a disposable needle for suture, and use to join tissue portions in
patients. Sutures are traditionally made of silk or synthetic
materials, and are not conductive.
[0154] As illustrated in FIG. 35, in a separate configuration the
GF-Pt fibers can be used as cortical electrodes for recording or
stimulation of brain or spinal cord tissue. The GP-Pt fibers can be
inserted into the tissue or, in the case of the spinal cord, be
tied around the dorsal or ventral roots for sensory and motor
interfacing. Stimulation of the dorsal roots can be used to control
pain. Panel A illustrated a photograph of an electrode inserted
into the rat cerebral cortex. Panel B of FIG. 35 illustrates a
single unit recording from a cortical neuron recorded by the GF-Pt
electrode.
[0155] As illustrated in FIG. 36, the GF-Pt fibers can be use also
to record and stimulate other tissue including skeletal muscle,
either epi or intramuscular. Panel A of FIG. 36 illustrates the use
of a needle 3601 where the nylon suture 3603 is tied to the GF-Pt.
Panel B of FIG. 36 illustrates an embodiment where the GP-Pt fiber
is driven into the muscle 3605.
[0156] The metalized graphene fibers described herein may be
manufactured using . Alternatively, or additionally, metalized
graphene fibers may also be produced by 3D printing, extrusion, wet
spinning and the like.
[0157] The metalized graphene fibers described herein may be used
in connection with any suitable muscle. For example, they can be
used into the heart as for pace makers or to record arrhythmias, it
can also be used over the skin, for transcutaneous of subdermal
stimulation. Additional application includes facial muscle muscles
for the treatment for ptosis, or migraines. This technology can be
also used directly on other organs including the stomach, the
liver, the kidney and spleen.
[0158] In some configurations, the metalized graphene fibers
described herein may be used to cell-culture recordings,
biochemical biosensing, molecular biosensing and the like. For
example, unmodified or functionalized graphene fibers can be used
to measure extracellular concentration of a number of metabolic and
biochemical biomarkers. These include reactive oxygen species such
as hydrogen peroxide and oxygen, as well as a number of important
neurotransmitters including serotonin, dopamine, glutamate, gamma
aminobutyric acid. Metabolic biomarker include glucose, caffeic
acid, and estradiol. Further, these can be used as single
biosensors or as multi-functional sensor array, and for a broad
range of samples including serum, urine, sweat, saliva, and others
alike.
[0159] In some configurations the fiber electrode may be connected
to a battery or to a wireless system for recording or stimulation.
In other embodiments, it may be connected to electrical, thermal or
radiofrequency energy sources, and be used for electrochemical
detection including that of dopamine. They also can be incorporated
as a component of other devices, including being part of a nerve
scaffold where the sutures that keep the nerve scaffold in place
are also conductive and can deliver electrical stimulation to
stimulate nerve regeneration. An additional application can be
transcutaneous placement of these fibers for applications similar
to those in acupuncture, with the advantage that these fibers can
be placed once and access as needed. These GP-Pt fibers can be used
to treat conditions addressed by acupuncture and others.
[0160] In some embodiments, the platinized graphene fibers
described herein may be used to record from and stimulate multiple
tissues and organs. For example the metalized graphene fibers may
be placed onto other organs such as the spleen, kidney, and the
like. In some embodiments, electrodes built in accordance with the
present disclosure can be wrapped around blood vessels or
neuro-vascular plexi for biosensing or neuromodulation. Further,
electrodes can be implanted inside, sutured through or over
internal organs, including but not limited to, heart, lungs,
stomach, liver, spleen, pancreas and other pelvic organs.
[0161] For example, in some embodiments the flexibility and
sensitivity of the fibers may allow for the placement of these
graphene fiber based electrodes on small neurovascular plexi in the
spleen, kidney, and other gastric and pelvic organs and ganglia
alike. In particular, in the spleen terminal neurovascular
branches, the graphene fibers can detect different types of
spontaneous and evoked activity in the form of compound action
potentials. From these recording and evoking their activity, for
example the contribution of specific groups of nerve fiber types to
the compound action potentials including A-alpha, A-beta, A-gamma,
A-delta/B, and C fibers may be estimated. Further, stimulation of
the splenic nerve may be used to neuromodulate the physiological
activity of the spleen, including the release of inflammatory
cytokines, which may be beneficial as a bioelectronic medical
approach for diseases including Reumatoid Arthritis and Cronn's and
the like.
[0162] Further, disclosed embodiments may be used for the
neuromodulation of somatic and autonomic ganglia, including, for
example, the nodose ganglia, carotid ganglia, and the mesenteric
and splachnic ganglia and alike. The disclosed fibers may be
directly inserted into neurogenic organs with intrinsic neural
networks such as the heart or the gut, so as to directly
neuromodulate their activity.
[0163] The platinized graphene fibers may be used as an implantable
conductive suture for neural and neuro-muscular interfaces in
chronic applications. For example, the described platinized
graphene fibers may be used to record, stimulate, and/or block
potentials in nerve and neuromuscular junctions thereby providing a
safe and long-term interface with high injection charge capacity,
adaptability for a variety of muscles and nerve geometries
including those blood vessels-nerve plexus complexes, and high
electrode sensitivity.
[0164] Embodiments built in accordance with the present disclosure
may be used to stimulate a number of tissues in the body including
nerves and muscles for the prevention of muscle atrophy
age-related, in rehabilitation to recover movements in limbs in
paraplegic patients and in those treatments that require punctual
electrical stimulation, such as tibial nerve stimulation and pelvic
floor for the treatment of urinary incontinence and stimulation of
muscles in the knee for osteoarthritis. Further, embodiments built
in accordance with the present disclosure may also be used as
bidirectional link with robotic prosthetic devices, peripheral
neuromodulation and bioelectronic medicine applications.
[0165] For example, a method of neural stimulation and/or neural
recording may include the step of implanting an electrode built in
accordance with the disclosure herein, in-vivo on nerves that
control internal organs including brain, heart, spleen, liver,
kidneys and the like.
[0166] In another example, a method of neural stimulation and/or
neural recording may include the step of implanting an electrode
built in accordance with the disclosure herein, in-vivo directly on
organs including brain, heart muscles both superficially or into
the organs.
[0167] In yet another example, a method of implantation may include
the step of placing an electrode built in accordance with the
disclosure herein over tissue, inside the tissue or sutured through
or over the tissue.
[0168] Optionally, electrodes built in accordance with the
disclosure herein may be used to stimulate a set of electrically
responsive cells including neurons and muscles cells by sending a
current through one or multiple implantable electrode.
Additionally, activity from electrogenic cells including neurons
and muscle cells by via the implantable electrodes built in
accordance with the disclosures herein.
[0169] As used in the description herein and throughout the claims
that follow, the meaning of "a", "an", and "the" includes plural
reference unless the context clearly dictates otherwise. The term
"about" in association with a numerical value means that the value
varies up or down by 5%. For example, for a value of about 100,
means 95 to 105 (or any value between 95 and 105).
[0170] The terms used in the specification generally have their
ordinary meanings in the art, within the context of the
compositions and methods described herein, and in the specific
context where each term is used. Some terms have been more
specifically defined above to provide additional guidance to the
practitioner regarding the description of the compositions and
methods.
[0171] All patents, patent applications, and other scientific or
technical writings referred to anywhere herein are incorporated by
reference herein in their entirety. The embodiments illustratively
described herein suitably can be practiced in the absence of any
element or elements, limitation or limitations that are not
specifically disclosed herein. Thus, for example, in each instance
herein any of the terms "comprising", "consisting essentially of",
and "consisting of" may be replaced with either of the other two
terms, while retaining their ordinary meanings. The terms and
expressions which have been employed are used as terms of
description and not of limitation, and there is no intention that
in the use of such terms and expressions of excluding any
equivalents of the features shown and described or portions
thereof, but it is recognized that various modifications are
possible within the scope of the invention claimed. Thus, it should
be understood that although the present invention has been
specifically disclosed by embodiments, optional features,
modification and variation of the concepts herein disclosed may be
resorted to by those skilled in the art, and that such
modifications and variations are considered to be within the scope
of this invention as defined by the description and the appended
claims.
[0172] Whenever a range is given in the specification, for example,
a temperature range, a time range, or a composition or
concentration range, all intermediate ranges and subranges, as well
as all individual values included in the ranges given are intended
to be included in the disclosure. It will be understood that any
subranges or individual values in a range or subrange that are
included in the description herein can be excluded from the aspects
herein. It will be understood that any elements or steps that are
included in the description herein can be excluded from the claimed
compositions or methods
[0173] In addition, where features or aspects of the invention are
described in terms of Markush groups or other grouping of
alternatives, those skilled in the art will recognize that the
invention is also thereby described in terms of any individual
member or subgroup of members of the Markush group or other
group.
[0174] Although the present disclosure has been described in
relation to particular embodiments thereof, many other variations
and modifications and other uses will become apparent to those
skilled in the art. It is preferred, therefore, that the present
disclosure be limited not by the specific disclosure herein, but
only by the appended claims.
* * * * *