CA1195736A - Conductive adhesive and biomedical electrode - Google Patents

Abstract

ABSTRACT

A disposable biomedical electrode is disclosed wherein the electrically-conductive material between the electrode plate and the skin comprises a swellable, conformable, cohesive, hydrophilic, electrically-conductive adhesive formed by an improved solventless process. The adhesive precursor comprises a polyhydric alcohol, a non-ionic unsaturated free radically polymerizable material, a free radical initiator, a crosslinking agent and a non-polymerizable ionizable salt. The adhesive precursor is polymerized after coating onto the electrode plate or releasable transfer sheet, preferably by exposure to ultra-violet radiation.

Description

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CONDUCTIVE AD~lESIVE AND BIOMEDICAI, ELECTRODE

Field of the Invention This invention relates to the fleld of conductive adhesives, particularly those used in biomedical electrodes to establish an electrlcal connection between the skln of the human anatomy and an electromedical apparatus, such as a high impedance electromyograph, electrocardiograph, electrical neurostimulator for pain relief, and the llke.
More particularly, it relates to conductive adhesives for use in so-called "dry" bioelectrodes which do not require the use of messy creams or gels to enhance conductivity between the skin and the electrode plate.

Background Art Copending Canadian Patent Application Serial No.
367,329 filed December 22, 1980, inventor Michael R. Engel, disclosed a conductive adhesive for biomedical electrode applications made by an improved solventless process. The adhesive is synthetic, dermally-nonirritating, conformable, cohesive, ionic and hydrophillic. The process by which the electrode is made involves the steps of: (1) forming an adhesive precursor comprising (a) a water-soluble polyhydric alcohol which is liquid at room temperature, (b) an ionic unsaturated free-radically polymerizable material which is soluble in the polydric alcohol, (c) a free radical initiator which is soluble in the polyhydric alcohol, and (d) a multi-funtional unsaturated free radically polymerizable cross-linking agent; (2) coating the adhesive precursor on one side of an electrode plate (conductive sensing element); and (3) polymerizing the coated precursor in situ.
In the preferred embodiment of the conductive adhesive of the aforementioned disclosure, the ionic monomer is acrylic acid neutralized with an inorganic base such as potassium hydroxide.
The conductive adhesives of my previous dis-closure are especially useful in electrosurgical grounding 3~

-2-plate electrodes. They offer significant advantages over pr~or art conductive adhesives such as those described by Berg in U.S. Patent No. 4,066,078. Berg discloses two classes of conductive adhesives plasticlzed with a polyhydric alcohol, viz., (1) polymers or copolymers derived from the polymerlzation of an ester of an olefinically unsaturated carboxylic ester and an alcohol havlng a quarternary ammonium group, and (2) sulfated cellulose esters. The processes by which these adhesives are formed into electrodes are much more tedlous and expensive than those described in my previous disclosure and do not result in as good overall adhesive properties.
The conductive adhesives of my previous disclosure are also an improvement over those specifically described in U.S.
Patent No. 4,352,359 to Larimore et al. The Larimore conductive lS adhesives may be formed from similar ionic monomers, but a more expensive process is used and no crosslinked polymers are disclosed. Crosslinking allows for higher amounts of polyhydric alcohol without reducing viscosity below acceptable levels. A higher polyhydric alcohol level enhances hydrophilicity, thereby improving electrical conductivity.
Although the conductive adhesives of my previous disclosure provide significant improvements over the prior art, particularly when used in grounding plate electrodes, one problem has been encountered with their use in ECG
electrodes. Electrodes utilizing my prior conductive adhesives do not recover satisfactorily following a defibrillation overload when used in disposable ECG electroces. Their polariza-tion potential is too high to meet standards proposed by the Association for the Advancement of Medical Instrumentation (AAMI).
I have now discovered that by the addition of ionic salts, preferably those con-taining a halide ion, to the electrically-conductive adnesives of my prior disclosure, I am able to produce non-polarizing electrodes.

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Since the added salts provide the conductivity needed for good electrical performance, inclusion of an ionic monomer in the adhesive precursor is no longer necessary.
Description of the Invention Accordin~ to the present invention, there is provided an essentially dry disposable biomedical electrode comprising an electrode plate or sensing element having a top surface and a bottom, skin-directed surface. The electrode plate has a means for electrical connection to a lead wire of an electro-medical device.
The bottom surface of the electrode plate is coated with a swell-able, non-water-soluble, eonformable, cohesive, dermally-non-irritating, hydrophilie eonductive material for enhancing the electrical connection with the skin. The conductive material is formed from an essentially solventless process ln situ on the electrode plate or a transfer sheet. The proeess involves first forming an adhesive precursor comprising (1) a water-soluble poiyhydric alcohol which is a liquid at about 20C; (2) at least one non-ionic unsaturated free radically polymerizable material soluble in said polyhydric alcohol; (3) a free radical initiator soluble in said polyhydric alcohol; (4) a crosslinking agent of a multifunctional unsaturated free radically polymerizable material soluble in said polyhydric alcohol; and (5) a non-polymerizable ionizable salt in an amount effective to render said adhesive pro-duct electrically conductive.
The non-ionic polymerizable material may comprise one non-ionic monomer or a mixture of non-ionic monomers. It is also contemplated that ionic polymerizable materials which are soluble

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-3~-in the polyhydric alcohol may be included in the precursor without departing from the spirit of the invention.
The adhesive precursor is coated directly onto one surface of the electrode plate or onto a releasable transfer surface. The precursor is polymerized ln situ, preferably by ultraviolet radiation. The cured conductive layer is then ready for use. If pol~merization occurs on a transfer surface, the adhesive layer is stripped from the transfer surface and applied to the e]ectrode plate. An ECG electrode containing the conductive adhesive of tha invention should exhibi~ a "Polarization Potential" (as hereinafter defined~ which does not exceed 100 millivolts.
The term l'solventless" is used herein to mean that there are substantially no materials present in the adhesive precursor which are not present in the final composition of the electrically conductive adhesive~
Stated another way, when the polymerization of the precursor is complete, and the adhesive is ready for use, at least 99% of the starting materials are still present.
The term "hydrophilic" is used herein to mean the conductive adhesive will absorb some water.
The term l'conformable" as used herein refers generally to the compliance of the conductive material. It must be suficiently compliant to conform to the surface of the skin beneath the electrode plate to provide a high surEace area of contact between the skin and the electrode plate.
The term "cohesive" refers to the internal integrity of the conductive material. Generally, the conductive material is film-forming and must be more cohesive than adhesive to the skin so that, when the electrode is removed from the skin, the conductive layer remains intact and does not leave an objectionable residue.
The term "swellable" refers to the imbibing of ~ solvPnts by the polymer matrix wi-th a concomitant increase in the volume of the polymer matrix.
The term "dermally non~irritating" means that the conductive adhesive can be used safely on mammalian skin without causiny an unacceptable amount of irritation or other toxic side effects.
The electrically conductive material is darived from the essentially solventless process of polymerizing the adhesive pracursor of which one component is the ~3~

water-soluble polyhydric alcohol. The term "polyhydric alcohol" as used herein refers to a compound or polymer having more than one hydroxyl yroup. rrhe polyhydric alcohol is water soluble and a li~luid at room temperature, e.y., approximately 20C. The polyhydric alcohol is present in the precursor in amounts oE ~rom 10 to 9~ parts per weight of the precursor, with 50 to about 70 be~ng pre~erred. Examples o~ useful polyhydric alcohols are propylene g:Lycol; 1,2,4 butane triol; polyethyleneoxide (e.g., "Carbowax" 400); and glycerol, with the latter being preferred. One skilled in the art will recognize that polyhydric alcohols which are not normally liquid at room temperature, may be mixed with those that are liquid at room temperature to form a material which is use-ful according to the present invention. One skilled in the art would also recognize that the dihydric alcohol ethylene glycol may be useful in the present invention, but may cause dermal reactions which limit its utility.
As stated above, the precursor is also comprised of at least one non-ionic unsaturated free radically polymerizable material which is soluble in the polyhydric alcohol. The total amount of polymerizable material (including any ionic monomers, if present) in the precursor will generally range from about 20 to 30, preferably about 25 to 28, parts by weight of the precursor. The type of non-ionic polymerizable material used is not critical so long as it provides the desired performance properties in the cured and crosslinked state, e.g., conformability, tackiness, cohesiveness, dermal nonirritability, etc.
Examples of useful non-ionic free radically polymerizable monomers which are soluble in the polyhydric alcohol are acrylic acid, methacrylic acid, hydroxyethyl methacrylate, and N-vinyl pyrrolidone. The most preferred performance properties for ECG electrodes are provided by acrylic acid in an arnount between about 25 and 28 parts by weight oE the precursor.
,-,,~,k 31~j The precursor is further comprised of 0.1 to 5 parts by weight per 100 parts of the unsaturated material of a crosslinking agent of a multiEunctional unsaturated Eree radically polymerizable material. Examples are triethylene-glycol-bis-methacrylate, ethyleneglycol-bis-methacrylate, bisacrylamide, and triethylene-glycol-bis-acrylate with the former heing preferred in amounts about 0.15 to about 1.5 parts by weight per 100 parts of the unsa-turated material.
The initiation of polymerization of the precursor is facilitated by the presence of at least 0.1 part by weight per 100 parts of the unsaturated material of a Eree radical initiator which is soluble in the polyhydric alcohol. The initiator may be of the thermal or photo class. The actual selection is dependent on the monomers and the polyhydric alcohol. An example of useful thermal initiators are benzoyl peroxide, azobisisobutyronitrile, di-t-butyl peroxide and cumyl peroxide. Examples of useful photo-initiators are disclosed in the article Photoinitiators - An Over-view by G. Berner et al in the Journal of Radiation Curing (April 1979), pp. 2 through 9. The preferred photoinitiator is benzil-dimethylketal.
The electrical conductivity of the adhesives of theinvention is provided by the addition of an effective amount of a non-polymerizable ionizable salt to the adhesive precursor. The salt is preferrably presen-t in an amount ranging frorn about 0.1 to 5.5 percent by weigh-t of the precursor. Any organic or inorganic ionizable salt may be used which provides the necessary electrical conductivity, is dermally-nonirritating, does not interfere with -6a-the physical proper-ties of the adhesive and, in the case of ~CG
electrodes, allows the electrode to exhibit -the required Polariz-ation Potential, i.e., recover rapidly followincJ defibrillation overload. It has been found that ionizable salts containinc3 halide ions provide the best overall results, especially inorganic halide salts containing chloride and bromide ions. Particularly preferred are inorganic chloride salts such as 7~

potassium chloride. The most preferred adhesive precursor contains potassium chloride in a concentration between 3.5 and 4.5 percent by weiyht oE the precursor.
In some cases, it may be necessary to add a small amount of water, e.g., 10 percent by weight or less, to the precursor to ensure complete solubili~ation oE the salt.
The water becomes part oE the conductive adhesive coating and may evaporate to some extent if the electrode is used or stored in environments of low humidity and/or high temperature. However, under normal conditions, the small water content appears to have little or no negative effect on the performance of the electrode.
It will be recognized by one skilled in the art that other additives (e.g., tackifers, such as polyacrylic acid) may be added to the precursorO In fact, the preferred precursor contains about 4.0 pereent by weight of polyaerylie aeid to inerease tackiness.
The essentially solventless precursor can be coated on to the electrode plate or transfer sheet and, depending on the free radieal initiator, exposed to either heat or aetinie radiation whieh results in the Eormation of an eleetrieally eonduetive pressure-sensitive adhesive.
The preeursor may also be exposed to eleetron beam radiation to facilitate the crosslinking.

Description of the Drawings A better understanding of the invention will be facilitated by reference to the aeeompanying drawings wherein:
Figure 1 is an exploded seetional view of a disposable ECG electrode containing the conductive adhesive of the invention;
Figure 2 is a top plan view of an alternative embodiment of the ECG eleetrode of Figure l;
Figure 3 is an exploded seetional view of the eleetrode of Figure 2; and Figure 4 is a eircuit used in the defibrillation 3~i overload recovery test (described in example 1 below).
Referring to Figure 1, a disposable ECG
electrode 10 is illustrated in which the electrode plate 12 is provided by a circular piece of nonwoven web 14 approxi-mately 1 3/16 inches in dialneter which has ~)een vaporcoated with sllver 16 on its lower surface. Electrode plate 12 is co~nected to an electrocardiograph (not shown) by means of a standar-l stud/eyelet connector. In the embodiment il~ustrated, stud 18 is made of stainless steel and eyelet 18 is formed of plastic (injection molded ABS) having a conventional silver/silver chloride coatin~.
Conductive adhesive layer 22, approximately 28 I-nils thick, covers the lower, skin-directed surface of the electrode plate 12. A release liner 24 protects the conductive adhesive prior to use.
The electrode 26 of Figures 2 and 3 colnprises a circular piece of standard pressure-sensitive adhesive tape 28 such as Micropore~ brand tape sold by the 3M Company, Saint Paul, Minnesota. Adhesive tape 28 is laminated to a disc of tin foil 30 approximately 1.7 mils thick and 1 1/4 inches in diameter. Tin foil disc 30 constitutes the conductive electrode plate of the electrode. Tab 32 extends from tape 28 and tin foil disc 30 to provide a means for connecting the electrode plate to an electro-cardiograph by way of any alligator clamp (not shown) orother suitable connector. Tab 32 is reinforced with a piece of polyethylene 34 (preferrably colored) so as to be readily visible to the user. Conductive adhesive layer 36, approximately 28 mils thick, is applied to the lower, skin-directed surface of tin foil disc 30. Release liner 38 is used to protect the adhesive prior to use.
No elaborate packaging is required for electrodes according to the invention since they are essentially "dry"
and moisture loss is generally not a problem.
The embodiments ill~strated in the drawings are merely illustrative. The specific construction of the electrode is not critical to the invention. The ECG elec-~5~73~
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trodes illustrated are designed to have a low Polarization Potential in accordance with the standards proposed by AAMI. It is well ]cnown to those skilled in the art that to achieve a low Polarization Potential the electrode plate must ~e selected so dS to be non~polariziny. Silver-silver chloride or tin electrode plates in combillation witll a conductive adhesive conta1nillg chloride :ion are pre~erably used. Other suitable materials include nobel metals, but they are not practica] on account o~ cost.
The conductive adhesives of the present invention may be used in biomedical electrodes other than non-polarizing ECG electrodes, such as electrosurgical grounding plate electrodes and electrodes Eor trans-cutaneous electrical nerve stimulation (TENS)o However, for such other applications, they offer no perceived advantages over the conductive adhesives described in my previous disclosure, Serial No. 367,329, filed December 22, 1980. In some cases they may be less desirable, particu-larly since the presence of an ionizable salt in the present adhesive may cause some corrosion problems when used in combination with certain metal electrode plates such as aluminum.
The invention is further illustrated by reference to the following non-limiting examples.

Example 1 Powdered polyacrylic acid as the sodium salt (18 grams) (X 739 from B. F. Goodrich Chemical Division, Cleveland, Ohio) is dissolved in warm distilled water (18 grams) by stirring for one hour, and added to a mixture of potassium chloride (17.1 grams), distilled water (25.0 grams), acrylic acid (115.0 grams), glycerine (250.0 grams), triethyleneglycol-bis-methacrylic (0.3 grams) and 0.35 grams of Irgacure 651 (a benzildimethylketal from Ciba-Geigy). The ingredients are mixed for ~ hours in a glass jar to insure dissolution of all components. During mixing, the jar is covered with aluminum foil to prevent premature polymerization.
This adhesive precursor is knife-coated onto 8-pound tissue paper (from Crystal Tissue Company) which is layered on 7G-poun-l silicone coated pa~er (froln the H. P. Smith Company). The resu1ting coating adhesive thickness is approxilnately 28 mi~s.
The coated substrate is then passed throucJh a 3-foot inert chamber (N2 atmosphere) under a bank of UV
lights consisting of thirty 18-inch "black liyht" tubes for one minute which results in the polymerization of the coating.
A 4 rllil web of nonwoven polyester number 760 from 3M Company, Industrial Electrical Products Division was vaporcoated with 2000A silver. Stainless steel studs and silver/silver chloride-plated plastic eyelets were crimped through the silver vaporcoated film. This film was then hand laminated to the polymerized conductive adhesive and 1 3/16 inch diameter electrodes as illustrated in Figure 1 were produced. These electrodes were allowed to equili-brate for one day at 50~ relative humidity (R.H.) and 74F.
After equilibrating for one day the samples were tested for conductivity and defibrillator recovery.

Impedence Impedence in ohms of the electrode was measured using a ~odel 4800A Vector Impedence Meter manufactured by Hewlett Packard, Palo Alto, Calif. Measurements were conducted in the conventional manner on electrode pairs connected face-to-face (adhesive-to-adhesive) using a low level signal suitable for measurements on ECG electrodes.
The impedence of the electrode at 10 Hz was found to be 185 Ohms.

Polarization Potential The Polarization Potential of the electrode was determined using the defibrillation overload recovery test set forth in "AAMI Draft Standard for Pregelled Disposable 3~i Electrodes", May, 1981, Section 2.2.2.4, Electrical Performance Standards. The test was conducted as follows uslng the clrcuit shown in Figure 4:
1. Two electrodes 40 and 42 are connected adheslve-to-adhesive and connected to the test circuit (~`igure 4) with switch 44 closed and switches 46 and 48 open.
2. At least 10 seconds are allowed for the capacitor 50 to fully charge to 200 V; switch 44 is then opened.
3. The capacitor 50 is discharged through the electrode pair by holding switch 46 closed long enough to discharge the capacitor 50 to less than 2 V. This time should be no longer than 2 seconds.

4. Switch 48 is closed immediately, and the electrode pair is connected to the offset measurement system (switch 46 is open).

5. The electrode offset is recorded to the nearest 1 mV, 5 seconds after the closure of switch 48 and every 10 seconds thereafter for the next 30 seconds. The overload and measurement is repeated three times.
The test circuit of Figure 4 should have the following characteristics: Resistor 52 has a resistance of 10 kilohms, and resistor 54 is a 5 watt, 100 ohm resistor. Capacitor 50 has a capacitance of lO~ F. All capacitors and resistors should be within 90 to 110 percent of the specified values.
The offset recorder input amplifier 56 has a resistance of 10 megohms and must have an input impedance from 0 to 10 Hz od 10 M, + 10 percent, and a bias current of less than 200 nA. The error of the voltage-recording equipment should be no greater than ~ 5 percent of full scale of l00 mV. A 10 mV change must be measurable with an error no yreater than + 1 mV. For this purpose, the full scale range and resolution of the recording instrument may be adjusted as needed.
The tes-t sequence (Steps 1-5) is repeated for 3 electrode pairs. The "Polarization Po-tential" (as used 3~

herein means the potential 15 second after the fourth pulse) should not exceed 100 m~ volts. The electrode of this example was found to have a Polarlzatlorl Potent~al of l8.8 millivolts.
Eollowing the manufacturing and testlng procedures set forth in Example~ 1, the following electrodes were made.
Example Amount Impedence Polarization No._ Saltgrams) %(10 Hz) Potential 2 Cacl28.6 1.97500 ohms 19.5mv 3 ICBr17.1 3.851600 7.2 4 NH4CL8.6 1.97770 18.0 NaCl17.1 1.97425 17.8

6 SnC1417.1 1.972900 15.5

7 KCl0.43 0.10850 91.0

8 KCl23.5 5.22240 14.7

9 None -- -- 1150 255.0 When no salt was used and 8 percent potassium hydroxide was present (according to the disclosure of Canadian Patent Application Serial No. 367,329 filed December 22, 1980, referred to on page 1), the impedance was 200 ohms and the Polarization Potential was 350 millivolts. A combination of potassium hydroxide and potassium chloride, 2% and 4~, respectively, brought the impedance down to 130 ohms and the Polarization Potential to 20 millivolts.
The following examples illustra-te adhesive precursors containing different nonionic monomers and an assessment of the adhesive properties (initial thumb tack) of the cured adhesive.

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E~ample 10 _ ~nount Ingredient(grams) In_tlal Thumb Taek KCl 5.7 5 Water distilled 8.3 Dissolved polyacrylic 12.0 acid (sodium salt) in water (50% by weight) Metllaerylic acid38.3 high taek

10 Irgaeure 651 .L2 Glycerine 83.3 TEGBM .1 Example 11 Amount Inc3redient(grams) Initial Thumb Taek -KCl 5 7 Water distilled 8.3 Dissolved polyaerylie 12.0 acid (sodium salt) in water (50% by weight) Hydroxyethyl methacrylate 38.3 low-medium taek Irgaeure 651 .12 Glyeerine 83.3 TEGBM .1 ~xample 12 Amount Ingredient(grams) Initial Thumb Taek ~Cl 17.1 Water 25.0 30 Dissolved poly aeylie36.0 aeid (sodium salt) in ~ater (50% by weight) N-vinyl pyrrolidone115.0 high taek Irgueure 651 .12 35 Glyeerine 250.0 TE~BM .3 Example 13 Amount _ Ingredient (grams) Initial Thumb_Tack KCl 5.7 5 Water 8.3 Dissolved poly acylic acid 12.0 (sodium salt) in water (50% by wei(3ht) Acrylic acid 20.0 hiyh tack Hydroxyethyl methacrylate 18.3 Irgucure 651 .12 Glycerine 83O3 TEGBM .1 _xample 14 Amount Ingredient (grams) Initial Thumb Tack KCl 17.1 Water 25.0 Acrylic acid 115.0 high tack 20 Irgacure 651 0.35 Glycerine 250.0 Triethylene glycol 0.3 dimethacrylate The following examples illustra-te adhesive precursors containing different polyhydric alcohols and an assessment of the adhesive properties of the cured adhesive.

Example 15 Amount Ingredient (grams) Initial Thumb Tack KCl 5.7 5 Water 8.3 Dissolved poly acrylic12.0 medium tack acid (sodiwn salt) in water (50~ by weiyht) Acrylic acid 38.3 Irgacure 651 .12 Propylene glycol 83.3 TEGBM .1 Example 16 Amount Ingredient (grams) Initial Thumb Tack KCl 5 7 Water 8.3 Dissolved poly acrylic1200 high taclc acid (sodium salt~ in water (50~ by weight) Acrylic acid 38.3 Irgacure 651 .12 1,2,4 Butanetriol 83~3 TEGBM .1 Example 17 ~nount _ Ingredient (grams? Initial Thumb Tack KCl 5 7 Water 8.3 30 Dissolved poly acrylic12.0 high tack acid (sodium salt) in water (50% by weight) Acrylic acid 38.3 Irgacure 651 .12 Carbowax~ ~400 poly-83.3 ethylene oxide TEGBM .1

Claims (15)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an essentially dry biomedical electrode comprising an electrode plate having an upper surface and a lower, skin-directed surface, said electrode plate having means for electrical connection to a lead wire of an electro-medical device, and a conductive material on said lower surface of said electrode plate for enhancing electrical connection with the skin, the improvement wherein said conductive material comprises a swellable, dermally-nonirritating, conformable, cohesive, hydrophilic polymer formed by the essentially solventless process of:
(a) compounding an adhesive precursor comprising (1) a water-soluble polyhydric alcohol which is a liquid at about 20°C;
(2) a non-ionic unsaturated free radically polymeriz-able material soluble in said polyhydric alcohol;
(3) a free radical initiator soluble in said polyhydric alcohol;
(4) a crosslinking agent of a multifunctional unsatur-ated free radically polymerizable material soluble in said polyhydric alcohol;
(5) a non-polymerizable ionizable salt in an amount effective to render said material electrically conductive;
(b) coating said adhesive precursor on said lower surface of said electrode plate or on a releasable transfer surface;
and (c) polymerizing said coated precursor to form an electrically conductive pressure-sensitive adhesive.

2. In an essentially dry ECG electrode comprising an electrode plate having an upper surface and a lower skin-directed surface, said electrode plate having means for electrical connec-tion to a lead wire of an electrocardiograph, and a conductive material on said lower surface of said electrode plate for enhanc-ing electrical connection with the skin, the improvement wherein said conductive material comprises a swellable, dermally-non-irriating, conformable, cohesive, hydrophilic polymer formed by the essentially solventless process of:
(a) compounding an adhesive precursor comprising (1) a water-soluble polyhydric alcohol which is a liquid at about 20 C;
(2) a non-ionic unsaturated free radically polymeriz-able material soluble in said polyhydric alcohol;
(3) a free radical initiator soluble in said polyhydric alcohol;
(4) a crosslinking agent of a multifunctional unsatur-ated free radically polymerizable material soluble in said polyhydric alcohol; and (5) a non-polymerizable ionizable salt in an amount effective to render said conductive material electrically conductive;
(b) coating said adhesive precursor onto said lower surface of said electrode plate or a releasable transfer surface;

(c) polymerizing said coated precursor to form an electrically conductive pressure-sensitive adhesive, said electrode having a Polarization Potential not greater than about 100 millivolts.

3. The electrode according to claim 2 wherein said ionizable salt contains a halide ion.

4. The electrode according to claim 3 wherein said halide ion is chloride.

5. The electrode according to claim 4 wherein said salt is potassium chloride.

6. The electrode according to claim 1 or 2 wherein said polyhydric alcohol comprises from about 10 to about 90 parts per weight of said precursor.

7. The electrode according to claim 1 or 2 wherein said polyhydric alcohol comprises from about 10 to about 90 parts per weight of said precursor, and said polyhydric alcohol is glycerol.

8. The electrode according to claim 1 or 2 wherein said non-ionizable material is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethylmethacrylate, and N-vinyl pyrrolidone.

9. The electrode according to claim 1 or 2 wherein said non-ionizable material is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethylmethacrylate, and N-vinyl pyrrolidone, and said nonionic material is acrylic acid.

10. The essentially dry biomedical electrode according to claim 1 or 2 wherein the free radical initiator is a photoinitiator.

11. The essentially dry biomedical electrode according to claim 1 or 2, wherein said non-ionizable material is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethylmethacrylate, and N-vinyl pyr-rolidone, and the free radical initiator is benzyldimethylketal.

12. The electrode according to claim 1 or 2, wherein said non-ionizable material is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethylmethacrylate, and N-vinyl pyrrolidone, and which further comprises a tackifier selected from the group consisting of polyacrylic acid and soluble salts thereof.

13. The electrode according to claim 2 wherein said electrode plate comprises a layer of metal foil.

14. The electrode according to claim 13 wherein said metal is tin.

15. The electrode according to claim 2 wherein said electrode plate comprises a non-woven web having metallic silver vapor-coated on the lower surface thereof.