Hydrogel for DC current application

Abstract

To provide hydrogel for DC current application with which a change in voltage when a DC current is applied is small, pain at the time of electrical stimulation can be suppressed, and a color change into yellow after the current application is small.SOLUTION: Provided is hydrogel for DC current application containing polymer matrix being a polymer of (meth)acrylic monomer, water, humectant, and electrolyte. The electrolyte contains at least one electrolyte selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a hydrogel for application of direct current. [Background technology]

[0002] Hydrogels are adhesive and conductive, and are therefore widely used as components of electrode pads and wound dressings that are applied to living bodies. Hydrogels are sometimes used in direct current therapy, such as in direct current bioelectrical therapy devices and non-invasive brain stimulation methods that use direct current, such as transcranial direct current stimulation (tDCS). Because direct current has a stronger therapeutic effect than alternating current, there is a need for hydrogels that are suitable for application of direct current.

[0003] Patent Document 1 discloses a conductive laminated hydrogel sheet that can be used for applying direct current, which has at least two hydrogel sheet layers, in which a hydrogel sheet A layer with a thickness of a mm and a hydrogel sheet B layer with a thickness of b mm are alternately laminated, the hydrogel sheet A layer contains at least one inorganic salt in a total content of X wt % relative to the total weight of the hydrogel sheet A layer, and the hydrogel sheet B layer contains at least one inorganic salt in a total content of Y wt % relative to the total weight of the hydrogel sheet B layer, where Y is less than X, and the hydrogel sheet B layer contains at least one acid.

[0004] In Patent Document 1, two hydrogel sheet layers with different inorganic salt contents within a predetermined range are alternately laminated to suppress the increase in pH and the decrease in conductivity when a direct current is applied for a certain period of time. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-51155 Summary of the Invention [Problem to be solved by the invention]

[0006] In the conductive laminated hydrogel sheet of Patent Document 1, although the decrease in conductivity is suppressed by laminating, there is an issue of pain when stimulated. The problem to be solved by the present invention is to provide a hydrogel for application of direct current, which has little change in voltage when direct current is applied, can suppress pain during electrical stimulation, and has little yellowing after current application. [Means for solving the problem]

[0007] The present invention encompasses the embodiments described below. Section 1. A hydrogel for applying direct current, comprising a polymer matrix which is a polymer of a (meth)acrylic monomer, water, a humectant, and an electrolyte, wherein the electrolyte contains at least one electrolyte selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate. Section 2. Item 1. A hydrogel for application of direct current according to Item 1, wherein the voltage value 1 minute after the start of application of a direct current of 2 mA is 9 V or more.

[0008] Section 3. Item 2. The hydrogel for applying direct current according to Item 1, wherein the content of the at least one electrolyte is 0.10 to 5.0% by mass relative to 100% by mass of the hydrogel. Section 4. Item 1. The hydrogel for applying direct current according to Item 1, which has a thickness of 0.30 to 10 mm.

[0009] Section 5. Item 2. The hydrogel for application of direct current according to Item 1, further comprising at least one pair of organic acid and organic acid salt selected from the group consisting of succinic acid and a succinate salt, and malic acid and a malate salt. Section 6. Item 6. The hydrogel for applying direct current according to Item 5, wherein the total content of the organic acid and the organic acid salt is 0.50 to 10% by mass relative to 100% by mass of the hydrogel.

[0010] Section 7. Item 1. The hydrogel for applying a direct current according to Item 1, which is formed into a sheet shape. Section 8. Item 8. A bioelectrode hydrogel for application to the skin, comprising the hydrogel for direct current application according to any one of Items 1 to 7. Section 9. 8. An electrode pad comprising the hydrogel for applying direct current according to any one of items 1 to 7 and an electrode electrically connected to the hydrogel for applying direct current. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a hydrogel for application of direct current, which has little change in voltage when a direct current is applied, can suppress pain during electrical stimulation, and has little yellowing after application of current. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of a hydrogel according to one embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view of a hydrogel according to another embodiment of the present invention. [Figure 3] FIG. 2 is a schematic cross-sectional view of an electrode pad according to an embodiment. [Figure 4] FIG. 10 is a schematic cross-sectional view of an electrode pad according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] As used herein, "(meth)acrylic monomer" refers to an acrylic and / or methacrylic monomer, "(meth)acrylate" refers to an acrylate and / or methacrylate, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid, "(meth)acryloyl" refers to acryloyl and / or methacryloyl, and "(meth)acrylamide" refers to acrylamide and / or methacrylamide.

[0014] In this specification, a "sheet" refers to a layered body having a thickness of 200 μm or more, and a "film" refers to a layered body having a thickness of less than 200 μm.

[0015] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. Furthermore, in this specification, numerical values ​​connected with "to" mean a numerical range that includes the numbers before and after "to" as the upper and lower limits.

[0016] Hydrogel for DC current application A hydrogel for applying direct current (hereinafter simply referred to as "hydrogel" or "gel") according to an embodiment of the present invention is a hydrogel containing a polymer matrix that is a polymer of a (meth)acrylic monomer, water, a humectant, and an electrolyte, wherein the electrolyte contains at least one electrolyte selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate.

[0017] The hydrogel for direct current application according to an embodiment of the present invention contains a polymer matrix which is a polymer of a (meth)acrylic monomer. The polymer matrix may be a copolymer of a (meth)acrylic monomer and a crosslinkable monomer.

[0018] The content of the polymer matrix in the hydrogel for direct current application is preferably 5.0 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 13 to 35 mass %.

[0019] A (meth)acrylic monomer is a general term for a monomer that has an acryloyl group (HC=CH-C(=O)-) or a methacryloyl group (HC=C(CH)-C(=O)-), and can be polymerized to form a polymer. A (meth)acrylic monomer is a (meth)acrylic monomer that has one polymerizable carbon-carbon double bond in the molecule, and is a non-crosslinking monomer.

[0020] The (meth)acrylic monomer is not particularly limited, but examples thereof include (meth)acrylamide monomers, (meth)acrylic acid esters, and (meth)acrylic acid. One or more selected from the (meth)acrylamide monomers and (meth)acrylic acid esters are preferred, and (meth)acrylamide monomers are more preferred.

[0021] Specific examples of (meth)acrylamide monomers include (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; N-alkyl(meth)acrylamides such as N-isopropyl(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide and N-propyl(meth)acrylamide; N-hydroxyalkyl(meth)acrylamides such as N-hydroxyethyl(meth)acrylamide and N-hydroxymethyl(meth)acrylamide; N-ethoxymethyl(meth)acrylamide, N-propoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-iso ... Examples of the acrylic acid monomer include N-alkoxyalkyl (meth)acrylamides such as N-dimethyl(meth)acrylamide, N-pentoxymethyl(meth)acrylamide, N-hexyloxymethyl(meth)acrylamide, N-heptoxymethyl(meth)acrylamide, N-octoxymethyl(meth)acrylamide, N-ethoxyethyl(meth)acrylamide, N-propoxyethyl(meth)acrylamide, and N-butoxyethyl(meth)acrylamide; cationic acrylamide compounds containing an amino group such as dimethylaminopropyl(meth)acrylamide; anionic (meth)acrylic monomers containing a sulfonic acid group such as 4-acryloylmorpholine and tert-butylacrylamidosulfonic acid, or salts thereof; and derivatives thereof. Among these, one or more selected from the group consisting of (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, 4-acryloylmorpholine, tert-butylacrylamidosulfonic acid and salts thereof are preferred, but are not limited thereto.

[0022] Specific examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 18 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. (meth)acrylic acid alkyl esters such as n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-pentyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-lauryl (meth)acrylate, tridecyl (meth)acrylate, and n-stearyl (meth)acrylate; alicyclic (meth)acrylic acid esters such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and 1-adamantyl (meth)acrylate; 2-methoxyethyl (meth)acrylate, Examples of the acrylate include, but are not limited to, one or more selected from the group consisting of alkoxy group-containing (meth)acrylic acid esters such as ethoxyethoxyethyl (meth)acrylate and methoxypolyethylene glycol (meth)acrylates such as methoxytriethylene glycol (meth)acrylate; hydroxyalkyl (meth)acrylates (in which an aryl group may be bonded to the hydroxyalkyl group via an ether bond) such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate; glycerin mono(meth)acrylate; polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate and polyethylene glycol-polypropylene glycol copolymer; (meth)acrylic acid esters having an aromatic ring such as benzyl (meth)acrylate; and (meth)acrylic acid esters having a heterocyclic ring such as tetrahydrofurfuryl (meth)acrylate.

[0023] The hydrogel may or may not contain acrylic acid as a (meth)acrylic monomer. When the hydrogel contains acrylic acid, the amount of acrylic acid in the hydrogel is preferably small, for example, 15% by mass or less, preferably 5% by mass or less, relative to 100% by mass of the hydrogel.

[0024] The amount of (meth)acrylic monomer added is preferably 98.50 to 99.98% by mass, more preferably 99.50 to 99.85% by mass, of the total amount of monomers constituting the polymer matrix in terms of forming a hydrogel. Similarly, the content of structural units derived from (meth)acrylic monomers in the polymer matrix is ​​preferably 98.50 to 99.98% by mass, more preferably 99.50 to 99.85% by mass, of the total amount of polymer matrix.

[0025] Furthermore, the amount of the (meth)acrylic monomer added is preferably 5.0 to 50% by mass relative to 100% by mass of the hydrogel from the viewpoints of forming the hydrogel, resistance to tearing, and hardness. From the viewpoint of allowing ion migration within the hydrogel, the content of the (meth)acrylic monomer in the hydrogel is preferably 60% by mass or less.

[0026] The crosslinkable monomer preferably has two or more polymerizable carbon-carbon double bonds in its molecule. Specific examples include polyfunctional (meth)acrylamides or polyfunctional (meth)acrylic acid esters such as methylene bis(meth)acrylamide, ethylene bis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, glycerin di(meth)acrylate, and glycerin tri(meth)acrylate, as well as tetraallyloxyethane and diallylammonium chloride. These may be used alone or in combination. Furthermore, the crosslinkable monomer having two or more polymerizable double bonds in its molecule may also be a polyglycerin derivative, which is a polyfunctional compound having two or more (meth)acryloyl or vinyl groups and a molecular weight of 400 or more, as described in Japanese Patent Publication No. 2803886. The above polyfunctional (meth)acrylamides, the above polyfunctional (meth)acrylic acid esters, and polyglycerin derivatives are included in the (meth)acrylic monomers.

[0027] From the viewpoints of adhesive strength and hardness, the amount of crosslinkable monomer added is preferably 0.020 to 1.5% by mass, more preferably 0.15 to 0.50% by mass, relative to the total amount of monomers constituting the polymer matrix. When the amount of crosslinkable monomer added is 0.020% by mass or more, the crosslink density is maintained, the shape stability is good, and the adhesive strength can be sufficiently increased. Furthermore, when the amount of crosslinkable monomer added is 1.5% by mass or less, the adhesive strength and / or repeated adhesiveness can be maintained high, and a flexible gel can be obtained. Similarly, the content of structural units derived from the crosslinkable monomer in the polymer matrix is ​​preferably in the range of 0.020 to 1.5% by mass, more preferably 0.15 to 0.50% by mass.

[0028] Furthermore, the amount of crosslinkable monomer added is preferably 0.010 to 0.10% by mass relative to 100% by mass of the hydrogel, from the viewpoints of adhesive strength, handleability, etc. of the gel or gel sheet. Similarly, the content of structural units derived from the crosslinkable monomer in the hydrogel is preferably 0.010 to 0.10% by mass.

[0029] From the viewpoint of adhesion and hardness, it is preferable that the amount of (meth)acrylic monomer added as a constituent monomer of the polymer matrix is ​​98.5 to 99.98 mass% and the amount of crosslinkable monomer added is 0.020 to 1.5 mass% relative to the total amount of the polymer matrix, and it is more preferable that the amount of (meth)acrylic monomer added is 99.5 to 99.85 mass% and the amount of crosslinkable monomer added is 0.15 to 0.50 mass%.

[0030] The copolymer of a (meth)acrylic monomer and a crosslinkable monomer preferably does not contain any additional monomer constituting the copolymer other than the (meth)acrylic monomer and the crosslinkable monomer, but may contain such an additional monomer.

[0031] The hydrogels of the present embodiments further contain water. The water content of the hydrogel is not particularly limited, but is preferably 10 to 60% by mass relative to 100% by mass of the hydrogel. In one embodiment, it is 10 to 45% by mass. In another embodiment, it is 15 to 30% by mass. When the water content is 10% by mass or more, the water content relative to the equilibrium water content of the hydrogel is sufficient. Furthermore, when the water content is 60% by mass or less, shrinkage and changes in physical properties of the hydrogel due to drying are unlikely to occur.

[0032] The hydrogels of the present embodiments further contain a humectant. The humectant is added to impart wettability to the hydrogel, and examples of the humectant include polyhydric alcohols, which are not particularly limited and include diols such as ethylene glycol, triethylene glycol, 1,6-hexanediol, 1,9-nonanediol, propylene glycol, and butanediol; trihydric or higher polyhydric alcohols such as glycerin, pentaerythritol, and sorbitol; polyhydric alcohol condensates such as polyethylene glycol, polypropylene glycol, and polyglycerin; and polyhydric alcohol denaturants such as polyoxyethyleneglycerin.

[0033] Among polyhydric alcohols, it is preferable to use polyhydric alcohols that are liquid in the temperature range in which the hydrogel is used (for example, around 20°C when used indoors), and specifically, one or more selected from the group consisting of ethylene glycol, triethylene glycol, propylene glycol, polypropylene glycol, polyethylene glycol, polyglycerin, and glycerin are preferred.

[0034] The content of the humectant, particularly the polyhydric alcohol, in the hydrogel is not particularly limited, but is preferably 20 to 70% by mass, and more preferably 25 to 65% by mass, relative to 100% by mass of the hydrogel. The humectant content is preferably greater than the water content, but may be less than or equal to the water content. A humectant content of 20% by mass or greater is advantageous in terms of the moisturizing power, flexibility, and stability over time of the hydrogel. Furthermore, a humectant content of 70% by mass or less is generally an amount of humectant that can be retained by the polymer matrix, and is also advantageous in terms of sufficient adhesiveness of the hydrogel.

[0035] The hydrogel of an embodiment of the present invention contains at least one electrolyte (hereinafter sometimes referred to as electrolyte A) selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate, which reduces the change in voltage when a direct current is applied to the hydrogel, thereby reducing the pain felt by the user (e.g., patient) during electrical stimulation and reducing the yellowing of the hydrogel after application of current. Sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate may be used alone or in combination of two or more.

[0036] The content of the electrolyte A in the hydrogel is not particularly limited, but in order to provide a hydrogel for direct current application that shows little change in voltage when a direct current is applied, can suppress pain during electrical stimulation, and shows little yellowing after current application, the content is preferably 0.10 to 5.0% by mass relative to 100% by mass of the hydrogel, more preferably 0.10 to 4.5% by mass relative to 100% by mass of the hydrogel, and even more preferably 0.30 to 4.0% by mass relative to 100% by mass of the hydrogel. In terms of moles, the hydrogel preferably contains 0.050 to 50 mmol of the electrolyte A.

[0037] The hydrogel according to the embodiment of the present invention may further contain at least one electrolyte other than electrolyte A (hereinafter, sometimes referred to as electrolyte B) selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate.

[0038] The electrolyte B is not particularly limited, and examples thereof include hypochlorite, chlorite, chlorate, perchlorate, hydrochloride, sulfate, carbonate, nitrate, and phosphate salts of various metals. Examples of such metal salts include, but are not limited to, metal chlorides with low skin irritation, such as sodium chloride, potassium chloride, and magnesium chloride. Furthermore, inorganic salts such as ammonium salts and various complex salts; metal salts of organic carboxylic acids such as trisodium citrate, tripotassium citrate, sodium propionate, and potassium propionate; and organic ammonium salts can also be used as the electrolyte.

[0039] When the hydrogel contains electrolyte B, the content of electrolyte B is preferably 5.0% by mass or less, and more preferably 0.10 to 4.0% by mass, relative to 100% by mass of the hydrogel.

[0040] The hydrogels of the present embodiments may further contain a combination of an organic acid and an organic acid salt, which acts as a buffering agent. Examples of organic acids and organic acid salts include succinic acid and succinate salts, malic acid and malate salts, tartaric acid and tartrate salts, gluconic acid and gluconate salts, or lactic acid and lactate salts, as well as combinations of two or more pairs of these organic acids and organic acid salts. In a preferred embodiment, the organic acid and organic acid salt include at least one pair of organic acid and organic acid salt selected from the group consisting of succinic acid and succinate salts, and malic acid and malate salts, which are highly effective in suppressing pH changes in the hydrogel after application of direct current. The total content of the organic acid and organic acid salt in the hydrogel is preferably 0.50 to 10% by mass relative to 100% by mass of the hydrogel, from the viewpoint of the effect of suppressing the pH change of the hydrogel after application of a direct current.

[0041] The hydrogel of the present invention may also contain a pH adjuster for adjusting the pH, such as a base such as sodium hydroxide.

[0042] Furthermore, the hydrogels of the present embodiments may optionally contain molecules such as polyacrylic acid or salts thereof to enhance adhesive strength.

[0043] The hydrogel according to the embodiment of the present invention may contain other additives as needed, such as rust inhibitors, antifungal agents, antioxidants, antifoaming agents, stabilizers, surfactants, colorants, etc.

[0044] The thickness of the hydrogel according to the embodiment of the present invention is not particularly limited, but is, for example, 0.30 to 10 mm, and more preferably, 0.30 to 3.0 mm.

[0045] In a preferred embodiment, the hydrogel for direct current application has a voltage value of 9 V or higher one minute after the start of application of a direct current of 2 mA to the hydrogel. One minute after the start of application of a direct current of 2 mA is the timing at which the voltage is maintained at a stable high level after the unstable voltage change at the start of the direct current application has passed. If the initial voltage one minute after the start of application of such direct current is low, the current will flow easily and the user will be more likely to feel pain during stimulation, but if the initial voltage is high, the pain felt by the user during stimulation can be more effectively suppressed.

[0046] The hydrogel according to an embodiment of the present invention preferably exhibits a voltage change rate of 15% or less, more preferably 10% or less, when a 2 mA DC current (constant current) is applied to a 30 mm diameter (φ) disk-shaped hydrogel for 15 minutes. Such hydrogels are less susceptible to voltage changes due to DC current. If the thickness of a single hydrogel is less than 0.30 mm, multiple hydrogels are stacked to a thickness of 0.30 to 10 mm, and the voltage change rate is measured. If the thickness of a single hydrogel is greater than 10 mm, the hydrogel is sliced ​​to a thickness of 0.30 to 10 mm, and the voltage change rate is measured. The voltage change rate is calculated by {(voltage 15 minutes after the start of DC current application)-(voltage 1 minute after the start of DC current application)} / (voltage 1 minute after the start of DC current application)}×100.

[0047] In a specific embodiment, the hydrogel is a hydrogel sheet having a thickness in the range of 0.30 to 10 mm, and exhibiting a voltage change rate of 10% or less when a direct current of 2 mA is applied for 15 minutes.

[0048] Manufacturing method of hydrogel for DC current application The hydrogel for application of direct current can be obtained by polymerizing and crosslinking a mixture (hereinafter also referred to as a composition for forming a hydrogel for application of direct current) in which the above-mentioned materials other than water constituting the hydrogel and a polymerization initiator are uniformly dispersed in water, by heating or irradiating with ultraviolet light, etc. Note that dispersion includes not only a state in which the solute is dispersed in water without mixing with water, but also a dissolution in which the solute mixes with water to form a homogeneous phase mixture.

[0049] The components ((meth)acrylic monomer, crosslinkable monomer, water, humectant, at least one electrolyte selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate, and optional other components) in the hydrogel-forming composition for application of direct current and their preferred contents are as described above for the hydrogel.

[0050] The polymerization initiator may be a thermal polymerization initiator, a photopolymerization initiator, or a redox initiator, and any known thermal polymerization initiator or photopolymerization initiator for polymerizing a (meth)acrylic monomer can be used. The content of the polymerization initiator is not particularly limited, but is preferably 0.010% by mass or more and 1.0% by mass or less of the blended liquid (direct current hydrogel-forming composition) before polymerization excluding the polymerization initiator.

[0051] When polymerizing by ultraviolet irradiation, the amount of ultraviolet irradiation is not particularly limited, but the peak intensity is preferably 50 to 150 mW / cm 2 It is preferable to irradiate the substrate with ultraviolet light having a peak intensity of 50 mW / cm. 2 Above this level, the adhesive function improves due to the increase in low molecular weight components in the hydrogel, and the2 The cumulative dose of ultraviolet light varies depending on the content of the polymerization initiator, etc., but is, for example, 800 to 10,000 mJ / cm 2 2 It is preferable that the range is 2000 to 10000 mJ / cm 2 It is more preferable that the range is within the range of

[0052] In a preferred embodiment, a method for producing a hydrogel for applying a direct current includes the steps of: producing a hydrogel having a peak intensity of 50 to 150 mW / cm for a blended solution containing a (meth)acrylic monomer, a crosslinkable monomer, water, a wetting agent, and at least one electrolyte selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate; 2 The method is characterized by including a step of irradiating the substrate with ultraviolet light.

[0053] Applications of DC current hydrogel The hydrogel for application of direct current according to an embodiment of the present invention can be formed into a desired shape, such as a sheet, by pouring a pre-polymerization mixture (a hydrogel-forming composition for application of direct current) into a container of a desired shape, such as a container with a bottom and a substantially rectangular cross section, and polymerizing the mixture by irradiation with ultraviolet light or the like. Hereinafter, a sheet-like hydrogel will be referred to as a "hydrogel sheet" or simply as a "gel sheet." The shape of the hydrogel sheet can be any shape suited to the purpose, and examples include, but are not limited to, substantially rectangular, substantially circular, etc.

[0054] If the thickness of the hydrogel sheet for applying direct current according to the embodiment of the present invention is too thick, the shear stress decreases, and if it is too thin, the cohesive force decreases. Furthermore, the thinner the hydrogel sheet for applying direct current, the greater the voltage change rate. Taking these factors into consideration, those skilled in the art can select an appropriate thickness. The thickness of the hydrogel sheet for applying direct current is preferably 0.30 to 10 mm, more preferably 0.60 to 3.0 mm, and even more preferably 1.0 to 3.0 mm.

[0055] The hydrogel sheet for direct current application according to an embodiment of the present invention may include an intermediate substrate. Such intermediate substrates are used in the art to reinforce and / or improve the shape retention of hydrogel sheets. The intermediate substrate is preferably embedded in the hydrogel so as to extend in a direction substantially parallel to a plane perpendicular to the thickness direction of the hydrogel. Specific embodiments of the intermediate substrate include nonwoven fabric or woven fabric. Examples of materials for nonwoven fabric and woven fabric include natural fibers such as cellulose, silk, and hemp, synthetic fibers such as polyester, nylon, rayon, polyethylene, polypropylene, and polyurethane, and blends thereof. The intermediate substrate may contain a binder as needed. The intermediate substrate may also be colored as needed.

[0056] The thickness of the intermediate substrate is not particularly limited, but is preferably 0.050 to 2.0 mm in terms of conductivity and reinforcement of the hydrogel sheet.

[0057] A base film may be disposed on the surface of the hydrogel sheet for applying direct current according to the embodiment of the present invention. The base film is preferably disposed so as to cover the entire surface of the hydrogel sheet facing the base film.

[0058] As the base film, for example, a resin film made of a resin such as polyester, polyolefin, polystyrene, or polyurethane, paper, or paper laminated with the above-mentioned resin film can be used.

[0059] The surface of the base film that contacts the hydrogel sheet is preferably subjected to a release treatment. Examples of the release treatment include silicone coating, and baked silicone coating, which undergoes a crosslinking or curing reaction with heat or ultraviolet light, is particularly preferred. Particularly preferred films to be subjected to the release treatment include biaxially stretched PET (polyethylene terephthalate) film and OPP (oriented polypropylene) film.

[0060] A top film may be placed on the surface of the hydrogel sheet for applying direct current according to an embodiment of the present invention. The top film may be made of the same material as the base film. For example, when a top film is placed on the hydrogel sheet and then irradiated with ultraviolet light or the like to cause polymerization, it is preferable to select a film made of a material that does not block light so as not to interfere with photopolymerization.

[0061] A top film may be placed on one surface of the hydrogel sheet for applying a direct current according to an embodiment of the present invention, and a base film may be placed on the other surface of the hydrogel sheet for applying a direct current according to an embodiment of the present invention.

[0062] The direct current application hydrogel (including hydrogel sheet) of the embodiment of the present invention is unlikely to cause a change in voltage even when a direct current is applied for a certain period of time. Therefore, the hydrogel of the embodiment of the present invention can be used as a bioelectrode hydrogel to be applied to the skin. Preferably, the hydrogel can be used as a bioelectrode hydrogel, particularly a medical electrode hydrogel, that is disposed between an electrode made of a conductive material and the skin surface. In this case, one side of the direct current application hydrogel can be in contact with the electrode, and the other side can be in contact with the skin surface. Furthermore, the direct current application hydrogel (including hydrogel sheet) of the embodiment of the present invention can be used as a component of an electrode pad having the direct current application hydrogel and an electrode electrically connected to the direct current application hydrogel.

[0063] The electrode pad can be applied to the electrode portions of various devices, for example, medical devices such as biomedical measuring devices or bioelectrical treatment devices, or industrial measuring devices such as measuring devices for inspecting the surface of ground or rock, and devices for detecting damage to water-leaking sheets at waste disposal sites, etc. In a preferred embodiment, the electrode pad is a biomedical electrode pad that can be applied to medical devices such as biomedical measuring devices or bioelectrical treatment devices.

[0064] Specific embodiments of the hydrogel sheet for applying direct current and the electrode pad of the present invention are described below.

[0065] 1 is a schematic cross-sectional view of a hydrogel sheet according to one embodiment of the present invention. The hydrogel sheet 1 comprises a hydrogel sheet layer 10 made of a hydrogel sheet according to an embodiment of the present invention, a base film 12 disposed on one side of the hydrogel sheet layer 10 in contact with the hydrogel sheet layer 10, and a top film 13 disposed on the opposite side of the hydrogel sheet layer 10 from the side on which the base film 12 is disposed in contact with the hydrogel sheet 10. The details of the hydrogel sheet layer 10, the base film 12, and the top film 13 are as described above. The base film 12 and / or the top film 13 may be omitted.

[0066] Fig. 2 is a schematic cross-sectional view of a hydrogel sheet according to another embodiment of the present invention. Compared to the hydrogel sheet 1 in Fig. 1, the hydrogel sheet 1 in Fig. 2 includes an intermediate substrate 11 embedded in a hydrogel sheet layer 10. The details of the intermediate substrate 11 are as described above.

[0067] 3 is a schematic cross-sectional view of an electrode pad comprising a hydrogel sheet according to one embodiment of the present invention. The electrode pad 2 comprises a hydrogel sheet layer 10 made of a hydrogel sheet according to one embodiment of the present invention, and an electrode 20 electrically connected to the hydrogel sheet layer 10. A support substrate 15 is disposed on the surface of the hydrogel sheet layer 10 in contact with the hydrogel sheet layer 10. The electrode 20 penetrates the support substrate 15 and extends into the hydrogel sheet layer 10.

[0068] A general insulating resin can be used as the supporting substrate 15. The supporting substrate 15 is preferably a film, foam, or nonwoven fabric containing polyester, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate (PET), polyurethane, silicone, or a combination of two or more of these resins, or rubber. The thickness of the supporting substrate 15 is preferably 10 to 500 μm.

[0069] The electrode 20 can typically be obtained using a predetermined conductive material. Examples of such conductive materials include conductive pastes prepared by mixing two or more of metals such as nickel, molybdenum, stainless steel, silver, or platinum, metal mixtures such as silver or silver-silver chloride, or materials such as carbon black or graphite. The electrode 20 can be obtained, for example, by printing a conductive paste on the surface of the support substrate 15 described above to form a conductive layer. Alternatively, the electrode 20 can be obtained by coating the surface of a resin molded product, such as an ABS resin molded product, with a conductive ink containing the conductive material described above. Alternatively, the electrode 20 can be obtained by laminating the support substrate 15 described above with a metal foil such as silver, aluminum, or tin, or a film containing the conductive material described above.

[0070] The electrode pad 2 can be attached to the surface 30 of the adherend via the surface of the hydrogel sheet layer 10, following the shape of the adherend. The electrode pad 2 is preferably a biological electrode pad. The adherend surface 30 is preferably the surface of human skin. With such an electrode pad 2, voltage changes are suppressed even when a direct current is applied for a certain period of time.

[0071] 4 is a schematic cross-sectional view of another electrode pad comprising a hydrogel sheet according to one embodiment of the present invention. The electrode pad 2 comprises a hydrogel sheet layer 10 made of the hydrogel sheet according to one embodiment of the present invention, an electrode 20 disposed on the surface of the hydrogel sheet layer 10 in contact with the hydrogel sheet layer 10, and a support substrate 15 disposed in contact with the surface of the electrode 20 opposite to the side in contact with the hydrogel sheet layer 10.

[0072] The electrode pad 2 can be attached to the surface 30 of the adherend via the surface of the hydrogel sheet layer 10, following the shape of the adherend surface 30. The adherend surface 30 is preferably the surface of human skin. With such an electrode pad 2, voltage changes are suppressed even when a direct current is applied for a certain period of time. [Example]

[0073] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0074] 1. Hydrogel Preparation (1) Preparation of monomer mixture Using a stirring / mixing vessel, 18 mass% of acrylamide as an acrylic monomer, 0.046 mass% of N,N'-methylenebisacrylamide (MBAA) as a crosslinking monomer, 16.4 mass% of ion-exchanged water, 60.194 mass% of glycerin as a humectant, 1.22 mass% of sodium sulfate as electrolyte A, 0.88 mass% of succinic acid as an organic acid, 0.88 mass% of disodium succinate as an organic acid salt, and 2.38 mass% in total of preservatives, initiators, adhesives, and chelating agents as other additives were added, as shown in Table 1, and stirred until completely dissolved, to obtain a blended liquid.

[0075] (2) Hydrogel production Example 1 The resulting mixture was poured into a silicone resin mold and spread evenly to a thickness of 3.0 mm. A metal halide lamp was used to apply the mixture, and the peak irradiance was 130 mW / cm. 2 , cumulative irradiation dose 3000mJ / cm 2 By irradiating the sheet with ultraviolet light at 1000 W / v, a hydrogel sheet having a thickness of 3.0 mm was obtained.

[0076] Examples 2 to 4 A hydrogel sheet was obtained in the same manner as in Example 1, except that the type and amount of electrolyte A added were changed as shown in Table 1.

[0077] (Examples 5 to 6) Hydrogel sheets were obtained in the same manner as in Example 1, except that the thickness, the type and amount of electrolyte A added were changed as shown in Table 1.

[0078] Example 7 A hydrogel sheet was obtained in the same manner as in Example 1, except that the type and amount of electrolyte A were changed as shown in Table 1, the type and amount of acrylic monomer, and the amount of crosslinkable monomer were changed, and a pH adjuster was added.

[0079] Example 8 Hydrogel sheets were obtained in the same manner as in Example 1, except that the type and amount of electrolyte A were changed as shown in Table 1, and the types and amounts of organic acids and organic acid salts were changed.

[0080] Example 9 Hydrogel sheets were obtained in the same manner as in Example 1, except that the type and amount of electrolyte A added was changed as shown in Table 1, and the amounts of organic acid and organic acid salt added were changed.

[0081] (Examples 10 to 11) A hydrogel sheet was obtained in the same manner as in Example 1, except that the type and amount of electrolyte A added were changed as shown in Table 1.

[0082] (Comparative Examples 1 to 7) A hydrogel sheet was obtained in the same manner as in Example 1, except that the type and amount of electrolyte A added were changed as shown in Table 1.

[0083] 2. Evaluation Method The obtained hydrogels of Examples 1 to 11 and Comparative Examples 1 to 7 were evaluated for each of the following items. (1) Voltage change evaluation Two test materials were prepared by sandwiching a hydrogel sheet of the Example or Comparative Example cut to a diameter (φ) of 30 mm between two SUS plates. One test material was connected to the positive terminal of a DC stabilized power supply, and the other test material was connected to the negative terminal, with a 1 kΩ resistor connected between the test materials. In the circuit, the resistor simulated the adherend surface, e.g., skin. Using a DC power supply (TEXIO, DC stabilized power supply PPX100-1), a constant current of 2 mA was applied to the circuit for 15 minutes. The initial voltage value was measured 1 minute after the start of current application, and compared with the voltage value 15 minutes after the start of current application. The voltage change rate was calculated using the following formula: It is calculated by {(voltage 15 minutes after the start of DC current application) - (voltage 1 minute after the start of DC current application)} / (voltage 1 minute after the start of DC current application)} x 100.

[0084] (2) Pain assessment Two test materials were prepared by attaching elements corresponding to the support substrate 15 and electrode 20 in Figure 3 to a hydrogel sheet of the Example or Comparative Example cut to a diameter (φ) of 30 mm. These test materials were attached to two random locations on the left arm. Pain was evaluated 1 minute after the start of current application using a DC power supply (TEXIO, DC stabilized power supply PPX100-1) in constant current mode (2 mA).

[0085] (3) Color evaluation Two test materials were prepared by sandwiching a hydrogel sheet of the Example or Comparative Example cut to a diameter (φ) of 30 mm between two SUS plates. One test material was connected to the positive terminal of a DC stabilized power supply, and the other test material was connected to the negative terminal, with a 1 kΩ resistor connected between the test materials. In the circuit, the resistor simulated the adherend surface, e.g., skin. A DC power supply (TEXIO, DC stabilized power supply PPX100-1) was used to apply a constant current of 2 mA to the circuit for 15 minutes. The color of the gel was evaluated 15 minutes after the start of current application.

[0086] 3. Evaluation criteria (1) Voltage change evaluation Voltage change was evaluated according to the following criteria. If the voltage changes and becomes too high, the electrode reaction is accelerated, causing more bubbles to form in the element. This can cause differences in current density, which can change the pain or create hot spots, potentially leading to skin disorders. For this reason, products with a large rate of change were evaluated as x. ○: Change rate is 15% or less △: Change rate exceeds 15% and is less than 60% ×: Change rate is 60% or more

[0087] (2) Pain assessment Using a DC power supply (TEXIO, DC stabilised power supply PPX100-1) in constant current mode (2mA), pain was assessed using a circle, triangle or cross one minute after the start of current application. O: I feel a tingling sensation but no pain. △: I feel some pain. ×: Severe pain.

[0088] (3) Color evaluation Using a DC power supply (TEXIO, DC stabilised power supply PPX100-1) in constant current mode (2 mA), the colour of the gel was evaluated with a mark of 'Yes' or 'No' 15 minutes after the start of current application. ◯: Remains transparent after application ×: Discolored yellow after application

[0089] (4) Overall evaluation 〇: No × or △ △: There is a total of 1 × and △ ×: There are two or more × and △ in total. [Table 1] [Table 1] [Explanation of symbols]

[0090] 1...Hydrogel sheet, 2...Electrode pad.

Claims

1. A hydrogel for applying direct current, comprising a polymer matrix which is a polymer of a (meth)acrylic monomer, water, a humectant, and an electrolyte, wherein the electrolyte includes at least one electrolyte selected from the group consisting of sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate.

2. 2. The hydrogel for applying a direct current according to claim 1, wherein the voltage value 1 minute after the start of application of a direct current of 2 mA is 9 V or more.

3. 2. The hydrogel for applying direct current according to claim 1, wherein the content of the at least one electrolyte is 0.10 to 5.0 mass % relative to 100 mass % of the hydrogel.

4. 2. The hydrogel for applying a direct current according to claim 1, which has a thickness of 0.30 to 10 mm.

5. 2. The hydrogel for applying direct current according to claim 1, further comprising at least one pair of an organic acid and an organic acid salt selected from the group consisting of succinic acid and a succinate salt, and malic acid and a malate salt.

6. 6. The hydrogel for applying direct current according to claim 5, wherein the total content of the organic acid and the organic acid salt is 0.50 to 10% by mass relative to 100% by mass of the hydrogel.

7. 2. The hydrogel for applying a direct current according to claim 1, which is formed into a sheet shape.

8. A bioelectrode hydrogel for application to the skin, comprising the hydrogel for direct current application according to any one of claims 1 to 7.

9. 8. An electrode pad comprising the hydrogel for applying direct current according to claim 1 and an electrode electrically connected to the hydrogel for applying direct current.

Images