Conductive foam material

Abstract

A conductive foam comprises (i) a conductive polymer composition comprising a mixture of conductive polymer and elastomer, adsorbed onto (ii) a polymer foam. The conductive foam has conductivity and impedance suitable for use as an electrode for monitoring human body functions and delivering stimulation thereto. The conductive foam is made, e.g. using an elastomer and a foam of the same polymer, by providing the polymer foam, providing a solution of the conductive polymer composition in a solvent, applying the solution onto the polymer foam and removing solvent to yield a dry, conductive foam.

Description

[0001] Conductive Foam Material

[0002] Introduction

[0003] The present invention relates to a conductive foam material and a method of manufacture thereof. The invention also relates to applications and uses of the foam material.

[0004] Background to the Invention

[0005] Electrically conductive materials are useful in a wide variety of applications, especially in healthcare settings where electrodes are used to record electrical signals from the body (for example in electrocardiography and electroencephalography) and to electrically stimulate the body (for example during physical therapy).

[0006] Metal is the most commonly used material for manufacture of electrically conductive materials. As a result, electrodes used in healthcare are typically metallic silver or silver-chloride wet electrodes which require skin preparation and conductive gel to make electrical contact with skin.

[0007] This technology has major limitations. First, skin preparation techniques, such as debridement of dead skin cells, can cause wounds on sensitive skin, for example the gel can cause allergies. Secondly, the gel dries out quickly such that electrodes and / or gel must be replaced frequently. Thirdly, it is necessary to wash the skin and hair with which the gel made contact after use, which can be an uncomfortable and tiresome process for patients who are less able.

[0008] Further, the rigidity and stiffness of metals, along with the need to use conductive gels, prevent the wider adoption of wearable electrodes in the clinic, for long-term monitoring and for at-home care, despite the multiple applications with established health benefits that require these electrodes.

[0009] Conductive materials which do not necessitate the use of gel are a promising replacement for these applications. Several types of non-metallic conductive materials have been developed both commercially and in academic settings, but these are typically produced as rigid structures coated with silver or gold for conductivity. Most commercially available conductive materials used as dry electrodes are therefore very stiff and can cause similar or even worse comfort issues to wet metal electrodes, making them unsuitable for comfortable long-term recording or clinical use. Further, the coatings used are inherently less durable as they eventually rub off, increasing impedance and reducing signal quality.

[0010] Flexible conductive materials have also been developed to permit fabrication of softer, smaller electrodes. These are composed of stiff conductive materials (such as metals) being coated onto softer ones, with the aim of achieving high enough conductivity while maintaining the elastic properties of the softer material; however, a common problem with these types of electrodes is delamination issues. The mechanical mismatch between the flexible substrate and the conductive coating causes moisture ingress, delamination and subsequent loss of conductivity as well as potential skin reactions.

[0011] In addition, carbon-derived compounds like carbon nanotubes or graphene fibres have shown promise as a replacement for metals, but they can be challenging to disperse in flexible substrates so production can be expensive and difficult. More importantly, carbon nanotubes have been shown to be cytotoxic and cause skin inflammation, limiting their use in bioelectronics applications.

[0012] One example of a conductive material is disclosed in EP 4245797 A, namely a self- healing electrically conducting elastomer comprising PEDOTPSS and a polyborosiloxane-based polymer.

[0013] Conducting polymers (CPs) have attracted significant interest for use in flexible bioelectronics due to their good electrochemical properties and relatively low cost of fabrication. CPs are brittle and stiff and have not been used successfully to date as electrodes in healthcare applications.

[0014] Thus, there is a need for an electrically conductive material having high conductivity but also high elasticity and being suitable for use in healthcare settings, without causing irritation or toxic effects to humans. Accordingly, the aim of the present invention is to provide an alternative electrically conductive material for use as, or in the fabrication of, electrodes for the monitoring of biosignals. An aim of particular embodiments is to provide a conductive material which can be used as a dry electrode without the need for gel or skin preparation, especially material that is flexible, soft, comfortable, and / or compressible, appropriate for longterm use and has comparable signal quality to wet metal electrodes.

[0015] Summary of the Invention

[0016] The invention provides a conductive foam, comprising (i) a conductive polymer composition comprising a mixture of conductive polymer and elastomer, and (ii) a polymer foam.

[0017] The conductive polymer and / or elastomer (or the conductive polymer composition) may be soluble in organic or aqueous solvent. In embodiments described in the examples below, the conductive polymer and elastomer are soluble in organic solvent.

[0018] The elastomer and polymer foam may consist of or comprise the same polymer. Alternatively, or additionally, the elastomer may consist of or comprise polyurethane. For example, the elastomer and polymer foam may both comprise polyurethane.

[0019] The conductive foam may comprise at least 25% by weight (e.g. 40-60% by weight) of the conductive polymer composition.

[0020] The conductive foam has conductivity and impedance suitable for use as an electrode for monitoring human body functions and delivering stimulation thereto. Electrodes for use on the human body and items of clothing comprise the conductive foam.

[0021] The conductive polymer composition can be made by a method comprising dissolving particles of a conductive polymer and particles of an elastomer in an organic solvent. The particles of conductive polymer and elastomer may be dry particles.

[0022] The conductive foam can be made by a method comprising: providing a polymer foam, making a solution of a solution of a conductive polymer composition in a solvent by the method described above, applying the solution onto the polymer foam; and removing solvent to yield a dry, conductive foam.

[0023] The conductive foam can also be made by a method comprising: providing a polymer foam, providing a solution of a conductive polymer composition in a solvent, said conductive polymer composition comprising a conductive polymer and an elastomer; applying the solution onto the polymer foam; and removing solvent to yield a dry, conductive foam.

[0024] The solvent for the method may be an organic solvent or an aqueous solvent. In embodiments described in the examples below, the solvent used in the method is an organic solvent.

[0025] Detailed Description of the Invention

[0026] A conductive foam of the invention is provided, comprising

[0027] (i) a conductive polymer composition comprising a mixture of conductive polymer and elastomer and

[0028] (ii) a polymer foam.

[0029] The conductive polymer composition is suitably attached to e.g. adsorbed onto a solid polymer foam, remaining attached during use of the foam, thus during flexing, compression and re-expansion of the foam.

[0030] Generally, the conductive polymer composition comprises 5-40% by weight of conductive polymer and 60-95% by weight elastomer, more suitably 10-30% by weight of conductive polymer and 70-90% by weight elastomer. In a specific example described in more detail below a conductive polymer composition had about 20-25% by weight of the conductive polymer and about 75-80% elastomer. By incorporating the elastomer into the foam, it is found that the conductive polymer, which provides the required electrical conductivity, has reduced, preferably little or substantially no, delamination from the foam, giving the end product longevity and retained function despite repeated flexing in use.

[0031] The conductive polymer composition can be applied to the foam in a spray or liquid form, generally in a solvent-containing format; more details are set out elsewhere. After drying to remove solvent the weight of the conductive polymer composition typically represents at least 25%, suitably at least 30%, more suitably at least 40% of the total weight of the conductive foam and I or 75% or less, suitably 70% or less, more suitably 60% or less of the total weight of the conductive foam. More commonly, the conductive polymer composition represents between 40% and 60% of the total weight of the conductive foam. Preferably, the conductive polymer composition represents between 40% and 50% of the total weight of the conductive foam, for example 45.5% of the total weight of the conductive foam in a specific example made and used below. This proportion can be varied according to the loading of the conductive polymer composition onto the foam; some applications requiring greater conductivity can have higher loadings, i.e. higher weight % of the conductive polymer composition by total conductive foam weight.

[0032] The conductive foam, i.e. the final product, may comprise up to 30%, or up to 24%, or up to 20%, or up to 16%, or up to 10% by weight of conductive polymer. Alternatively, or additionally, the conductive foam may comprise 1 % or more, 2% or more, or 3% or more, or 4% or more, or 5% or more by weight of conductive polymer. For example, the conductive foam may comprise between 2-16%, or between 3-24%, or between 4-20% by weight of conductive polymer. Preferably, the conductive foam comprises between 4-20% by weight of conductive polymer.

[0033] The material for the polymer foam can in general be substantially any polymer capable of providing a stable, solid polymer foam. Suitable polymers for the foam are conventional and commonplace in the art, and include polyurethane, polystyrene, and polyethylene. Mixtures of polymers and co-polymers may also be used. Also, generally, prior to combination with the conductive polymer composition the polymer foam is non-conductive. Separately, the foam may be open cell or closed cell. When closed cell foams are used these preferably dissolve in or at least partially dissolve in the solvent - hence, at least swell in the solvent, thus facilitating attachment of conductive polymer. Good results have been obtained using nearly closed cell foams.

[0034] Described later on in more detail is the elastomer component of the conductive polymer composition. In preferred embodiments of the invention, the elastomer and the polymer foam comprise or are made from the same polymer. For example, both the elastomer and the foam may comprise polyethylene, or both the elastomer and the foam may comprise polystyrene. In preferred embodiments, the polymer foam is or comprises polyurethane and in specific examples, described in more detail below the polymer foam comprises polyurethane and the elastomer comprises polyurethane.

[0035] The conductive polymer incorporated into the foam provides useful conductivity properties to the conductive foam of the invention. The end product foam conductivity is suitably at least 3 Siemens per centimetre (300 Siemens per metre (S / m)), more suitably at least 5 Siemens per centimetre (500 Siemens per metre (S / m)) and I or suitably 30 Siemens per centimetre or less (3000 Siemens per metre (S / m)), or 10 Siemens per centimetre (1000 Siemens per metre (S / m)) or less, or preferably 7 Siemens per centimetre (700 Siemens per metre (S / m)) of less. Typically, the end product foam conductivity is between 5 and 10 Siemens per centimetre, preferably between 5 and 7 Siemens per centimetre. Specific foams have to date been made using the conductive polymer poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOTPSS) and measured to have conductivities of hundreds of S / m. The end foam may also have impedance of up to 10 MegaOhms, more suitably up to 50 KiloOhms.

[0036] The conductive polymer may also be referred to as an intrinsically conducting polymer and many examples known in the art are believed to be suitable for use in the invention. Less conducting polymers may be loaded onto the foam at higher weight % to provide the required conductivity of the end product. Suitable conductive polymers include poly(fluorene)s, polyphenylenes, polypyrenes, polyazulenes, polynaphthalenes, polybenzodifurandiones, poly(pyrrole)s (PPY), polycarbazoles, polyindoles, polyazepines, polyanilines (PANI), poly(thiophene)s (PT), poly(3,4- ethylenedioxythiophene) (PEDOT), poly(p-phenylene sulfide) (PPS), poly(acetylene)s (PAC) and poly(p-phenylene vinylene) (PPV). Conductive polymers in widescale use include polythiophenes (one example being PEDOT), polyanilines, polyindoles and polypyrroles. Examples are described in: R. A. Green, N. H. Lovell, G. G. Wallace, and L. A. Poole-Warren, “Conducting polymers for neural interfaces: Challenges in developing an effective long-term implant,” Biomaterials, vol. 29, no. 24-25, pp. 3393- 3399, Aug. 2008.

[0037] The conductive polymer is also typically water dispersible or water soluble. This can facilitate application to the foam and then partial removal during curing and drying.

[0038] Suitable conductive polymer compositions may comprise one or more ionomers; suitably a first ionomer carrying a negative charge and a second ionomer carrying a positive charge. Suitable conductive polymer compositions may comprise mixtures or combinations of conductive polymers, and in examples we have used a conductive polymer composition comprising a mixture of two ionomers. In a specific embodiment, the conductive polymer composition comprises PEDOT and PSS. For this combination a ratio of about 3:1 PEDOTsulphonate is particularly preferred.

[0039] As described, the end product has the conductive polymer composition adsorbed onto the foam. This is conveniently achieved by combining (i) a preparation (e.g. solution) of the conductive polymer and the elastomer in a solvent with (ii) the polymer foam and removing the solvent. Solvent removal leaves behind the conductive polymer and the elastomer in a curing-type process resulting in their attachment to the foam.

[0040] The elastomer (and optionally also the conductive polymer) may be soluble in either organic solvent or aqueous solvent. For example, both the elastomer and the conductive polymer may be soluble in either organic solvent or aqueous solvent. In embodiments described in the examples below, the elastomer and conductive polymer are soluble in organic solvent. In embodiments, the elastomer (and optionally also the conductive polymer) may not be soluble in aqueous solvent. For example, both the elastomer and the conductive polymer are not soluble in aqueous solvent.

[0041] The solvent may be removed by solvent exchange. For example, solvent exchange may be used to displace a first solvent (e.g. an organic solvent) with a second solvent (e.g. an aqueous solvent). The second solvent may be removed by a drying step. The solvent exchange step (and drying step) typically results in the end product (i.e. the conductive foam) being more biocompatible I cytocompatibility because it ensures that substantially all solvent (e.g. especially organic solvent) is removed and no residual solvent is left.

[0042] Suitable elastomers for the invention include silicon rubbers, polymeric organosilicon compound-based elastomers, ether-based hydrophilic urethanes, thermoplastic urethanes, polyurethanes, polystyrenes, Pellethane® (in an example, specifically variant 80AE) and mixtures or co-polymers thereof. The elastomers can be thermoplastic elastomers, comprising a mixture of polymers having thermoplastic and elastomeric properties. Preferred elastomers are thermoplastic urethanes. Preferably, the elastomer does not comprise borosiloxane or polyborosiloxane. In other words, the elastomer is preferably not polyborosiloxane.

[0043] Suitable elastomeric preparations, generally solutions or suspensions, are made by dissolving or dispersing one or more elastomers in a solvent; these can then be used to apply the conductive polymer composition to the foam.

[0044] The solvent may be an organic solvent, including but not limited to ethanol, dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), tetrahydrofuran (THF), chloroform and mixtures thereof. The solvent may also be an aqueous solvent, including but not limited to mixtures of water and alcohols such as ethanol and methanol. In certain embodiments of the invention, the solvent is not an aqueous solvent. As will be appreciated, the solvent is suitably compatible with the elastomer and the conductive polymer and with the foam. Suitably, the elastomer and / or the conductive polymer (preferably both) may be soluble in organic solvent. Typically, the elastomer and / or the conductive polymer (preferably both) are not soluble in aqueous solvent. A combination of elastomers may be used, for example the preparation may comprise a polyurethane-based elastomer and a polymeric organosilicon compound-based elastomer. Preferably, the preparation is a solution of polyurethane in solvent, such as ethanol or DMAc.

[0045] In specific embodiments of the invention conductive foams are provided, comprising:

[0046] (i) a conductive polymer composition comprising a mixture of 10-30% by weight conductive polymer and 70-90% by weight elastomer, wherein the conductive polymer is or comprises PEDOTPSS and the elastomer is or comprises a thermoplastic urethane elastomer, and

[0047] (ii) a resiliently compressible polymer foam.

[0048] A specific embodiment of the invention, made and used in examples below, comprises

[0049] (i) a conductive polymer composition comprising a mixture of about 20% by weight PEDOTPSS and about 80% by weight Pellethane 80AE, and

[0050] (ii) a resiliently compressible polyurethane foam.

[0051] The conductive foam of the invention has many advantageous uses, such as for, or as part of, an electrode. Hence, an electrode of the invention for use on a human body comprises a conductive foam of the invention. Another electrode for non-human use comprises conductive foam of the invention; in use this electrode may be attached to any conductive surface, e.g. a vehicle or to an item in transport. Electrodes suitably are used with or comprise apparatus to apply the foam under pressure to a surface, the apparatus including e.g. a strap or elastic band or adhesive material such as tape. An advantage of the conductive foam of the invention is it can be used dry, e.g. without gel.

[0052] Also, an item of clothing for application onto a human body may comprise a conductive foam according to the invention. The clothing may be a headband, glasses, goggles or a facemask. Similarly, the conductive foam material may be used as an electrode for a wearable device.

[0053] The electrode may further comprise a rigid element e.g. a disk or plate made from metal which functions to reinforce the foam material. The rigid element (e.g. disk) may be attached to one or more sides of the conductive foam for reinforcement. Alternatively, or additionally, a conductive wire may be applied to the conductive foam material to enable signals to be passed to or from the conductive foam electrode to a monitoring device for patient monitoring or stimulation. In particular, a wire may be bonded to the conductive foam to produce a wired sensor for use in biosignal recording or electrical stimulation. The invention also provides a method of (i) stimulating a patient, or (ii) recording signals from a patient, comprising applying a conductive foam to the patient, e.g. using an electrode as described above.

[0054] To make the conductive foam, the conductive polymer and elastomer are attached to the starting material foam, especially by combining the conductive polymer plus elastomer in a solvent and then removing the solvent. Often the solvent is nonbiocompatible so to make a biocompatible conductive foam all or substantially all solvent is removed.

[0055] Specifically, to make the conductive polymer composition, the method may comprise dissolving particles of a conductive polymer and particles of an elastomer in an organic solvent. The particles of conductive polymer and elastomer may be dry particles; an advantage is this method results quickly in a solution of both conductive polymer and elastomer in the same, non-aqueous solvent. The method is simplified, and a later solvent exchange step is suitably used to remove organic solvent from the eventual product, especially it is to be for human use.

[0056] A specific method of making a conductive foam comprises providing a polymer foam, making a solution of a conductive polymer composition in a solvent according to the method described directly above, applying the solution onto the polymer foam; and removing solvent to yield a dry, conductive foam.

[0057] Another specific method of making a conductive foam comprises: providing a polymer foam, providing a preparation, e.g. a solution, of a conductive polymer composition in a solvent, said conductive polymer composition comprising a conductive polymer and an elastomer; applying the preparation, e.g. solution, onto the polymer foam; and removing solvent to yield a dry, conductive foam. Preferably, the solvent used in the methods is an organic solvent (i.e. not an aqueous solvent). Also preferably, the polymer foam and the elastomer used in the methods are made of or comprise the same polymer.

[0058] The solvent (e.g. the organic solvent, such as DMAc) may be removed by solvent exchange with a second solvent (e.g. an aqueous solvent). The method may further comprise a drying step to remove the second solvent.

[0059] The methods may be carried out in the absence of water (optionally, up until the solvent exchange step). This is because the elastomer (e.g. polyurethane) can be very water sensitive, especially when at elevated temperatures. As such, all reasonable steps may be taken to minimise the presence of water (up until the solvent exchange step). For example, molecular sieves may be used to dry the organic solvent before use and / or all glassware may be over-dried and / or the elastomer (and conductive polymer) may be present in the form of dry pellets which are mixed with organic solvent to form a solution (i.e. no aqueous dispersions are formed). The pellets may also be oven dried.

[0060] The elastomer (and conductive polymer) may be provided in a form in which they are ready to be dissolved in (organic) solvent to form a (organic) solution, e.g. in the form of pellets or particles or similar, as opposed to being formed in situ from two or more components. The pellets may be soluble so that a solution can be formed without the need for an aqueous dispersion to be formed. The methods also typically do not require surfactants (or adjuncts).

[0061] In carrying out the method according to the above, the polymer foam may be a closed cell foam, in which case the method suitably uses a solvent that is compatible with the polymer foam, meaning it is capable of dissolving the polymer foam or at least partially swelling the polymer foam. This compatibility allows opening up of the closed cell foam sufficient for conductive polymer and elastomer to attach thereto prior to solvent removal.

[0062] A conductive foam of the invention may thus be made by impregnating a non- conductive foam with a conductive polymer (CP) composition, thereby rendering the foam material electrically conductive. Typically, removal of solvent by a curing process then dries and attaches the conductive polymer composition onto the foam, yielding a conductive foam.

[0063] In an example described in more detail below, a first step involves fabrication of a CP composition which comprises one or more conductive polymers and one or more elastomers. Preferably the conductive polymer composition comprises a conductive polymer mixture dispersed in an elastomeric solution or suspension (e.g. one or more elastomers dissolved in solvent).

[0064] In a second step, the foam may be dipped into or soaked in the conductive polymer composite solution and then removed so excess solution can drip off. Residual solution may be removed by drying, giving a dry, conductive foam.

[0065] In the end product, the conductive polymer(s) and elastomer(s) may be chemically attached to or otherwise adsorbed to the foam yielding a conductive foam. Using a resilient, compressible foam enables production of a resilient, compressible conductive foam. It is found that including the elastomer in combination with the conductive polymers provides flexibility and reduces the brittleness of the conductive polymers. As a result, there is reduced delamination of the conductive polymer from the foam after the compression and expansion that is inevitable in use. The conductive foam product retains its integrity and conductivity after repeated compression and expansion and is thus useable as an electrode with advantageous durability and longevity despite being flexed in use.

[0066] The conductive foam may be non-healable. In other words, the conductive foam may not be self-healing or have self-healing properties. Alternatively, or additionally, the conductive foam may be a composite material, preferably a bulk composite material. In other words, the conductive foam is preferably not a multilayer material and / or the conductive foam is preferably not anisotropic.

[0067] Each of these features of the conductive foam, or the combination thereof, may lead to improved stability, stretchability, flexibility, bendability, transparency and / or electrical conductivity. They may also lead to increased cyclic stability and / or deformability. The conductive foam is therefore able to achieve increased conductivity, whilst not negatively impacting the mechanical I material properties and / or other functional properties.

[0068] Methods of making the conductive foam preferably do not require the use of a separate insulating phase. This is typically because the conductive foam is a composite material in which the elastomer and polymer foam comprise or consist of the same polymer (e.g. polyurethane). However, when an insulating phase is used (e.g. when the elastomer and polymer foam do not comprise or consist of the same polymer), the insulating phase may be polyurethane. Seamless bonds may be formed between the neat polyurethane and the conductive polymer composition (i.e. the conductive polymer and / or the elastomer). These bonds may give rise to the desired mechanical properties.

[0069] The curing may be achieved by solvent exchange, which involves one or more cycles of dipping the foam in conductive polymer composite solution followed by dipping in water or aqueous solution. The curing process, or the solvent exchange process, may also be followed by a gentler solvent removal process. Alternatively, curing may be achieved by thermal curing. Alternatively, still, curing may be achieved by solvent evaporation, in which the evaporation method may include use of an oven and / or reduced pressure. Whichever curing method is used, it is preferred that all or substantially all solvent is removed from the composition to ensure that the resulting conductive foam material is biocompatible. Preferably, the resulting conductive foam material meets the International Organization for Standardisation (ISO) standard for cytocompatibility for use in wearable and / or implantable devices.

[0070] The curing process may also involve forming a thin film or a thin film on a substrate with a release layer. This has the advantage of allowing the conductive polymer composition to be applied directly onto the polymer foam, thus simplifying the process of coating polymer foams of complicated 3D geometries with the conductive polymer.

[0071] The use of sophisticated curing processes such as those described above also means that the methods are less dependent on very specific drying conditions (e.g. time, temperature and humidity). The reduced dependency on these parameters results in the conductive foam material being much more stable and processable.

[0072] The methods of the invention are also less prone to issues cause by overmixing than known methods. Hence, the methods are not restricted by specific mixing conditions and are easily scaled up for industrial production of the conductive foam. In the methods of the invention, solutions can be left on heat or under stirring conditions for approximately a month without having any negative effects on the mechanical and / or electrical properties.

[0073] The methods of the present invention suitably do not require any additives or additional components, such as additional conductive fillers. The conductive polymer compositions are typically ready compatible with coating processes and / or capable of achieving high conductivities without the use of additional conductive fillers or additional method steps. This is generally because of the compatibility between the polymer and solvent systems used (e.g. the use of organic solvents in combination with elastomers and / or polymer foams which are soluble in organic solvents). Such compatibility enables chemical bonding between components of the reaction mixture, making it easier to seamlessly bond I integrate the materials (e.g. the conductive polymer composition and the polymer foam) and / or form a stable bulk composite.

[0074] Specifically, the methods of the present invention suitably do not rely on or involve the use of surfactants or other adjuncts which are likely to affect biocompatibility. The lack of presence of such components and / or optionally the removal of any residual solvent may lead to increased cytocompatibility, without significantly reducing conductivity.

[0075] In use the resulting conductive elastomer foam material retains high conductivity as well as high elasticity, making it soft, flexible and compressible. Uses of the material included any applications requiring a flexible conductive material, for example wearable skin electrodes. Hence the material is appropriate for incorporation into medical devices comprising an electrode component (e.g. for cardiac or brain monitoring) for use in healthcare settings such as clinics or at-home care. Additional uses include pre-clinical research using electrodes and non-clinical commercial uses (e.g. selling consumer-grade electroencephalogram (EEG) devices for gaming or personal health tracking).

[0076] Embodiments

[0077] The invention thus provides the following embodiments:

[0078] 1 . A conductive foam, comprising

[0079] (i) a conductive polymer composition comprising a mixture of conductive polymer and elastomer, and

[0080] (ii) a polymer foam, wherein the elastomer and the polymer foam comprise the same polymer.

[0081] 2. A conductive foam according to embodiment 1 , wherein the elastomer and the polymer foam both comprise polyurethane.

[0082] 3. A conductive foam, comprising

[0083] (i) a conductive polymer composition comprising a mixture of conductive polymer and elastomer, and

[0084] (ii) a polymer foam, wherein the elastomer comprises polyurethane.

[0085] 4. A conductive foam, comprising

[0086] (i) at least 25% by weight of a conductive polymer composition comprising a mixture of conductive polymer and elastomer, and

[0087] (ii) a polymer foam.

[0088] 5. A conductive polymer according to any preceding embodiment, wherein the elastomer and the conductive polymer are both soluble in organic solvent.

[0089] 6. A conductive polymer according to any of embodiments 1 to 4, wherein the elastomer and the conductive polymer are both soluble in aqueous solvent.

[0090] 7. A conductive foam according to any preceding embodiment, wherein the conductive polymer composition comprises 5-40% by weight of conductive polymer and 60-95% by weight elastomer.

[0091] 8. A conductive foam according to embodiment 7, wherein the conductive polymer composition comprises

[0092] 10-30% by weight of conductive polymer and

[0093] 70-90% by weight elastomer.

[0094] 9. A conductive foam according to any preceding embodiment, comprising at least 25% by weight of conductive polymer composition.

[0095] 10. A conductive foam according to any preceding embodiment, comprising from 40-60% by weight of conductive polymer composition.

[0096] 11. A conductive foam according to any preceding embodiment, wherein the conductive foam comprises 4-20% by weight of the conductive polymer.

[0097] 12. A conductive foam according to any previous embodiment, wherein the conductive polymer comprises one or more ionomers, e.g. a first ionomer carrying a negative charge and a second ionomer carrying a positive charge.

[0098] 13. A conductive foam according to embodiment 12, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOTPSS).

[0099] 14. A conductive foam according to any preceding embodiment, made by a method comprising combining (i) a solution of the conductive polymer and the elastomer in a solvent with (ii) the polymer foam, and removing the solvent.

[0100] 15. A conductive foam according to embodiment 14, wherein the solvent is aqueous solvent.

[0101] 16. A conductive foam according to embodiment 14, wherein the solvent is organic. 17. A conductive foam according to embodiment 16, wherein the method comprises removing the organic solvent by solvent exchange with a second solvent.

[0102] 18. A conductive foam according to embodiment 17, wherein the method comprises a drying step to remove the second solvent.

[0103] 19. A conductive foam according to embodiment 17 or 18, wherein the second solvent is an aqueous solvent.

[0104] 20. A conductive foam according to any of embodiments 16 to 19, wherein the solvent comprises ethanol, DMAc, DMSO, DMF or a mixture of two or more thereof, preferably DMAc or DMSO, or a mixture thereof, especially DMAc.

[0105] 21 . A conductive foam according to any previous embodiment, having conductivity of 5 siemens per centimetre or greater.

[0106] 22. A conductive foam according to any previous embodiment, having conductivity of between 5 and 10 siemens per centimetre and / or an impedance of up to 10 MegaOhms.

[0107] 23. A conductive foam according to any preceding embodiment, comprising:

[0108] (i) a conductive polymer composition comprising a mixture of 10-30% by weight conductive polymer and 70-90% by weight elastomer, wherein the conductive polymer is or comprises PEDOTPSS and the elastomer is or comprises a thermoplastic urethane elastomer, and

[0109] (ii) a resiliently compressible polymer foam.

[0110] 24. An electrode for use on a human body, comprising a conductive foam according to any previous embodiment.

[0111] 25. An item of clothing for application onto a human body, comprising an electrode or a conductive foam according to any previous embodiment. 26. An electrode for non-human use, e.g. a conductive surface in a vehicle or item of transport, comprising a conductive foam according to any of embodiments 1 to 23.

[0112] 27. A method of making a conductive polymer composition, comprising, dissolving particles of a conductive polymer and particles of an elastomer in an organic solvent.

[0113] 28. A method of making a conductive polymer composition according to embodiment 27, wherein the particles of conductive polymer and elastomer are dry particles.

[0114] 29. A method of making a conductive polymer composition according to embodiment 27 or 28, wherein the conductive polymer composition is as defined in any of embodiments 1 to 23.

[0115] 30. A method of making a conductive foam, comprising providing a polymer foam, making a solution of a conductive polymer composition in a solvent according to the method of any of embodiments 27 to 29, applying the solution onto the polymer foam; and removing solvent to yield a dry, conductive foam.

[0116] 31 . A method of making a conductive foam according to embodiment 30, wherein the method comprises removing the organic solvent by solvent exchange with a second solvent.

[0117] 32. A method of making a conductive foam according to embodiment 31 , wherein the method comprises a drying step to remove the second solvent.

[0118] 33. A method of making a conductive foam according to embodiment 32, wherein the second solvent is an aqueous solvent. 34. A method of making a conductive foam according to any of embodiments 30 to 33, wherein the organic solvent comprises ethanol, DMAc, DMSO, DMF or a mixture of two or more thereof.

[0119] 35. A method of making a conductive foam according to embodiment 34, wherein the organic solvent comprises DMAc or DMSO, or a mixture thereof, especially DMAc.

[0120] 36. A method of making a conductive foam according to any of embodiments 1 to 23, comprising providing a polymer foam, providing a solution of a conductive polymer composition in a solvent, said conductive polymer composition comprising a conductive polymer and an elastomer; applying the solution onto the polymer foam; and removing solvent to yield a dry, conductive foam.

[0121] 37. A method of making a conductive foam according to embodiment 36, wherein the solvent is an organic solvent and the method comprises removing the organic solvent by solvent exchange with a second solvent.

[0122] 38. A method of making a conductive foam according to embodiment 37, wherein the method comprises a drying step to remove the second solvent.

[0123] 39. A method of making a conductive foam according to embodiment 38, wherein the second solvent is an aqueous solvent.

[0124] 40. A method of making a conductive foam according to any of embodiments 37 to 39, wherein the organic solvent comprises ethanol, DMAc, DMSO, DMF or a mixture of two or more thereof.

[0125] 41 . A method of making a conductive foam according to embodiment 40, wherein the organic solvent comprises DMAc or DMSO, or a mixture thereof, especially DMAc.

[0126] 42. A method according to any of embodiments 30 to 41 , wherein the polymer foam is a closed cell foam and the solvent is compatible with the polymer foam and capable of dissolving the polymer of the foam or at least partially swelling the polymer of the foam.

[0127] Examples

[0128] Each step of the fabrication process is described in more detail in the following examples, examples 1 to 3.

[0129] Example 1 - Preparation of a solution of conductive polymer composition

[0130] Polyurethane (Pll) pellets made from Pellethane 2363-80AE, an ether based polyurethane elastomer, were dissolved in DMAc solvent at a 5% (w / v) concentration. The solution was then placed in a 60°C silicone oil bath and mechanically stirred at 300 rpm for 24 hours.

[0131] After checking that thorough swelling of the Pll pellets into the DMAc had taken place, lithium perchlorate (LiCIC ) was added at a concentration of 0.3 mmol / g Pll. The PU / LiCIO4 solution was then stirred at 300 rpm at 60°C in a silicone oil bath for 10 hours or longer.

[0132] Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOTPSS) pellets (Orgacon) were added to the PU / DMAC solution at the desired loading, on a dry basis

[0133] The solution then continued to be heated at 60°C and stirred at 180 rpm in an oil bath for 3 days until the PEDOT was totally dispersed throughout the solution.

[0134] Polyurethanes can be very water sensitive, especially when at elevated temperatures. As such, all reasonable steps were taken to minimise the presence of water. For example, molecular sieves were used to dry the solvent before use and all glassware was over-dried and the raw Pll was also oven-dried.

[0135] Example 2 - Preparation of a Conductive Foam Electrode (Part 1 ) Polyurethane foam (3M foam: Product Number 1100C30, ID 7100141468, UPC 05902658102851 ,05902658102844,05902658102837) was cut into cylinders, each having a diameter of 1 cm (0.1 m).

[0136] The foam cylinders were allowed to take their initial, non-compressed shape and each foam cylinder was put on the top of a syringe needle (for handling). The samples were then ready for the dip coating procedure.

[0137] The foam cylinders were dip coated in the 20 wt% conductive polymer composite solution made by the process described in Example 1. This process involved briefly (less than 1 second) submerging the cylinders before transferring them to water dip / soak. They were left to soak in the water for more than 2 minutes before the excess water was gently blotted off with paper towel to dry it. The foam cylinders were then left in the fume hood until dry (i.e. until there was no surface water left).

[0138] The dip-coat procedure was repeated 2 times, after which the foams were placed in oven at 37°C to dry overnight.

[0139] Example 3 - Assembly of a Conductive Foam Electrode

[0140] The coated foam electrodes, made by the process explained in Example 2, were connected to silver-coated copper wires to enable connection with hardware. The electrode foam conductivity was measured as being the range 5-7 Siemens per centimetre.

[0141] Impedance

[0142] To evaluate the impedance of the exemplified electrodes, a two-probe set-up was used on human skin. The working electrode was placed on the ulnar prominence and the reference / counter electrode was located on the antecubital fossa. Both electrodes were conductive foam electrodes connected via the wires and attached to the skin using a disposable adhesive. Impedance measurements were then being performed using electrical impedance spectroscopy (EIS).

[0143] Hence, a conductive foam was prepared suitable for widespread use in healthcare and other applications.

Claims

CLAIMS1 . A conductive foam, comprising(i) a conductive polymer composition comprising a mixture of conductive polymer and elastomer, and(ii) a polymer foam, wherein the elastomer and the polymer foam comprise the same polymer.

2. A conductive foam according to claim 1 , wherein the elastomer and the polymer foam both comprise polyurethane.

3. A conductive foam, comprising(i) a conductive polymer composition comprising a mixture of conductive polymer and elastomer, and(ii) a polymer foam, wherein the elastomer comprises polyurethane.

4. A conductive foam, comprising(i) at least 25% by weight of a conductive polymer composition comprising a mixture of conductive polymer and elastomer, and(ii) a polymer foam.

5. A conductive polymer according to any preceding claim, wherein the elastomer and the conductive polymer are both soluble in organic solvent.

6. A conductive polymer according to any of claims 1 to 4, wherein the elastomer and the conductive polymer are both soluble in aqueous solvent.

7. A conductive foam according to any preceding claim, wherein the conductive polymer composition comprises5-40% by weight of conductive polymer and60-95% by weight elastomer.

8. A conductive foam according to claim 7, wherein the conductive polymer composition comprises10-30% by weight of conductive polymer and70-90% by weight elastomer.

9. A conductive foam according to any preceding claim, comprising at least 25% by weight of conductive polymer composition.

10. A conductive foam according to any preceding claim, comprising from 40-60% by weight of conductive polymer composition.

11. A conductive foam according to any preceding claim, wherein the conductive foam comprises 4-20% by weight of the conductive polymer.

12. A conductive foam according to any previous claim, wherein the conductive polymer comprises one or more ionomers, e.g. a first ionomer carrying a negative charge and a second ionomer carrying a positive charge.

13. A conductive foam according to claim 12, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOTPSS).

14. A conductive foam according to any preceding claim, made by a method comprising combining (i) a solution of the conductive polymer and the elastomer in a solvent with (ii) the polymer foam, and removing the solvent.

15. A conductive foam according to claim 14, wherein the solvent is aqueous solvent.

16. A conductive foam according to claim 14, wherein the solvent is organic.

17. A conductive foam according to claim 16, wherein the method comprises removing the organic solvent by solvent exchange with a second solvent.

18. A conductive foam according to claim 17, wherein the method comprises a drying step to remove the second solvent.

19. A conductive foam according to claim 17 or 18, wherein the second solvent is an aqueous solvent.

20. A conductive foam according to any of claims 16 to 19, wherein the solvent comprises ethanol, DMAc, DMSO, DMF or a mixture of two or more thereof, preferably DMAc or DMSO, or a mixture thereof, especially DMAc.

21. A conductive foam according to any previous claim, having conductivity of 5 siemens per centimetre or greater.

22. A conductive foam according to any previous claim, having conductivity of between 5 and 10 siemens per centimetre and / or an impedance of up to 10 MegaOhms.

23. A conductive foam according to any preceding claim, comprising:(i) a conductive polymer composition comprising a mixture of 10-30% by weight conductive polymer and 70-90% by weight elastomer, wherein the conductive polymer is or comprises PEDOTPSS and the elastomer is or comprises a thermoplastic urethane elastomer, and(ii) a resiliently compressible polymer foam.

24. An electrode for use on a human body, comprising a conductive foam according to any previous claim.

25. An item of clothing for application onto a human body, comprising an electrode or a conductive foam according to any previous claim.

26. An electrode for non-human use, e.g. a conductive surface in a vehicle or item of transport, comprising a conductive foam according to any of claims 1 to 23.

27. A method of making a conductive polymer composition, comprising,dissolving particles of a conductive polymer and particles of an elastomer in an organic solvent.

28. A method of making a conductive polymer composition according to claim 27, wherein the particles of conductive polymer and elastomer are dry particles.

29. A method of making a conductive polymer composition according to claim 27 or 28, wherein the conductive polymer composition is as defined in any of claims 1 to 23.

30. A method of making a conductive foam, comprising providing a polymer foam, making a solution of a conductive polymer composition in a solvent according to the method of any of claims 27 to 29, applying the solution onto the polymer foam; and removing solvent to yield a dry, conductive foam.31 . A method of making a conductive foam according to claim 30, wherein the method comprises removing the organic solvent by solvent exchange with a second solvent.

32. A method of making a conductive foam according to claim 31 , wherein the method comprises a drying step to remove the second solvent.

33. A method of making a conductive foam according to claim 32, wherein the second solvent is an aqueous solvent.

34. A method of making a conductive foam according to any of claims 30 to 33, wherein the organic solvent comprises ethanol, DMAc, DMSO, DMF or a mixture of two or more thereof.

35. A method of making a conductive foam according to claim 34, wherein the organic solvent comprises DMAc or DMSO, or a mixture thereof, especially DMAc.

36. A method of making a conductive foam according to any of claims 1 to 23, comprising providing a polymer foam, providing a solution of a conductive polymer composition in a solvent, said conductive polymer composition comprising a conductive polymer and an elastomer; applying the solution onto the polymer foam; and removing solvent to yield a dry, conductive foam.

37. A method of making a conductive foam according to claim 36, wherein the solvent is an organic solvent and the method comprises removing the organic solvent by solvent exchange with a second solvent.

38. A method of making a conductive foam according to claim 37, wherein the method comprises a drying step to remove the second solvent.

39. A method of making a conductive foam according to claim 38, wherein the second solvent is an aqueous solvent.

40. A method of making a conductive foam according to any of claims 37 to 39, wherein the organic solvent comprises ethanol, DMAc, DMSO, DMF or a mixture of two or more thereof.41 . A method of making a conductive foam according to claim 40, wherein the organic solvent comprises DMAc or DMSO, or a mixture thereof, especially DMAc.

42. A method according to any of claims 30 to 41 , wherein the polymer foam is a closed cell foam and the solvent is compatible with the polymer foam and capable of dissolving the polymer of the foam or at least partially swelling the polymer of the foam.

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