Note: Descriptions are shown in the official language in which they were submitted.
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POLYMER-METAL FOIL STRUCTURE
FOR NEURAL STIMULATING ELECTRODES
Backctround of the Invention
The present invention relates to the biomedical
arts. It finds particular application in conjunction
with cuff electrodes for stimulating nerves and will be
described with particular reference thereto. It will be
appreciated, however, that the present invention is also
applicable to other types of implanted electrodes and
biomedical devices.
Many types of nerve tissue damage do not heal.
Such injuries leave a patient permanently without an
appropriate nerve path for electrical signals or action
potentials which travel from the brain to muscles or
other biological tissue to cause a biological response.
Similarly, such a discontinuity prevents action
potentials from carrying sensory information or other
biological feedback from the tissues to the brain.
Moreover, there is also a tendency for action potentials
to commence propagating naturally from below the injury
~ site to the biological tissue causing an unconscious and
unwanted biological response. Analogously, action
potentials can propagate from above the injury site to
the brain causing pain and erroneous sensory feedback.
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Electrical potentials can be applied to nerve
trunks and fibers to block the propagation of action
potentials and for controllably initiating the
propagation of action potentials in an upstream
direction, a downstream direction, or both. Neural
electrodes, such as illustrated in U.S. Pat. No.
4,602,624 to Naples, Sweeney, and Mortimer, and U.S.
Pat. No. 5,324,322 to Grill, Jr., Creasey, Ksienski,
Veraart and Mortimer controllably initiate and/or block
action potentials in the nerves.
Although the prior art neural electrodes have
proven effective, they do have drawbacks. Initially,
certain types of prior art neural electrodes are labor
intensive to manufacture, requiring the hand of a
skilled fabricator to weld conducting wires to foil and
fitting these foil conductors to silicone rubber
coverings. Hand fabrication results in various
problems, including the tendency of the foil conductors
buckling when the metal-silicone structure is flexed.
The flexure causes the foil to. work harden and
ultimately become a source for mechanical failure,
stress corrosion, cracking and/or subsequent conduction
failure.
Also, for neural electrodes whose patterns are
formed with a metal deposition on a flexible substrate
(e. g., silicone rubber or polyamide) there is a tendency
for the metal to crack. The cracks on the surface
appear as "cracked mud" at a microscopic level. Such
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cracks have the tendency to fill with uncured polymer when
pxessure is applied to a metal-polymer structure. This causes
the uncontrol~.ed formation of metal "islands," separated by the
nonconducting polymer. Nonconducting polymer between "islands"
eliminates electrical conduction along a trace by causing
multiple open cixcuits.
The present invention provides a new and improved neural
electrode and method of manufacture which overcomes the ai~ove-
Zo referenced problems and others.
$LimmarY of the Ix7.ventipn
In accordance with the present invention, there is
provided: a zzeural stimulating electrode structure, comprising:
a sheet of metal foil having a first face and a second
face, with holes located within the metal foil, the holes formed
in predetermined patte~'ns allowing the metal. foil to flex
without buckling, metal foil between the holes defining a
plurality of discrete electrodes on the metal foil when the foil
is cut;
2o a first polymeric base layer covering the first face of the
metal foil;
a second polymeric base layer covering the second face of
the metal foil, the first and second polymeric base layers
further filling the holes in the metal foil;
a third polymeric base layer covering at least one of the
first and second polymeric base layers; and
external connection poizzts, formed at locations where
portions of the third polymeric base layer and one of the first
arid second polymeric base layers have been removed, c-.ach of the
connectior~ points corresponding to metal, foz~. betoreer_ a pair of
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holes associated with one of the discrete electrodes, at least
one of the discrete electrodes at least one of contacting
tissue, passing current and measuring voltage.
A neural stimulating electrode structure, comprising.
a sheet of metal foil having a first face and a second
face, with holes forming a mesh, the mesh allowing the metal
foil to flex without buckling when subjected to compressive
forces, the mesh also enabling electrical conduction in a first
direction and a second direction across the metal foil, the
metal foil mesh between the holes defining at least one
electrically isolated region;
a first polymeric base layer covering the first face of the
metal foil;
a second polymeric base layer covering the second face of
the metal foil, the first and second polymeric base layers
filling the holes defined by the mesh;
a third polymeric base layer covering at least one of the
first and second polymeric base layers; and
external connection points, formed at locations where
portions of the third polymeric base layer and one of the first
and second polymeric base layers have been removed, wherein
portions of the metal foil axe exposed, the exposed metal fail
portions corresponding to metal foil between a pair of holes,
each pair of holes being associated with one oP the electrically
isolated regions oa the metal foil.
An electrode structure, comprising:
a common structure including an electrically conductivr~
material;
~0 at least one lead pad electrode formed within the common
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structure;
at least one connection pad electrode fozmed within the
structure;
at Least one conductive path formed within the common
structure, each of the conductive paths defining an electrical
connection between a unique one of the Lead pad electrode;a and a
unique cax'respondirig one of the connection pad electrodes, each
of the conduct~.ve paths inc3.ud~.ng a plurality of voids: and
z0 at least one non-conductive interconnection electrically
isolating (i? each of the lead pad electrodes from each of the
ether lead gad electrodes, (iii each of the connection pad
electrodes from each of the other connection pad electrodes,
(iii! each of the lead pad electrodes from each of the
connect~.on pad electrodes, and (iv) each of the conductive paths
from at least one of the other conductive paths.
A metkrod of manufacturing a neural stimulating electrode
structure, comprising;
farming holes into a metal fail sheet for forming patterns
and allowing the metal foil to flex without buckling when
subjected to compressive forces, segments of the metal foil
between the holes defining a plurality of discrete electrodes;
filzing the holes with a laser curable polymer, the polymer
accommodating the compressive forces;
sandwiching the metal foil between two layers of the
polymer;
cutting the sandwiched metal foil. to form at least one of
the discrete electrodes within the metal foil, each of the
discrete electrodes being electrically isolated from each o~ the '
3Q otk~er discrete electrodes;
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covering the at least two discrete electrodes with a seCOnd
coating of the polymex; and,
creating ore pair of openings for each of the at Least two
electrodes, one opening in, each of the pairs of openings
exposing a respective portion of the metal foil for interfacing
Ghe respective portion of the metal foil with one of tissue and
an electrical lead.
A principal advantage of the present invention i, that
voids formed in the metal foil filled with silicone rubber form
islands of insulating material, which along with regions o.E
conducting material create a continuous composite structures with
a conducting surface that accommodates compression (i.e.,
bend~.ng) without buckling.
Anothe~C advantage of the present invention is that it
reduces manual labor and manufacturing time.
Still another advantage of the present invention is treat it
facilitates automated, mass production techniques bIr using laser
cutablt materials (e. g., platinum or silicone rubber) aloz-ig with
chemical etchable materials.
Yet, anothex advantage of the present invention is that it
facilitates implantation and interconnection with electrical
leads.
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Still yet another advantage of the present
invention is that it prolongs electrode life.
A further advantage of the present invention is
that the electrode is electrically insulated and more
flexible than solid-foil sheets sandwiched between two
layers of polymer.
Still further advantages of the present invention
will become apparent to those of ordinary skill in the
art upon reading and understanding the following
detailed description of the preferred embodiments.
Brief Description of the Drawinc,~s
The invention may take form in various components
and arrangements of components, and in various steps and
arrangements of steps. The drawings are only for
purposes of illustrating a preferred embodiment and are
not to be construed as limiting the invention.
FIGURE 1 is a top elevational view of an electrode
construction in accordance with a first embodiment the
present invention;
FIGURE 2 is a flow chart for manufacturing an
electrode in accordance with the present invention;
FIGURE 3a is a top elevational view of sheet of
metal foil;
FIGURE 3b is a top elevational view of a sheet of
~ 25 metal containing voids;
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FIGURE 3c is a top elevational view of a partially
constructed electrode consisting of a metal sandwiched
between two layers of a polymer; .
FIGURE 4 is a cross-sectional side view of the
z
polymer-metal-polymer structure shown in FIGURE 3c;
FIGURE 5 is a top elevational view of a completed
electrode according to the first embodiment;
FIGURE 6a is a graphic representation of an
electrode structure which has been prestressed to form
the structure with a curved surface;
FIGURE 6b is an enlarged elevational view of a
portion of FIGURE 1 with compression forces;
FIGURE 7 is a top elevational view of the metal
sheet having holes forming a mesh;
FIGURE 8 is a top elevational view of a partially
constructed electrode consisting of a metal sandwiched
between two layers of a polymer;
FIGURE 9 is a cross-sectional side view of the
polymer-metal-polymer structure shown in FIGURE 8;
. FIGURE 10 is a top elevational view.of a completed
electrode according to the second embodiment;
FIGURE 11 is a top elevational view of a portion of
FIGURE 8 illustrating that longitudinal loads may be
accommodated by the planar structure while avoiding
buckling; and,
FIGURE 12 is a cross-sectional side view of a two-
layer electrode structure.
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Detailed Description of the Preferred Embodiments
FIGURE 1 sets forth a cut-out trace of an electrode
structure 24 (FIGURE 5). The cut-out trace 24 includes
a plurality of electrodes, each composed of a conductive
path I6 connected to an electrical lead pad 10 at one
end and an electrical connection portion 12 at a second
end. A polymer 14 provides mechanical interconnections
between the lead pads 10 and connection portions 12. It
is also noted that in the preferred embodiment, the
polymer is a laser cutable polymer.
The construction of the electrode structure begins
with a sheet of metal foil 18 (FIGURE 3a). In the
preferred embodiment, the thickness of the foil 18 is
preferably between about 10~.m and about 75~Cm. With
reference to the flow chart of FIGURE 2 and the
illustration of FIGURE 3b, holes 19 are cut or etched
into the foil 18 in a cutting or etching step A. The
holes 19 are cut to form patterns for creating the
multiple electrodes within the foil sheet 18. If
-20 desired, residual internal stresses are then removed
from the foil 18 in an annealing step B.
Next, the laser cutable polymer 14 is introduced
into the holes 19 of the metal foil 18 in a filling step
C. The laser cutable polymer 14 is preferably silicone
rubber. However, other materials with similar qualities
- are also contemplated. The resulting metal-polymer
combination is then sandwiched between two layers of the
polymer 14 in a covering step D to form a polymer-metal
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_g_
polymer structure 22 (see FIGURES 3c and 4). It is
appreciated that fill step C can be accomplished as part
of course step D, and that when fill step C and cover
step D are distinct steps, it is possible to use
different polymers in steps C and D. The electrodes are
then defined within the polymer-metal-polymer structure
22 in a tracing step E. The cut-out trace 24, having
lead pads 10 and connection portions 12, is then created
from the tracing in a cutting step F (see FIGURE 1)-
To complete the construction of the electrode
structure 26, the cut-out trace 24 is laminated with an
additional polymer layer or sheet of the laser cutable
polymer 14 in step G to form a laminated sheet of
electrodes 26 (see FIGURE 5). Either one or both
surfaces of cut-out trace 24 can be laminated.
Alternatively, the cut-out trace 24 itself may be used
or the cut-out trace 24 may be associated in some other
manner to a non-conducive surface. Lead pads 10 and
connection portions 12 are created in the electrode
structure 26 in a create. openings step H. Preferably,
a laser cutting device is used to create the openings.
However, the openings may also be created mechanically.
The beam properties (e. g_, intensity, wavelength, etc.)
of the laser are adjusted so that the laser cutting
device cuts through the laminated layer and polymer
layer of step D while leaving the metal foil 18 intact. '
Therefore, the foil 18 is exposed to form connection
portions 12 which provide metal to tissue contact for
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passage of current or measurement of voltage. The
openings 28 expose the lead pads 10 and connection
portions 12. The lead pads 10 are connected to
respective connection portions 12 via covered paths 16.
A prestressing step I optionally forms the
electrode structure 26 into a curved surface as shown in
FIGURE 6a. A curved surface is useful for conforming
the electrode structure to an outside surface of a nerve
or other similar structure 27.
FIGURE 6b shows a portion of the connection path
16. Arrows in FIGURE 6b represent compressive forces
experienced by the foil 18 when it is flexed. The holes
cut in the metal foil 18, in conjunction with the
polymer filling 14, allow the foil to flex without
buckling when subjected to these compressive forces.
A second embodiment of the invention will be
described with reference to FIGURES 2 and 7-11. The
construction of the electrode structure begins with a
sheet of metal foil 18.
With reference to FIGURE 2, holes are cut or etched
into the foil 18 during the cutting step A to form a
mesh pattern (see FIGURE 7?. The holes could be cut
into rectangular, or other geometric circular shapes.
After the holes are cut, residual internal stresses may
optionally be removed from the foil 18 during the
annealing step B.
Next, the laser cutable polymer 14 is introduced
into the holes of the metal foil 18 in the filling step
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C. The laser cutable polymer 14 is preferably silicone
rubber. However, other materials with similar qualities
are also contemplated. The resulting metal-polymer '
combination is then sandwiched between two layers of the
polymer 14 in the covering step D to form the polymer-
metal-polymer structure 22 (see FIGURES 8 and 9). The
metal layer of the resulting polymer-metal-polymer
structure 22 is electrically conductive in both the X
and Y planes.
20 The tracing of desired electrodes is then formed
from the polymer-metal-polymer structure 22 in the
tracing step E (see FIGURE 10). The cutting step F
includes cutting holes through the tracing to create
isolated regions of electrical conduction. The cutting ,
Z5 is preferably done using a laser device.
To complete the construction of the electrode
structure, the cut-out trace 24 is laminated in coating
step G. The lead pads 10 and electrical connection
portions 12 are created in the coated tracing in the
20 create opening step H. Preferably, a laser. cutting
device is used to create the openings. A beam intensity
of the laser is adjusted so that the laser cutting
device cuts through the laminated layer and polymer
layer while leaving the metal foil 18 intact. The foil
25 18 is exposed at the lead pads 10 and connection
portions I2 to provide metal to tissue contact for
passage of current or measurement of voltage. In FIGURE
10, Lead pad 10-1 and connector 12-1 are electrically
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connected to each other and electrically isolated from
all other lead pads and connectors on the electrode
structure. Similar connections exist between lead pads
10-2, 10-3 and connectors I2-2, 12-3, respectively.
y
FIGURE 11 shows a portion of the foil mesh 18.
Arrows in FIGURE 11 represent compressive forces
experienced by the foil mesh 18 when it is flexed. The
holes cut in the foil mesh 18, in conjunction with the
polymer filling 14, allow the foil to flex without
buckling when subjected to these compressive forces.
FIGURE 12 illustrates a two-layer electrode
structure created by stacking two polymer-mesh-polymer
structures on top of one another. Other multiple-layer
electrode structures are also contemplated.
3.5 The invention has been described with reference to
the preferred embodiment. Obviously, modifications and
alterations will occur to others upon reading and
understanding the preceding detailed description. It is
intended that the invention be construed as including
a.ll such modifications and alterations. insofar as they
come within the scope of the appended claims or the
equivalents thereof.
