WO2019119045A1

WO2019119045A1 - Anisotropically conductive material for use with a biological surface

Info

Publication number: WO2019119045A1
Application number: PCT/AU2018/051366
Authority: WO
Inventors: Warren Smith; Dusan Milojevic
Original assignee: Ti2 Medical Pty Ltd
Priority date: 2017-12-22
Filing date: 2018-12-20
Publication date: 2019-06-27
Also published as: AU2017279796A1

Abstract

An anisotropically electrically conductive material (1) to electrically interface an electrode with a portion of a biological surface is described, along with methods of forming the anisotropically electrically conductive material. The conductive material (1) includes a substrate (10) having first and second surfaces (11,12) on opposite sides, respectively, of the substrate (10); a first removable layer (17), the first removable (17) layer being located over the first surface (11); a plurality of discrete perforations (101), each perforation extending through the substrate (10) and the first removable layer (17); and a plurality of discrete electrically conductive elements (13), each conductive element formed in a respective one of the perforations (101) such as to extend through the substrate (10) and at least partially through the first removable layer (17).

Description

Anisotropically conductive material for use with a biological surface

Cross-Reference to Related Applications

[0001] The present application claims priority to Australian patent application no. 2017279796, filed 22 December 2017, the contents of which application is incorporated herein by reference in its entirety.

Technical Field

[0002] The present disclosure relates to the interfacing of an electrode with a biological surface of a subject for therapeutic, diagnostic and/or general body characterisation purposes.

Background

[0003] The detection of electrical signals from, and application of electrical signals to, a human or animal subject, is commonplace in a variety of therapeutic, diagnostic and general body characterisation fields.

[0004] Typically, electrical signals are applied to a subject and/or detected from a subject transcutaneously, using electrodes placed on or in close proximity to a biological surface of the subject, such as a skin surface. Transcutaneous electrical stimulation and bioelectrical impedance monitoring are two technologies, therapeutic and diagnostic, respectively, that use electrodes in this manner and which are becoming increasingly popular among medical practitioners. Other established techniques in this area include electrocardiography (ECG), electroencephalography (EEG), electromyography (EMG), targeted muscle reinnervation (TMR), electrocorticography, electrooculography, electroretinography, electroantennography, audiology and

electrocochleography.

[0005] Due to the complexity of biological and physiological electrical signals, the quality and reproducibility of measurement and/or stimulation between an electrode and tissue is highly dependent on the nature of the interface between the electrode and the skin surface (electrode/skin interface). In diagnostics, it is desirable to measure as accurately as possible a biological electrical signal while minimising non-biological variations, which can occur due to changes in the effective electrode area and noise from the electrode/skin interface. The measured signal is generally proportional in size to the effective electrode area. The size of the effective electrode area can differ from the size of the actual physical electrode area, the physical electrode area being defined by a surface of the electrode that is to contact the skin. In general, the degree of size difference between the physical electrode area and the effective electrode area will depend on the degree and quality of electrical contact between the contact surface and the skin surface. While it is not always necessary that the effective electrode area is the same as the physical electrode area, it can be highly desirable for the size of the effective electrode area to be easily reproducible to ensure measurement consistency.

[0006] In order to improve contact at the electrode/skin interface, an electrically conductive gel or solution is typically used as a compliant interfacing layer, primarily to minimise contact impedance and achieve a reproducible effective electrode area. Conductive gel is typically applied to the skin surface and/or electrode as free-running gel. Where a conductive solution (e.g. sodium chloride) is used, it can be soaked in an absorbent medium such as gauze that is placed on the skin prior to placement of an electrode thereon. The electrode is typically held in place relative to the skin surface by medical tape or elastic bands etc. Often, however, the area of contact of the gel or solution, which is an important determinant of contact impedance, will be undefined and inconsistent, and therefore tend to degrade any measurement or stimulation reproducibility. Thus, the use of conductive gel or solution when applying electrodes to skin includes a number of shortcomings, most notably through the high dependence on the skill of the user that must precisely apply the electrodes to the subject, and the lack of measurement or stimulation reproducibility. The use of conductive gel or solution can also be messy and awkward, requiring extensive cleaning of the subject’s skin or electrode after completion, potentially decreasing use or compliance.

[0007] In an attempt to address these shortcomings, a newer generation of electrode contains a self-adhesive conductive layer, typically in the form of a semi-rigid conductive gel/polymer layer that is situated on the electrode surface. The layer has adhesive properties to ensure that the electrode, once placed on the skin, can stay in contact with the skin surface. Electrodes configured in the manner are typically disposable.

[0008] While a step forward, electrodes with self-adhesive conductive layers also have shortcomings. For example, where the electrode is to be kept in contact with the skin surface for an extended period of time, e.g., for hours or even days, changes in composition of the conductive layer may occur, potentially affecting measurement or stimulation reproducibility. Moreover, the application of such electrodes to a skin surface for extended periods of time can cause discomfort to the subject, decreasing patient compliance. Additionally, some users can have allergic sensitization to the self-adhesive conductive layers. Another problem that has emerged is the difficulty and cost of manufacturing of these types of electrodes, as the self-adhesive conductive layers have to be deposited in a highly precise and accurate manner onto an electrode surface, requiring complex and expensive equipment.

[0009] Existing electrodes are designed, predominantly, to conform to relatively flat skin surfaces, featuring small or substantially no curvature. As the use of electrotherapeutic and electrodiagnostic techniques increases, however, demand has increased for electrodes that can interface with highly curved anatomical features, such as fingers, toes, joints, and various facial locations. The provision of a conductive gel/polymer layer on an electrode can add significantly to the rigidity of the electrode, reducing the ability for the electrode to flex and conform to curved skin surfaces.

[0010] Electrodes that employ gel or conductive solution are generally not suitable when used at or adjacent to compromised skin surfaces. Compromised skin surfaces can include wounds ranging from acute cuts and bruises, to more chronic conditions, such as diabetic ulcers, for example.

When the skin surface is compromised, the electrodes have limited benefits in most diagnostic and therapeutic systems. In general, conductive gels and solutions are not formulated to promote healing and any adhesiveness can cause further damage to fragile skin and cause pain to the subject upon removal.

[0011] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

Summary

[0012] In one aspect, the present disclosure provides an anisotropically electrically conductive material to electrically interface an electrode with a portion of a biological surface, the conductive material comprising:

a substrate having first and second surfaces on opposite sides, respectively, of the substrate;

a first removable layer, the first removable layer being located over the first surface; a plurality of discrete perforations, each perforation extending through the substrate and the first removable layer; and

a plurality of discrete electrically conductive elements, each conductive element formed in a respective one of the perforations such as to extend through the substrate and at least partially through the first removable layer.

[0013] The conductive material may further comprise a second removable layer, the second removable layer being located over the second surface. Each of the perforations may extend through the second removable layer in addition to extending through the substrate and the first removable layer.

[0014] In one aspect, there is provided a method of forming an anisotropically electrically conductive material to electrically interface an electrode with a portion of a biological surface, the method comprising:

providing a substrate having first and second surfaces on opposite sides, respectively, of the substrate, a first removable layer being located over the first surface, a plurality of perforations extending through the substrate and the first removable layer;

applying a conductive substance to the plurality of perforations to form a plurality of discrete electrically conductive elements, wherein the applying is such that, for each perforation, the conductive element extends through the substrate and at least partially through the first removable layer.

[0015] A second removable layer may be located over the second surface and each of the perforations may additionally extend through the second removable layer. The applying of the conductive substance may be such that each conductive element additionally extends at least partially through the second removable layer.

[0016] In the above aspects, each of the perforations may define openings in the substrate, the first removable layer and the second removable layer if present. When conductive substance is applied to the plurality of perforations, the conductive substance can substantially fill, for each perforation, the opening in the substrate, the opening in the first removable layer and the opening in the second removable layer, if present.

[0017] Related to this, in accordance with one aspect, the present disclosure provides a method of forming an anisotropically electrically conductive material to electrically interface an electrode with a portion of a biological surface, the method comprising:

providing a substrate having first and second surfaces on opposite sides, respectively, of the substrate, a first removable layer being located on the first surface, a plurality of perforations extending through the substrate and the first removable layer such that each perforation defines an opening in the substrate and an opening in the first layer;

applying a conductive substance to the plurality of perforations to form a plurality of discrete electrically conductive elements, wherein the applying is such that, for each perforation, the conductive substance substantially fills the opening in the substrate and the opening in the first layer.

[0018] In this aspect, again a second removable layer may be located over the second surface and each of the perforations may additionally extend through the second removable layer and may define an opening in the second removable layer. The applying of the conductive substance may be such that, for each perforation, the conductive substance substantially fills the opening in the second removable layer in addition to the opening in the substrate and the opening in the first removable layer.

[0019] In any of the aspects described herein, the substantial filling of the openings in the substrate and the first and second layers may comprise filling at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the volume of each opening. The substantial filling may be such that there is a continuous connection between the conductive substance between each opening of the perforation.

[0020] In any aspects described herein, the conductive material may comprise one or more adhesive portions such as an adhesive layer or element. For example, a first adhesive portion such as a first adhesive layer may be provided between the first surface of the substrate and the first removable layer. Additionally or alternatively, a second adhesive portion such as a second adhesive layer may be provided between the second surface of the substrate and the second removable layer. Each perforation may extend through the adhesive layer(s) in addition to extending through the substrate and the removable layer(s). Each perforation may define an opening in the adhesive layer(s) in addition to the substrate and the removable layer(s). The adhesive layers may be used to releasably adhere the first and/or second removable layers to the substrate. Nevertheless, adhesion between the first and/or second removable layers to the substrate may be achieved by other means, e.g. via van der Walls forces or otherwise. Additionally or alternatively, the adhesive layers may be used to releasably adhere the conductive material to the biological surface and/or to the electrode, e.g., after removal of one or both of the first and second removable layers.

[0021] In any of the aspects described herein, more than one first removable layer may be located over the first surface of the substrate and/or more than one second removable layer may be located over the second surface of the substrate.

[0022] In any of the aspects described herein, the perforations may provide moulds for forming of the conductive elements. The conductive substance may be a fluid, paste or gel when applied to the plurality of perforations and may solidify after being applied to the perforations, e.g. after filling the openings in the substrate, in the first layer and in the second layer if present.

[0023] A first end of each of the conductive elements may align with an outer surface of the first removable layer and a second opposite end of each of the conductive elements may align with the second surface of the substrate or, if the second removable layer is present, with the outer surface of the second removable layer. Alternatively, the first end of each of the conductive elements may locate between the first surface of the substrate and the outer surface of the first removable layer and the second end of each of the conductive elements may locate between the second surface of the substrate and the outer surface of the second removable layer.

[0024] Once the conductive elements are formed in the conductive material, one or both of the first and second removable layers may be removed. [0025] The first and second removable layers may have a variety of different functions. One function of the first and second removable layers may be to assist with the formation of conductive elements that have first and second ends that protrude from the first and second surfaces, respectively, of the substrate. As indicated, openings in the removable layer(s) may act, in concert with an opening in the substrate (and openings in adhesive portion(s) if present), as moulds for forming the conductive elements. The removable layer(s) can be retained over the substrate while forming the conductive elements. However, the removable layer(s) can be removed subsequently, exposing the first and/or second ends of the substrate as they protrude from the substrate or from other layers such as adhesive layers located over the substrate if present. By being exposed at and protruding from the substrate or other layers over the substrate, the first and second ends can achieve better electrical contact with a biological or electrode surface, e.g. in comparison to an arrangement where the first and second ends are aligned with or even stop short of the first and second surfaces of the substrate or other layers located over the substrate.

[0026] Nevertheless, after assisting with formation of the conductive elements, one or both of the first and second removable layers may be kept in position over the respective first and second surfaces to perform additional functions. For example, one or both of the first and second removable layers can act as protective layers or masks that expose only ends of the conductive elements while covering the surfaces of the substrates and any adhesive portions or other layers located thereon. As such, the first and second removable layers can prevent these underlying portions of the material from being contaminated with conductive substances that could potentially degrade material anisotropy following the formation of the conductive elements. Such

contamination could occur during stacking, rolling or processing of the conductive material, for example. The conductive material can otherwise be vulnerable to contamination, not least when portions underlying the removable layers have adhesive character. When the removable layers are removed, any potentially contaminating substances can be removed with the layers, leaving behind a clean, anisotropic underlying structure ready for contact with a biological surface and electrode, for example.

[0027] In some embodiments, it may be desirable to contact one or both ends of the conductive elements with a further substance which promotes interfacial conductance, such as water, a conductive liquid or gel or conductive adhesive, for example, which substance may coat one or both of the ends of the conductive elements and/or be absorbed into the conductive elements, dependent on their material properties. One or both of the first and second removable layers can prevent underlying portions of the material from being contacted by that further conductive substance, which could potentially degrade material anisotropy. Moreover, in cases where the underlying portions have adhesive character, the removable layers may prevent contact of a further conductive substance that could adversely affect the adhesive character. When the removable layers are removed, any of the further conductive substance that is not coating or absorbed into the conductive elements, and which might otherwise cause electrical connection between adjacent conductive elements, can be removed with the layers, leaving behind an anisotropic underlying structure ready for contact with a biological surface and electrode, for example.

[0028] In use, the first surface of the substrate, or any adhesive portion located over the first surface of the substrate, may be located in close proximity to a biological surface such that the protruding first ends of the discrete conductive elements electrically contact the biological surface. The biological surface may be a tissue surface such as a skin surface, including the epidermis, dermis or hypodermis, for example, although the conductive material may be used in conjunction with any biological surface of a subject, including surfaces of other tissues and/or organs such as bone, heart, liver, kidneys, lungs, stomach, eyes, brain, bladder, prostate, pancreas, or thyroid. Moreover, the biological surface may be a surface of tissue and/or of an organ that has been excised from a body, e.g., for transplant, research purposes or otherwise. The first surface of the substrate may contact, or at least face, the biological surface. The second surface of the substrate, or any adhesive portion located over the second surface of the substrate, may be located in close proximity to an electrode such that the second ends of a subset of the plurality of discrete conductive elements, which may also protrude, electrically contact simultaneously a contact surface of the electrode.

[0029] An electrode may be positioned anywhere on or over the second surface of the substrate such that its contact surface electrically contacts the second ends of conductive elements of different subsets of the plurality of discrete conductive elements. For example, the electrode may contact a first subset of the plurality of discrete conductive elements and then may be moved to contact a second subset of the plurality of discrete conductive elements. Each subset of the discrete conductive elements may be defined, generally, by the area across which the contact surface of the electrode extends and will generally include multiple discrete conductive elements. For example, each subset may comprise 2 or more conductive elements, 3 or more conductive elements, 5 or more conductive elements, 10 or more conductive elements, 20 or more conductive elements, 50 or more conductive elements, 100 or more conductive elements or otherwise. By contacting the second ends of any subset of conductive elements, the electrode electrically interfaces with the portion of the biological surface that is in electrical contact with the first ends of that subset of conductive elements. Due to the anisotropicity of the conductive material, there may be substantially no electrical interfacing between the electrode and the rest of the biological surface.

[0030] The perforations may be distributed across the substrate in an array, e.g. in a substantially uniform array. The perforations may be provided in a regular array. The array may include equidistant rows and columns across the substrate, offset rows and columns or otherwise.

Nevertheless, alternative distributions of perforations are possible such as rectilinear arrays, curvilinear arrays, hexagonal arrays or otherwise. In some embodiments, the perforations may be in a line, or arranged in different shapes and patterns, e.g. in clusters of perforations such as circular clusters of perforations.

[0031] The perforations may have a shape, in a plane perpendicular to their direction of extension through the conductive material, that is circular, square, triangular, irregular or otherwise. The shape of the perforations may be substantially the same through the entire depth of the conductive material.

[0032] The perforations may extend in a direction that is perpendicular to the first and/or second surfaces of the substrate or that is at an angle to the first and/or second surfaces of the substrate.

The perforations may extend in a straight line.

[0033] The perforations may have an aspect ratio, i.e. a total perforation depth through the different layers of the conductive material to perforation diameter in the range of 1.0 to 4.0, e.g. about 2.0, for example.

[0034] The spacing between perforations (inter-perforation spacing) may be selected dependent on factors such as the desired density, conductance and/or lateral resistance of the conductive elements and the mechanical strength of conductive material. Too high a density may lead to the conductive material substrate tearing during or after application to the biological surface.

[0035] The perforations may be formed by any one or more of laser perforation, ultrasonic perforation, cold or hot needle perforation, electrostatic discharge perforation, water jet perforation, drilling or otherwise.

[0036] The conductive substance applied to the perforations and the resultant conductive elements may comprise conductive matter such as carbon, graphite, graphene, silver, gold, copper, carbon nanotubes, conducting polymers, polymer electrolytes, salts and/or combinations thereof. The conductive matter may in some embodiments be combined with carrier matter such polymers, solvents (e.g. water, organic solvents or otherwise) or otherwise. The carrier matter may optimise physical properties of the conductive substance when applied to the perforations and/or optimise the physical properties of the conductive elements formed in the perforations. The carrier matter may serves as a binder, water absorber, adhesion promoter, flexibility enhancer or otherwise. The carrier matter may ensure that the conductive substance can be applied more easily to the perforations, e.g., so that it can enter and fill the openings provided by the perforations, for example. The carrier matter may ensure that the conductive substance will adhere to the substrate, for example. The conductive substance may be homogeneous or heterogeneous. The conductive substance may be biocompatible.

[0037] The conductive substance as applied to the plurality of perforations may be an ink. The ink may comprise carrier matter comprising a solvent and may comprise conductive matter such as carbon, graphite, graphene, silver, gold, copper, carbon nanotubes, conducting polymers, polymer electrolytes, salts, and/or combinations thereof as indicated above. In some embodiments, however, solvent-free inks may be used, which may comprise UV or electron-beam curable carrier matter, for example._The conductive substance may be applied as a solid, liquid, gel or paste, e.g. depending on the presence and type of any carrier matter combined with the conductive matter, for example. In some embodiments, ink formulations may be either a single formulation or a two-part formulation that reacts upon mixing.

[0038] In some embodiments, the properties of the conductive substance, e.g. the ink formulation, and/or the properties of the substrate, first removable layer and/or second removable layer, may be selected to ensure an adhesion strength of the conductive elements to the substrate that is greater than an adhesion strength of the conductive elements to the first and/or second removable layers.

[0039] After application to the perforations, the conductive substance may be subjected to a drying process (e.g. thermal, vacuum or air flow drying treatment) or a curing process (e.g.

thermal, UV, electron beam curing) or otherwise. If thermal treatment is used, temperatures may be selected to avoid damaging parts of the conductive material, including any adhesive portions that may be provided.

[0040] As applied to the perforations, the conductive substance may completely fill the perforations. When the conductive substance is subject to subsequent processing to form the final conductive elements, however, the size of the conductive elements may change. For example, if the conductive substance comprises a solvent, the solvent may evaporate following thermal treatment, causing the conductive elements to reduce in size, e.g. so that they do not completely fill the perforations. Nevertheless, the conductive elements can still have a sufficient length to extend through the substrate and at least partially through the first layer and through the second layer if present.

[0041] The conductive substance may be applied to the perforations by any one or more of: screen printing, doctor blading, inkjet printing, pad printing, flexographic printing, gravure printing spraying, dip coating or otherwise. [0042] In some embodiments, it may be preferable to apply the conductive substance to the side from which perforations are formed, e.g. the side from which a laser or other tool is used to bore into the material to form the perforations.

[0043] The plurality of conductive elements may be distributed across the substrate in an array, e.g. in a substantially uniform array. The conductive elements may be provided in a regular array. The array may include equidistant rows and columns across the substrate, offset rows and columns or otherwise. Nevertheless, alternative distributions of perforations are possible such as rectilinear arrays, curvilinear arrays, hexagonal arrays or otherwise. In some embodiments, the conductive elements may be in a line, or arranged in different shapes and patterns, e.g. in clusters of conductive such as circular clusters of conductive elements.

[0044] The conductive elements may have a shape, in a plane perpendicular to their direction of extension through the conductive material, that is circular, square, triangular, irregular or otherwise.

[0045] The conductive elements may extend in a direction that is perpendicular to the first and/or second surfaces of the substrate or that is at an angle to the first and/or second surfaces of the substrate.

[0046] The conductive elements may take the form of pillars or pylons, e.g. micro-pillars or micro-pylons. The conductive elements may be monolithic.

[0047] The conductive elements may have an aspect ratio, i.e. a total conductive element depth through the different layers of the conductive material to conductive element diameter in the range of 1.0 to 4.0, e.g. about 2.0, for example.

[0048] The spacing between conductive elements may be selected dependent on factors such as the desired density, conductance and/or lateral resistance of the conductive elements and the mechanical strength of conductive material. Too high a density may lead to the conductive material substrate tearing during or after application to the biological surface.

[0049] At the surface of the substrate, the distance between adjacent conductive elements (e.g. between adjacent first or adjacent second ends of conductive elements) may be greater or less than a maximum dimension of the conductive elements across the surface of the substrate. At least where the distance between adjacent conductive elements is less than the maximum dimension of the conductive elements, a higher density array of conductive elements may be provided.

[0050] By employing a substantially uniform array of substantially identical conductive elements, conductance of the conductive material may be substantially constant over any area comprising a plurality of the conductive elements. Nevertheless, substantially constant conductance may still be achieved, particularly over larger areas, even where an irregular array and/or non-identical conductive elements are employed. Moreover, in some embodiments it may be desirable to vary the conductive properties of the conductive material over different areas of the conductive material, depending on its desired use.

[0051] It may be desirable to reduce the occurrence of electrical cross-talk or short-circuiting between neighbouring conductive elements, particularly when pressure is applied to protruding ends of the conductive elements that could cause deformation of the ends of the conductive elements. A reduction may be achieved by ensuring that the height of the protruding ends of the conductive elements, relative to the adjacent surfaces of the substrate, is less than half of the spacing between neighbouring conductive elements.

[0052] So that multiple discrete conductive elements are available for contact with an electrode contact surface having a variety of different sizes, a relatively large number of conductive elements may be provided, the conductive elements may be relatively small in comparison to the electrode contact surface and the conductive elements may have a relatively high density distribution across the conductive material.

[0053] For example, the total number of conductive elements distributed across the conductive material may be greater than 10, greater than 20, greater than 50, greater than 100, greater than 500, or greater than 1000. For example, the density of conductive elements across the conductive material may be at least 1 per cm², at least 2 per cm², at least 5 per cm², at least 10 per cm² _, at least 50 per cm _, at least 100 per cm _, at least 200 per cm _, at least 300 per cm _, at least 400 per cm’ at least 500 per cm² _, at least 750 per cm² _, or at least 1000 per cm². For example, the area of each conductive element at its first or second end, in a plane substantially parallel to the first and/or second surfaces of the substrate, may be less than 0.5 cm², less than 0.25 cm², less than 0.1 cm² or less than 0.05 cm², less than 0.01 cm², less than 0.001 cm², or less than 0.0001 cm². For example, the maximum distances between neighbouring conductive elements may be less than 1.0 cm, less than 0.75 cm, less than 0.5 cm, less than 0.25 cm, less than 0.1 cm, less than 0.05cm less than 0.01 cm, or less than 0.001 cm. In some embodiments, therefore, conductive elements may be distributed in a macroscopic or a microscopic scale. For example, when distributed in a microscopic scale, the surface area of each conductive element at its first or second end, in a plane substantially parallel to the first and second surfaces of the substrate, may be less than O.OOOlcm². Moreover, the maximum distances between the ends of neighbouring conductive elements may be less than 0. lcm or 0.2cm or otherwise.

[0054] The substrate, and the conductive material comprising the substrate, may be flexible. The conductive material may therefore be bendable to follow the curvature of a biological surface or other surface to which it is to make contact. The conductive material may be configured so that, upon bending during normal use, electrical independence of the discrete conductive elements may still be maintained (i.e. the discrete conductive elements may not come into electrical contact with each other).

[0055] The substrate may comprise a single layer of material or multiple layers of material, e.g. multiple layers of material stacked on top of each other. The substrate may comprise a non- conductive (i.e. insulating) material such as nylon, polyurethane, polyester, silicones,

polyvinylalcohol, polyimide, natural polymer such as chitosan, foam such as polyurethane foam, natural polysaccharide alginate foam, hydrocolloids such as those formed from carboxymethyl- cellulose, alginate and elastomer, pre-swollen hydrogel of collagen or elastin, hyaluronic acid, or synthetic hydrogels of cross-linked poly( vinyl alcohol), polyvinylpyrrolidone or methacrylate. The substrate may be hydrophobic or hydrophilic. The substrate may be biodegradable. The substrate may be formed of medical grade material. The substrate may be at least partially transparent or translucent, e.g. so that target sites on the biological surface for electrical interfacing can be identified through the substrate, or opaque. The substrate may be coloured or clear. The substrate may be substantially flat or it can be have a three-dimensional shape, e.g. a curved or otherwise structured shape. The three-dimensional shape may be pre-formed in the substrate. The substrate may have a thickness of between 5pm and 2mm or otherwise.

[0056] The first and/or second removable layer may comprise a film of material, e.g. a waterproof film. The first and/or second removably layers may comprise polyethylene, polypropylene, polyester, polystyrene, silicone, fluoropolymer, non wovens, polyethylene -coated kraft paper, glassine, clay-coated kraft paper or otherwise.

[0057] The first and/or second removable layer may have a thickness of between 3 pm and 500 pm, for example. The thickness may be selected depending on the desired degree of protrusion of the conductive elements. Where protrusion of a conductive element is not desired, a removable layer may be omitted, for example.

[0058] The adhesive portions, such as the adhesive layers, may comprise medically approved adhesive suitable for short or long term contact with a biological surface. The strength of the adhesive may be selected based on the particular intended application, the target biological surface site, or the intended length of use, for example. Advanced medically-approved adhesive layers which become adhesive (or non-adhesive) upon application of a selected“trigger” such as moisture or biological surface temperature may also be used. The adhesive portions or layers may comprise acrylic, hydrocolloid, rubber, hydrogel, polyurethane, and/or silicone (e.g. soft silicone), for example. Each adhesive layer may have a thickness in the range of lp to 200pm, for example. [0059] In aspects disclosed herein, the conductive material may provide an anisotropic conductive medium having good electrical conductance through the thickness of the material, i.e. in a direction substantially perpendicular to the first and second surfaces, but little or no electrical conductance laterally, i.e. in a direction parallel to the first and second surfaces.

[0060] Different subsets of the conductive elements may be selected as desired by varying the position of the electrode at the second surface and/or by varying the shape or size of the electrode contact surface. Different subsets of the conductive elements may be selected in order to electrically‘probe’ different parts of the biological surface, e.g. to enable surface potential monitoring (e.g. ECG monitoring) and/or bioimpedance monitoring and/or to apply electro stimulation across different regions of tissue. Moreover, the conductive material may be used with multiple electrodes simultaneously, each electrode being connected to a different, discrete subset of the conductive elements. For a single electrode it may be desirable that, wherever the electrode is located with respect to the second surface of the substrate, its contact surface will electrically contact a subset of the plurality of conductive elements that contains substantially the same number of conductive elements. This may be desirable particularly where the conductive elements have substantially uniform sizes and shapes and therefore substantially the same electrical properties. Whether or not all of the conductive elements have substantially uniform sizes and shapes, the conductivity of the conductive material may be substantially constant over any area comprising multiple conductive elements.

[0061] In addition to or as an alternative to varying the position of the electrode at the second surface and varying the shape or size of the electrode contact surface, different subsets of conductive elements may also be selected by provision of a non-conductive, insulating layer, providing a mask element between the electrode and the conductive material. The mask element may locate between a portion of the electrode contact surface and the second surface of the conductive material, preventing electrical contact between the electrode and some of the conductive elements over which the electrode is located. The mask element may comprise a sheet of non-conductive material that includes, for example, a hole or recess that defines the desired area of electrical contact between the electrode contact surface and the second surface of the conductive material. The mask element may comprise adhesive to attach the mask element to the second surface of the conductive material or to the electrode contact surface, or may be a mobile mask element that is designed to rest against rather than be attached to the electrode or conductive material.

[0062] The conductive material may be used in addition to, or more preferably as replacement for, a conductive gel or conductive solution as an interface between an electrode and a biological surface. The conductive material may maintain low contact impedances and introduce high reproducibility in the quality of electrical contact and therefore measurement or stimulation values. The conductive material may provide a hygienic barrier between the biological surface and the electrode and associated electrical componentry. The conductive material, including the substrate thereof, may be substantially non-porous to prevent propagation of biological material such as body surface exudates and bacteria between the electrode and the biological surface. To achieve non porosity, the conductive elements may be sealingly engaged with the substrate as they extend through the substrate. The conductive material may provide a non-diffusive barrier. Moreover, the conductive material may be movable relative to the biological surface, reducing the possibility of irritation to the subject occurring in comparison to an approach where the conductive material is adhered directly to the biological surface, for example. Despite this, in some embodiments, the conductive material may be adapted to adhere to the biological surface as discussed above.

[0063] Through use of multiple conductive elements to transfer electrical signals between the electrode and the biological surface, a signal-to-noise ratio may be improved. Each conductive element carries an individual signal component and an individual noise component. The overall signal transferred is a sum of the individual signals components, which are generally in phase with each other such that constructive interference between the individual signal components can occur. Similarly, the overall noise transferred is a sum of the individual noise components. However, since the individual noise components are random in nature, destructive interference between the individual noise components can occur. Therefore, the overall signal amplitude may be increased in comparison to the overall noise signal, improving the signal-to-noise ratio.

[0064] The conductive material may provide, or may be comprised in, a medical interface such as a medical dressing. The medical dressing may be a pad, a compress, bandage or tape (including kinesiology tape) configured for application to tissue to promote healing of tissue, to protect the tissue from harm, to restrict or control movement of the tissue, and/or to generally allow monitoring of the tissue. The conductive material may be held in place by, or may be comprised in, a bandage, plaster, belt or band (e.g. a headband or wristband), for example. Additionally or alternatively, the conductive material may be held in place using adhesive tape, and/or through use of an adhesive layer that may form part of the dressing. The conductive material may provide an electrically conductive path to tissue for the purpose of monitoring the tissue, electrostimulation of the tissue or otherwise. The electrically conductive path may extend through a thickness of the conductive material. The conductive material may provide for, or enable contact with, an electrode. The tissue at which the conductive material, e.g. in the form of a medical dressing, may be applied may include a wound or other types of tissue damage and/or imperfections. For example, the conductive material may be applied at or in close proximity to tissue including a cut, burn, surgical wound, chronic wound, abrasion, abscess, carbuncle, blister, wart, rash, scar, infection, bedsore, disease, muscle tear, ligament tear or otherwise.

[0065] The conductive material may be formed by processing of a pre-existing product such as a medical dressing, e.g. a pad, a compress, bandage, plaster, patch or tape. The pre-existing product may include a substrate, a first layer and optionally a second layer as described above, for example. In this regard, medical dressings commonly include a substrate and a removable layer located over an adhesive layer on one surface of the substrate and in some instances a second removable layer located over a second surface of the substrate. Thus processing of the pre-existing product may include forming perforations in the product, including in the first and optionally second removable layers of the product, and applying a conductive substance to the perforations to form conductive elements in accordance with discussions above. The pre-existing product may be processed in various forms, e.g. as strips, sheets or rolls of material, etc.

[0066] Conductive substance may be applied to the perforations via one or both sides of the multi-layer construct. Where first and second layers are provided that have a different

configuration it may be preferable to apply the conductive material via one of the first and second layers and not the other. In some embodiments, it may be preferable to apply the conductive substance to the side from which perforations are formed, e.g. the side from which a laser or other tool is used to bore into the material to form the perforations.

[0067] In discussions above, an anisotropically conductive material is described relative to which an electrode can be moved in order to electrically interface with different portions of a biological surface over which the conductive material is placed. However, the conductive material may be adapted to be used in a fixed relationship relative to one or more electrodes. The conductive material may form part of an electrode device. For example, to form an electrode device, one or more conductive members, e.g. one or more conductive layers, may be introduced in a fixed relationship with the conductive material, and which electrically contact second ends of a plurality of the conductive elements.

[0068] A single conductive member may be provided. The single conductive member may be connected to second ends of some or all of the plurality of conductive elements, for example. Alternatively, multiple conductive members may be provided, each conductive member being connected to second ends of different subsets of the plurality of conductive elements.

[0069] Each conductive member may be in the form of a conductive layer that electrically contacts second ends of the conductive elements. Each conductive member may provide an electrode, which is fixed relative to the substrate, and which is wired to enable connection with external electrical componentry such as monitoring or electrostimulation apparatus and/or which includes a contact portion that can be releasably electrically connected to external electrical componentry as desired. The contact portion may be in the form of a tab. The tab may extend beyond an edge of the substrate, for example, or may be located over the substrate, e.g. at an end of the substrate or other layer located over the substrate. Other contact portions are possible such as a stud or a pre -wired contact.

[0070] In some embodiments, at least two conductive members, e.g. at least two electrodes, may be electrically connected to different subsets of the conductive elements. In some embodiments, four conductive members, e.g. four electrodes, may be electrically connected to different subsets of the conductive elements.

[0071] The conductive material may be formed so that conductive elements which are contacted by the conductive members are provided only. In other words, there may be no conductive elements that are not contacted by at least one of the conductive members. Depending on the size and positioning of the conductive members across the conductive material, this may mean that a non-uniform distribution of conductive elements is provided across the substrate. For example, there may be a plurality of clusters of conductive elements, each cluster being contacted by a respective conductive member. There may be no conductive elements provided between the clusters of conductive elements.

[0072] Alternatively, the conductive material may be formed with a uniform and/or wide distribution of conductive elements, with only some of the conductive elements being contacted by the conductive members.

[0073] An insulating layer may be provided over the conductive members and/or a top layer of the conductive material from which the second ends of the conductive elements protrude, reducing the risk of any short-circuiting occurring between the conductive members and/or the conductive elements, e.g. by preventing contact with an external conductor such as a finger or hand or an item such as scissors. The insulating layer may also provide protection against damage to these or other components of the electrode device.

[0074] The conductive material used in the electrode device may be formed in accordance with conductive material described in preceding aspects. For example, the conductive material may include first and/or second removable layers located over first and second sides of the substrate, respectively. Additionally or alternatively, the conductive material may include first and/or second adhesive elements or layers located over the first and second sides of the substrate, e.g. between the substrate and the first and/or second removable layers. The first and/or second removable layers may be removed prior to contact being made between the conductive members and the conductive elements. For example, the second removable layer may be removed to expose protruding second ends of the conductive elements which are subsequently contacted by the conductive members. Nevertheless, contact may be made between the second ends of the conductive elements that are not arranged to protrude.

[0075] When the electrode device includes adhesive elements or layers, the adhesive may be used to adhere the electrode device to the biological surface.

[0076] In some embodiments, anisotropically conductive material or an electrode device comprising the anisotropically conductive material as described herein, may be comprised in a garment. The garment may be any type of garment suitable to extend over a portion of a subject’s body in a close -fit manner. By extending in a close -fit manner, the conductive material may rest on a biological surface, particularly a skin surface, enabling good electrical contact to be achieved with the skin surface. Suitable garments may include, for example, gloves, socks (including compression socks), hats, helmets, wrist bands, head bands, arm bands, ankle straps, shoulder straps, belts or otherwise.

[0077] The garment may be formed entirely of the conductive material or the conductive material may form one of multiple portions, e.g. layers, of the garment. For example, the conductive material may provide a liner of the garment, acting as a hygienic barrier between a main body of the garment and the skin surface. In this example, the main body (e.g. an outer layer of the garment) may include one or more electrodes integrated therein, the electrodes being adapted to electrically interface with the skin surface through the liner comprising the conductive material.

[0078] The conductive material or electrode device of the present disclosure may have a wide variety of applications where electrical signals are to be applied to and/or detected from a subject transcutaneously. For example, applications may include bioimpedance monitoring,

electrostimulation, electrocardiography (ECG), electroencephalography (EEG), electromyography (EMG), targeted muscle reinnervation (TMR), electrocorticography, electrooculography, electroretinography, electroantennography, audiology and electrocochleography.

[0079] The construction of the conductive material or electrode device may reduce a dependence on the skill of the person applying electrodes to a biological surface to achieve high quality electrode contact and measurement reproducibility. The construction may also reduce any mess or awkwardness associated with the application of electrodes to a biological surface.

[0080] The conductive material or electrode device may be suitable for use in a wide variety of conditions, including where an electrode is to be interfaced with a biological surface for extended periods of time, e.g., for longer than a few minutes, such as hours or even one or more days.

Moreover, the conductive material or electrode device may be sufficiently flexible to conform to both flat anatomical features and curved anatomical features, such as fingers, toes, joints, and various facial locations, for example. Further, the conductive material or electrode device may be used in contact or close proximity with compromised skin or other biological surfaces, since it may provide a relatively soft, supple, dry and inert contact surface. For example, the conductive material or electrode device may be used in contact with or in close proximity to wounds, ranging from acute cuts and bruises, to more chronic conditions, such as diabetic ulcers.

[0081] The conductive material or electrode device may be easy to position on the biological surface. The quality of the electrical contact may be high, contact impedances may be low, and measurement and stimulation values may be consistent and reproducible. The conductive material or electrode device may have simple, reliable construction, providing for ease of manufacture at reduced costs. Reduced costs may allow the conductive material to be used as a disposable item. However, the conductive material or electrode device may also be suitable for washing, enabling reuse while maintaining sterility.

[0082] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0083] Throughout this specification, unless indicated otherwise, the word“conductive” is used to refer to material that is electrically conductive. Similarly, the words“non-conductive” and “insulating” are used to refer to material that is substantially not electrically conductive.

Brief Description of Drawings

[0084] By way of example only, embodiments of the present disclosure are now described with reference to accompanying drawings in which

[0085] Fig. la and lb show oblique and cross-sectional views, respectively, of conductive material according to an embodiment of the present disclosure;

[0086] Fig. 2a and 2b show oblique and cross-sectional views, respectively, of the conductive material of Figs la and lb having removable layers located thereon according to an embodiment of the present disclosure;

[0087] Figs. 3a and 3b show oblique and cross-sectional views, respectively of a multilayer structure used in the formation of conductive material according to an embodiment of the present disclosure;

[0088] Figs. 4a and 4b show oblique and cross-sectional views, respectively, of the multilayer structure of Figs. 3a and 3b with perforations formed therein; [0089] Figs. 5a and 5b show oblique and cross-sectional views, respectively, of the multilayer structure of Figs. 4a and 4b with conductive elements formed in the perforations;

[0090] Figs. 6a and 6b show oblique and cross-sectional views, respectively, of the multilayer structure of Figs. 5a and 5b with removable layers partially removed;

[0091] Figs. 7a and 7b show oblique and cross-sectional views, respectively, of the multilayer structure of Figs. 5a and 5b with removable layers completely removed;

[0092] Figs. 8a and 8b show cross-sectional views of conductive material according to the present disclosure with, respectively, a contaminant and a further conductive substance located thereon;

[0093] Fig. 9a shows a cross-sectional view of conductive material according to an embodiment of the present disclosure adjacent a skin surface and having an electrode located thereon;

[0094] Fig. 9b shows a cross-sectional view of the conductive material of Fig. 9a having an electrode repositioned thereon;

[0095] Fig. 9c shows a cross-sectional view of the conductive material of Fig. 9a having two electrodes located thereon;

[0096] Fig. lOa shows an oblique view of a glove comprising conductive material according to an embodiment of the present disclosure;

[0097] Fig. lOb shows an oblique view of a medical dressing comprising conductive material according to an embodiment of the present disclosure;

[0098] Fig. 11 shows a cross-sectional view of an electrode device according to an embodiment of the present disclosure;

[0099] Figs. l2a to l2d show top and cross-sectional views of a multilayer structure as it is processed to form an electrode device according to an embodiment of the present disclosure;

[0100] Figs. l3a to l3d show top and cross-sectional views of a multilayer structure as it is processed to form an electrode device according to another embodiment of the present disclosure;

[0101] Figs. l4a to l4d show top and cross-sectional views of a multilayer structure as it is processed to form an electrode device according to another embodiment of the present disclosure;

[0102] Figs. l5a to l5d show top and cross-sectional views of a multilayer structure as it is processed to form an electrode device according to another embodiment of the present disclosure;

[0103] Figs. l6a and l6b show top views of dressings according to embodiments of the present disclosure that include an exposed and covered opening, respectively; [0104] Figs. l7a and l7b show top views of electrode devices according to embodiments of the present disclosure that include an exposed and covered opening, respectively;

[0105] Figs. l8a and 18b show top views of a treatment patch and an electrode device according to an embodiment of the present disclosure retaining the treatment patch, respectively;

[0106] Figs. l9a to l9c show photographs of different samples of conductive material formed in an example according to the present disclosure;

[0107] Fig. 20 shows another photograph of a sample of conductive material formed in an example according to the present disclosure; and

[0108] Fig. 21 shows a schematic view of apparatus used to test samples in an example according to the present disclosure.

Description of Embodiments

[0109] A portion of conductive material 1 according to an embodiment of the present disclosure is illustrated in Figs la and lb. The material 1 includes a flexible substrate 10 having first and second surfaces 11, 12, the first and second surfaces 11, 12 being located on substantially opposite sides of the substrate 10. The material 1 also includes a plurality of discrete conductive elements 13 distributed within respective perforations 101 in an array across the substrate 10. As seen in Fig. lb, each conductive element 13 extends through a respective perforation 101 in the substrate 10 such that a first end 131 of each conductive element 13 is exposed at and protrudes from the first surface 11 of the substrate 10 and a second end 132 of each conductive element 13 is exposed at and protrudes from the second surface 12 of the substrate 10. The substrate 10 is formed substantially of non-conductive material such as a polymeric foam or film, and therefore the discrete conductive elements 13 are electrically isolated from each other through the substrate 10. In particular, the conductive material 1 provides an anisotropic conductive medium having good electrical conductance through the thickness of the material 1 (the thickness direction being indicated by arrow T in Fig. lb), but little or no electrical conductance laterally through the material 1 (the lateral direction being indicated by arrow L in Fig. lb).

[0110] In this embodiment, an adhesive layer 14 is also located over the first surface of the substrate. In addition to being exposed at and protruding from the first surface 11 of the substrate 10, the first ends 131 of the conductive elements 131 are also exposed at and protrude from the adhesive layer 14.

[0111] In use, as represented in Fig. lb, the first surface 11 of the substrate 10 is located in close proximity to a biological surface such as a skin surface 16 of a subject such that the first surface 11 faces the skin surface 16 and the first ends 131 of the conductive elements 13 each electrically contact the skin surface 16. The adhesive layer 14 over the first surface 11 may at least partly contact and adhere to the skin surface 16, maintaining the position of the conductive material on the skin surface 16. An electrode 15 can be located in close proximity to the second surface 12 of the substrate 10 such that a contact surface 151 of the electrode 15 faces the second surface 12 and the second ends 132 of a subset of the conductive elements 13 each electrically contact the contact surface 151 of the electrode 15. The second surface 12 may at least partly contact the contact surface 151 of the electrode 15 or may be spaced slightly from the contact surface 151 by virtue of a protrusion of the second ends 132 of the conductive elements 13.

[0112] As indicated, Figs la and lb show the conductive material in an electrical use state. As a precursor to this state, as shown in Figs. 2a and 2b, the conductive material 1 can additionally comprise first and/or second removable layers 17, 18 located over the first and second surfaces 11, 12 of the substrate 10, respectively. The first removable layer 17 can be held in position over the first surface 11 by releasably adhering to the adhesive layer 14. The second removable layer 18 can be held in position over the second surface 12 by other forces, such as a van der Waals forces, for example. In alternative embodiments, the first removable layer may be held in position over the first surface by other forces such as a van der Waals forces, for example, and/or the second removable layer may be held in position over the second by releasably adhering to an adhesive layer. When one or more adhesive layers are provided, each adhesive layer may be fixed to the substrate and releasable from the respective removable layer or fixed to the respective removable layer and releasable from the substrate.

[0113] As seen in Fig. 2b, when the first and second removable layers 17, 18 are located over the substrate 10, the perforations 14 continuously extend through the substrate 10, the adhesive layer 14 and the first and second layers 17, 18

[0114] A method of forming the conductive material 1 according to an embodiment of the present disclosure is now described with reference to Figs 3 a to 7b.

[0115] With reference to Figs. 3a and 3b in particular, a substrate 10 is provided having first and second surfaces 11, 12 on opposite sides, respectively, of the substrate 10. A first removable layer 17 is located over the first surface 11, and specifically over an adhesive layer 14 that is also located over the first surface 11, and a second removable layer 18 is located over the second surface 12.

[0116] The substrate 10 is flexible, meaning that it may bend to follow the curvature of a biological surface or other surface to which it is to make contact. In general, the substrate 10, and the conductive material 1 comprising the substrate, may be configured so that, upon bending during normal use, electrical independence of discrete conductive elements in the conductive material may be maintained. [0117] The substrate 10 can comprise a single layer of material as shown in Figs. 2a and 2b or multiple layers of material, e.g. multiple layers of material stacked on top of each other. The substrate 10 can comprise a non-conductive (i.e. insulating) material such as nylon, polyurethane, polyester, silicones, polyvinylalcohol, polyimide, natural polymer such as chitosan, foam such as polyurethane foam, natural polysaccharide alginate foam, hydrocolloids such as those formed from carboxymethyl-cellulose, alginate and elastomer, pre-swollen hydrogel of collagen or elastin, hyaluronic acid, or synthetic hydrogels of cross-linked poly(vinyl alcohol), polyvinylpyrrolidone or methacrylate. The substrate 10 can be hydrophobic or hydrophilic. The substrate 10 can be biodegradable. The substrate 10 can be formed of medical grade material. The substrate 10 can be at least partially transparent or translucent, e.g. so that target sites on the biological surface for electrical interfacing can be identified through the substrate, or opaque. The substrate 10 can be coloured or clear. The substrate 10 can be substantially flat as shown in Figs. 2a and 2b or it can be have a three-dimensional shape, e.g. a curved or otherwise structured shape. The three- dimensional shape may be pre-formed in the substrate 10. The substrate 10 can have a thickness of between 5pm and 2mm or otherwise.

[0118] The adhesive layer 14 can comprise a medically approved adhesive suitable for short or long term contact with a biological surface. The strength of the adhesive of the layer 14 may be selected based on the particular intended application, the target biological surface site, or the intended length of use, for example. Advanced medically-approved adhesive layers which become adhesive (or non-adhesive) upon application of a selected“trigger” such as moisture or biological surface temperature may also be used. The adhesive layer 14 can comprise acrylic, hydrocolloid, rubber, hydrogel, polyurethane, and/or silicone (e.g. soft silicone), for example. The adhesive layer 14 can have a thickness in the range of 1m to 200pm, for example. While a single adhesive layer 14 is provided over the first surface 11 of the substrate 10 in this embodiment, in alternative embodiments an adhesive layer may be provided over each of the first and second surfaces 11, 12 or over the second surface of the substrate only. Alternatively, an adhesive layer may not be provided over either over the first and second surfaces 11, 12.

[0119] With reference to Figs. 4a and 4b a plurality of perforations 101 are formed through the substrate 10, the adhesive layer 14, the first removable layer 17 and the second removable layer 18. Thus, each perforation 101 defines an opening in each layer, including an opening 102 in the substrate, an opening 172 in the first removable layer 17 and an opening 182 in the second removable layer 18, along with an opening 142 in the adhesive layer 14. Opposite ends of each perforation 101 terminate at respective outer surfaces of the first and second removable layers 17,

18 where the perforations have respective first and second apertures 173, 183 through which access to the openings of the perforation 101 is possible. [0120] The perforations 101 can be formed by any one or more of laser perforation, ultrasonic perforation, cold or hot needle perforation, electrostatic discharge perforation, water jet perforation, drilling or otherwise.

[0121] In this embodiment, the perforations 101 are distributed across the substrate 10 in an array, e.g. a substantially uniform array, the array having equidistant rows and columns across the substrate 10. Nevertheless, alternative distributions of perforations 101 are possible such as rectilinear arrays, curvilinear arrays, hexagonal arrays or otherwise. In some embodiments, the perforations may be in a line, in a staggered arrangement, or arranged in different shapes and patterns, e.g. in clusters of perforations such as circular clusters of perforations.

[0122] In this embodiment, the perforations 101 have a shape, in a plane perpendicular to their direction of extension through the conductive material, that is circular. However, in alternative embodiments, the shape may be square, triangular, irregular or otherwise, and may differ for different perforations.

[0123] In this embodiment, the perforations 101 extend in a direction that is perpendicular to the first and second surfaces 11, 12 of the substrate 10. However, in alternative embodiments, the perforations may extend at an angle to the first and/or second surfaces of the substrate.

[0124] In this embodiment the conductive elements 13 take the form of pillars or pylons, e.g. micro-pillars or micro-pylons and the conductive elements are monolithic through forming in one- piece.

[0125] In this embodiment, the perforations 101 have an aspect ratio, i.e. a total perforation depth through the different layers of the conductive material to perforation diameter in the range of about 1.0 to 4.0.

[0126] In this embodiment, the spacing between perforations 101 (inter-perforation spacing) is selected to provide a desired density, conductance and lateral resistance of the conductive elements and the mechanical strength of conductive material 1.

[0127] With reference to Figs. 5a and 5b, a conductive substance is applied to the plurality of perforations 101 to form the plurality of discrete electrically conductive elements 13. The conductive substance can be applied via the first aperture 173 and/or second aperture 183 of each perforation 101. In some embodiments, it may be preferable to apply the conductive substance to the side from which perforations are formed, e.g. the side from which a laser or other tool is used to bore into the material to form the perforations 101. [0128] The conductive substance can be applied to the perforations 101 by any one or more of: screen printing, doctor blading, inkjet printing, pad printing, flexographic printing, gravure printing spraying, dip coating or otherwise.

[0129] In this embodiment, as evident from Fig. 5b, the applying of the conductive substance is such that, for each perforation 101, the conductive substance substantially fills the opening 102 in the substrate 10, the opening 172 in the first removable layer 17 and the opening 182 in the second removable layer, along with the opening 142 in the adhesive layer 14. A first end 131 of each resulting conductive element 13 substantially aligns with an outer surface of the first removable layer 17 and a second opposite end 132 of the conductive element 13 substantially aligns with the outer surface of the second removable layer 18.

[0130] The conductive substance applied to the perforations 101 and the resultant conductive elements 13 can comprise conductive matter such as carbon, graphite, graphene, silver, gold, copper, carbon nanotubes, conducting polymers, polymer electrolytes, salts and/or combinations thereof. The conductive matter can in some embodiments be combined with carrier matter such polymers, solvents (e.g. water, organic solvents or otherwise), UV or electron-beam curable matter, or therapeutic agents such as drugs, or otherwise. The carrier matter can optimise physical properties of the conductive substance when applied to the perforations and/or optimise the physical properties of the conductive elements formed in the perforations. The carrier matter can serves as a binder, water absorber, adhesion promoter, flexibility enhancer or otherwise. The carrier matter can ensure that the conductive substance can be applied more easily to the perforations, e.g., so that it can enter and fill the openings 102, 142, 172, 182 provided by the perforations 101, for example. The carrier matter can ensure that the conductive substance will adhere to the substrate, for example. The conductive substance can be homogeneous or heterogeneous. The conductive substance can be biocompatible.

[0131] The conductive substance as applied to the plurality of perforations 101 can be an ink. The ink can comprise carrier matter comprising a solvent and can comprise conductive matter such as carbon, graphite, graphene, silver, gold, copper, carbon nanotubes, conducting polymers, polymer electrolytes, salts and/or combinations thereof as indicated above. In some embodiments, however, solvent-free inks may be used, which may comprise UV or electron-beam curable carrier matter, for example. The conductive substance can be applied as a solid, liquid or paste, e.g. depending on the presence and type of carrier matter combined with the conductive matter, for example. In some embodiments, ink formulations can be either a single formulation or a two-part formulation that reacts upon mixing.

[0132] After application to the perforations, the conductive substance can be subjected to a drying process (e.g. thermal, vacuum or air flow drying treatment) or a curing process (e.g. thermal, UV, electron beam curing) or otherwise. If thermal treatment is used, temperatures can be selected to avoid damaging parts of the conductive material 1, including the adhesive layer 14.

[0133] As applied to the perforations 101, the conductive substance can completely fill the perforations as illustrated in Fig. 5b. When the conductive substance 1 is subject to subsequent processing to form the final conductive elements 13, however, the size of the conductive elements can change in some embodiments. For example, if the conductive substance comprises a solvent, the solvent may evaporate following thermal treatment, causing the conductive elements to reduce in size, e.g. so that they do not completely fill the perforations. Nevertheless, the conductive elements may still have a sufficient length to extend through the substrate and at least partially through the first layer and through the second layer if present.

[0134] Once the conductive elements 13 are formed, an anisotropically electrically conductive material 1 is provided that can be used to electrically interface an electrode with a portion of a biological surface, as described above. Nevertheless, prior to use, and with reference to Figs. 6a and 6b and Figs. 7a and 7b, the first and second removable layers 17, 18 can be removed from the substrate 10, e.g. by peeling or otherwise.

[0135] The first and second removable layers 17, 18 have a variety of different functions. One function of the first and second removable layers 17, 18 is to assist with the formation of the conductive elements 13 that have first and second end 131, 132 that protrude from the first and second surfaces 11, 12, respectively, of the substrate 10. As is evident from the discussions above, the perforations 101, including the openings 102, 172, 182, 142 in the various layers 10, 17, 18, 14, act as moulds for forming the conductive elements 13. The removable layers 17, 18 are retained over the substrate 10 while forming the conductive elements 13. Flowever, subsequent removal of the first and second removable layers 17, 18, as illustrated in Figs. 6a and 6b and Figs. 7a and 7b, causes the first and second ends 131, 132 of conductive elements 13 to be exposed as they protrude from the substrate 10/ adhesive layer 14. By being exposed and protruding, the first and second ends 131, 132 can achieve better electrical contact with the biological surface 16 or the electrode surface 151, e.g. in comparison to an arrangement where the first and second ends are aligned with or even stop short of the first and second surfaces 11, 12 of the substrate 10 or of the adhesive layer 14 located thereon.

[0136] Nevertheless, after assisting with formation of the conductive elements 13, one or both of the first and second removable layers 17, 18 may be kept in position over the respective first and second surfaces 11, 12 to perform additional functions. For example, one or both of the first and second removable layers 17, 18 can act as protective layers or masks that expose only ends of the conductive elements while covering the surfaces 11, 12 of the substrates 10 and adhesive layer 14 located thereon. As such, and as represented in Fig. 8a, the first and second removable layers 17, 18 can each prevent underlying portions of the material 1 from being subsequently contaminated with conductive contaminants 1100 that could potentially degrade material anisotropy prior to use. Such contamination may occur during stacking, rolling or processing of the conductive material 1 , for example. When one or both of the removable layers 17, 18 are removed, as partially illustrated in Fig. 8a, any potentially contaminating substances 1100 can be removed with the layers 17, 18, leaving behind a clean, anisotropic underlying structure ready for contact with a biological surface 16 and electrode 15, for example.

[0137] In some embodiments, it may be desirable to contact one or both ends 131, 132 of the conductive elements 13 with a further substance 1200, which promotes interfacial conductance, such as water or a conductive liquid or gel, which substance 1200 can coat one or both of the ends 131, 132 of the conductive elements 13 and/or be absorbed into the conductive elements 13, dependent on their material properties. As represented in Fig. 8b, one or both of the first and second removable layers 17, 18 can prevent or mask underlying portions of the material 1 from being contacted by that further conductive substance 1200, which could potentially degrade material anisotropy or reduce the adhesive character of the layer 14. When the removable layers 17, 18 are removed, as partially illustrated in Fig. 8b, the further conductive substance 1200, other than portions l200a that coat or are absorbed into the conductive elements 13, can be removed with the layers 17, 18, leaving behind an anisotropic underlying structure ready for contact with a biological surface 16 and electrode 15, for example.

[0138] In the embodiments described above, both first and second removable layers 17, 18 are provided. Flowever, in alternative embodiments, only one of the first and second removable layers may be provided, e.g. if it is only desired to form conductive elements that protrude on one side of the substrate only, and not on the other side. When only one of the first and second removable layers is provided, a first end of each of the conductive elements may align with an outer surface of the first removable layer and a second opposite end of each of the conductive elements may align with the second surface of the substrate, or a second end of each of the conductive elements may align with an outer surface of the second removable layer and a first opposite end of each of the conductive elements may align with the first surface of the substrate.

[0139] As indicated, different subsets of the conductive elements 13 can be contacted by the electrode 15. For example, as illustrated in Fig. 9a, a subset of conductive elements l3a is defined, generally, by the area across which the contact surface 151 of the electrode 15 extends. By contacting the second ends 132 of the conductive elements 13 of the subset l3a, the electrode 15 will electrically interface with a portion of the skin surface 16 that is in contact with the first ends 131 of the conductive elements 13 of the subset l3a. Since the conductivity of the material 1 is anisotropic, there may be substantially no electrical interfacing between the electrode and the rest of the skin surface 16.

[0140] Different subsets of the conductive elements 13 can be selected as desired by varying the position of the electrode 15 on the second surface 12 of the substrate 10 and/or by varying the shape or size of the electrode 15. Different subsets of the conductive elements 13 can be selected in order to electrically‘probe’ different parts of the skin surface 16 of the subject, e.g. to enable bioimpedance monitoring and/or to apply electro-stimulation across different regions of tissue of the subject. As an example, after using the electrode 15 to electrically probe the area of the skin surface 16 that is in contact with the first subset l3a of conductive elements, as illustrated in Fig. 9a, the electrode 15 may be shifted, as illustrated in Fig. 9b, to electrically probe an area of the skin surface 16 that is in contact with a second subset l3b of conductive elements 13. As another example, as illustrated in Fig. 9c, more than one electrode l5a, l5b may be used to electrically probe different areas of the skin surface 16 at the same time by simultaneously contacting discrete, electrically isolated subsets l3c, l3d of the conductive elements 13.

[0141] So that the electrodes 15 can contact multiple discrete conductive elements 13 that form each subset l3a, l3b, l3c, l3d of the conductive elements 13, the conductive elements are relatively small in comparison to the electrode contact surface 151 and the conductive elements have a relatively high distribution density across the substrate 10. In general, it is not intended that the electrode contacts only one conductive element. Rather, it is intended that the electrode contacts multiple conductive elements that form a subset of the plurality of conductive elements.

[0142] In the portion of conductive material illustrated in Fig. la, fifty-four conductive elements are shown distributed across the substrate. Flowever, depending on the size of the substrate, the size of the conductive elements, and the distribution density of the conductive elements, the total number of conductive elements is essentially limitless. The total number of conductive elements distributed across the substrate can be greater than 50, greater than 100, greater than 500, or greater than 1000, for example.

[0143] The density of conductive elements across the substrate can be at least 1 per cm2, at least

2 per cm 2 , at least 5 per cm 2 , at least 10 per cm 2 at least 50 per cm 2 at least 100 per cm 2 at least

200 per cm at least 300 per cm at least 400 per cm’ at least 500 per cm at least 750 per cm or at least 1000 per cm², for example. The area of each conductive element at its first or second end, in a plane substantially parallel to the first and second surfaces of the substrate, may be less than 0.5 cm , less than 0.25 cm , less than 0.1 cm or less than 0.05 cm less than 0.01 cm , less than 0.001 cm², or less than 0.0001 cm², for example. The maximum distances between the ends of neighbouring conductive elements may be less than 1.0 cm, less than 0.75 cm, less than 0.5 cm, less than 0.25 cm, less than 0.1 cm, less than 0.05cm, less than 0.01 cm, or less than 0.001 cm, for example. In some embodiments, the conductive elements may therefore be distributed in a macroscopic or microscopic scale. For example, when distributed in a microscopic scale, the surface area of each conductive element at its first or second end, in a plane substantially parallel to the first and second surfaces of the substrate, may be less than O.OOOlcm². Moreover, the maximum distances between the ends of neighbouring conductive elements may be less than O.lcm, or 0.2cm or otherwise.

[0144] Generally, to the extent that conductive elements can remain electrically separated (i.e. that lateral resistance in the substrate can be maintained), the higher the density of conductive elements, the closer the effective electrode area of the electrode 15 may be in size and shape to the physical electrode area of the electrode 15. The size and shape of the physical electrode area corresponds to the size and shape of the electrode contact surface 151. However, the size and shape of the effective electrode area is dependent on the number of conductive elements 13 in the subset, and the shape and size of each conductive element 13 in the subset, particularly where they contact the skin surface 16.

[0145] In general, the conductive material 1 can provide a biological interface for achieving electrical contact between an electrode and a biological surface such as a skin surface on which the conductive material 1 is located. The conductive material 1 may be provided in the form of a patch or cloth that is freely locatable over any skin surface prior to electrode contact. As an alternative, the conductive material 1 may form all or part of a garment.

[0146] In one embodiment, as illustrated in Fig. lOa, the conductive material 1 forms part of a glove 2 that is configured to fit over a hand in a tight-fit manner. The conductive material 1 provides a panel of the glove 2 adapted to locate over the back of the hand, although it may be provided in other parts of the glove, e.g. the fingers or thumb of the glove, or the entire glove may be formed of the conductive material 1. Other garments into which the conductive material 1 can be integrated include, for example, socks (including compression socks), hats, wrist bands, head bands, arm bands, ankle straps, and shoulder straps, belts etc.

[0147] In the embodiment of Fig. lOa, an electrode 15 can be electrically interfaced with a portion of the skin surface 16 of the hand by electrically contacting any subset of the conductive elements 13 across which the contact surface of electrode 15 can reach. For example, a subset of electrodes that may be contacted by the electrode 15 is indicated in Fig. lOa by circle 21.

[0148] In the embodiment of Fig. lOa, the conductive material 1 forms part of a main body of the garment. In an alternative embodiment, the conductive material 1 can provide a liner of a garment, acting as a hygienic barrier between a main body of the garment and the skin surface. The main body may include electrodes integrated therein, the electrodes being adapted to electrically interface with the skin surface through the conductive material of the liner.

[0149] In yet another alternative embodiment, with reference to Fig. lOb, the conductive material 1 is provided in a medical interface and specifically in this embodiment a medical dressing such as a wound dressing 20. In this embodiment, the wound dressing 20 is comprised in a bandage 22 (located over a leg 23 in this example). An electrode can be brought into contact with the dressing 20 to electrically contact the wound and/or tissue surrounding the wound. The wound dressing 20 including the conductive material 1 can therefore provide protection and promote healing of a wound while also providing an electrically conductive path to the wound or tissue surrounding the wound, for the purpose of monitoring of the wound, electrostimulation or the wound, or otherwise. The tissue at which medical dressings according to the present disclosure may be applied may include a wound or other types of tissue damage and/or imperfections. For example, the dressing may be applied at or in close proximity to tissue including a cut, burn, sore, abscess, carbuncle, blister, wart, rash, scar, infection, disease, muscle tear, ligament tear or otherwise.

[0150] In some embodiments, the conductive material 1 may be formed by processing of a pre existing product such as a medical dressing, e.g. a pad, a compress, bandage, plaster or tape. The pre-existing product may include a substrate, a first and optionally a second layer (e.g. a carrier layer), the first and second layers being removable. Medical dressings commonly include a substrate and a removable layer (e.g. a release layer) located over an adhesive layer on one surface of the substrate and in some instances a second removable layer (e.g. a carrier layer) located over a second surface of the substrate. Thus processing of the pre-existing product may include forming perforations in the product and applying a conductive substance to the perforations to form conductive elements in accordance with discussions above. Alternatively, the pre-existing product may not include first and/or second removable layers and the pre-existing product may be modified to include one or both of these layers.

[0151] In discussions above, an anisotropically conductive material is described relative to which an electrode can be moved in order to electrically interface with different portions of a biological surface over which the conductive material is placed. Flowever, the conductive material may be adapted to be used in a fixed relationship relative to one or more electrodes. The conductive material may form part of an electrode device. For example, to form an electrode device, one or more conductive members, e.g. one or more electrodes, may be introduced in a fixed relationship with the substrate, and which electrically contact second ends of a plurality of the conductive elements.

[0152] A single conductive member may be provided. The single conductive member may be connected to second ends of some or ah of the plurality of conductive elements, for example. Alternatively, multiple conductive members may be provided, each conductive member being connected to second ends of different subsets of the plurality of conductive elements.

[0153] An electrode device 3 according to an embodiment of the present disclosure is illustrated in Fig. 11. The electrode device 3 can be integrated into a garment or used independently of any garment. The electrode device 3 includes components that are also present in the conductive material 1 described above with reference to preceding Figures, such as a substrate 10, and adhesive layer 14 and conductive elements 13, which can be formed in accordance with methods described above. In contrast to the embodiments described above, particularly with reference to Figs. 9a to 9c, for example, the second ends 132 of the conductive elements 13 are not configured to be selectively contacted by one or more electrodes. Rather, an electrically conductive member, in particular an electrically conductive electrode layer 31 , is fixed to conductive material 1 so that it extends over the second surface 12 of the substrate 10 and contacts the second ends 132 of the conductive elements 13. The conductive layer 31 electrically contacts the second ends 132 of each one of the conductive elements 13. The conductive layer 31 includes a conductive tab 311 at one side, which tab 311 extends beyond an edge of the substrate 10. The tab 311 can be electrically connected, through hard wiring or a releasable wired connection, to external componentry. A releasable wired connection may utilise a conductive clip such as a spring or“crocodile” clip, which releasably attaches to the tab 311. Other contact portions are possible such as a stud or a pre-wired contact.

[0154] In one embodiment, the electrode device 3, with or without the adhesive layer 311, may provide a medical interface, e.g. a medical dressing such as a wound dressing, or any other type of biological interface. The dressing may function in a similar manner to the dressing 20 discussed above with reference to Fig. lOb, for example. Flowever, rather than relying on an external electrode to electrically contact the conductive elements of the dressing and define an effective electrode contact area, the integrated conductive electrode layer 31 is in permanent contact with the conductive elements, such as to define an effective electrode contact area in a predetermined manner. In each case, the effective electrode contact area extends to the outer perimeter of the conductive elements that are electrically contacted. In one embodiment, the electrode device 3 may provide a general form of electrode.

[0155] Variations of the electrode device 3 are possible, as evident, for example, from the following embodiments, described with reference to Figs. l2a to l5d. In these embodiments, rather than a single conductive member 31 as shown in Figs. 11, multiple conductive members are fixed to conductive material to contact second ends conductive elements.

[0156] For example, to form an electrode device 4 according to one embodiment, a substrate 410 is provided as shown in Fig. l2a, the substrate 410 having a first removable layer 417 located over a first surface 411 of the substrate and an adhesive layer 414 also located over the first surface 411 of the substrate 410 between the first surface 411 and the first removable layer 417.

[0157] As also shown in Fig. l2a, clusters 4012 of perforations 4101 are formed that extend through the substrate 410, the adhesive layer 414 and the first removable layer 417. The perforations can be formed according to methods as described above. Four clusters 4102 of perforations 4101 are formed in particular, the clusters 4102 each including a plurality of perforations 4101 that are distributed across respective substantially circular regions of the substrate 410. The clusters 4102 of perforations 4101 are spaced from each other, e.g., along a longitudinal axis of the substrate 410. In this embodiment, there are no perforations provided between the clusters 4102.

[0158] As shown in Fig. l2b, conductive substance is applied to the perforations 4101, e.g. in accordance with methods described above, to form a plurality of discrete electrically conductive elements 413 that are in clusters 4131 according to the clustered arrangement of perforations. The electrically conductive elements 413 extend through the substrate 410, through the adhesive layer 414 and at least partially through the first removable layer 417.

[0159] As shown in Fig. l2c, adjacent the second surface 412 of the substrate 410, a conductive member, and specifically an electrode 419, is formed, e.g. by printing, over each one of the clusters 4131 of conductive elements 413 to contact second ends of the conductive elements 413.

Conductive tracks 4191 are also formed, e.g. by printing, over the second surface 412 of the substrate 410, the conductive tracks 4191 electrically connecting to each electrode 419 and extending across the second surface to a longitudinal end 4103 of the substrate 410. At the longitudinal end 4103, ends 4192 of the tracks 4191 may interface with external electrical componentry such as monitoring or electrostimulation apparatus for example.

[0160] As shown in Fig. l2d, an insulating layer 420 is located over the electrodes 419 and the conductive tracks 4191, leaving only the ends 4192 of the conductive tracks 4191 that are adjacent the longitudinal end 4103 of the substrate 410 exposed for contact.

[0161] The resultant electrode device 4 can be used to electrically contact four discrete regions of a biological surface by bringing the first ends of the conductive elements 413 of each cluster 4131 into contact with the biological surface. Prior to contact, the first removable layer 417 may be removed, exposing the first ends of the conductive elements 413 such that they protrude from the electrode device 4 ensuring more reliable contact with the biological surface. Removing of the layer 417 may also be conducted to remove contaminants or extraneous conductive gel, etc., as described above for preceding embodiments. [0162] A number of variations to the approach are possible, including the number and shape of the clusters and electrodes, which may be controlled to improve mechanical strength or ease of electrical connection, or in accordance with the purpose of electrical contact with the biological surface.

[0163] A variation of the technique for forming an electrode device is illustrated in Figs. l3a to l3d, where a second removable layer 518 is additionally provided in order to form the electrode device 5.

[0164] In more detail, to form the electrode device 5 according to an embodiment of the present disclosure, a substrate 510 is provided as shown in Fig. l3a, a first removable layer 517 being located over a first surface 511 of the substrate 510, an adhesive layer 514 also located over the first surface 511 of the substrate 510 between the first surface 511 and the first removable layer 517. Moreover, a second removable layer 518 is located over a second surface 512 of the substrate 510

[0165] As also shown in Fig. l3a, clusters 5012 of perforations 5101 are formed that extend through the substrate 510, the adhesive layer 514, the first removable layer 517 and the second removable layer 518. The perforations 5101 can be formed according to methods as described above. Four clusters 5102 of perforations 5101 are formed in particular, the clusters 5102 each including a plurality of perforations 5101 that are distributed across respective substantially circular regions of the substrate 510. The clusters 5102 of perforations 5101 are spaced from each other, e.g., along a longitudinal axis of the substrate 510. In this embodiment, there are again no perforations provided between the clusters 5102.

[0166] As shown in Fig. l3b, conductive substance is applied to the perforations 5101, e.g. in accordance with methods described above, to form a plurality of discrete electrically conductive elements 513 that are in clusters 5131 according to the clustered arrangement of perforations. The electrically conductive elements 513 extend through the substrate 510, through the adhesive layer 514, at least partially through the first removable layer 517 and at least partially through the second removable layer 518.

[0167] As shown in Fig. l3c, the second removable layer 518 is removed to expose the second surface 512 of the substrate 510, where second ends of the conductive elements 513 are exposed at and protrude from the second surface 512 of the substrate 510. Adjacent the second surface 512 of the substrate 510, a conductive member, and specifically an electrode 519, is formed, e.g. by printing, over each one of the clusters 5131 of conductive elements 513 to reach over and contact the second ends of the conductive elements 513. Conductive tracks 5191 are also formed, e.g. by printing, over the second surface 512 of the substrate 510, the conductive tracks 5191 electrically connecting to each electrode 519 and extending across the second surface 512 to a longitudinal end 5103 of the substrate 510. At the longitudinal end 5103, ends 5192 of the tracks 5191 may interface with external electrical componentry such as monitoring or electrostimulation apparatus for example.

[0168] As shown in Fig. l3d, an insulating layer 520 is located over the electrodes 519 and the conductive tracks 5191, leaving only the ends 5192 of the conductive tracks 5191 that are adjacent the longitudinal end 5103 of the substrate 510 exposed for contact.

[0169] The resultant electrode device 5 can again be used to electrically contact four discrete regions of a biological surface by bringing the first ends of the conductive elements 513 of each cluster 5131 into contact with the biological surface. Prior to contact, the first removable layer 517 may be removed, exposing the first ends of the conductive elements 513 such that they protrude from the electrode device 5 ensuring more reliable contact with the biological surface. Removing of the layer 517 may also be conducted to remove contaminants or extraneous conductive gel, etc., as described above for preceding embodiments.

[0170] A further variation of the technique for forming an electrode device is illustrated in Figs. l4a to l4d, where an electrode device 6 is formed that, instead of having clusters of conductive elements, has a uniform and/or more widespread distribution of conductive elements, contact being made between electrodes and discrete subsets of the conductive elements.

[0171] In more detail, to form the electrode device 6 according to an embodiment of the present disclosure, a substrate 610 is provided as shown in Fig. l4a, a first removable layer 617 being located over a first surface 611 of the substrate 610, an adhesive layer 614 also located over the first surface 611 of the substrate 610 between the first surface 611 and the first removable layer 617.

[0172] As also shown in Fig. l4a, a uniform and/or relatively widespread distribution of perforations 6101 is formed across the substrate 610, the perforations 6101 extending through the substrate 610, the adhesive layer 614, and the first removable layer 617. The perforations 6101 can be formed according to methods as described above.

[0173] As shown in Fig. l4b, conductive substance is applied to the perforations 6101, e.g. in accordance with methods described above, to form a plurality of discrete electrically conductive elements 613. The electrically conductive elements 613 extend through the substrate 610, through the adhesive layer 614, and at least partially through the first removable layer 617.

[0174] As shown in Fig. l4c, an insulating layer 620 is applied over the second surface 612 of the substrate such that it extends over the second ends of the conductive elements 613, except at four discrete circular regions 6201 (which may have non-circular shapes in other embodiments) that are spaced apart, e.g., along the longitudinal axis of the substrate 610.

[0175] As shown in Fig. l4d, a conductive member, and specifically an electrode 619, is formed, e.g. by printing, over each one of the circular regions 621 to contact second ends of the conductive elements 613. Conductive tracks 6191 are also formed, e.g. by printing, over the insulating layer 620, the conductive tracks 620 electrically connecting to each electrode 619 and extending across the insulating layer to a longitudinal end 6103 of the substrate 610. At the longitudinal end 6103, ends 6192 of the tracks 6191 may interface with external electrical componentry such as monitoring or electrostimulation apparatus for example.

[0176] Although not shown, a further insulating layer 520 may be located over the electrodes 619 and the conductive tracks 6191, leaving only the ends 6192 of the conductive tracks 6191 that are adjacent the longitudinal end 6103 of the substrate 610 exposed. Moreover, in alternative embodiments, a second removable layer may initially be provided over the second surface of the substrate so that the conductive elements are formed to protrude from the second surface (e.g. similar to Fig. l3c).

[0177] The resultant electrode device 6 can again be used to electrically contact four discrete regions of a biological surface by bringing the first ends of the conductive elements 613 into contact with the biological surface. Prior to contact, the first removable layer 617 may be removed, exposing the first ends of the conductive elements 613 such that they protrude from the electrode device 6 ensuring more reliable contact with the biological surface. Removing of the layer 617 may also be conducted to remove contaminants or extraneous conductive gel, etc., as described above for preceding embodiments.

[0178] A further variation of the technique for forming the electrode device is illustrated in Figs. l5a to l5d, where an electrode device 7 is formed that is similar to the electrode device 6 but includes conductive elements formed in only some of the perforations, and specifically those positioned where contact with conductive members is to be made.

[0179] In more detail, to form the electrode device 7 according to an embodiment of the present disclosure, a substrate 710 is provided as shown in Fig. l5a, a first removable layer 717 being located over a first surface 711 of the substrate 710, an adhesive layer 714 also located over the first surface 711 of the substrate 710 between the first surface 711 and the first removable layer 717.

[0180] As also shown in Fig. l5a, a uniform and/or relatively widespread distribution of perforations 7101 is formed across the substrate 610, the perforations 7101 extending through the substrate 710, the adhesive layer 714, and the first removable layer 111. The perforations 7101 can be formed according to methods as described above.

[0181] As shown in Fig. l5b, an insulating layer 720 is applied over the second surface 712 of the substrate 710 such that it extends over the perforations 7101, except at four discrete circular regions 7201 (which may have non-circular shapes in other embodiments) that are spaced apart, e.g., along the longitudinal axis of the substrate 710.

[0182] As shown in Fig. l5c, conductive substance is applied to the perforations 7101, but the insulating layer 720 ensures that only the perforations 7101 exposed via the circular regions 7201 receive the conductive substance to form a plurality of discrete electrically conductive elements 713. The electrically conductive elements 713 extend through the substrate 710, through the adhesive layer 714, and at least partially through the first removable layer 717.

[0183] As shown in Fig. l5d, a conductive member, and specifically an electrode 719, is formed, e.g. by printing, over each one of the circular regions 721 to contact second ends of the conductive elements 713 (in other embodiments, the insulating layer 720 may be removed prior to forming of the conductive members). Conductive tracks 7191 are also formed, e.g. by printing, over the insulating layer 720 (or the second surface 712 of the substrate 710 if the insulating layer 720 has been removed), the conductive tracks 720 electrically connecting to each electrode 719 and extending across the insulating layer to a longitudinal end 7103 of the substrate 710. At the longitudinal end 7103, ends 7192 of the tracks 7191 may interface with external electrical componentry such as monitoring or electrostimulation apparatus for example.

[0184] Although not shown, a further insulating layer may be located over the electrodes 719 and the conductive tracks 7191, leaving only the ends 7192 of the conductive tracks 7191 that are adjacent the longitudinal end 7103 of the substrate 710 exposed. Moreover, in alternative embodiments, a second removable layer may initially be provided over the second surface of the substrate so that the conductive elements are formed to protrude from the second surface (e.g. similar to Fig. l3c). Moreover, in alternative embodiments, the electrodes and/or conductive tracks may be formed at the same time as the application of the conductive substance to the perforations.

[0185] The resultant electrode device 7 can again be used to electrically contact four discrete regions of a biological surface by bringing the first ends of the conductive elements 713 into contact with the biological surface. Prior to contact, the first removable layer 717 may be removed, exposing the first ends of the conductive elements 713 such that they protrude from the electrode device 7 ensuring more reliable contact with the biological surface. Removing of the layer 717 may also be conducted to remove contaminants or extraneous conductive gel, etc., as described above for preceding embodiments. [0186] In the embodiments described above with reference to Figs. l2a to l5d, electrode devices with four electrodes/four regions of electrical contact are provided. However, other numbers of electrodes/regions of electrical contact may be provided. Merely as one example, the electrode devices may be modified to include two electrodes/two regions of electrical contact.

[0187] As illustrated in Figs. l6a to l7b, conductive material 1 according to the embodiments of the present disclosure may be provided, e.g. as a part of a dressing 30, 30’, or as part of an electrode device 40, 40’, or otherwise, where the conductive material includes an opening 31,31’, 41, 41’. The opening 31, 31’, 41 , 41’may be partially or entirely surrounded by the conductive elements 13 of the conductive material 1, or located between conductive members or electrodes 42 of the electrode device 40, 40’, and may allow direct access to a biological surface underneath, e.g. to allow observation of the biological surface and/or to allow application of treatment to the biological surface, such as heat, cold, topical drugs or ultrasound therapy. In some embodiments, as shown in Figs. l5b and l6b, the opening may be covered by a transparent window 31’, 41’, again allowing observation and/or providing a means for application of phototherapy or otherwise.

[0188] As illustrated in Figs l8a and 18b, a dressing, electrode device 4 or other construct such as tape, bandage or otherwise, that comprises conductive material according to embodiments of the present disclosure, may be used as a means of retaining an item 8 in place at a biological surface. The retained item 8 may be a medical device or dressing, such as a primary dressing (e.g. a treatment patch that is used to speed up wound healing or to provide muscle conditioning, prevention of muscle spasms, promotion of blood circulation, etc.). In addition to retaining the item, the construct 4 may enable electrical analysis of the biological surface that is subject to the treatment to be made. The approach may allow an assessment and tracking of the biological tissue beneath the primary dressing to be made. Primary dressings can be any of a vast type of dressings ranging from conventional (hydrogels, hydrocolloids, hydrofibre etc.) to active (silver based, microcell battery-based e.g. Procellera™ , honey, etc) that further promote wound healing, and/or provide antibacterial action, etc.

Example

[0189] Multiple commercial wound dressings were used to provide multilayer components for forming different conductive material samples. Each dressing had a substrate bounded on opposing surfaces by removable polyethylene liners, adhesive being located between the substrate and one of the liners (a“support” liner) only. The specific construction was as follows: polyethylene (carrier) liner (45pm)/polyurethane substrate (25pm)/acrylic adhesive(45pm)/ polyethylene (support) liner (l30pm).

[0190] Each wound dressing was laser perforated from the support liner side, the perforations (holes) extending through each layer. Silver ink was applied to the perforations using a screen printer in doctor blade mode to form conductive elements extending through the different layers to form each conductive material sample.

[0191] Samples differed by the perforation hole diameter, the inter-perforation spacing, and the side to which the conductive material was applied.

[0192] Resistance through each sample was tested in accordance with the experimental set-up generally as illustrated in Fig. 21. After removing the removable layers, the sample 90 material including silver-based conductive elements 901 was adhered to a conductive substrate 91

(aluminium foil) and two 10 mm diameter metal contact pads 92 were placed 20mm apart (centre to centre) on the top of the material. Resistance was measured using a multimeter 93 from one contact pad, through the material, along the conductive foil substrate, and up through the second contact pad. Additionally, each sample was also adhered to a non-conductive substrate of PET film and tested as described above, to verify that there was no lateral conductance across the material. The results of testing are presented in Table 1 in which the stability of the resistance measurements was also considered along with an estimate of the percentage of the perforations that were successfully filled with silver.

[0193] As can be seen from Table 1, coating on the support side (the side exposed to the laser during perforation) was more successful than coating from the opposite side, resulting in higher retention of silver particles in the holes, and higher quality of conductive elements (silver micro pylons) formed. Moreover, again referring to Table 1, with regard to hole size (diameter), it was found that 60pm holes (aspect ratio 4.1) were more difficult to fill with silver and 250pm holes (aspect ratio 1.2) had poorer retention of silver, especially upon removal of the liner layers and during handling. l20pm (aspect ratio 2.0) holes by comparison were found to be more suitable, with a generally high percentage of hole filling (up to 95%), good retention while handling, and high anisotropic conductivity. In terms of aspect ratios therefore, l20pm holes with aspect ratio 2.0 performed better than those with aspect ratios considerable smaller or larger than this value. [0194] No sample was found to be conductive laterally (i.e. across the sample), showing that each silver micro-pylon was electrical isolated from adjacent micro-pylons. The only conductance that was measurable was through the dressing. This is a favourable result given the intended use of the dressings as anisotropic biological interfaces.

Table 1: Measured resistance of silver impregnated anisotropic dressings

[0195] Figure l9a, l9b and l9c show examples of samples with l20pm hole diameter silver- impregnated from the support side, and with hole spacings 0.5mm, 0.75mm and l.Omm, respectively. Polyethylene liners on both surfaces have been peeled away and the strips are shown adhering onto PET film to provide good contrast for photography.

[0196] Figure 20 shows an oblique view of the electrode contacting surface of one of the samples silver-impregnated from the support side having hole diameter of l20pm and hole spacing 0.5mm. Protrusions of silver micro-pylons, after removal of polyethylene liners, can readily be seen.

[0197] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. An anisotropically electrically conductive material to electrically interface an electrode with a portion of a biological surface, the conductive material comprising:

2. The conductive material of claim 1, comprising a second removable layer, the second removable layer being located over the second surface of the substrate, wherein each of the perforations extends through the second removable layer in addition to extending through the substrate and the first removable layer.

3. The conductive material of claim 1, wherein each of the perforations defines an opening in the substrate and an opening in the first removable layer.

4. The conductive material of claim 2, wherein each of the perforations defines an opening in the substrate, an opening in the first removable layer and an opening in the second removable layer.

5. The conductive material of claim 3 or 4, wherein the conductive elements fill at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the volume of each opening.

7. The conductive material of any one of the preceding claims, comprising a first adhesive layer located over the first surface of the substrate between the first surface of the substrate and the first removable layer.

8. The conductive material of any one of the preceding claims, comprising a second adhesive layer located over the second surface of the substrate.

9. The conductive material of any one of the preceding claims, wherein the shape of each perforation, in a plane perpendicular to its direction of extension through the conductive material, is substantially the same through the entire depth of the conductive material.

10. The conductive material of any one of the preceding claims, wherein each perforation extends in a straight line.

11. The conductive material of any one of the preceding claims, wherein each conductive element is a pillar of conductive material.

12. An electrode device comprising conductive material according to claim 1, wherein second ends of each conductive element are exposed at the second surface of the substrate and wherein the electrode device comprises one or more conductive members, each conductive member being connected to second ends of a different subset of the plurality of conductive elements.

13. The electrode device of claim 12 comprising at least two of the conductive members.

14. The electrode device of claim 12 or 13, wherein each subset of the plurality of conductive elements is provided by a respective cluster of the conductive elements.

15. The electrode device of claim 14, comprising at least two clusters of conductive elements connected to the respective conductive members and wherein no conductive elements are provided between the clusters of conductive elements.

16. The electrode device of any one of claims 12 to 15, wherein one or more insulating layers are located over the second surface of the substrate, optionally over the conductive members.

17. The electrode device of any one of claims 12 to 16, wherein conductive tracks extend from the one or more conductive members to an end of the electrode device.

18. The conductive material of any one of claims 1 to 11 or the electrode device of any one of claims 12 to 17, comprising an opening for observation of the biological surface and/or treatment of the biological surface.

19. A method of forming an anisotropically electrically conductive material to electrically interface an electrode with a portion of a biological surface, the method comprising:

20. The method of claim 19, wherein a second removable layer is located over the second surface of the substrate and each of the perforations additionally extend through the second removable layer, and wherein the applying of the conductive substance is such that each conductive element additionally extends at least partially through the second removable layer.

21. The method of claim 19, wherein each of the perforations defines an opening in the substrate and an opening in the first removable layer.

22. The method of claim 20, wherein each of the perforations defines an opening in the substrate, an opening in the first removable layer and an opening in the second removable layer.

23. The method of claim 21 or 22, wherein the conductive elements fill at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the volume of each opening.

24. The method of any one of claims 19 to 23, comprising forming the perforations by any one or more of: laser perforation, ultrasonic perforation, cold or hot needle perforation, electrostatic discharge perforation, water jet perforation, or drilling.

25. The method of any one of claims 19 to 24, wherein the conductive substance applied to the perforations comprises conductive matter optionally combined with carrier matter.

26. The method of any one of claims 19 to 25, wherein the conductive substance when applied to the plurality of perforations is a fluid, paste or gel and the conductive substance is solidified after being applied to the perforations.

27. The method of any one of claims 19 to 26, wherein the conductive substance is an ink.

28. The method of any one of claims 19 to 27, wherein the conductive substance as applied to the perforations completely fills the perforations.

29. The method of any one of claims 19 to 28, wherein the conductive substance is applied to the perforations by any one or more of: screen printing, doctor blading, inkjet printing, pad printing, flexographic printing, gravure printing spraying, or dip coating.

30. The method of any one of claims 19 to 29, wherein at least the substrate and the first removable layer are comprised in a medical dressing.

31. The method of any one of claims 19 to 30, wherein a first adhesive layer is located over the first surface of the substrate between the first surface of the substrate and the first removable layer.

32. The method of any one of claims 19 to 31, wherein a second adhesive layer is located over the second surface of the substrate.

33. The method of any one of claims 19 to 32, wherein the shape of each perforation, in a plane perpendicular to its direction of extension through the conductive material, is substantially the same through the entire depth of the conductive material.

34. The method of any one of claims 19 to 33, wherein each perforation extends in a straight line.

35. The method of any one of claims 19 to 34, wherein each conductive element is a pillar of conductive material.

36. A method of forming an electrode device to electrically interface with a portion of a biological surface, the method comprising:

providing a substrate having first and second surfaces on opposite sides, respectively, of the substrate, a first removable layer being located over the first surface, a plurality of perforations extending through the substrate and the first removable layer; and

applying a conductive substance to the plurality of perforations to form a plurality of discrete electrically conductive elements, wherein the applying is such that, for each perforation, the conductive element extends through the substrate and at least partially through the first removable layer;

wherein second ends of each conductive element are exposed at the second surface of the substrate and wherein the method further comprises connecting one or more conductive members to second ends of different respective subsets of the plurality of conductive elements.

37. The method of claim 36 comprising connecting at least two of the conductive members.

38. The method of claim 36 or 37, wherein each subset of the plurality of conductive elements is provided by a respective cluster of the conductive elements.

39. The method of claim 38, wherein at least two clusters of conductive elements are connected to the respective conductive members and wherein no conductive elements are provided between the clusters of conductive elements.

40. The method of any one of claims 36 to 39, wherein an insulating layer is located over the second surface of the substrate before or after the connection of the conductive members.

41. The method of 40, comprising forming conductive tracks that extend from the one or more conductive members to an end of the electrode device.