Conductive hydrogels and physiological electrodes and electrode assemblies therefrom

• US 5,622,168 A
• Filed: 03/03/1995
• Issued: 04/22/1997
• Est. Priority Date: 11/18/1992
• Status: Expired due to Fees

• Current Assignee: John L. Essmyer
• Original Assignee: John L. Essmyer
• Inventors: Keusch, Preston, Essmyer, John L.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US08/400,273
• Time in Patent Office: 781 Days
• Field of Search: 128/635-641, 128/644, 607/145, 607/152, 607/153, 252/500
• US Class Current: 600/391
• CPC Class Codes: A61B 5/266 containing electrolytes, conductive gels or pastes
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/398 Electrooculography [EOG], e.g. detecting nystagmus; Electroretinography [ERG]
• CPC Class Codes: A61N 1/0551 Spinal or peripheral nerve electrodes

Abstract

A highly conductive hydrophilic gel comprising a uniform aqueous solution of a crosslinked water-soluble polymer, an amount of a water-soluble electrolyte effective to reduce the transverse electrical resistance of said aqueous mixture to an impedance at 60 Hz less than about 1,000 ohm, which hydrophilic gel also contains a humectant in an amount effective to retard the drying of the conductive hydrophilic gel when it is exposed to the atmosphere while being used. A physiological electrode adapted for providing electrical contact with a surface of a sentient creature and comprising a sheet of the conductive viscoelastic hydrophilic gel.

Claims

1. A highly conductive hydrophilic gel composition comprising (a) a uniform aqueous solution of a water-soluble polymer crosslinked by high-energy irradiation in the essential absence of a humectant and an amount of a water-soluble electrolyte effective to reduce the transverse electrical resistance of said aqueous solution to an impedance at 60 Hz less than about 1,000 ohm, and (b) a humectant added to the aqueous solution after the water-soluble polymer is crosslinked, in an amount within the concentration of about 2 to about 15 wt % which is effective to retard the drying of the conductive hydrophilic gel composition when it is exposed to the atmosphere while being used.

2. The hydrophilic gel of claim 1 in which the water-soluble polymer is selected from the group consisting of poly(ethylene oxide), poly(vinyl pyrrolidone), polyacrylamide, and mixtures, blends and copolymers thereof.

3. The hydrophilic gel of claim 1 in which the gel is comprised of poly(ethylene oxide) in an amount of about 3 to about 35%.

4. The hydrophilic gel of claim 1 in which the gel is adhesive and is comprised of poly(ethylene oxide) in an amount of about 6 to about 18%.

5. The hydrophilic gel of claim 1 in which the gel is adhesive and is comprised of poly(ethylene oxide) in an amount of about 6 to about 12%.

6. The hydrophilic gel of claim 1, wherein the water-soluble polymer is a linear poly(ethylene oxide) having a molecular weight of about 0.2×

10⁶ Dalton to about 10×

10⁶ Dalton.

7. The hydrophilic gel of claim 1, wherein the water-soluble polymer is a linear poly(ethylene oxide) having a molecular weight of about 2×

10⁶ Dalton to about 6×

10⁶ Dalton.

8. The hydrophilic gel of claim 1, wherein the water-soluble polymer is a linear poly(ethylene oxide) having a molecular weight of about 0.8×

10⁶ Dalton to about 1.2×

10⁶ Dalton.

9. The hydrophilic gel of claim 1, wherein the gel is formed from a linear poly(ethylene oxide) that is crosslinked by a dose of high energy irradiation of from about 5 to about 20 KGy.

10. The hydrophilic gel of claim 1, wherein the water soluble polymer is poly(vinyl pyrrolidone) having a molecular weight of about 0.2×

10⁶ Dalton to about 4×

10⁶ Dalton.

11. The hydrophilic gel of claim 1, wherein the water soluble polymer is poly(vinyl pyrrolidone) having a molecular weight of about 0.6×

10⁶ Dalton to about 2×

10⁶ Dalton.

12. The hydrophilic gel of claim 1 in which the gel is comprised of poly(vinyl pyrrolidone) in an amount of about 8 to about 35%.

13. The hydrophilic gel of claim 1 in which the gel is comprised of poly(vinyl pyrrolidone) in an amount of about 12 to about 25%.

14. The hydrophilic gel of claim 1 in which the gel is comprised of poly(vinyl pyrrolidone) in an amount of about 15 to about 20%.

15. The hydrophilic gel of claim 1, wherein the gel is formed from a poly(vinyl pyrrolidone) that is crosslinked by a dose of high energy irradiation of from about 5 KGy to about 40 KGy.

16. The hydrophilic gel of claim 1, wherein the gel is formed from a poly(vinyl pyrrolidone) that is crosslinked by a dose of high energy irradiation of from about 5 KGy to about 50 KGy.

17. The hydrophilic gel of claim 1 in which said water-soluble electrolyte is an inorganic salt.

18. The hydrophilic gel of claim 1 in which said water-soluble electrolyte is present in the gel in an amount sufficient to reduce the transverse electrical resistance of said aqueous solution to an impedance at 60 Hz less than about 1,000 ohms and yet not sufficient to adversely affect the gel.

19. The hydrophilic gel of claim 1 in which said water-soluble electrolyte is selected from the group consisting of potassium salts, sodium salts, magnesium salts, calcium salts, and mixtures thereof.

20. The hydrophilic gel of claim 1 in which said water-soluble electrolyte is selected from the group consisting of potassium chloride, sodium chloride, magnesium sulfate, magnesium acetate, and mixtures thereof.

21. An electrode according to claim 1, wherein the electrolyte is a water soluble salt present in a concentration of about 0.1 to about 15 wt %.

22. An electrode according to claim 1, wherein the electrolyte is potassium chloride or sodium chloride in a concentration of about 0.1 to about 15 wt %.

23. The hydrophilic gel of claim 1 in which said transverse electrical impedance of said aqueous solution is reduced to an impedance at frequencies between about 10 to about 60 Hz of less than about 100 ohms.

24. The hydrophilic gel of claim 1 in which said humectant is glycerol, sorbitol, poly(ethylene glycol), propylene glycol, or poly(propylene glycol).

25. The hydrophilic gel of claim 1 in which the humectant is a mixture of glycerol and one or more of the poly(ethylene glycols) or propylene glycol.

26. The hydrophilic gel of claim 1 in which as the humectant glycerol or poly(ethylene glycol) is present in the gel at a total concentration of from about 2 to about 15%.

27. The hydrophilic gel of claim 1 in which as the humectant glycerol or poly(ethylene glycol) is present in the gel at a total concentration of from about 7 to about 13%.

28. The hydrophilic gel of claim 1 which further comprises an additive uniformly dispersed therein.

29. The hydrophilic gel of claim 1 which further comprises an additive uniformly dispersed therein selected from the group consisting of preservatives, stabilizers, fire retardants, pigments, refractive particles, bactericides, antibiotics, cosmetics, moisturizers, pharmaceuticals, and mixtures thereof.

30. The hydrophilic gel of claim 1 which further comprises a biocide uniformly dispersed therein.

31. The hydrophilic gel of claim 1 which further comprises a low area-weight scrim in intimate contact therewith.

32. The hydrophilic gel of claim 1 which further comprises a low area-weight scrim which is manufactured from a synthetic water-insoluble polymer in initmate contact with the hydrophilic gel.

33. A physiological electrode adapted for providing electrical contact with a surface of a sentient creature and comprising:

a. means for interfacing with a surface of a sentient creature comprising a sheet of a conductive viscoelastic hydrophilic gel composition, wherein the hydrophilic gel composition is a homogeneous aqueous mixture, substantially free of unbound water, monomers and cross-linking agents, the hydrophilic gel composition comprising;

i. A uniform aqueous solution of a water-soluble polymer cross-linked by high energy irradiation in the essential absence of a humectant,

ii. a water-soluble electrolyte in an amount sufficient to reduce the transverse electrical impedance of said aqueous solution to an impedance at 60 Hz of less than about 1000 ohm,

iii. a humectant added to the hydrophilic gel composition after it is crosslinked, in an amount within a concentration of about 2 to about 15 wt %, which is sufficient to retard the drying of the conductive hydrophilic gel composition, to keep it soft and pliable when it is exposed to the atmosphere or being used, and

b. a conductive member including means for connecting the physiological electrode to an external electrical apparatus;

said means for interfacing with a surface of a sentient creature (a) connected electrically with the conductive member (b) and having a face adapted for interfacing electrically with the surface of the sentient creature to which it is affixed, which gel sheet is more cohesive than it is adhesive to the surface of the sentient creature and is mechanically connected more firmly to the conductive member (b) than it can be adhesively affixed to the surface of the sentient creature, thereby enabling concurrent removal of the conductive member (b) and the means for interfacing with a surface of a sentient creature (a) from the surface of the sentient creature after use without leaving a noticeable polymeric residue on the surface of the sentient creature.

34. An electrode according to claim 33, wherein the water-soluble polymer is poly(ethylene oxide), poly(vinyl pyrrolidone), or polyacrylamide.

35. An electrode according to claim 33, wherein poly(ethylene oxide) is the water-soluble polymer in the hydrophilic gel composition and is present in a concentration of about 3 to about 25 wt %.

36. An electrode according to claim 33, wherein poly(ethylene oxide) is the water-soluble polymer in the hydrophilic gel composition and is present in a concentration of about 6 to about 12 wt %.

37. An electrode according to claim 33, wherein linear poly(ethylene oxide) is the water-soluble polymer and has a molecular weight of about 0.2×

10⁶ to about 10×

10⁶ Daltons.

38. An electrode according to claim 33, wherein the electrolyte is a water soluble salt present in a concentration of about 0.1 to about 15 wt %.

39. An electrode according to claim 33, wherein the electrolyte is selected from the group consisting of potassium salts, sodium salts, magnesium salts, calcium salts, and mixtures thereof.

40. An electrode according to claim 33, wherein the electrolyte is potassium chloride, sodium chloride or magnesium acetate in a concentration of about 0.1 to about 15 wt %.

41. An electrode according to claim 33, wherein the humectant is glycerol, sorbitol, poly(ethylene glycol), propylene glycol, or poly(propylene glycol).

42. An electrode according to claim 33, wherein glycerol is present in the hydrophilic gel composition in a concentration of about 2 to about 20 wt %.

43. An electrode according to claim 33, wherein glycerol is present in the hydrophilic gel composition in a concentration of about 7 to about 13 wt %.

44. An electrode according to claim 33, wherein a conductive ink coating is on the gel sheet face opposite that face to be applied to the skin.

45. An electrode according to claim 33, wherein a low area-weight scrim is immersed in the hydrophilic gel composition.

46. An electrode according to claim 33, wherein a low area-weight scrim comprised of a sheet of non-woven polyethylene is immersed in the hydrophilic gel composition.

47. An electrode according to claim 33, wherein a conductive scrim is immersed in the hydrophilic gel composition.

48. An electrode according to claim 33, wherein immersed in the hydrophilic gel composition is a metallic scrim or a metallized polymeric scrim which does not undesirably corrode in the use intended for the electrode.

49. An electrode according to claim 33, wherein immersed in the hydrophilic gel composition is a nylon scrim plated with a noble metal.

50. An electrode according to claim 33, wherein immersed in the hydrophilic gel composition is a gold-plated nylon scrim.

51. An electrode according to claim 33, wherein the face of the interfacing means (b) adapted for interfacing with a human'"'"'s skin is covered by a protective backing sheet which is peelably removable therefrom.

52. An electrode according to claim 33, wherein a low area-weight scrim is immersed in the hydrophilic gel composition;

wherein the electrolyte is a water-soluble salt present in a concentration of about 0.1 to about 15 wt %;

wherein the water-soluble polymer is linear poly(ethylene oxide) that has a molecular weight of about 0.5 to about 5×

10⁶ Daltons and is present in the hydrophilic gel composition at a concentration of about 4 to about 25%;

wherein glycerol is present in the hydrophilic gel composition in a concentration of about 2 to about 10%; and

wherein the face of the sheet adapted for interfacing with the sentient creature'"'"'s skin is covered by a backing sheet which is peelably removable therefrom.

53. An electrode according to claim 33, wherein the water-soluble polymer is linear poly(ethylene oxide), has a molecular weight of about 0.5 to 5×

10⁶ Daltons and is present in the hydrophilic gel composition at a concentration of about to about 25 w %;

wherein as the electrolyte potassium chloride or sodium chloride is present in the hydrophilic gel composition in a concentration of about 0.1 to about 10 w %;

wherein glycerol is present in the hydrophilic gel composition in a concentration of about 2 to about 10 w %;

wherein a low area-weight scrim formed of a sheet of non-woven polyethylene is immersed in the hydrophilic gel composition; and

wherein the face of the sheet that is adapted for interfacing with a human'"'"'s skin is covered by a release sheet which is peelably removable therefrom.

54. An array of electrodes as claimed in claim 33, wherein the electrodes are spatially and removably arranged in a desired configuration on a flexible polymeric substrate adapted to be placed conformably on the surface of a sentient creature so that the electrodes are in contact with the desired areas of the surface of the sentient creature.

55. An array of electrodes according to claim 33, wherein the individual electrodes are layered for shielding and signal transmission.

56. A modular band comprised of a sensor module and a substrate module, the sensor module being comprised of an array of conductive hydrogel electrodes as claimed in claim 33, spatially arranged on the sensor module so that the electrodes are adapted to make contact with specific sensing spots on a sentient being, an electrical connector being attached to each electrode, the substrate module being adapted to maintain the sensor module in the desired contact with the sentient being.

57. A modular headband comprised of a sensor module and a substrate module, the sensor module being comprised of an array of conductive hydrogel electrodes as claimed in claim 33, spatially arranged on the sensor module so that the electrodes are adapted to make contact with specific sensing spots on the forehead of a mammal in the case of most of the electrodes and with specific areas on at least one cheek in the case of at least one electrode, an electrical connector being attached to each electrode, the substrate module being adapted to maintain the sensor module in the desired contact with a mammal.