Patent Application
20080008734
In particular, the present invention provides an electrode suitable for providing electrical contact with a patent's skin which electrode includes a conductive member adapted for connection to an external electrical apparatus and a non-liquid or solid water-containing film for electrically interfacing to said patent's skin, said non-liquid film being electrically and mechanically connected to said conductive member. The non-liquid water-containing film includes an electrically conductive organic polymer derived from a monomer mixture which undergoes free radical catalyzed polymerization in the presence of UV light and a photoinitiator to provide said organic polymer, wherein said monomer mixture further comprises a chemical moiety, which is a precursor of an antioxidant, which chemical moiety does not react with the free radicals derived from said photoinitiator under polymerization conditions but, upon contact with the skin of a patient, is converted into said antioxidant. Said antioxidant is preferably a vitamin, e.g. Vitamin A, C, or E, and more preferably said vitamin is a water-soluble vitamin, e.g. Vitamin C.
The electrode configuration is shown in
Alternately, other metallic foils, conductive polymers, graphitized or metalized cloth or wire mesh may be used as the conductive member. In particular, the knit conductive fabric disclosed in U.S. Pat. No. 4,722,354 to Axelgaard, et al. may be utilized as the conductive member. For each material, an appropriate strength and thickness is to be chosen to yield a pliable, yet sufficiently strong member 11. When the conductive member 11 is of metal foil, it usually is of 1-10 mil thickness.
Secured to the outer surface of the conductive member 11 is a connector 13 for providing a medium to which external signal cables may be attached for electrically communicating with the conductive member 11. This connector 13 may be a conductive swaged snap fastener 13, as shown in the accompanying drawings, which is available commercially. This fastener 13 is mechanically and electrically attached to the conductive member 11, extending perpendicularly from the outer surface of this member 11. Alternatively, when the conductive member is a knit conductive fabric, the electrical connector may be stranded stainless steel as shown in U.S. Pat. No. 4,722,354.
Abutting the inner surface of the conductive member 11 is an electrically conductive skin-interface substrate 15. This substrate 15 is a layer of material being typically a film or sheet which will be described below.
The conductive substrate 15 is shaped correspondingly to the conductive member 11. When constructed in combination with a rectangular member 11, the substrate 15 is also rectangular. The film thickness of this substrate 15 is uniform throughout, however, this uniform film may be of various thicknesses. A range of 10 to 100 mils, e.g., about 50 mils is common.
As will be discussed below, the substrate 15 is a film or sheet having adhesive properties, thus when it is brought into contact with the conductive member 11, it will adhere to that member 11 providing electrical connection with it.
A supporting scrim 17,
The scrim 17 is positioned within and through the thickness of the substrate 15, in alignment with the conductive member 11, and is of a size to extend completely under the conductive member 11. The scrim 17 can be a woven or non-woven spun-bonded polyester fabric, a net of a stretched, embossed melt-extruded polymeric film, a sheet of polyolefin monofilaments heat-sealed together at their interstices, a thin sheet of a thermoplastic polymer with holes heat-stamped in a geometric pattern or any other supportive media. The scrim 17 may be any material allowing transmission of light for curing if only cured from one side. Also, the scrim 17 should retain most of its strength when wetted by the monomer mixture.
Suitable monomer mixtures for use in the practice of the present invention are found in U.S. Pat. No. 6,842,636 to Perrault, et al. and U.S. Pat. No. 6,115,625 to Heard, et al. both of which are hereby incorporated in their entirety for the description of the various suitable monomer mixtures, the polymerization thereof and the fabrication and resulting structure of the medical electrodes of this invention.
The electrically conductive organic polymers that are utilized in preparing the conductive adhesive may be derived from the polymerization of the water soluble monomer mixture, e.g. an acrylic acid or methacrylic acid containing monomer mixture and preferably by the copolymerization of a mixture of monomer acrylic acid and monomers glycolvinylether and/or vinylpyrrolidone. (Metha)crylics are electron accepting monomers and glycol vinyl ether and vinylpyrrolidone are electron donating monomers. Said organic polymer may comprise 25 to 75 parts per hundred, by weight (pph), e.g., 30 to 60 pph, acrylic acid and 75 to 25 pph, e.g. 70 to 40 pph, of a glycolvinylether and/or vinylpyrrolidone. In addition, the above mixture of comonomers, the organic polymer, may further include additional comonomers; in particular, the acrylic acid may be completely or partially replaced with AMPS.
Preferably, the glycolvinylether may be selected from the group consisting of hydroxybutyl vinyl ether, ethyleneglycolvinylether, diethyleneglycolmonovinylether, and triethyleneglycolmethylvinylether. Most preferably the glycolvinyl ether is diethylene glycol monovinyl ether.
Furthermore, the organic polymer may comprise about 0.01 to 1.5 pph of a crosslinking agent, such as methylene bisacrylamide, to increase the molecular weight and cohesivity of the conductive organic polymer through crosslinking. Other comonomers having at least two copolymerizable olefinic moieties, especially difunctional or trifunctional derivatives of acrylic acids, may be utilized. For example, polyethylene glycol dimethacrylates and diacrylates having a molecular weight of from about 200 to about 600 and ethoxylated trimethlolpropane triacrylate (ETMPTA) are preferred crosslinking agents.
The comonomer mixture that is copolymerized to provide the conductive organic polymer may also include a polyhydric alcohol, e.g. polyhydroxyhydrocarbons and oxyalkyls, e.g., polyetheneglycol, sorbitol, glycerol, etc. to plasticize the organic polymer. The polyhydric functions as a humecant, i.e., it absorbs moisture and promotes conductivity of the adhesive. The polyhydric alcohol may comprise from 25 to 75 pph, preferably from 40 to 60 pph, e.g., about 37 to 53 pph of the comonomer mixture. Most preferably, the polyhydric alcohol is glycerol.
The comonomer mixture that is copolymerized to provide the conductive organic polymer may also include a thickening agent. The thickening agent may be a high molecular weight polymer or copolymer such as a N-vinylpyrrolidone/vinylacetate copolymer (Luviskol VA 73W or VA 64W) available from BASF; methylvinylether/maleic anhybride copolymer (Gantrez® S95), which is available from ISP; ethylene/maleic anhydride (EMA) Copolymer, which is available from Zeeland Chemical; and N-vinylpyrrolidone/acrylic acid Acrylidone® (ACP-1041 or Acrylidone 1005), which is available from ISP, and may comprise from about 0.5 to 8 pph of the comonomer mixture, e.g. about 2 to 5 pph. The N-vinyl pyrrolidone/vinylacetate copolymer disclosed above is especially preferred for use in the compositions of this invention.
Magnesium acetate may also be included when the electrode is utilized as a stimulating electrode. Potassium chloride may be added when the electrode is utilized as a sensing electrode.
The above comonomer mixture is copolymerized or cured by thermal or ultraviolet (UV) radiation to provide the necessary free radicals. Therefore, an ultraviolet sensitive curing agent is provided in the comonomer mixture at a concentration of from 0.05 to 3 pph, preferably from 0.5 to 2.0 pph. Suitable curing agents are 2-hydroxy-2 methyl-1-phenyl-propan-2-one (available as Darocur 1173®), 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-phenyl(2-hydroxy-2-propyl)ketone (available as Darocur 2959®), 2,2-dimethoxy-2-phenyl acetophenone (available as Irgacure® 651), 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (available as Irgacure® 2959) or 1-hydroxycyclohexylphenylketone (available as Irgacure 184), all of which are available from Ciba-Geigy and trimethyl benzoyl diphenyl phosphine oxide (available as Esacure DP250 from Lamberti).
Thus, to prepare conductive adhesive, the following gelled comonomer mixtures may be subjected to chemical, thermal or ultraviolet polymerization conditions:
The acrylic acid is preferably partially neutralized with a basic potassium or sodium oxide, hydroxide, or carbonate or amine, e.g. triethanolamine. For example, from 25 to 75 molar percent acrylic acid may be neutralized.
A buffer may also be included in the comonomer mixture, e.g. from 0.2 to 2 pph of potassium sodium tartrate, or aluminum potassium sulfate (a further function of the AL+3 ion of the above buffer and Mg+2 ions, as well, is that such ions function as firming agents for compositions of this invention).
As previously discussed, the medical electrodes of the prior art, even the improved electrodes described in U.S. Pat. No. 6,115,625 and U.S. Pat. No. 6,842,636 may cause erythema under normal conditions of use, e.g. for stimulation and/or monitoring, whereby said electrode is adhered to the skin of a patient. Thus, the present invention provides a suitable antioxidant to prevent or alleviate the erythema resulting from the generation of free radicals, as discussed above, under normal conditions of use. Suitable antioxidants may be selected from known antioxidants that interact with the above free radical oxygen moieties described above to convert said free radicals into innocuous compounds, e.g. water, etc.
In Particular, said Antioxidants may be Selected from the Following Groups:
Group I. Phenolic compounds that contain one or more hydroxyl groups (—OH) connected directly to a benzene ring and to another unsaturated chemical grouping. Preferred examples of such compounds include hydroquinone, butylated hydroxyl toluene, butylated hydroxyl anisole, MEHQ, chlorogenic acid, caffeoylquinic acid, cinnamoylquinic acid, glabridin (also known as “PT-40”), bioflavonoids of flavone, isoflavone and flavonol structural type in both glycosilated and non-glycosilated forms, camosic acid (also known as “rosemary extract” or “oxyless R”), naringenin, naringin, hesperetin, hesperedin, citrus bioflavenoid complexes, quercetin, rutin, ellagic acid, tocopherols and their derivatives (for example, Vitamin E acetate), ascorbic acid and its derivatives (for example Sodium Ascorbyl Phosphate), propyl gallate, sylibin (also known as “silymarin”), cycloartenyl ferrulate, gamma-oryzanol, benzotriazole, tolyltriazole, Irganox 1010, and caffeic acid.
Group II. Sulfur-containing compounds that contain one or more sulfhydryl groups (—SH) or one or more disulfide groups (—S—S—). Preferred examples of such sulfhydryl compounds include glutathione, cysteine, N-acetyl cysteine, cysteine hydrochloride, alpha-lipoic acid, dihydrolipoic acid, thiolactic acid, sodium sulfite, sodium metabisulfite, sodium bisulfite, sodium thiosulfite, sodium formaldehyde sulfoxylate, thioglycerol, thiosorbitol, thiourea, thioglycolic acid, and zinc dithiophosphate.
Group III. Polyene compounds that have conjugated systems of double bonds. Preferred examples of such polyene compounds include sorbic acid, carotenoids, beta-carotene, lycopene, retinoids (for example, Vitamin A alcohol), Astaxanthin, and lutein.
Minerals such as selenium and manganese can also be efficacious in combating the tissue damage caused by reactive oxygen species. Synthetic antioxidants which are inherently skin irritants such as hexamethylene tetramine are not to be considered.
As further noted above, said antioxidants may interfere with the free radical catalyzed polymerization of the monomer mixture that is utilized to prepare the conductive adhesive for the above medical electrodes. Thus, the antioxidant is provided in the form of a compound that is inactive as regarding its ability to interfere with the above free radical polymerization but is converted upon contact with the skin of a patient, over time, into the antioxidant.
As will be appreciated, many of the above antioxidants have functional groups which can be conveniently converted into forms wherein the resulting molecule will not interfere with the free radical polymerization process but in the presence of endogenous enzymes will be “reconverted” into the active antioxidant.
For example, antioxidants having hydroxyl, carboxylic acid or phosphate functional groups can be converted into esters which do not interfere with the free radical polymerization process, but will be converted by an endogenous hydrolase and/or phosphatase into the active antioxidant.
The antioxidant will be provided in an amount sufficient to prevent and/or alleviate erythema under normal conditions of use. For example, the antioxidant, in the form of a antioxidant precursor which is a chemical moiety which does not interfere with the free radical polymerization of the monomer mixture but upon contact with the skin of a patient converts to said antioxidant, will comprise from 0.01 to 10%, by weight, of the monomer mixture, preferably from 0.20 to 3.0%, by weight of said mixture.
As stated above, the antioxidant is preferably a vitamin and, more preferably, a water-soluble vitamin such as Vitamin C. Most preferably, said antioxidant precursor is sodium ascorbyl phosphate.
When the antioxidant is a vitamin, the precursor may be defined as a prodrug. Prodrugs of the above antioxidants are well known in the art and include the following:
Sodium ascorbyl phosphate, magnesium ascorbyl phosphate, sodium ascorbyl 2-phosphate 6-palmitate, disodium ascorbyl sulfate, magnesium boroascorbate, ascorbyl tetraisopalmitate, tocopheryl acetate, tocopheryl succinate, tocopherol 1000 PEG succinate, tocopheryl phosphate, delta-tocopherol glucoside, tocopheryl nicotinate, retinyl acetate, retinyl palmitate, caffeic acid phenetyl ester, octyl caffeate, magnesium thiosulfate, zinc dithiophosphate, and selenium proteinate.
The monomer mixture, including the prodrug, may be further stabilized against interference with the free radical catalyzed polymerization process by the prodrug and/or any antioxidant, prematurely derived therefrom, by the incorporation of a suitable nonionic surfactant. An especially suitable class of nonionic surfactants are the polyoxy ethylene adducts of fatty acids, e.g. polyoxyethylene sorbitan monooleates. These surfactants are sold under the conventional name of Polysorbates.
The invention is further illustrated by the following examples which are illustrative of a specific mode of practicing the invention and is not intended as limiting the scope of the appended claims.
A solution of 2.0% (by weight) Sodium Ascorbyl Phosphate in deionized water was prepared with 2.0% Polysorbate 20 and 0.1% MEHQ added for stability. The solution was applied by laboratory swab to the skin sites of 1 of 2 each skin electrodes to be tested. The electrodes were constructed of an electron beam crosslinked polyvinylpyrrolidone hydrogel conductive adhesive, stainless steel wire—polyester knit fabric conductor, and standard NMES leadwire.
The stimulation was done with an EMPI Focus stimulator through subject electrodes for 40 minutes. The setting on the stimulator was a balanced biphasic waveform of 40 milliamp amplitude, 35 Hz frequency, and 200 microsecond pulse width with an On/Off duty cycle of 7 and 12 seconds respectively.
When stimulation was completed and electrodes removed, typical stimulation erythema was observed on the untreated skin. This transient erythema remained for over an hour. The treated skin had very little erythema and this was resolved in a matter of minutes. These results are shown in
An antioxidant lotion was prepared from an example formulation in the BASF Technical Bulletin for Sodium Ascorbyl Phosphate dated January 2003. It was denoted as BASF 53/00186NDE. The active ingredients were 1.0% Sodium Ascorbyl Phosphate and 0.5% Tocopheryl (Vitamin E) Acetate.
Conductive hydrogel adhesives were UV cured from the formulas in Table 1 below. The coatings were 35 mil (0.035 inch) thick and were made in 2 inch by 2 inch electrodes with carbon filled PVC film conductor and standard NMES leadwires.
The antioxidants used in these six solid hydrogel adhesive examples were MEHQ (in addition to what was already in the acrylic monomers as received), Benzophenone, Ciba Irganox 1010, Vitamin E acetate, and Sodium Ascorbyl Phosphate with Polysorbate 20 for additional aqueous stability.
These antioxidants may be used within the following ranges to obtain an electrode adhesive having suitable mechanical and adhesive properties for use as a biomedical electrode without causing erythema under normal conditions of use.
Stimulation was carried out as in Example 1 for these electrodes. The result is shown in
The following oil-in-water emulsion-was prepared per BASF 62/00109 formulation example with BASF RetiSTAR (a stabilized retinol), applied prior to stimulation and allowed to dry, and gave results similar to
Phases A and B were heated separately to about 80 C. Phase B was stirred into phase A and homogenized. Phase C was then added and homogenized. The mixture was then cooled to about 40 C then phase D was added with enough phase E to bring the pH to 6.5 with stirring. Phase F was added and the mixture homogenized then cooled to room temperature. The lotion was applied and allowed to dry. The test was carried out as in Example 1 and yielded similar results as in
Although there has been hereinabove described a composition and method for reduction of skin irritation caused by electrical stimulation through use of antioxidants in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it should be appreciated that the invention is not limited thereto. In particular, the antioxidant precursor may be incorporated in the electrode adhesive or separately applied to the skin of a patient prior to attachment of the biomedical electrode. In addition, the present invention comprises a kit including a biomedical electrode, as described above, and said antioxidant precursor in a form suitable for application to the skin of a patient and packaged for distribution, which advises a medical technician how to utilize the antioxidant precursor to prevent and/or amelliorate erythema prior to the use of said biomedical electrode to monitor and or stimulate a patient. Moreover, said invention comprises an article of manufacture which comprises 2000-30,000 ppm of Sodium Ascorbyl Phosphate. Finally, the present invention may suitably comprise, consist of, or consist essentially of the recited elements. Further, the invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the present invention as defined in the appended claims.
