Method of making a stimulator electrode with a conductive polymer coating

• US 6,718,628 B2
• Filed: 02/26/2001
• Issued: 04/13/2004
• Est. Priority Date: 03/13/1998
• Status: Expired due to Term

• Current Assignee: Intermedics Incorporated
• Original Assignee: Intermedics Incorporated
• Inventors: Munshi, M. Zafar Amin
• Primary Examiner(s): Arbes, Carl J.
• Application Number:
  US09/793,000
• Publication Number:
  US 20010037134A1
• Time in Patent Office: 1,142 Days
• Field of Search: 298/25, 298/82, 298/83
• US Class Current: 29/825
• CPC Class Codes: A61N 1/375 Constructional arrangements, e.g. casings
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing
• CPC Class Codes: Y10T 29/49218 with deforming
• CPC Class Codes: Y10T 29/4922 with molding of insulation

Abstract

A method of making a stimulator electrode with a conductive polymer coating is disclosed. A polymeric coating, such as polyethylene oxide containing NaCl or a similar ionic medium, coats and fills the pores of a high surface area electrode to provide a continuous ionic network from the can to the adjacent body tissue. In certain embodiments, the underlying high surface area, porous electrode is made by chemically etching a smooth electrode surface, such as that of a conventional titanium housing, followed by applying a thin coating of a noble metal such as platinum. In other embodiments, a noble metal or an oxide thereof, such as platinum black or iridium oxide, is applied to a titanium housing to form a porous, high surface area electrode. The conductive polymeric coating is then applied over the porous noble metal or metal oxide. The electrically conductive polymeric material is biocompatible, chemically and mechanically stable and does not dissolve or leach out over the useful lifetime of the defibrillator. A hot can defibrillator employing the new polymeric coating avoids development of high polarization at the can/tissue interface and maintains a more uniform defibrillation threshold than conventional implantable defibrillators, thus increasing the feasibility of pectoral implantation, particularly in a “dry pocket” environment.

Claims

1. A method of making an implantable electrode comprising:

forming a rough or porous surface on a conductive substrate; and

impregnating and coating the conductive substrate with an ionically conductive biocompatible polymer coating capable of reversible reduction-oxidation, the polymer coating forming a smooth outer surface on the electrode.

2. The method of claim 1 wherein forming a rough or porous surface comprises applying a surface treatment on the conductive substrate.

3. The method of claim 2 wherein applying a surface treatment comprises etching.

4. The method of claim 3 wherein the conductive substrate is titanium and etching comprises:

applying oxalic acid to the titanium surface for 1 to 2 hours, the oxalic acid having a temperature of 80 degrees C.

5. The method of claim 3 wherein etching comprises etching to a depth of 5 to 10 microns.

6. The method of claim 3 wherein the conductive substrate is titanium and etching comprises:

applying a 10% oxalic acid solution to the substrate surface for about 1 hour, the oxalic acid having a temperature of 80 degrees C. creating an etched surface;

washing the etched surface;

ultrasonicating the etched surface in deionized water;

neutralizing the etched surface from the acid with a 5% sodium bicarbonate solution; and

washing the etched surface in deionized water.

7. The method of claim 2 wherein the conductive substrate comprises titanium.

8. The method of claim 7 wherein applying a surface treatment comprises applying a roughened or porous conductive metal or metal oxide layer over the conductive substrate.

9. The method of claim 8 wherein applying a roughened or porous electrically conductive metal or metal oxide layer comprises depositing a coating of metal or metal oxide by ion beam deposition, sputtering, evaporation, plasma spraying, or chemical methods.

10. The method of claim 8 wherein the metal or metal oxide layer is selected from the group consisting of platinum black, and oxides of platinum, ruthenium, rhodium, palladium, osmium, and iridium.

11. The method of claim 8 wherein the conductive metal comprises porous platinum.

12. The method of claim 11 wherein depositing porous platinum comprises:

depositing a layer of one or more species of platinum precursors onto the substrate; and

heating the layer of one or more species of platinum precursors at elevated temperature sufficient to form a platinum black coating.

13. The method of claim 12 wherein the one or more species of platinum precursors comprises H₂PtCl₆.

14. The method of claim 8 wherein the conductive metal oxide layer comprises iridium oxide.

15. The method of claim 14 wherein applying the iridium oxide layer comprises:

etching the surface of the substrate; and

applying iridium oxide by a method comprising physical vapor deposition or plasma spray.

16. The method of claim 14 wherein applying the iridium oxide layer comprises:

etching the surface of the substrate;

applying iridium by chemical vapor deposition; and

heating the iridium coated substrate at about 350 degrees C.

17. The method of claim 1 further comprising:

applying a metal coating on the rough or porous surface, the metal coating adapted to substantially conform to the rough or porous surface while substantially retaining the rough surface characteristics.

18. The method of claim 17 wherein the substrate comprises titanium.

19. The method of claim 18 wherein the metal coating comprises a noble metal or oxides thereof.

20. The method of claim 18 wherein applying a roughened or porous electrically conductive metal or metal oxide layer comprises applying platinum to a thickness of 0.1 F.

21. The method of claim 19 wherein the metal coating is selected from the group consisting of platinum, ruthenium, rhodium, palladium, osmium, iridium and alloys thereof.

22. The method of claim 1 wherein the ionically conductive biocompatible polymer comprises an electrically conductive ionic species.

23. The method of claim 1 wherein the ionically conductive biocompatible polymer further comprises antithrombotic, anticoagulant, anti-infection or thrombolytic agents, or a combination thereof.

24. The method of claim 1 wherein the ionically conductive biocompatible polymer further comprises plasticizer salts.

25. The method of claim 1 wherein impregnating and coating the rough or porous surface with an ionically conductive biocompatible polymer comprises:

soaking the surface in a solution comprising;

a biocompatible polymer;

a biocompatible ionic carrier; and

a solvent; and

evaporating the solvent from the surface to form a smooth polymeric outer surface of the electrode.

26. The method of claim 25 wherein the polymer is selected from the group consisting of polyethylene oxide, polyethylene terpthalate, hydrogels and polyacrylates.

27. The method of claim 1 wherein impregnating and coating the rough surface comprises:

soaking the rough surface in a solution comprising 5-10% polyethylene oxide and 1-2% NaCl and alcohol; and

evaporating the solution.

28. The method of claim 1 wherein impregnating and coating the rough or porous surface further comprises removing entrapped gas from the rough or porous surface.

29. The method of claim 25 wherein soaking comprises ultrasonicating the rough or porous surface in the solution.

30. The method of claim 1 wherein the impregnating and coating the rough or porous surface with a conductive polymer comprises:

soaking the rough surface for 5 to 10 minutes with an electroconductive polymeric solution comprising 5-10% solution of polyethylene oxide and 1-2% NaCl prepared in 50;

50 alcohol;

water, the polyethylene oxide having a molecular weight from about 100 kd to about 5,000 kd, the soaking conducted under reduced atmosphere sufficient to remove entrapped gas from the rough surface; and

evaporating the alcohol and water.

31. The method of claim 1 wherein the impregnating and coating the rough or porous surface with a conductive polymer comprises:

ultrasonicating the rough surface for 5 to 10 minutes with an electroconductive polymeric solution comprising 5-10% solution of polyethylene oxide and 1-2% NaCl prepared in 50;

50 alcohol;

water, the polyethylene oxide having a molecular weight from about 100 kd to about 5,000 kd; and

evaporating the alcohol and water.

32. The method of claim 1 wherein the polymer coating further comprises an inorganic filler.

33. The method of claim 32 wherein the inorganic filler is selected from the group consisting of high surface area alumina and high surface area silica.

34. The method of claim 1 wherein impregnating and coating the rough or porous surface comprises:

soaking the rough surface with a precursor polymer solution; and

curing the solution by radiation, heat or chemical means, or a combination thereof.

35. The method of claim 1 wherein the method further comprises:

coating the substrate with an insulating, non-conductive material such that at least a portion of the substrate is not covered by the insulating, non-conductive material.

36. The method of claim 35 wherein the insulating, non-conductive material comprises parylene.

37. The method of claim 1 wherein the conductive substrate is adapted for use as an implantable cardiac stimulus electrode.

38. The method of claim 1 wherein the conductive substrate is adapted for use as an implantable cardiac stimulator housing, at least a portion of which comprises an electrode.

39. The method of claim 38 wherein adapting the conductive substrate to form at least a portion of a stimulator housing comprises adapting the conductive substrate to enclose at least a portion of an assembly of stimulator components.

40. The method of claim 1 wherein the conductive substrate is adapted for use as an implantable cardiac stimulator hot can, the hot can comprising a housing, at least a portion of which adapted to be an electrode.

41. The method of claim 1 wherein said electrode comprises a defibrillating electrode.

42. The method of claim 1 wherein said electrode comprises a stimulus electrode.

43. The method of claim 1 wherein said electrode comprises a cardiac stimulator hot can electrode.

44. The method of claim 1 wherein the conductive substrate conforms to at least a portion of an enclosure.

45. The method of claim 1 wherein the conductive substrate is an enclosure adapted to house a stimulus generator.

46. A method of making an implantable electrode comprising:

forming a titanium substrate adapted for use as an implantable cardiac stimulator hot can, the hot can comprising a housing having an exterior surface, at least a portion of which adapted to be an electrode;

applying a surface treatment to the exterior surface forming a rough or porous surface, the surface treatment comprising;

applying a 10% oxalic acid solution to the exterior surface for about 1 hour, the oxalic acid having a temperature of 80 degrees C. creating an etched surface;

washing the etched surface;

ultrasonicating the etched surface in deionized water;

neutralizing the etched surface from the acid with a 5% sodium bicarbonate solution; and

washing the etched surface in deionized water;

applying a metal coating on the rough surface, the metal coating adapted to substantially conform to the rough surface while substantially retaining the rough surface characteristics, the metal coating selected from the group consisting of platinum, ruthenium, rhodium, palladium, osmium, iridium and alloys thereof;

impregnating and coating the rough surface with an ionically conductive biocompatible polymer coating capable of reversible reduction-oxidation, the polymer coating forming a smooth outer surface of the electrode, the impregnating and coating comprising;

soaking the rough surface for 5 to 10 minutes with an electroconductive polymeric solution comprising 5-10% solution of polyethylene oxide and 1-2% NaCl prepared in 50;

50 alcohol;

water, the solution further comprising a high surface area alumina filler, the polyethylene oxide having a molecular weight from about 100 kd to about 5,000 kd, the soaking conducted under reduced atmosphere sufficient to remove entrapped gas from the rough surface; and

evaporating the alcohol and water; and

coating the substrate with parylene such that at least a portion of the substrate is not covered with parylene, wherein the uncovered portion comprises said electrode.

47. A method of making an implantable electrode comprising:

forming a titanium substrate adapted for use as an implantable cardiac stimulator hot can, the hot can comprising a housing having an exterior surface, at least a portion of which adapted to be an electrode;

depositing porous platinum to the exterior surface forming a rough or porous surface, the depositing comprising;

depositing a layer of one or more species of platinum precursors onto

the exterior surface by dipping the exterior surface into a solution of platinum precursors, the one or more species of platinum precursors comprising H₂PtCl₆; and

heating the layer of one or more species of platinum precursors at elevated temperature sufficient to form a platinum black coating;

impregnating and coating the rough or porous surface with an ionically conductive biocompatible polymer coating capable of reversible reduction-oxidation, the polymer coating forming a smooth outer surface of the electrode, the impregnating and coating comprising;

soaking and ultrasonicating the rough surface for 5 to 10 minutes with an

electroconductive polymeric solution comprising 5-10% solution of polyethylene oxide and 1-2% NaCl prepared in 50;

50 alcohol;

water, the polyethylene oxide having a molecular weight from about 100 kd to about 5,000 kd; and

evaporating the alcohol and water; and

coating the substrate with an insulating, non-conductive material such that at least a portion of the substrate is not covered with the insulating, non-conductive material, wherein the uncovered portion comprises said electrode.