Electrode for living bodies and method for manufacturing same

Abstract

This electrode for living bodies is provided with: a porous base material in which a plurality of pores are formed; and a conductive coating material that coats the surface of the porous base material and the inner surfaces of the plurality of pores.

Description

Bioelectrode and its manufacturing method

[0001] The present invention relates to a biological electrode that comes into contact with the surface of a living body.

[0002] Various devices, such as electrical muscle stimulation (EMS) devices, low-frequency therapy devices, and biomeasuring devices, are equipped with bioelectrodes that come into contact with the surface of a living body. For example, Patent Document 1 discloses a bioelectrode formed from a resin material kneaded with a conductive filler. Patent Document 2 discloses a bioelectrode having a structure in which a conductor formed from PEDOT-PSS is attached to a substrate.

[0003] Patent Document 1: JP 2001-292972 A, International Publication No. 2013 / 073673

[0004] However, biomedical electrodes made of resin materials kneaded with conductive fillers, as in Patent Document 1, tend to have low flexibility. Therefore, the biomedical electrode cannot be sufficiently deformed to conform to the surface of the living body, making it difficult to reduce the contact impedance between the biomedical electrode and the living body surface. Furthermore, in a configuration in which a conductor is formed on the surface of a substrate, as in Patent Document 2, defects such as breakage or peeling of the conductor may occur due to deformation (e.g., expansion and contraction) of the substrate. In consideration of the above circumstances, one aspect of the present disclosure aims to achieve both flexibility and conductivity in a biomedical electrode.

[0005] In order to solve the above problems, a biological electrode according to one aspect of the present disclosure comprises a porous substrate having a plurality of pores formed therein, and a conductive coating material that covers the surface of the porous substrate and the inner surfaces of the plurality of pores.

[0006] A method for manufacturing a biological electrode according to one aspect of the present disclosure includes a molding step of molding a porous substrate having a plurality of pores formed therein, and a coating step of coating the surface of the porous substrate and the inner surfaces of the plurality of pores with a conductive coating material.

[0007] It is a cross-sectional view of the biological electrode according to the embodiment. It is an explanatory diagram of the effect of the embodiment. It is a flowchart illustrating a method for manufacturing the biological electrode.

[0008] The embodiments for carrying out the present disclosure will be described with reference to the drawings. Note that the dimensions and scale of each element in each drawing may differ from those of the actual product. Furthermore, the embodiment described below is an exemplary embodiment that may be envisioned when carrying out the present disclosure. Therefore, the scope of the present disclosure is not limited to the embodiment exemplified below.

[0009] A: Structure of the bioelectrode 100 FIG. 1 is a cross-sectional view of a bioelectrode 100 according to one embodiment of the present disclosure. The bioelectrode 100 of this embodiment is an electrode device that contacts the surface of a living body (i.e., the skin). For example, the bioelectrode 100 is used in an EMS device or low-frequency therapy device that stimulates a living body by supplying current. The bioelectrode 100 is also used in a biomeasurement device that measures bioinformation. The biomeasurement device is, for example, an electrocardiograph that detects the electrocardiogram of a living body, an electromyograph that detects the electromyogram of a living body, or an electroencephalograph that detects the electroencephalogram of a living body. As illustrated in FIG. 1, the bioelectrode 100 comprises a porous substrate 10 and a covering material 20.

[0010] The porous substrate 10 is a flat plate-shaped molded body formed to a predetermined thickness. The surface of the porous substrate 10 includes a first surface 11 and a second surface 12. The first surface 11 faces the surface of a living body. The second surface 12 is the surface opposite to the first surface 11. The porous substrate 10 may be formed into any planar shape, such as a rectangular or circular shape.

[0011] A plurality of pores 13 (voids) are formed inside the porous substrate 10. Each pore 13 is a spherical bubble formed with a diameter sufficiently smaller than the plate thickness of the porous substrate 10. The porous substrate 10 of this embodiment has a continuous pore structure in which the plurality of pores 13 communicate between the first surface 11 and the second surface 12. That is, the plurality of pores 13 communicate over the entire range from the first surface 11 to the second surface 12. Pores 13 open on each of the first surface 11 and the second surface 12, and the space facing the first surface 11 and the space facing the second surface 12 communicate through the plurality of pores 13. Note that the plurality of pores 13 in the porous substrate 10 also include individual pores 13 that do not communicate with other pores 13.

[0012] The porous substrate 10 is a flexible substrate formed from an insulating resin material. That is, the porous substrate 10 is flexibly and elastically deformable so as to conform to the shape of the biological surface. Specifically, the porous substrate 10 is formed from a rubber material such as polyurethane rubber (PUR), polyolefin rubber (PO), silicone rubber (SR), ethylene propylene diene rubber (EPDM), or fluorosilicone rubber (FVMQ). The porous substrate 10 of this embodiment does not include a conductive material such as a conductive filler.

[0013] The coating material 20 is a conductive film (coating) formed on the porous substrate 10. Specifically, the coating material 20 covers the first surface 11 and the second surface 12 of the porous substrate 10 and the inner surfaces of the plurality of pores 13. That is, the coating material 20 is formed not only on the outer surface of the porous substrate 10 but also inside the porous substrate 10. The portions of the coating material 20 that cover the first surface 11 and the second surface 12 are formed in a planar shape with a predetermined film thickness.

[0014] The film thickness of the coating material 20 is sufficiently smaller than the radius of each pore 13. Therefore, a space is formed inside the coating material 20 that coats the inner surface of each pore 13. That is, the coating material 20 inside each pore 13 is formed in the shape of a spherical shell. The coating material 20 is formed so as to be continuous across the plurality of pores 13 that communicate between the first surface 11 and the second surface 12. Therefore, the portion of the coating material 20 that coats the first surface 11 (first portion) and the portion that coats the second surface 12 (second portion) are mutually conductive via the portion that coats the inner surface of each pore 13 (third portion).

[0015] The coating material 20 is made of an intrinsically conducting polymer (ICP). Specifically, the coating material 20 contains PEDOT (poly(3,4-ethylenedioxythiophene)), which is an example of a conductive polymer. For example, the coating material 20 is formed of a mixture of PEDOT and PSS (polystyrene sulfonic acid). As described above, in this embodiment, the coating material 20 is made of a conductive polymer. Therefore, the coating material 20 can be easily formed on the inner surfaces of the plurality of pores 13 in the porous substrate 10. Note that the material of the coating material 20 is not limited to the above examples.

[0016] As described above, this embodiment utilizes a porous substrate 10 having a plurality of pores 13 formed therein. Therefore, flexibility is easier to ensure compared to, for example, a bioelectrode formed from a resin material kneaded with a conductive filler. That is, in this embodiment, the bioelectrode 100 sufficiently deforms to conform to the biosurface, so that the bioelectrode 100 adheres stably to the biosurface. Therefore, the contact impedance between the bioelectrode 100 and the biosurface can be reduced.

[0017] Figure 2 shows the results of contact impedance measurement, showing the results of an embodiment in which a conductive polymer coating material 20 is formed on a porous substrate 10, as well as the results of several comparative examples (Comparative Examples 1 to 3).

[0018] The contact impedance was measured using an LCR meter (model number: ZM2371) manufactured by NF Circuit Design Block Co., Ltd. Specifically, the measurement object was a biological electrode 100 measuring 15 mm x 15 mm x 2 mm, and the contact impedance was measured when a voltage of 1 Vrms (effective value) was applied at a frequency of 10 Hz.

[0019] Comparative Example 1 has an electrode formed on the surface of a fabric substrate. As can be seen from FIG. 2, the contact impedance of Comparative Example 1 is sufficiently large, making it difficult to use alone. Comparative Example 2 has an electrode made of fabric similar to that of Comparative Example 1, but impregnated with water. The contact impedance is reduced by the impregnation with water. However, in Comparative Example 2, the electrode must be impregnated with water to reduce the contact impedance. Therefore, Comparative Example 2 has problems such as discomfort to the user due to the adhesion of water or the inconvenience to the user.

[0020] In contrast to Comparative Example 2, according to this embodiment, the conductive coating material 20 is formed inside the porous substrate 10, so that the contact impedance can be sufficiently reduced without the need for the water impregnation method of Comparative Example 2. As described above, since water impregnation is not required, the biological electrode 100 can be used in a dry state. Therefore, it is possible to reduce, for example, the discomfort of the user caused by the adhesion of water and the effort required by the user to impregnate the electrode with water.

[0021] Comparative Example 3 shows an embodiment in which the electrodes are formed from a resin material kneaded with a conductive filler. According to Comparative Example 3, the contact impedance is reduced compared to Comparative Example 1. However, since it is difficult to ensure the flexibility of the electrodes in Comparative Example 3, the effect of reducing the contact impedance is limited. According to the present embodiment, the conductive coating material 20 is formed inside the porous substrate 10, so that the contact impedance can be sufficiently reduced compared to Comparative Example 3.

[0022] By reducing the contact impedance as described above, the EMS device or low-frequency therapy device can provide a moderate stimulation to the living body. Specifically, it can reduce the possibility of providing a sharp, tingling pain to the living body, or the possibility of providing a stimulation that is not perceptible to the living body. Furthermore, as a result of the reduced contact impedance, the biometric device can measure biological information with high accuracy.

[0023] Furthermore, in addition to the surface of the porous substrate 10, the inner surfaces of the plurality of pores 13 are covered with the conductive coating material 20. According to the above configuration, a sufficient contact area between the porous substrate 10 and the coating material 20 is ensured compared to a configuration in which the coating material 20 is formed only on the first surface 11 and the second surface 12 of the porous substrate 10. Therefore, even when the porous substrate 10 is deformed (e.g., expanded or contracted), defects such as damage or peeling of the coating material 20 are unlikely to occur. For example, compared to a configuration in which an electrode is formed only on the surface of a flat substrate, the conductivity of the biological electrode 100 is more easily maintained. As described above, according to this embodiment, the biological electrode 100 can achieve both flexibility and conductivity.

[0024] In this embodiment, the inner surfaces of the plurality of pores 13 that communicate between the first surface 11 and the second surface 12 of the porous substrate 10 are coated with the conductive coating material 20. Therefore, it is easy to ensure conductivity between the first surface 11 and the second surface 12.

[0025] B: Method for Manufacturing the Biomedical Electrode 100 FIG. 3 is a flowchart illustrating a method for manufacturing the biomedical electrode 100 described above.

[0026] First, in the molding step P1, a porous substrate 10 having a plurality of pores 13 formed therein is formed. Specifically, a resin material mixed with a foaming agent is heated and foamed to form a flat plate. As described above, various conditions for the molding step P1 are selected so that a continuous pore structure is formed inside the porous substrate 10. Note that the method for forming the porous substrate 10 is not limited to the above examples.

[0027] In the coating process P2 after the molding process P1, a conductive coating material 20 is formed to cover the porous substrate 10. As described above, the coating material 20 is formed so as to cover the first surface 11 and the second surface 12 of the porous substrate 10 and the inner surfaces of the plurality of pores 13. As explained above, in this embodiment, the conductive polymer is not added when the porous substrate 10 is molded (molding process P1), but the conductive polymer coating material 20 is formed after the porous substrate 10 is molded. The coating process P2 in this embodiment includes an impregnation process P21 and a drying process P22.

[0028] In the impregnation step P21, the porous substrate 10 is impregnated with a coating solution containing a conductive polymer (PEDOT). The coating solution is, for example, a solution in which a mixture of PEDOT and PSS is dispersed in a solvent. The solvent for the coating solution is, for example, pure water or an organic solvent (e.g., ethanol). For example, with the entire porous substrate 10 immersed in the coating solution, the air in the working space is discharged to the outside (vacuum drawing), whereby the coating solution penetrates into the multiple pores 13 inside the porous substrate 10.

[0029] In the drying step P22, the porous substrate 10 impregnated with the coating solution is dried to form the coating material 20. That is, for example, the solvent of the coating solution is volatilized by heating, resulting in the formation of a thin film-like coating material 20 that covers the first surface 11 and the second surface 12 of the porous substrate 10 and the inner surfaces of the plurality of pores 13.

[0030] According to the manufacturing method described above, as mentioned above, it is possible to manufacture a biological electrode 100 that is capable of achieving both flexibility and conductivity. In particular, in this embodiment, the coating material 20 is formed by impregnating the formed porous substrate 10 with a coating solution containing a conductive polymer, and then volatilizing the solvent of the coating solution by drying the porous substrate 10. Therefore, the biological electrode 100 can be manufactured by a simple process.

[0031] C: Modifications Specific modifications that can be added to the above-mentioned embodiments are exemplified below. Two or more embodiments arbitrarily selected from the following examples may be combined as appropriate within the scope of not mutually contradicting each other.

[0032] (1) In the above-described embodiment, the pores 13 are uniformly distributed throughout the entire porous substrate 10, but the pores 13 may be distributed unevenly. For example, the distribution density of the pores 13 may differ between a portion close to the first surface 11 and a portion close to the second surface 12 in the thickness direction of the porous substrate 10. Furthermore, for example, within a plane along the surface (first surface 11, second surface 12) of the porous substrate 10, the distribution density of the pores 13 may differ between a portion close to the periphery of the biological electrode 100 and a portion close to the center.

[0033] (2) In the above-described embodiment, the multiple pores 13 formed inside the porous substrate 10 have the same diameter. However, multiple pores 13 having different inner diameters may be formed inside the porous substrate 10.

[0034] (3) In the above-described embodiment, the porous substrate 10 is formed of a single layer, but the porous substrate 10 may be formed of a laminate of multiple layers made of different materials. The multiple pores 13 are formed to be in communication with each other across the multiple layers. In the above-described embodiment, the covering material 20 is formed of a single layer, but the covering material 20 may be formed of a laminate of multiple layers made of different materials.

[0035] (4) In the above embodiment, the porous substrate 10 is shaped like a flat plate, but the shape of the porous substrate 10 is not limited to the above example. For example, the porous substrate 10 may be shaped into a three-dimensional shape, such as a band shape that can be wrapped around a part of a living body, such as the wrist or ankle.

[0036] (5) In the above embodiment, the porous substrate 10 is an insulator, but the porous substrate 10 may be a conductor. For example, the porous substrate 10 may be formed from a resin material in which a conductive material such as a conductive filler is dispersed, or from various conductive polymers.

[0037] As mentioned above, resin materials kneaded with conductive fillers tend to have low flexibility. According to the biomedical electrode 100 of the present disclosure, the formation of the covering material 20 ensures the conductivity of the biomedical electrode 100. Therefore, even if a conductive filler is dispersed in the porous substrate 10, the amount of conductive filler required to ensure sufficient conductivity is reduced compared to conventional configurations in which the covering material 20 is not formed. In other words, the lack of flexibility of the porous substrate 10 caused by the conductive filler is alleviated. Furthermore, in the present disclosure, the multiple pores 13 also contribute to the flexibility of the porous substrate 10. Therefore, even if the porous substrate 10 contains a conductive filler, the aforementioned effect of achieving both flexibility and conductivity of the biomedical electrode 100 is achieved compared to configurations in which the covering material 20 or multiple pores 13 is not formed.

[0038] (6) The biological electrode 100 may be used for any purpose. That is, the scope of application of the present disclosure is not limited to the EMS device, low-frequency therapy device, or biometric device exemplified in the above-described embodiments.

[0039] D: Supplementary Notes From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0040] A biological electrode according to one aspect (Aspect 1) of the present disclosure comprises a porous substrate having a plurality of pores formed therein and a conductive coating material that coats the surface of the porous substrate and the inner surfaces of the plurality of pores. In the above aspect, a porous substrate having a plurality of pores (voids) formed therein is used, which makes it easier to ensure flexibility compared to, for example, a biological electrode made of a resin material kneaded with a conductive filler. Therefore, the contact impedance between the biological electrode and the biological surface can be reduced. Furthermore, because the inner surfaces of the plurality of pores, in addition to the surface of the porous substrate, are covered with a conductive coating material, defects such as breakage or peeling of the coating material are less likely to occur even when the porous substrate is deformed. Therefore, conductivity is easier to maintain compared to a configuration in which an electrode is formed on the surface of a substrate. As described above, according to the present disclosure, both flexibility and conductivity of the biological electrode can be achieved.

[0041] In a specific example (Aspect 2) of Aspect 1, the surface of the porous substrate includes a first surface and a second surface located opposite each other, and the porous substrate has a continuous pore structure in which two or more of the plurality of pores are continuous throughout the entire range from the first surface to the second surface. In the above aspect, the inner surfaces of the two or more pores that are continuous between the first surface and the second surface are coated with a conductive coating material. Therefore, it is easy to ensure conductivity between the first surface and the second surface.

[0042] In a specific example (Aspect 3) of Aspect 2, the coating material includes a first portion covering the first surface, a second portion covering the second surface, and a third portion covering the inner surfaces of the plurality of pores, and the first portion and the second portion are electrically connected to each other via the third portion. According to the above aspect, it is possible to pass a current between the first portion and the second portion.

[0043] In a specific example (Aspect 4) of any of Aspects 1 to 3, the coating material is formed of a conductive polymer. In the above aspects, the coating material is formed of a conductive polymer. Therefore, the coating material can be easily formed on the inner surfaces of the multiple pores in the porous substrate. In a specific example (Aspect 5) of Aspect 4, the conductive polymer contains, for example, PEDOT.

[0044] In a specific example (Aspect 6) of any of Aspects 1 to 5, the film thickness of the coating material is smaller than the radius of each of the plurality of pores. In the above aspects, a space is formed inside the coating material that covers the inner surface of each pore. That is, the coating material inside each pore is formed in a spherical shell shape. Therefore, it is easier to ensure the flexibility of the biological electrode compared to an embodiment in which the coating material fills each pore entirely.

[0045] A method for manufacturing a biological electrode according to one aspect (aspect 7) of the present disclosure includes a molding step of molding a porous substrate having a plurality of pores formed therein and a coating step of coating the surface of the porous substrate and the inner surfaces of the plurality of pores with a conductive coating material. In the above aspect, a porous substrate having a plurality of pores formed therein is used, which makes it easier to ensure flexibility compared to, for example, a biological electrode made of a resin material kneaded with a conductive filler. Therefore, the contact impedance between the biological electrode and the biological surface can be reduced. Furthermore, because the inner surfaces of the plurality of pores, in addition to the surface of the porous substrate, are coated with a conductive coating material, defects such as breakage or peeling of the coating material are less likely to occur even when the porous substrate is deformed. Therefore, conductivity is easier to maintain compared to a configuration in which an electrode is formed on the surface of a substrate. As described above, according to the present disclosure, both flexibility and conductivity of the biological electrode can be achieved.

[0046] In a specific example (Aspect 8) of Aspect 7, the coating step includes an impregnation step of impregnating the porous substrate with a solution containing a conductive polymer, and a drying step of drying the porous substrate impregnated with the solution to form the coating material. In the above aspect, the coating material is formed by impregnating the formed porous substrate with a solution containing a conductive polymer, and then drying the porous substrate to volatilize the solvent. Therefore, a biological electrode can be manufactured by a simple process.

[0047] 100...biological electrode, 10...porous substrate, 11...first surface, 12...second surface, 13...pore, 20...coating material.

Claims

1. A biological electrode comprising: a porous substrate having a plurality of pores formed therein; and a conductive coating material that covers the surface of the porous substrate and the inner surfaces of the plurality of pores.

2. The biological electrode of claim 1, wherein the surface of the porous substrate includes a first side and a second side located opposite each other, and the porous substrate has a continuous pore structure in which two or more of the plurality of pores are connected over the entire area from the first side to the second side.

3. The biological electrode of claim 2, wherein the covering material includes a first portion covering the first surface, a second portion covering the second surface, and a third portion covering the inner surfaces of the plurality of pores, and the first portion and the second portion are mutually conductive via the third portion.

4. A biological electrode according to any one of claims 1 to 3, wherein the covering material is formed from a conductive polymer.

5. The bioelectrode according to claim 4, wherein the conductive polymer contains PEDOT.

6. A biological electrode according to any one of claims 1 to 5, wherein the thickness of the coating material is smaller than the radius of each of the plurality of pores.

7. A method for manufacturing a biological electrode, comprising: a molding step of molding a porous substrate having a plurality of pores formed therein; and a coating step of coating a surface of the porous substrate and the inner surfaces of the plurality of pores with a conductive coating material.

8. The method for manufacturing a biological electrode according to claim 7, wherein the coating process includes an impregnation process of impregnating the porous substrate with a solution containing a conductive polymer, and a drying process of drying the porous substrate impregnated with the solution to form the coating material.

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