JPS6330011B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is often used to establish an electrical connection between the human skin and biomedical devices such as high impedance electromyography, electrocardiography, pain relief electrical stimulators, and the like. It concerns disposable electrodes, referred to as "medical" electrodes. More particularly, it concerns so-called "dry" bioelectrodes, which do not require the use of harsh creams or gels to enhance the conductivity between the skin and the electrode plate. A variety of disposable biomedical electrodes are known in the art. They generally include a metal electrode plate adapted to connect to a conductive wire, which in turn is connected to an electromedical device. Typically, pastes, creams or gels containing ionic materials are relied upon to conduct electrical current to improve the electrical connection between the patient's skin and the electrode plates. Adhesive tape is usually used to attach the entire device to the skin. Examples of this general type of electrode are described in US Pat. Nos. 3,587,565 and 3,805,769. The conductive pastes, creams, or gels used in these prior art biomedical electrodes are unpleasant to use, messy, and often irritate the skin due to their ionic nature, especially before electrode application. This is the case when the skin is cleaned and rubbed. Since all these electrodes contain water as a major component to dissolve the ions present and act as a medium through which the dissolved ions move, they must be carefully packaged to prevent water loss before use. There is a need. Moreover, they leave a residue on the skin after electrode removal, which needs to be cleaned. A further disadvantage of conductive paste, cream and gel type electrodes is that unless the surface of the electrode plate is made of expensive silver/silver chloride, they can cause overpotentials in myofiber defibrillation procedures. The unpleasant and inconvenient nature of electrodes using conductive gels or creams can be overcome by impregnating the porous pad with conductive material, as shown, for example, in U.S. Pat. Nos. 3,845,757 and 3,901,218. The situation has eased somewhat. However, careful packaging is still necessary, and during use the gel becomes dry, causing deviations in the electrical impedance and subsequent signal characteristics. To overcome many of the problems associated with so-called "wet" electrodes, biomedical electrodes have been proposed that utilize "dry" conductors. U.S. Patent No. 3565059 and
No. 3,911,906 discloses biomedical electrodes that utilize adhesives containing conductive particles. These adhesives serve the dual purpose of promoting conductivity with the skin and securing the electrodes to the skin. Although avoiding the unsightliness and packaging problems associated with gels and pastes, such electrodes generally do not provide a satisfactory electrical connection to the skin, since the presence of conductive filler This is because it produces a high signal-to-noise ratio and is detrimental to adhesion. It has been found that the use of inhomogeneous conductive formulations in biomedical electrodes generally produces noisy electrical signals. It is assumed that the dispersed metal or salt particles in the bonding matrix form discontinuous conductive paths, which develop any non-uniform electric fields between the particles, which causes noise. US Pat. No. 3,993,049 discloses a biomedical electrode having a salt dispersed in an adhesive layer. The attachment layer secures the electrodes to the skin, and the salt serves as the current carrier. Desirably, the salt has a cation of the metal forming the surface of the electrode plate, for example silver halide in the case of a silver electrode plate. It is also desirable to include metal powder in the adhesive or to provide a metal mesh supporting the adhesive thereon. Desirable adhesives are water soluble. This biomedical electrode requires external substances in the adhesive, ie, salt solutions and metal powders, to obtain acceptable conductivity.
This increases the potential for skin irritation as well as the overall cost of the electrode. Although, as mentioned above, much of the technology in the field of biomedical electrodes is directed toward recording electrodes that are useful for diagnosis, grounding electrodes and the use of A growing number of technologies appear to describe electrodes for electrical stimulation. For the most part, the variously described grounding and stimulation bioelectrodes have larger areas than recording electrodes, so that greater current densities can be used without heating body tissue. Again, these larger electrodes commonly use electrolyte solutions, gels, or pastes to provide electrical contact between the body surface and the electrodes. Patents describing such electrodes include, for example, U.S. Pat. U.S. Pat. No. 3,848,600, which describes a contoured electrode that utilizes an aqueous salt solution; and U.S. Pat. No. 3,964,477, which utilizes a porous silver/silver chloride electrode and an electrolyte solution.
Including issue. All of these electrodes utilize undesirably harsh electrolytes. Another biomedical electrode used for electrical neutral stimulation across the skin that has come to the applicant's attention utilizes a natural polymer, namely Karaya gum, to secure the electrode to the skin. Karaya gum is a complex polysaccharide bound to certain metal cations such as sodium, potassium, calcium, or magnesium. Gums are insoluble in water but swell into a pasty gel (Kirk/Othmer, Encyclopedia of Chemical Technology, Vol. 10, 1966). Because natural polymers occur in nature with varying soil and climatic conditions, and because the conditions under which they are collected and processed are variable, there are large discrepancies in the physical and chemical properties of natural polymers and the amount of impurities present. exist. Such mismatches lead to variations in the electrical performance of biomedical electrodes made from natural polymers. This variation in electrical performance is unacceptable in biomedical electrodes where consistent electrical properties are important. Moreover, natural polymers are generally undesirable because they support microbial growth and can cause adverse skin sensitivities, including allergic and antigenic reactions (Merck Index, 8th edition,
1969, p. 598). "Dry" stimulation electrodes are also known. U.S. Pat. No. 3,812,861 teaches a ground electrode consisting of a flexible sheet of paperboard coated on both sides with conductive foil electrically connected together and having means for securing the device around the limb. Such electrodes with metal-to-tissue interfaces are undesirable due to the bio-incompatibility of most metals and the difficulty of obtaining reasonable compatibility with human body surfaces. US Patent No.
No. 3,994,302 describes a telescoping stimulating electrode in which the tissue contacting surface is an ion-exchange resin material, such as quaternized vinyl pyridine grafted to polyethylene. For use, the electrode can be activated by an aqueous solution. This electrode does not appear to be useful on skin surfaces. According to the present invention, it has been found that the presence of a salt or a dispersed conductive material in the interfacial material between the skin and the electrode plate is not a prerequisite for a usable biomedical electrode. Additionally, it has been discovered that certain non-ionic hydrophilic synthetic polymers can act as effective electrical conductors in biomedical electrodes. According to the invention, on one surface thereof electrical connection means to an electromedical device and on the opposite side thereof,
comprising an electrode plate having an electrically conductive material on its surface in contact with the body, where the electrically conductive material is non-
Improved, essentially consisting of nonionic synthetic hydrophilic polymers that are irritating, compatible, and adhesive.
An essentially dry disposable biomedical electrode is provided. The biomedical electrode of the present invention has an impedance value of 500K ohms or less at a frequency of 10 Hertz. The dry bioelectrode of the present invention offers several advantages over the conventional prior art. Since large amounts of water are not required, the need for expensive electrode packaging and other means designed to ensure water retention is no longer necessary. No packaging is required other than a covering to protect the adhesive surface. Application of the electrode is dry and not harsh or harsh, and no messy residue is left on the skin when the electrode is removed from the patient's skin. Skin preparation can be performed with water or normal saline instead of the irritating alcohol. Adhesion of the electrode to the skin is improved somewhat by moistening the skin, so there is no need to wait for the skin to dry completely before applying the electrode. This electrode can be made smaller in diameter and thickness than currently available disposable electrodes, thus providing comfort and convenience.
Especially improved in long-term observation. Moreover, there is no need for costly surface treatments of the electrode plates to make them suitable for use in connection with myofibrillation procedures. As used herein, the term "compatible" generally refers to the compliance of a conductor. It must be sufficiently compliant to conform to the surface of the skin beneath the electrode plate in order to provide a large area of contact between the skin and the electrode plate. Important compatibility requirements for materials used in accordance with the present invention are determined by Williams plasticity values for thermoplastic resin formulations (U.S. Pat.
3725121) generally between 0.5 and 4.0 mm. When the interpolymers are subsequently cross-linked by one of a variety of known procedures to improve their tack, the cross-linking renders the formulation insoluble and non-flowable. That's probably why. Such materials cannot be evaluated by Williams plasticity measurements, which require flowability. Glass transition temperature descriptions are useful in distinguishing suitable compatible materials of this type. A general discussion of glass transition temperatures and physical properties can be found in the textbook entitled "Viscoelastic Properties of Polymers" by J. D. Fehrey [Wiley: New York, Chapter 2 (1970)]. Generally, cross-linked polymers having a glass transition temperature between -20°C and -95°C are suitable. As used herein, the term "non-ionic hydrophilic polymer" refers to macromolecules composed of a sufficient number of repeating small chemical units such that at least 15 mole percent of the units are water-soluble and non-ionic. and has film-forming properties and generally has a weight average molecular weight of at least about 10,000. The polymer does not contain ionic groups. As used herein, the term "synthetic" refers to materials that have been collected in their natural state and have simply been processed to remove foreign substances such as dirt, leaves, and insects, and no chemical reactions have been performed on them. Synthesized hydrophilic polymers as opposed to polymers.
The term "synthetic" also includes polymers made by chemically modifying natural polymers to change their chemical structure and standardize their chemical and physical properties. The term "cohesive" refers to the internal connectivity of a conductor.
Generally, the conductor must be film-forming and tacky rather than adhesive to the skin, so that when the electrode is removed from the skin, the conductive layer remains intact, which is undesirable. Leaves no residue on the skin. Non-ionic hydrophilic polymers suitable for use as electrical conductors in the biomedical electrodes of the invention are non-skin-irritating, adhesive, film-forming synthetic hydrophilic polymers selected from the following types: Any of the following polymers are possible: B non-ionic water-soluble interpolymers of water-soluble monomers and water-insoluble monomers; and C water-insoluble polymers containing at least 15 mole % copolymerizable water-soluble monomers with water-soluble polymers. A non-ionic water-insoluble interpolymer with monomers. B-class non-ionic hydrophilic interpolymers result from the copolymerization of a major amount of the above-mentioned addition-polymerizable, water-soluble monomers with a minor amount of non-ionic addition-polymerizable, water-insoluble monomers, the latter monomers includes, but is not limited to: acrylate esters such as methyl acrylate, methyl methacrylate, butyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, dodecyl methacrylate, octadecyl methacrylate, and cyclohexyl acrylate. vinyl ethers such as 2-ethylhexyl vinyl ether, decyl vinyl ether, and octadecyl vinyl ether; vinyl acrylates such as vinyl acetate, vinyl butyrate, and vinyl dodecanoate; ethylene, propylene, styrene, α-methylstyrene, 4-chloro Olefins such as styrene, iso-butylene, and vinylcyclohexane; Olefinic polycarboxylic acid esters such as dimethyl maleate, dimethyl fumarate, and diethyl itaconate; and halogenated compounds such as vinyl chloride and vinylidene dichloride. vinyl. It is clear to those skilled in the art that the specific minimum concentration of water-soluble monomer required to impart water solubility to the copolymer depends on the nature of both the water-soluble and water-insoluble monomers. It cannot be given because it will vary significantly depending on the situation. The preferred hydrophilic polymers of this invention are of the C class, non-ionic hydrophilic water-insoluble interpolymers. The B-class interpolymers discussed above represent a special class of C-class interpolymers, the former being distinguished by their solubility in water. C class interpolymers are
Although not water soluble, they are hydrophilic and are made using the same addition polymerizable non-ionic water soluble and water insoluble monomers discussed above. The benefits to be attributed to C-class materials are as follows: water-soluble monomer levels greater than 15 mol % will result in 500K ohms (determined to represent a practical upper limit for the state of electrocardiograph and bio-automated electrical instrumentation technology). )
impedance values are achieved and the pressure sensitive adhesive performance is optimal. Materials that are pressure-sensitive adhesives are particularly desirable materials of the present invention, since no additional means are required to secure the electrodes to the skin. Pressure sensitive adhesives are well known in the art and are best described as having a balance of four properties: adhesive, tack, extensibility and elasticity...as discussed in, for example, US Re, 24906. be done. This performance balance is most commonly achieved by a relatively high glass transition temperature (approximately
copolymerization of monomers or so-called "hard" monomers which, if homopolymerized, give rise to polymers with a relatively low glass transition temperature (approximately -25 °C) or so-called "soft" monomers. achieved by. The "hard" monomers used in the present invention are the generally non-ionic, water-soluble, addition-polymerizable monomers described above, whereas the "soft" monomers are the non-ionic, water-insoluble, addition-polymerizable monomers described above. monomers having relatively large alkyl residues having about 4 to 12 carbon atoms. Particularly desirable "soft" monomers include alkyl acrylates and methacrylates and alkyl vinyl ethers. The charge of "hard" and "soft" monomers is manipulated so as to obtain a copolymer with a glass transition temperature below -25°C. If the previously mentioned polymers alone are not sufficiently compatible under the conditions of use, it is generally possible to bring them within the aforementioned range by plasticization. The copolymerization of the "hard" and "soft" monomers discussed above with B-class and C-class materials is referred to herein as "internal" plasticization.
Particularly for C-class materials, large bulky,
Copolymerization of "soft" monomers with pendant alkyl substituents and "hard" monomers will provide sufficient fluidity to the copolymer. For example, when 85 mol parts of isooctyl acrylate is copolymerized with 15 mol parts of acrylic acid, the Williams plasticity value is 2.5 mm.
A copolymer exhibiting the following is produced. Isooctyl acrylate is a "soft" monomer that internally plasticizes "hard" acrylic acid, which by itself becomes a too brittle homopolymer to evaluate using Williams plasticity measurements. Alternatively, plasticization of the polymers and interpolymers of the present invention can be accomplished by adding more "flowable" components to the polymer or interpolymer. This procedure is referred to herein as "external" plasticization. Generally, it is desirable that the external plasticizer be compatible with the polymer.
The external plasticizer can be any material that can transform a brittle polymer into a compatible polymer such that the Williams plasticity value and/or glass transition temperature criteria described above are met. The effectiveness of this technique is demonstrated by the addition of 85 parts of poly(acrylic acid) (based on 100 parts of poly(acrylic acid)) of glycerol to produce a Williams plasticity value of 2.5 mm. Suitable external plasticizers include poly(hydroxyalkanes) such as glycerol, poly(oxyalkylene) alcohols such as poly(oxypropylene) glycol, and the like. It is also contemplated within the scope of this invention to impart tackiness to the formulations described herein, if necessary, particularly when creating a pressure sensitive adhesive, which is a preferred embodiment of this invention. Suitable tackifiers for all classes of the present invention are derivatives of naturally occurring rosin acids, such as abietic acid. This acid or its hydrogenated form can be reacted with a base to form a water-soluble tackifier for water-soluble A class and B class polymers and interpolymers, respectively, or can be esterified or reduced. Water-insoluble tackifiers suitable for C-class materials can be made by Many other tackifiers are commercially available and are particularly suitable for Class C materials, which are the preferred materials of this invention. Examples of desirable conductive non-ionic polymers for use in the electrodes of the present invention are listed in the table below. All ratios are molar ratios. Desired B class interpolymer copoly(vinyl acetate:vinyl alcohol)
(30:70) Copoly (n-butyl acrylate: acrylic acid)
(5:95) Copoly(2-ethylhexyl methacrylate: methacrylic acid) (2:98) Desirable C class interpolymer copoly(isooctyl acrylate: acrylic acid) (61:39) Copoly(isooctyl acrylate: acrylic acid) ( 48:52) Copoly(butyl acrylate: itaconic acid)
(67:33) Copoly (lauryl methacrylate: methacrylic acid) (34:66) Copoly (vinyl acetate: vinyl alcohol)
(70:30) Copoly (vinyl chloride: vinyl alcohol)
(60:40) Copoly(ethylene:vinyl alcohol) (60:
40) Copoly(butyl acrylate:3-dimethylaminopropylacrylamide) (60:40) A further understanding of the present invention will be facilitated by reference to the accompanying drawings, in which: 2 is an enlarged cross-sectional view of the electrode taken along line 2--2 of FIG. 1; FIG. In Figures 1 and 2, the electrode 10 is made of a conductive material such as rustproof steel, silver, nickel or the like, compressed carbon or graphite, or metal-coated plastic, fabric, or conductive plastic material. It includes an electrode plate 12 configured.
The electrode plate has associated therewith electrical connection means to a conductor, the latter in turn being connected to an electromedical device.
In the electrode 10 the means for electrical connection to the conductor is illustrated by a connecting stud 14, ie an upright extension of the electrode plate 12. The connecting stud 14 is adapted to fit into the female receptacle of the connector. Electrode plate 12
The skin-contacting surface of is coated with a layer 18 of conductor as defined below. Layer 18 is typically between 25 and 100 microns thick. Overlying the entire upper surface of the electrode plate and extending outwardly from its periphery is a patch of adhesive tape 20. Adhesive tape 20
helps secure the electrode to the patient's skin. In a preferred embodiment of the invention, the conductors of layer 18 are sufficiently adhesive to help hold the electrodes to the skin. Because layer 18 is conformable and generally adhesive, it provides a good electrical bond between the electrode plate and the skin without the need for large and bulky adhesive tapes as required in many prior art disposable electrodes. I will provide a. Therefore, the electrodes of the present invention can be made smaller and are easier to handle. The side of the layer 18 opposite to that fixed to the electrode plate is optionally provided with a protective peel backing 22. Release backing 22 protects the conductive layer 18 and adhesive side of patch 20 from contamination prior to use. It will be apparent to those skilled in the art that the biomedical electrodes of the present invention may be assembled by a variety of methods. The illustrated embodiment is just one example of a typical disposable electrode of the recording type.
Electrodes used for other purposes, such as stimulation, grounding in electrosurgery, and bioautomatic control, have different requirements and must be constructed to meet these requirements. All types of non-invasive electrodes that use the conductor of the present invention at the electrode-skin interface are contemplated as being within the scope of the present invention. The invention is further illustrated by the following non-limiting examples. Example Preparation of poly(acrylic acid) (100 parts) and glycerol (60 parts) Poly(acrylic acid) having a weight average molecular weight of approximately 120,000 (5.29 g polymer in 25.3 g water)
and glycerol (3.18 g) were thoroughly mixed. The electrodes were made by applying the plasticized polymer onto a nickel disc having an area of approximately 127 mm ² and allowed to dry overnight. A polymer layer with a thickness of 75±25 microns was obtained. Impedance values were obtained by applying electrodes to the skin on the inner side of the forearm of a male subject. The skin area was lightly sanded with 220-grit open-coat aluminum oxide sandpaper, and the sanded area was moistened with two 2-inch (5 cm) pieces of normal saline solution.
Prepared by wiping with a 12-inch (5 cm) gauze sponge. While the skin area is still visibly moist, remove a piece of 3M Trademarked Micropore Tape (2.5 cm
The electrodes were attached to the skin site by 4cm x 4cm). Impedance measurements were made using the method reported by Spatsch et al. [Circulation 34649-656 (1966)]. All impedance measurements were made at a frequency of 10 Hertz. The electrode was found to have an impedance value of 20K ohms.
Other electrodes were constructed and tested using water-soluble polymers as conductors. In some cases, only water was used to prepare the skin instead of the commonly used saline solution. The results are summarized in the table below.

[Table] The conductors of Examples 1-5 were easily compatible but not sticky, except for Examples 2 and 3.
All were tacky formulations under the conditions used. Example 6 Preparation of copoly(iso-octyl acrylate-acrylic acid) (78:22) In a one-fill tan glass bottle, isooctyl acrylate (252.0 g), acrylic acid (28.0 g), and azubis(iso-butyronitrile) (0.700 g)
g; 0.25% by weight based on monomer) in acetone (420g; monomer solids was 40.00% by weight)
melted inside. The resulting solution was briefly flushed with nitrogen to remove dissolved oxygen, sealed, and heated with stirring at 53° C. for 24 hours. The solids content of the resulting copolymer was 38.3% by weight, and the intrinsic viscosity at 30°C in tetrahydrofuran (100 g
0.15g copolymer in solvent) was 1.71. Electrodes were made using copolymers according to the method described in Example 1. The electrode was tested and found to have an impedance value of 160. Other conductors were made and formulated into electrodes using the method of Example 6. These electrodes are listed together in the table below.

[Table] Example 12 Copoly (vinyl acetate-vinyl alcohol)
(54:46) (100 parts) and glycerol (100 parts)
Preparation of copoly(vinyl acetate: vinyl alcohol)
(54:46) (commercially obtained from Watzker Chemie) (6.3 g) and glycerol (6.3 g).
g of isopropanol/water (50:50 weight ratio). This sample was coated and evaluated as described in Example 1 to yield an impedance value of 26K ohms. The dry material was a non-tacky, conformable film.

[Brief explanation of drawings]

The accompanying drawings are intended to assist in understanding the present invention, and include: FIG. 1 is a top perspective view of a typical disposable biomedical electrode in one embodiment of the invention; and FIG. The figure is an enlarged sectional view of the electrode taken along line 2--2 in FIG.

Claims (1)

[Scope of Claims] 1. A dry method comprising an electrode plate, an attachment means for coupling a conductor to the electrode plate, and a conductor on the body-contacting surface of the electrode plate for strengthening the electrical connection with the skin. In a disposable biomedical electrode, said conductor consists essentially of a skin-nonirritating, compatible, cohesive, nonionic synthetic hydrophilic polymer, and said polymer is pressure sensitive adhesive. (B) a nonionic water-soluble interpolymer of a water-soluble monomer and a water-insoluble monomer; and (C) a non-ionic water-soluble interpolymer of a water-soluble monomer and a water-insoluble monomer comprising at least 15 mole percent of the water-soluble monomer. selected from the group consisting of ionic water-insoluble interpolymers, said electrodes at a frequency of 10 hertz.
Dry disposable biomedical electrode characterized by having an impedance of 500K ohms or less. 2. The electrode according to claim 1, wherein the polymer is plasticized. 3. The electrode according to claim 2, wherein the polymer is plasticized with glycerol. 4. Electrode according to claim 1, characterized in that the polymer is a water-insoluble interpolymer of a water-soluble monomer and a water-insoluble monomer comprising at least 15 mol % of the water-soluble monomer. 5. The electrode of claim 4, wherein said water-insoluble monomer contains an alkyl group containing about 4 to 12 carbon atoms. 6. Electrode according to claim 4, characterized in that said water-insoluble monomer is selected from the group consisting of alkyl acrylates, alkyl methacrylates and alkyl vinyl ethers. 7. Claim 6, characterized in that said water-insoluble monomer is selected from the group consisting of butyl acrylate, 2-ethylhexyl methacrylate, iso-octyl acrylate, butyl acrylate and lauryl methacrylate. Electrodes described in Section. 8. Electrode according to claim 4, characterized in that said water-soluble monomer is selected from the group consisting of acrylic acid and methacrylic acid. 9. Claim 8, wherein the water-insoluble monomer is iso-acrylate.
Electrodes described in Section.