Note: Descriptions are shown in the official language in which they were submitted.
1
POLYMER-BASED BIOPOTENTIAL SENSING SYSTEMS, MATERIALS AND
SELECTION METHODS
FIELD OF THE DESCRIPTION
[0001] The following relates to sensing systems and materials, composed
of one or
more elements of sensors created from polymer composite materials to contact
the skin,
circuitry to detect, record, or process the signals, an interface to transport
the signals from
the skin surface contact material to the circuitry, a processor to collect and
record the
signals, and methods for the selection and optimization of such sensor and
sensor
materials to meet the needs of desired specifications or applications. The
following also
relates to selection methods for optimizing the same, where such sensor
materials are
optimized to non-invasively detect one or more of electrical, thermal,
mechanical, or
chemical signals when in contact with skin in the absence of conductive gels,
and can have
one or more properties that are biocompatible, flexible, soft, elastic, self-
adhesive, and
conductive, and are developed for continuous wear in electronic devices for
consumer,
health, or medical applications.
BACKGROUND
[0002] The use of electrodes on the skin is commonly practiced for the
acquisition of
non-invasive biopotential signals, such as electroencephalography (EEG) to
study brain
activity, electrooculography (EOG) to track eye motion, electromyography (EMG)
to monitor
muscular impulses, and electrocardiography (ECG) for monitoring heart
function. For the
purposes of collecting biopotential signals related to the brain and brain
function, these
electrodes are typically placed on locations on the head or face of a user;
however, the
reliable and high-quality EEG recording using conventional electrodes from
these areas is
challenging due to their complex topologies. Current medical grade EEG
electrodes are
made of gold, silver/silver chloride (Ag/AgCI), or other metals, and to ensure
low
skin-electrode interface impedance and high quality of signal recording8,
contact to the
skin is facilitated by two means: adhesive electrical conduits, such as
conductive gels, and
mechanical pressure, such as that created by tight head caps or adhesives.
Typically,
Date Recue/Date Received 2022-06-17
2
conductive gels use a saline (NaCI) or silver/silver chloride (Ag/AgCI)
solution to enhance
the conductivity between the electrode and skin, which requires additional
preparation time,
as it is recommended to clean the area of the skin before application, provide
microabrasions to facilitate better signal quality, and remove any interfering
hair by
shaving. Head caps and adhesives require a second party to apply the
electrodes, often
requiring specific positioning of electrodes. However, such arrangement would
not be
suitable for the long-term EEG recording since the gel dries out by time and
results in
increasing the skin-electrode interface impedance and reducing signal to noise
ratio (SNR)
(Krummel, T. M. 2019).
[0003] Previous work has been done to develop sensor electrodes that do
not
require conductive gels or mechanical pressure. Dry electrodes made of metal
films or
electrically conductive polymer composites are widely used in wearable
technology
(Stauffer, et al., 2018; Kin, et al., 2016; Kim, et al., 2011, Xu, et al.,
2016); however, it is
hard to make conformal contact between these electrodes and skin due to two
main
reasons: first, the complex topology of targeted recording region and in some
individuals
existence of hairs that avoids stable direct and intimate contact between
electrodes with
planar geometry and skin; second, the mechanical mismatch between the
electrodes and
skin results in significant motion artifacts. In one attempt to secure an
electrode to the skin
without conductive gels, a patent (U.S. Pat. No. 7,032,301) discloses a dry
electrode that
pierces the skin in order to obtain constant contact for a biopotential
signal, which can
irritate the skin and is not suitable for repeated wear.
[0004] Alternatively, polymer material with conductive fillers are
described to be able
to sense the electrical signals generated by the body (U520160089045A1,
U5959197962),
though these sensors are not optimized for certain applications, locations, or
target signals,
and are limited only to electrical signals.
[0005] More recently, some groups have attempted to make polymer-based
sensors
that are not homogeneous, made by layering different materials with specific
properties to
construct sensors (W02021089593A1). Such sensors require multiple processes to
fabricate due to the dissimilarity of the materials, and are not durable, as
the contact
boundary between different materials provide sources of failure due to bonding
where
breaks are more common to occur.
Date Recue/Date Received 2022-06-17
3
[0006] Polymer composite based electrodes are mechanically flexible but
most of
them are stiffer than skin (Stauffer, et al., 2018; Kin, et al., 2016; Kim, et
al., 2011). That is
because most of the electrically conductive fillers such as carbon nanotubes
(CNT),
graphene and metallic nanoparticles have high Young's modulus and in order to
achieve
full percolation and high electrical conductivity required for EEG, relatively
high weight
percentage of these nano materials are added to the polymer precursor. In most
cases this
will affect the mechanical characteristics of the polymer composites
drastically and
consequently will result in the mechanical mismatch between the skin and
sensors, high
skin- electrode interface impedance, low quality of signal recording, low
signal to noise
ratio and motion artifact. In order to address such issues, forming conformal
contact to skin
is necessary, but making such contact especially on complex topologies using
conventional
electrodes with planar contact-surface without the use of wet-gels is a
challenge. Recently,
polymer composites based dry sensors with pillar-structures formed at their
contact-surface
have been developed, however these sensors are not suitable for mobile and
long-time
sensing during daily activity due to unstable contact to skin (Hwang, et al.,
2018; Krahn, et
al., 2011; Kwak, et al., 2011; Thanh-Vinh, et al., 2011). Sensing using such
sensors
significantly suffers from motion artifacts. The innovation disclosed herein
describes
effective sensors and hardware that enable reliable recording of biopotential
signals of
interest. These sensors are capable of recording signals from the area behind
the ears,
and within the ears' canals using proper sensors. Furthermore, the sensors
must be
mechanically soft, have low electrode-skin interface and form stable and
conformal dry
contact to skin in order to avoid motion artifacts in long term recording
during daily
activities. The innovation presented herein discloses sensor materials,
designs, systems,
and selection methods capable of achieving such desired signals from the skin
of a user.
SUMMARY OF THE DESCRIPTION
[0007] In one aspect, the enclosed relates to sensing systems optimized
to sense
high fidelity signals of one or more of electrical, mechanical, thermal, or
chemical signals
from the surface of the human skin, the sensing system composed of one or a
combination
of one or more sensors created from one or more polymer composite materials
and
Date Recue/Date Received 2022-06-17
4
designed as skin-contact sensors to optimize sensing the signals from dry or
wet contact
with the skin; circuitry to detect, record, or process said signals sensed by
the materials in
contact with the skin; an interface to transport the signal from the contact
surface of the
polymer composite material to the circuitry; a processor to collect and record
the signals or
provide determinations based on the signals; where the polymer composite
materials
having been selected and optimized using a selection method designed to choose
materials and fabrication processes to meet the needs or specifications of
intended
applications or desired signals.
[0008] In a further aspect, the system can be a system that requires
circuitry, such
as those incorporated into electronic devices, wearable devices, or e-skin
applications; or
purely a sensor, such as tattoo electrodes and other sensors made with
composite polymer
material.
[0009] In a further aspect, the materials and systems are less
susceptible to noise or
artifacts, such as movement, interference from hair, skin conditions, sweat,
temperature or
other conditions.
[0010] In a further aspect, the electrical signals that are sensed can be
one or more
of electroencephalography (EEG), electrooculography (EOG), electromyography
(EMG), or
electrocardiography (ECG), and the signals can be used raw or processed to
provide
indications of auditory attention, auditory attention envelope of sound,
visual attentional
direction, physical orientations of the user's head, gaze, and trunk,
saccades, blink, facial
movements, jaw movements, emotions, fatigue, activity level, temperature,
injury, illness,
disease, sleep state, narcolepsy, seizures, blood oxygen level, pH level, and
other
indicators regarding the status of the user.
[0011] In a further aspect, the system can be configured to provide that
the blink
signal is a function (f) of one or more or an average of multiple signals from
the left
amplified voltages Vleft, signal=f(VIeft), or right amplified voltages Vright,
signal=f(Vright) or
from the difference between one or more or an average of multiple signals of
the left and
right amplified voltages Vleft and Vright, signal=f(VIeft-Vright).
[0012] In a further aspect, the processor can accept data in, but not
limited to, the
following forms and their combinations: raw data, filtered data, low-pass
filtered data,
bandpass filtered data, averaged data, subtraction of left from right data,
subtraction of
Date Recue/Date Received 2022-06-17
5
right from left data, subtraction of left average from right average,
subtraction of right
average from left average, etc.
[0013] In a further aspect, the material is a composite material composed
of specific
measurements or ratios of a matrix of at least one polymer and filler
inclusions of at least
one material, the polymer matrix composed of one or more of thermoplastic
elastomers,
TPU, P/PC acrylonitrile- butadiene- styrene, ABS, styrenic block copolymer
TPS, PP/PE,
styrene- ethylene- butadiene- styrene, TPE, polyetherimide copolymer, low
density
polyethylene copolymer, or other such material as appreciated by someone
skilled in the
art; and wherein the filler elements could be conductive, such as one or a
combination of
carbon-based particles such as graphite, graphene, single-walled carbon
nanotubes,
multi-walled carbon nanotubes, carbon black, or carbon nanofibers; silica-
based particles,
such as glass, zirconia or silica, in microstructures such as spheres, flakes,
leaves or
dendrites; metal-based particles, such as silver, gold, copper, nickel,
aluminum, chromium,
titanium, tungsten, in the form of nanowires, spheres, flakes, or dendrites;
or metal-coated
particles, including organic, in-organic, carbon fiber, or others as
appreciated by a person
skilled in the art. Furthermore, the polymer matrix and/or composite has
traits of one or
more of biocompatible, flexible, soft, conductive, or adhesive.
[0014] In a further aspect, the properties, such as hardness modulus or
volume
resistivity, can be adapted to a desired value based on traditional electrodes
or a gold
standard for a particular field of application.
[0015] In a further aspect, the surface is surface treated to enhance
specific
properties of the material, which treatment can be one or more of an exposure
of internal
structure, chemical treating, coating, or other processes.
[0016] In a further aspect, the sensor design can be optimized for data
collection
given the location of application, such as hairless skin surface contact,
hairy skin surface
contact, in-ear skin surface contact, skin surface contact on the face, etc.;
the intended
use, and the target signals.
[0017] In a further aspect, the sensor geometry, design, or mechanical
properties
are optimized to attain the target signals for the desired location,
including, but not limited
to, flat surface contact, comb pillar contact, webbed contact, clamping
contact, scaffolding
contact, vacuum contact through suction, etc.
Date Recue/Date Received 2022-06-17
6
[0018] In a further aspect, the sensor is optimized to be used in a
specific
configuration among one or more other sensors, such configuration can include
one or
both of a ground electrode and reference electrode located to result in
highest signal to
noise ratio to capture desired signals, where such electrodes can be located
on the same
side of the head with active electrodes on the opposite side of the head, in
positions
around the ear, on the mastoid area, in the ear, on the nose, on the forehead,
on the
temple, or other locations across the face or head, or others.
[0019] In a further aspect, the sensor is optimized to be incorporated
into electronic
devices, wearable electronic devices, smart clothing or fabric, skin-worn
patches, or other
items to contact the skin.
[0020] In a further aspect, one or more faces of the sensor has specified
microstructures and/or macrostructures on its surface.
[0021] In a further aspect, one or more faces of the sensor creates a
vacuum
between the skin and sensor, resulting in reduced movement between the skin
and sensor
and higher contact reliability to enhance the transfer of signals from the
skin to the
electrode.
[0022] In a further aspect, the sensor is optimized to transmit data to a
device.
[0023] In a further aspect, a sensor fabrication process involves
creating sensors
with specific geometries and sizes from a mixture of conductive polymer
composite
material; the fabrication process involving one or more of mixing raw elements
using a
mixer, spreading a mixture using a roller, casting a raw mixture into molds,
manipulating
the viscosity, adhesiveness, or surface tension of a raw mixture to achieve a
desired
geometry, curing a raw mixture to preserve a desired geometry, including by
the means of
applying one or more of heat, chemical curing agents, plasma, coating
treatment, UV
treatment, dehydration, or extended exposure to ambient conditions.
[0024] In a further aspect, a material selection method, wherein inputs
can be
entered into a platform that can include one or more desired applications or
properties and
outputs a list of one or more optimal materials in, interpolated from, or
extrapolated from a
database to achieve desired applications or properties. Inputs can take into
consideration
aspects such as the human physiology, distance of sensors to the source of
signal activity,
properties of skin in the desired region of application, such as conductivity,
presence of
Date Recue/Date Received 2022-06-17
7
hair, perspiration, etc., as well as desired applications, measures of
electrical conductivity,
hardness, chemical sensitivity, adhesiveness, flexibility, thermal
conductivity, or gold
standard specifications.
[0025] In a further aspect, the platform can involve applying filters to
a database to
provide a list of one or more suitable materials, applying linear or non-
linear models such
as artificial neural network models, including deep and/or shallow artificial
neural network
models, wherein the models can be one or more of a combination of predictive
models.
[0026] In a further aspect, the database can include material data from
one or more
of published literature, experimentation results, simulation results, or other
sources of data.
[0027] In a further aspect, the material selection platform outputs can
include
materials and associated specifications for one or both of relevant
fabrication processes
and designs to meet the input specifications, including information regarding
materials,
material weight percentages, material molecular, nano-, micro-, or macro-
structures,
polymer matrix material weight percentage, filler material weight percentage,
mixing
process, shaping process, curing process, ideal geometry, and other relevant
information.
BRIEF DESCRIPTION OF THE FIGURES
[0028] Embodiments will now be described by way of example only with
reference to
the appended drawings wherein:
[0029] FIG. 1 is a representation of the microstructure of a polymer-
filler composite
with no fillers 101, tube-shaped or wire-shaped fillers, such as single-walled
carbon
nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes,
nanofibers,
nanowires, or other tube-shaped or wire-shaped fillers 102; particle-shaped
fillers, such as
carbon black, graphene, or other carbon, silica, or metal based structures in
the form of
spheres, flakes, leaves, or dendrites 103; and a combination of tube-shaped,
wire-shaped,
or particle-shaped fillers 104.
[0030] FIG. 2 depicts a schematic illustration of a top isometric view of
an in-ear
sensor design 201, bottom isometric view of an in-ear sensor design 202,
isometric view of
a comb sensor designed to reach past hair 203, and base view of a comb sensor
design
204.
Date Recue/Date Received 2022-06-17
8
[0031] FIG. 3 is a block diagram of a material and fabrication process
selection
model, with inputs such as desired sensing capabilities, characteristics,
and/or gold
standard specifications 301; model selection of material and fabrication
processes from
existing database 302; and output material with associated fabrication
processes 303.
DETAILED DESCRIPTION
[0032] The described innovations are sensor systems, materials, and
selection
methods, including polymer material sensor material, design, fabrication
process, and
selection platform that is capable of detecting signals from the surface of
the skin. The
sensing systems can contain sensing materials fabricated to contact the skin
independently
of or in combination with one or more of circuitry to detect, record, or
process signals, an
interface to transport signals from the contact surface to the circuitry, and
a processor to
collect and record signals or to provide determinations based on the signals.
The sensing
system can be a subsystem of a larger sensor system, system, or device, or can
be an
independent sensur such as tattoo electrodes. The sensing system is optimized
to achieve
desired signals or increase signal to noise ratio of desired signals. The
enclosed polymer
material observes properties of flexibility, elasticity, hardness,
conductivity, chemical
sensitivity, and biocompatibility, and can be tuned to raise or lower certain
characteristics in
order to optimize the material for an intended purpose. Resulting properties
of the
polymer-filler composite material are subject to many factors, including
composition,
fabrication, and design; thus this patent explains their interdependence and
the process by
which materials can be tuned to achieve specific properties.
[0033] First, its properties are affected primarily by its composition.
The composite
material involves a polymer matrix composed of one or more polymers, with a
certain
weight distribution of filler materials. Polymer matrices can be one or more
of thermoplastic
elastomers, TPU, P/PC acrylonitrile- butadiene- styrene, ABS, styrenic block
copolymer
TPS, PP/PE, styrene- ethylene- butadiene- styrene, TPE, polyetherimide
copolymer, low
density polyethylene copolymer, or other polymer materials. Filler materials
can be one of
multiple elements, or a combination of elements, and generally fall into one
of three
categories: carbon-based, silica-based, and metal-based. Carbon-based filler
materials
Date Recue/Date Received 2022-06-17
9
include carbon particles with varying natural and synthetic geometries, such
as graphite,
graphene, carbon black, single- or multi-walled carbon nanotubes, or carbon
nanofibers.
Silica-based particles are made of materials such as glass, zirconia or
silica, and come in
varying microstructures, such as spheres, flakes, leaves or dendrites. Metal-
based filler
materials can be made from silver, gold, copper, nickel, aluminum, chromium,
titanium,
tungsten, or other metals, and can take the microstructures of nanowires,
spheres, flakes,
dendrites, or metal-coated particles.
[0034]
These sensor materials contain specific formulas and ratios of polymer and
filler, and undergo specific fabrication processes that further tune their
properties; and thus,
the second condition to affect the properties of the material is its
fabrication process.
Generally, the process is as follows. First, polymer and filler materials are
measured to
precise weight ratios. These materials are then mixed together to achieve an
even
distribution, or dispersion, of filler materials in the polymer matrix, to
achieve most
predictable results. Mixing can be performed with standard mixers, single,
dual, or multi
screw turners, stirrers, rollers and mills, kneaders, or other mechanical
mixing methods.
Additionally, distributed materials can be further processed by placement in
the presence of
a magnetic field. This is used to align filler particles to conduct
electricity in specified
directions. Then, the material is shaped. Flat geometries are achieved by
rolling, spin
coating, pressing, or other similar techniques, typically followed by cutting
to achieve
specific shapes. Thin cords are produced through extrusion. More complex
geometries are
achieved through mold casting. To do this, a negative impression is created in
a secondary
material of higher hardness. The conductive filler is then poured, injected,
or otherwise
"cast" into the mold. Alternate methods to manipulate the geometry are also
performed. For
instance, glass beads may be dipped onto the surface of a polymer precursor,
then
removed to a certain distance and suspended, capitalizing on the adhesiveness
and
surface tension of a material in order to create "tulip-like" structures with
a cup at the end of
a stem. To solidify the material, it undergoes a curing process. Curing is
often catalyzed or
accelerated using a variety of curing methods. Most commonly, this is
performed by
"baking" the material at a certain temperature for a period of time, though
curing can also
be performed by exposure to ultraviolet (UV) light, chemical curing agents,
plasma, coating
treatment, or extended time. After the material is finalized, a coating can be
applied to
Date Recue/Date Received 2022-06-17
10
change the surface properties of the material. For instance, a typical example
of this would
be the coating using a conductive ink, such as Ag/AgCI, to tune the surface
conductivity
properties of a material, or other surface treatments to expose the conductive
filler
materials. In this fabrication process, by manipulating one or more of these
steps,
additional material properties can be achieved. For instance, by curing a
material such as
PDMS at a higher temperature, it is possible to make the resulting material
more brittle;
conversely, by curing the material at a lower temperature, the material will
be more pliable.
[0035] Finally, because of the many variables that affect the ability to
detect signals
from the surface of human skin, geometry is another element that can
dramatically
influence a sensor's performance. Surface-contact sensors, such as the
material sensors
described in this patent, achieve highest performance when movement and other
disturbances are limited. Thus, sensors must be designed to reduce movement
and
maintain consistent contact between the sensor and the skin. For in-ear
sensors, this can
be achieved by manipulating the geometry of the sensor to comfortably anchor
within the
ear or ear canal. For skin-surface applications, because of both macro-scale
variables,
such as the presence of hair, and micro-scale variables, such as level of
perspiration, this
can be achieved macroscopically, with the design of pillars to reach past hair
or suction cup
geometries to anchor to the skin similar to a sucker on an octopus's
tentacles, or
microscopically, with an adhesive surface structure with ridges or hooks
similar to the feet
of a gecko.
[0036] Thus, the material can detect biopotential signals, such as
electroencephalography (EEG), electrooculography (EOG), electromyography
(EMG), or
electrocardiography (ECG); temperature; chemical properties, such as
perspiration
moisture level, pH level, glucose concentration, and others.
[0037] Because of the many variables affecting the characteristics and
quality of the
composite polymer material, a selection method is developed to select the
optimal material
given a set of requirements or intended characteristics. Such selection
methods can
involve a database composed of data from literature, experimental data, data
derived from
simulations, or other sources, applying filters to said database to provide a
list of one or
more suitable materials, with their associated fabrication processes and
designs, or linear
or non-linear models, such as artificial neural network models. These
predictive models
Date Recue/Date Received 2022-06-17
11
can input conditions, desired applications, properties, or locations into the
model can
include one or more of a range of sensing specifications, such as electrical
conductivity,
thermal conductivity, chemical sensitivity, or other traits; a range of
mechanical properties,
such as hardness, tensile strength, elasticity, impact resistance,
brittleness, toughness,
viscosity, or other traits; a range of chemical properties, such as
biocompatibility, reactivity,
flammability, oxidizability, and other traits; and a gold standard
specifications as used in the
industry. The model searches the database, and produces an output of material
selections
and fabrication processes that can meet the desired properties. Furthermore,
additional
materials can be output based on interpolation or extrapolation techniques. In
this way,
using the gold standard, a material can be reverse engineered to determine the
optimal
materials and processes to develop the material with the properties.
[0038]
Resulting sensor systems can be configured as part of a larger sensor
system, system, or device. These can be used to provide signals to be
processed, wherein
the processor can accept data in, but not limited to, the following forms and
their
combinations: raw data, filtered data, low-pass filtered data, bandpass
filtered data,
averaged data, subtraction of left from right data, subtraction of right from
left data,
subtraction of left average from right average, subtraction of right average
from left
average, etc. Collected data can be collected by the sensing system and
processed to
provide indications of auditory attention, auditory attention envelope of
sound, visual
attentional direction, physical orientations of the user's head, gaze, and
trunk, saccades,
blink, facial movements, jaw movements, emotions, fatigue, activity level,
temperature,
injury, illness, disease, sleep state, narcolepsy, seizures, blood oxygen
level, pH level, and
other indicators regarding the status of the user.
References:
Chardonnens, S., Bachmann, S., Fumm, A., Junker, K., Zortea, L., Vollenweider,
A. (n.d.).
Apparatus for measuring bio-signals.
Hwang, I., et al., Multifunctional smart skin adhesive patches for advanced
health care. Adv
Healthc Mater 2018, 7 (15), e1800275.
Date Recue/Date Received 2022-06-17
12
Kim, T., et al., Bioinspired, Highly Stretchable, and Conductive Dry Adhesives
Based on
1D-2D Hybrid Carbon Nanocomposites for All-in-One ECG Electrodes. ACS Nano,
2016. 10(4): p. 4770-8.
Kim, D. H., et al., Epidermal electronics. Science 2011, 333 (6044), 838-843.
13. Xu, M., et
al., Carbon nanotube dry adhesives with temperature-enhanced adhesion over a
large temperature range. Nat Commun 2016, 7.
Krahn, J., et al., A tailless timing belt climbing platform utilizing dry
adhesives with
mushroom caps. Smart Mater Struct 2011, 20(11).
Krummel, T. M., The rise of wearable technology in health care. JAMA Netw Open
2019, 2
(2), e187672.
Kwak, M. K., et al., Towards the next level of bioinspired dry adhesives: new
designs and
applications. Adv Funct Mater 2011, 21(19), 3606-3616.
Sadeghian-Motahar, S., Bradley, R. K. (2018, May 29). Bio-potential sensing
materials as
dry electrodes and devices.
Schmidt, R. N., Lisy, F. J., Skebe, G. G., Prince, T. S. (2006, April 25). Dry
physiological
recording electrode.
Searle, A., et al., A direct comparison of wet, dry and insulating bioelectric
recording
electrodes. Physiol Meas 2000, 21(2), 271-83.
Stauffer, F., et al., Skin Conformal Polymer Electrodes for Clinical ECG and
EEG
Recordings. Adv Healthc Mater, 2018. 7(7): p. e1700994.
Taranekar, P., Venkatesan, A., Negandhi, N., Banerjie, A. (2017, March 14).
Polymer
nano-composites as dry sensor material for biosignal sensing.
Thanh-Vinh, N., et. al., Micro suction cup array for wet/dry adhesion. Proc
IEEE Micr Elect
2011, 284-287.
Xu, M., et al., Carbon nanotube dry adhesives with temperature-enhanced
adhesion over a
large temperature range. Nat Commun 2016, 7. 1
Date Recue/Date Received 2022-06-17
