WO1996039930A1

WO1996039930A1 - Biomedical electrode having backing with integral connecting stud

Info

Publication number: WO1996039930A1
Application number: PCT/US1996/005838
Authority: WO
Inventors: Mandel L. Desnick; Leon D. Blankenfield
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1995-06-07
Filing date: 1996-04-26
Publication date: 1996-12-19

Abstract

A biomedical electrode (10) of the type configured to be positioned on the skin of a patient to provide an electrical interface between the patient and a medical instrument. The electrode includes a backing member (12), a silver/silver chloride conductive layer (20) overlaying the backing (12) and a layer of conductive adhesive (22) overlaying the conductive layer (20). The backing (12) is formed from a sheet of conductive polymer and includes an integral snap-type connector stud (14) molded therein.

Description

BIOMEDICAL ELECTRODE HAVING BACKING WITH INTEGRAL

CONNECTING STUD

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to medical electrodes. Description of the Related Art

Medical electrodes are well known and in widespread use. Electrodes of this type are, for example, disclosed generally in the following United States Patents:

Inventor Patent No.

Novello 4,282,878

Cartmel et al. 4,685,467

Takata 4,787,390 Electrodes of the type disclosed in the above-identified patents typically have a backing member, a layer of conductive material overlaying one side of the backing member, and electrolyte gel or conductive adhesive overlaying the conductive material layer. An electrical connector stud in contact with the layer of conductive material extends through the backing member and is configured for electrical interconnection to an instrument lead wire connector. Metallic and conductive polymer studs configured for use with mating snap-type eyelet connectors are especially common. Unfortunately, electrodes including connector studs of these types are relatively inefficient to manufacture.

There remains a continuing need for improved medical electrodes. In particular, there is a need for electrodes that can be efficiently manufactured. The connecting stud on any such electrode must be capable of reliably maintaining a high-quality electrical and physical contact to the mating lead wire connector with which it is used. An electrode having these characteristics which is also translucent to x-rays would be particularly desirable. SUMMARY OF THE INVENTION

The present invention is an efficient-to-manufacture electrode of the type configured to be positioned on the skin of a patient to provide an electrical interface between the patient and a medical instrument. One embodiment of the electrode includes a backing member formed from a layer or sheet of conductive polymer material, and a connector stud configured for electrical interconnection to a medical instrument integrally formed in and extending from the sheet of conductive material. The connector stud provides a high-quality electrical and physical contact to mating lead wire connectors with which it is used.

Another embodiment of the electrode includes a silver/silver chloride conductive layer overlaying the side of the backing member opposite the stud and a layer of conductive adhesive overlaying the conductive layer. The connector stud can be molded from a laminated web of material including the conductive polymer, conductive material and conductive adhesive layers. The stud is molded by preheating a central strip of the web, continuously indexing the web to a stud forming position in a die, and forcing a mandrel into engagement with the web at the forming position. BRD5F DESCRIPTION OF THE DRAWINGS

Figure 1 is a top view of a first embodiment of a medical electrode which includes a conductive polymer backing member having an integral connector stud in accordance with the present invention.

Figure 2 is a sectional view of the electrode shown in Figure 1 taken along lines 2—2, with a lead wire snap connector configured to mate with the connector stud shown in phantom.

Figure 3 is a sectional view of a laminated web of material from which the electrode shown in Figure 1 can be fabricated.

Figure 4 is a cross-sectional view of the web shown in figure 3 being advanced through a pair of dies to form the connector stud of the electrode shown in Figure 1 in accordance with a first manufacturing method embodiment of the present invention.

Figures 5a-5d are cross-sectional views of the web shown in Figure 3 being advanced through a die to form the connector stud of the electrode shown in Figure 1 in accordance with a second manufacturing method embodiment of the present invention. Figure 6 is a top view of a second embodiment of an electrode in accordance with the present invention.

Figure 7 is a cross-sectional view of the electrode shown in Figure 6 taken along lines 7—7. Figure 8 is a cross-sectional view of a third embodiment of an electrode in accordance with the present invention.

Figure 9 is a detailed cross-sectional view of the connector stud of the electrode shown in Figure 8.

Figure 10 is an illustration of a die which can be used to fabricate the electrode shown in Figures 8-9 from the web of material shown in Figure 3.

DETAILED DESCRD7TION OF THE PREFERRED EMBODIMENT A biomedical electrode 10 in accordance with the present invention is illustrated generally in Figures 1 and 2. As shown, electrode 10 includes a backing member 12 having an integral connector stud 14 extending from one side thereof, a layer 20 of conductive material overlaying the surface of the backing member opposite stud 14, and a layer 22 of conductive adhesive or other electrolyte overlaying the layer of conductive material. A release liner 23 is positioned over the layer 22 to protect the layer prior to use of the electrode. Backing member 12 is a sheet 13 of conductive plastic or other polymer. As described in greater detail below, stud 14 is molded into sheet 13 in such a manner as to provide an undercut 16 to enable eyelet-type snap connectors such as 18 (shown in phantom in Figure 2) to be securely yet releasably fastened to a stud for a high-quality electrical and physical connection. Conductive material layer 20 can be a silver/silver chloride layer adhered to backing 13 by plating, printing or vapor deposition techniques. Vapor deposition techniques such as those disclosed in U.S. Patent 5,506,059 can be used for this purpose.

A laminated web 24 which can be used to fabricate electrode 10 is illustrated generally in Figure 3. In the embodiment shown, web 24 includes conductive polymer sheet 13 which functions as backing member 12, silver/silver chloride layer 20 and conductive adhesive layer 22. In other embodiments (not shown) the web includes only the sheet 13 and layer 20, with the conductive adhesive 22 being applied following the formation of stud 14.

A set of dies 26 and 40 which can be used to form stud 14 in laminated web 24 during the fabrication of electrode 10 is illustrated in Figure 4. Die 40 is a performing die which includes upper die member 42 and lower die member 46. A recess 44 in the upper die member 42 has sloping side walls which are flat in cross- section. A dome-shaped projection 48 extends from lower die member 46 into recess 44. Upper die member 42 can be cooled in a conventional manner by fluid from coolant source 43. Similarly, lower die member 46 can be heated in a conventional manner by heat source 45.

Die 40 is used to preform a raised dimple in web 24 at the location of stud 14 prior to final stud forming by die 26. During this preforming step, the web 24 is indexed into die 40 when die members 42 and 46 are open. Die members 42 and 46 are then closed, with the projection 48 drawing an adjacent portion of web 24 into recess 44. The raised dimple is thereby formed in web 24, with the concave surface of the dimple taking the shape of projection 48. Following this preforming step, die members 42 and 46 are opened and the web is indexed to position the dimple within die 26.

Die 26 includes upper die member 28 and lower die member 32. Upper die member 28 has a stud-forming recess or cavity 30 having a shape corresponding to the desired shape of the outer surface of connector stud 14. Lower die member 32 includes a bore 34 which is axially aligned with cavity 30 in upper die member 28. A mandrel 36 is reciprocally driven within bore 34 by piston 38. The tip portion of mandrel 36 which extends into cavity 30 is formed from resilient deformable material. As shown, upper die member 28 can be cooled in a conventional manner with coolant from source 43. Similarly, lower die member 32 can be heated in a conventional manner by heat source 45. Circular sealing rims 33 on lower die 32 and upper die 28 can be included to control material flow during the deformation step described above and to provide a seal for pressurized gas during the forming process as described below. The final deforming step begins with die members 28 and 32 open and mandrel 36 retracted within bore 34. Web 24 is then advanced between die members 28 and 32 to position the preformed dimple below recess 30, and the members closed to clamp web 24 therebetween. Piston 38 is then advanced to force mandrel 36 into cavity 30. A portion of the web 24 adjacent mandrel 36, including the preformed dimple, is thereby drawn into cavity 30. Since the mandrel 36 is formed from resilient deformable material, the mandrel will expand under the force of piston 38 and draw web 34 into the shape of cavity 30. Stud 14 having undercut 16 is thereby formed in the web 24. As described below, air or other gas pressure can be used in place of the deformable tip of mandrel 36.

Piston 38 is retracted to withdraw mandrel 36 from the formed stud 14 in cavity 30. If the material from which web 24 is formed is sufficiently flexible and resilient, die members 28 and 32 can be opened to expose formed stud 14. Alternatively, upper die member 28 can be formed from two members which are separable along a parting line 31 which is generally parallel to the axis of bore 34. The sections of die member 28 can then be separated to remove the formed stud 14 from die 26.

As shown in Figure 4, a heating chamber 47 can also be used to preheat the web 24 before the web is formed by dies 40 and/or 26. In one embodiment, heating chamber 47 heats a centrally elongated strip of web 44, while leaving the outer edges of the web relatively unheated or at ambient temperature. Preheating the central portion of web 24 facilitates the formation of stud 14. Since the outer edges of web 24 remain at ambient temperature, they provide support for the heated central section of the web as the web is indexed through the dies 40 and/or 26. Conventional electrode manufacturing procedures can be used to complete electrodes 10 following the formation of studs 14 in web 24. By way of example, other components such as the release liner 23 and conductive adhesive layer 22 (in those embodiments in which the stud is formed in a web not having the conductive adhesive layer) can be added to the web. Individual electrodes 10 are then cut from the web and packaged for distribution. A die 26' which can be used to form connector studs 14 in web 24 in accordance with a second manufacturing method of embodiment of the present invention is illustrated in Figures 5a-5d. Die 26' is similar to die 26 described above with reference to Figure 4, and features of die 26' which are structurally and/or functionally the same as corresponding features on die 26 are indicated by identical but primed (i.e., "x"') reference numerals.

Die 26' includes a passage 102 which extends through upper die member 28' and communicates with cavity 30'. Pressurized air from source 100 is provided to cavity 30' through passage 102, and is used during the formation of studs 14 in the manner described below. Lower member 32' includes a circular sealing ring 33', and a recess 104 on the upper surface of the die member within the sealing ring. Piston 38' and mandrel 36' include a passage 106 which communicates with the free end of the mandrel. Like passage 102, passage 106 is coupled to a source of pressurized air which is used during the fabrication of studs 14. Although not shown in Figures 5a-5d, a coolant source 43 and heat source 45 such as those described above with reference to Figure 4 can be coupled to die members 28' and 32', respectively. The central strip of web 24 can also be preheated in a heating chamber 47 of the type described above with reference to Figure 4.

Die members 28' and 32' are shown closed in Figure 5a, with web 24 clamped therebetween. Pressurized air from source 100 is then provided to cavity 30' through passage 102 to force the portion of web 24 within ring 33' onto mandrel 36' and the surface of recess 104. The use of recess 104 enables a substantial surface area of the web 24 to be recruited for formation around mandrel 36', thereby providing a thicker wall on stud 14. After preforming the central portion of web 24 around the tip of mandrel

36', piston 38' is actuated to force mandrel 36' and web 24 into cavity 3. Deformation of the tip of mandrel 36' forces the web 24 to conform to the shape of cavity 30' in a manner described above with reference to mold 26. Pressurized air can also be forced from the tip of mandrel 36' through passage 106 to complete the formation of stud 14 as shown in Figure 5c. Following the formation of stud 14, die 26' is opened in a manner described above with reference to die 26 to remove web 24 and the integral stud 14.

Biomedical electrode 50, a second electrode embodiment of the present invention, is illustrated in Figures 6 and 7. Features of electrode 50 which can be structurally and/or functionally similar to corresponding features of electrode 10 are indicated by identical but primed (i.e., "x"') reference numerals in Figures 6 and 7. Electrode 50 is configured for use in applications such as cardiac monitoring which require a greater degree of adhesion to the patient's skin than can be provided by conductive adhesive layer 22'. Accordingly, electrode 50 includes an adhesive film layer 54 which overlays electrode backing 12' and has a border 52 which extends beyond the edges of the backing. An aperture 60 in adhesive layer 54 enables connector stud 14 to extend through the layer. The adhesive 56 on layer 54 secures the layer to backing member 12', while the adhesive on border 52 cooperates with the conductive adhesive layer 22' to securely fasten electrode 50 to the patient's skin. In the embodiment shown in Figure 6, layer 54 also includes a tab 58 which extends from border 52. Tab 58 does not have adhesive 56, and can therefore be grasped to facilitate removal of electrode 50 from its release liner 23'.

Electrode 200, a third electrode embodiment of the present invention, is illustrated in Figure 8. Electrode 200 includes a generally cylindrical connector stud 214 having vertical and straight side walls 216. Unlike electrode 10 described above with reference to Figures 1 and 2, the stud 214 of electrode 200 does not include an undercut 16. Electrode 200 can be otherwise identical to electrode 10 described above, and features of electrode 200 which are structurally and/or functionally identical to those of electrode 10 are shown in Figure 7 with identical but double primed (i.e., "x"") reference numerals.

As shown in Figure 9, the eyelet ring 220 of a snap-type connector such as that shown in Figure 2 will engage and deform side walls 216 of stud 214 when the connector is forced onto the stud. The deformation of stud 214 enables the connector to provide a high quality electrical and physical contact with stud 214. Edges 218 on the top of side walls 216 can be contoured to facilitate the attachment of eyelet ring 220 to the stud. The side walls 216 of stud 214 can be thinner than the top wall to enable the deformation by ring 220 while providing sufficient structural integrity to the stud.

Figures 10a- lOd illustrate a die 26" which can be used to mold connector studs 214 in a web 24 such as that described above with reference to Figure 3. Die 26" includes an upper die member 28" having a recess 230 with generally flat (in cross-section) and outwardly sloping side walls 232. Unlike recess 30' of die 26', recess 230 is larger than the desired external shape of the connecting studs 214 being formed therein. Mandrel 236 differs from mandrel 36' of die 26' in that it is fabricated from solid material. Other than these differences, die 26" can be similar to die 26' described above with reference to Figures 5a-5d, and features of die 26" which are structurally and/or functionally similar to corresponding features of die 26' are indicated by identical but double primed (i.e., "x"") reference numerals.

As shown in Figures 10a and 10b, the web 24 from which stud 214 is to be formed is indexed between die members 28" and 32", and the die members closed. Piston 38" and mandrel 236 are then extended to engage the portion of web 24 between ring 33", and to force the web into recess 230. Pressurized air is also forced into the recess through passage 106" in mandrel 236 (i.e., into the recess on the same side of the web as the mandrel) to force the web into engagement with the walls 232 of recess 230. As shown in Figure 10c, pressurized air is then forced into recess 230 through passage 102" (i.e., into the recess on the side of the web opposite the mandrel). Web 24 is thereby forced around the tip of mandrel 236 to form stud 214. Following the formation of stud 214, mandrel 236 is retracted and die 26" opened to release the web as shown in Figure lOd.

The conductive plastic sheet 13 can, for example, be a carbon loaded ABS, commercially available as RTP 687 from RTP Company of Winona, Minnesota, U.S.A. This material is translucent to x-rays. Alternatively, conductive polymers such as doped organic polymers with long-distance π-electron conjugation such as polyacetylene or polypyrrole may be suitable. A brief description of such materials can be found in Properties of Polymers, by D.W. VanKrevelan, Elsevier Co., 1990, pages 330-337. When an adhesive border is to be used, a number of different materials are suitable, so long as they have reasonable tensile strength and flexibility, and compatibility with the skin adhesive that is chosen. Polymer foams, including polyethylene foams, polyester and other non-wovens, and certain types of paper can all be used. Non-wovens made from melt blown polyurethane, which exhibit exceptional flexibility, stretch recovery, and breathability, and in particular, a melt blown polyurethane of the type disclosed in commonly assigned U.S. Patent

5,078,138 can be used.

Acrylic adhesives, particularly acrylate ester copolymer adhesives, can be used for adhesive 56 on layer 54. Materials of this type are described in U.S. Patent

2,973,826. Commercially available or otherwise known conductive adhesives can be used for layer 22. A conductive adhesive such as that disclosed in U.S. Patent

4,848,353 can also be used. Alternatively, the conductive adhesive disclosed in

U.S. Patent No. 4,848,353 can be modified and the following ingredients used:

Dry Weight Percent

Copolymer:

Acrylic Acid 10.00

N-vinyl pyrrolidone 10.00

Glycerine 50.88

Guar gum 0.12

Water 26.00

Sodium hydroxide 2.80

Irgacure 0.07

TEGBM .13

100.00

Alternatively, and particularly for monitoring applications, a sticky hydrogel of the type disclosed in U.S. Patent No. 5,489,624 may be used. Other conductive materials can be substituted for the silver/silver chloride described herein for layer 20. Die 26 can be made from an appropriate metal, such as tooling grade bronze commercially available as Ampco 940 from Ampco- Pittsburgh of Milwaukee, Wisconsin, U.S.A. The mandrel 36 used in the deforming step can be made from such a metal, or if a deformable mandrel is desired, a tough heat-resistant elastomer is preferred, such as polyvinylidene fluoride commercially available as Fluorel™ from the 3M Company of St. Paul, MN. Although the invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A biomedical electrode of the type configured to be positioned on the skin of a patient to provide an electrical interface between the patient and a medical instrument, the electrode including: a backing member formed from a sheet of conductive polymer material; and a connector stud configured for electrical interconnection to a medical instrument integrally formed in and extending from the sheet of conductive polymer material.

2. The electrode of claim 1 wherein the connector stud includes side walls having an undercut and is configured for interconnection to a snap-type eyelet connector.

3. The electrode of claim 1 wherein the connector stud is a generally cylindrical member including straight side walls.

4. The electrode of claim 1 and further including a layer of conductive material overlaying the backing member.

5. The electrode of claim 4 wherein the layer of conductive material includes a layer of silver/silver chloride.

6. The electrode of claim 5 and further including a layer of conductive adhesive overlaying the layer of silver/silver chloride.

7. The electrode of claim 4 and further including a layer of conductive adhesive overlaying the layer of conductive material.

8. The electrode of claim 1 and further including an adhesive border extending from and around the backing member.

9. The electrode of claim 1 and further including a sheet of adhesive overlaying the side of the backing member from which the stud extends, and extending beyond the backing member to form an adhesive border.

10. The electrode of claim 9 and further including an adhesiveless tab extending from the adhesive border.

11. A method for manufacturing a biomedical electrode of the type configured to be positioned on the skin of a patient to provide an electrical interface between the patient and a medical instrument, the method including: providing a sheet of conductive polymer; and deforming the sheet to form an integral connector stud extending from the sheet and configured for electrical interconnection to a medical instrument.

12. The method of claim 11 wherein deforming the sheet includes: providing first and second die members, the first die member including a stud-forming recess and the second die member including a mandrel-receiving bore; providing a mandrel in the bore of the second die member; clamping the sheet of conductive polymer between the first and second die members; and forcing the mandrel into engagement with the sheet of polymer and into the stud-forming recess.

13. The method of claim 12 and further including forcing pressurized gas into the stud-forming recess on the side of the sheet of polymer opposite the mandrel to form the sheet around the mandrel.

14. The method of claim 13 and further including forcing pressurized gas into the stud-forming recess on the same side of the sheet of polymer as the mandrel to form the sheet to the shape of the recess.

15. The method of claim 14 wherein : providing the first die member includes providing a first die member having a stud-shaped recess; and forcing pressurized gas into the recess includes forcing pressurized gas into the stud-forming recess on the same side of the sheet of polymer as the mandrel to form the stud to the shape of the recess.

16. The method of claim 12 wherein: providing the first die member includes providing a first die member having a stud-shaped recess; providing the mandrel includes providing a mandrel having a resilient tip; and forcing the mandrel into the recess includes forcing the mandrel into the recess to deform the mandrel to form the stud to the shape of the recess.

17. The method of claim 12 wherein: providing a mandrel includes providing a mandrel having a generally cylindrical tip; and the method further includes forcing pressurized gas into the stud-forming recess on the side of the sheet of polymer opposite the mandrel to form a generally cylindrically shaped stud around the mandrel.

18. The method of claim 12 and further including preheating the sheet of polymer before clamping the sheet between the die members.

19. The method of claim 18 wherein preheating the sheet of polymer includes preheating the center of the sheet, but not the sides of the sheet.

20. The method of claim 12 wherein: the sheet of polymer material is provided as a web; and the method further includes continuously indexing the web through the die following the formation of the studs.

21. The electrode of claim 1 wherein the backing member is formed from a sheet of x-ray transluscent material.

22. The electrode of claim 1 wherein the stud includes a top wall and side walls, and the side walls are thinner than the top wall.