Flat, conformable, biomedical electrode
BACKGROUND OF THE INVENTION 
     The present invention relates generally to biomedical electrodes. 
     Biomedical electrodes are useful for both stimulation and body monitoring functions. Stimulation uses of biomedical electrodes include transcutaneous electronic nerve stimulation (TENS) for the treatment of pain and neuromuscular stimulation (NMS) as, for example, treatment for scoliosis. Body monitoring uses for biomedical electrodes include electrocardiogram (ECG) for monitoring heart activity. 
     Among biomedical electrodes in existence are those of Phipps et al, Cartmell and Larimore. Phipps et al in U.S. Pat. No. 3,170,459 discloses a biomedical instrumentation electrode constructed from multiple plies of discs made from a relatively inflexible material, i.e., cork. The electrode utilizes a conductive gel to establish electrical contact with the body. Cartmell in U.S. Pat. No. 4,543,958 discloses a medical electrode assembly. The electrode has a flexible, dimensionally stable substrate which is striped with an electrically conductive paint. The electrode is then clamped into a bulky cable connector. Larimore in U.S. Pat. No. 4,458,696 (assigned to Minnesota Mining and Manufacturing Company) discloses a TENS electrode with a raised structure to permit entry of and attachment to a tubular electrical conductor. 
     These electrodes suffer from several deficiencies including that all are &#34;high profile&#34; electrodes and that the electrodes do not &#34;conform&#34; well to the body. 
     SUMMARY OF THE INVENTION 
     The present invention provides a biomedical electrode which is (1) flatter and more conformable, (2) has a very low profile, (3) may be trimmed to differing shapes, (4) has flexibility in lead wire insertion direction, and (5) allows the reuse of the lead wire. The electrode of the present invention is flatter and more conformable to body contours and body movement than prior electrodes. The electrode relies on an adhesive contact with a flat electrical conductor as opposed to rubber connector strips or snaps. The electrode has a very low profile which makes it suitable to be worn under tight clothing and to be comfortable when slept upon or when leaned against, as for example, when sitting in a chair. The electrode may be trimmed to virtually any size or shape to allow adaptability in placement and location. The electrode allows for flexibility in lead wire insertion and allows for the lead wire to be inserted from the end of the electrode or from either side. The reuseability of the lead wire leads to economy for use of the biomedical electrode. 
     The present invention provides a biomedical electrode which is adapted to be applied to a body and adapted to be electrically and mechanically connected to an electrical lead wire. The electrode contains a protective, electrically insulative web, an electrically conductive adhesive adjacent one side of the protective, insulative web, that side being adapted to be oriented toward the body, and a release liner between the protective, electrically insulative web and the electrically conductive adhesive. The release liner has a release agent facing the conductive adhesive. The release liner covers only a portion of the surface area of the protective insulative web. In a preferred embodiment, a pressure sensitive adhesive is located between the release liner and the protective, electrically insulative web. In a preferred embodiment, the protective insulative web is perforated. 
     In another embodiment, the present invention is a biomedical electrode adapted to be applied to a body. The electrode has a protective, electrically insulative web. The electrode also has an electrically conductive adhesive adjacent one side of the protective insulative web, that side adapted to be oriented toward the body. The electrode contains a removeable release liner between the protective, electrically insulative web and the electrically conductive adhesive. The release liner has a release agent facing the conductive adhesive. The release liner covers only a portion of the surface area of the protective, electrically insulative web. The electrode also has an insertable electrical lead wire having an uninsulated portion and an insulated portion. The uninsulated portion of the electrical lead wire is insertable between the conductive adhesive and said protective, electrically insulative web. At least part of the insulated portion of the electrical lead wire extends beyond an edge of the protective, electrically insulative web. An electrode constructed in this manner provides an electrode in which the removeable release liner may be discarded, the insertable electrical lead wire may be positioned and the protective, electrically insulative web may be secured over the uninsulated portion of the electrical lead wire and secured in place by the electrical conductive adhesive. 
     The present invention, in another embodiment, provides a biomedical electrode adapted to be applied to a body and adapted to be electrically and mechanically connected to an electrical lead wire. The electrode has a protective, electrically insulated web. The electrode also has a first layer of adhesive adjacent one side of the protective, electrically insulative web that side adapted to be oriented toward the body. The electrode has a release liner adjacent the first layer of adhesive opposite said protective, electrically web. The release liner has a release agent facing the first layer of adhesive the release liner covering only a portion of the surface area of the protective, electrically insulative web. A second layer of electrically conductive adhesive is positioned adjacent the release liner opposite from the protective, electrically insulative web. The electrode also contains an electrically conductive film positioned adjacent the second layer of adhesive opposite said release liner. The electrode further contains a third layer of adhesive which is electrically conductive and positioned adjacent the electrically conductive film opposite the second layer of conductive adhesive and adapted to be applied to the body. In a preferred embodiment, the electrically conductive film is a metallic coating on a self supporting conductive film. In a preferred embodiment, the electrode further has a pressure sensitive adhesive between the release liner and the protective, electrically insulative web. In another preferred embodiment, the second layer of adhesive contains silver particles. 
     In another embodiment, the invention provides a biomedical electrode adapted to be applied to a body. The electrode contains a protective, electrically insulative web. The electrode also contains a first layer of adhesive adjacent one side of the protective, electrically insulative web, that side adapted to be oriented toward the body. The electrode contains a removeable release liner adjacent the first layer of adhesive opposite from the protective, electrically insulative web the release liner having a release agent facing the first layer of adhesive. The release liner covers only a portion of the surface area of the protective, electrically insulative web. The electrode also contains a second layer of adhesive which is electrically conductive and positioned adjacent the release liner opposite from the protective, electrically insulative web. The electrode also contains an electrically conductive film positioned adjacent the second layer of adhesive opposite the release liner. The electrode also contains a third layer of adhesive which is electrically conductive and positioned adjacent the electrically conductive film opposite the second layer of adhesive and adapted to be applied to the body. Further, the electrode contains an insertable electrical lead wire having an uninsulated portion and an insulated portion. The uninsulated portion of the electrical lead wire is insertable between the first layer of adhesive and the second layer of adhesive and at least part of the insulated portion of the electrical lead wire extends under the edge of the protective, electrically insulative web. In an electrode constructed in this manner, the removeable release liner may be discarded, the insertable electrical lead wire may be positioned and the protective, electrically insulative web may be secured over the uninsulated portion of the electrical lead wire and secured in place by the first layer of adhesive and the second layer of adhesive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings in which: 
     FIG. 1 is isometric view the biomedical electrode of the present invention; 
     FIG. 2 is a side view of an embodiment of the biomedical electrode of the present invention with a double coated release liner and electrical lead wire illustrated; 
     FIG. 3 is a side view of an embodiment of the biomedical electrode of the present invention with an extended release liner; 
     FIG. 4 is a side view of an embodiment of the biomedical electrode of the present invention with a center located release liner; 
     FIG. 5 is a side view of an embodiment of the biomedical electrode of the present invention with a single sided folded release liner; and 
     FIG. 6 is a side view of an embodiment of the biomedical electrode of the present invention with an extended release liner and protective web. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an isometric view of a preferred embodiment view of the biomedical electrode 10 of the present invention. The biomedical electrode 10 is also shown in expanded side view in FIG. 2. The top of biomedical electrode 10 is a protective, electrically insulative web 12. Web 12 protects the top of biomedical electrode 10 from physical damage and covers lead wire 14 when it is inserted in the biomedical electrode 10 to help secure lead wire 14 in place. Web 12 is electrically insulative to confine the electrical signals used in the biomedical electrode to the lead wire 14 or to the body (not shown). As shown in FIG. 1, web 12 is preferably perforated making web 12 more conformable to the body contour and for asthetics. The perforations also assist in the tearability of web 12 once it is desired to remove lead wire 14 from the biomedical electrode 10. In a preferred embodiment, web 12 is appoximately 4 mils (1.0 millimeters) thick and is constructed from a pigmented low molecular weight polyethylene film. 
     Web 12 is attached to the remainder of biomedical electrode 10 with a pressure sensitive adhesive 16. In a preferred embodiment, the pressure sensitive adhesive 16 is an acrylate adhesive. A release liner 18, which is removeable, is placed beneath pressure sensitive adhesive 16 covering a portion of the surface area of biomedical electrode 10. Release liner 18 facilitates the lifting of web 12 away from the remainder of the biomedical electrode 10 in order that lead wire 14 may be inserted and web 12 subsequently reapplied securing lead wire 14 in biomedical electrode 10. In a preferred embodiment, release liner 18 is a Polyslick™ material as manufactured by James River Corporation, H. P. Smith Division, Bedford Park, Ill. A conductive adhesive 20 is positioned in the biomedical electrode 10 below release liner 18. Conductive adhesive 20 need only cover a portion of the surface area of biomedical electrode 10 to which lead wire 14 may be positioned. In a preferred embodiment, conductive adhesive 20 covers approximately the same surface area of biomedical electrode 10 as does release liner 18. This allows for relative general ease in the positioning of lead wire 14 once release liner 18 has been removed. In a preferred embodiment, conductive adhesive 20 is made conductive through the inclusion of silver particles. In a preferred embodiment, a resistivity measurement using a one inch square brass plate above and below the adhesive measures approximately 0.01 ohms. The exact conductivity of conductive adhesive 20, of course, depends upon the end use to which biomedical electrode 10 is intended. Generally, it is expected that resistivities of conductive adhesive may generally range up to one ohm. In another embodiment, approximately ten ohms may be sufficient and higher resistivities may be allowable in other embodiments and other uses for biomedical electrode 10. Conductive adhesives, especially conductive adhesives containing silver particles are widely available. An example of a suitable adhesive is a solvent based acrylate adhesive containing silver particles about 3 mils (0.76 mm) in diameter which is coated through a knife coater at about 12 mils (3.05 mm) thickness. The coated adhesive is heated to drive off the solvent resulting in an adhesive layer of about 1.5 mils (0.38 mm) in thickness. Note that the silver particles are larger than the thickness of the resulting adhesive giving the layer is needed electrical conductivity. An adhesive similar to this but which has been coated on aluminum is available as X1170 foil tape from Minnesota Mining and Manufacturing Company, St. Paul, Minn. Below conductive adhesive 20 an electrically conductive film 22, preferably a metal vapor coated conductive film, covers a large portion of the surface area of biomedical electrode and, in a preferred embodiment, covers the entire surface of biomedical electrode 10. The purpose of electrically conductive film 22 is to disburse the current delivered by or received by biomedical electrode 10 over a larger portion of the surface area of biomedical electrode 10. Electrically conductive film 22 may also operate to provide an ion barrier between the insertable lead wire 14 and the body. In a preferred embodiment, the electrically conductive film is an ethylene vinyl acetate loaded with approximately 28% carbon or a, Velostat™ film manufactured by Minnesota Mining and Manufacturing Company, Saint Paul, Minn. in either case coated top side with a 7×10 -8  to 1.2×10 -7  meters thick vapor coat of aluminum or silver. In a preferred embodiment, electrically conductive film 22 is approximately 3 mils (0.76 millimeters) thick. As indicated, conductive adhesive 24 operates to secure biomedical electrode 10 to the body and to provide through electrical conductivity from the body to biomedical electrode 10 or visa versa. It is preferred that conductive adhesive 24 have better cohesion than adhesion in order to facilitate the ease in which the biomedical electrode 10 may be removed from the body. Conductive adhesive 24 may generally have a volume resistivity of the range from 50 to 200 ohm-centimeters although lower and higher volume resistivities may work for some uses of the biomedical electrode 10. In a preferred embodiment, conductive adhesive 24 is from 10 mils (2.5 millimeters) to 60 mils (15.2 millimeters) thick. In a reuseable electrode it is preferred that the conductive adhesive 24 be from 30 mils (7.6 mm) to 44 mils (11.2 mm) thick. In a disposable electrode it is preferred that the conductive adhesive be from 10 mils (2.5 mm) to 25 mils (6.3 mm) thick. An example of a conductive adhesive 24 desirable for a reuseable electrode is described in U.S. Pat. No. 3,865,770, Blake, Water-Dispersable Pressure-Sensitive Adhesive, Tape Made Therewith, and Novel Tackifiers Therefor, which is hereby incorporated by reference. It is preferred that the adhesive in Blake be modified and the following ingredients used: 
     
         ______________________________________                                    
                   Dry Weight Dry Weight                                  
Ingredient         Grams      Percent                                     
______________________________________                                    
Copolymer: Butyl Acrylate &amp;                                               
                   83.177     40.945                                      
Acrylic Acid in 3:1 ratio                                                 
Glycerin           20         9.8452                                      
Butanediol         20         9.8452                                      
Sorbitol           20         9.8452                                      
Methyl diethanolamine (MDEA)                                              
                   28         13.783                                      
Potassium Chloride (KCl)                                                  
                   6.9678     3.4300                                      
Foral AX (hydrogenated wood                                               
                   25         12.306                                      
rosin)                                                                    
Total              203.14     100.04                                      
______________________________________                                    
 
    
     An example of a conductive adhesive 24 desireable for a disposable electrode is described in U.S. Pat. No. 4,554,924, Engel, Conductive Adhesive and Biomedical Electrode, which is hereby incorporated by reference. It is preferred that the adhesive in Engel be modified and the following ingredients be used: 
     
         ______________________________________                                    
                 Dry Weight  Dry Weight                                   
Ingredient       Grams       Percent                                      
______________________________________                                    
1,4 Butanediol   45          6.3993                                       
Glycerin         75          10.665                                       
Sorbitol         290         41.240                                       
K739, Polyacrylic                                                         
                 17          2.4175                                       
Potassium Hydroxide                                                       
                 3.25        0.46217                                      
Total Water      155         22.042                                       
Acrylic Acid     115         16.354                                       
Irgacure         0.51635     0.07343                                      
Tegbm            2.3186      0.32972                                      
Methyl ethyl hydroquinone                                                 
                 0.12        0.01706                                      
Total            703.20      100.04                                       
______________________________________                                    
 
    
     Optionally, a second release liner (not shown) may be provided below conductive adhesive 24 to facilitate transportion and storage of biomedical electrode 10 before use or between uses. 
     Biomedical electrode 10 may be utilized by applying the biomedical electrode 10 to a body being secured by conductive adhesive 24. The protective, electrically insulative web 12 may be lifted since release liner 18 prevents the protective, electrically insulative web 12 from sticking to conductive adhesive 20. Once the protective insulative web 12 is lifted, release liner 18 may be removed and discarded. At this time, lead wire 14 may be inserted so that noninsulated portion 26 of lead wire 14 is positioned over conductive adhesive 20. Lead wire 14 also has an insulative portion 28 which extends from beneath the confines of protective, electrically insulative web 12 and may be connected to suitable electronic equipment intended to utilize biomedical electrode 10. Lead wire 14 may be a copper wire whose insulated portion 28 is insulated with any suitable insulation, as for example, rubber or plastic. The end of noninsulated portion 26 of lead wire 14 is a flat crimped on conductor plate 30. Conductor plate 30 is flat which facilitates the biomedical electrode 10 being of low profile, flat and conformable to the body. Conductor plate 30 may, for example, be a zinc plated copper or, optionally, a silver plated copper with a chloride treatment. 
     FIG. 3 illustrates an alternative embodiment for the biomedical electrode 10A of the present invention. The construction of the biomedical electrode 10A in FIG. 3 is similar to the biomedical electrode 10 in FIG. 2 except that protective, electrically insulative web 12, pressure sensitive adhesive 16 and release liner 18 extend from one edge of conductive adhesive 20, electrically conductive film 22 and conductive adhesive 24. Having these items extend beyond the edge facilitates the lifting of protective, electrically insulative web 12 in order that release liner 18 may be removed and lead wire 14 inserted. 
     FIG. 4 illustrates another expanded side view of another embodiment of the biomedical electrode 10B of the present invention. The embodiment illustrated in FIG. 4 is similar with that as biomedical electrode 10 illustrated in FIG. 2 with the exception that the portion of the surface area of biomedical electrode 10 which is covered by release liner 18 and conductive adhesive 20 is positioned centrally in the biomedical electrode 10. This embodiment illustrates that protective insulative web 12, as well as pressure sensitive adhesive 16, may be separated into two portions. Biomedical electrode 10B as illustrated in FIG. 4 operates as before, protective insulative web 12 is lifted, release liner 18 is removed and lead wire 14 is inserted over conductive adhesive 20. 
     In the embodiments of biomedical electrode illustrated in FIGS. 1-4, a single sheet release liner 18 is illustrated. In these embodiments, release liner 18 is coated both sides with a release agent allowing the release liner 18 to release both from presssure sensitive adhesive 16 and conductive adhesive 20. 
     Another embodiment of biomedical electrode 10C is illustrated in a side exploded view in FIG. 5. The biomedical electrode 10C illustrated in FIG. 5 also contains a protective, electrically insulative web 12 and a pressure sensitive adhesive 16. The biomedical electrode 10 also contains a release liner 18. Release liner 18 is illustrated as being folded with the closed side fold being positioned interiorly with respect to biomedical electrode 10 and the open side fold being positioned near an edge of the protective, electrically insulative web 12. The release liner 18 as illustrated in FIG. 5 may be coated on only one side, the outside of release liner 18 as it is folded so that the release agent still contacts pressure sensitive adhesive 16 and conductive adhesive 24. As in the other embodiments, the biomedical electrode 10C illustrated in FIG. 5 contains conductive adhesive 24 preferably along the entire bottom surface area of biomedical electrode 10. Conductive adhesive 24 is the same as and performs the same purpose as conductive adhesive 24 in FIGS. 1-4. Note that the biomedical electrode 10C illustrated in FIG. 5 is missing electrically conductive adhesive 20 and electrically conductive film 22. As noted earlier, electrically conductive film 22 was used to facilitate the dispersion of electrical currents over the entire surface of biomedical electrode. In situations where such dispersion is not required or such dispersion is not required to be achieved as well as can be achieved with the electrically conductive film 22, the electrically conductive film 22 may be omitted. With the omission of electrically conductive film 22, electrically conductive adhesive 20 is also no longer needed. Electrically conductive adhesive 20 was utilized to secure lead wire 14 when it was positioned within biomedical electrode 10. With the embodiment of the biomedical electrode 10C illustrated in FIG. 5 when release liner 18 is removed, lead wire 14 may be inserted in its place and is secured between protective insulative web 12 by pressure sensitive adhesive 16 and conductive adhesive 24. 
     The biomedical electrode 10D as illustrated in FIG. 6 is constructed similarly to the embodiment of biomedical electrode 10C illustrated in FIG. 5 with the exception being that protective insulative web 12, pressure sensitive adhesive 16 and release liner 18 extend beyond an edge of conductive adhesive 24 (as in FIG. 3) to facilitate lifting of protective insulative web 12 and removal of release liner 18. 
     Although biomedical electrode 10 has been illustrated as being in generally rectangular shaped it is to recognized and understood that any suitable shape, size or configuration of biomedical electrode 10 may be utilized to fit or suit the particular environment or body part to which it is adapted to be applied. 
     Thus, it can be seen that there has been shown and described a novel, flat, conformable, biomedical electrode. It is to be recognized and understood, however, that various changes, modifications and substitutions in the form and of the details of the present invention can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims.