Patent Description:
Biopotential measurements in the form of, for example, electrocardiograms (ECG) electroencephalograms (EEG), electrooculograms (EOG) and electromyograms (EMG) are used to monitor the activity of organs, for example the heart, brain, eyes and muscles.

Biopotential measurements can be made by placing non-invasive surface electrodes on the body.

In examples, it is beneficial for the electrodes to adhere well to the body part and to include electrolyte, such as an electrolyte layer, to enable better biopotential measurements to be obtained.

<CIT>) relates to a glucose sensor in the form of a skin patch that has a microneedle which penetrates the skin to draw out interstitial fluid. According to D1, the interstitial fluid passes to a common entrance port. In D1, a series of microchannels is provided on the skin patch. According to D1, the fluid drawn onto the patch is selectively switched between a number of microchannels by means of electro-osmotic pumps and hydrophobic gates. In D1, each microchannel has an electrochemical detector for sensing glucose concentration. According to D1, also disclosed in D1 is a monolithic device with an integrated lance.

<CIT> (D4) relates to devices, systems and methods for epidermal monitoring of a fluid on skin. According to D4, in some aspects, a device includes an electrochemical sensor comprising two or more electrodes disposed on a first flexible substrate; a microfluidic device comprising a second flexible substrate coupled to the first substrate and structured to include (i) a channel in a first cavity of the second substrate, (ii) one or more holes that connect to the channel and provide one or more inlets, and (iii) a reservoir connected to the channel, in which the electrochemical sensor is aligned with the reservoir; and an adhesion layer coupled to the microfluidic device and attachable to skin, and the device being operable to detect a biomarker in a fluid in secreted by the skin into the microfluidic device.

The examples and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

According to various, but not necessarily all, embodiments there is provided an electrode apparatus and a method according to the appended claims.

According to various examples there is provided an electrode apparatus comprising:.

The electrode apparatus comprises at least one first microfluidic channel and at least one second microfluidic channel.

In some but not necessarily all examples, the electrode apparatus comprises at least one reservoir configured to perform at least one of absorbing, by capillary action, liquid from the second microfluidic channel and supplying, by capillary action, liquid stored in the at least one reservoir to the second microfluidic channel.

In some but not necessarily all examples, the at least one reservoir comprises at least one microfluidic channel having a larger section than the second microfluidic channel.

In some but not necessarily all examples, the at least one reservoir comprises a plurality of connections to the second microfluidic channel.

In some but not necessarily all examples, the at least one reservoir is enclosed within the substrate. In some examples the at least one reservoir can be considered to be fully enclosed within the substrate.

In some but not necessarily all examples, the conduits narrow from the first microfluidic channel towards the second microfluidic channel.

In some but not necessarily all examples, the substrate is formed from at least one class of conformable and/or self-adhesive polymer material.

According to various examples there is provided a method comprising:.

The method comprises forming at least one first microfluidic channel and forming at least one second microfluidic channel.

In some but not necessarily all examples, forming the first microfluidic channel and forming the at least one conduit comprises fabricating electrically conductive material in the form of the first microfluidic channel and at least one conduit.

In some but not necessarily all examples, forming the second microfluidic channel comprises fabricating removable mould material in the form of the second microfluidic channel.

In some but not necessarily all examples, the method comprises forming a substrate around the formed first microfluidic channel, second microfluidic channel and at least one conduit.

In some but not necessarily all examples, the method comprises removing the removable mould material.

In some but not necessarily all examples, forming the first microfluidic channel, the second microfluidic channel and the at least one conduit comprises:.

In some but not necessarily all examples, the method comprises forming at least one reservoir configured to perform at least one of absorbing, by capillary action, liquid from the second microfluidic channel and supplying, by capillary action, liquid stored in the at least one reservoir to the second microfluidic channel.

According to various examples there is provided a system comprising:
an apparatus for making one or more biopotential measurements; and at least one electrode apparatus as described herein.

In some but not necessarily all examples, the system comprises a plurality of electrode apparatuses as described herein.

Examples of the disclosure relate to an electrode apparatus <NUM> and method <NUM>, <NUM> for forming an electrode apparatus <NUM>.

In examples, the electrode apparatus <NUM> comprises a substrate <NUM>, the substrate comprising a first microfluidic channel <NUM>; a second microfluidic channel <NUM>; and at least one conduit <NUM> extending between the first microfluidic channel <NUM> and the second microfluidic channel <NUM>.

In examples, the first microfluidic channel <NUM> can be considered at least one first microfluidic channel <NUM>.

In examples, the second microfluidic channel <NUM> can be considered at least one second microfluidic channel <NUM>.

The first microfluidic channel <NUM> and the at least one conduit <NUM> comprise electrically conductive material <NUM>, and the second microfluidic channel <NUM> is exposed to the external environment <NUM> and configured to absorb liquid <NUM> by capillary action.

The at least one conduit <NUM> comprising electrically conductive material <NUM> is configured to operate as an electrode or micro-electrode.

The second microfluidic channel <NUM> is configured to absorb and retain liquid <NUM>, such as a liquid electrolyte, sweat, water, adjacent to the at least one conduit <NUM> to assist in, for example, biopotential measurements.

The second microfluidic channel <NUM> is exposed to the external environment <NUM> to allow the second microfluidic channel <NUM> to absorb, by capillary action, liquid from the external environment <NUM>. In examples, the external environment can be considered to be the environment external to the electrode apparatus <NUM>.

For example, the second microfluidic channel <NUM> can be configured to absorb, by capillary action, sweat from a subject when the electrode apparatus <NUM> is placed on the subject's body to make biopotential measurements.

The substrate <NUM> of the electrode apparatus <NUM> can be formed from material that can conform and adhere to a subject's body without any additives or adhesives.

The electrode apparatus <NUM> can therefore be configured to be reusable without the need for adhesive, which can dry out after multiple uses, which is advantageous. The electrode apparatus <NUM> is also advantageous as the second microfluidic channel <NUM> is configured to continually provide and/or retain liquid adjacent the at least one conduit <NUM> to provide functionality equivalent to a micro-wet-electrode.

Furthermore, the electrode apparatus <NUM> provides for a high density of electrodes for use in, for example, biopotential measurements.

Examples of the disclosure therefore provide an electrode apparatus <NUM> which does not comprise a gel electrolyte layer that can dry out and also adheres well without the use of an adhesive layer which can result in discomfort for a subject.

In addition, examples of the disclosure provide a sustained, impedance controlled, long-term operating electrode skin interface that is easy to put on and take off.

This is beneficial in, for example, applications that require long-term continuous monitoring of biopotential measurements or other applications where an electrode is placed and removed many times. For example, in applications such as smart clothing and wearable devices.

<FIG> schematically illustrates an example of an electrode apparatus <NUM>.

Various features referred to in relation to <FIG> can be found in the other figures.

In <FIG>, the electrode apparatus <NUM> comprises a substrate <NUM>, the substrate <NUM> comprising a first microfluidic channel <NUM>, a second microfluidic channel <NUM> and at least one conduit <NUM> extending between the first microfluidic channel <NUM> and the second microfluidic channel <NUM>.

The first microfluidic channel <NUM> and the at least one conduit <NUM> comprise electrically conductive material <NUM>.

The second microfluidic channel <NUM> is exposed to the external environment <NUM> and configured to absorb liquid <NUM> by capillary action.

In examples, the microfluidic channels can be considered microchannels and/or microscale channels.

The electrode apparatus <NUM> can comprise any suitable number of first microfluidic channels <NUM>.

The first microfluidic channel <NUM> comprises electrically conductive material <NUM> and is configured to electrically interconnect one or more of the at least one conduit <NUM>.

The first microfluidic channel <NUM> is configured to allow connection of the electrode apparatus <NUM> to a suitable apparatus to allow, for example, one or more biopotential measurements to be made. See, for example, <FIG>.

The first microfluidic channel <NUM>, comprising the electrically conductive material <NUM>, can be considered conductive microfluidic channel(s).

In examples, the first microfluidic channel <NUM> can have any suitable size, shape and/or form. For example, the first microfluidic channel can have any suitable size, shape and/or form to allow a large number of conduits <NUM> to be present in the electrode apparatus <NUM>.

In examples the first microfluidic channel <NUM> can have any suitable size, shape and/or form to allow the first microfluidic channel <NUM> to contain electrically conductive material <NUM> to provide an electrical connection between the conduit(s) <NUM> and a measuring apparatus.

The size, shape and/or form of the first microfluidic channel <NUM> can be limited by the size, shape and/or form of the electrode apparatus <NUM>.

In examples, the first microfluidic channel <NUM> has any suitable width.

The at least one conduit <NUM> extends between the first microfluidic channel <NUM> and the second microfluidic channel <NUM>.

In examples, the at least one conduit <NUM> can be considered to link and/or connect and/or join and/or associate and/or attach and/or couple the first microfluidic channel <NUM> and the second microfluidic channel <NUM>.

The at least one conduit <NUM> can have any suitable size, shape and/or form. In examples, the electrode apparatus <NUM> can comprise any suitable number of conduits <NUM>.

In examples, one or more of the at least one conduits <NUM> can have different sizes, shapes and/or forms.

In examples, the one or more conduits <NUM> have a width in the range of <NUM> to <NUM> micrometers. However, in examples, any suitable width can be used.

In examples the one or more conduits <NUM> have a width to extend across multiple areas of the second microfluidic channel <NUM>.

In some, but not necessarily all, examples, the conduit(s) <NUM> narrow from the first microfluidic channel <NUM> towards the second microfluidic channel <NUM>.

In such examples the conduit(s) have a first width in the region of the first microfluidic channel(s) <NUM> and a second, smaller width in the region of the second microfluidic channel(s) <NUM>.

The second width in the region of the second microfluidic channel(s) <NUM> can be in the range of <NUM> to <NUM> micrometers, with the first width in the region of the first microfluidic channel <NUM> being larger.

The at least one conduit <NUM> comprising electrically conductive material <NUM> is configured to function as an electrode or micro-electrode.

In examples, the conduits <NUM> narrow from the first microfluidic channel <NUM> towards the second microfluidic channel <NUM>.

The at least one conduit <NUM> comprising electrically conductive material <NUM> can be considered to be a pin, a micro-contacting pin, a protrusion, an electrode, a micro-electrode and so on.

In examples, the at least one conduit <NUM> comprising electrically conductive material <NUM> can be considered to be exposed micro-contacting pin(s) as the end of the at least one conduit <NUM> is exposed to the second microfluidic channel <NUM>.

The electrically conductive material <NUM> can comprise any suitable electrically conductive material or materials. For example, the electrically conductive material <NUM> can comprise one or more conductive materials of electrical resistivity lower than <NUM> Ohm·cm.

In examples, the electrically conductive material <NUM> comprises one or more electrically conductive fluids.

The electrically conductive material <NUM> can comprise one or more electrically conductive fluids. The electrically conductive fluid can be solidified once in the first microfluidic channel(s) <NUM> and may or may not be electrically conductive in its fluid form.

The electrically conductive fluid may be or comprise an electrically conductive ink or paste. The electrically conductive ink or paste may have a viscosity of between <NUM> mPa·s and <NUM> mPa·s.

In examples the electrically conductive ink can comprise a nanoparticle ink, a metalloorganic decomposition ink and/or a UV-curable ink.

The electrically conductive fluid can comprise one or more of conductive silver ink(s), silver/silver chloride ink(s), silver/carbon ink(s), silver/chloride/carbon ink(s), carbon ink(s) and so on and/or any suitable combination of such ink(s) and/or any other conductive carbo-based, metal-based and/or polymer-based ink(s).

In examples, the first microfluidic channel <NUM> and/or the at least one conduit <NUM> can be considered to be filled with electrically conductive material <NUM>.

The external environment <NUM> can be considered to be any environment external to the electrode apparatus <NUM>. For example, the external environment <NUM> can be considered to be the environment around or adjacent to the electrode apparatus <NUM>.

In examples the external environment <NUM> can be considered to be the space or volume around the electrode apparatus <NUM> from which the second microfluidic channel <NUM> can absorb liquid <NUM> by capillary action. For example, liquid introduced to the surface of the electrode apparatus <NUM> to be absorbed by the second microfluidic channel <NUM> can be considered to be from the external environment <NUM>.

In examples the external environment <NUM> can comprise one or more surfaces, such as a subject's skin, upon which the electrode apparatus can located or placed.

The electrode apparatus <NUM> can comprise any suitable number of second microfluidic channels <NUM>.

The second microfluidic channel <NUM> can have any suitable size, shape and/or form. For example, the second microfluidic channel can have any suitable size, shape and/or form to absorb, by capillary action, liquid from the external environment.

In examples, the second microfluidic channel <NUM> is located at a surface of the substrate <NUM> of the electrode apparatus <NUM> to allow the second microfluidic channel <NUM> to be exposed to the external environment <NUM>.

The size, shape and/or form of the second microfluidic channel can be configured to maximize the surface coverage and therefore the liquid-absorbing ability of the second microfluidic channel <NUM>. See, for example.

The second microfluidic channel <NUM> can be considered an open and/or empty microfluidic channel.

The second microfluidic channel <NUM> can be considered to be an open channel as at least a portion of the second microfluidic channel <NUM> is at a surface of the substrate <NUM> and is exposed to the external environment <NUM> outside of the electrode apparatus <NUM>.

The second microfluidic channel <NUM> can be considered to be an open channel as at least a portion of the second microfluidic channel <NUM> is not enclosed within the electrode apparatus <NUM>.

In examples the second microfluidic channel <NUM> can be configured as a trough or groove at the lower surface of the electrode apparatus <NUM>.

The second microfluidic channel <NUM> can be considered to absorb liquid by capillary action and/or capillarity. Additionally or alternatively, the second microfluidic channel <NUM> can be considered to wick liquid that the second microfluidic channel <NUM> comes into contact with.

However, in other examples not necessarily falling within the scope of the claimed invention the second microfluidic channel can be configured to absorb liquid by any suitable mechanism.

The second microfluidic channel <NUM> can have any suitable size to allow the second microfluidic channel(s) <NUM> to absorb liquid, for example, from the skin of a subject.

In examples, the second microfluidic channel <NUM> can be considered to be liquid absorbing microfluidic channel. The second microfluidic channel <NUM> can have a width in the range of <NUM> to <NUM> micrometers. In examples the second microfluidic channel can have a width in the range of <NUM> to <NUM> micrometers.

The second microfluidic channel <NUM> is configured to absorb and retain liquid which can act as an electrolyte, or electrolyte layer, for use in biopotential measurements made using the electrode apparatus <NUM>.

In examples, the second microfluidic channel <NUM> can be considered to be adjacent the ends of the at least one conduit <NUM> to allow liquid absorbed by the second microfluidic channel <NUM> to be retained in position to act as an electrolyte for measurements made using the electrode apparatus <NUM>.

In examples, an end portion of the at least one conduit/pin <NUM> is adjacent to/in fluidic communication with the second microfluidic channel <NUM>.

This is advantageous as, for example, the second microfluidic channel <NUM> can, for example, absorb/wick sweat from a subject's body to provide a supply of liquid electrolyte for use in biopotential measurements using the electrode apparatus <NUM>.

Accordingly, in examples, the subject can act as a source of liquid electrolyte through their sweat, which the electrode apparatus <NUM> can absorb/wick using the second microfluidic channel <NUM> for use as an electrolyte, or electrolyte layer, for biopotential measurements.

The absorption/wicking of liquid/electrolyte in this way provides for the conduit(s)/pin(s) <NUM> to be configured as micro-wet electrodes. In examples, the electrode apparatus <NUM> can comprise many conduits <NUM> configured to operate as micro-wet electrodes with a high density in the electrode apparatus <NUM>. This is also advantageous.

The substrate <NUM> can comprise any suitable size, shape and/or form and can be comprised of any suitable material or materials.

For example, the substrate <NUM> can be comprised of any suitable material having natural reversible adhesion.

In examples, the substrate <NUM> can conform and adhere to, for example, a subject's body to allow the electrode apparatus <NUM> to be repeatedly used to make, for example, biopotential measurements.

In examples, the substrate <NUM> is formed from at least one class of conformable and/or self-adhesive polymer material.

In some examples the substrate <NUM> is formed from at least one of a polydimethylsiloxane classed material a polyurethane classed material, a polyfluoropolyether classed material, a polyfluoroethylene classed material, a polystyrene classed material, a polyethylene classed material, a polypropylene classed material, a polyvinyl chloride classed material, a poly(styrene-isoprene-styrene) classed material and a cellulose based material. See, for example, <FIG>.

In examples, the electrode apparatus <NUM> comprises at least one reservoir <NUM> configured to absorb, by capillary action, liquid <NUM> from and/or supply, by capillary action, stored liquid <NUM> to of the second microfluidic channel <NUM>.

In examples, the at least one reservoir <NUM> can be considered to be configured to perform at least one of absorbing, by capillary action, liquid <NUM> from the second microfluidic channel <NUM> and supplying, by capillary action, liquid stored in the at least one reservoir <NUM> to the second microfluidic channel <NUM>.

This is illustrated in the example of <FIG> by the dashed box next to the second microfluidic channel(s) <NUM>.

In examples, the at least one reservoir <NUM> comprises at least one microfluidic channel having a larger section than the second microfluidic channel <NUM>.

In examples, having a larger section means that for a given channel length a larger volume of liquid can be stored in the reservoir <NUM> compared to the second microfluidic channel <NUM>.

In examples, the at least one reservoir <NUM> is connected/linked to the second microfluidic channel <NUM> by one or more connections to allow the at least one reservoir <NUM> to absorb liquid <NUM> from and/or supply liquid <NUM> to the second microfluidic channel <NUM>.

In examples, the at least one reservoir <NUM> comprises a plurality of connections to the second microfluidic channel <NUM>.

In examples, the at least one reservoir <NUM> is enclosed within the substrate <NUM>. This means the at least one reservoir <NUM> is not directly exposed to the external environment <NUM>.

In some examples the at least one reservoir <NUM> can be considered to be fully enclosed within the substrate <NUM>.

In some examples the at least one reservoir <NUM> can be considered to be encapsulated within the substrate <NUM>.

The use of at least one reservoir <NUM> is advantageous as, for example, it allows liquid <NUM> absorbed via the second microfluidic channel <NUM> to be stored within the reservoir <NUM> for use when the external environment is dry. In such environments the stored liquid can then be supplied back to the second microfluidic channel <NUM> to ensure liquid/electrolyte is still present for use in, for example, biopotential measurements.

In some examples the at least one reservoir <NUM> can be preloaded with liquid <NUM> to allow the electrode apparatus <NUM> to operate in dry environments for longer.

The fluid can move automatically between the second microfluidic channel <NUM> and the at last one reservoir <NUM> by capillary action/capillarity/wicking.

The reservoir <NUM> can be refilled at intervals, for examples by using water, or can be refilled by absorbing excess sweat for use later, when sweat is not present. This can, for example, improve skin contact for biopotential measurements.

Accordingly, in examples, the electrode apparatus <NUM> can be considered to be a dry electrode that acts or operates as a wet electrode.

In examples, the electrode apparatus can be considered to be activated when liquid <NUM> is present in the second microfluidic <NUM> channel. In examples the electrode apparatus can be activated prior to use by applying liquid <NUM> to the second microfluidic channel <NUM>.

In some examples, an apparatus comprising one or more microfluidic channels and one or more reservoirs can be used to maintain low contact resistance, for example, in scenarios where electrical connection is not easily accessed for maintenance.

Additionally or alternatively, such a system can be used with deoxidizing additive in the liquid which could help to maintain an electrical connection for contacts which are subject to corrosion.

<FIG> illustrates an example of an electrode apparatus <NUM>.

One or more elements of the electrode apparatus <NUM> can be as described in relation to <FIG>.

<FIG>, part A, illustrates a top view of the electrode apparatus <NUM>.

In the illustrated view the upper surface of the substrate <NUM> is not shown and the first microfluidic channel <NUM> comprising electrically conductive material <NUM> can be seen.

However, in examples, the substrate <NUM> of the electrode apparatus <NUM> does not comprise material covering the upper surface of the electrode apparatus <NUM>.

In the illustrated example, the electrode apparatus <NUM> comprises a single, continuous first microfluidic channel <NUM> comprising electrically conductive material <NUM>.

However, in examples, the electrode apparatus <NUM> can comprise any suitable number of separate first microfluidic channels <NUM>.

The first microfluidic channel <NUM> is shaped in a form that repeatedly turns back on itself.

Part B of <FIG> illustrates a bottom view of the electrode apparatus <NUM>.

In part B of <FIG> the second microfluidic channel <NUM> can be seen. In the example of <FIG> the second microfluidic channel <NUM> comprises a single continuous microfluidic channel <NUM> having a similar shape as the first microfluidic channel <NUM>, but rotated by <NUM>°.

However, in examples, the electrode apparatus <NUM> can comprise any suitable number of separate second microfluidic channels <NUM>.

In the example of part B of <FIG> the ends of the conduits <NUM>, comprising electrically conductive material <NUM>, can also be seen.

In the example of <FIG> the conduits <NUM> are substantially regularly spaced. However, in examples, any suitable number and/or layout/configuration of conduits <NUM> can be used.

In the example of <FIG> the conduits/pins <NUM> are spaced substantially evenly or regularly along the length of the first and second microfluidic channels <NUM>, <NUM>.

The second microfluidic channel <NUM> is exposed to the external environment <NUM>. In the example of <FIG>, the second microfluidic channel <NUM> is located at the lower surface of the substrate <NUM> of the electrode apparatus <NUM> allowing the second microfluidic channel <NUM> to be exposed to the external environment <NUM>.

Part C of the example of <FIG> illustrate a cross-section through the electrode apparatus <NUM> taken at the dashed line indicated A-A in part B of <FIG>.

In part C of <FIG> a plurality of conduits <NUM> comprising conductive material <NUM> can be seen extending between the first microfluidic channel <NUM> and the second microfluidic channel <NUM>.

The ends of the conduits <NUM> are adjacent/proximate to the open, second microfluidic channel <NUM>.

Accordingly, the ends/end portions of the conduits <NUM> are in fluidic communication with the second microfluidic channel <NUM> which is exposed to the external environment <NUM>.

If the electrode apparatus <NUM> exposed to liquid <NUM> at the lower surface, the second microfluidic channel <NUM> will absorb the liquid <NUM> which can then act as an electrolyte layer in, for example, the use of the electrode apparatus <NUM>, providing a sustained lowimpedance interface to make low-noise biopotential measurements.

For example, if the electrode apparatus <NUM> is placed on the skin of a subject the second microfluidic channel <NUM> can absorb/wick sweat from the subject, the sweat acting as an electrolyte layer in between the electrically conductive conduits <NUM> of the electrode apparatus <NUM> and the skin.

An area <NUM> of the electrode apparatus <NUM> in part C of <FIG> is circled. The highlighted area <NUM> is enlarged in the example of <FIG>.

<FIG> illustrates an enlarged section of the electrode apparatus <NUM> illustrated in the example of <FIG>.

In part A of <FIG> the lower portion of the electrode apparatus <NUM> is shown.

In the illustrated example, three conduits/pins <NUM> can be seen adjacent to portions of the second microfluidic channel <NUM>.

In part A of <FIG> the second microfluidic channel <NUM> is empty.

In part B of <FIG>, the electrode apparatus <NUM> has been placed on the skin <NUM> of a subject.

In part B of <FIG> liquid <NUM> has been absorbed by the second microfluidic channel <NUM> from the skin <NUM> of the subject.

The absorbed liquid <NUM> acts as an electrolyte layer, between the electrically conductive conduits <NUM> of the electrode apparatus <NUM> and the skin, in biopotential measurement using the electrode apparatus <NUM>.

That is, in examples, the dry electrode apparatus <NUM> can be placed on the skin and the activation of the electrode apparatus <NUM> happens over a period of time in which sweat is absorbed into the second microfluidic channel(s) <NUM>.

In examples, the electrode apparatus <NUM> can be activated prior to placing it on the skin of a subject. For example, this can be done by introducing liquid <NUM> to the lower surface of the electrode apparatus <NUM> in any suitable way. In examples, a moist towel can be wiped on the lower surface and/or liquid sprayed on the bottom face of the electrode apparatus <NUM>. Then, the second microfluidic channel(s) <NUM> can absorb the liquid <NUM> by capillary action.

In examples, the electrode apparatus <NUM> illustrated in <FIG> can comprise one or more reservoirs <NUM> (not illustrated).

<FIG> illustrates examples of an electrode apparatus <NUM>. One or more elements of the electrode apparatus <NUM> illustrated in <FIG> can be as described in relation to <FIG>.

The examples of <FIG> show bottom views of the electrode apparatus <NUM>.

In part A of <FIG>, the second microfluidic channel <NUM> and the ends of the at least one conduit <NUM> comprising electrically conductive material <NUM> can be seen.

Part A of <FIG> is similar to part B of <FIG>, however in part A of <FIG> the second microfluidic channel <NUM> comprises a crosshatch pattern with fewer conduits <NUM> regularly spaced around the second microfluidic channel <NUM>.

Parts B and C of <FIG> illustrate two further examples of the second microfluidic channel <NUM>.

In the examples of parts B and C of <FIG> the second microfluidic channels <NUM> are designed to maximise surface coverage to enhance the liquid absorbing ability of the microfluidic channel network, which in turn can, for example, reduce noise during biopotential measurements.

In part B of <FIG> the second microfluidic channel <NUM> has a repeating meandering/serpentine pattern of an extended S.

In part C of <FIG> the second microfluidic channel <NUM> comprises a series of circles.

In parts B and C of <FIG> the conduits/pins <NUM> are not shown for the sake of clarity.

<FIG> illustrates an example of part of an electrode apparatus <NUM>. One or more elements of the electrode apparatus <NUM> can be as described in relation to <FIG>.

The examples illustrated in <FIG> show an enlarged section of an electrode apparatus <NUM>. The examples illustrated in <FIG> are similar to those illustrated in <FIG>.

However, in the examples of <FIG> the electrode apparatus <NUM> comprises two reservoirs <NUM>. In examples, any suitable number of reservoirs <NUM> can be used.

In the examples illustrated in <FIG> the reservoirs <NUM> are large-section microfluidic channels enclosed within the substrate <NUM>. Therefore, the reservoirs <NUM> are not directly exposed to the external environment <NUM>, but are in fluidic communication with the external environment <NUM> via the microfluidic channel <NUM>.

In part A of <FIG> liquid <NUM> is present in the second microfluidic channel <NUM>. The liquid <NUM> can be present as a result of application of liquid onto the electrode <NUM> and/or absorption/wicking of liquid/sweat from a subject's skin.

In part A of <FIG> the reservoirs <NUM> are empty.

In part B of <FIG> the liquid <NUM> flows into the reservoirs <NUM> by capillary action.

In part C of <FIG> the liquid <NUM> stored within the reservoirs <NUM> is supplied back to the second microfluidic channel <NUM> when the second microfluidic channel <NUM>, exposed to a dry environment for a time, is about to become depleted of liquid <NUM>. This ensures continuous presence of liquid <NUM> within the second microfluidic channel <NUM>, liquid <NUM> which acts as an electrolyte layer in between the electrically conductive conduits <NUM> and the external environment <NUM>, for example the skin <NUM> of the subject when the electrode apparatus <NUM> is placed on the subject <NUM>.

In examples, the reservoirs <NUM> have a plurality of connections to the second microfluidic channel <NUM> allowing liquid <NUM> to move freely throughout the network of reservoirs and second microfluidic channel(s) <NUM> without clogging and/or becoming airlocked.

<FIG> illustrates an example of a method <NUM>. In the example of <FIG>, the method <NUM> is a method of forming an electrode apparatus <NUM>.

In examples, the method <NUM> can be considered a method of fabricating and/or providing and/or manufacturing an electrode apparatus <NUM>.

Accordingly, where the term form, forming and so on is used it should be understood that this is intended to also include provide/providing, manufacture/manufacturing, fabricate/fabricating and so on.

In examples, the electrode apparatus <NUM> can be as described herein. For example, the electrode apparatus <NUM> can be as described in relation to at least one of <FIG>, <FIG>, <FIG>, <FIG> and/or <NUM>.

At block <NUM> a first microfluidic channel <NUM> comprising electrically conductive material <NUM> is formed.

In examples at least one first microfluidic channel <NUM> comprising electrically conductive material <NUM> is formed.

Any suitable method for forming a first microfluidic channel <NUM> comprising electrically conductive material <NUM> can be used. For example, a substrate <NUM> can be formed comprising a microfluidic channel <NUM> and electrically conductive material <NUM> introduced/provided to the first microfluidic channel <NUM>.

In examples any suitable method to form a first microfluidic channel <NUM> within the substrate <NUM> can be used. For example, any suitable layer-by-layer assembly approach can be used to form the substrate <NUM>. In examples, soft lithography fabrication techniques can be used to form the first microfluidic channel <NUM> in the corresponding layers of the substrate <NUM>.

In some examples, electrically conductive material <NUM> can be provided in the shape of the first microfluidic channel <NUM> and a substrate <NUM> provided around the electrically conductive material <NUM>.

Any suitable method for providing electrically conductive material <NUM> in the shape of the first microfluidic channel <NUM> can be used. In examples, the electrically conductive material <NUM> can be printed in the shape of the first microfluidic channel <NUM>, for example using any suitable three-dimensional printing technique.

In examples, any suitable method of forming the substrate <NUM> around the first microfluidic channel(s) <NUM> can be used. For example, the substrate can be cast around the existing channel(s) <NUM>.

At block <NUM> a second microfluidic channel <NUM> is formed, the second microfluidic channel exposed to the external environment and configured to absorb liquid <NUM> by capillary action.

In examples at least one second microfluidic channel <NUM> is formed, the at least one second microfluidic channel exposed to the external environment and configured to absorb liquid <NUM> by capillary action.

Any suitable method for forming a second microfluidic channel <NUM> can be used.

For example, a substrate <NUM> can be formed comprising the second microfluidic channel <NUM>.

In examples any suitable method to form the second microfluidic channel <NUM> within the substrate <NUM> can be used. For example, any suitable layer-by-layer assembly approach can be used to form the substrate <NUM>. In examples, soft lithography fabrication techniques can be used to form the second microfluidic channel <NUM> in the corresponding layers of the substrate <NUM>.

In some examples, removable mould material can be provided in the shape of the second microfluidic channel <NUM>, a substrate <NUM> provided around the material and then the material removed to leave empty the second microfluidic channel <NUM> in the substrate <NUM>.

Any suitable method for providing material in the shape of the second microfluidic channel <NUM> can be used. In examples, the removable mould material can be printed in the shape of the second microfluidic channel <NUM>, for example using any suitable three-dimensional printing technique.

In examples, any suitable method of forming the substrate <NUM> around the second microfluidic channel(s) <NUM> can be used. For example, the substrate can be cast around the existing channel(s) <NUM>.

In examples, any suitable method for removing removable mould material in the shape of the second microfluidic channel can be used. In examples, the removable mould material can be removed by dissolving the material using any suitable solvent.

At block <NUM> the at least one conduit <NUM> extending between the first microfluidic channel <NUM> and the second microfluidic channel <NUM> is formed, the at least one conduit comprising electrically conductive material <NUM>.

Any suitable method for forming the at least one conduit <NUM> extending between the first microfluidic channel <NUM> and the second microfluidic channel <NUM> and comprising electrically conductive material <NUM> can be used.

For example, any suitable method can be used to form the at least one conduit <NUM> in the corresponding layers of the substrate <NUM>.

For example, a substrate <NUM> can be formed comprising at least one conduit <NUM> and electrically conductive material <NUM> introduced/provided to the at least one conduit <NUM>.

In examples any suitable method to form the substrate <NUM> can be used. For example, any suitable layer-by-layer assembly approach can be used to form the substrate <NUM>. In examples, soft lithography fabrication techniques can be used.

Any suitable method for introducing the electrically conductive material <NUM> into the first microfluidic channel <NUM> and conduits <NUM> can be used.

For example, the electrically conductive material <NUM> can be squeegeed into the first microfluidic channel <NUM> and/or conduits <NUM>. Additionally or alternative, a vacuum pump or a pressure press can be used to push the electrically conductive material <NUM> into the apparatus.

In examples, electrically conductive material <NUM> can be provided in the shape of the at least one conduit <NUM> and a substrate <NUM> formed around the at least one conduit <NUM>.

Any suitable method for providing electrically conductive material <NUM> in the shape of the at least conduit <NUM> can be used. In examples, the electrically conductive material <NUM> can be printed in the shape of the at least one conduit <NUM>, for example using any suitable three-dimensional printing technique.

Accordingly, in examples, forming the first microfluidic channel <NUM> and forming the at least one conduit <NUM> comprise fabricating electrically conductive material <NUM> in the form of the first microfluidic channel <NUM> and at least one conduit <NUM>.

In examples, forming a second microfluidic channel <NUM> comprises fabricating removable mould material in the form of the second microfluidic channel <NUM>. In some examples the removable mould material comprises soluble mould material <NUM>.

In examples, the method <NUM> comprises forming a substrate around the formed first microfluidic channel <NUM>, second microfluidic channel <NUM> and at least one conduit <NUM>.

In examples, the method <NUM> comprises removing the removable mould material. In some examples the method <NUM> comprises dissolving soluble mould material by using any suitable solvent.

Accordingly, there is provided a method <NUM> comprising:.

In examples, there is provided a method <NUM> comprising fabricating electrically conductive material in the form of afirst microfluidic channel <NUM> and at least one conduit <NUM>, fabricating removable mould material in the form of a second microfluidic channel <NUM>, forming a substrate <NUM> around the formed first microfluidic channel <NUM>, second microfluidic channel <NUM> and at least one conduit <NUM> and removing the removable mould material.

In some examples, forming the first microfluidic channel <NUM>, the second microfluidic channel <NUM> and the at least one conduit <NUM> comprises forming a substrate <NUM> layer by layer to form the first microfluidic channel <NUM>, the second microfluidic channel <NUM> and at least one conduit <NUM>; and providing electrically conductive material <NUM> in the first microfluidic channel <NUM> and the at least one conduit <NUM>.

Accordingly, examples provide for a method that comprises forming a substrate <NUM> layer by layer to form a first microfluidic channel <NUM> and at least one conduit <NUM>, the at least one conduit <NUM> extending between the first microfluidic channel <NUM> and second microfluidic channel <NUM>, and introducing/providing electrically conductive material in the first microfluidic channel <NUM> and the at least one conduit <NUM>.

In examples, the method comprises forming at least one reservoir <NUM> configured to perform at least one of absorbing, by capillary action, liquid <NUM> from the second microfluidic channel <NUM> and supplying, by capillary action, liquid stored in the at least one reservoir <NUM> to the second microfluidic channel <NUM>.

In examples the method can be considered to comprise forming at least one reservoir <NUM> configured to absorb, by capillary action, liquid <NUM> from and/or supply liquid stored in the at least one reservoir <NUM> to the second microfluidic channel <NUM>.

Any suitable method for forming at least one reservoir <NUM> configured to perform at least one of absorbing, by capillary action, liquid <NUM> from the second microfluidic channel <NUM> and supplying, by capillary action, liquid stored in the reservoir <NUM> to the second microfluidic channel <NUM> can be used.

For example, a substrate <NUM> can be formed comprising the at least one reservoir <NUM>.

In examples, removable mould material can be provided in the form of the at least one reservoir <NUM> and a substrate <NUM> formed around the material with the material subsequently being removed.

In examples, one or more blocks of the method <NUM> can be altered or omitted. For example, the order of one or more actions can be altered and/or one or more actions omitted.

Additionally or alternatively one or more actions of method <NUM> can be combined. For example, blocks <NUM> and <NUM> can be combined.

<FIG> schematically illustrates an example of a method <NUM>. In the illustrated example, the method <NUM> is a method of forming an electrode apparatus <NUM>.

In the example, the electrode apparatus <NUM> can be as described herein.

The left side of <FIG> illustrates a cross-sectional view of the electrode apparatus <NUM> and the right side shows a perspective view.

Part A of <FIG> illustrates a layer-by-layer assembly of a first microfluidic channel <NUM>, a plurality of conduits <NUM> and an upper surface of the substrate <NUM>.

In the perspective view of part A of <FIG> the plane <NUM> is shown from which the cross-sectional view is taken.

Any suitable layer by layer assembly approach can be used to form the substrate <NUM>. For example, each layer can be fabricated using standard soft lithography fabric techniques.

In part B of <FIG> a support <NUM> is introduced at the bottom of the electrode apparatus <NUM> and electrically conductive material <NUM> provided in the first microfluidic channel <NUM> and conduits <NUM>.

In the illustrated example, the electrically conductive material <NUM> is introduced via an aperture in the upper surface of the substrate <NUM>.

For example, the electrically conductive material <NUM> can be squeegeed into the first microfluidic channel <NUM> and/or conduits <NUM>. Additionally or alternatively, a vacuum pump or a pressure press can be used to push the electrically conductive material <NUM> into the apparatus.

When the electrically conductive material <NUM> has been introduced into the first microfluidic channel <NUM> and conduits <NUM> the electrically conductive material <NUM> can, in examples, be solidified and/or cured and the support <NUM> at the bottom removed.

The result of this can be seen in part C of <FIG> in which the substrate <NUM> comprises a first microfluidic channel <NUM> and a plurality of conduits <NUM> comprising electrically conductive material <NUM>.

At part D of <FIG> a second microfluidic channel <NUM> is formed in a further layer and added to the formed apparatus to provide the electrode apparatus <NUM> comprising a first microfluidic channel <NUM>, second microfluidic channel <NUM> and a plurality of conduits <NUM>, the first microfluidic channel <NUM> and conduits <NUM> comprising electrically conductive material <NUM> as illustrated in part E of <FIG>.

As can be seen in <FIG> the second microfluidic channel <NUM> is adjacent to the ends of the conduits <NUM> and located at the bottom surface of the substrate <NUM> to allow the second microfluidic channel <NUM> to be exposed to the external environment <NUM>.

In examples, one or more blocks of the method <NUM> can be altered or omitted.

<FIG> illustrates an example of a substrate material <NUM>.

In the example of <FIG>, a substrate material <NUM> is located on the arm <NUM> of a subject.

In the illustrated example, the substrate <NUM> is a PDMS-substrate material which has natural reversible adhesion and can therefore be removed and placed on a subject's arm <NUM> repeatedly.

The substrate material <NUM> can be placed onto the skin without any additives or adhesives.

Accordingly, an electrode apparatus <NUM> formed in a substrate <NUM> illustrated in the example of <FIG> can be applied to the skin of a subject multiple times without any additives or adhesives while providing a high number of electrodes in the substrate material <NUM>.

The natural tendency of the material to adhere to the skin provides the benefit of better skin contact in contact-based biopotential measurements such as EMG, ECG, EEG and so on without, for example, the need for tightening straps.

In addition, PDMS, for example, is safe to use on the skin, can be sterilized and is resistant to bacterial growth.

<FIG> illustrates an example of a system <NUM>.

In the example of <FIG> the system <NUM> comprises an apparatus for making one or more biopotential measurements <NUM> and; at least one electrode apparatus <NUM> as described herein.

For example, the at least one electrode apparatus <NUM> can be as described in relation to one or more of <FIG>.

In examples, the at least one electrode apparatus <NUM> is placed on a subject's body to enable one or more biopotential measurements to be made.

Any suitable apparatus for making one or more biopotential measurements <NUM> can be used. For example, biopotential amplifier implementation and/or amplifier microchip system can be used.

In the example of <FIG>, information can be passed between the electrode apparatus <NUM> and the at least one apparatus for making one or more biopotential measurements <NUM> to allow one or more measurement to be made. This is illustrated by the doubleended arrow between the apparatus <NUM> and the electrode apparatus <NUM>.

The electrode apparatus <NUM> is operationally coupled to the apparatus <NUM> and any number of intervening elements can be present, including no intervening elements.

In examples, any suitable connection for transferring information between the apparatus <NUM> and the electrode apparatus <NUM> can be used.

In examples, the electrode apparatus <NUM> is connected to the apparatus <NUM> via one or more wires and/or wireless connections.

In examples, the system <NUM> can comprise any suitable number of electrode apparatus <NUM>. For example, the system <NUM> can comprise arrays of electrode apparatus <NUM> connected to the apparatus <NUM>.

This is illustrated in the example of <FIG> by the dashed box indicating one or more electrode apparatus <NUM>.

In examples, there is provided a wearable electronic device comprising one or more electrode apparatus <NUM> as described herein and/or one or more systems <NUM> as described herein.

In examples, the wearable electronic device comprises a device for fitness tracking and/or smart clothing.

Examples of the disclosure are advantageous. Examples provide for an electrode apparatus <NUM> that can self-adhere to skin, is not size limited and is comfortable to wear and is functionally sustainable to provide long-term continuous tracking of, for example, biopotential information.

Examples provide for an electrode apparatus <NUM> that does not require gel and adhesive layers but can perform as a sticky wet gel electrode.

Additionally or alternatively, examples provide for an electrode apparatus <NUM> that can be used in applications where the electrode needs to go on and come off the skin many times without leaving a residue.

Examples provide for an electrode apparatus <NUM> that can be integrated into smart garments to measure biopotential measurements.

In examples the electrode apparatus <NUM> can be washed and dried as is done for other garments.

In examples the electrode apparatus <NUM> can be used in electromyograms (EMG) and can be used for gesture recognition for controlling devices or for controlling things in virtual reality among other things.

The blocks illustrated in the <FIG> and <FIG> may represent steps in a method. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

The term 'a' or 'the' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a' or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of 'at least one' or 'one or more' may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer and exclusive meaning.

Claim 1:
An electrode apparatus (<NUM>) comprising:
a substrate (<NUM>), the substrate (<NUM>) comprising:
a first microfluidic channel (<NUM>);
a second microfluidic channel (<NUM>); and
at least one conduit (<NUM>) extending between the first microfluidic channel (<NUM>) and the second microfluidic channel (<NUM>);
wherein the first microfluidic channel (<NUM>) and the at least one conduit (<NUM>) comprise electrically conductive material (<NUM>), the at least one conduit (<NUM>) is configured to operate as an electrode or micro-electrode, and the first microfluidic channel (<NUM>) is configured to electrically interconnect one or more of the at least one conduit (<NUM>) and the first microfluidic channel (<NUM>) is configured to allow connection of the electrode apparatus (<NUM>) to another apparatus, and
wherein at least a portion of the second microfluidic channel (<NUM>) is at a surface of the substrate (<NUM>) and is exposed to the external environment (<NUM>) and is configured to absorb liquid by capillary action, and wherein the second microfluidic channel (<NUM>) is configured to retain absorbed liquid adjacent the at least one conduit (<NUM>) to act as an electrolyte for measurements made using the electrode apparatus (<NUM>).