Implantable electrode

1. An implantable electrode having an electrically conductive porous material comprising metal carbide, metal nitride, metal carbonitride, metal oxide or metal oxynitride and one or more coating layers on a surface of said material, said coating layer or at least one of said coating layers being for contact with body tissue when the electrode is implanted, and each said coating layer being an electrically conductive layer of polymer having a polypyrrole polymeric backbone or polythiophene polypyrrole substituted at the 1-position (N-atom) or the 3-position with a substituent —A-X or an allyl-terminated pendent group, or is a polythiophene substituted at the 3-position with a substituent —X, —A-X, or an allyl-terminated pendent group, wherein:

A is alkylene or alkenylene of 1-6 carbon atoms;

X is —COOH, —COO - , —COOR′, —CONH 2 , —CONHR′, —CON(R′) 2 , —COR′, —F, —Cl, —Br, —I, —CN, —NO 2 , —OH, —OR′, —SH, —SR′, —O-CO-R′, —NH 2 , —NHR′, —NH(R′) 2 , —N(R′) 3 + , —NH-CO-R′, —NH-CO-H, —NR′-CO-R′, —NR′-SO 2 H, —NR′-SO 2 R′, —SO 2 R′, —OSO 2 R′ or —OPO;

R′ is alkyl or alkenyl of 1-6 carbon atoms; and

the allyl-terminated pendent group comprises —O-CH 2 -CH=CH 2 , —S-CH 2 - CH=CH 2 , —S(=O)-CH 2 -CH=CH 2 , —Se-CH 2 -CH=CH 2 , or —Se(=O)-CH 2 -CH=CH 2 .

2. An implantable electrode according to claim 1 , wherein the at least one said coating layer is a polypyrrole derivative in the form of polypyrrole substituted at the 1-position (N-atom) and the 3-position.

3. An implantable electrode according to claim 1 , wherein the electrically conductive porous material comprises metal carbide, metal nitride or metal carbonitride.

4. An implantable electrode according to claim 3 , wherein the metal carbide, metal nitride or metal carbonitride is TiC, TiN, ZrC, ZrN, TaC, TaN or Ti(C,N).

5. An implantable tissue stimulator having an electrode according to claim 3 .

6. An implantable tissue stimulator according to claim 5 , having electrical power supply means and means for applying electrical stimulation pulses to the electrode using electrical power from the power supply means.

7. An implantable tissue stimulator according to claim 5 , which is a pacemaker, a defibrillator, a bone stimulator or a neuro-stimulator.

8. An implantable electrode according to claim 1 , wherein the porous material is supported on a metallic base body, and the coating layer has a thickness in the range from a molecular monolayer to 10 μm.

9. An implantable electrode according to claim 8 , wherein the coating layer has a thickness in the range from 0.01 μm to 1 μm.

10. An implantable electrode according to claim 1 , having at least two said coating layers which have respectively different substituted pyrrole monomeric units or different substituted thiophene monomeric units.

11. An implantable electrode according to claim 1 , wherein the or each said coating layer is free of non-exchangeable or non-mobile anions extraneous to said polymer.

12. An implantable tissue stimulator having an electrode according to claim 1 .

13. An implantable tissue stimulator according to claim 12 , having electrical power supply means and means for applying electrical stimulation pulses to the electrode using electrical power from the power supply means.

14. An implantable tissue stimulator according to claim 12 , which is a pacemaker, a defibrillator, a bone stimulator or a neuro-stimulator.

15. A method of making an implantable electrode acording to claim 1 , the method including the step of electropolymerizing pyrrole, a substituted pyrrole, thiophene or a substituted thiophene in situ on the electrically conductive porous material to form the coating layer as an electropolymerized polymer.

16. A method according to claim 15 , including the step of reacting the electropolymerized polymer after polymerization to add a substituent or change the substituent.

17. A method according to claim 15 , wherein the electrically conductive porous material comprises metal carbide, metal nitride or metal carbonitride.

18. An implantable electrode according to claim 1 , wherein the substituent is —A-X and A is alkylene or alkenylene having 1-3 carbon atoms.

19. An implantable electrode according to claim 1 , wherein the substituent is —A-X and A is unbranched alkylene or unbranched alkenylene.

20. An implantable electrode according to claim 1 , wherein the substituent is —A-X and A is unsubstituted.

21. An implantable electrode according to claim 1 , wherein the substituent is —A-X and A is substituted.

22. An implantable electrode according to claim 1 , wherein the substituent is —A-X and A is substituted with —COOH, —COO - , —COOR′, —CONH 2 , —CONHR′, —CON(R′) 2 , —COR′, —F, —Cl, —Br, —I, —CN, —NO 2 , —OH, —OR′, —SH, —SR′, —O-CO-R′, —NH 2 , —NHR′, —NH(R′) 2 , —N(R′) 3 + , —NH-CO-R′, —NH-CO-H, —NR′-CO-R′, —NR′-SO 2 H, —NR′-SO 2 R′, —SO 2 R′, —OSO 2 R′, or OPO 3 wherein R′ is alkyl or alkenyl of 1-6 carbon atoms.

23. An implantable electrode according to claim 1 , wherein R′ of the substituent group is from 1-4 carbon atoms.

24. An implantable electrode according to claim 1 , wherein X of the substituent group at the 3 position of pyrrole or thiophene is —COOH, —COO - , —COOR , —Cl, —SH, or —OPO 3 .

25. An implantable electrode according to claim 1 , wherein X of the substituent group at the 3 position of pyrrole or thiophene is —COOH or —COO - or —SH.

26. An implantable electrode according to claim 1 , wherein X of the substitutent group at the 3 position of pyrrole or thiophene is —COOH or —COO - .

27. An implantable electrode according to claim 1 , wherein the polypyrrole or the polythiophene has an allyl-terminated pendent group comprising —C(=O)-O-CH 2 -CH=CH 2 , —S-S-CH 2 -CH=CH 2 , —S(=O)-S-CH 2 -CH=CH 2 , —CH 2 -S(=O)-CH 2 -CH=CH 2 , or —S-S(=O)-CH 2 -CH=CH 2 .

28. An implantable electrode according to claim 1 , wherein the polypyrrole or the polythiopene has an allyl-terminated pendent group bound to a pyrrole or a thiophene ring via an amido, ester or ether moiety.

29. An implantable electrode according to claim 1 , wherein the polypyrrole or the polythiophene has an allyl-terminated pendent group and is derived from a monomer A*-B-C-D-E wherein:

A* is a pyrrole ring or a thiophene ring;

B is absent or C 1 -C 20 alkylene;

C is —CO-NH—, —CO-O—or —O—;

D is absent or C 1 -C 20 alkylene; and

E is the allyl-terminated pendent group.

30. An implantable electrode according to claim 29 , wherein B or D is absent.

31. An implantable electrode according to claim 29 , wherein B and D are absent.

32. An implantable electrode according to claim 29 , wherein B or D is C 1 -C 20 alkylene.

33. An implantable electrode according to claim 29 , wherein B and D are C 1 -C 20 alkylene.

34. An implantable electrode according to claim 29 , wherein B or D are branched C 1 -C 20 alkylene.

35. An implantable electrode according to claim 29 , wherein B or D are unbranched C 1 -C 20 alkylene.

36. An implantable electrode according to claim 29 , wherein C is —CO-NH—.

37. An implantable electrode according to claim 29 , wherein B or D is C 1 -C 20 alkylene substituted with —COOH, —COO - , —COOR′, —CONH 2 , —CONHR′, —CON(R′) 2 , —COR′, —F, —Cl, —Br, —I, —CN, —NO 2 , —OH, —OR′, —SH, —SR′, —O-CO-R′, —NH 2 , —NHR′, —NH(R′) 2 , —N(R′) 3 + , —NH-CO-R′, —NH-CO-H, —NR′-CO-R′, —NR′-SO 2 H, —NR′-SO 2 R′, —SO 2 R′, —OSO 2 R′, —OPO 3 , —C 5 —C 20 aryl, —C 1 C 7 alkyl-C 5 -C 20 aryl, or —C 1 —C 7 alkenyl-C 5 —C 20 aryl wherein R′ is alkyl or alkenyl of 1-6 carbon atoms .

38. An implantable electrode according to claim 1 , wherein the substituent is —X.