Implantable device for recording intracranial pressures

• US 20080139959A1
• Filed: 10/25/2007
• Published: 06/12/2008
• Est. Priority Date: 04/30/2005
• Status: Active Grant

• Current Assignee: Christoph Miethke GmbH & Co. KG, Aesculap AG (Lonza Group AG)
• Original Assignee: Christoph Miethke GmbH & Co. KG, Aesculap AG (Lonza Group AG)
• Inventors: Lutze, Theodor, Miethke, Christoph, Schauer, Dirk
• Granted Patent: US 7,785,268 B2
• Time in Patent Office: Days
• US Class Current: 600/561
• CPC Class Codes: A61B 2562/02 Details of sensors specially adapted for in-vivo measurements
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/031 Intracranial pressure

Abstract

To assure, in the case of an implantable device for determining intracranial pressures, the biocompatibility of the implant in the long term, wherein a pressure measuring device is used, which is operatively connected to a sensor for a telemetric measured value transfer, it is proposed that the pressure measuring device is a microchip, that the microchip is located in a rigid housing, and that the pressure transfer from the outside inwards occurs through a very thin biocompatible membrane, the pressure-dependent movement of which acts on the pressure measuring device via a transfer medium.

Claims

1. Implantable device for determining intracranial pressures, comprising:

a pressure sensor,

a pressure measuring device operatively connected to the sensor for a telemetric measured value transfer, wherein;

the pressure measuring device is a microchip,

the microchip is located in a rigid housing, and

pressure transfer from outside inwards occurs through a very thin biocompatible membrane, and

a pressure-dependent movement of the membrane acts on the pressure measuring device via a transfer medium.

2. Device according to claim 1, wherein:

the transfer medium comprises one of air, a special gas, or a liquid, and

a chamber inside the rigid housing is filled with the transfer medium.

3. Device according to claim 1, wherein the transfer medium comprises a gas from the group of noble gases.

4. Device according to claim 1, wherein:

a gas is used as transfer medium, and

a gas volume of the gas is less than a cubic millimetre.

5. Device according to claim 1, wherein a housing interior is filled with a gas-displacing filler material except for a provided volume of the transfer medium.

6. Device according to claim 5, wherein the filler material is one of plastic, ceramic or a metal material.

7. Device according to claim 5, wherein:

the filler material leaves a minimum-volume pressure chamber including a supply duct free on pressure-sensitive faces of the microchip,

the filler material leaves a housing cavity as pressure chamber free below the membrane, and

the two pressure chambers are connected by a small-volume conduit.

8. Device according to claim 1, the transfer medium has at least one mechanical transfer member which is movable by the membrane.

9. Device according to claim 8, the transfer member is held on the microchip or on a support receiving the microchip.

10. Device according to claim 8, wherein the transfer member is held on the membrane.

11. Device according to claim 8, wherein the transfer member is a pressure foot.

12. Device according to claim 8, wherein the transfer member is a spring.

13. Device according to claim 12, wherein the spring is a U-shaped leaf spring.

14. Device according to claim 12, wherein the spring is held on the housing or a support by means of holding elements.

15. Device according to claim 8, wherein the transfer member has a clip, which is disposed on the housing or on a support receiving the microchip and which abuts against the microchip or the membrane respectively with a foot.

16. Device according to claim 8, wherein stop elements are provided, which restrict the movement of the mechanical transfer member.

17. Device according to claim 1, wherein the transfer medium is a highly viscous oil.

18. Device according to claim 1, wherein the transfer medium is one of a vulcanised or polymerised material.

19. Device according to claim 18, wherein the transfer medium is silicone.

20. Device according to claim 18, wherein the microchip is encapsulated with the vulcanised or polymerised material.

21. Device according to claim 18, wherein the microchip is covered with the vulcanised or polymerised material only in a region of the pressure sensor.

22. Device according to claim 20, wherein the vulcanised or polymerised material abuts against the membrane only in a region of the pressure sensor.

23. Device according to claim 18, wherein the membrane is covered with the vulcanised or polymerised material in a region located opposite the pressure sensor of the microchip and this material abuts against the microchip at least in a region of the pressure sensor.

24. Device according to claim 23, wherein the vulcanised or polymerised material abuts against the microchip only in a region of the pressure sensor.

25. Device according to claim 1, wherein the housing is made of ceramic.

26. Device according to claim 1, wherein the housing is made of a biocompatible plastic.

27. Device according to claim 26, wherein the housing is made of one of polyether ether ketone or polyether ketone ketone.

28. Device according to claim 1, wherein the housing is made of metal.

29. Device according to claim 28, wherein the housing is made of one of titanium or a titanium alloy.

30. Device according to claim 1, wherein the membrane is made of metal.

31. Device according to claim 30, wherein the membrane is made of one of titanium or a titanium alloy.

32. Device according to claim 1, wherein the membrane has a thickness of less than 0.05 millimetres.

33. Device according to claim 1, wherein the membrane has a flexible surface of about one of 100 mm², 1 mm², and 4 mm².

34. Device according to claim 1, wherein the membrane is welded to the housing.

35. Device according to claim 34, wherein the membrane is provided with a sheet metal frame and is welded with the frame to the housing.

36. Device according to claim 35, wherein:

the housing is a tubular housing, and

the frame is formed by a sleeve, which can be slid onto the tubular housing.

37. Device according to claim 36, wherein:

the sleeve is welded simultaneously with the membrane on the tubular housing along an outer edge of the sleeve, and

a hole in the housing wall is closed precisely so that the membrane, and not the sleeve, comes to lie over the hole and is secured there.

38. Device according to claim 16, wherein the membrane is configured in one piece with the housing.

39. Device according to claim 16, wherein the membrane has regions of different thickness.

40. Device according to claim 39, wherein the membrane is thicker in its edge regions than in its central region.

41. Device according to claim 1, wherein besides the pressure sensor, the microchip has at least one further sensor.

42. Device according to claim 41, wherein the microchip further comprises an analog-to-digital converter, which converts the analog electrical signals of the sensors into digital signals.

43. Device according to claim 1, the microchip is arranged on a support.

44. Device according to claim 43, wherein the support is bend-resistant.

45. Device according to claim 43, wherein the support carries further electronic components.

46. Device according to claim 45, wherein the support has connection leads for at least one of the microchip and the further electronic components.

47. Device according to claim 43, wherein the microchip or the support is connected to a power and signal transmission line, which line connects to a data processing device outside a body or to a transmission coil.

48. Device according to claim 47, wherein the transmission coil is arranged in the rigid housing.

49. Device according to claim 47, wherein the power and signal transmission line is guided out of the rigid housing through a hermetically sealed bushing.

50. Device according to claim 47, wherein a releasable coupling is arranged in the power and signal transmission line.

51. Device according to claim 50, wherein the coupling is configured as one of a plug contact or a screw contact.

52. Device according to claim 1, wherein the rigid housing is partially provided with a plastic casing or a plastic covering, which leaves at the least the surface of the membrane free.

53. Device according to claim 1, wherein the rigid housing is tubular in configuration.

54. Device according to claim 53, wherein a window, which is closed by the membrane, is provided in a housing wall.

55. Device according to claim 53, wherein a diameter of the housing lies between 2 mm and 3.5 mm.

56. Device according to claim 53, wherein a length of the housing lies between 10 mm and 30 mm, about 20 mm.

57. Device according to claim 56, wherein the pressure sensor is arranged approximately in the center of a longitudinal extent of the housing.

58. Device according to claim 53, wherein a length of the housing lies between 80 mm and 120 mm.

59. Device according to claim 58, wherein the microchip and the membrane are arranged at one end of the tubular housing and a transmission coil is arranged at the opposite end.

60. Device according to claim 1, wherein the rigid housing has a closed fluid chamber, which adjoins the membrane on an outside and is connected to a supply conduit for fluid.

61. Device according to claim 60, wherein the fluid chamber additionally has a drainage pipe for brain fluid.

62. Device according to claim 60, wherein the rigid housing has the shape of a shallow can with an upper measurement chamber receiving the microchip and the transfer medium and a lower region forming the fluid chamber.

63. Device according to claim 62, wherein the membrane divides an interior of the housing into the measurement chamber and the fluid chamber.

64. Device according to claim 60, wherein the supply conduit for the fluid runs substantially perpendicular in relation to a lower boundary wall of the fluid chamber.

65. Device according to claim 64, wherein the supply conduit for the fluid enters the fluid chamber approximately centrally.

66. Device according to claim 60, wherein the supply conduit for the fluid runs parallel in relation to a lower boundary wall of the fluid chamber.

67. Device according to claim 61 wherein the drainage pipe for the brain fluid runs parallel to a floor surface of the fluid chamber.

68. Device according to claim 61, wherein a non-return valve is arranged in the drainage pipe.

69. Device according to claim 61, wherein the drainage pipe opens into a reservoir.

70. Device according to claim 60, wherein the supply conduit is connected to an extension tube, which is open at its end remote from the fluid chamber.

71. Device according to claim 60, wherein:

the supply conduit is connected to an extension tube, which is closed at its end remote from the fluid chamber by means of a flexible membrane, and

the fluid chamber filled with a liquid or a gas is closed off except for the supply conduit.

72. Device according to claim 1, wherein a wall thickness of the rigid housing lies between 0.3 mm and 0.2 mm.

73. Device according to claim 1, wherein walls of the rigid housing are protected against deformation by reinforcement structures.

74. Device according to claim 62, wherein:

the measurement chamber is arranged in an insert, which can be inserted into the housing and closes is the housing in the manner of a cover, and

the insert carries the membrane (3), which separates the measurement chamber from an interior of the housing forming the fluid chamber.

75. Device according to claim 74, wherein the membrane is a metal foil, which is soldered or welded to the insert receiving the measurement chamber.

76. Device according to claim 75, wherein:

the insert receiving the measurement chamber (84) has a planar rim, against which the membrane lies flat,

an annular abutment element is arranged opposite the planar rim on the side opposite the element, and

the membrane is soldered or welded both to the element structural part and to the abutment element.

77. Device according to claim 75, wherein, the element is made of metal.

78. Device according to claim 76, wherein the abutment element is made of metal.

79. Device according to claim 75, wherein the membrane is made of metal.

80. Device according to claim 79, wherein the thickness of the membrane lies between 1/100 mm and 5/100 mm.

81. Device according to claim 76, wherein the abutment element has a height of between 2/10 and 8/10 mm.

82. Process for the production of a rigid housing with a membrane for an implantable device, comprising:

weakening a specific wall region of the otherwise rigid housing by one of a chemical etching process or electrolytic removal process to such an extent that the wall region forms a flexible membranes

wherein the implantable device comprises;

a pressure sensor;

a pressure measuring device operatively connected to the sensor for a telemetric measured value transfer, wherein;

the pressure measuring device is a microchip,

the microchip is located in the rigid housing, and

a pressure transfer from outside inwards occurs through a very thin biocompatible membrane, and

a pressure-dependent movement of the membrane acts on the pressure measuring device via a transfer medium.

83. Process according to claim 82, wherein the thickness of the specific wall region is reduced by machining before the etching or removal process.

84. Process according to claim 83, wherein the thickness of the specific wall region is reduced by differing extents by machining before the etching or removal process.

85. Process according to claim 84, wherein the thickness of the specific wall region is reduced to a lesser degree in the outer wall regions than in the central region before the etching or removal process.

86. Process according to claim 84, wherein:

a membrane is laid flat against a planar rim of a structural part receiving a measurement chamber,

on a side opposite the structural part an annular abutment element located opposite the rim is laid flat against the membrane,

said membrane is clamped between the structural part and the abutment element, and then the structural part, the membrane and the annular abutment element are soldered or welded together.

87. Process according to claim 86, wherein:

the membrane is allowed to project slightly beyond the contour of one of the structural part and the annular abutment elements and

the soldering or welding is conducted completely or partially on this projecting edge strip.